SCHOOL OF PHYSICS :: Seminars

Seminars

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Tue Aug 19, 2025 (1404/5/28)

	Aug 19 1404/5/28	14:00	Exploring the Nucleon Structure Using Higher Twist Effects in Polarized Parton Distributions Show Abstract Abstract:Parton Distribution Functions (PDFs) are key to understanding the momentum and spin distributions of fundamental particles inside the nucleon, and their precise determination is crucial for rigorous tests of the Standard Model and for predicting outcomes in high-energy collider experiments. In this study, we employ Gegenbauer polynomialsâ??a set of orthogonal polynomials with strong convergence properties and superior ability to model the detailed shape of distributionsâ??to parameterize the polarized parton distribution functions (PPDFs). These polynomials are defined by two key parameters, and by fitting experimental data, unknown parameters are extracted that provide deeper insights into the protonâ??s structure. By analyzing comprehensive datasets, especially the final JLAB CLAS/EG1b data for proton and deuteron, the essential role of higher twist effects in accurately determining the PPDFs is demonstrated. The polarized structure functions of the proton, neutron, and deuteron are studied at NLO accuracy, both with and without considering higher twist effects. Additionally, the polarized Bjorken sum rule and proton helicity sum rule are examined to validate the fitting results. The findings show strong agreement with existing data and various parameterization models, indicating that this approach effectively decodes the complex structure of the nucleon and opens new horizons in understanding the behavior of fundamental particles at high energies. Lecturer(s): Hamed Abdolmaleki From : School of Physics, IPM Research Group: HEPCO Group Weekly Seminar More Info. : Link
Tue Aug 12, 2025 (1404/5/21)

	Aug 12 1404/5/21	14:00	A solution to the KM3NeT and IceCube tension over KM3-230213A Show Abstract Abstract:We entertain the possibility that transient astrophysical sources can produce a flux of dark particles that induce ultra-high-energy signatures at neutrino telescopes such as IceCube and KM3NeT. We construct scenarios where such â??dark fluxâ?� can produce meta-stable dark particles inside the Earth that subsequently decay to muons, inducing through-going tracks in large-volume neutrino detectors. We consider such a scenario in light of the O(70) PeV ultra-high-energy muon observed by KM3NeT and argue that because of its location in the sky and the strong geometrical dependence of the signal, such events would not necessarily have been observed by IceCube. Our model relies on the upscattering of a new particle X onto new metastable particles that decay to dimuons with decay lengths of O(100) km. This scenario can explain the observation by KM3NeT without being in conflict with the IceCube data. Lecturer(s): Yasaman Farzan From : School of Physics, IPM Research Group: HEPCO Group Weekly Seminar More Info. : Link
Tue Jul 29, 2025 (1404/5/7)

	Jul 29 1404/5/7	14:00	The X17 Journey: From Nuclear Experiments to Atomic Electron Motion. Show Abstract Abstract:The ATOMKI collaboration measured excesses in electron-positron production from nuclear transitions of beryllium, helium and carbon nuclei. All these excesses are compatible with the emission of a new boson with mass around 17 MeV, denoted X17. An independent search for this particle, harnessing a particle physics experiment, was performed at the Positron Annihilation into Dark Matter Experiment (PADME), where a positron beam collided against a diamond target expecting to produce resonantly the X17 particle. Given the presumably narrow width of this particle, a precise theoretical computation of the signal shape was required to account for electron motion within the target. After including the theoretical modelling of this effect in their analysis, the PADME collaboration has reported an excess in electron-positron events centered around 17 MeV. This excess was later independently shown to largely reduce the uncertainty on the expected X17 mass when combined with nuclear observables. As a byproduct of these studies, electron motion in large Z materials has been shown to enhance centre-of-mass energy in fixed-target experiments and allow for a new energy scan mechanism relevant for the measurement of the hadronic vacuum polarization contribution to the muon anomalous magnetic moment. Lecturer(s): Fernando Arias-Aragon From : National Institute for Nuclear Physics (INFN), Frascati National Laboratory Research Group: HEPCO Group Weekly Seminar More Info. : Link
Tue Jul 22, 2025 (1404/4/31)

	Jul 22 1404/4/31	11:00	Listening to the Universe with Quantum Ears: Precision Experiments and the Quantum Nature of Gravity Show Abstract Abstract:This talk addresses the intersection of physics at the smallest and largest scales, where quantum mechanics meets cosmology. We highlight the relevance of this interplay to foundational problems in both cosmology and high energy physics. Our discussion spans the potential quantum features manifesting at galactic or cosmological scales, as well as the role of quantum interferometry in enabling ultra-sensitive measurements in high-energy experiments. These experimental advances not only push the boundaries of precision measurement (such as the detection of gravitational waves), but also open promising avenues for probing quantum aspects of gravity, one of the most profound unresolved questions in theoretical physics. Lecturer(s): Alireza Maleki From : Sharif University of Technology Research Group: HEPCO Group Weekly Seminar More Info. : Link
Tue Jul 15, 2025 (1404/4/24)

	Jul 15 1404/4/24	14:00	CMB constraints on U (1) Axion warm inflation Show Abstract Abstract:In this talk, I will explain a model of warm inflation driven by axion-like particles interacting with $U(1)$ gauge fields, with implications for the early universe's thermal evolution. By extending traditional warm inflation models, we introduce a dissipation mechanism through the thermal fluctuations of electromagnetic fields, leading to a non-trivial backreaction on the inflaton's dynamics. Our results are consistent with CMB observations, even for a natural sub-Plankian Axion decay constant $f Lecturer(s): Vahid Kamali From : McGill University Research Group: HEPCO Group Weekly Seminar More Info. : Link
Tue Jun 10, 2025 (1404/3/20)

	Jun 10 1404/3/20	14:00	Unveiling neutrino physics with early universe probes Show Abstract Abstract:After a brief summary of our knowledge of the role of neutrinos in the early universe, we review the most important cosmological observables and discuss how they can help in our understanding of neutrinos and their properties. In particular, we focus on how neutrino properties change the effective number of relativistic species (Neff). Among new physics scenarios, we discuss the case of light sterile neutrinos and non-standard interactions between neutrinos and electrons or neutrinos and nucleons, presenting how they affect Neff and Big Bang Nucleosynthesis (BBN). We also show a low-temperature reheating model, which provides modifications to the expansion rate that also can affect Neff and BBN predictions.. Lecturer(s): Stefano Gariazzo From : University of Turin Research Group: HEPCO Group Weekly Seminar More Info. : Link
Tue May 27, 2025 (1404/3/6)

	May 27 1404/3/6	14:00	Fracton and Non-Lorentzian Particle Duality Show Abstract Abstract:Fractons, characterized by restricted mobility and governed by higher-moment conservation laws, represent a novel phase of matter with profound connections to tensor gauge theories and emergent gravity. I will systematically explore the duality between fractons and non-Lorentzian particlesâ??specifically, Carroll and Galilean particlesâ??within electromagnetic (EM) fields. By constructing canonical actions for fractons in rank-2 gauge fields, we derive their equations of motion and demonstrate that static fractons exhibit duality with the electric sector of Carroll particles, while mobile fracton dipoles correspond to both the electric and magnetic sectors of Galilean particles. Furthermore, by gauging the fracton algebra, we develop a geometric framework for fracton gravity, linking it to non-Lorentzian spacetime geometries. These results unify fracton dynamics with the non-relativistic and ultra-relativistic limits of physics, offering insights into emergent gravity and exotic condensed matter systems. Lecturer(s): Mohammad Mehdi Ahmadi Jahmani From : Ferdowsi University of Mashhad Research Group: HEPCO Group Weekly Seminar More Info. : Link
Wed May 21, 2025 (1404/2/31)

	May 21 1404/2/31	18:00	Do we understand early universe cosmology? Show Abstract Abstract:I will argue that the usual effective field theory techniques break down in the rapdily expanding background of the early universe. The TCC ("Trans-Planckian Censorship Criterion") plays a key role in the argument. I will then discuss an attempt to obtain an emerging metric space-time and early universe cosmology starting from a quantum mechanical matrix model. Lecturer(s): Robert Brandenberger From : McGill University Research Group: Physics Colloquium More Info. : Link
Tue May 20, 2025 (1404/2/30)

	May 20 1404/2/30	14:00	Confronting the KM3-230213A Ultra-High-Energy Neutrino event with IceCube data Show Abstract Abstract:High-energy neutrinos are extremely valuable cosmic messengers, as they not only carry unique information about the most extreme astrophysical environments, but also provide an opportunity to probe different aspects of particle physics. When talking about extremes, the ultra-high-energy neutrino event KM3-230213A, recently reported by the KM3NeT collaboration, stands out due to being the most energetic event ever observed, lying in the multi-PeV to EeV range. This observation is remarkable in itself, but several questions arise due to the non-observation of similar events at the IceCube neutrino observatory, which has been running for longer with a larger effective area. In this talk, I will try to confront the KM3-230213A event with IceCube data in the context of different hypotheses about its origin. I will focus on discussing the different tensions and difficulties that arise when trying to place this event in the global high-energy neutrino picture. Lecturer(s): Daniel Naredo-Tuero From : Universidad AutÃ³noma de Madrid Research Group: HEPCO Group Weekly Seminar More Info. : Link
Tue May 13, 2025 (1404/2/23)

	May 13 1404/2/23	14:00	Freelance Holography Show Abstract Abstract:AdS/CFT provides the most well-established example of holography, positing a duality between a quantum gravitational theory in an asymptotically AdS spacetime and a quantum field theory living on its asymptotic timelike boundary. However, this framework comes with certain limitations: it is confined to the asymptotic boundary, and the bulk gravitational fields are required to satisfy Dirichlet boundary conditions. In this talk, I will present a formulation of holography at finite distances in AdS spacetimes, which accommodates arbitrary boundary conditions for the bulk fields. We refer to this approach as freelance holography â?? a generalization that liberates the standard AdS/CFT duality from the constraints of Dirichlet conditions and asymptotic boundaries. Lecturer(s): Vahid Taghiloo From : School of Physics, IPM Research Group: HEPCO Group Weekly Seminar More Info. : Link
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