Monitoring survey of pulsating giant stars in the Local Group dwarf galaxies
الهام صارمی
پژوهشکده نجوم پژوهشگاه دانش های بنیادی IPM
Abstract: The population of nearby dwarf galaxies in the Local Group constitutes a complete galactic environment, perfect suited for studying the connection between stellar populations and galaxy evolution. In this study, we have conducted an optical monitoring survey of the majority of dwarf galaxies in the Local Group, with the Isaac Newton Telescope (INT), to identify long period variable stars (LPVs). These stars are at the end points of their evolution and therefore their luminosity can be directly translated into their birth mass; this enables us to reconstruct the star formation history. LPVs are also the main source of dust; in combination with Spitzer Space Telescope images at mid-IR wavelengths we will quantify the mass loss, and provide a detailed map of the mass feedback into the interstellar medium.
On torsional ambiguity of Chiral anomaly and a model for Leptogenesis
آیدا مهین رسولیان
دانشکده فیزیک دانشگاه صنعتی شریف
Abstract: There is a problem in calculation of chiral anomaly in the presence of torsion where a divergent cut off dependent term appears that depends on the Nieh Yan term. Here we propose a resolution to this issue and use the resulting formula for chiral anomaly in a torsional model for Leptogenesis.
Is there a fundamental acceleration scale in galaxies?
زهرا داوری
دانشکده فیزیک دانشگاه صنعتی شریف
Abstract: As we know, the mass discrepancy or missing mass problem has been found for many years in the galactic scale. Therefore, it seems that there is a need for a significant amount of non-luminous matter, i.e. the dark matter in galaxy system but up to now, no direct evidence of its existence has been found. One of the successful alternatives to the dark matter is Milgrom’s modified Newtonian dynamics (MOND) that could explain well the mass discrepancy problem in the galaxy without invoking dark matter. The MOND theory predicts a universal constant acceleration scale in the galaxy, below which the Newtonian dynamics is no longer valid. We analyzed 193 high-quality disk galaxies by using Bayesian inference and we concluded that the probability of the existence of a fundamental acceleration scale is essentially zero. However, there still exist evidence that rejects MOND as a fundamental theory and we conclude that a0 is of emergent nature.
عبدالعلی بنی هاشمی (دانشکده فیزیک دانشگاه شهید بهشتی)
Abstract: In this talk, first we will take a brief look at some LCDM tensions; then we explain our idea for lessening them by giving a new model for the evolution of the universe. Our idea is based on supposing a phase transition for Dark Energy, where we study this phase transition in the framework of Landau-Ginzburg theory. In the end, we will show that the results of our model are promising and reduce the tensions.
Department of Theoretical Physics of the University of Geneva
Abstract: I’m going to introduce a new instability in partial differential equations, which also can be present in some dark energy and cosmological models. We have studied k-essence scalar field and have developed an N-body code, k-evolution, in which we consider non-linearities. We have proved that the k-essence non-linearities suffer from the new instability and blowup in finite time; I’ll show the solution and blowup time for different initial conditions. Moreover, to understand the new instability, I will solve the traffic flow as a similar dynamical system and show how shock waves are produced in the traffic flow.
