SCHOOL OF PHYSICS :: Seminars

Seminars

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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
Tue May 06, 2025 (1404/2/16)

	May 06 1404/2/16	14:00	Geometric Classical and Quantum Mechanics Show Abstract Abstract: Date and time Tuesday, May 6th, 2025 (Ordibehesht 16st, 1404), 2:00 pm (Tehran zone) Location Room C, Floor 2, Farmanieh Building, No. 70, Lavasani St. Link https://www.skyroom.online/ch/schoolofphysics/highenergyseminar Abstract The coupling of space and time that leads to the concept of spacetime is complemented by the Minkowski metric. On the other hand, the coupling of position and momentum that leads to the concept of phase space is complemented by the canonical symplectic form. In this talk, we modify the symplectic geometry of both classical and quantum phase space by completing its symplectic form by adding to its canonical symplectic form, which is an anti-symmetric form, a symmetric form which is nothing other than the Euclidean metric of classical and quantum phase space. Thus we modify the Hamilton and SchrÃ¶dinger equations. The consequences are that an arrow of time is obtained and although the canonical energy, i.e. the Hamiltonian, decreases but the law of conservation of energy holds. Moreover, the system always evolves to the stationary states which are critical points of the Hamiltonian. As some applications, this model can be used to explain the accelerated expansion of cosmos and dark energy and the jumps between stationary orbits in quantum atomic model. Lecturer(s): Seyed Ebrahim Akrami From : IPM, School of Physics Research Group: HEPCo Group Seminar More Info. : Link
Tue Apr 29, 2025 (1404/2/9)

	Apr 29 1404/2/9	14:00	Modular Invariance, the strong CP Problem, baryogenesis, its tests via optical gravitational waves Show Abstract Abstract:I will show that spontaneous CP violation, automatically realized in theories with modular invariance, offers a novel solution to the strong CP problem (arXiv:2305.08908, arXiv:2406.01689). I will then show that the cosmological evolution of the CP-breaking scalar modulus can drive baryogenesis (arXiv:2504.03506). Finally, I will present a distinctive signal of these heavy gravitational scalars: their cosmological decays into gravitons generate gravitational waves that today redshift to optical frequencies (arXiv:2501.16427). Lecturer(s): Alessandro Strumia From : University of Pisa, Italy Research Group: HEPCO Group Weekly Seminar More Info. : Link
Wed Apr 16, 2025 (1404/1/27)

	Apr 16 1404/1/27	18:00	Copenhagen Survey on Black Holes and Fundamental Physics Show Abstract Abstract:The purpose of this survey is to take a snapshot of the attitudes of physicists working on some of the most pressing questions in modern physics, which may be useful to sociologists and historians of science. For this study, a total of 85 completed surveys were returned out of 151 registered participants of the ``Black holes Inside and out'' conference, held in Copenhagen in 2024. The survey asked questions about some of the most contentious issues in fundamental physics, including the nature of black holes and dark energy. A number of surprising results were found. For example, some of the leading frameworks, such as the cosmological constant, cosmic inflation, or string theory - while most popular - gain less than the majority of votes from the participants. The only statement that gains majority approval (by 68% of participants) was that the Big Bang meant â??the universe evolved from a hot dense stateâ?�, not â??an absolute beginning timeâ?�. These results provide reasons for caution in describing ideas as consensus in the scientific community when a more nuanced view may be justified. Lecturer(s): Niayesh Afshordi From : Peremeter Institute Research Group: Physics Colloquium More Info. : Link
Tue Apr 08, 2025 (1404/1/19)

	Apr 08 1404/1/19	19:00	Daily modulation of low-energy nuclear recoils from sub-GeV dark matter Show Abstract Abstract:At sufficiently low nuclear recoil energy, the scattering of dark matter (DM) in crystals gives rise to single phonon and multiphonon excitations. In anisotropic crystals, the scattering rate into phonons modulates over each sidereal day as the crystal rotates with respect to the DM wind. This gives a potential avenue for directional detection of DM. The daily modulation for single phonons has previously been calculated. Here we calculate the daily modulation for multiphonon excitations from DM in the mass range 1 MeV-1 GeV. We generalize previous multiphonon calculations, which made an isotropic approximation, and implement results in the DarkELF package. We find daily modulation rates up to 1-10 percent for an Al2O3 target and DM mass below 30 MeV, depending on the recoil energies probed. We obtain similar results for SiC, while modulation in Si, GaAs and SiO2 is negligible. Lecturer(s): Connor Stratman From : University of California, San Diego Research Group: HEPCo Group Weekly Seminar More Info. : Link
Tue Mar 11, 2025 (1403/12/21)

	Mar 11 1403/12/21	14:00	A proposal for a Covariant Arrow of Time Show Abstract Abstract:While fundamental formulations of physics, such as Newtonian mechanics, General Relativity (GR), and Quantum Mechanics, are time-symmetric, the universe around us is clearly not. The quest for an arrow of time has been a longstanding issue. In this talk, I propose a â??generally covariant arrow of timeâ?� based on quantum (semiclassical) considerations in GR. Lecturer(s): Shahin Sheikh Jabbari From : School of Physics, IPM Research Group: HEPCO Group Weekly Seminar More Info. : Room C, Floor 2, Farmanieh Building, No. 70, Lavasani St. Link
Tue Feb 25, 2025 (1403/12/7)

	Feb 25 1403/12/7	14:00	Gravitational Stress Tensor and Current at Null Infinity in Three Dimensions Show Abstract Abstract:We develop the framework that reveals the intrinsic conserved stress tensor and current associated with the null infinity of a three-dimensional (3d) asymptotically flat spacetime. These are, respectively, canonical conjugates of degenerate metric and Ehresmann connection of the boundary Carrollian geometry. Their conservation reproduces the Bondi-mass and angular momentum conservation equations if the asymptotic boundary is endowed with a torsional affine connection that we specify. Our analysis and results shed further light on the 3d flat holography; the stress tensor and current give rise to an asymptotically flat fluid/gravity correspondence. The requirement of a well-defined 3d action principle yields Schwarzian action at null infinity governing the dynamics induced by reparametrizations over the celestial circle, in accord with the codimension $2$ holography of 3d flat spacetimes. Lecturer(s): Hamed Adami From : Fudan University & Shanghai institute for mathematics and interdisciplinary sciences Research Group: HEPCO Group Weekly Seminar More Info. : Link
Tue Feb 18, 2025 (1403/11/30)

	Feb 18 1403/11/30	14:00	Search for CP-violation as a guiding star towards new physics Show Abstract Abstract:Within the relativistic field theory, CPT is proved to be conserved. However, CP can be broken. The violation of CP can induce electric dipole moment for elementary fermions. Indeed, CP is broken in the Standard Model (SM) of particles. However, the predicted value of the electron electric dipole moment within the SM is too small to be resolvable by present and upcoming experiments. In this talk after a short review of the phenomenological impact of CV-violation, I will discuss our project on the CP-violation carried out in collaboration with late Prof. Demir. Lecturer(s): Yasaman Farzan From : School Of Physics, IPM Research Group: HEPCO Group Weekly Seminar More Info. : Link
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