S@INT Seminars

Online Seminar:

"Magnetohydrodynamic Stability of Magnetar Cores and Crusts" [PDF] [Video]

Peter Rau - Cornell University

Thursday, July 15, 2021, 10:30 AM Pacific Time

Abstract:
Magnetars are neutron stars possessing the strongest known magnetic fields, with surface fields of 1e14-1e15 G and interior fields likely one or two orders of magnitude stronger. At these field strengths, Landau quantization of fermions modifies the thermodynamic and transport properties of neutron star matter. I will discuss how Landau quantization can also affect the magnetohydrodynamic (MHD) stability of a neutron star threaded by magnetar-strength magnetic fields. First, I will describe its effects on the stability of the core fluid, where an ideal MHD canonical energy principle is used to determine the stability of a toroidal field. The existence of an instability analogous to that of flux tubes in magnetized superconducting fluids will be detailed, and connected to the formation of magnetic domains within the core. I will then discuss how the strong-field Landau quantization effects modify the MHD oscillation modes of a neutron star crust, in particular discussing how the Hall (whistler) modes in this region can become unstable. This instability is demonstrated using linear mode analysis and preliminary numerical simulations.


Zoom link will be available via announcement email, or by contacting: ikolbe[at]uw.edu.

Online Seminar:

"Stiffening of matter in quark-hadron continuity" [PDF] [Video]

Toru Kojo - Central China Normal University

Thursday, July 8, 2021, 10:30 AM Pacific Time

Abstract:
We discuss stiffening of matter in quark-hadron continuity. We introduce a model that relates quark wavefunctions in a baryon and the occupation probability of states for baryons and quarks in dense matter. In dilute regime, the confined quarks contribute to the energy density through the masses of baryons, but do not directly contribute to the pressure, hence the equations of state are very soft. This dilute regime continues until the low momentum states for quarks get saturated; this may happen even before baryons fully overlap, possibly at density slightly above the nuclear saturation density. After the saturation the pressure grows rapidly while changes in energy density are modest, producing a peak in the speed of sound. If we use baryonic descriptions for quark distributions near the Fermi surface, we reach a description similar to the quarkyonic matter model of McLerran and Reddy. With a simple adjustment of quark interactions to get the nucleon mass, our model becomes consistent with the constraints from 1.4-solar mass neutron stars, but the high density part is too soft to account for two-solar mass neutron stars. We suggest interactions that leave low density equations of state unchanged but stiffen the high density part.


Zoom link will be available via announcement email, or by contacting: ikolbe[at]uw.edu.

Online Seminar:

"Exploring jet time-structure for QGP studies"

Liliana Apolinário - Laboratorio de Instrumentacao e Fisica Experimental de Particulas (LIP), Lisbon

Thursday, June 17, 2021, 10:30 AM Pacific Time

Abstract:
The physics program of ultra-relativistic heavy-ion collisions at the Large Hadron Collider (LHC) and Relativistic Heavy-Ion Collider (RHIC) has brought a unique insight into the hot and dense QCD matter created in such collisions, the Quark-Gluon Plasma (QGP). Jet quenching, a collection of medium-induced modifications of the jets' internal structure that occur through their development in dense QCD matter, has a unique potential to assess the time structure of the produced medium. In this work, we perform an exploratory study to identify jet reclustering tools that can potentiate future QGP tomographic measurements with jets at current energies. By using the inverse of formation time to obtain the jet clustering history, one can identify the QCD parton shower more accurately, even in the presence of in-medium QGP interactions. The results can be further used to select different magnitudes of jet quenching, thus contributing to an accurate evaluation of the QGP parameters.


Zoom link will be available via announcement email, or by contacting: ikolbe[at]uw.edu.

Online Seminar:

"Reconstructing PDFs from Mellin moments: the pion and kaon case" [PDF]

Martha Constantinou - Temple University

Thursday, June 10, 2021, 10:30 AM Pacific Time

Abstract:
Quantum Chromodynamics (QCD) is characterized by several emergent phenomena not apparent in the QCD Lagrangian, such as the dynamical chiral symmetry breaking (DCSB). In QCD, DCSB leads to an octet of Nambu-Goldstone bosons, which includes the triplet of pions and the four kaons. Kaons are particularly interesting because of the valence strange quark, which has a much larger mass than the up and down quarks that form the pions. Due to the presence of a valence strange quark in the kaon, a comparison between pion and kaon observables provides a unique window into the interplay between QCD dynamics and quark mass effects. Significant SU(3) flavor breaking effects have already been observed in the pion and kaon. Therefore, the study of quark contributions to the parton distribution functions is important for the qualitative understanding of these features.

While the proton has been extensively studied in lattice QCD, there are only limited pion and kaon structure studies. Given the relatively small number of experimental data, it is crucial to obtain results from first principles. In this talk, we present a direct lattice QCD calculation of the pion and kaon Mellin moments <x^2> with n<4. We use one ensemble of Nf=2+1+1 gauge configurations of maximally twisted mass fermions improved with a clover term. The ensemble corresponds to a pion mass of about 260 MeV and a kaon mass of about 530 MeV. We study excited-states contamination in detail using several values of the source-sink time separation within the range of 1.12 - 2.23fm. We use operators that are free of mixing and apply a multiplicative renormalization function calculated non-perturbatively. For <x>, we explore both the rest and boosted frame to draw conclusions on the excited states.

The most notable aspect is the reconstruction of the x-dependence of the pion and kaon PDFs using the Mellin moments calculated in this work. We find that the reconstruction is feasible, and we draw qualitative conclusions on the large-x behavior. The PDF reconstruction also allows the extraction of higher moments with reasonable statistical errors. Finally, we compare the pion and kaon PDFs, as well as the ratios of their moments, to address the effect of SU(3) flavor symmetry breaking.

Zoom link will be available via announcement email, or by contacting: ikolbe[at]uw.edu.

Online Seminar:

"Modeling binary neutron star merger remnants" [PDF]

Giovanni Camelio, Nicolaus Copernicus Astronomical Center, Warsaw, Poland.

Thursday, June 3, 2021, 10:30 AM Pacific Time

Abstract:

In order to study the properties of a neutron star it is important to determine its stationary structure given the physical conditions (eg, rotation and temperature) and a microphysical equation of state. Moreover, this stationary configuration can be used as initial condition for more resource demanding hydrodynamic simulations. This is particularly relevant for the hot (5e10 K ≲ T ≲ 1e12 K) and differentially rotating compact remnant of a binary neutron star merger, because the theoretical predictions can be confirmed with the observed gravitational, electromagnetic, and (potentially) neutrino radiation. A key approximation made for computing the stationary structure of hot and rotating neutron stars is that of barotropicity, namely that all thermodynamic quantities are in a one-to-one relationship. However, this is a poor approximation for the remnant of a binary neutron star merger or of a core-collapse supernova. In this talk I will describe a new method to determine the structure of neutron stars without the barotropic approximation, its application to the modeling of binary neutron star merger remnants, and an extensive study of the parameter space of the model.

Zoom link will be available via announcement email, or by contacting: ikolbe[at]uw.edu.

Online Seminar:

"Classical Algorithms for Quantum Dynamics: Progress and Prospects"

Scott Lawrence - University of Colorado Boulder

Thursday, May 27th, 2021, 10:30 AM Pacific Time

Abstract:

Standard Monte Carlo techniques are unable to access real-time quantum dynamics due to a sign problem. A wide variety of methods have arisen for overcoming this obstacle, many inspired by analogous methods for the fermion sign problem. I will discuss machine-learning-inspired approaches for the real-time sign problem. One such approach, based on the complexification of "normalizing flows", connects naturally to the Lefschetz thimble program for the fermionic case. Considering the behavior of these complexified normalizing flows as a function of coupling suggests that manifolds exactly solving bosonic, real-time sign problems exist in all cases. Although efficient algorithms for finding these manifolds are not known, various approximations are available.

In some cases, overcoming the sign problem is probably hard in the following sense: in some field theories, arbitrary correlation functions can be shown to be BQP-hard to compute. I will describe the extension of this result to the computation of S-matrix elements (albeit for a smaller class of field theories). I will conclude by outlining the landscape of computational tasks in field theories: what is provably intractable, what is doable today, and what we might hope for in the future.

Zoom link will be available via announcement email, or by contacting: ikolbe[at]uw.edu.


Online Seminar:

"Deterministic randomness in relativistic hydrodynamics" [PDF]

Misha Stephanov, University of Illinois

Thursday, May 13, 2021, 10:30 AM Pacific Time

Abstract:
We usually think of hydrodynamics as a deterministic description of fluid motion. The focus of this talk is on random fluctuations in hydrodynamics caused by thermal noise, inherent in a system with dissipation. The interest in this subject is driven by the progress of heavy-ion collision experiments and, in particular, by the search for the QCD critical point at the Relativistic Heavy-Ion Collider. I will discuss the role the fluctuations play in hydrodynamics and how we can describe their evolution in a deterministic formalism.

Zoom link will be available via announcement email, or by contacting: ikolbe[at]uw.edu.

Online Seminar:

"What can we learn about exotic matter from neutron stars and their mergers?" [PDF]

Veronica Dexheimer, Kent State University

Thursday, May 6, 2021, 10:30 AM Pacific Time

Abstract:
The large density reached in neutron stars and the large density and temperature reached in neutron-star mergers create ideal testing grounds in which to learn about exotic matter, namely hyperons and deconfined quarks. The presence of exotic matter can strongly affect the interior of neutron stars but cannot be easily observed. New electromagnetic and gravitational wave constraints have been slowly narrowing down the dense and cold equation of state and allowing us to learn more about the strong interaction. Nevertheless, constraints on dense and hot matter depend on the not yet observed post-merger portion of gravitational waves from neutron-star mergers and non-trivial comparisons with particle collisions. In this talk, I address these issues, giving special attention to possible constraints coming from extremely massive neutron stars and magnetic-field effects.

Zoom link will be available via announcement email, or by contacting: ikolbe[at]uw.edu.

Online Seminar:

"Three-Dimensional Simulations of the Neutrino Fast Flavor Instability" [PDF]

Sherwood Richers, UC Berkeley

Thursday, April 29, 2021, 10:30 AM Pacific Time

Abstract:
Neutrinos transport energy, drive outflows, and determine the ratio of electrons to protons in the ejecta from neutron star mergers that enriches the surrounding universe with heavy elements. Only electron flavor neutrinos and antineutrinos modify the composition of the ejecta and thus directly affect the synthesis of heavy elements. Instabilities that cause rapid mixing of neutrino flavor are likely ubiquitous in mergers, but are poorly understood and are absent from global simulations. I will present the first (local) simulations of this instability using the new open-source particle-in-cell neutrino quantum kinetics code Emu. I will demonstrate that the growth phase of the instability matches theoretical predictions, describe abundances of each neutrino species after the instability saturates, and discuss the implications for nucleosynthesis in neutron star mergers. Then I will show the emergence of multidimensional flavor turbulence in three-dimensional simulations and show the relationship to 1D and 2D simulations.


Zoom link will be available via announcement email, or by contacting: ikolbe[at]uw.edu.

Online Seminar:

"NICER Measurements of Pulsars PSR J0030+0451 and PSR J0740+6620" [PDF]

M. Coleman Miller, University of Maryland

Thursday, April 22, 2021, 10:30 AM Pacific Time

Abstract:
Precise and reliable measurements of neutron star radii are essential to our understanding of cold, catalyzed matter beyond nuclear saturation density. Recently, NASA's Neutron Star Interior Composition Explorer (NICER) satellite has provided high-quality data sets that have yielded measurements of the mass (M=1.44+-0.15 Msun) and radius (R=13+1.2-1.0 km) of the 206 Hz pulsar PSR J0030+0451, and of the radius (R=13.7+2.6-1.5 km) of the M=2.08+-0.07 Msun, 346 Hz pulsar PSR J0740+6620. I will discuss our group's work on these pulsars and will in particular discuss the assumptions that have gone into our analyses, to help the assessment of our results. I will also discuss the implications of our results for the properties of the dense matter in the cores of neutron stars.

Zoom link will be available via announcement email, or by contacting: ikolbe[at]uw.edu.

Online Seminar:

"IceCube: Cosmic Neutrinos and Multimessenger Astronomy" [PDF]

Francis Halzen
Wisconsin IceCube Particle Astrophysics Center & Department of Physics, University of Wisconsin–Madison

Tuesday, April 6, 2021, 10:30 AM Pacific Time

Abstract:
IceCube detects more than 100,000 neutrinos per year in the GeV to 10 PeV energy range. Among those, we have isolated a flux of high-energy neutrinos of cosmic origin, with an energy density in the extreme universe similar to that of high-energy photons and cosmic rays. We identified their first source: on September 22, 2017, following an IceCube neutrino alert, observations by other astronomical telescopes pinpointed a flaring active galaxy, powered by a supermassive black hole, as the source of a cosmic neutrino with an energy of 290 TeV. We will review recent progress in measuring the cosmic neutrino spectrum and in identifying its origin.


Zoom link will be available via announcement email, or by contacting: ikolbe[at]uw.edu.

Online Seminar:

"Exploring the phase diagram of hot Quantum Chromodynamics"

Roy Lacey, Stony Brook University

Thursday, February 25, 2021, 10:30 AM Pacific Time

Abstract:

A primary focus of current heavy-ion research at several accelerator facilities is the study of QCD matter under extreme conditions. I will discuss recent progress involving investigations spanning a broad range of systems and beam collision energies to; (I) develop a comprehensive understanding of reaction dynamics, (II) chart the phase structure of the QCD phase diagram, and (III) delineate the thermodynamic, topological, and transport properties of the respective QCD phases. These studies emphasize the synergistic data sets obtained at the LHC and the comprehensive RHIC data sets for different beam energies and collision systems to explore a broad domain of the (T, \mu_{B})-plane of the QCD phase diagram.

Zoom link will be available via announcement email, or by contacting: ikolbe[at]uw.edu.

Online Seminar:

"High-Energy Showing inside the QGP: weak vs. strong coupling" [PDF]

Peter Arnold, University of Virginia

Thursday, January 28, 2021, 10:30 AM Pacific Time

Abstract:

Consider a very high-energy parton (E >> T) traveling through a quark-gluon plasma (QGP). The parton can lose energy by showering inside the medium, like a cosmic ray showers in the atmosphere. There are two extremes for picturing such a shower: If we imagine that the running strong coupling is at least moderately small at the relevant energy scale, we can calculate the development of the shower by picturing the shower as a collection of individual high-energy partons that keep splitting via bremsstrahlung and pair production. If we instead imagine that the running strong coupling is very strong, we cannot treat the high-energy partons individually, and we might, for example, turn to AdS/CFT descriptions of the process for qualitative insight. As one increases coupling, when does the (weak-coupling) particle picture of the shower irretrievably break down? In this talk, I will discuss the current status of field theory calculations meant to address that question (in simple situations) by calculating the size of corrections to the weak-coupling picture of high-energy parton showers. The discussion involves investigating what happens when the quantum durations of consecutive splittings of a parton in the shower overlap each other. The calculation requires a significant generalization of the Landau-Pomeranchuk-Migdal (LPM) effect, which plays a roll in the theory of both cosmic ray showers and jets in quark-gluon plasmas.

Zoom link will be available via announcement email, or by contacting: ikolbe[at]uw.edu.

Online Seminar:

"PREX-II: Measuring the Neutral Weak Form-Factor of 208Pb" [PDF]

Caryn Palatchi, University of Virginia

Thursday, January 21, 2021, 10:30 AM Pacific Time

Abstract:

The recent PREX-II experiment has measured the parity-violating asymmetry in elastic electron scattering off the lead-208 nucleus. This new result will be presented alongside the experimental methods used to perform the challenging measurement. Precise measurement of Apv provides a determination of the neutron skin thickness in lead-208 and constrains the density dependence of the symmetry energy in the nuclear equation of state. PREX-II has implications for the central density of saturated nuclear matter and astronomical observations of neutron stars.

Zoom link will be available via announcement email, or by contacting: ikolbe[at]uw.edu.

Online Seminar:

"Near-Earth Supernova Explosions Revealed by Deep-Ocean and Lunar Radioactivity"

Brian Fields, University of Illinois

Thursday, January 14, 2021, 10:30 AM Pacific Time

Abstract:

Supernovae are central actors in galaxy evolution, multimessenger particle engines, and create many of the elements essential for planets and life. Yet these awesome events take a sinister shade when they occur close to home, because an explosion very nearby would pose a grave threat to Earthlings. We will show how radionuclides produced by supernovae can reveal nearby events in the geologic past, and we will highlight isotopes of interest. In particular, geological evidence for live 60Fe has recently been confirmed globally in multiple sites of deep-ocean material, in cosmic rays, and in lunar samples. We will review astrophysical 60Fe production sites and show that the data demand that at least one core-collapse supernova exploded near the Earth over the past few Myr, and explain how debris from the explosion was transported to the Earth as a “radioactive rain.” Deep-ocean and lunar 60Fe measurements thus represent a laboratory for supernova astrophysics, but also with implications for geology, astrobiology, and possibly terrestrial evolutionary biology--possibly including biological extinction events at the end of the Devonian period 360 Myr ago.

Zoom link will be available via announcement email, or by contacting: ikolbe[at]uw.edu.

Online Seminar:

"Quarkyonic model for neutron stars" [PDF]

Sri Sen, Iowa State University

Tuesday, December 15, 2020, 10:30 AM Pacific Time

Abstract:

The observed mass and radius relations of neutron stars can be explained remarkably well using a model of dense matter known as quarkyonic matter. I describe how the quarkyonic model can arise dynamically from an excluded volume model for nuclear interactions. I also discuss how thermal effects can be incorporated in such a model.

Zoom link will be available via announcement email, or by contacting: ikolbe[at]uw.edu.

Online Seminar:

"Deconstructing General-Relativistic Viscous Fluid Dynamics"

Jorge Noronha, University of Illinois at Urbana-Champaign

Thursday, December 10, 2020, 10:30 AM Pacific Time

Abstract:

With the dawn of the multi-messenger astronomy era marked by the detection of a binary neutron star merger, it became imperative to understand how extremely dense fluids behave under very strong gravitational fields. In this talk I will critically review the foundations of relativistic viscous fluid dynamics and its formulation in curved spacetime. I will present the first set of fluid dynamic equations that satisfies all of the following properties: (a) the system when coupled to Einstein’s equations is causal and strongly hyperbolic (the initial value problem is well-posed); (b) equilibrium states are stable; (c) all leading dissipative contributions are present, i.e., shear viscosity, bulk viscosity, and thermal conductivity; (d) effects from non-zero baryon number are included; (e) entropy production is non-negative in the regime of validity of the theory. The properties above hold in the nonlinear regime without any simplifying symmetry assumptions and are mathematically rigorously established. This is achieved using a new formulation of relativistic fluid dynamics containing only the hydrodynamic variables and their first-order derivatives. The framework presented here provides the starting point for systematic investigations of general-relativistic viscous phenomena in neutron star mergers.

Zoom link will be available via announcement email, or by contacting: ikolbe[at]uw.edu.

Online Seminar:

"Tests of lepton flavor universality and CKM unitarity" [PDF]

Martin Hoferichter , University of Bern, Institute for Theoretical Physics

Thursday, December 3, 2020, 10:30 AM Pacific Time

Abstract:

Absent direct evidence at high-energy colliders, low-energy precision searches are becoming increasingly important as complementary probes of physics beyond the Standard Model. In recent years, tensions with the Standard Model have been observed in several search channels, including the anomalous magnetic moments of muon and electron, semi-leptonic B-decays, and tests of CKM unitarity.

In the talk, I will give an overview of the present situation, arguing that all these tensions could be related to the violation of lepton flavor universality.

Zoom link will be available via announcement email, or by contacting: ikolbe[at]uw.edu.

Online Seminar:

"Hot Neutrons From The Lattice" [PDF]

Neill C. Warrington, Institute for Nuclear Theory

Tuesday, November 24, 2020, 10:30 AM Pacific Time

Abstract:

I present a model-independent calculation of the structure factors of neutron matter using a lattice formulation of leading-order pionless effective field theory. I analyze conditions relevant to both neutron star mergers and supernovae, where precise knowledge of these quantities is valuable. Importing methods from lattice QCD, all errors, both systematic and statistical, are controlled for.

Zoom link will be available via announcement email, or by contacting: ikolbe[at]uw.edu.

Online Seminar:

"Renormalization group advances for nuclei and strong interaction matter" [PDF]

Achim Schwenk, TU Darmstadt

Thursday, November 19, 2020, 10:30 AM Pacific Time

Abstract:

The field of ab initio calculations has seen dramatic progress in the past years to access nuclei up to mass number A~100. These advances promise a first principles understanding of the nuclear chart, including electroweak interactions in nuclei that are key for neutrino and astroparticle physics.

A powerful and flexible method that has significantly expanded the ab initio reach is the in-medium similarity renormalization group (IM-SRG). The IM-SRG uses flow equations combined with normal ordering to decouple higher-lying states from a reference state or from low-lying configurations. This decoupling can be adapted flexibly, making it a very versatile many-body method. This talk will discuss recent IM-SRG achievements and outstanding challenges for nuclei, and discuss new results for strong interaction matter.

Zoom link will be available via announcement email, or by contacting: ikolbe[at]uw.edu.

Online Seminar:

"Heavy-Quark Brownian Motion and sQGP"

Ralf Rapp, Texas A&M University

Thursday, October 22, 2020, 10:30 AM Pacific Time

Abstract:

The microscopic properties of the strongly coupled quark-gluon plasma (QGP) remain a topic of great current interest. We discuss a quantum many-body approach based on quark and gluon degrees of freedom that tries to address this challenge. Its starting point is the heavy-flavor sector where the large masses of the charm and bottom quarks enable substantial simplifications in the treatment of the in-medium one- and two-body correlation functions. The key ingredient is the in-medium two-body force which we constrain through lattice-QCD data for the heavy-quark free energy and euclidean quarkonium correlation functions. We apply this framework to compute transport parameters for heavy-quark diffusion and quarkonium kinetics and pertinent observables in heavy-ion collisions. Finally, based on a fit to the lattice-QCD equation of state using thermal quark and gluon masses, we proceed to analyze the spectral and transport properties of the QGP. Remnants of the confining force in the QGP are found to play a dual role of generating its strong-coupling behavior while also triggering a transition from melting-parton to broad hadronic-bound state degrees of freedom.

Zoom link will be available via announcement email, or by contacting: ikolbe[at]uw.edu.

Online Seminar:

"What Heavy Ion Collisions Can Teach Us About The Nuclear Equation of State" [PDF]

Bjoern Schenke, Brookhaven National Laboratory

Tuesday, October 20, 2020, 10:30 AM Pacific Time

Abstract:

I will discuss the potential of measurements in the RHIC Beam Energy Scan (BES) I+II to provide information on the nuclear equation of state (EoS). Indications of a softest point of the EoS, and even critical behavior have been seen in the BES I data. I will discuss caveats with the interpretation of the data and necessary theoretical developments, that will allow us to draw clean conclusions from future BES II data. In particular, I will discuss new developments of comprehensive simulations employing dynamical 3D initial states, 3+1 dimensional viscous fluid dynamics, the inclusion of a sophisticated EoS, and a proper prescription of the conversion to particles.

Zoom link will be available via announcement email, or by contacting: ikolbe[at]uw.edu.

Online Seminar:

"Discrete Scale Invariance and Structure"

U. van Kolck, Centre National de la Recherche Scientifique and University of Arizona

Thursday, October 8, 2020, 10:30 AM Pacific Time

Abstract:

When nonrelativistic particles interact through short-range forces near the unitarity limit, the two-body system is approximately scale invariant. Renormalization for more-body systems requires a three-body force, which lies on a limit cycle and breaks the symmetry to a discrete subgroup. The remaining, approximate discrete scale invariance gives rise to nearly geometric towers of excited states, including the famous Efimov three-body spectrum. In leading order, all energies are related through the one dimensionful parameter of the three-body force, an example being the Tjon correlation between three- and four-body ground-state energies. I discuss the implications for larger systems, in particular saturation for bosons (such as certain atoms near Feshbach resonances) and clustering for (multi-component) fermions (such as nucleons).

Zoom link will be available via announcement email, or by contacting: ikolbe[at]uw.edu.

Online Seminar:

"Nuclear reactions for astrophysics: a story from the reaction theory perspective" [PDF]

Filomena Nunes, FRIB / Michigan State University

Thursday, October 1, 2020, 10:30 AM Pacific Time

Abstract:

Nuclear reactions fuel many astrophysical events, including stars, novae, supernovae and neutron star mergers. Often, the rates needed for the astrophysical simulations are not known and require indirect experimental methods. Over the last decade, several indirect methods have been successfully implemented, showing the importance of a close collaboration between theory and experiment. A birds eye view of these methods will be presented, followed by some highlights on impactful theoretical developments. In closing, I will present my personal view on the exciting reaction theory challenges that lie ahead.

Zoom link will be available via announcement email, or by contacting: ikolbe[at]uw.edu.

Online Seminar:

"Relativistic Navier-Stokes equations" [PDF]

Pavel Kovtun, University of Victoria

Thursday, September 24, 2020, 10:30 AM Pacific Time

Abstract:

It has been widely believed that the relativistic Navier-Stokes equations violate the basic physical requirements of equilibrium stability and causality, and therefore can not be used for practical simulations of relativistic fluids. In this talk, I will discuss why this belief is unfounded. There is not one, but infinitely many Navier-Stokes equations because there are infinitely many conventions that can be used to define what one means by "fluid temperature", "fluid velocity" etc. out of equilibrium. The early works on relativistic hydrodynamics (Eckart, Landau-Lifshitz) have indeed adopted conventions that lead to unphysical predictions. On the other hand, when one adopts physically sensible conventions, the resulting relativistic Navier-Stokes equations are both stable and causal.

Zoom link will be available via announcement email, or by contacting: ikolbe[at]uw.edu.

Online Seminar:

"What can we learn from heavy neutron stars?" [PDF]

Jacquelyn Noronha-Hostler, University of Illinois at Urbana-Champaign

Thursday, September 17, 2020, 10:30 AM Pacific Time

Abstract:

The observation of gravitational waves from an asymmetric binary opens the possibility for heavy neutron stars (potentially seen in GW190814), but these pose challenges to models of the neutron star equation of state. We construct heavy neutron stars by introducing non-trivial structure in the speed of sound sourced by changes in the degrees of freedom of dense QCD matter, which cannot be well recovered by spectral representations. Their moment of inertia, Love number and quadrupole moment are very small, so a tenfold increase in sensitivity may be needed to test this possibility with gravitational waves, which is feasible with third-generation detectors.

Online Seminar:

"Progress in nuclear quantum Monte Carlo" [PDF]

Alessandro Lovato, Argonne National Lab

Tuesday, September 15, 2020, 10:30 AM Pacific Time

Abstract:

The last decades have witnessed tremendous progress in nuclear many-body theory, aiming to understand how nuclei emerge from the individual interactions among protons and neutrons. Effective field theories exploit the symmetries of quantum chromo-dynamics to construct realistic nuclear potentials and consistent electroweak currents in a systematic fashion. They are the input to “ab-initio” many-body methods that solve the many-body Schrödinger equation with controlled approximations. Among them, quantum Monte Carlo approaches are known for their accuracy and capability to treat on the same footing long-range structure and short-range dynamics of nuclear systems. I will report on recent quantum Monte Carlo progresses towards a comprehensive description of the spectrum of light nuclei, their interactions with neutrinos, and the nucleonic matter equation of state. A novel representation of the nuclear many-body wave function in terms of artificial neural networks, suitable to extend the reach of quantum Monte Carlo to medium-mass nuclei, will also be discussed.

Online Seminar:

"Quantum Computing – an Introduction" [PDF]

Martin Savage, Institute for Nuclear Theory

Thursday, September 10, 2020, 10:30 AM Pacific Time

Abstract:

Precise and accurate theoretical predictions of the properties and dynamics of dense quantum many-body systems, such as in the early universe and in the interior of neutron stars, require beyond classical computational resources. As highlighted by Feynman and others, such systems may be amenable to quantum simulations. I will present an introduction to quantum computing in the context of quantum simulations for nuclear physics.

Online Seminar:

"r-process: from simulations to observations and back"

Almudena Arcones, Technische Universität Darmstadt

Thursday, September 3, 2020, 10:30 AM Pacific Time

Abstract:

Our understanding of the origin of heavy elements by the r-process has made great progress in the last years. In addition to the gravitational wave and kilonova observations for GW170817, there have been major advances in the hydrodynamical simulations of neutron star mergers and core-collapse supernovae, in the microphysics included in those simulations (neutrinos and high density equation of state (EoS)), in galactic chemical evolution models, in observations of old stars in our galaxy and in dwarf galaxies. This talk will discuss these new advances. First, we will explore the impact of the EoS in neutron star merger nucleosynthesis and kilonova. Investigation of the EoS in core-collapse supernovae demonstrates that the effective mass governs the neutron star contraction. We will then discuss the first magneto-rotational supernova simulations with detailed neutrino transport and their nucleosynthesis. Observations of old stars and meteorites can strongly constrain the astrophysical site of the r-process, once the nuclear physics uncertainties of extreme neutron-rich nuclei are reduced by experiments and by improved theoretical models.

Online Seminar:

"Hard-core deconfinement and soft-surface delocalization from nuclear to quark matter" [PDF]

Toru Kojo, Central China Normal University

Tuesday, September 1, 2020, 10:30 AM Pacific Time

Abstract:

We propose a novel concept of hard and soft realizations of deconfinement from nuclear to quark matter. Hard Deconfinement takes place when bulk thermodynamics is dominated by the core properties. The energy density and mechanical pressure in a nucleon, which are related to the gravitational form factor in scattering experiments, are found to be consistent with high density constraints known from neutron star phenomenology. Meanwhile Soft Deconfinement is driven by quark exchanges at intermediate distance and begins before Hard Deconfinement happens. To describe this phenomenon we use a model of quantum percolation, and discuss a quantum mechanical problem of quarks hopping among baryons. We describe delocalization of quark wavefunctions as well as the Anderson localization. Finally we discuss how the quark Fermi sea is developed as nuclear matter transforms into quark matter, and conjecture a scenario leading to a momentum shell model in Quarkyonic Matter.

Online Seminar:

"Quark matter in the cores of neutron stars"

Aleksi Kurkela, Stavanger University

Thursday, August 27, 2020, 10:30 AM Pacific Time

Abstract:

Neutron stars are the densest astrophysical objects in the universe. Cores of neutron stars reach densities that are as high as those realized in ultrarelativistic heavy-ion collisions where ordinary nuclear matter melts into a new phase of matter, the quark matter. This naturally raises the question: does quark matter also exist inside neutron stars? In my talk, I describe how recent advancements in theory of superdense matter and in observations of neutron stars—such as the LIGO/Virgo detection of gravitational waves arising from a merger of two neutron stars—can inform us about what lies in the centers of neutron stars. I discuss how the different constraints point to the existence of quark matter in the cores of most massive neutron stars.

Online Seminar:

"Factorized approach to radiative corrections for inelastic lepton-hadron collisions" [PDF]

Jianwei Qiu, Jefferson Lab

Thursday, August 20, 2020, 10:30 AM Pacific Time

Abstract:

In a recent paper, we proposed a new factorized approach to QED radiative corrections (RCs) in inclusive and semi-inclusive lepton-hadron deep-inelastic scattering. The method allows the systematic resummation of the logarithmically enhanced RCs into factorized lepton distribution and fragmentation (or jet) functions that are universal for all final states. The new approach provides a uniform treatment of RCs for the extraction of parton distribution functions, transverse momentum dependent distributions, and other partonic correlation functions from lepton-hadron collision data. Our unified factorization approach to QCD and QED dynamics has important implications for future analyses of hard scattering at the EIC.

Online Seminar:

"Efficient emulators for scattering using eigenvector continuation" [PDF]

Xilin Zhang, The Ohio State University

Thursday, August 13, 2020, 10:30 AM Pacific Time

Abstract:

Bayesian inference is increasingly favored for uncertainty quantification in nuclear physics, but its parameter estimation generally requires Monte Carlo sampling of a model’s parameter space. Each evaluation of the model’s prediction may be so computationally expensive that the inference becomes infeasible. Eigenvector continuation (EC), as coupled with variational method, has recently shown that it can be used as an efficient and accurate emulator to ameliorate this problem for computing nuclear bound-state properties from chiral effective field theory (Chiral EFT) Hamiltonians [1909.08446, 1910.02922].

In this talk, I will discuss our extension [2007.03635] of this approach to two-body scattering, by combining Kohn variational method with the EC. Tests of the emulators will be presented for the scatterings from various potentials. The efficiency will also be discussed. I will briefly mention our ongoing generalization of the method to the three-body systems. These emulators would have a wide range of applications, such as fitting the Chiral EFT to nucleon-deuteron scattering data and nuclear optical potentials to nuclear scattering/reaction data. I will also speculate how this method could be applied to analyze the results from ab initio calculations, including Lattice QCD and a newly developed Luscher-type calculation [2004.13575] for low-energy nuclear scattering.

Online Seminar:

"Nuclear Lattice EFT: Status & Perspectives" [PDF]

Ulf-G. Meißner, Universitat Bonn & Forschungszentrum Julich

Tuesday, August 11, 2020, 10:30 AM Pacific Time

Abstract:

I give an outline of the recent developments in nuclear lattice effective field theory, which is continuing to push the boundaries of ab initio nuclear many-body calculations, both in terms of nuclear structure and nuclear reactions. This remarkable progress has been made possible by recent dramatic increases in HPC resources, as well as advances in computational methods and algorithmic developments. Some of these new algorithms are brieflly explained. As applications I consider the essentials of nuclear binding, ab initio nuclear thermodynamics and the physics of hypernuclei.

Online Seminar:

"Exotic Atoms and Molecules for Nuclear Science" [PDF]

Ronald Garcia Ruiz, MIT

Thursday, August 6, 2020, 10:30 AM Pacific Time

Abstract:

Precise knowledge of the interaction between the atomic nucleus and the surrounding electrons offers a complementary insight into the atomic nucleus and the fundamental particles and forces of nature. Exotic atoms and molecules - those containing nuclei with extreme proton-to-neutron ratios - can be made to investigate a particular nuclear structure or symmetry-violating effect. Thereby offering high sensitivity to explore diverse nuclear phenomena, to study the violation of fundamental symmetries, and to search for new physics. In this seminar, I will present recent highlights from laser spectroscopy experiments of these exotic species, containing isotopes produced in extreme regions of the nuclear chart. The relevance of these results to some of the pressing questions of nuclear science will be discussed.

Online Seminar:

"Large-momentum effective theory for partons"

Xiangdong Ji, Center for Nuclear Femtography, SURA and University of Maryland

Thursday, July 30, 2020, 10:30 AM Pacific Time

Abstract:

Parton distributions are the momentum distributions of quarks and gluons in a hadron travelling with infinite momentum or at the speed of light. They can be obtained through a system expansion of the momentum distributions in a large but finite momentum (P) state in terms of a small parameter Lambda_{QCD}/P. Non-analyticity at P=infinity, however, requires using EFT technology of matching and running to recover partons. This large-momentum effective theory strategy can be applied to calculating parton physics of hadrons such as the standard PDFs, generalized parton distributions, transverse-momentum-dependent PDFs, as well as light-front wave functions through lattice QCD simulations. For a non-technical discussion, see https://arxiv.org/abs/2007.06613

Online Seminar:

"From quarks to nuclei: machine learning the structure of matter" [PDF]

Phiala Shanahan, MIT

Thursday, July 23, 2020, 10:30 AM Pacific Time

Abstract:

With advances in supercomputing, we are beginning to quantitatively understand nuclear structure and interactions directly from the fundamental quark and gluon degrees of freedom of the Standard Model. Recent studies provide insight into the neutrino-nucleus interactions relevant to long-baseline neutrino experiments, double beta decay, and nuclear sigma terms needed for theory predictions of dark matter cross-sections at underground detectors. The rapid progress in this field has been possible because of new algorithms, but challenges still remain to achieve full systematic control. I will describe the physics challenges, and outline how new machine learning tools have the potential to provide a revolutionary way to enable currently-intractable calculations to reveal the physics of nuclei from the Standard Model.

Online Seminar:

"Exploring beyond the Standard Model with Lattice QCD"

Amy Nicholson, University of North Carolina, Chapel Hill

Tuesday, July 21, 2020, 10:30 AM Pacific Time

Abstract:

While the Standard Model (SM) of particle physics has been enormously successful in describing the world around us, there still remain many important and unanswered questions requiring Beyond the SM (BSM) physics. One way to experimentally probe the limits of the SM is to search for potential violations of its fundamental symmetries through precision low-energy tests involving nucleons or nuclei. Connecting experimental signals from nuclear environments to a particular BSM model involves the numerical solution of Quantum Chromodynamics (QCD), a cornerstone of the SM which governs the nuclear interactions. In this talk I will discuss the use of Lattice QCD as a tool for numerically calculating quantities relevant for experimental BSM searches. I will use neutrinoless double beta decay, which, if observed, could offer an explanation for the matter-antimatter asymmetry of the universe, as a key example.

Online Seminar:

"Exotica and Heavy Ion Collision"

Su Houng Lee, Yonsei University

Thursday, July 9, 2020, 10:30 AM Pacific Time

Abstract:

Relativistic heavy ion collisions provide an excellent venue to produce some of the recently observed and theoretically proposed exotic states because they contain heavy quarks, which are profusely produced in these experiments. We first discuss the difference between a molecular configuration and a compact multiquark states from the view point of the short distance interaction between hadrons using a quark model. We then point out possible flavor exotic states and why heavy quarks are needed to make them more stable. We finally show how measurements in heavy ion can be used to discriminate the structure of exotic particles. Some comments are made about the recent measurements of X(3872) in heavy ion collision.

Online Seminar:

"Many-body factorization and new measurements of short-range correlations" [PDF]

Or Hen, MIT

Thursday, June 25, 2020, 10:30 AM Pacific Time

Abstract:

In this talk I will present new results from measurements of short-range correlations (SRC) using inverse kinematics proton-scattering at the JINR in Dubna and well as fix-target electron scattering at JLab. The measurements use kinematical pre-selection (JLab) and fragment tagging post-selection (JINR) techniques to suppress contributions from reaction mechanisms other than the hard breakup of SRC pairs and provide new insights to (A) the nature of the strong nuclear interaction at short-distance, (B) its impact on the short-range structure of neutron-rich nuclei, and (C) the factorization of SRCs from the many-body nuclear wave-function.

The data are shown to be well reproduced by new Generalized Contact Formalism (GCF) calculations with input from ab-initio many-body calculations. This observed data-theory agreement also provides new insight to the interplay between short-distance and mean-filed nuclear dynamics in SRC formation.

Last, plans and prospects for additional inverse kinematics measurements at FAIR, FRIB, and JINR will be discussed as a new frontier for SRC studies using radioactive nuclear beams.

Online Seminar:

"Nucleon Electromagnetic Form Factors - Measurements, Meanings and Messages" [PDF]

Gerald A. Miller, University of Washington

Thursday, June 18, 2020, 10:30 AM Pacific Time

Abstract:

Electron scattering measurements at JLab, Mainz and Bates have led to substantial changes in our understanding of the proton and neutron. The key results and their interpretation will be reviewed. The essential findings are that the non-relativistic quark model is not accurate, the proton is not round, the charge density of the neutron is determined by the pion cloud, and the central charge density of the neutron is negative.

Online Seminar:

"Inference as a means to constrain dynamical models of neutrino flavor transformation" [PDF]

Eve Armstrong , New York Institute of Technology

Thursday, June 11, 2020, 1:00 PM Pacific Time

Abstract:

The multi-messenger astrophysics of compact objects presents a vast range of environments where neutrino flavor transformation may occur and may be important for nucleosynthesis, dynamics, and a detected neutrino signal. Development of efficient techniques for surveying flavor evolution solution spaces in these diverse environments, and which augment and complement existing sophisticated computational tools, could leverage progress in this field. To this end, we explore the use of statistical data assimilation (SDA) to identify solutions to a small-scale model of neutrino flavor transformation. SDA is a machine learning (ML) formula wherein a dynamical model is assumed to generate any measured quantities. Our example study seeks to infer the flavor transformation histories of two mono-energetic neutrino beams coherently interacting with each other and with a matter background. We require that the solution be consistent with measured neutrino flavor fluxes at the point of detection, and with constraints placed upon the flavor content at various locations along their trajectories, such as the point of emission, and the locations of the Mikheyev–Smirnov–Wolfenstein (MSW) resonances. We show how the procedure efficiently identifies solution regimes, and rules out regimes where solutions are infeasible. Overall, results intimate the promise of this "variational annealing" methodology to efficiently probe an array of fundamental questions that traditional numerical simulation codes render difficult to access.

Zoom link will be available via announcement email, or by contacting: stroberg[at]uw.edu.

Online Seminar:

"Asymptotically Free Quantum Fields from Dimensional Reduction of Discrete Variables"

Uwe-Jens Wiese, Institute for Theoretical Physics,

Albert Einstein Center for Fundamental Physics, Bern University

Thursday, June 4, 2020, 10:30 AM Pacific Time

Abstract:

Quantum Chromodynamics (QCD) --- the (3+1)-d asymptotically free SU(3) gauge theory that describes the strong interaction --- is usually formulated in terms of fundamental quark and gluon fields. CP(N-1) models in (1+1)-d have a global SU(N) symmetry and share many features with QCD. They are also asymptotically free, have a non-perturbatively generated mass gap, and non-trivial theta-vacuum states. CP(N-1) models can be regularized unconventionally by using discrete SU(N) quantum spins forming a (2+1)-d spin ladder that consists of n transversely coupled quantum spin chains. The (1+1)-d asymptotically free CP(N-1) fields then emerge from dimensional reduction when n is increased. Even n leads to the vacuum angle theta = 0, while odd n leads to theta = pi. In a similar way, gluon fields emerge naturally from the dimensional reduction of (4+1)-d quantum links, which are discrete gauge variables that generalize quantum spins. In this formulation quarks arise as domain wall fermions. In contrast to the usual quantum fields, quantum spins and quantum links realize asymptotically free field theories with finite-dimensional local Hilbert spaces. This is advantageous in the context of quantum simulation experiments. Both CP(N-1) models and QCD can be quantum simulated with ultra-cold alkaline-earth atoms in optical super-lattices. When CP(N-1) models are studied at non-zero chemical potential, non-trivial condensed matter physics arises in these quantum field theories. In particular, there are Bose-Einstein condensates, with or without ferromagnetism.

Zoom link will be available via announcement email, or by contacting: stroberg[at]uw.edu.

Online Seminar:

"Quantifying uncertainties in the nuclear-matter equation of state" [PDF]

Christian Drischler, University of California, Berkeley, and Lawrence Berkeley National Laboratory

Thursday, May 28, 2020, 10:30 AM Pacific Time

Abstract:

How well do we know the neutron-matter equation of state (EOS) at the densities inside neutron stars? And the nuclear saturation properties of symmetric matter? Chiral effective field theory (EFT) is widely used to predict the nuclear-matter EOS. What is needed now are statistically meaningful comparisons between nuclear theory and recent observational constraints, e.g., from NICER and direct detection of gravitational waves.

In this talk I report on the BUQEYE collaboration's [1] recent statistical analysis of EFT truncation errors in the infinite-matter EOS derived from chiral EFT [2,3]. Bayesian machine learning, via Gaussian Processes with physics-based hyperparameters, allows us to efficiently quantify and propagate theoretical uncertainties of the EOS (such as correlated EFT truncation errors) to derived quantities. In particular, I will explain why an understanding of truncation-error correlations between different densities and observables is crucial for reliable EOS uncertainty quantification.

[1] https://buqeye.github.io/

[2] Drischler, Furnstahl, Melendez, and Phillips, arXiv:2004.07232

[3] Drischler, Melendez, Furnstahl, and Phillips, arXiv:2004.07805

Zoom link will be available via announcement email, or by contacting: stroberg[at]uw.edu.

Online Seminar:

"Effective Field Theory Approach to Neutrinoless Double Beta Decay" [PDF]

Vincenzo Cirigliano, Los Alamos National Lab

Tuesday, May 26, 2020, 10:30 AM Pacific Time

Abstract:

In this talk I will discuss neutrinoless double beta decay and lepton number violation (LNV).

I will describe an end-to-end effective field theory (EFT) framework connecting the possibly very high scale at which LNV originates to the nuclear scale. Such a framework is crucial to assess the discovery potential and model diagnosing power of neutrinoless double beta decay searches. At the high-energy end, the EFT allows one to classify the various sources of LNV. At the low-energy end, the EFT allows one to organize contributions to hadronic and nuclear matrix elements in a systematic expansion, which is the basis to reach controlled uncertainties in the near future. I will discuss recent developments in the EFT approach and illustrate the framework through explicit examples, such as the high-scale seesaw and the TeV scale left-right-symmetric model.

Zoom link will be available via announcement email, or by contacting: stroberg[at]uw.edu.


Online Seminar:

"NS 1987A in SN 1987A"

Dany Page, Instituto de Astronomia, Universidad Nacional Autonoma de Mexico

Thursday, May 21, 2020, 10:30 AM Pacific Time

Abstract:

The possible detection of a compact object in the remnant of SN 1987A presents an unprecedented opportunity to follow its early evolution. The suspected detection stems from an excess of infrared emission from a dust blob near the compact object's predicted position. The infrared excess could be due to the decay of isotopes like 44Ti, accretion luminosity from a neutron star or black hole, magnetospheric emission or a wind originating from the spindown of a pulsar, or thermal emission from an embedded, cooling neutron star (NS 1987A).

It is shown that the last possibility is the most plausible as the other explanations are disfavored by other observations and/or require fine-tuning of parameters.

Not only are there indications the dust blob overlaps the predicted location of a kicked compact remnant, but its excess luminosity also matches the expected thermal power of a 30 year old neutron star. Furthermore, models of cooling neutron stars within the Minimal Cooling paradigm readily fit both NS 1987A and Cas A, the next-youngest known neutron star. If correct, a long heat transport timescale in the crust and a large effective stellar temperature are favored, implying relatively limited crustal n-1S0 superfluidity and an envelope with a thick layer of light elements, respectively. If the locations don't overlap, then pulsar spindown or accretion might be more likely, but the pulsar's period and magnetic field or the accretion rate must be rather finely tuned. In this case, NS 1987A may have enhanced cooling and/or a heavy-element envelope.

Zoom link will be available via announcement email, or by contacting: stroberg[at]uw.edu.


Online Seminar:

"Quantified Nuclear Structure Theory" [PDF]

Witold Nazarewicz

Department of Physics & Astronomy, and Facility for Rare Isotope Beams

Michigan State University

Thursday, May 14, 2020, 10:30 AM Pacific Time

Abstract:

To an increasing extent, theoretical nuclear physics involves statistical inference on computationally-demanding theoretical models that often combine heterogeneous datasets. Advanced statistical approaches can enhance the quality of nuclear modeling in many ways. First, the statistical tools of uncertainty quantification can be used to estimate theoretical errors on computed observables. Second, they can help to assess the information content of measured observables with respect to theoretical models and assess the information content of present-day theoretical models with respect to measured observables. Importantly, they can be used to understand a model's structure through parameter estimation and model reduction. Finally, statistical tools can improve predictive capability and optimize knowledge extraction by extrapolating beyond the regions reached by experiments to provide meaningful input to applications and planned measurements.

In this presentation, after presenting a brief summary of machine learning applications to low-energy nuclear theory, I will employ Bayesian machine learning tools to assess the predictive power of global mass models towards more unstable nuclei and provide uncertainty quantification of predictions. The proposed robust statistical approach to extrapolations can be useful for assessing the impact of current and future experiments in the context of model developments.

Zoom link will be available via announcement email, or by contacting: stroberg[at]uw.edu.

Online Seminar:

"Inference as a means to constrain dynamical models of neutrino flavor transformation"

Eve Armstrong , New York Institute of Technology

Thursday, May 7, 2020, 1:00 PM Pacific Time

CANCELLED

Abstract:

We employ statistical data assimilation (SDA), a type of machine learning (ML), to identify an optimal solution to a small-scale model of neutrino flavor transformation in core-collapse supernovae. SDA is a ML formula wherein a dynamical model is assumed to generate any measured quantities. Specifically, we use an optimization formulation of SDA wherein a cost function is extremized via the variational method. As the cost function is non-convex, we employ a method of simulated annealing to identify a lowest-minimum. The cost function corresponds to the physical Action of a path in state space. Regions of state space in which the extremization identifies the global minimum of the Action will correspond to parameter regimes in which a model solution can exist; it is in this sense that the optimization procedure can efficiently identify regimes of interest and rule out others. Our example study seeks to infer the neutrino flavor transformation histories, as well as unknown model parameters such as the strength of the matter potential, in a simple model consisting of two mono-energetic neutrino beams coherently interacting with each other and with a matter background. We show how the SDA procedure identifies a solution that is consistent with a measured neutrino flux at a detector. Time-permitting, I will discuss current work on placing theoretical constraints upon the location of the MSW (Mikheyev-Smirnov-Wolfenstein) resonances, in addition to the measurements at the detector. In this framework, we require that a solution be consistent with both the measurements and the constraints - with the aim to identify promising theoretical avenues. Overall, results intimate the promise of this "variational annealing" methodology to efficiently probe an array of fundamental questions that traditional numerical simulation codes render difficult to access.

Zoom link will be available via announcement email, or by contacting: stroberg[at]uw.edu.

Online Seminar:

"Advances in coupled-cluster computations of nuclei" [PDF]

Gaute Hagen, Oak Ridge National Laboratory

Thursday, April 30, 10:30 AM Pacific Time

Abstract:

In this talk I will report on recent advances in ab-initio coupled-cluster computations of nuclei starting chiral Hamiltonians with two- and three-nucleon forces. Using high precision coupled-cluster methods we addressed the quenching puzzle of β-decays in nuclei. We showed that this quenching can be explained from two-body currents and many-body correlations. In particular, we made predictions for the Gamow-Teller decay of the heavy nucleus 100Sn [1,2], and our result is consistent with the recent high precision measurement at RIKEN [3]. I will also show very recent results for medium-mass nuclei and nuclear matter using optimized chiral interactions with explicit delta degrees of freedom. Binding energies, radii, and saturation properties in nuclear matter are improved compared to existing chiral Hamiltonians. We have also started computations of deformed nuclei using a coupled-cluster approach starting from a deformed Hartree-Fock reference state with promising results for nuclei up to mass A~50. Last, but not least, I will present a new method that allows for the computation of bulk properties of an atomic nucleus for a million of different model parameters in less than one hour on a standard laptop. The equivalent set of ab-initio coupled-cluster computations would require about 20 years. This speedup enables statistical computing of the chiral nuclear Hamiltonian, and entirely new ways to use experimental data across the nuclear chart to generate new knowledge about the strong nuclear interaction [4].

[1] T. D. Morris, et al, Phys. Rev. Lett. 120, 152503 (2018)

[2] P. Gysbers, et al, Nature Physics 15, 428–431 (2019)

[3] D. Lubos et al., Phys. Rev. Lett. 122, 222502 (2019)

[4] A. Ekström and G. Hagen, Phys. Rev. Lett. 123, 252501 (2019)

Zoom link will be available via announcement email, or by contacting: stroberg[at]uw.edu.

Online Seminar:

"Developments in the Theory of Double-Beta Decay" [PDF]

Jonathan Engel, University of North Carolina at Chapel Hill

Thursday, April 23, 10:30 AM Pacific Time

Abstract:

After briefly discussing the significance of experiments to observe neutrinoless double-beta decay, I present recent developments in the nuclear theory needed to interpret those experiments, many obtained under the aegis of the DOE Topical Collaboration on Double-Beta Decay and Fundamental Symmetries. The developments include both new techniques for solving the nuclear many-body problem and applications of chiral effective field theory.

Online Seminar:

"Light at the end of the tunnel: The Electron-Ion Collider and QCD at high energies" [PDF]

Raju Venugopalan, Brookhaven National Lab

Thursday, April 16, 10:30 AM Pacific Time

Abstract:

I will outline the science and status of the EIC. I will then discuss some of my on-going research on the infrared structure of QCD at high energies, with emphasis on the potential insight provided by new theory techniques and from unanticipated interdisciplinary connections.

Online Seminar:

"Hydrodynamics attractors, initial state energy and particle production in relativistic nuclear collisions" [PDF]

Soeren Schlichting, Bielefeld University

Thursday, April 9, 10:00 AM Pacific Time

Abstract:

Explaining how a nearly equilibrated Quark-Gluon plasma emerges in the collision of heavy nuclei has been one of the central goals of the heavy ion theory community. We exploit recent advances in the theoretical understanding to establish a macroscopic description of the early-time out-of-equilibrium dynamics of high energy heavy-ion collisions and investigate phenomenological consequences of the pre-equilibrium phase. One direct consequence is a general relation between the initial state energy and the produced particle multiplicities measured in experiments. When combined with an ab initio model of energy deposition, the entropy production during the pre-equilibrium phase naturally explains the universal centrality dependence of the measured charged particle yields in nucleus-nucleus collisions. We further estimate the energy density of the far-from-equilibrium initial state and discuss how our results can be used to constrain non-equilibrium properties of the quark-gluon plasma.


Online Seminar:

"Surprises in large N Thermodynamics" [PDF]

Tom Cohen, University of Maryland

Thursday, April 2, 10:00 AM Pacific Time

Abstract:

The thermodynamic behavior of QCD at large N has been studied for decades. Despite this, there are a number of features that are not widely appreciated and are quite surprising. I this talk we note a few of these under the assumption that QCD has a generic first-order phase transition at large N as one sees for pure gauge theory. The existence of a first-order transition implies metastable phases. One surprise is that under this assumption large N QCD has a supercooled metastable plasma phase with negative absolute pressure---that is a pressure below that of the vacuum. Another surprise concerns the region beyond the endpoint of the superheated hadronic which, though both globally and locally unstable is never-the-less parametrically long lived at large N.


"From two to three-body systems in lattice QCD"

Ruairí Brett, The George Washington University

Thursday, March 5, 2020, 2:30 PM, PAT C421

Abstract:

Much of the resonant spectrum of QCD consists of states which decay strongly into two- and three-body states. Lattice QCD calculations have matured to the stage where these states can be reliably resolved in first principles numerical calculations. While connecting these finite-volume results to infinite-volume scattering processes is now commonplace in the two-body sector, three-body physics presents more difficulties. Building upon results in the two-body sector, I will describe a recent calculation involving three pions in maximal isospin, and compare to predictions from a state-of-the-art phenomenological formalism. We find agreement between predictions and lattice results, indicating the reliability of the approach.

All interested graduate students and faculty are invited to attend.

"Delineating the properties of neutron star matter in cold, dense QCD"

Toru Kojo, Central China Normal University

Thursday, February 27, 2020, 2:30 PM, PAT C421



All interested graduate students and faculty are invited to attend.

"Conformal spacelike-timelike correspondence in QCD"

Alfred Mueller, Columbia University

Thursday, February 20, 2020, 2:30 PM, PAT C421

Abstract:

This paper is a study of a spacelike-timelike conformal correspondence in QCD. When the times at vertices are fixed in an A+ = 0 gauge calculation the distribution of gluons in a highly virtual decay have an exact correspondence with the gluons in the lightcone wavefunction of a high energy dipole with the identification of angles in the timelike case and transverse coordinates in the lightcone wavefunction. Divergences show up when the time integrals are done. A procedure for dropping these divergences, analogous to the Gell-Mann Low procedure in QED, allows one to define a conformal QCD, at least through NLO. Possible uses of such a conformal QCD are discussed.

All interested graduate students and faculty are invited to attend.

"Exact representations of many body interactions from Restricted Boltzmann Machine neural networks"

Ermal Rrapaj, University of Berkeley, University of Minnesota

Thursday, February 6, 2020, 2:30 PM, PAT C421

Abstract:

In recent decades, machine learning in the form of deep neural networks, has been effectively used in diverse industrial applications. In physics, deep learning has been used to analyse particle accelerator data, discover phases of matter, represent ground states of quantum many body systems, and accelerate numerical algorithms. This talk will focus on the Restricted Boltzmann Machine and how it can be used to derive exact representations of many body forces with applications in quantum Monte Carlo simulations and quantum annealing. I conclude with implications for training this type of architecture based on its connection to physical systems.

All interested graduate students and faculty are invited to attend.

"Fermionic Sign Problem: an exaggerated myth"

Nikolay Prokofiev, University of Massachusetts

Thursday, January 23, 2020, 2:30 PM, PAT C421

Abstract:

Feynman diagrams are the most celebrated and powerful tool of theoretical physics usually associated with the analytic approach. I will argue that diagrammatic expansions are also an ideal numerical tool with enormous and yet to be explored potential for solving interacting fermionic systems by direct simulation of connected Feynman diagrams. Though the original series based on bare propagators and interaction vertexes are sign-alternating and often divergent one can determine the answer behind them by using appropriate series re-summation techniques, conformal mappings, asymptotic series analysis, and shifted action tools, including sequences based on the skeleton diagrams. In this formulation, the fermionic sign problem is simply absent for regular (as opposed to random) systems because the entire setup is valid in the thermodynamic limit. Instead, fermionic sign is a “blessing” because it leads to massive cancellation of high-order diagrams and ultimate convergence of the re-summed series. For illustration, I will discuss results for the unitary Fermi gas and the Fermi-Hubbard model.

All interested graduate students and faculty are invited to attend.

"Constraining the equation of state of dense nuclear matter from multimessenger observations of binary neutron stars"

Collin Capano, Max Planck Institute for Gravitational Physics (Albert Einstein Institute) Hannover

Thursday, November 14, 2019, 2:30 PM, PAT C421

Abstract:

The first direct detection of a gravitational wave from a binary neutron star merger, GW170817, was also the first event to be observed both by gravitational-wave detectors and telescopes. These “multimessenger” observations provided an opportunity to constrain the equation of state of the dense nuclear matter inside of neutron stars. The equation of state determines the size of the stars, as well as how much they are tidally deformed as they spiral into each other. The stars' tidal deformability is encoded in the emitted gravitational wave. However, the gravitational wave is only weakly dependent on the these parameters, making the equation of state difficult to infer from gravitational-wave data alone. I will show how combining chiral effective field theory with multimessenger observations of GW170817 yields the most stringent constrains on neutron-star radii to date. I will also discuss the implications of this measurement for future detections.

All interested graduate students and faculty are invited to attend.

"Nuclear Physics and Quantum Information Science : Report to NSAC - October 2019 "

Martin Savage, Institute for Nuclear Theory

and

David Hertzog, University of Washington

Thursday, October 24, 2019, 2:00 PM, PAA 102

Abstract:

The Nuclear Science Advisory Committee was charged by DOE and NSF to provide an assessment of the potential impact that QIS may have on Nuclear Physics research, and also unique opportunities for NP research to make advances in QIS. An NSAC Subcommittee was created in late 2018 to address this charge, and produced a report that has recently been provided to NSAC, and will be presented on October 18 in DC. This presentation will summarize the report.

All interested graduate students and faculty are invited to attend.

"Chiral charge dynamics in Abelian gauge theories at finite temperature "

Adrien Florio

Ecole Polytechnique Federale de Lausanne

Thursday, October 17, 2019, 2:00 PM, C421

Abstract:

The chiral anomaly present in the standard model can have important phenomenological consequences, especially in cosmology and heavy-ions physics. In this talk, I will focus on the contribution from the Abelian gauge fields. Despite an absence of topologically distinct sectors, they have a surprisingly rich vacuum dynamics, partly because of the chiral anomaly. I will present results obtained from real-time classical lattice simulations of a U(1) gauge field in the presence of a chiral chemical potential. They account for short distance fluctuations, contrary to effective descriptions such as Magneto-Hydrodynamics (MHD). I will discuss various phenomena, like inverse magnetic cascade, which occur in this system. In particular, in presence of a background magnetic field, the chemical potential exponentially decays. The associated chiral decay rate is related to the diffusion of the Abelian Chern-Simons number in a magnetic background, in the absence of chemical potential. The rate obtained from the simulations is an order of magnitude larger than the one predicted by MHD. If this result is shown to be robust under corrections such as Hard Thermal Loops, it will call for a revision of the implications of fermion number and chiral number non-conservation in Abelian theory at finite temperature.

All interested graduate students and faculty are invited to attend.

"Eigenvalues and eigenstates of the many-body collective neutrino oscillation Hamiltonian"

Amol Patwardhan

University of California, Berkeley

Thursday, June 27, 2019, 3:00 PM, C421

Abstract:

We demonstrate a method to systematically obtain eigenvalues and eigenstates of a many-body Hamiltonian describing collective neutrino oscillations. The method is derived from the Richardson-Gaudin framework, which involves casting the eigenproblem as a set of coupled nonlinear “Bethe ansatz equations,” the solutions of which can then be used to parametrize the eigenvalues and eigenvectors. The specific approach outlined here consists of defining auxiliary variables that are related to the Bethe ansatz parameters, thereby transforming the Bethe ansatz equations into a different set of equations that are numerically better behaved and more tractable. We show that it is possible to express not only the eigenvalues, but also the eigenstates, directly in terms of these auxiliary variables without involving the Bethe ansatz parameters themselves. The eigenvalues and eigenstates can then be used to study the adiabatic evolution of the many-body Hamiltonian, and to facilitate a comparison with the corresponding results in the mean field limit.

All interested graduate students and faculty are invited to attend.

"Fission and lanthanide production in r-process nucleosynthesis"

Nicole Vassh

University of Notre Dame

Thursday, June 6, 2019, 3:00 PM, C421

Abstract:

The observations of the GW170817 electromagnetic counterpart suggested lanthanides were produced in this neutron star merger event. Lanthanide production in heavy element nucleosynthesis is subject to large uncertainties from nuclear physics and astrophysics unknowns. Specifically, the rare-earth abundance peak, a feature of enhanced lanthanide production at A~164 seen in the solar r-process residuals, is not robustly produced in r-process calculations. The proposed dynamical mechanism of peak formation requires the presence of a nuclear physics feature in the rare-earth region which may be within reach of experiments performed at, for example, the CPT at CARIBU and the upcoming FRIB. To take full advantage of such measurements, we employ Markov Chain Monte Carlo to "reverse engineer" the nuclear masses capable of producing a peak compatible with the observed solar r-process abundances and compare directly with experimental mass data. Here I will present our latest results and demonstrate how the method may be used to the learn which astrophysical conditions are consistent with both observational and experimental data. Uncertainties in the astrophysical conditions also make it difficult to know if merger events are responsible for populating the heaviest observed nuclei, the actinides. Here I will discuss a potential direct signature of actinide production in merger environments. However, an r process which reaches the actinides is also likely to host fission, which is largely experimentally uncharted for neutron-rich nuclei. The influence of fission on lanthanide abundances, and the potential for future experimental and theoretical efforts to refine our knowledge of fission in the r process, will be discussed. The question of where nature primarily produces the heavy elements can only be answered through such collaborative efforts between experiment, theory, and observation.


All interested graduate students and faculty are invited to attend.

"Entanglement entropy, dualities, and deconfinement in gauge theories"

Mohamed Anber

Lewis & Clark College

Thursday, April 25, 2019, 3:00 PM, C520

Abstract:

Computing entanglement entropy (EE) and other information-theoretic quantities in gauge theories is often accompanied by difficulties and ambiguities. In this talk, I show that one can gain new insights into these computations by considering gauge theories compactified on a small circle. In particular, I study Yang-Mills theory compactified on a circle with a double-trace deformation or adjoint fermions and hold it at temperatures near the deconfinement transition. This theory is dual to a multi-component (electric-magnetic) Coulomb gas that can be mapped to an XY-spin model with Z_p preserving perturbations. With the help of a T-duality, I compute Renyi mutual information (RMI) of the XY-spin model by means of the replica trick and Monte Carlo simulations. The simulations indicate that RMI follows the area law scaling, with subleading corrections, and this quantity can be used as a genuine probe to detect deconfinement transitions. I also discuss the effect of fundamental matter on RMI and the implications of these findings in gauge theories and beyond.

All interested graduate students and faculty are invited to attend.

"Scattering Observables from Lattice QCD: progress in three-particle channels"

Steve Sharpe

University of Washington

Thursday, March 21, 2019, 3:00 PM, C421

Abstract:

Lattice QCD calculations have made great strides towards calculating resonance properties and decay amplitudes in cases where only two-particle channels are present. This required development of both theoretical formalism and simulation methods. However, many problems of interest involve three-particle channels, e.g. the Roper resonance and K -> 3 pion decays and for these, the theoretical formalism to relate the finite-volume lattice results to infinite-volume scattering quantities has been lacking.

After reviewing methods and results involving two particles, I describe recent work with Raul Briceno and Max Hansen in which we have developed the needed formalism in a generic relativistic field theory of identical scalar particles, and present results from a numerical implementation of the formalism in the isotropic approximation.

I close with a discussion of work with Tyler Blanton and Fernando Romero-López in which we go beyond the isotropic approximation and include d-wave interactions.

All interested graduate students and faculty are invited to attend.

"The road from nuclear forces to nuclear structure"

Dean Lee

Michigan State University

Thursday, March 14, 2019, 3:00 PM, C421

Abstract:

Several different research groups have independently found that state-of-the-art microscopic nuclear forces do not guarantee an accurate description of nuclear structure beyond light nuclei. I discuss recent results using lattice simulations and effective field theory that illuminate what is the problem and a viable path forward. Along the way, we investigate what are the essential elements for nuclear binding.

All interested graduate students and faculty are invited to attend.

"Effective field theory of (magneto) hydrodynamics and its gravity dual"

Paolo Glorioso

University of Chicago

Thursday, February 28, 2019, 3:30 PM, C421

Abstract:

In the first part I will review our work on formulating hydrodynamics as an effective field theory (EFT), which is based on the Schwinger-Keldysh formalism and is implemented in terms of a suitable set of degrees of freedom and symmetries. I will then show how this leads to a well-defined systematic framework to compute loop corrections around the equations of motion of hydrodynamics. I will also show how the formalism extends to magnetohydrodynamics by adding suitable degrees of freedom associated to a magnetic 1-form U(1) symmetry. Finally, I will outline the holographic construction of the EFT of diffusion, which is a baby version of the EFT of hydrodynamics. A crucial ingredient in the holographic derivation is a new analytic continuation in a double-sided black brane geometry.

All interested graduate students and faculty are invited to attend.

"Photoproduction of the rho resonance on the lattice"

Luka Leskovec

Jefferson Lab

Thursday, February 21, 2019, 3:00 PM, C421

Abstract:

I will present results on the rho resonance photoproduction from our recent lattice QCD study with N_f=2+1 clover fermions at a pion mass of approximately 320 MeV and lattice size 3.6 fm. The transition amplitude describing the photoproduction of the rho resonance on a pion is obtained from the more general process pi gamma to pi pi where the final state is in P-wave with quantum numbers I=1 and J^P=1^-. We employ the Briceno-Hansen-Walker-Loud approach to determine the pi gamma to pi pi transition amplitude in the invariant mass region near the rho resonance for both space- and time-like photon momentum. By analytic continuation to the rho pole we calculate also the rho radiative decay width.

All interested graduate students and faculty are invited to attend.

"Direct Detection of Composite Dark Matter"

Dorota Grabowska

University of California, Berkeley

Thursday, February 7, 2019, 3:00 PM, C421

Abstract:

Strongly interacting theories generically give rise to composite bound states; a strongly interacting dark sector is no different. These bound states may be comprised of just a few constituents or an exponentially large number, depending on factors such as other forces present in the sector and the mass of the constituents themselves. I will first present several possible mechanisms for the formations of these Dark Matter bound states in the Early Universe. I will then discuss various avenues for detection, focusing particularly on their detectability using both current and near future direct detection experiments.

All interested graduate students and faculty are invited to attend.

"Effective Field theory for Heavy dark matter annihilation"

Varun Pradeep Vaidya

Los Alamos National Laboratory

Thursday, January 24, 2019, 2:00 PM, C421

Abstract:

We construct an effective field theory (EFT) description of the hard photon spectrum for heavy WIMP annihilation. This facilitates precision predictions relevant for line searches, and allows the incorporation of non-trivial energy resolution effects. Our framework combines techniques from non-relativistic EFTs and soft-collinear effective theory (SCET), as well as its multi-scale extensions that have been recently introduced for studying jet substructure. We derive a factorization formula that enables both the resummation of the leading large Sudakov double logarithms that appear in the perturbative spectrum, and the inclusion of Sommerfeld enhancement effects. Consistency of this factorization is demonstrated to next to -leading logarithmic order through explicit calculation. Our final result contains both the exclusive and the inclusive limits, thereby providing a unifying description of these two previously-considered approximations. We estimate the impact on experimental sensitivity, focusing for concreteness on an triplet fermion dark matter — the pure wino — where the strongest constraints are due to a search for gamma-ray lines from the Galactic Center. We find numerically significant corrections compared to previous results, thereby highlighting the importance of accounting for the photon spectrum when interpreting data indirect detection experiments. Our calculation provides a state of the art prediction for the hard photon spectrum that can be easily generalized to other DM candidates, allowing for the robust interpretation of data collected by current and future indirect detection experiments.

All interested graduate students and faculty are invited to attend.

"Spectroscopy on the lattice"

Raul Briceno

Jefferson Lab

Thursday, January 10, 2019, 2:00 PM, C421

Abstract:

In order to decipher the underlying rules governing the non-perturbative behavior of quarks and gluons inside the bound states of QCD, we must first determine and understand the spectrum of the theory. In recent years we have seen increased interest in hadron spectroscopy, triggered primarily by the experimental discovery of states that challenged previous existing conventions. Experimental data alone is not sufficient to confirm the existence of a state or provide a detailed picture of its nature. As a result, it is necessary to carry a parallel theoretical program, and lattice QCD is the natural tool to base this effort on. In this talk, I review the progress in determining and understanding the QCD spectrum using lattice QCD.

All interested graduate students and faculty are invited to attend.

"Neutron rich dense matter, neutron star mergers, and laboratory experiments"

Charles J. Horowitz

Indiana University

Thursday, November 29, 2018, 2:30 PM, C421

Abstract:

I review gravitational wave and E+M observations of the neutron star merger GW170817 and discuss what we are learning about dense neutron rich matter and the origin of the heavy elements. Equation of state (pressure versus density) constraints from these gravitational wave observations are compared to information from the Jefferson Laboratory PREX and CREX experiments. These experiments also probe neutron rich matter by measuring the neutron skins of the nuclei 208Pb and 48Ca with parity violating electron scattering. Finally, heat capacity and neutrino cooling observations of neutron stars have interesting implications for the degrees of freedom, quark and hadron, of dense matter.

All interested graduate students and faculty are invited to attend.

"Nuclear response at finite temperature "

Elena Litvinova

Western Michigan University

National Superconducting Cyclotron Laboratory

Thursday, November 15, 2018, 2:00 PM, C421

Abstract:

Recent developments of the relativistic nuclear field theory on the finite-temperature response will be presented. The general non-perturbative framework, which advances the nuclear response theory beyond the random phase approximation (RPA), is formulated in terms of a closed system of non-linear equations for the two-body Green’s functions. This provides a direct link to ab initio theories and allows for controlled approximate solutions.

The response theory beyond RPA is extended to the case of finite temperature. For this purpose, the time blocking approximation to the time-dependent part of the in-medium nucleon-nucleon interaction amplitude is adopted for the thermal Green’s function formalism. The method is implemented in a parameter-free way on the base of Quantum Hadrodynamics with effective meson-nucleon coupling adjusted on the mean-field level. In this framework, we investigate the temperature dependence of dipole spectra in the even-even medium-heavy nuclei with a special focus on the giant dipole resonance’s width problem and on the low-energy dipole strength distribution. Its behavior, together with the temperature dependence of the charge-exchange resonances, are studied for their potential impact on the r-process nucleosynthesis.

All interested graduate students and faculty are invited to attend.

"Neutron star matter constraints from gravitational wave observations"

Jocelyn Read

California State University, Fullerton

Thursday, October 4, 2018, 2:00 PM, C421


Abstract:

Neutron stars host the densest stable matter in the universe. Accurately modeling their multi-messenger astrophysics relies on a detailed description of the equation of state above nuclear density. Astronomical observations of neutron stars can in turn be used to constrain the properties of this dense matter.


On August 17, 2017 the Advanced LIGO and Advanced Virgo detectors discovered the first gravitational-wave signal consistent with a binary neutron star inspiral. The three-dimensional localization of the source using LIGO and Virgo data enabled a successful electromagnetic follow-up campaign that identified an associated kilonova in a galaxy ~40 Mpc from Earth. We are also able to constrain the equation of state of dense matter in neutron stars using the observed gravitational waves. I will outline how these constraints are made, how they connect with other astronomical observations, and outline future prospects for connecting gravitational-wave astronomy with above-nuclear-density physics.

All interested graduate students and faculty are invited to attend.

"Hadronic corrections to the anomalous magnetic moment of the muon"

Peter Stoffer

University of California, San Diego

Thursday, September 27, 2018, 2:30 PM, C421


Abstract:

The anomalous magnetic moment of the muon g-2 has been measured and computed to very high precision of about 0.5 ppm. For more than a decade, a discrepancy has persisted between experiment and Standard Model prediction, now of about 3-4 sigma. The main uncertainty of the theory prediction is due to strong-interaction effects, the hadronic vacuum polarisation (HVP) and hadronic light-by-light (HLbL) contributions.


While the most precise HVP evaluation is based on dispersion relations and data input, HLbL is currently plagued by uncontrolled model uncertainties. Within a dispersive framework based on unitarity and analyticity, we scrutinize the uncertainty estimates for the two-pion HVP channel and we calculate model-independently two-pion contributions in HLbL, which shows an avenue towards a data-driven evaluation of g-2 of the muon.

All interested graduate students and faculty are invited to attend.

"Light-cone PDFs from Lattice QCD"

Martha Constantinou

Temple University

Thursday, August 23, 2018, 2:00 PM, C421


Abstract:

Lattice QCD (LQCD) is a theoretical non-perturbative approach for the study of QCD dynamics numerically and from first principles. For more than a decade, LQCD has been very successful in the calculation of the hadronic spectrum, making postdictions of well-measured hadronic masses, as well as, predictions. Nowadays, LQCD is widely used for hadron structure calculations and is becoming a reliable tool, providing input to the experimental and phenomenological communities. Over the last years, progress in the simulation of LQCD has been impressive, driven by improvements in the algorithms and increase in computational power, that have enabled simulations to be carried out at parameters very close to their physical values (physical point).


In this talk I will present recent results for the so-called quasi-PDFs, a new direct approach to compute parton distributions functions (PDFs) directly in LQCD. The quasi-PDF approach was introduced by Xiangdong Ji in 2013 and was intensively developed thereafter. We present results for the unpolarized, helicity and transversity PDFs calculated at the physical point. A careful investigation of systematic uncertainties, such as excited states and renormalization will be presented, that aims at obtaining reliable estimates. The light-cone PDFs are reconstructed using large momentum effective theory (LaMET) that allows comparison with phenomenological parameterizations of experimental data. We find several similarities between the lattice and phenomenological estimates of PDFs, and demonstrate the importance of simulations at the physical point. Of particular importance are the results on the transversity PDFs, that are not well-constrained experimentally, This presents a major success for the emerging field of direct calculations of quark distributions using Lattice QCD.

All interested graduate students and faculty are invited to attend.

"Many-Body Perturbation Theory for Nuclear Matter at High Orders"

Christian Drischler

University of California, Berkeley

Thursday, June 21, 2018, 2:00 PM, C421


Abstract:

Nuclear matter is an ideal testbed for nuclear interactions with important consequences for nuclear astrophysics as well as finite nuclei. In particular, recent ab initio calculations of medium-mass to heavy nuclei have demonstrated the importance of realistic saturation properties of infinite matter for nuclear forces. We present an efficient Monte-Carlo framework for perturbative calculations of infinite nuclear matter based on two-, three-, and four-nucleon forces derived within chiral effective field theory. It enables to incorporate all many-body contributions in a transparent and also straightforward way, making it well-suited for pushing the limits of current state-of-the-art calculations to high orders in both the chiral as well as the many-body expansion. Furthermore, uncertainty estimates can be systematically extracted by order-by-order calculations, which provides important insights into the rate of convergence of each of the two expansions. After demonstrating its versatility, we make use of this novel framework to explore new chiral interactions up to next-to-next-to-next-to-leading order (N3LO) and study the equation of state of neutron and symmetric nuclear matter. Remarkably, simultaneous fits to the triton and to saturation properties can be achieved with natural 3N low-energy couplings. Taking advantage of the framework's efficacy, future chiral potentials may be optimized with respect to empirical saturation properties.

All interested graduate students and faculty are invited to attend.

"Locating the Quantum Chromodynamic Critical Point"

Jacquelyn Noronha-Hostler

Rutgers University

Thursday, June 7, 2018, 2:00 PM, C421


Abstract:

Strongly interacting matter undergoes a crossover phase transition at high temperatures T ~ 10^12 K and zero net-baryon density. A fundamental question in the theory of strong interactions, Quantum Chromodynamics (QCD), is whether a hot and dense system of quarks and gluons displays critical phenomena when doped with more quarks than antiquarks, where net-baryon number fluctuations diverge. Recent lattice QCD work indicates that such a critical point can only occur in the baryon dense regime of the theory, which defies a description from first principles calculations due to the Fermi sign problem. In this talk, the latest Lattice QCD efforts to find the QCD critical point will be discussed in the context of the interplay between strange and light flavors in the crossover section of the phase diagram. In the baryon dense regime where Lattice QCD results are not yet available I will show how the holographic correspondence can be used to map the fluctuations of baryon charge in the dense quark-gluon liquid onto a numerically tractable gravitational problem involving the charge fluctuations of holographic black holes.

All interested graduate students and faculty are invited to attend.

"Chiral vortical effect for higher spin particles"

Andrey Sadofyev

Los Alamos National Laboratory

Thursday, May 17, 2018, 2:00 PM, C421


Abstract:

In a medium of massless fermions rotation can source a polarization current known as chiral vortical effect (CVE). Within a semi-classical description this phenomenon originates in the Berry phase and can be seen as a 3d analogue of the spin-Hall effect. It is well known that the spin-Hall effect takes place also for photons indicating a more general nature of topological polarization effects. In this talk we will discuss how CVE can be generalized to a system of massless particles with an arbitrary spin.

All interested graduate students and faculty are invited to attend.

"Exploiting Machine Learning Techniques in High Energy Nuclear Physics"

Raghav Kunnawalkam Elayavalli

Wayne State University

Thursday, May 10, 2018, 2:00 PM, C421


Abstract:

The high energy physics community at the LHC have utilized state of the art machine learning (ML) techniques quite successfully including the discovery of the Higgs boson. While such methods are quite common and readily applicable in big data style analysis, they are only recently being formulated and employed in nuclear physics. We shall go through a very brief overview of machine learning techniques and some of its recent applications to the study of the Quark Gluon Plasma. We study the phenomenon of jet quenching utilizing quark and gluon jet substructures as independent probes of heavy ion collisions. We exploit jet and sub-jet features to highlight differences between quark and gluon jets in vacuum and in a medium with the jet-quenching model implemented in JEWEL MC. To systematically extract jet substructure information, we introduce the telescoping deconstruction framework exploiting subjet kinematics at multiple angular scales. We find that the quark gluon discrimination performance worsens in heavy ion jets due to significant soft event activity affecting the soft jet substructure. Our work suggests a systematically improvable framework for studying modifications to quark and gluon jet substructures and facilitating direct comparisons between theoretical calculations, simulations and measurements in heavy ion collisions.

All interested graduate students and faculty are invited to attend.

"The Photon PDF"

Aneesh Manohar

University of California, San Diego

Thursday, April 26, 2018, 2:00 PM, C421


Abstract:

The photon PDF of the proton is needed for precision comparisons of LHC cross sections with theoretical predictions. A new approach allows the photon PDF to be computed in terms of proton deep-inelastic structure functions, reducing the uncertainty over previous methods by about a factor of 40. W and Z PDFs can be computed by similar methods. The talk discusses the determination of the photon and electroweak gauge boson PDFs.

All interested graduate students and faculty are invited to attend.