امیرفرزان اسماعیلی (دانشکده فیزیک دانشگاه صنعتی شریف )
استاد راهنما: شانت باغرام، مهدی ترابیان
شنبه 29 دی 1397، ساعت 14:30
دانشکده فیزیک، تالار پرتوی – طبقه 4
نیما رونقی (دانشکده فیزیک دانشگاه صنعتی شریف )
استاد راهنما: شانت باغرام، سامان مقیمی
شنبه 29 دی 1397، ساعت 13:00
دانشکده فیزیک، تالار پرتوی – طبقه 4
فربد حسنی
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.
یکشنبه 16 دی 1397، ساعت 15:00
دانشکده فیزیک، طبقه اول کلاس فیزیک 3
چهارشنبه 12 دی ماه 1397 ساعت 9:00 الی 11:15
طبقه چهار دانشکده فیزیک (تالار پرتوی)
فرنیک نیک اختر
Department of Physics and Astronomy at the University of Pennsylvania
Abstract: Nonlinear structure formation is an important area in the modern cosmology, where deep questions can be addressed by large-scale structure data, especially the questions which are related to the dark universe – the physics of dark matter and dark energy. In this arena, the abundance and clustering of dark matter halos probe important features of the standard model of cosmology. The excursion set approach is a framework for estimating how the statistical properties of nonlinear structures in the cosmos depend on the history of the universe and the nature of gravity. In this theory, one associates a random walk with each position in the initial density field, and the barrier to be crossed is determined by the collapse model. The main problem here is the first passage time problem and the first up-crossing distribution is the quantity which is related to the abundance of nonlinear objects. My recent work is about approximations of the first up-crossing distribution (for non-Markovian walks) and modeling the abundance of halos, and in this talk, I would like to show the associated implications for halo bias.
یکشنبه 9 دی 1397، ساعت 15:00
دانشکده فیزیک، طبقه اول کلاس فیزیک 3
فرنیک نیک اختر
Department of Physics and Astronomy at the University of Pennsylvania
“Gaia is an ambitious mission to chart a three-dimensional map of our Galaxy, the Milky Way, in the process revealing the composition, formation and evolution of the Galaxy. Gaia will provide unprecedented positional and radial velocity measurements with the accuracies needed to produce a stereoscopic and kinematic census of about one billion stars in our Galaxy and throughout the Local Group. This amounts to about 1 per cent of the Galactic stellar population.” From http://sci.esa.int/gaia/
For registration: Send an email to baghram@sharif.edu till Sunday December 30, 2018 with the title GAIA-Workshop.
The workshop is limited to 15 participants.
چهارشنبه 12 دی 1397، ساعت 11:00 الی 16:00
دانشکده فیزیک، طبقه سوم – سایت کامپیوتر
مونا جلیلوند
Department of Theoretical Physics of the University of Geneva
Abstract: My talk has two parts. First, I talk about second order lensing of 21cm intensity mapping (IM). Like the CMB, 21cm IM temperature fluctuations have second and higher order lensing and no first order lensing. We find a new (third order) lensing term that is neglected in the CMB lensing but is important for 21cm IM. We study the detectability of 21cm IM lensing with a Fisher matrix approach for the redshift range of z=2 to z=6 and find that with optimistic assumptions, we obtain a signal-to-noise of ~10 for futuristic surveys like SKA2.
In the second part, I talk about our current project on estimating the first order lensing from cross correlation between 21cm IM and galaxy surveys. We introduce two new lensing estimators that have higher signal-to-noise compared to the estimator that is currently used for lensing detection.
یکشنبه 2 دی 1397، ساعت 15:00
دانشکده فیزیک، طبقه اول کلاس فیزیک 3
علیرضا اله یاری (پژوهشکده نجوم پژوهشگاه دانش های بنیادی – IPM )
Abstract: We consider the polarization characteristics of the electromagnetic (EM) counterpart of the gravitational wave (GW) created by coalescence of the binary sources. Here, we explore the impact of the photon-graviton interaction on the polarization evolution of X-ray emission of Gamma-Ray Bursts (GRBs). We show that significant circular polarization can be generated due to the gravitational wave from the binary merger. The circular polarization besides photon energy depends on parameters of GW source such as the chirp mass of the binary, frequency of the GWs and radial distance from the source. Our predicted signal can be used as an indirect probe for GW events and also the nature of photon-graviton interaction. We argue that this polarization signal might be in sensitivity range of upcoming X-ray polarimetry missions.
یکشنبه 11 آذر 1397، ساعت 15:00
دانشکده فیزیک، طبقه اول کلاس فیزیک 3
سینا تاملی (دانشکده فیزیک دانشگاه صنعتی شریف )
Abstract: Filaments are one of the components of the cosmic web which can be seen in observations and simulations. They are also considered as a potential solution to missing baryon problem as the host of the baryons which does not reside in dark matter halos. The statistics of the filament could also be used as a probe for cosmology. To benefit from these applications, we need a precise definition for the filaments. There are some models, proposed by the community in order to explain these objects. In this work, we provide a route to find out the statistics of the filaments, regarding them as the saddle points of the density field, through the excursion set approach and ellipsoidal collapse model. In this presentation, I am going to provide an introduction to Excursion Set of Peaks and saddle points, ellipsoidal collapse model, and the prediction of this framework about the length, number density and mass fraction of the filaments.
یکشنبه 27 آبان 1397، ساعت 15:00
دانشکده فیزیک، طبقه اول کلاس فیزیک 3