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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
Tue Sep 10, 2024 (1403/6/20)

	Sep 10 1403/6/20	14:00	Interaction of Kerr-Newman Electromagnetic Fields Show Abstract Abstract:In this talk, I will discuss some properties of the Kerr-Newman (KN) Electromagnetic Fields, which is the G â?? 0 limit of the KN solution of Einstein-Maxwell equations. In this limit, the electromagnetic sector of the solution survives, while the background becomes locally flat with nontrivial topology. The discussion includes the complex transformation between the non-spinning Coulomb solution and the spinning KN, the g = 2 gyromagnetic ratio of the solution noted by Carter, and the corresponding multipole structure. The topological conserved charges of the electromagnetic field, i.e. the classical helicity and classical spin, are calculated for this solution. Moreover, we studied the interaction of two such solutions by evaluating the Lagrangian for the superposition of those fields. This yields a correction to the interaction potential beyond the Coulomb interaction due to the spin of the fields. The talk is based on: https://arxiv.org/pdf/2405.12602. Lecturer(s): Sajad Aghapour From : Max Planck Institute for Gravitational Physics (Albert Einstein Institute) Research Group: HEPCO Group Weekly Seminar More Info. : Link
Tue Aug 27, 2024 (1403/6/6)

	Aug 27 1403/6/6	14:00	A novel global charge conservation in the symmetric phase of the early Universe Show Abstract Abstract:In the Standard Model at high temperatures, anomalous effects contribute to the violation of baryon number ($B$) and lepton number ($L$), separately, while $B-L$ remains conserved. There are also corresponding changes in the helicity of the hypermagnetic field ($h$) and the Chern-Simons numbers of the non-Abelian gauge fields ($N_{\rm CS,W}$ and $N_{\rm CS,S}$). In this study, we investigate a baryogenesis process in the symmetric phase of the early Universe by taking into account the Abelian and non-Abelian anomalous effects as well as the perturbative chirality-flip processes of all fermions. We calculate explicitly the time evolution of all relevant physical quantities, including those of $h$ and $N_{\rm CS,W}$, and show that there is another conserved global charge involving total matter-antimatter asymmetry $B+L$, hypermagnetic helicity $h_B$ and $N_{\rm CS,W}$. Lecturer(s): Saeed Abbaslu From : School of Physics, IPM Research Group: HEPCO Group Weekly Seminar More Info. : Link
Tue Aug 20, 2024 (1403/5/30)

	Aug 20 1403/5/30	14:00	Bulk Reconstruction: 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 : SISSA Research Group: HEPCO Group Weekly Seminar More Info. : Link
Sat Aug 17, 2024 (1403/5/27)

	Aug 17 1403/5/27	10:00	Influential female scientists in the history of particle physics Poster Lecturer(s): Yasaman Farzan From : School of Physics, IPM Research Group: Special Seminar More Info. : Link
Tue Aug 13, 2024 (1403/5/23)

	Aug 13 1403/5/23	14:00	2D Bi-Scalar Gravity from 4D Horndeski Theory Show Abstract Abstract:In this talk, I will present aspects of 2D scalar-tensor theories. First, I will construct a 2D bi-scalar gravity from a 4D Horndeski theory using a Kaluza-Klein (KK) dimensional reduction on a 2-sphere. I will then provide some identities to write the action in a more compact form and use these to develop a more generalized 2D bi-scalar theory. Following this, I will use the KK reduction process to map 4D Horndeski solutions to 2D bi-scalar theory solutions. In the second half of the talk, I will explore the single-scalar version of the 2D bi-scalar gravity. I will discuss how some important 2D single-scalar theories may have a 4D origin. I will then investigate the relationship between some key 2D single-scalar tensor theories, explaining how the 2D Horndeski theory and GRZ model can be derived from JT gravity using disformal transformation. Lecturer(s): Mohanna Shams From : Institute for advanced studies in basic sciences (IASBS) Research Group: HEPCO Group Weekly Seminar More Info. : Link
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