SCHOOL OF PHYSICS :: Seminars

Seminars

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Tue Feb 10, 2026 (1404/11/21)

	Feb 10 1404/11/21	14:00	Scaling Symmetry and Carrollian Gravity Show Abstract Abstract:In this presentation, we formulate matter-coupled scaling-Carroll gravity as a gauge theory and analyze its associated gravity multiplet. After fixing the scaling symmetry, the theory is governed by the trace of the extrinsic curvature, the Carroll boost symmetry, and a vector field derived from dilatation. We demonstrate that appropriate gauge choices and geometric constraints lead to distinct regimes, including dynamical Carroll gravity, Aristotelian gravity, and a fracton gauge theory coupled to Aristotelian geometry. In the fracton phase, the Carroll boost parameter functions as a vector-charge gauge symmetry. Lecturer(s): Mehdi Ahmadi-Jahmani From : Ferdowsi University of Mashhad Research Group: HEPCO Group Weekly Seminar More Info. : Link
Tue Feb 03, 2026 (1404/11/14)

	Feb 03 1404/11/14	14:00	How light can ALP dark matter? Show Abstract Abstract:I discuss lower bounds on the mass of axion-like particles, assuming they make up all of dark matter. Distinguishing between pre- and post-inflationary symmetry breaking, I identify the allowed parameter space in terms of the axion mass and the inflationary energy scale. In the post-inflationary scenario, recent simulations show that axion radiation from cosmic strings dominates dark matter production, leading to significantly weaker isocurvature constraints than previously thought. Combining these with limits from black hole superradiance and free streaming yields a generic bound maâ?³10^{â??17}â??eVm_a \gtrsim 10^{-17}\,\mathrm{eV}, with possible relaxation in specific scenarios. I also show that the absence of CMB tensor modes can impose much stronger bounds, reaching maâ?³5Ã?10 ^{â??17}â?? â??eVm_a \gtrsim 5 \times 10^{-7}\,\mathr for low reheating efficiencies. Lecturer(s): Kierthika Chathirathas From : Institute for Astroparticle Physics (IAP), Karlsruhe Institute of Technology (KIT) Research Group: HEPCO Group Weekly Seminar More Info. : Link
Tue Jan 27, 2026 (1404/11/7)

	Jan 27 1404/11/7	14:00	Weak Decays of the \Omega_{b}^{} Baryon and Their Role in Its Experimental Establishment Show Abstract Abstract:The spin-3/2 ground-state bottom baryon \Omega^{}_{b} remains one of the least explored members of the heavy-baryon spectrum. Owing to the absence of any Okubo-Zweig-Iizuka (OZI)-allowed strong decay channels, together with the presence of a soft photon in its radiative decay, experimental establishment of \Omega^{}_{b} is particularly challenging. In this talk, we present a detailed study of the weak decays of \Omega^{}_{b} as a promising pathway toward its experimental establishment. We analyze both semileptonic and nonleptonic weak decays of the transition \Omega^{}_{b} --> \Omega^{}_{c}, treating them within a unified theoretical framework. First, the transition form factors governing this heavy-to-heavy baryonic process are calculated using the QCD sum rule approach, ensuring consistency with Lorentz invariance and the spin- 3/2 nature of the participating baryons. These form factors are then employed to compute decay amplitudes, and decay widths for the semileptonic channels \Omega^{}_{b} \Omega^{}_{c} --> \ell\bar{\nu}_{\ell} and nonleptonic transitions \Omega^{}_{b}--> \Omega^{}_{c}M, where M denotes a pseudoscalar or vector meson. Taken together, the results demonstrate that weak decay modes provide a coherent and realistic strategy for the experimental identification of the \Omega^{}_{b} baryon at current and future hadron experiments. Lecturer(s):* Amir Amiri From : Ferdowsi University of Mashhad Research Group: HEPCO Group Weekly Seminar More Info. : Link
Tue Jan 06, 2026 (1404/10/16)

	Jan 06 1404/10/16	14:00	Dark Secrets of Baryons: Illuminating Dark Matter-Baryon Interactions with JWST Show Abstract Abstract:The James Webb Space Telescope (JWST) has discovered numerous bright galaxies at high redshifts (z~ 10-14). Many astrophysical models and beyond the Standard Model physics scenarios have been proposed to explain these observations. We investigate, for the first time, the implications of dark matter (DM) scattering with baryons (protons and electrons) in light of the JWST UV luminosity function (UVLF) observations. These interactions suppress structure formation on galactic scales, which may have an observable effect on the UVLF measurements at high redshifts. Using a recent galaxy formation model designed to explain high-redshift observations, we obtain strong upper limits on DM-baryon scattering cross-sections and explore new regions of the parameter space. For DM-proton scattering with cross-section velocity dependence v^(-2), we obtain the strongest limit for DM masses of 1 MeV-500 MeV. For other cases that we study, our limits are competitive with those obtained from other cosmological observables. Our study highlights the potential of JWST observations as a novel and powerful probe of non-gravitational interactions of DM. Lecturer(s): Abhijeet Singh From : Centre for High Energy Physics, Indian Institute of Science, India Research Group: HEPCO Group Weekly Seminar More Info. : Link
Tue Dec 16, 2025 (1404/9/25)

	Dec 16 1404/9/25	14:00	A New Derivation of Classical Gravitational Second Law of Thermodynamics Show Abstract Abstract:We present a new, fully covariant derivation of a classical gravitational second law of thermodynamics that applies beyond horizon geometries. Working in the covariant phase space formalism and using a first-order description of general relativity, we define gravitational entropy as a surface charge associated with local Lorentz boosts in the two-dimensional normal plane to a compact spacelike codimension-2 surface~$\Sigma$. For Einstein--Hilbert gravity, this charge reduces to the familiar area law but with a conceptually distinct origin from standard Noether-charge constructions based on diffeomorphism or Killing symmetries. We then study the evolution of~$\Sigma$ along an arbitrary future--directed causal curve~$\gamma$, which generates a causal hypersurface~$\Gamma$. Using a $2+(D-2)$ decomposition, Raychaudhuri-type equations for the null congruences, and Einstein's equations, we express the entropy variation $\delta_\gamma S$ as an integral over~$\Gamma$ in terms of shear, curvature components, and matter contributions. Exploiting the freedom of local null boosts and path reparametrizations, we obtain a manifestly gauge-independent expression and show that $\delta_\gamma S \ge 0$ is guaranteed if the strong energy condition (SEC) holds along~$\gamma$. In an appropriate null limit of the observer's worldline, this result reduces to a null-surface version controlled by the null energy condition (NEC). Our construction yields a (quasi-)local, covariant second law for gravitating systems that is not restricted to black hole or cosmological horizons and provides a natural framework for extensions to higher-curvature theories of gravity and cosmological settings. Lecturer(s): Vahid Reza Shajiee From : School of Physics, IPM Research Group: HEPCO Group Weekly Seminar More Info. : Link
Tue Dec 09, 2025 (1404/9/18)

	Dec 09 1404/9/18	14:00	Probing Neutrino and light DM with Cosmic Gravitational focusing Best Show Abstract Abstract:The cosmic gravitational focusing (CGF) of relic provides an independent measurement of the cosmic relics such as cosmic neutrinos and light dark matter (DM). This effect eventually produces a dipole density distribution that can affect the galaxy formation and thus can be reconstructed with galaxy surveys such as DESI. For cosmic neutrinos, the CGF have a mass forth power dependence which can help determine neutrino mass ordering. Also, for light DM, the mass dependence scales as second power. The CGF is most sensitive in the region 0.1-100 eV, where it offers a sensitivity two orders of magnitude stronger than the existing constraints from the Lyman-$\alpha$ and $\Delta N_{\rm eff}$. Lecturer(s): Liang Tan From : Shanghai Jiao Tong University, China Research Group: HEPCO Group Weekly Seminar More Info. : Link
Tue Nov 25, 2025 (1404/9/4)

	Nov 25 1404/9/4	14:00	Gravity Is Induced By Renormalization Group Flow Show Abstract Abstract:In this talk, we study the renormalization group (RG) flow of a holographic CFT in the AdS5/CFT4 framework. Moving from the UV toward the IR along the RG trajectory of the boundary theory, we find that gravitational couplings are gradually generated, giving rise to a dynamical boundary gravity. This surprising result suggests that gravity can emerge dynamically in the infrared rather than being a fundamental interaction. We derive the explicit form of the induced boundary gravitational action in the IR regime. The resulting effective theory includes Einstein gravity with a cosmological constant, supplemented by a single higher-derivative correction in the form of a Weyl-squared term. This provides a concrete realization of gravity emerging from holographic renormalization group flow. Lecturer(s): Vahid Taghiloo From : School of Physics, IPM Research Group: HEPCO Group Weekly Seminar More Info. : Link
Mon Nov 24, 2025 (1404/9/3)

	Nov 24 1404/9/3	18:00	Systematic Reduction of Quantum Many-Body Problems via Few-Body Expansions Show Abstract Abstract:Quantum many-body problems are notoriously difficult, with complexity growing exponentially with system size. Perturbative methods often fail in strongly interacting systems or in the presence of flat bands or van Hove singularities. Inspired by the concept of local integrals of motion, we present a non-perturbative approach that systematically reduces many-body properties to exact solutions of more tractable few-body problems. By mapping wavefunctions to Slater-determinant-like states defined by occupation numbers, we show that observables can be expressed as polynomials in these numbers, with coefficients determined by solving n-body problems (n <= p). For nearly integrable systems, the expansion truncates, allowing few-body solutions to yield nearly exact results for finite-density many-body systems. We validate the method on the 2D interacting models. Lecturer(s): Abolhassan Vaezi From : Sharif University of Technology Research Group: Physics Colloquium More Info. : Link
Tue Nov 18, 2025 (1404/8/27)

	Nov 18 1404/8/27	14:00	Gravitational Wave Signature and the Nature of Neutrino Masses: Majorana, Dirac, or Pseudo-Dirac? Show Abstract Abstract:In this talk, I will explore how gravitational-wave (GW) signatures can reveal the nature of neutrino massesâ??Dirac, Majorana, or pseudo-Dirac. Within the minimal $B-L$ gauge extension of the Standard Model, I will show that Majorana neutrinos with high-scale breaking produce flat GW spectra from cosmic strings, Dirac neutrinos with low-scale breaking generate peaked spectra from first-order phase transitions, and pseudo-Dirac scenarios lead to kink-like features from domain wall annihilation. Lecturer(s): Sudip Manna From : Harish-Chandra Research Institute Research Group: HEPCO Group Weekly Seminar More Info. : Link
Tue Nov 04, 2025 (1404/8/13)

	Nov 04 1404/8/13	14:00	Probing Dark Matter with Gravitational-Wave Laser Interferometers in Space Show Abstract Abstract:The discovery of gravitational waves has opened a new window for exploring the universe. This talk will discuss the use of gravitational wave observations for probing dark matter. It will focus on two types of dark matter candidates, WIMPs and ultra-light dark matter. The former can form dark matter spikes around black holes, affecting the motion of compact astrophysical objects through dynamical friction effects, thereby altering the gravitational waveforms emitted by the system, potentially observable by space-based gravitational-wave Laser Interferometers, such as LISA, Taiji and Tianqin. Ultra-light dark matter can directly interact with detectors, influencing the instruments, and can also be probed through gravitational wave experiments. Lecturer(s): Yong Tang From : University of Chinese Academy of Sciences (UCAS), Beijing, China Research Group: HEPCO Group Weekly Seminar More Info. : Link
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