Embedded Files
December 19, 2025
(CET = Central European Time, IST = Indian Standard Time)
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12:00 - 12:30 CET / 16:30 - 17:00 IST
Speaker: Joydeep Naskar (Northeastern University, Boston)
Title: Holographic Entropy Inequalities.
Abstract: We propose a triality between holographic entropy inequality, contraction maps and graph maps between partial cubes, connecting the disciplines of physics, computer science and mathematics. We use the triality to find all holographic entropy inequalities. More specifically, the validity of a holographic entropy inequality is implied by the existence of a contraction map, which we prove to be equivalent to finding an isometric embedding of a contracted graph. Thus, by virtue of the completeness of the contraction map proof method, the problem of finding all holographic entropy inequalities is equivalent to the problem of finding all
contraction maps, which we translate to a problem of finding all image graph partial cubes. We give an algorithmic solution to this problem and characterize the complexity of our method.
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12:30 - 13:00 CET / 17:00 - 17:30 IST
Speaker: Rudnei O. Ramos (Rio de Janeiro State University, Brazil)
Title: Some Recent Developments in Warm Inflation.
Abstract: In this seminar, I briefly review the basic idea of warm inflation and highlight its differences with respect to the standard cold inflation paradigm. I then discuss the main model-building frameworks that lead to warm inflation, emphasizing constructions motivated by particle physics. Finally, I present an overview of some recent results and advances in the study of warm inflation.
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13:00 - 13:30 CET / 17:30 - 18:00 IST
Speaker: Nishant Agarwal (University of Massachusetts Lowell, USA)
Title: Mutual information as a measure of renormalizability.
Abstract: Renormalization is an essential technique in field-theoretic descriptions of natural phenomena, where the absence of a UV-complete description yields an abundance of divergent quantities. While the renormalization prescription has been thoroughly refined for equilibrium systems, consistently extending it to out-of-equilibrium systems is an active area of research. In the first part of my talk, I will consider a toy model of out-of-equilibrium quantum field theory (QFT) in Minkowski spacetime where time-dependence is introduced by performing an interaction quench at some initial time. I will show that additional initial state counterterms may be needed to renormalize correlations in this case, depending on the type of interaction. In the second part of my talk, I will relate initial state counterterms to entanglement between ultraviolet (UV) and infrared (IR) modes and argue that mutual information between infinitesimal shells in momentum space should capture any UV-IR correlation. Specifically, I will show that the logarithmic derivative of mutual information with mode separation, at large mode separation, is a measure of renormalizability for both equilibrium and out-of-equilibrium QFTs.
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December 12, 2025
(CET = Central European Time, IST = Indian Standard Time)
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12:00 - 12:35 CET / 16:30 - 17:05 IST
Speaker: Tanmoy Paul (Visva-Bharati University, India)
Title: Natural validation of first and second law of thermodynamics in cosmology (with / without viscosity)
Abstract: The purpose of this talk is two folded: (1) in the first part, I will discuss why thermodynamics is important in cosmology, and then, (2) I will show that the laws of thermodynamics (including the second law) gets naturally satisfied during the entire cosmic evolution of the universe starting from inflation to the late dark energy era, without imposing any exotic condition. The first part is based on how the matter fields inside the horizon exhibit a flux during the cosmic expansion of the universe. Regarding the thermodynamic laws in cosmology, it is individually showed for two different class of gravitational theories: (a) having one thermodynamic degree of freedom, and (b) having more than one thermodynamics degrees of freedom. These make the inter-connection between cosmology and thermodynamics more concrete. Consequently, it also depicts that why the matter fields are not in thermal equilibrium with the apparent horizon during most of the cosmic era of the universe, except for the fluids with ω = −1/3 leading to the transitions of the universe from an accelerating to a decelerating era and vice-versa. The effect of viscosity on thermodynamic laws will be discussed as well. We will explicitly show the viscosity makes the universe expansion more irreversible compared to the case in absence of viscosity.
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12:35 - 13:10 CET / 17:05 - 17:40 IST
Speaker: Alessandro Tronconi (INFN and Bologna University)
Title: Primordial Black Holes and a Non-Minimally Coupled Inflaton
Abstract: The generation of large curvature perturbations associated with the formation of primordial black holes in the context of a single-field inflaton with non-minimal coupling is discussed. To enable such amplification, we consider the dynamics of inflationary models in the presence of higher-dimensional operators. Within a minimal EFT framework, we finally present two viable extensions of "vanilla" Higgs Inflation in which the curvature perturbation spectrum generated by the Higgs field remains consistent with CMB observations and can lead to the formation of primordial black holes in the asteroid-mass range, potentially accounting for the entirety of dark matter.
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December 05, 2025
(CET = Central European Time, IST = Indian Standard Time)
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12:00 - 12:45 CET / 16:30 - 17:15 IST
Speaker: Enrico Pajer (Department of Applied Mathematics and Theoretical Physics, University of Cambridge, UK)
Title: An open system approach to cosmology
Abstract: Cosmological models and predictions rely extensively on the well-established field theory framework of particle physics. However, a qualitatively new challenge arises: cosmological systems inherently contain substances with poorly constrained macroscopic properties and entirely unknown microphysics, such as the inflaton sector, dark matter, and dark energy. This results in a rich array of novel phenomena, including dissipation, stochastic fluctuations, out-of-equilibrium dynamics, and non-unitary macroscopic evolution. Moreover, since gravitational observables are of primary interest, and gravity universally couples to all forms of matter, a precise description of all cosmic constituents is required—something feasible only in the simplest toy models. To address these challenges, I propose an open system approach to cosmology.
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12:45 - 13:30 CET / 17:15 - 18:00 IST
Speaker: Saurya Das (University of Lethbridge)
Title: A singularity free classical theory of gravity
Abstract: We present a classical theory of gravity, which is singularity free at short distances and reduces to General Relativity at large distances. We discuss its implications for quantum gravity and cosmology.
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November 28, 2025
(CET = Central European Time, IST = Indian Standard Time)
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12:00 - 12:45 CET / 16:30 - 17:15 IST
Speaker: Yusuke Manita (Perimeter Institute)
Title: Nonlinear Quasinormal Mode Resonance in Kerr Black Holes
Abstract: In this presentation, we analyze the nonlinear effects of perturbations in Kerr black hole spacetime, focusing specifically on resonance phenomena between quasi-normal modes (QNMs). We investigate the resonance structure that emerges when the frequency of the nonlinear QNM, generated by the third-order nonlinear interaction of the fundamental mode, approaches the eigenfrequency of the linear first overtone. Based on an analysis based on the Teukolsky equation, we demonstrate that this nonlinear interaction introduces a new pole, which can be formulated as a nonlinear excitation factor.
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12:45 - 13:30 CET / 17:15 - 18:00 IST
Speaker: Timothy Cohen (CERN,Switzerland/ UOregon, USA)
Title: What is the Geometry of Effective Field Theories?
Abstract: It is well known that the observables for some classes of EFTs (e.g. the non-linear sigma model) naturally can be cast in terms of geometric quantities that are defined on a field space manifold. One of the main benefits of this geometric approach is that it makes the field redefinition invariance of on-shell amplitudes manifest. However, the standard approach does not apply to general EFTs; additionally, the field space geometry picture breaks down when one performs field redefinitions that involve derivatives. In this talk, I will present a proposal for how to extend the notion of field space geometry to general EFTs in such a way as to accommodate general field redefinitions. I will introduce the framework we call “functional geometry,” and will argue that this approach lays the groundwork for many new developments towards understanding properties of EFTs that circumvents issues associated with field redefinition ambiguities.
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13:30 - 14:15 CET / 18:00 - 18:45 IST
Speaker: Rodrigo Gonzalez Quaglia (University of Groningen and UNAM)
Title: Post-inflationary sourcing of adiabatic perturbations.
Abstract: One of the main distinctions between single- and multi-field models of inflation is that, on superhorizon scales, the curvature perturbation power spectrum is generally not frozen, as it is sourced by the isocurvature component. This behavior arises from the multi-field background dynamics, which typically involve turns in field space. In this talk, however, I will show that even when the background trajectory does not turn during inflation, there can still be a sourcing of curvature perturbations after inflation. I will illustrate this effect within a modular-invariant model and discuss the impact of this post-inflationary enhancement of the curvature power spectrum on CMB observables.
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November 21, 2025
(CET = Central European Time, IST = Indian Standard Time)
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12:00 - 12:45 CET / 16:30 - 17:15 IST
Speaker: Sébastien Renaux-Petel (Institut d'Astrophysique de Paris, CNRS, France)
Title: Inflation beyond perturbation theory.
Abstract: The wavefunction of the universe contains the full information about primordial fluctuations. I will show how to determine it in a non-perturbative manner in a large class of inflationary scenarios, using the example of models with small and rapid oscillations in the inflaton potential. Our study reveals a profound asymmetry between maxima and minima of the density fluctuations, and indicates that even minute oscillations give large effects on the tail of the distribution. Eventually, I will describe a qualitatively new regime in which most of the information of inflationary correlators appears in higher-order correlation functions with large n.
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12:45 - 13:30 CET / 17:15 - 18:00 IST
Speaker: Saarik Kalia (Institut de Física d'Altes Energies (IFAE), Barcelona, Spain)
Title: Dynamically generated tilt of isocurvature fluctuations.
Abstract: Light scalar fields acquire isocurvature fluctuations during inflation. While these fluctuations could lead to interesting observable signatures at small scales, they are strongly constrained on large scales by cosmic microwave background observations. When the mass of the scalar is much lighter than the inflationary Hubble scale, $m\ll H_I$, the spectrum of these fluctuations is flat. Meanwhile, if $m\gg H_I$, the fluctuations are suppressed. A blue-tilted isocurvature spectrum which exhibits enhanced structure on small scales but avoids observational constraints on large scales therefore requires a coincidence of scales $m\sim H_I$ for a free massive scalar. In this talk, I will show that if a scalar field possesses a nontrivial potential, its inflationary dynamics naturally cause this condition to be satisfied, and so a blue-tilted spectrum is generically expected for a large class of potentials. Specifically, if its potential $V$ exhibits a region which satisfies the slow-roll condition $V''<3H_I^2$, the scalar condensate will spend most of inflation close to the boundary of this region, so that its effective mass is typically close to $H_I$. The resulting blue tilt is inversely proportional to the number of $e$-folds of inflation prior to horizon crossing. If the scalar is long-lived, this mechanism leads to an attractor prediction for its relic abundance, which is insensitive to initial conditions of the scalar. In particular, a scalar field with quartic self-interactions can achieve the correct abundance to constitute all of the dark matter for a wide range of masses. I will show the relationship between the mass and self-coupling of quartic dark matter predicted by this mechanism.
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13:30 - 14:15 CET / 18:00 - 18:45 IST
Speaker: Gabriel Luis Dizon (National Institute of Physics, University of the Philippines Diliman, Philippines)
Title: Primordial black hole abundance constraint projections for binary mergers with unequal mass ratios.
Abstract: In this talk, we explore the impact of considering a wide range of unequal binary mass ratios (1 < q < 1000) arising from extended mass distributions on primordial black hole (PBH) abundance constraint projections from upcoming gravitational-wave (GW) observations. We note that constraint projections for LISA and the Einstein Telescope are relatively robust to naive changes in the mass distribution sampled by the 2-body merger channel. Once we incorporate initial clustering, modeled with initial mass ratio dependence, we find changes in the constraint projection window that imply an enhancement of the 2-body merger rate for lower mass binaries. We also touch upon current difficulties in modeling the merger rates of unequal mass ratio binaries, along with possible approaches to tackle these problems.
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14:15 - 15:00 CET / 18:45 - 19:30 IST
Speaker: Gordan Krnjaic (Fermilab, US)
Title: Observable CMB B-modes from cosmological phase transitions.
Abstract: A B-mode polarization signal in the cosmic microwave background (CMB) is widely regarded as smoking gun evidence for gravitational waves produced during inflation. Here we demonstrate that tensor perturbations from a cosmological phase transition can produce a B-mode signal whose strength rivals that of testable inflationary predictions across a range of observable scales. Although phase transitions arise from causal sub-horizon physics, they nevertheless exhibit a white noise power spectrum on super-horizon scales. Power is suppressed on the large scales relevant for CMB B-mode polarization, but it is not necessarily negligible. For appropriately chosen phase transition parameters, the maximal B-mode amplitude can compete with inflationary predictions that can be tested with current and future experiments. These scenarios can be differentiated by performing measurements on multiple angular scales, since the phase transition signal predicts peak power on smaller scales.
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November 14, 2025
(CET = Central European Time, IST = Indian Standard Time)
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17:15 - 18:00 CET / 21:45 - 22:30 IST
Speaker: Stefano Profumo (University of California, Santa Cruz, USA)
Title: Black Holes and Dark Matter.
Abstract: The possibility that some of the black holes in the universe have a non-stellar origin and that they play a significant role in cosmology - including being some or all of the dark matter - is both timely and intriguing. I will review the status of the field, describe search strategies and future prospects for detection across many decades in mass, discuss how primordial black holes could seed both baryonic and particle dark matter in the very early universe, and argue that the search for sub-solar mass black holes may lead to a deeper understanding of the elusive Galactic "rogue planets".
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18:00 - 18:45 CET / 22:30 - 23:15 IST
Speaker: Katherine Freese (University of Texas, US; Stockholm University & NORDITA, Sweden; University of Michigan, US)
Title: Has the James Webb Space Telescope discovered Dark Stars --- made of ordinary matter but powered by Dark Matter?
Abstract: Dark Stars may be the first stars to ever form in the Universe, when it was 200 Myr old. Dark Stars are made (almost entirely) of hydrogen and helium, but powered by the heat from Dark Matter annihilation, rather than by fusion. They are real stars, in hydrostatic and thermal equilibrium. As a power source for heating the stars we studied Weakly Interacting Massive Particles (WIMPs), and Self Interacting Dark Matter (SIDM). Although dark matter constitutes only ≲0.1% of the stellar mass, this amount is sufficient to power the star for millions to billions of years. They are very bright diffuse puffy objects (10 AU in radius) and grow to be very massive. In fact, they can grow up to ten million solar masses with up to ten billion solar luminosities. The James Webb Space Telescope has found large numbers of high redshift objects (z>10), far too many to be compatible with the number of galaxies predicted in LCDM. Some could instead be Dark Stars. We show that JADES objects in James Webb Space Telescope (JWST) data could in fact be Supermassive Dark Stars: the spectra are a good match, and in the future with better spectra the detection of a HeII 1640 absorption line would be a smoking gun for a Dark Star vs an early galaxy. Once the dark matter fuel runs out and the dark star dies, it may collapse to a million solar mass black hole. Thus dark stars may provide seeds for as yet unexplained supermassive black holes observed at early times as well as in galaxies today.
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November 7, 2025
(CET = Central European Time, IST = Indian Standard Time)
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12:00 - 12:30 CET / 16:30 - 17:00 IST
Speaker: Sumit Ghosh (Maulana Azad National Institute of Technology, Bhopal, India)
Title: Non-Standard Neutrino Interactions Mediated by Light Mediators.
Abstract: Neutrino masses and oscillations are well-established phenomena, yet the underlying mechanism responsible for neutrino mass generation remains unknown. Extensions of the Standard Model often predict non-standard interactions (NSI) in the neutrino sector, which, if observed, would provide unambiguous evidence of new physics beyond the Standard Model. In particular, light scalar or vector mediators can induce non-standard neutrino–electron interactions, naturally arising in many low-scale models. We investigate the prospects of probing or constraining such models in reactor-based neutrino experiments employing low-threshold Ge/Si detectors. Furthermore, we explore the implications of these interactions for neutrino oscillation physics, focusing on their potential impact on CP-violation measurements at long-baseline experiments such as DUNE.
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12:30 - 13:00 CET / 17:00 - 17:30 IST
Speaker: Nidhi Sudhir (University of Wisconsin-Madison)
Title: A topological contribution to Bogoliubov coefficient for cosmological particle production.
Abstract: In scenarios, where particles are produced due to coupling to a time dependent background and the time dependence may be approximated as $\omega^2 \approx k^2+\eta^n$, we present an analytic estimate of the long wavelength Bogoliubov coefficients using Stokes phenomenon. In this limit, the $Z_(n+2)$ phase rotation symmetry of the mode equation fixes the Stokes data and allows an interpretation of the Bogoliubov coefficient in terms of topological properties of asymptotic expansions. Extending the above to non-zero $k$, we realise that symmetries are insufficient to constrain the leading order $k$ dependence of the Bogoliubov coefficient for which we then present a numerical estimate. Finally, we look at models in which the topological contribution to the Bogoliubov coefficient makes a significant contribution to the total particle production.
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13:00 - 13:30 CET / 17:30 - 18:00 IST
Speaker: Manuel Ettengruber (Institute of Theoretical Physics (IPhT))
Title: The search for the fundamental scale of gravity.
Abstract: Already within the Standard Model, we expect that the fundamental scale of gravity, the scale where gravity becomes strong, is slightly lower than the Planck scale. Theories with extra dimensions or with many additional particle species enhance this effect and are motivated by giving a unified solution to the Hierarchy problem, Dark Matter, and neutrino masses. In this talk, we will discuss their phenomenology in low-energy experiments, their unique astrophysical signatures, and present recent experimental results.
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October 24, 2025
(CEST = Central European Summer Time, IST = Indian Standard Time)
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12:00 - 12:45 CEST / 15:30 - 16:15 IST
Speaker: Sabino Matarrese (Universita' degli Studi di Padova, Italy)
Title: Going beyond linear theory with cosmological observables.
Abstract: For several decades, linear perturbation theory has played a fundamental role in predicting the most important cosmological observables.On the other hand, going beyond linearity is a mandatory step when analyzing e.g. quantities related to deviations from Gaussianity. I'll review here a variety of original results which have been obtained in recent years in connection with higher-order perturbation theory and/or non-perturbative calculations. These include well-known effects such as scalar-induced gravitational waves, but also less known effects such as tensor-induced scalar modes generated during and after inflation, the quantum production of gravitons after inflation and many other interesting effects.
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12:45 - 13:30 CEST / 16:15 - 17:00 IST
Speaker: David Langlois (APC, Paris)
Title: Modified gravity and black holes.
Abstract: This talk will present a very broad family of scalar-tensor theories of gravity that contain a single scalar degree of freedom, in addition to the usual tensor modes. These theories, known as Degenerate Higher-Order Scalar-Tensor (DHOST) theories, include and extend traditional scalar-tensor theories as well as the so-called Horndeski theories. I will then discuss black hole solutions in these theories and their perturbations, illustrated by some particular cases.
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October 17, 2025
(CEST = Central European Summer Time, IST = Indian Standard Time)
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12:00 - 12:45 CEST / 15:30 - 16:15 IST
Speaker: Jason Kristiano (Yukawa Institute for Theoretical Physics, Kyoto University, Japan)
Title: Cosmic Inflation: From Small to Large Scales.
Abstract: Structures in the universe can be formed because of small inhomogeneities at a very early time. These inhomogeneities originate from quantum fluctuations stretched by cosmic inflation. As we know from wave mechanics, fluctuations are characterized by amplitude and wavelength. Fluctuations with wavelength as long as observable universe, with amplitude around 0.00001, can explain cosmic microwave background observations and galaxies density correlations in large-scale structures. However, for the short-wavelength one, so far there have been no observational constraints on the amplitude. If the amplitude exceeds 0.1, they can collapse to form primordial black holes. These primordial black holes can have interesting consequences, such as explaining dark matter or LIGO-Virgo-KAGRA black holes. So far, these theoretical predictions rely on linear perturbation theory. However, it is reasonable to expect large nonlinearities due to large fluctuations, which are manifested in coupling between small and large scales. In this talk, I will review primordial black holes formation in single-field inflation and recent progress on nonlinear computation. I will argue that large amplitudes of short-wavelength fluctuations can coherently amplify the long-wavelength one by loop corrections. I will also explain some issues on regularization and renormalization of these loops.
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12:45 - 13:30 CEST / 16:15 - 17:00 IST
Speaker: Ruth Durrer (Department of Theoretical Physics, Geneva University, Switzerland)
Title: Testing General Relativity with Cosmological Large Scale Structure Observations.
Abstract: General Relativity (GR) is immensely successful. With the late discovery of gravitational waves from black hole and neutron star mergers, it has passed all the tests with flying colors. But so far, all observations have mainly tested the vacuum equations of GR. The most important non-vacuum case, cosmology, is in agreement with GR only after the introduction of two otherwise unknown components, 'Dark Matter' and 'Dark Energy' which amount to about 95% of the total energy budget of the present Universe. This lead people in the field to question the validity of GR for cosmology. Might it be that GR is flawed on large, cosmological scales? Or in the presence of matter in general? But how can we test Einstein's equation in the presence of matter? Can't we simply move any modification of the Einstein tensor to the right hand side and call it a 'dark matter/energy' component? In my talk I shall discuss possible ways (partially) out of this dilemma. How to test both, the left and the right hand side of Einstein's equations with cosmological observations.
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13:30 - 14:15 CEST / 17:00 - 17:45 IST
Speaker: Samuel Sanchez Lopez (Institute of Mathematical Sciences (IMSc), India)
Title: Aspects of cosmology in Palatini gravity.
Abstract: I will start this talk with an overview of f(R) gravity, highlighting the differences between the Palatini and metric formalisms, which predict vastly different dynamics. The main body of my talk will then be devoted to the description of different aspects of the phenomenology of Palatini f(R) gravity, in the context of cosmological model building. In particular, I will show how it can be useful for inflationary model building, being able to rescue models currently discarded by the data. Regarding the late universe, I will also discuss how recent BAO measurements by the DESI collaboration seem to suggest the preference for non-minimal couplings between quintessence and gravity. Lastly, I will comment on a newly developed framework for the study of scalar-induced gravitational waves (SIGWs). I will show that the resulting density spectrum deviates not only from the prediction of GR, but also from that of metric $f(R)$ gravity. These differences highlight the potential of SIGWs as a sensitive probe of gravitational degrees of freedom and a promising tool to test extensions of Einstein's theory, with the advent of gravitational-wave experiments such as LISA or ET.
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October 10, 2025
(CEST = Central European Summer Time, IST = Indian Standard Time)
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12:00 - 12:45 CEST / 15:30 - 16:15 IST
Speaker: Christoph Englert (University of Manchester, UK)
Title: Effective theories for the weak scale and beyond
Abstract: A decade after the discovery of the Higgs boson at the Large Hadron Collider, a microscopic understanding of the nature of the electroweak scale remains elusive. This is particularly puzzling as we know that the Standard Model of Particle Physics cannot be the final answer, given its apparent shortcomings. In this talk, I will discuss ways to move, with theoretical precision, away from constraining phenomenological patterns of the electroweak scale as predicted by the SM or even its effective generalisation. I will discuss how such an approach, inspired by geometry, can inform the search for physics beyond the Standard Model in the Higgs sector, charting BSM possibilities for particle physics at the TeV scale. Time permitting, I will demonstrate how these insights can be applied in other phenomenological contexts, offering new directions for the potential connection between the electroweak scale and theories of dark matter.
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12:45 - 13:30 CEST / 16:15 - 17:00 IST
Speaker: Carlos Henrique de Lima (TRIUMF, Canada)
Title: New tool to study strongly coupled gauge theories.
Abstract: In this talk, we will discuss a recent proposed framework to obtain calculable results for QCD-like theories by deforming their supersymmetric versions with anomaly-mediated supersymmetry breaking (AMSB). This method allows for a controlled study of strongly coupled gauge dynamics, including when there are massless fermions. We focus on theories with $N_f = N_C + 1$ vector-like massless fermions and show that chiral symmetry breaking occurs for arbitrary values of the SUSY-breaking scale. We also discuss the same theory at finite chemical potential and showcase novel symmetry-breaking patterns in regions inaccessible to traditional theoretical methods.
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13:30 - 14:15 CEST / 17:00 - 17:45 IST
Speaker: Koki Tokeshi (Institute for Cosmic Ray Research (ICRR), University of Tokyo, Japan)
Title: O(d)-symmetric multifield models and stochastic effects.
Abstract:In multifield inflationary models, the noise-induced centrifugal force extends the duration of inflation depending on the number of fields, even when the stochastic noises themselves are small. The number of fields then discriminates whether inflation terminates in a finite time or lasts forever, from which the theoretical bound on the number of fields is found.
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September 26, 2025
(CEST = Central European Summer Time, IST = Indian Standard Time)
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12:00 - 12:45 CEST / 15:30 - 16:15 IST
Speaker: Angelo Caravano (Institut d'Astrophysique de Paris)
Title: Backreaction and cosmic butterflies: non-perturbative insights into the small-scale physics of inflation.
Abstract: The small-scale physics of inflation can leave unique observational signatures in the gravitational wave background and may also generate primordial black holes as a dark matter candidate. These phenomena often involve a significant enhancement of inflationary fluctuations, potentially leading to the breakdown of standard perturbation theory. In this talk, I will discuss how lattice simulations provide a crucial tool for addressing these challenges. Focusing on single-field inflationary models with deviations from slow-roll, I will demonstrate how nonlinear physics can significantly alter the inflationary dynamics and their predictions, even in regimes where perturbation theory is typically assumed valid. This highlights the indispensable role of lattice simulations in probing inflation with current and future gravitational wave experiments.
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12:45 - 13:30 CEST / 16:15 - 17:00 IST
Speaker: Amit Bhoonah (University of Pittsburgh, USA.)
Title: Baryon and Lepton Number Violation at LHC Accessible energies.
Abstract: Proton decay experiments typically constrain baryon number violation to the scale of grand unified theories. From a phenomenological point of view, this makes direct probing of the associated new resonances, such as the X and Y bosons, out of reach for even the most optimistic future experiments. It has, however, been known that certain specific patterns of baryon and lepton number violation can suppress proton decay by multiple powers of the masses of the heavy resonances involved, opening the possibility that the observed limits on the proton lifetime are consistent with baryon number violating physics at energy scales much lower than that of grand unification. We construct an explicit example of such a model which violates baryon number by one unit, ΔB=−1, and lepton number by three units, ΔL=−3, and show that despite stringent limits on the predicted proton decay searches by the Super-Kamiokande experiment, the masses of the newly introduced elementary particles can be O(TeV). We identify interesting unique signatures of baryon number violation of this model that can be probed both with currently available LHC data and with the upcoming High-Luminosity LHC.
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September 19, 2025
(CEST = Central European Summer Time, IST = Indian Standard Time)
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12:00 - 12:45 CEST / 15:30 - 16:15 IST
Speaker: Angelo Ricciardone (U. Pisa (main) and INFN, Pisa and U. Padua, Dept. Phys. Astron., Italy)
Title: Impact of correlated noise on the reconstruction of the stochastic gravitational wave background with Einstein Telescope
Abstract: The Einstein Telescope (ET) will have unprecedented sensitivity, aiming the detection of the stochastic gravitational-wave background (SGWB) from astrophysical and cosmological sources. ET's triangular configuration offers advantages such as enhanced sky coverage and polarization sensitivity, but it faces challenges from correlated seismic Newtonian noise, which affects low-frequency SGWB detection. In this talk, I will present a Bayesian analysis using mock simulated data, demonstrating that accurate SGWB parameter reconstruction is achievable when correlated noise is properly modeled. I demonstrate that neglecting these correlations results in significant biases.
Comparing the triangular configuration with a two-detector L-shaped (2L) setup, I show that while the 2L design offers slightly better parameter estimation, the triangular configuration remains highly competitive, when correlated noise is handled correctly.
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12:45 - 13:30 CEST / 16:15 - 17:00 IST
Speaker: Alessandro Podo (Institut des Hautes Études Scientifiques, Bures-sur-Yvette, France)
Title: Microcausality in Lorentz-breaking backgrounds.
Abstract: I will describe how causality implies certain non-perturbative analyticity and exponential boundedness conditions on correlators of relativistic QFTs, in a mixed (t,k) representation. I will then discuss their implications for correlators in Lorentz-breaking backgrounds, including finite-density states and cosmological spacetimes, and show how they can be used to derive a positivity condition on inflationary theories. Along the way, I will compare with the case of S-matrix positivity in flat space Lorentz-invariant theories.
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13:30 - 14:15 CEST / 17:00 - 17:45 IST
Speaker: Salvatore Capozziello (Università di Napoli, Federico II, Italy)
Title: Avoiding singularities in Lorentzian-Euclidean black holes: The role of atemporality.
Abstract: We investigate a Schwarzschild metric exhibiting a signature change across the event horizon, which gives rise to what we term a Lorentzian-Euclidean black hole. The resulting geometry is regularized employing the Hadamard partie finie technique, which allows us to prove that the metric represents a solution of vacuum Einstein equations. In this framework, we introduce the concept of atemporality as the dynamical mechanism responsible for the transition from a regime with a real-valued time variable to a new one featuring an imaginary time. We show that this mechanism prevents the occurrence of the singularity and discuss that, thanks to the regularized Kretschmann invariant, the atemporality can be considered as a characteristic feature of this black hole.
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September 12, 2025
(CEST = Central European Summer Time, IST = Indian Standard Time)
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12:00 - 12:45 CEST / 15:30 - 16:15 IST
Speaker: Carlo Branchina (Università della Calabria, Italy)
Title: Effective action in quantum gravity and the cosmological constant
Abstract: If quantum gravity is described by a quantum field theory, two cases are possible: either it is an effective theory valid up to its physical UV cutoff scale, or it exhibits a UV fixed-point that makes it non-perturbatively renormalizable. Typical calculations of the (euclidean) effective action in quantum gravity give rise to quartic and quadratic UV-sensitive contributions to the vacuum energy. In this talk, I will report on recent advances in the calculation of the gravitational effective action. We will see that when the path integral measure is included and the UV-cutoff carefully introduced, these large contributions are absent, and the vacuum energy only presents a mild logarithmic sensitivity to the UV scale. This has profound consequences on the renormalization group flow of the theory and on the possible existence of a UV fixed point that is at the core of the asymptotic safety scenario. I will thoroughly explain why quartic and quadratic UV-terms are found in typical calculations but not in ours.
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12:45 - 13:30 CEST / 16:15 - 17:00 IST
Speaker: Minxi He (Institute for Basic Science (South Korea))
Title: Unitarity of Higgs inflation and UV extension
Abstract: The Standard Model Higgs field can play an essential role in the very early Universe to realize the cosmic inflation, providing proper initial conditions for the hot big bang theory. However, the vanilla Higgs inflation model suffers from the unitarity problem when the Higgs field decays into gauge bosons after inflation, as the momentum of the produced gauge bosons can be higher than the UV cutoff of the model. Such inconsistency can be resolved by considering the UV extended Higgs inflation with an R^2 operator. In this talk, I will introduce a new geometric method to unambiguously determine the cutoff scale of general nonlinear sigma models, including the Higgs inflation, and discuss the unitarity problem of the Higgs inflation. I will show that the R^2 corrected model, namely the mixed Higgs-R^2 inflation, is free from such problem up to Planck scale. I will briefly extend this discussion to the Einstein—Cartan Higgs inflation which is a general framework that includes a large class of Higgs inflation models.
September 5, 2025
(CEST = Central European Summer Time, IST = Indian Standard Time)
12:00 - 12:45 CEST / 15:30 - 16:15 IST
Speaker: Abhishek Kumar Mehta (IISER, Pune, India)
Title: Non-thermodynamic Black Hole Evaporation
Abstract: In this talk, we will investigate black hole evaporation from the path integral and effective field theory perspective. I will show that besides the standard thermodynamic mode, there are non-thermodynamic modes of black hole evaporation which demonstrate remnant end-stages. This talk will be based on the following pre-print: https://arxiv.org/pdf/2505.06859
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12:45 - 13:30 CEST / 16:15 - 17:00 IST
Speaker: Francesco Costa (IPNP, Charles University, Prague)
Title: Low reheating temperature freeze-in dark matter
Abstract: Gravitational production hinders the predictivity of many non-thermal dark matter models. Nevertheless, if the reheating temperature is low, the gravitationally produced relics can be diluted. We study the freeze-in production mechanism at temperatures below the dark matter mass. In this case, the production rate is exponentially suppressed, and the coupling to the thermal bath has to be significant to account for the observed dark matter relic density. As a result, the direct dark matter detection experiments already probe such freeze-in models, excluding significant parts of the parameter space.
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13:30 - 14:15 CEST / 17:00 - 17:45 IST
Speaker: Ayngaran Thavanesan (EPFL (currently at DAMTP, University of Cambridge))
Title: Holographic Cosmology through the Cosmological CPT Theorem
Abstract: The original CPT theorem is restricted to flat spacetime and does not allow converse statements. In this talk, I will present a reformulation of the CPT theorem based on symmetry arguments, enabling us to make converse statements and to extend the theorem beyond flat space. This leads to a non-perturbative formulation of unitarity in cosmology.
I will show how this applies to the wavefunction of the universe studied in cosmological settings, and how the resulting constraints can be expressed perturbatively at each loop order. Remarkably, these constraints determine the exact phase of the wavefunction to any loop order, placing powerful restrictions on the structure of cosmological correlators as well as implications for quantum gravity; specifically our non-perturbative unitarity condition enables us to identify classes of gauge theories that may serve as holographic duals for cosmological (time-dependent) backgrounds in string theory.
This talk is based on arXiv:2408.17406, in collaboration with Harry Goodhew and Aron Wall as well as my paper arXiv:2501.06383, and ongoing work with Aron Wall.
August 29, 2025
12:45 - 13:30 CEST / 16:15 - 17:00 IST
Speaker: Quim Iguaz Juan (Mass Amherst, USA)
Title: Exploring Primordial Black Holes: Gamma-ray and Neutrino Signatures
Abstract: Observation of an exploding black hole would provide the first direct evidence of primordial black holes, of Hawking radiation, and provide definitive information on the particle spectrum of nature. Interestingly, a black hole explosion would produce large amounts of both photons and neutrinos, which we could detect with currently operating telescopes. However, indirect constraints suggest that direct observation of an exploding Schwarzschild black hole is implausible. We introduce a dark-QED toy model consisting of a dark photon and a heavy dark electron. For the first time we show that a population of primordial black holes can become quasi-extremal and significantly weaken the indirect constraints, before the black holes discharge towards the end of their lives and exhibit a Schwarzschild-like final explosion. In this scenario the answer is ``yes'', it is possible that we could directly observe an exploding black hole in the near future. We also link the recent KM3NeT observation to an exploding black hole and find a plausible explanation that can solve some tensions with IceCube and account for DM at the same time.
August 29, 2025
12:00 - 12:45 CEST / 15:30 - 16:15 IST
Speaker: Andrea Tesi (University and INFN Florence)
Title: Exploring ultra-high energy neutrino experiments through the lens of the transport equation
Abstract: We develop a first-principles formalism, based on the transport equation in the line-of-sight approximation, to link the expected number of muons at neutrino telescopes to the flux of neutrinos at the Earth's surface. We compute the distribution of muons inside Earth, arising from the up-scattering of neutrinos close to the detector, as well as from the decay of taus produced farther away. This framework allows one to account for systematic uncertainties, as well as to clarify the assumptions behind definitions commonly used in the literature, such as the effective area. We apply this formalism to analyze the high-energy muon event recorded by KM3NeT, with a reconstructed energy of approximately 120 PeV, in comparison with the non-observation of similar events by IceCube. We find a 3.1 σ tension between the two experiments, assuming a diffuse neutrino source with a power-law energy dependence. Combining both datasets leads to a preference for a very low number of expected events at KM3NeT, in stark contrast to the observed data. The tension increases both in the case of a diffuse source peaking at the KM3NeT energy and of a steady point source, whereas a transient source may reduce the tension down to 1.6 σ. The formalism allows one to treat potential beyond-the-Standard-Model sources of muons, and we speculate on this possibility to explain the tension.
August 22, 2025
12:00 - 12:45 CEST / 15:30 - 16:15 IST
Speaker: Hamsa Padmanabhan (University of Geneva, the Switzerland)
Title: Insights from data-driven techniques: from the distant cosmos to pre-historic Earth
Abstract: Hydrogen is the most abundant element in the Universe, and as such, mapping its evolution across cosmic time promises deep insights into cosmology and — in the future — theories of physics. Intensity mapping (IM) is an emerging technique that measures the integrated emission of radiation over cosmological volumes, and has the potential to unlock significantly more information than we presently have from galaxy surveys. I will describe a novel, data-driven framework which utilises our current astrophysical knowledge to interpret future IM observations of cosmological hydrogen. It readily enables synergies with other line-intensity mapping surveys and traditional galaxy observations. Extending this approach allows insights into the properties of the earliest black holes, using multi-messenger observations from the James Webb Space Telescope (JWST) and gravitational waves from Pulsar Timing Arrays (PTAs).
I will briefly describe how these methods find applications to several unsolved issues in the Earth’s paleo-climate, such as modelling the carbon dioxide content of the Earth across the most destructive extinction event in geological history (called the Permian Triassic Mass Extinction (PTME), which took place around 252 million years ago and destroyed about 96% of all marine and 70% of all terrestrial species). This extinction is believed to have been triggered by a runaway greenhouse effect, and relating it to the current global warming scenario promises invaluable lessons for the tackling of our climate crisis.
August 22, 2025
12:45 - 13:30 CEST / 16:15 - 17:00 IST
Speaker: Kshitij Gupta (University of California, San Diego, USA)
Title: Soft Metric Fluctuations During Inflation
Abstract: We use EFT techniques to show the all orders conservation of the super-horizon scalar and tensor modes during inflation. The EFT is built in analogy with Soft de Sitter EFT. Power counting and symmetry arguments are used to directly constrain the time evolution. We also introduce Mellin representation as an advantageous scheme to connect the UV and EFT descriptions.
August 08, 2025
12:00 - 12:45 CEST / 15:30 - 16:15 IST
Speaker: Garv Chauhan (Arizona State University, USA)
Title: Supernova Gamma-Ray Constraints from Radiative Particle Decays
Abstract: Core-collapse supernovae (CCSNe) are one of the most energetic particle generators due to their extremely high densities and temperatures. If new physics such as sterile neutrinos or axions exist, these may also be produced in the supernova core. These particles can escape the stellar envelope and then decay into photons, which can be detected at gamma-ray telescopes. In this talk, I will first revisit the existing gamma ray constraints on the sterile neutrino parameter space from the non-observation of gamma-rays from SN1987A. In addition, I will introduce a novel class of gamma-ray bound with an application to the case of axions. Finally, I will discuss the sensitivity of several present and near future gamma-ray telescopes assuming a future galactic CCSN.
August 01, 2025
12:00 - 12:45 CEST / 15:30 - 16:15 IST
Speaker: Wen-Yuan Ai (Institute of High Energy Physics, Austrian Academy of Sciences)
Title: Primordial black hole formation from an aborted phase transition
Abstract: The matter-antimatter asymmetry in the Universe remains one of the most profound mysteries in cosmology and particle physics. Electroweak baryogenesis (EWBG) is a mechanism in the early Universe that generates this asymmetry between baryons and anti-baryons during the electroweak phase transition. However, the electroweak phase transition in the Standard Model (SM) is not strong enough to explain the observed baryon asymmetry. As a result, we investigate the EWBG in the real singlet extension of the SM, including dimension-six operators, which couple the Higgs boson to a real singlet scalar field. We show that the electroweak phase transition is a one-step or a two-step phase transition, depending on the parameters of the singlet extension. Interestingly, the real singlet extension explains the observed baryon asymmetry of the Universe, introducing an additional source of CP violation in the SM via a second dimension-six operator, which contributes to the top-quark mass. These results provide new pathways for EWBG, expanding the viable parameter space for future collider and gravitational wave experiments, especially for low singlet masses.
July 25, 2025
12:00 - 12:45 CEST / 15:30 - 16:15 IST
Speaker: Apostolos Giovanakis (Federal Institute of Technology Zurich (ETH Zurich), Switzerland)
Title: Electroweak Baryogenesis in the Standard Model and Beyond
Abstract: The matter-antimatter asymmetry in the Universe remains one of the most profound mysteries in cosmology and particle physics. Electroweak baryogenesis (EWBG) is a mechanism in the early Universe that generates this asymmetry between baryons and anti-baryons during the electroweak phase transition. However, the electroweak phase transition in the Standard Model (SM) is not strong enough to explain the observed baryon asymmetry. As a result, we investigate the EWBG in the real singlet extension of the SM, including dimension-six operators, which couple the Higgs boson to a real singlet scalar field. We show that the electroweak phase transition is a one-step or a two-step phase transition, depending on the parameters of the singlet extension. Interestingly, the real singlet extension explains the observed baryon asymmetry of the Universe, introducing an additional source of CP violation in the SM via a second dimension-six operator, which contributes to the top-quark mass. These results provide new pathways for EWBG, expanding the viable parameter space for future collider and gravitational wave experiments, especially for low singlet masses.
July 25, 2025
12:45 - 13:30 CEST / 16:15 - 17:00 IST
Speaker: Subham Dutta Chowdhury (ICTP, Trieste, Italy)
Title: Symmetry and causality constraints on Fermi liquids
Abstract: Fermi liquids describe a wide range of systems at finite density, from electrons in metals to cold atoms and neutron stars. In this talk, I’ll explain how symmetry and causality place powerful constraints on their behavior. Boost symmetry—Galilean or Lorentz—involves a well-known constraint on the first Landau parameter, F_1. I will show that scale invariance similarly constrains the zeroth parameter, F_0. In conformal Fermi liquids, causality imposes even tighter bounds, especially on the particle-hole continuum and the collective excitations, carving out a restricted region of allowed interactions. Going beyond linear response, I’ll discuss how non-linear response reveals new structure through "generalized" Landau parameters, which are also constrained by such symmetries. Throughout, I will test these ideas in concrete microscopic models which exhibit Fermi liquid phases.
July 18, 2025
12:00 - 12:45 CEST / 15:30 - 16:15 IST
Speaker: Lucas Pinol (LPENS (Laboratoire de Physique de l'Ecole Normale Supérieure), CNRS, Paris, France)
Title: One-loop freezing of the primordial curvature perturbation
Abstract: Although the detailed microphysics of our very early Universe remains elusive, much progress was obtained in the last decade to pinpoint realistic inflationary scenarios that leave unique observational imprints. This progress hinges on the existence of a conserved quantity on super-horizon scales called the primordial curvature perturbation. This crucial property enables theoretical cosmologists to propagate the statistics of the primordial fluctuations from the end of inflation to the onset of the hot Big Bang cosmology, and connect to astronomical observations. In this series of works, we delve into the details of the one-loop corrections to the primordial curvature perturbation from unavoidable nonlinear gravitational interactions during inflation. By carefully renormalizing the effective field theory of inflationary fluctuations in a way that respect spacetime symmetries, we prove that this quantity remains exactly conserved at the one-loop level. We conclude that predictivity is a robust property of any single-clock inflationary scenario. I will mention how this work could be extended to address recent debates about the robustness of predictions in inflationary models with interesting small-scale phenomenology, such as scalar-induced gravitational waves and primordial black holes.
July 18, 2025:
12:45 - 13:30 CEST / 16:15 - 17:00 IST
Speaker: Shuailiang Ge (LPENS (Korea Advanced Institute of Science and Technology (KAIST))
Title: Detection of ultralight dark matter using radio telescopes and satellites
Abstract: Ultralight axions and dark photons are compelling dark matter candidates. In this talk, I will focus on detecting radio-frequency axions and dark photons based on terrestrial telescopes and space satellites, including FAST, LOFAR, and Parker Solar Probe. The detectability relies on two underlying mechanisms. One mechanism involves local dark photon dark matter inducing harmonic oscillations of electrons within the antenna of radio telescopes such as FAST. This process results in local radio electromagnetic (EM) signals that can be captured by telescope receivers. The other mechanism is the resonant conversion of dark photons into EM waves in the solar plasma when their mass matches the plasma frequency. This mechanism is also applicable to axions due to the solar magnetic field. Parker Solar Probe, the first and only man-made detector that can venture into solar corona, can make in situ measurements of such converted dark matter signals. Based on these state-of-the-art facilities, we have set the most stringent constraints on the kinetic mixing constant between dark photon and photon in multiple radio frequencies.
July 18, 2025:
16:00 - 16:45 CEST / 19:30 - 20:15 IST
Speaker: Garv Chauhan (Arizona State University, USA)
Title: Supernova Gamma-Ray Constraints from Radiative Particle Decays
Abstract: Core-collapse supernovae (CCSNe) are one of the most energetic particle generators due to their extremely high densities and temperatures. If new physics such as sterile neutrinos or axions exist, these may also be produced in the supernova core. These particles can escape the stellar envelope and then decay into photons, which can be detected at gamma-ray telescopes. In this talk, I will first revisit the existing gamma ray constraints on the sterile neutrino parameter space from the non-observation of gamma-rays from SN1987A. In addition, I will introduce a novel class of gamma-ray bound with an application to the case of axions. Finally, I will discuss the sensitivity of several present and near future gamma-ray telescopes assuming a future galactic CCSN.
July 04, 2025: (12:00 - 12:45 CEST/ 15:30 - 16:15 IST)
Title: Curvature perturbations from non-equilibrium phenomena in the very early universe
Abstract: Curvature perturbations act as seeds for structure formation as well as the temperature fluctuations observed in the cosmic microwave background. A light scalar field during inflation develops significant quantum fluctuations on super-horizon scales. If the amount by which space expands depends on the local value of the light field, then its quantum fluctuations are converted into curvature perturbations.
Furthermore if the expansion of space is a non-linear function of the light field, which is generally the case when the field modulates some non-equilibrium process, then the curvature perturbations will also be significantly non-Gaussian. This non-Gaussianity is measured by cosmological experiments.
I will present general methods to estimate the non-Gaussianity arising from the non-equilibrium phenomena of vacuum transition during inflation and preheating after inflation. The calculation for vacuum transition proceeds by finding the instanton solution in de Sitter space, while for preheating it involves lattice simulations. I will illustrate the methods by applying them to realistic Higgs inflation and alpha-attractor models.
June 20, 2025: (12:00 - 12:45 CEST/ 15:30 - 16:15 IST)
Title: Strongly Coupled Sectors in Inflation: Gapless Theories and Unparticles
Abstract: In this talk, I will discuss the primordial universe scenarios where the inflaton is weakly coupled to a strongly-self-interacting theory, and study the imprints in cosmological correlators. There are three general scenarios for the strongly coupled sector based on its mass gap in Hubble units. I will focus on the gapless scenario, which I fully solved. Depending on the value of the unparticle scaling dimension, I will classify three characteristic shapes for the inflationary bispectra, including near-equilateral, near-orthogonal, and a novel shape which appears when the scaling dimensions are close to half-integers. If time permits, I will discuss the ongoing work about the gapped scenarios and possible model building.
June 20, 2025: (12:45 - 13:30 CEST/ 16:15 - 17:00 IST)
Title: Emergent Quantum Gravity from Irreversible Vierbein: A Scale-Invariant Realization
Abstract: We propose a novel approach to quantum gravity based on the irreversible vierbein postulate, in which the inverse vierbein is absent at the fundamental level. In this framework, spacetime structures—including an invertible metric and the Planck mass—can dynamically emerge through quantum effects. To explicitly demonstrate how this scenario can be realized, we present a concrete scale-invariant model. Within this realization, fermionic fluctuations trigger a quantum phase transition, naturally generating spacetime and gravitational scales. In this talk, we clarify the physical motivations behind the irreversible vierbein approach, outline the general formalism, and discuss possible implications for cosmology and gravitational phenomenology.
June 06, 2025: (12:00 - 12:45 CEST/ 15:30 - 16:15 IST)
Title: Primordial black hole formation from an aborted phase transition
Abstract: Primordial black holes may be produced from cosmological first-order phase transitions. I will discuss a new mechanism for PBH formation based on an aborted heating phase transition during reheating. Here "heating" means that the phase transition occurs as the temperature increases during the earlier stage of reheating (when the Universe is still matter-dominated). "Aborted" means that there are bubble nucleation but the nucleation rate is so low such that there is no coalescence for these nucleated bubbles. The particular evolution of the effective potential during reheating makes the bubble expand first, then shrink, and finally disappear. However, such disappeared bubbles generate perturbed spherical regions with over-density in energy, which would accrete the surrounding matter (reheaton) and collapse into black holes.
May 30, 2025: (12:00 - 12:45 CEST/ 15:30 - 16:15 IST)
Title: Primordial black hole mergers as a cosmological probe
Abstract: Since the detection of the first gravitational wave (GW) event GW150914, primordial black hole (PBH) scenario is a potential explanation for the merger rate of detected GW events in LVK. In this talk, I will discuss the future perspectives of PBH merger rate as a cosmological probe in next-generation GW detectors. By using the PBH merger rate population and its evolution in redshift space, it can help study cosmology on background level: tracking the history of cosmic expansion, and first order level: structure growth and dark matter distribution.
May 23, 2025: (12:00 - 12:45 CEST/ 15:30 - 16:15 IST)
Title: Uplifting Massive Graphs from Minkowski to de Sitter
Abstract: Identifying useful flat-space limits for cosmological correlators—where they can be expressed in terms of observables in Minkowski space—is nontrivial due to their scale-invariant nature. In this talk, I present a massive flat-space limit in which cosmological correlators, induced by the exchange of heavy fields, can be expressed in terms of massive Feynman graphs in flat space. As a phenomenological application, I apply this flat space limit to compute specific one-loop contributions from heavy fields to primordial non-Gaussianity.
May 23, 2025: (12:45 - 13:30 CEST/ 16:15 - 17:00 IST)
Title: Gravitational wave science in the SKAO era
Abstract: Pulsar timing array detection of a gravitational wave background represents a milestone in the field of gravitational wave astronomy. However, the origin of such a signal is still a matter of intense debate: while supermassive black hole binaries formed as a result of galaxy mergers represent the most obvious candidate for the gravitational wave signal, many "new Physics" models can potentially explain at least part of the detected background. In this seminar I will review the current observational and theoretical status of the field, with particular emphasis on the science cases that are currently being explored by members of the SKAO Gravitational Wave Working Group. Moreover, I will discuss how radio observations with the SKAO can contribute to this broader context, and, in particular, I will focus on a possible background detection strategy that involves both pulsar timing array and cosmological observables.
May 16, 2025: (12:00 - 12:45 CEST/ 15:30 - 16:15 IST)
Title: Mineral Detection of Neutrinos and Dark Matter
Abstract: Minerals are solid state nuclear track detectors - nuclear recoils in a mineral leave latent damage to the crystal structure. Depending on the mineral and its temperature, the damage features are retained in the material from minutes to timescales much larger than the age of the Solar System. The damage features from the fission fragments left by spontaneous fission of heavy unstable isotopes have long been used for fission track dating of geological samples. Laboratory studies have demonstrated the readout of defects caused by nuclear recoils with energies as small as ~1 keV. Using natural minerals, one could use the damage features accumulated over geological timescales to measure astrophysical neutrino fluxes (from the Sun, supernovae, or cosmic rays interacting with the atmosphere) as well as search for Dark Matter. Research groups in Europe, Asia, and America have started developing microscopy techniques to read out the nanoscale damage features in crystals left by keV nuclear recoils. The research program towards the realization of such mineral detectors is highly interdisciplinary, combining geoscience, material science, applied and fundamental physics with techniques from quantum information and Artificial Intelligence. In this talk, I will highlight the scientific potential of Dark Matter searches with mineral detectors and briefly describe status and plans of the Mineral Detection of Neutrinos and Dark Matter (MDvDM) community.
[Cancelled]
May 02, 2025: (12:45 - 13:30 CEST/ 16:15 - 17:00 IST)
Title: Proving chiral symmetry breaking in QCD with ’t Hooft anomaly matching
Abstract: Chiral symmetry breaking in QCD is a well-established phenomenon, yet it has been a challenge to derive this phenomenon from the theoretical viewpoint. In the seminal 1979 Cargese lectures, ’t Hooft showed how to use anomaly matching to prove chiral symmetry breaking, he showed some examples but didn’t give the general proof. In this talk, I will present a new strategy which can lead to a general proof. This talk is based on the papers: hep-th/2212.02930, 2404.02971, 2404.02967.
May 02, 2025: (12:45 - 13:30 CEST/ 16:15 - 17:00 IST)
Title: Primordial Black Holes and Gravitational Waves from Axion Topological Defects
Abstract: I present a new mechanism of primordial black hole (PBH) formation from QCD axion in the context of the Peccei-Quinn symmetry breaking during inflation. The axion string-wall network re-enters horizon sufficiently late, so the closed domain walls that naturally arise in the network are sufficiently large to collapse into PBHs. Besides, free axions from the collapse of open walls bounded by strings account for dark matter. Intriguingly, our PBHs can naturally explain the gravitational microlensing events observed by the OGLE collaboration. In addition, the collapse of string-wall network will release gravitational waves (GWs), which is drastically different from that in the scaling regime. For certain parameter space of axion-like particles, such GW spectra could possibly account for the reported nano-Hz stochastic GW background and can be tested by various GW interferometry experiments.
May 02, 2025: (13:30 - 14:15 CEST/ 17:00 - 17:45 IST)
Title: Observable CMB B-Modes from Cosmological Phase Transitions
Abstract: A B-mode polarization signal in the cosmic microwave background (CMB) is widely regarded as smoking gun evidence for gravitational waves produced during inflation. In this talk, I demonstrate that tensor perturbations from a cosmological phase transition can produce a B-mode signal whose strength rivals that from inflationary predictions across a range of observable scales. Although phase transitions arise from sub-horizon physics, they nevertheless exhibit a white noise power spectrum on super-horizon scales. Power is suppressed on the large scales relevant for CMB B-mode polarization, but it is not necessarily negligible. For appropriately chosen phase transition parameters, the maximal B-mode amplitude can compete with inflationary predictions that can be tested with current and future experiments. These scenarios can be differentiated by performing measurements on multiple angular scales, since the phase transition signal predicts peak power on smaller scales.
May 02, 2025: (14:15 - 15:00 CEST/ 17:45 - 18:30 IST)
Title: Uplifting Massive Graphs from Minkowski to de Sitter
Abstract: Identifying useful flat-space limits for cosmological correlators—where they can be expressed in terms of observables in Minkowski space—is nontrivial due to their scale-invariant nature. In this talk, I present a massive flat-space limit in which cosmological correlators, induced by the exchange of heavy fields, can be expressed in terms of massive Feynman graphs in flat space. As a phenomenological application, I apply this flat space limit to compute specific one-loop contributions from heavy fields to primordial non-Gaussianity.
April 25, 2025: (12:00 - 12:45 CEST/ 15:30 - 16:15 IST)
Title: Dark matter from the dark axion portal
Abstract: In this talk, I will discuss dark matter production through the "pure dark axion portal", which describes the interaction between axions, photons, and dark photons. Under certain conditions, dark matter is produced via the freeze-in mechanism, leading to rich phenomenology. In particular, the heaviest particle in the dark sector decays into a lighter one and a photon. This model predicts a well-defined parameter space featuring a cold dark matter candidate that can be searched for. It also presents unique features that can be tested through cosmological and laboratory observations.
April 25, 2025: (12:45 - 13:30 CEST/ 16:15 - 17:00 IST)
Title: Gravitational Waves from Stochastic Scalar Fluctuations
Abstract: In this talk, we will present a novel mechanism for gravitational wave generation in the early Universe. Light spectator scalar fields during inflation can acquire a blue-tilted power spectrum due to stochastic effects. We show that this effect can lead to large curvature perturbations at small scales (induced by the spectator field fluctuations) while maintaining the observed, slightly red-tilted curvature perturbations at large cosmological scales (induced by inflaton fluctuations). Along with other observational signatures, such as enhanced dark matter substructure, large curvature perturbations can induce a stochastic gravitational wave background (SGWB). We will discuss this mechanism in detail and present several benchmark scenarios that result in gravitational wave strengths visible to near-future detectors.
DESI-PDF.pdfApril 11, 2025: (12:00 - 14:00 CEST/ 15:30 - 17:30 IST)
Time: 12:00 - 12:30 CEST/ 15:30 - 16:00 IST
Title: Hints of Evolving Dark Energy
Abstract: The accelerated expansion of our universe, driven by the enigmatic dark energy, remains one of the most profound mysteries in modern physics. Unraveling its nature requires a synergistic approach, combining cutting-edge observations and theoretical frameworks. The Dark Energy Spectroscopic Instrument (DESI) is at the forefront of this quest.
In this talk, I will discuss how DESI's unprecedented 3D mapping of millions of galaxies, coupled with Cosmic Microwave Background (CMB) and Supernovae observations, are providing unprecedented insights into the cosmic web and the distribution of matter on large scales. By analyzing the imprints left by dark energy and neutrino masses on these intricate structures, we aim to unravel the fundamental constituents of our universe. I will present the latest results from these collaborations and the theoretical developments employed to extract their profound cosmological signatures.
Time: 12:30 - 13:00 CEST/ 16:00 - 16:30 IST
Title: DESI 2024 Results: Full-Shape analysis
Abstract: In my presentation, I will explain the full-shape analysis of the DESI 2024 data. I will describe the perturbation theory model used to describe the nonlinear evolution of the matter power spectrum and the redshift-space distortions. Additionally, I will outline the blinding approach at the catalogue level to avoid confirmation bias. Finally, I will discuss the constraints on cosmological parameters derived from the DESI Y1 BAO and DESI Y1 RSD data.
Time: 13:00 - 13:30 CEST/ 16:30 - 17:00 IST
Title: On Dark Radiation, varying Dark Energy and neutrinos with DESI BAO
Abstract: I will discuss some consequences of the new cosmological Baryon Acoustic Oscillations (BAO) measurements by the DESI collaboration. First, I will consider models with Dark Radiation: while using DESI+Planck+Supernova data such models can decrease the Hubble tension below the 2 sigma level, it turns out that the new ACT DR6 CMB data are now in disagreement with such a possibility. Then I will discuss varying Dark Energy parameterizations, restricting to healthy regions of parameter space. I will also discuss the impact of Supernova data (DES vs Pantheon) on varying dark energy vs LCDM. Finally I will discuss neutrino mass bounds from DESI.
Group discussion
Group discussion
Time: 13:30 - 14:00 CEST/ 17:00 - 17:30 IST
April 04, 2025: (12:00 - 12:45 CEST/ 15:30 - 16:15 IST)
Title: Primordial Black Holes as a dark matter candidate
Abstract: Primordial Black Holes (PBHs), black holes formed from over-densities in the early Universe, have become a popular dark matter candidate. I will overview the formation of PBHs, observational probes of their abundance and the key open questions in the field.
April 04, 2025: (12:45 - 13:30 CEST/ 16:15 - 17:00 IST)
Title: Simplicity of Cosmological Correlators
Abstract: We analyze in-in correlators (cosmological correlators) and the wave function of the universe in dS at tree and loop level. We find a hidden simplicity in the structure of in-in correlators compared to the wave function and find a new integral representation for in-in correlators and comment on the nature of the functions in the final expressions. Since the wave functions are equivalent to AdS correlators by analytic continuation, this analysis is also valid for correlators in AdS.
April 04, 2025: (13:30 - 14:15 CEST/ 17:00 - 17:45 IST)
Title: Axio-dilatons: A Dark Horse for the Dark Sector
Abstract: We live in remarkable times: the recent advent of gravitational-wave observations allows testing gravity in a strongly relativistic regime. We also have plausible candidates for UV physics that can reconcile General Relativity with Quantum Mechanics. Primordial cosmic fluctuations might even provide direct observational evidence for gravitating quantum physics at very high energies. But a central organizing feature of Nature - Decoupling - beautifully explains why low-energy measurements are largely insensitive to UV details and so at first sight seems to thwart the extraction of fundamental insights about UV physics from astrophysical or cosmological observations. This talk argues that a few UV features can penetrate the fog of decoupling in interesting ways. Decoupling constraints are less pressing (but still present) for inflationary expansion in the very early universe, but are crucial at the low energies being explored in the present-day universe. I argue that decoupling ideas point to a class of late-universe cosmologies that are relatively poorly explored. They are also timely given recent indications that the Dark Energy might be more complicated than had been thought.
April 04, 2025: (16:00 - 16:45 CEST/ 19:30 - 20:15 IST)
Title: Probing Reheating Cosmology with Dark-Sector Searches:Cosmic Millicharged Background
Abstract: We demonstrate that the searches for dark sector particles can provide probes of reheating scenarios, focusing on the cosmic millicharge background produced in the early universe. We discuss two types of millicharge particles (mCPs): either with, or without, an accompanying dark photon. These two types of mCPs have distinct theoretical motivations and cosmological signatures. We discuss constraints from the overproduction and mCP-baryon interactions of the mCP without an accompanying dark photon, with different reheating temperatures. We also consider the ΔNeff constraints on the mCPs from kinetic mixing, varying the reheating temperature. The regions of interest in which the accelerator and other experiments can probe the reheating scenarios are identified in this paper for both scenarios. These probes can potentially allow us to set an upper bound on the reheating temperature down to ∼10 MeV, much lower than the previously considered upper bound from inflationary cosmology at around ∼10^16 GeV. In addition, we find parameter regions in which the two mCP scenarios may be differentiated by cosmological considerations. Finally, we discuss the implications of dedicated mCP searches and future CMB-S4 observations.
March 28, 2025: (12:45 - 13:30 CET/ 17:15 - 18:00 IST)
Title: Generation of Magnetic Fields during Inflation
Abstract: Magnetic fields have been observed in galaxies, galaxy clusters, and even in the intergalactic medium. While astrophysical mechanisms can account for the magnetic fields in galaxies and galaxy clusters, they may not fully explain the presence of magnetic fields in the intergalactic medium. In this talk, I will discuss the generation of these large-scale magnetic fields in the early universe, potentially arising during the inflationary era. I will present my work, which addresses the challenges associated with generating these fields during inflation. Furthermore, I will discuss our recent work exploring the possibility of magnetic field generation. In the Spectator Chromo-Natural Inflation (SCNI) model. In this model, inflationary magnetogenesis is realized by identifying the non-Abelian sector of SCNI with the SU(2)_L sector of the Standard Model, providing a novel mechanism for the emergence of primordial magnetic fields during inflation.
March 28, 2025: (13:30 - 14:15 CET/ 18:00 - 18:45 IST)
Title: How light can dark matter particles be?
Abstract: I will argue that if dark matter is produced via processes with finite correlation length in the early universe, then there is a lower bound on the mass of dark matter particles [m > 10^(-19) eV]. For such dark matter, there is both (i) a free streaming suppression and (ii) white-noise enhancement in the dark matter density power spectrum. The absence of these in the existing observational data (for example, Ly-a) provides a bound on the mass. This relatively model independent bound will improve rapidly as observations probe dark matter at even smaller length scales. The bound can also be made stronger by many orders of magnitude if additional model-dependent assumptions are included. Time permitting, I will discuss a framework to calculate structure formation in presence of both significant velocity dispersion and small number densities of composite dark matter structures.
March 21, 2025: (12:00 - 12:45 CET/ 16:30 - 17:15 IST)
Title: Testing Frogatt-Nielsen flavour models with gravitational waves
Abstract: I will present a recent work where we assessed the capability of Gravitational Wave (GW) experiments to probe the origin of the flavour sector of the Standard Model. Within the context of the Froggatt-Nielsen mechanism to generate the hierarchical patterns of fermion masses and mixing based on a gauged U(1) flavour symmetry, we investigated the formation of cosmic strings and the resulting GW background (GWB), estimating the sensitivity to the model’s parameter space of future GW observatories. Comparing these results with the bounds from low-energy flavour observables, we found that these two types of experimental probes of the model are nicely complementary. In certain scenarios, the combination of flavour constraints and future GW bounds can bring about a complete closure of the parameter space, which (once again) illustrates the potential of GWB searches to test fundamental interactions at ultra-high energy scales beyond the reach of laboratory experiments.
March 21, 2025: (12:45 - 13:30 CET/ 17:15 - 18:00 IST)
Title: Renormalons as Saddle Points
Abstract: Renormalons play an important role in connecting non-perturbative power corrections to high-order perturbative predictions in QCD. Associated with branch points in the Borel transform of asymptotic series, they have largely been studied diagrammatically in perturbation theory. Similar statements can be made about instantons, though these have been shown to be non-perturbative saddle points of the path integral. We demonstrate that, in a similar vein, renormalons can be understood as saddle points of the one-loop effective action in the path integral, thereby opening new avenues for probing their existence beyond diagrammatics.
March 14, 2025: (12:00 - 12:45 CET/ 16:30 - 17:15 IST)
Title: Using group extensions to construct flavour symmetric models: a way to kill two birds with one stone
Abstract: Flavon models in the literature assume constraints on the components of the vacuum expectation values (vevs) of flavons, and typically, these constraints are not fully determined by the residual symmetry group of the set of vevs. This poses a problem because the general potential of the flavons cannot have a minimum that leads to such constraints unless additional mechanisms involving supersymmetry, extra dimensions etc., are invoked. In this seminar, we discuss a solution, namely the framework of the auxiliary group, which posits group extensions acting on flavons but not on fermions and generates vevs satisfying the required constraints naturally. Using this framework, we construct a highly predictive neutrino flavon model and its general renormalizable potential without invoking additional mechanisms. We show that this potential has the required minimum.
March 03, 2025: (12:00 - 13:00 CET/ 16:30 - 17:30 IST)
Title: Scrutinizing the bedrock of contemporary cosmology
Abstract: The remarkable success of recent cosmology in pinpointing a consistent concordance model relies on few foundational assumptions of homogeneity, isotropy of the universe, scale independence, etc. Increasingly precise cosmological observations, such as the exquisite measurements of the CMB sky from ESA Planck space mission, have opened the possibility of robust independent tests of these assumptions. I will present key results from our two decades on research program on this theme.
February 28, 2025: (12:00 - 12:45 CET/ 16:30 - 17:15 IST)
Title: Probe of spatial geometry from scalar-induced gravitational waves
Abstract: We investigate a novel probe of the spatial geometry of the Universe through the observation of gravitational waves (GWs) induced by first-order curvature perturbations. The existence of spatial curvature leaves imprints on the gravitational wave spectrum and the formation of primordial black holes. Given the peaked scalar spectrum, the induced spectrum deviates from the flat space power spectrum and the deviation is dependent on the spatial curvature K and reheating temperature Trh. For prolonged reheating and negative spatial curvature, the spectrum is amplified enough and exhibits an additional peak solely due to K indicating a possible detection by future gravitational wave experiments including LISA and DECIGO. We also observe that the presence of negative spatial curvature improves the constraints on PBH formation, increasing the mass of black holes which are viable dark matter candidates.
February 28, 2025: (12:45 - 13:30 CET/ 17:15 - 18:00 IST)
Title: Explorations between Theory and AI in Cosmology
Abstract: In the first part of my talk, I will describe challenges and opportunities in using machine learning to constrain primordial physics from cosmology. While machine learning models are often strong on the training data, it is difficult to marginalize over uncertainties on non-linear scales, and thus obtain reliable measurements. In this talk I will show that the situation is better for squeezed limit observables, such as local primordial non-Gaussianity. In this case, one can train a machine learning method that allows to marginalize over unknown biases, and is thus equally robust to non-linear physics as the traditional method, but more statistically sensitive.
In the second part of my talk I will discuss the possibility of using large language models for theoretical physics reasoning. I will present the results of our new benchmark data set TPBench, which spans problems from undergraduate up to research level in theoretical physics. I will show how quickly these models have improved over the last year, but also demonstrate their significant shortcomings. Finally I will discuss how the theoretical physics community can contribute to improving them.
February 21, 2025: (13:00 - 13:45 CET/ 17:30 - 18:15 IST)
Title: Superfluid dark matter: from theory to observations.
Abstract: In this talk we will review the model of superfluid dark matter, based on the existence of sub-eV particles with repulsive self-interactions. These particles are able to generate a superfluid core in galaxies upon Bose-Einstein condensation and thermalisation. We will delve into the various phenomenological implications of the model, including the formation of vortices, the behaviour around black holes and dynamical friction, and discuss prospects of detectability through gravitational wave experiments.
February 21, 2025: (13:45 - 14:30 CET/ 18:15 - 19:00 IST)
Title: Finding Evidence of Inflation and Galactic Magnetic Fields with CMB Surveys
Abstract: Magnetic fields of strength ~μG are observed in galaxies today, but their origin is unknown. A promising scenario is that magnetic fields larger than 0.1 nG at Mpc scales generated during inflation were adiabatically compressed during structure formation to give rise to the μG fields in galaxies. Thus, detecting a scale-invariant primordial magnetic field (PMF) above 0.1 nG on Mpc scales just after recombination would indicate an inflationary origin of galactic magnetic fields. Such a detection would also provide compelling evidence that inflation occurred, since such a strong, scale-invariant magnetic field on Mpc scales could only arise from inflation. If the scale-invariant PMF strength is constrained to be below 0.1 nG, it would imply that the inflationary scenario is not the primary origin, since such weak PMFs cannot be amplified enough via adiabatic compression to produce the strength of the galactic fields we observe today. We find that measurements of anisotropic birefringence by future CMB surveys will be able to improve the sensitivity to Mpc-scale inflationary PMFs by an order of magnitude. In particular, the CMB-HD experiment would lower the upper bound to 0.072 nG at the 95% CL, which is below the critical 0.1 nG threshold for ruling out a purely inflationary origin. If inflationary PMFs exist, a CMB-HD survey would be able to detect them with at least 3σ significance, providing evidence for inflation itself.
February 07, 2025: (12:00 - 12:45 CET/ 16:30 - 17:15 IST)
Title: Back to the origins of brane-antibrane Inflation.
Abstract: We study a new framework for brane-antibrane inflation where moduli stabilisation relies purely on perturbative corrections to the effective action. This guarantees that the model does not suffer from the eta-problem. The inflationary potential has two contributions: the tension of an antibrane at the tip of a warped throat, and its Coulomb interaction with a mobile brane. This represents the first realisation of the original idea of brane-antibrane inflation, as opposed to inflection point inflation which arises when the moduli are fixed with non-perturbative effects. Moreover, we formulate the brane-antibrane dynamics as an F-term potential of a nilpotent superfield in a manifestly supersymmetric effective theory. We impose compatibility with data and consistency conditions on control over the approximations and find that slow-roll inflation can occur in a large region of the underlying parameter space. The scalar spectral index is in agreement with data and the tensor-to-scalar ratio is beyond current observational reach. Interestingly, after the end of inflation the volume mode can, but does not need to, evolve towards a late-time minimum at larger values.
February 07, 2025: (12:45 - 13:30 CET/ 17:15 - 18:00 IST)
Title: A Closer Look at Gravitational Production of Particles during Reheating
Abstract: Gravity plays in many ways a crucial role in the evolution of the universe. In this talk, I will focus on gravity as a source of particle production during reheating. All the particles, including dark matter, can inevitably be created after the end of inflation. I will discuss both the perturbative and non-perturbative aspects of this process, to gain a deeper understanding of gravitational particle production.
January 31, 2025: (12:00 - 12:45 CET/ 16:30 - 17:15 IST)
Title: Path integrals and thimbles
Abstract: Quantum mechanics may be tackled using Heisenberg, Schrodinger or Feynman approaches. In this talk I will discuss methods for tackling the path integral as applied to real-time dynamics. I will describe how this rather badly-behaved integral can be tamed using thimbles, whose solution may then be attempted with Monte-Carlo techniques.
January 10, 2025: (15:00 - 16:00 CET/ 19:30 - 20:30 IST)
Title: A Grand unified solution to the Axion Quality Problem
Abstract: Invisible axion models that solve the strong CP problem via the Peccei-Quinn (PQ) mechanism typically have a quality problem that arises from quantum gravity effects which violate all global symmetries. These models therefore require extreme fine-tuning of parameters for consistency. We present a new class of solutions to the quality problem in a unified SO(10) × U(1)a gauge model, where U(1)a is an anomaly free axial gauge symmetry. PQ symmetry emerges as an accidental symmetry in this setup, which admits a PQ breaking scale as large as 4 × 1011 GeV, allowing for the axion to be the cosmological dark matter. Furthermore, the model has no domain wall problem and it provides a realistic and predictive framework for fermion masses and mixings.
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