SCHOOL OF PHYSICS :: Seminars

Seminars

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Tue Jul 30, 2024 (1403/5/9)

	Jul 30 1403/5/9	17:00	Does the Sun Have a Dark Disk? Show Abstract Abstract:The Sunâ??s oblateness has been measured using optical observations. Its gravitational quadrupole moment has been deduced through helioseismology and measurements of its gravitational effects on Mercuryâ??s orbit. The distribution of mass within Mercuryâ??s orbit would only impact the orbital determination, suggesting that discrepancies among various types of assessments may indicate the possible existence of a non-luminous mass. For the first time, we have developed a method to combine these differing measurements to yield new, highly sensitive constraints on the mass distribution within Mercuryâ??s orbit. In this talk, we will show that the most precise measurements indicate the existence of a non-luminous disk within Mercuryâ??s orbit, with a mass significantly heavier than the modeled mass for the circumsolar dust ring observed by the Solar TErrestrial RElations Observatory (STEREO) mission. This suggests a substantial dark matter contribution. Furthermore, the long-standing inconsistency between the element abundances determined from the spectroscopy of the Sunâ??s surface, and those inferred from its interior through helioseismology, can be reconciled if the Sun formed within a protoplanetary disk. We will discuss how our findings limit the presence of a dark disk or a spherical halo near the Sun and highlight the potential of future orbital measurements of Mercury and near-Sun asteroids to refine these constraints further. Lecturer(s): Mohammadreza Zakeri From : University of Kentucky Research Group: HEPCo Weekly Seminar Group More Info. : Link
Tue Jul 23, 2024 (1403/5/2)

	Jul 23 1403/5/2	16:00	Resolving Angular Momentum Flux Non-Invariance in 4D Asymptotically Flat Spacetimes Show Abstract Abstract:The Bondi-Metzner-Sachs group is the asymptotic symmetry group of asymptotically flat spacetimes in 4D. After briefly introducing this group, I will discuss the angular momentum problem. Following an overview of possible solutions, I will present the primary issue that will be addressed in this talk: the non-invariance of the angular momentum flux. The flux of angular momentum is a quantity that is significant from both a theoretical and a numerical perspective. Theoretically, it's important to eliminate ambiguity in the definition of the flux, while in simulations, it has a direct impact on the results. I will conclude by outlining the solution to this problem. Lecturer(s): Reza Javadi Nezhad From : New York University Research Group: HEPCO Group Weekly Seminar More Info. : Link
Tue Jul 09, 2024 (1403/4/19)

	Jul 09 1403/4/19	14:00	Solar neutrinos and leptonic spin forces Show Abstract Abstract:We quantify the effects on the evolution of solar neutrinos of light spin-zero particles with pseudoscalar couplings to leptons and scalar couplings to nucleons. In this scenario the matter potential sourced by the nucleons in the Sun's matter gives rise to spin precession of the relativistic neutrino ensemble. As such the effects in the solar observables are different if neutrinos are Dirac or Majorana particles. For Dirac neutrinos the spin-flavour precession results into left-handed neutrino to right-handed neutrino (i.e., active--sterile) oscillations, while for Majorana neutrinos it results into left-handed neutrino to right-handed antineutrino (i.e., active-active) oscillations. In both cases this leads to distortions in the solar neutrino spectrum which we use to derive constraints on the allowed values of the mediator mass and couplings via a global analysis of the solar neutrino data. In addition for Majorana neutrinos spin-flavour precession results into a potentially observable flux of solar electron antineutrinos at the Earth which we quantify and constrain with the existing bounds from Borexino and KamLAND. Lecturer(s): Joao Paulo Pinheiro From : University of Barcelona Research Group: HEPCO Group Weekly Seminar More Info. : Link
Tue Jun 11, 2024 (1403/3/22)

	Jun 11 1403/3/22	14:00	Probing Boosted Dark Matter through Small-Scale Astrophysical Structures Show Abstract Abstract:The cosmological data from a small-scale astrophysical structure and future gravitational wave (GW) experiments hold great promise in shedding light on the nature of dark matter (DM). First, we explore a two-component DM model with a sizable mass splitting and self-interaction for a light component. By delving into temperature evolution, density perturbation, and N-body simulation, we find that the annihilation of the heavier components to the lighter ones effectively endows the latter with warm DM-like behavior. It takes advantage of all the distinct features that warm DM offers without observational mass constraints on the warm DM masses. Second, we explore a black hole binary system in the presence of the DM and corresponding GW signals. The dense region of DM can lead to the dephasing of gravitational waveforms, which can be detected by upcoming experiments such as LISA. Lecturer(s): Jeong Han Kim From : Chungbuk National University Research Group: HEPCO Group Weekly Seminar More Info. : Link
Tue May 21, 2024 (1403/3/1)

	May 21 1403/3/1	14:00	The impact of massive neutrinos on the morphology of the Universe Show Abstract Abstract:The morphology of the cosmos provides valuable information about the structure of the cosmic web, which can be used for cosmological inferences. In this talk, I will discuss the capability of Persistent Homology (PH) as a morphological tool to investigate the impact of massive neutrinos on the Large-Scale Structure (LSS). PH naturally addresses the multi-scale topological characteristics of the LSS as a distribution of clusters, loops, and voids. Utilizing the Fisher forecast formalism, I will provide a quantitative assessment about the constraining power of some PH vectorizations to estimate the parameters of the $\nu \Lambda CDM$ model. Lecturer(s): Mohammad Jalali From : Shahid Beheshti University Research Group: HEPCO Group Weekly Seminar More Info. : Link
Wed May 15, 2024 (1403/2/26)

	May 15 1403/2/26	18:00	Investigation of the Heisenberg's Uncertainty Principle and the Entropy Uncertainty Relation Show Abstract Abstract:Quantum mechanics provided precise and accurate explanations for the experiments conducted at the end of the 19th century. This led to the rapid development of quantum mechanics between 1905 and 1923, capturing the scientific community's attention. At the Solvay Conference in 1927, Werner Heisenberg, a leading figure of the Copenhagen interpretation, presented the uncertainty principle within quantum mechanics. In this lecture, we will explore the significance of Heisenberg's uncertainty principle, discuss a fundamental problem in its original formulation, and introduce the entropy uncertainty relation as an alternative. Furthermore, we will investigate into quantum entanglement and quantum discord, highlighting their crucial roles in precisely determining entropy uncertainty relation. Lecturer(s): Shahriar Salimi From : University of Kurdistan Research Group: Physics Colloquium More Info. : Link
Tue May 07, 2024 (1403/2/18)

	May 07 1403/2/18	14:00	Flat Connections from Irregular Conformal Blocks Show Abstract Abstract:I will talk about Liouville conformal blocks with degenerate primaries and one operator in an irregular representation of the Virasoro algebra. Using an algebraic approach, we derive modified BPZ equations satisfied by such blocks and subsequently construct corresponding integral representations based on integration over non-compact Lefschetz cycles. The integral representations are then used to derive novel types of flat connections on the irregular conformal block bundle. Lecturer(s): Babak Haghighat From : Tsinghua University Research Group: HEPCO Group Weekly Seminar More Info. : Link
Tue Apr 23, 2024 (1403/2/4)

	Apr 23 1403/2/4	14:00	General Quantum Mechanics; a program for the resolution of the main issues in quantum theory, as a reconciliation of classical mechanics over phase space, general relativity and quantum mechanics. Show Abstract Abstract:General relativity is over the configuration space and is a Lagrangian mechanics. While quantum mechanics is quantization of classical mechanics over phase space which is a Hamiltonian mechanics. Thus it is difficult to reconciliate these two theories. Therefore, we first reestablish general relativity over phase space of spacetime and then combine it with quantum mechanics and the result is a new mechanics called general quantum mechanics. In general relativity, the acceleration of a test particle is defined relative to the metric of spacetime while in classical mechanics over phase space the metric has no role in the acceleration. Also in classical mechanics over phase space the measurement of a given observable has no role in the acceleration of a test particle unlike quantum mechanics which obeys Born rule which states that how the measurement makes an impact on the acceleration of the test particle. We reconciliate general relativity with classical mechanics over phase space and quantum mechanics by defining the acceleration of a test particle over phase space relative to the metric of phase space and also relative to a given observable. In general quantum mechanics, we have an equation for the collapse phenomenon which is the counterpart of geodesic equation in general relativity. The collapse equation is a nonlinear modification of the linear SchrÃ¶dinger equation. We also have an equation for the metric of phase space which is the counterpart of the Einstein field equation and is obtained by the least action principle over an action functional which is similar to the Hilbert action for the Einstein field equation. Namely, the Lagrangian of the action is a new type of curvature different than the Riemann curvature. As a result, we have a proposal for the resolution of the measurement problem in quantum mechanics. Lecturer(s): Seyed Ebrahim Akrami Sanzigh From : Semnan University Research Group: HEPCO Group Weekly Seminar More Info. : Link
Tue Apr 09, 2024 (1403/1/21)

	Apr 09 1403/1/21	14:00	Model Selection Approach and Tension Metrics in Cosmology Show Abstract Abstract:Cosmology is a field that deals with a vast amount of data, and it is crucial to ensure consistency and measure the tension between data sets. Tension indicates either discordance between data sets or a problem with the underlying model. One of the most famous examples of tension in cosmology is the Hubble tension, which is a 3.5Ï? discrepancy between supernovae and CMB data in estimating the age of the Universe. While alternative models have been introduced to resolve this tension, it is necessary to use tension metrics to verify if these data sets are still discordant or in agreement even in alternative models. Furthermore, the existence of different models means that one has to choose the best model among competing models that fits observational data. Nested Sampling, a recent computational algorithm, enables us to perform a model selection approach alongside quantifying tension between different data sets. In this talk, we will discuss the tension metric and the model selection approach in cosmology. Lecturer(s): Mohsen Khorasani From : School of Physics, IPM Research Group: HEPCO Group Weekly Seminar More Info. : Link
Tue Apr 02, 2024 (1403/1/14)

	Apr 02 1403/1/14	14:00	Anthropic Carbon Emission And the footprint of HEPCO researchers on Earth Show Abstract Abstract:The atmospheric CO2 has reached unprecedented amounts and the impact of human activities on the current situation is undeniable. In this talk, I briefly explain the problem of atmospheric CO2 variation and introduce the main strategies to control our carbon footprint as a HEPCO researcher according to the Arxiv 2403.03308 Lecturer(s): Saeed Ansari Fard From : School of Physics, IPM Research Group: HEPCO Weekly Seminar Special Series More Info. : Link
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