SCHOOL OF PHYSICS :: Seminars

Seminars

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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
Tue Feb 11, 2025 (1403/11/23)

	Feb 11 1403/11/23	14:00	What is the origin of cosmological neutrino mass bounds? Background versus perturbations Show Abstract Abstract:The cosmological upper bound on the total neutrino mass is the dominant limit on this fundamental parameter. Recent observations have strongly tightened it, approaching the lower limit set by oscillation data. Understanding its physical origin, robustness, and model-independence becomes pressing. In this seminar I will introduce a novel framework to explicitly separate for the first time the two distinct cosmological neutrino-mass effects. On the one hand, the impact on background evolution, related to the energy in neutrino masses; on the other hand, the "kinematic" impact on perturbations, related to neutrino free-streaming. I will didactically explain how these effects separately modify CMB anisotropies, by introducing two effective masses enclosing background and perturbations effects. I will explain the results of analyzing CMB data in this framework, which show that the neutrino-mass bound is mostly a background measurement, i.e., how the neutrino energy density evolves with time. The results also quantify the difficulty of measuring the neutrino "kinematical" mass, whose bound is relaxed by 3 orders of magnitude. Lecturer(s): Toni Bertolez Martinez From : ICCUB Research Group: HEPCO Group Weekly Seminar More Info. : Link
Tue Feb 04, 2025 (1403/11/16)

	Feb 04 1403/11/16	14:00	Three unique analyses for three new neutrino detectors Show Abstract Abstract:Next-generation neutrino experiments, such as JUNO, Hyper-K, and DUNE, offer new, unique probes into neutrino and beyond the standard model physics. In this talk, I will discuss how each detector's target material (or size) will lead to distinct signatures and how they could be used in new physics and precision studies. For JUNO, we will utilize low-energy neutrino signals in Carbon to discover the atmospheric tau-neutrino flux. For DUNE, nuclear transitions in Argon allow for new and exciting measurements of solar neutrinos Ã la SNO. Finally, for Hyper-K, its size, and sensitivity to low-energy neutrinos will allow it to measure neutrinos coming from dark matter annihilating within Jupiter's core, reaching sensitivities similar to current direct detection experiments. Lecturer(s): Stephan Meighen-Berger From : University of Melbourne Research Group: HEPCO Group Weekly Seminar More Info. : Link
Tue Jan 21, 2025 (1403/11/2)

	Jan 21 1403/11/2	14:13	Dark Acoustic Oscillation Faces the Cosmological Tension Show Abstract Abstract:With the growing precision of cosmological measurements, tensions in the determination of cosmological parameters have arisen that might be the first manifestations of physics going beyond Lambda CDM. We propose a new class of interacting dark sector models, which lead to qualitatively distinct cosmological behavior, dark acoustic oscillation, which can potentially simultaneously address the two most important tensions in cosmological data, the H0 and S8 tensions. The main ingredients in this class of models are self-interacting dark radiation and its dark acoustic oscillation induced by strong interactions with a fraction of dark matter. I will also present the latest results from applying this model across various combinations of cosmological data, illustrating the improvement it provides over Lambda CDM. Lecturer(s): Taewook Youn From : Cornell University, Korea Institute for Advanced Study Research Group: HEPCO Group Weekly Seminar More Info. : Link
Tue Dec 31, 2024 (1403/10/11)

	Dec 31 1403/10/11	14:00	Looping story in early universe cosmology Show Abstract Abstract:We will review the ongoing debates on loop corrections in the multi-phase inflationary universe and their controversial results. Then, we will show that quantum effects can dramatically affect the long CMB-scale modes after regularizing and renormalizing divergences in different stages of inflationary evolution. Lecturer(s): Haidar Sheikhahmadi From : School Of Astronomy, IPM Research Group: HEPCO Group Weekly Seminar More Info. : Link
Tue Dec 17, 2024 (1403/9/27)

	Dec 17 1403/9/27	14:00	Null Boundary Poisson Brackets Show Abstract Abstract:In physics, we often encounter different types of boundaries: spacelike, timelike, and null boundaries. Spacelike boundaries (e.g., constant time slices) are used for initial value problems, while timelike boundaries (e.g., constant radial surfaces) are suited for boundary value problems. Null boundaries are unique because they share characteristics of both, conceptually lying between spacelike and timelike boundaries. Examples include black hole horizons and null infinity in asymptotically flat spacetimes. In this talk, I will discuss Einstein's gravity in the presence of a generic null boundary and examine the structure of Poisson brackets defined on it. Key results include the ultralocal nature of these brackets and the Carrollian structure of the null boundary solution space. Lecturer(s): Vahid Taghiloo From : School Of Physics, IPM Research Group: HEPCO Group Weekly Seminar More Info. : Link
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