SCHOOL OF PHYSICS :: Seminars

Seminars

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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
Tue Dec 03, 2024 (1403/9/13)

	Dec 03 1403/9/13	14:00	Entanglement in Lifshitz Fermion Theories Show Abstract Abstract:I will discuss the static entanglement structure in (1+1)-dimensional free Dirac-fermion theory with Lifshitz symmetry, focusing on arbitrary integer dynamical critical exponents. My presentation will examine the behavior of various entanglement measures in both pure and mixed states. I will also highlight the distinctive properties of Dirac-Lifshitz fermions, particularly their locality, which contrasts with the non-local behavior of scalar counterparts and plays a crucial role in shaping their entanglement structure. Lecturer(s): Mohammad Javad Vasli From : University of Guilan Research Group: HEPCO Group Weekly Seminar More Info. : Link
Tue Nov 26, 2024 (1403/9/6)

	Nov 26 1403/9/6	14:00	A Quantum Description of Wave Dark Matter (Arxiv no: 2408.04696) Show Abstract Abstract:In this talk, I will outline a fundamentally quantum description of bosonic dark matter. Following a quantum optics inspired approach, I will show the density operator of dark matter, which takes a mixed Gaussian form over a coherent state basis. This formalism also allows a precise description of quantities related to dark matter coherence. I will further give a continuous description of dark matter through the wave-particle transition, where the density fluctuation in various scales evolves between the two limits, showing a unique behavior near the boundary of these descriptions. Lecturer(s): Dhong Yeon Cheong From : Yonsei University, Seoul, Republic of Korea Research Group: HEPCO Group Weekly Seminar More Info. : Link
Tue Nov 12, 2024 (1403/8/22)

	Nov 12 1403/8/22	14:00	Explicit Entanglement Wedge Reconstruction via Petz Map Show Abstract Abstract:We revisit entanglement wedge reconstruction in AdS/CFT using the Petz recovery channel. In the case of a spherical region on the boundary, we show that the Petz map reproduces the AdS-Rindler HKLL reconstruction. Moreover, for a generic subregion of the boundary, we could obtain the same boundary representation of a local bulk field lies in the entanglement wedge as the one proposed earlier in JLMS paper using properties of the modular flow. Lecturer(s): Niloofar Vardian From : Sharif University of Technology Research Group: HEPCO Group Weekly Seminar More Info. : Link
Tue Nov 05, 2024 (1403/8/15)

	Nov 05 1403/8/15	14:00	The charge and magnetic radii of the nucleons from the generalized parton distributions Show Abstract Abstract:The proton-radius puzzle refers to the discrepancy observed in measurements of the proton's charge radius when using different methods. This inconsistency has prompted extensive research and debate within the physics community, as it challenges the understanding of quantum electrodynamics and the fundamental properties of protons. In the present study, we determine the charge and magnetic radii of the proton and neutron through a global analysis of the generalized parton distributions (GPDs) at zero skewness for the first time. Our results challenge the measurements or analyses in which the nucleon's radii are extracted considering just a particular experiment or observable, or using only data points covering particular kinematic regions. We emphasize that simultaneous analysis of all available experimental data related to the radii of the nucleons would be preferable to determine their exact values. The final results obtained from our analysis by this way are: rpE=0.8558Â±0.0135 fm, rpM=0.8268Â±0.0533 fm, â?¨r2nEâ?©=â??0.1181Â±0.0270 fm2, and rnM=0.8367Â±0.0845 fm. Lecturer(s): Muhammad Goharipour From : School of Physics, IPM Research Group: HEPCO Group Weekly Seminar More Info. : Link
Tue Oct 29, 2024 (1403/8/8)

	Oct 29 1403/8/8	14:00	Stochastic Gravitational Wave Background in the present and future planned experiments Show Abstract Abstract:I will talk about a particular class of inflation, named hybrid inflation. I will describe the formation of one of the topological defects, Cosmic Strings, after inflation as a result of phase transition to be a promising phenomenon for probing the unseen universe via a Stochastic Gravitational Wave Background. Cosmic Strings may have an imprint on the Cosmic Microwave Background (CMB). I will briefly talk about how we can see their footprints in the CMB and constrain the Cosmic String tension. Recently, International Pulsar Timing Arrays (IPTAs) have found strong evidence for the SGWB. But the quest for the inverse problem is still there. I will discuss how we can address it. Lecturer(s): Adeela Afzal From : Quaid-i-Azam University, Islamabad, Pakistan Research Group: HEPCO Group Weekly Seminar More Info. : Link
Wed Oct 23, 2024 (1403/8/2)

	Oct 23 1403/8/2	18:00	Bayesian view to frequentist statistics Show Abstract Abstract:In this talk, I will start with a brief introduction of the two statistical approaches for probabilistic inference, namely, the frequentist and the Bayesian methods. Then, I will bridge between them by asking how the frequentist inference may be understood from the Bayesian perspective. If time permits, I turn to a discussion on "forecasting" (which is usually viewed as a frequentist question) and advocate a method of Bayesian forecasting. Lecturer(s): Mohammad Hossein Namjoo From : School of Astronomy, IPM Research Group: HEPCO Group Weekly Seminar More Info. : Video
Tue Oct 15, 2024 (1403/7/24)

	Oct 15 1403/7/24	14:00	A brane-world proposal for the de Sitter phases Show Abstract Abstract:Abstract In previous work, we introduced an effective brane-world model for de Sitter space-time with no explicit dependence on brane tension or bulk cosmological constant. In this model the 4D de Sitter space emerges on a brane near the horizon of a 5D black hole. In the current work, we study the effective gravity on the brane beyond the linear level, with an approximate Z2 symmetry assumption, up to a conformal factor, and find that the evolution of the effective cosmological constant on the brane depends on the flux of energy towards and away from the black hole in the bulk. In this setup the presence of the black hole horizon sets the initial condition for the brane's evolution and the brane approaches its null configuration with de Sitter length approximately equal to the 5D Planck's length, as soon as the horizon forms. During the last stages of collapse following this phase (or further flux of matter in the bulk after the horizon is formed), the effective de Sitter length on the brane increases due to the in-falling flux. This phase is tentatively the transition between a low-scale inflationary phase and a late dark energy phase. Also we observe that the increase in the de Sitter length is accompanied with a flux of energy entering the brane due to the jump in the bulk flux across the brane. Considering the initial state of the brane to be in the proper Planck's distance neighborhood of the horizon, the configuration which is below the horizon is Euclidean AdS. This can be interpreted as a boundary proposal for the resulting cosmology. Lecturer(s): Ida Rasulian From : School of Physics, IPM Research Group: HEPCO Group Weekly Seminar More Info. : Place: Room D, Farmanieh Building
Tue Oct 08, 2024 (1403/7/17)

	Oct 08 1403/7/17	14:00	Majorana neutrinos in the seesaw mechanism and pseudo-C symmetry Show Abstract Abstract:The specific transformation used to define the Majorana fermions in the conventional seesaw mechanism, and customarily identified as "charge conjugation", is not supported by a consistent unitary operator and thus it leads to mathematical (operatorial) ambiguities. It also fails as a classical transformation law in a Lorentz invariant field theory. To distinguish it from the standard charge conjugation symmetry, it has been named pseudo C-symmetry. The problematic aspects of pseudo-C transformation are circumvented in the seesaw mechanism if one uses Pauli-Guersey (or Bogoliubov-type) transformations to convert the class of Majorana neutrinos defined in terms of Weyl fields only by CP, to another class defined in terms of chiral fermions, with proper C, P and CP properties. Open problems regarding the nature of neutrino masses and Weinberg's dimension 5 operator will also be discussed. Lecturer(s): Anca Tureanu From : Department of Physics, University of Helsinki, and Helsinki Institute of Physics Research Group: HEPCO Group Weekly Seminar More Info. : Link
Tue Sep 17, 2024 (1403/6/27)

	Sep 17 1403/6/27	14:00	From WIMPs to FIMPs with Low Reheating Temperatures Show Abstract Abstract:Weakly- and Feebly-Interacting Massive Particles (WIMPs and FIMPs) are among the best-motivated dark matter (DM) candidates. In this paper, we investigate the production of DM through the WIMP and FIMP mechanisms during inflationary reheating. We show that the details of the reheating, such as the inflaton potential and the reheating temperature, have a strong impact on the genesis of DM. The strong entropy injection caused by the inflaton decay has to be compensated by a reduction of the portal coupling in the case of WIMPs, or by an increase in the case of FIMPs. We pinpoint the smooth transition between the WIMP and the FIMP regimes in the case of low reheating temperature. As an example, we perform a full numerical analysis of the singlet-scalar DM model; however, our results are generic and adaptable to other particle DM candidates. Interestingly, in the singlet-scalar DM model with low-reheating temperature, regions favored by the FIMP mechanism are already being tested by direct detection experiments such as LZ and XENONnT. Lecturer(s): Nicolas Bernal From : New York University Abu Dhabi Research Group: HEPCO Group Weekly Seminar More Info. : Link
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