Marzieh Farhang

Department of Physics, Shahid Beheshti University

Search for The Missing Pieces in Cosmology

Abstract: The LambdaCDM model has been extraordinarily successful in describing the observed cosmos. There are however hints that this picture is missing serious pieces. In this talk, we discuss the various systematic approaches for the exploration of the beyond LCDM world.

یکشنبه 14 آذر 1400، ساعت 19:00

Sunday 5 December 2021 – 19:00 Tehran Time

اتاق سمینار مجازی –Virtual Seminar Room

https://vc.sharif.edu/ch/cosmology

گزینه ورود به صورت مهمان – Enter as a Guest

Cora Uhlemann

School of Mathematics, Statistics and Physics, Newcastle University

Nuw Cosmology beyond the average from one-point statistics

Abstract: Nonlinear gravitational collapse shaped the cosmic web and created a plethora of different density environments – from voids through filaments to galaxy groups. To realise the full potential of galaxy surveys, we need to dissect different density environments that are lumped together in traditional two-point statistics. This is particularly important for detecting extensions of LCDM including massive neutrinos (Nu), dynamical dark energy (w) and modified gravity. I will show how to extract additional information from the mildly nonlinear one-point statistics of matter densities and associated galaxy survey observables. We showed that using the lensing PDF jointly with the 2pt correlation could improve parameter constraints on nuLCDM/wCDM models by 40% when combined with Planck. Recently, we demonstrated the strong discriminating power of the matter PDF for modified gravity finding an up to sixfold increase of the detection significance compared to the power spectrum alone.

یکشنبه 7 آذر 1400، ساعت 19:00

Sunday 28 November 2021 – 19:00 Tehran Time

اتاق سمینار مجازی –Virtual Seminar Room

https://vc.sharif.edu/ch/cosmology

گزینه ورود به صورت مهمان – Enter as a Guest

Aseem Paranjape

Inter-University Centre for Astronomy & Astrophysics (IUCAA)

 Pune, India

The radial acceleration relation in a LCDM universe

Abstract: I will discuss some recent analytical insights into the nature of the `radial acceleration relation’ (RAR) between total and baryonic centripetal acceleration profiles of central galaxies in the Lambda-cold dark matter (LCDM) framework. Specifically, there is an intimate connection between the RAR and the physics of quasi-adiabatic relaxation of dark matter in the presence of baryons in the galaxy’s parent halo. Using analytical approximations and a realistic LCDM mock galaxy catalog, we have explored the sensitivity of the RAR in different acceleration regimes to quasi-adiabatic relaxation physics, halo mass and concentration, and the abundance of diffuse gas in the halo outskirts. These results cleanly demonstrate how the mean RAR and its scatter emerge from the interplay of dark matter and baryons in the LCDM paradigm. Time permitting, I will also discuss some new results demonstrating that LCDM predicts a statistical `external field effect’ in which the shape of the RAR of any galaxy correlates with the gravitational acceleration due to mass external to the galaxy, without any violation of the strong equivalence principle.

یکشنبه 30 آبان 1400، ساعت 19:00

Sunday 21 November 2021 – 19:00 Tehran Time

اتاق سمینار مجازی –Virtual Seminar Room

https://vc.sharif.edu/ch/cosmology

گزینه ورود به صورت مهمان – Enter as a Guest

Vahid Kamali

Department of Physics, Bu-Ali Sina (Avicenna) University

Warm inflation and string theory conjectures 

Abstract: In early time cosmology, inflation is the most interesting scenario originating from effective field theory. It can answer some significant questions regarding hot big bang cosmology. Taking the linear perturbation theory into account, inflation can explain how large-scale structures form. In recent years, the field theory of inflation has been challenged by some conjectures motivated by string theory. As part of this talk, I will discuss a special scenario of inflation where the inflaton is coupled with light fields in a thermal bath. I will demonstrate how this model can be out of swampland.

یکشنبه 23 آبان 1400، ساعت 15:00

Sunday 14 November 2021 – 15:00 Tehran Time

اتاق سمینار مجازی –Virtual Seminar Room

https://vc.sharif.edu/ch/cosmology

گزینه ورود به صورت مهمان – Enter as a Guest

Hee-Jong Seo

Department of Physics and Astronomy, Ohio University

Reconstructing the primordial universe from galaxy surveys

Abstract: The observable Universe today contains ample information on the underlying, fundamental physics behind the formation and the evolution of our Universe.  Some challenges are faced in extracting the cosmological information due to the nonlinear structure growth and the observational systematics, particularly for upcoming surveys that will conduct cosmological tests at an unprecedented precision.  In my talk, I will present the ongoing work of my group that focuses on two aspects of reconstructing primordial cosmological information from the late time galaxy clustering. One is reconstructing the primordial clustering information from the nonlinear structure growth and the other is reconstructing the primordial information from observational systematics, by better mitigating the systematic effects using a Deep-Learning based method.

یکشنبه 16 آبان 1400، ساعت 19:00

Sunday 7 November 2021 – 19:00 Tehran Time

اتاق سمینار مجازی –Virtual Seminar Room

https://vc.sharif.edu/ch/cosmology

گزینه ورود به صورت مهمان – Enter as a Guest

Saba Etezadrazavi

Department of Physics, Sharif University of Technology

Constraining temperature fluctuations in IGM using XQ-100 legacy survey 

Abstract:  Arriving at the peak of Quasar activities, the UV background emitted by the Quasars forced the IGM to experience another re-ionization phase after the hydrogen re-ionization, namely the Helium re-ionization epoch. Investigating this epoch is a crucial step toward understanding the relationship between quasars and their environment as one of the most active cosmological mediums. The XQ-100 legacy survey by VLT X-shooter had provided us with one of the highest resolution Quasar surveys at high redshifts. Armed with this spectroscopic Quasar data and newly developed PCA methods, we can recover the Quasar’s un-absorbed spectrum knowing all the error’s sources and quantify IGM’s thermodynamical quantities around the Helium-reionization epoch. Knowing the IGM absorptions and our error model, for the first time, we are able to constrain temperature fluctuations resulting from the Helium re-ionization observationally that can be used to rule out some of the known re-ionization models.

یکشنبه  9 آبان 1400، ساعت 15:00

Sunday 31 October 2021 – 15:00 Tehran Time

اتاق سمینار مجازی –Virtual Seminar Room

https://vc.sharif.edu/ch/cosmology

گزینه ورود به صورت مهمان – Enter as a Guest

Robyn E. Sanderson

Department of Physics & Astronomy University of Pennsylvania

Dynamical Tests of Dark Matter in the Milky Way

Abstract: The results of the Gaia astrometric mission have ushered in a new era of “precision Galactic dynamics”. Using this new phase-space map of Galactic stars with unprecedented volume and accuracy, we are beginning to obtain new insights into the dark matter distribution in our Galaxy as well as its formation history. Thanks to significant advances on the computational front, meanwhile, we can now compare these insights directly with, and test our modeling strategies on, simulations of Milky-Way-mass galaxies where the influence of baryons and the cosmological context on the dark matter structure are realistically taken into account. I will demonstrate how this convergence of new data and better models improve our understanding of the Milky Way’s dark matter distribution, leading to better constraints on the nature of dark matter.

یکشنبه  25 مهر 1400، ساعت 19:00

Sunday 17 October 2021 – 19:00 Tehran Time

اتاق سمینار مجازی –Virtual Seminar Room

https://vc.sharif.edu/ch/cosmology

گزینه ورود به صورت مهمان – Enter as a Guest

ماورای مدل استاندارد کیهانشناسی

Beyond the cosmological standard model

Sohrab Rahvar

Department of Physics, Sharif University of Technology

Some of the Observational effects of Primordial Black Holes

بعضی از اثرات مشاهداتی سیاهچاله های اولیه

Abstract: This talk will be based on

1)    https://journals.aps.org/prd/abstract/10.1103/PhysRevD.103.084001

2)    https://academic.oup.com/mnras/article-abstract/507/1/914/6339282?redirectedFrom=fulltext

یکشنبه 4 مهر 1400، ساعت 19:00

Sunday 26 September 2021 – 19:00 Tehran Time

اتاق سمینار مجازی –Virtual Seminar Room

https://vc.sharif.edu/ch/cosmology

گزینه ورود به صورت مهمان – Enter as a Guest

Amir Yarahmadi

Department of Physics, Sharif University of Technology

Reheating the Universe after Inflation via Resonant Interactions 

Abstract: The inflation paradigm solves the problems of flatness and homogeneity of the standard cosmological model by considering the exponential expansion for the early universe. It also provides a mechanism for generating density perturbations, which are the core of large-scale structures. One of the successes of inflation is the anticipation of a range of irregular scale perturbations which is well in line with the observations of cosmic background radiation. But after a period of exponential expansion, there will be a cold, empty universe of matter, so there needs to be a process that, after inflation, leads to a hot, standard universe of particles. The two main proposals for achieving standard cosmology are the two theories of warming and hot inflation. In post-inflation reheating theory, considering the coupling between the inflation field and the field as a representative of the standard model field, and considering the effect of the inflation oscillation field, an explosion of particles in the thermal equilibrium can be had. In this study, we examine the effects of producing particles of an extra degree of freedom during and after inflation.

یکشنبه  7 شهریور 1400، ساعت 15:00

Sunday 29 August 2021 – 15:00 Tehran Time

اتاق سمینار مجازی –Virtual Seminar Room

https://vc.sharif.edu/ch/cosmology

گزینه ورود به صورت مهمان – Enter as a Guest