Past Events

2023

November 15th, 9pm (GMT-3): Mei Huang (University of the Chinese Academy of Science)

QCD matter under magnetic field

I will introduce some recent progress on understanding QCD matter properties under magnetic fields, as well as the recently developed chiral anomaly transport (CAT) model to trace the evolution of the topological charge and the generation of the charge separation in heavy ion collisions.

October 11th, 2pm (GMT-3): Igor Shovkovy (Arizona State University): Scalar boson emission from a magnetized relativistic plasma

I will present our recent study of the differential emission rate of neutral scalar bosons from a highly magnetized relativistic plasma [1]. The scalar production comes from three processes at the leading order: particle splitting, antiparticle splitting, and particle-antiparticle annihilation. It is unlike the scenario with zero magnetic field, where only the annihilation processes contribute to boson production. The impact of Landau-level quantization on the energy dependence of the rate is examined, and the angular distribution of emitted scalar bosons is investigated. The differential rate resulting from both (anti-)particle splitting and annihilation processes are typically suppressed in the direction of the magnetic field and enhanced in perpendicular directions. Overall, the background magnetic field significantly amplifies the total emission rate. The model study provides valuable theoretical insights.

[1] Jorge Jaber-Urquiza and Igor A. Shovkovy, arXiv:2310.00050.

September 13th, 2pm (GMT-3): Veronica Dexheimer (Kent State University, USA)

Neutron stars populate a very important part of the high-energy or QCD phase diagram, where fundamental information is currently provided by theory, laboratory experiments, and astrophysics. How to translate between results obtained from different environments that produce different conditions is one of the most important open questions in nuclear and high-energy physics today. I review the current knowledge of the QCD phase diagram and address how differences in isospin, strangeness, and magnetic field strength can modify the structure and position of deconfinement to quark matter, emphasizing on neutron star observables.

June 7th, 2pm (GMT-3): Jinfeng Liao (Indiana University Bloomington, USA)

In the first part of this talk, I will give a general discussion on the recent interest and developments regarding the spin transport in heavy ion collisions. The second part of the talk will then focus on one novel example: the chiral magnetic effect (CME), which is a nontrivial macroscopic transport phenomenon arising from microscopic quantum anomaly of underlying fermions in a chiral material (e.g. a Dirac/Weyl semimetal or a quark-gluon plasma). In the context of heavy ion collisions, CME provides a unique way to directly access and manifest gauge field configurations with nontrivial topological structures, which are known to play crucial roles in many fundamental aspects of the Standard Model. Potential discovery of CME in heavy ion collisions is of utmost significance, with extensive experimental searches carried out over the past decade. Some fourteen years after the initial hint of a possible CME signal, we are getting closer and closer to a quantitative understanding of both the signal and backgrounds entangled in the abundance of experimental data from RHIC to the LHC. This talk will evaluate the implications of these latest progress for the search of CME as well as discuss important issues to be further addressed with near-term theoretical/experimental efforts in order to reach a conclusive interpretation of current and future measurements.

May 3th, 2pm (GMT-3): Débora Menezes (Universidade Federal de Santa Catarina, Brazil)

Strong magnetic fields exist(ed) in the early Universe, in non-central heavy ion collisions and in magnetars. Hence, a natural question arises: what would be the consequences on the QCD phase diagram if matter were subject to strong magnetic fields? I will try to answer it, at least partially, with the help of different models. Different versions of the NJL model were used to calculate the critical chemical potential and the critical endpoint. As far as magnetars are concerned, the crust-core transition was obtained with the help of spinodals and binodals and the inner constituents of magnetars were calculated with different hadronic models. I also discuss how to deal with anisotropic effects in magnetars and finally, I show how to build the QCD phase diagram with various recipes taking into account two models: one for the hadronic phase and another one for the quark phase both subject to strong magnetic fields.

April 7th, 11am (GMT-3): Koichi Hattori (Zhejiang University, China) - Competition between the magnetic catalysis and the QCD Kondo effect in strong magnetic fields

Abstract: We discuss the QCD phase diagram in the presence of strong magnetic fields. It is known that the chiral symmetry is inevitably broken by the celebrated mechanism of the "magnetic catalysis" induced by the effective dimensional reduction in strong magnetic fields. We add heavy-quark impurities into the light-quark matter. The dimensional reduction also inevitably gives rise to the "QCD Kondo effect" with the formation of the heavy-light quark condensate [1, 2]. We therefore address the competition between the magnetic catalysis and the QCD Kondo effect to determine the true ground state within the mean-field approximation [3]. We find that the competition induces a quantum critical point where the true vacuum switches over from one to the other.

[1] K. Hattori, K. Itakura, S. Osaki, and S. Yasui,Phys.Rev.D 92 (2015) 065003 [1504.07619 [hep-ph]]

[2] S. Ozaki, K. Itakura, and Y. Kuramoto, Phys.Rev.D 94 (2016) 074013 [1509.06966 [hep-ph]]

[3] K. Hattori, D. Suenaga, K. Suzuki, S. Yasui, 2211.16150 [hep-ph]

March 8th, 2pm (GMT-3): Kirill Tuchin (Iowa State University, USA) - At the frontier of the magnetic field and rotation

Abstract: I discuss the synchrotron radiation emitted by a rigidly rotating charged fermion in a constant magnetic field B. The rigid rotation means that the fermion is immersed into a rotating medium that drags it along. It is classical and independent of the magnetic field. The angular velocity of rotation is assumed to be much smaller than the inverse magnetic length which allows us to ignore the boundary effects at the light cylinder. I refer to such rotation as slow, even though in absolute value it may be an extremely rapid rotation. Using the exact solution of the Dirac equation we obtained the analytical and numerical results for the intensity of electromagnetic radiation, its spectrum and chirality. The effect of rotation turns out to be quite large and relevant to the relativistic heavy-ion phenomenology. I then discuss extension of this formalism for very fast rotation and related problems.

2022

June 8th, 2pm (GMT-3): Mássimo D'Elia (Pisa University, Italy) "Phase Diagram of Quantum Chromodynamics in a Magnetic Field".
Abstract: I will review results regarding the QCD Phase Diagram in the presence of a magnetic field, with a focus on lattice QCD simulations and on recent evidence about the existence and location of a critical endpoint at which the QCD crossover turns into a first order phase transition.

May 4th, 2pm (GMT-3): Norberto Scoccolla (Department of Theoretical Physics, Comision nacional Energia Atomica, Argentina) "Strong magnetic fields in the NJL model: regularization issues and treatment of charged mesons"
Abstract: In this talk I will first review the different methods of regularization used in the literature for the Nambu-Jona-Lasinio model in the presence of a strong magnetic field B. I will then compare the corresponding predictions for B-dependence of the chiral condensate with those obtained using LQCD simulations. Finally, I will briefly discuss how to account for the non-vanishing Schwinger phase that appears in the calculation of the charged meson properties.

April 6th, 2pm (GMT-3): Daniel Brandenburg (Brookhaven National Laboratory, USA) "Utilizing Photon-mediated Processes to Probe the Ultra-strong Electromagnetic fields of Heavy-ion Collisions"
Abstract: Ultra-relativistic heavy-ion collisions are expected to produce the strongest electromagnetic fields in the known Universe. These highly-Lorentz contracted fields can manifest themselves as linearly polarized quasi-real photons that can interact via the Breit-Wheeler process to produce lepton anti-lepton pairs. In so-called photo-nuclear interactions, a photon from the field of one nucleus may fluctuate into a quark anti-quark pair and thereby interact directly with the other nucleus. The production rates of these processes provide insight into the strength of the electromagnetic fields produced in heavy-ion collisions. Recently it has been realized that detailed measurements of the produced particles' kinematics can further elucidate the strength and distribution of the colliding fields. For instance, in the two-photon process, the energy and momentum distribution of the produced dileptons provide pristine information about the strength and spatial distribution of the colliding fields. Recently it has been demonstrated that photons from these fields can interact even in heavy-ion collisions with hadronic overlap, providing a purely electromagnetic probe of the produced medium. Therefore, these events provide an in-situ probe of the electromagnetic fields produced simultaneously with a quark-gluon plasma, potentially useful for studying the lifetime of the electromagnetic fields and electrical properties of the quark-gluon plasma.
In this talk I discuss the recent theoretical progress and experimental advances for mapping the ultra-strong electromagnetic fields produced in heavy-ion collisions via measurement of the Breit-Wheeler process and photo-nuclear interactions. Finally, I will present new results from the STAR experiment employing some of these ideas and techniques to investigate the electromagnetic field at play in the recent isobar collisions, Zr+Zr and Ru+Ru.

March 9th, 2pm (GMT-3): Luis Hernandez (Universidad Autónoma Metropolitana, Mexico), "Ideas on identifying the vacuum terms in magnetized systems".
Abstract: In this talk, we will try to discuss some ideas about the analytic structure obtained from quantum correction in presence of uniform and constant magnetic fields. We will use theories like $\lambda phi^4$ and scalar QED in order to show if it is possible to split these quantum corrections in two pieces, vacuum and finite magnetic field pieces. Finally, we will discuss the meaning of the vacuum contribution when we want to analyze the magnetic modifications.