Arman Shafieloo

Korea Astronomy and Space Science Institute, (KASI), South Korea; University of Science and Technology, South Korea

Status of the Concordance Model of Cosmology

Abstract:  I review the status of the standard model of cosmology in light of recent observations discussing the current tensions and some different alternatives including some early and late universe solutions to the problem. I will also briefly discuss the near-future of the field at the era of the next generation of astronomical/cosmological surveys.

سه شنبه 27 تیر 1402، ساعت 10:00

Tuesday 18 July 2023 – 10:00 Tehran Time

Hybrid Seminar

دانشکده فیزیک – طبقه 4 – تالار پرتوی Physics Department – fourth floor – Partovi Hall/

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

گزینه ورود به صورت مهمان – Enter as a Guest

Seminar 1: Dipole Cosmology: The Dipole ΛCDM Model

Vahid Forghanipour

Department of Physics, Sharif University of Technology

Seminar 2: Investigating the halo distribution inside cosmic voids in excursion set theory and the dependence of void galaxies on large-scale environment

Zeynab Ashuri

Department of Physics, Sharif University of Technology

Abstract 1: Is our universe actually homogenous and isotropic on large scales? New observation in last two decades cast some shadow of doubts on standard model of cosmology and FLRW paradigm. In this Seminar we discuss and review the recently published article, “Towards A Realistic Dipole Cosmology: The Dipole ΛCDM Model”, by Ehsan Ebrahimian and M. M. Sheikh-Jabbari. the dipole cosmological principle is the idea that the Universe is a maximally Copernican cosmology, compatible with a cosmic flow. It serves as the most symmetric paradigm that generalizes the FLRW ansatz. In this article they assess the possibility of model building within the dipole cosmology paradigm, and discuss the dynamics of expansion rate, anisotropic shear and tilt, in various examples. A key observation is that the cosmic flow (tilt) can grow even while the anisotropy (shear) dies down. Remarkably, this can happen even in an era of late time acceleration.

Abstract 2: Investigating the formation and evolution of large-scale structures, as one of the main observables in cosmology, is of particular importance. Excursion Set Theory is one of the methods of investigating the statistics of halos and web structures of the universe.

In the standard approach, in this theory, we consider the Sharp-K window function to smooth the matter density perturbation field, which causes the paths to proceed a Markovian random walk. As a result, the statistics of the first up-crossing of the critical barrier and the statistics of the halos can be obtained analytically. Similar procedures can be followed to find Halos which reside inside cosmic voids. The aim of this talk will be to review the distribution of structures inside voids, and to analyze the environmental dependence of galaxy luminosity inside the void halos, in the framework of the Excursion Set theory.

یکشنبه 25 تیر 1402، ساعت 9:30

Sunday 16 July 2023 – 9:30 Tehran Time

Hybrid Seminar

دانشکده فیزیک – طبقه 5 – اتاق 512Physics Department – fifth floor – Room 512/

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

گزینه ورود به صورت مهمان – Enter as a Guest

Seminar 1: Frequency Shift in Binary Lensing System

Samaneh Sarbaz

Department of Physics, Sharif University of Technology

Seminar 2: About Primordial Black Holes: From Inflation to Formation

Mohammad Amin Hejazi

Department of Physics, Sharif University of Technology

Abstract 1: Gravitational microlensing with binary lenses is one of the channels for the detection of exoplanets. Due to the degenerated nature of the solutions for the binary microlensing, additional features such as parallax and finite-size effects need to break the degeneracy between the lens parameters. Here in this work, we introduce the application of the frequency shift effect in the binary microlensing observations where the single lens has been studied in \cite{Rahvar_2020}. The frequency shift is the relativistic analogy of the gravity assist for the photons. We derive the frequency shift in the binary lenses and the relative frequency shift during the caustic crossing. We also investigate the practical feasibility of the detection of this effect by high-resolution spectrographs such as ESPRESSO in VLT telescope.

Abstract 2: Primordial black holes (PBHs) are a theoretical prediction from the early universe. They are believed to form when fluctuations with sufficient amplitude collapse after re-entering the Hubble horizon. Some observational evidence, such as heavy black hole mergers and the nature of dark matter, has sparked interest in PBH physics.

In this talk, I will provide an overview of PBHs, starting with their historical background and then discussing the formation process and the role of inflation. Finally, I will delve into PBH statistics and their constraints.

یکشنبه 18 تیر 1402، ساعت 10:00

Sunday 9 July 2023 – 10:00 Tehran Time

Hybrid Seminar

دانشکده فیزیک – طبقه 5 – اتاق 512Physics Department – fifth floor – Room 512/

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

گزینه ورود به صورت مهمان – Enter as a Guest

با عرض پوزش، به دلیل برگزاری کنکور سراسری در دانشگاه سمینار روز چهارشنبه به تعویق می افتد.

Arman Shafieloo

Korea Astronomy and Space Science Institute, (KASI), South Korea; University of Science and Technology, South Korea

Status of the Concordance Model of Cosmology

Abstract:  I review the status of the standard model of cosmology in light of recent observations discussing the current tensions and some different alternatives including some early and late universe solutions to the problem. I will also briefly discuss the near-future of the field at the era of the next generation of astronomical/cosmological surveys.

چهارشنبه 14 تیر 1402، ساعت 10:00

Wednesday 5 July 2023 – 10:00 Tehran Time

Hybrid Seminar

دانشکده فیزیک – طبقه 5 – اتاق 512Physics Department – fifth floor – Room 512/ 

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

گزینه ورود به صورت مهمان – Enter as a Guest

Arman Shafieloo

Korea Astronomy and Space Science Institute, (KASI), South Korea; University of Science and Technology, South Korea

Cosmology with Small Telescopes

Abstract:  In the era of large telescopes and space satellites it is very challenging to do competitive research with small size telescopes to address important problems in cosmology and astrophysics.

 In my talk I will discuss the possibility of using small size telescopes (0.5 ~ 1.0 meter) to detect and observe strongly lensed supernovae. Due to possible substantial gravitational magnifications such strongly lensed supernovae can be detected at redshifts much higher than the range a small telescope can generally probe. I will also discuss the importance of strongly lensed objects for cosmology and to probe the expansion history of the universe.

سه شنبه 13 تیر 1402، ساعت 10:00

Tuesday 4 July 2023 – 10:00 Tehran Time

Hybrid Seminar

دانشکده فیزیک – طبقه 5 – اتاق 512Physics Department – fifth floor – Room 512/

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

گزینه ورود به صورت مهمان – Enter as a Guest

همانطور که اطلاع دارید جایزه مرکز بین‌المللی فیزیک نظری  (عبدالاسلام) سال ۲۰۲۲ به  آقای دکتر شانت باغرام از دانشکده فیزیک دانشگاه شریف و آقای دکتر نامجو از مرکز تحقیقات فیزیک نظری اعطا شده است. ضمن تبریک مجدد به این دو همکار عزیز و گرامی و آرزوی پیروزی و سربلندی برای ایشان به اطلاع میرساند، میتوانید مراسم اهدای این جایزه را امروز از کانال یوتیوب زیر به صورت زنده امروز چهارشنبه ۳۱ خرداد ماه از ساعت ۱۵:۳۰ مشاهده بفرمایید.

https://www.youtube.com/live/W_QStz2JVV8?feature=share

Aryana Haghjoo

Physics Department, McGill University

Unraveling non-standard physics through global 21cm signal

Abstract: The global 21cm signal is a modern tool to study the period between the end of the cosmic dark ages and the epoch of ionization (EoR).

In this talk, we explore the potential of this signal to reveal non-standard physics by means of providing a new path to test fundamental physical theories. The 21cm signal is sensitive to the density and temperature of neutral hydrogen in the early universe and the formation of the first stars and galaxies. Therefore, any deviation from the predictions of the standard cosmological model of this signal could indicate the presence of new physics beyond the standard model.

We will briefly revisit the theoretical basis of the global 21cm signal (Wouthuysen-Field coupling) and the current international efforts to detect it through radio interferometers. Then, we will pave the way to analyze the upcoming data by introducing a special method for parameter estimation of the global 21cm signal. We adopt the Markov Chain Monte Carlo (MCMC) method combined with the Levenberg Marquardt (LM) algorithm to estimate the best-fit physical parameters (e.g., clumping factor, star formation efficiency). We use the Accelerated Reionization Era Simulations (ARES) to generate models for the global 21-cm signal. This method provides comprehensive control over the parameters of the algorithm, allowing to opt for any combination of parameters available within the ARES framework.

The knowledge of these best-fit parameters will help us to constrain future proposed models and set theoretical limits for the precision of upcoming experiments to observe non-standard effects.

یکشنبه 21 خرداد 1402، ساعت 20:00

Sunday 11 June 2023 – 20:00 Tehran Time

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

گزینه ورود به صورت مهمان – Enter as a Guest

Ehsan Fasihi Moghaddam

Physics Department, Sharif University of Technology

Cosmological Perturbation Theory in Brane Cosmology

Abstract:  Brane cosmology is one of the theoretical branches of cosmology inspired by string theory and may provide some new insights into the most fundamental aspects of cosmology. On the other hand, cosmological perturbation theory is a robust framework for studying the evolution of fluctuations on top of the isotropic and homogeneous background in cosmology.

Our research combines these two arenas. Based on previous works, we will mainly concentrate on superhorizon curvature perturbation during inflation, radiation-dominated and matter-dominated eras. For this purpose, we’ll be able to cover some steps.

 First, we will review the concept of brane cosmology. Afterward, we tend to investigate cosmic inflation within the brane cosmology scenario. Finally, we will study the associated cosmological perturbation theory in the inflation, radiation-dominated and matter-dominated eras. The calculation will be within the general theory of relativity and inspired by the phenomenological models in string theory. In this talk, we introduce Brane’s cosmology briefly and then explain the ideas and works that have been done in this theory. Since the cosmological perturbation theory still needs to be fully developed for the Brane cosmology model, the possible result of this thesis may be a step toward investigating the predictions of these models through cosmological perturbation theory.

یکشنبه 7 خرداد 1402، ساعت 17:30

Sunday 28 May 2023 – 17:30 Tehran Time

Hybrid Seminar

آمفی تئاتر دانشکده فیزیک-تالار جنابPhysics Department – Amphitheater- Jenab Hall/

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

گزینه ورود به صورت مهمان – Enter as a Guest

Zahra Sattari

Department of Physics and Astronomy, University of California, Riverside; The Observatories of the Carnegie Institution for Science, USA

Fraction of Clumpy Star-Forming Galaxies at 0.5≤z≤3 in UVCANDELS: Dependence on Stellar Mass and Environment

Abstract: High-resolution imaging of galaxies in rest-frame UV has revealed the existence of giant star-forming clumps prevalent in high redshift galaxies. Studying these sub-structures provides important information about their formation and evolution and informs theoretical galaxy evolution models. We present a new method to identify clumps in galaxies’ high-resolution rest-frame UV images. Using imaging data from CANDELS and UVCANDELS, we identify star-forming clumps in an HST/F160W≤ 25 AB mag sample of 6767 galaxies at 0.5 ≤ z ≤ 3 in four fields, GOODS-N, GOODS-S, EGS, and COSMOS. We use a low-pass band filter in Fourier space to reconstruct the background image of a galaxy and detect small-scale features (clumps) on the background-subtracted image. Clumpy galaxies are defined as those having at least one off-center clump that contributes a minimum of 10% of the galaxy’s total rest-frame UV flux. We measure the fraction of clumpy galaxies (f_clumpy) as a function of stellar mass, redshift, and galaxy environment. Our results indicate that f_clumpy increases with redshift, reaching ∼ 65% at z ∼ 1.5. We also find that f_clumpy in low-mass galaxies (9.5 ≤ log(M∗/M⊙) ≤ 10) is 10% higher compared to that of their high-mass counterparts (log(M∗/M⊙) > 10.5). Moreover, we find no evidence of significant environmental dependence of f_clumpy for galaxies at the redshift range of this study. Our results suggest that the fragmentation of gas clouds under violent disk instability remains the primary driving mechanism for clump formation, and incidents common in dense environments, such as mergers, are not the dominant processes.

یکشنبه 31 اردیبهشت 1402، ساعت 20:00

Sunday 21 May 2023 – 20:00 Tehran Time

Hybrid Seminar

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

گزینه ورود به صورت مهمان – Enter as a Guest

Henrique Rubira

Physik Department, Technische Universität München (TUM), Garching, Germany

Gravitational waves from first-order phase transitions (and how they are affected by defects)

Abstract: First-order cosmological phase transitions (PTs) in the early Universe source sound waves and, subsequently, a background of stochastic gravitational waves (GWs). In this talk, I will present the Higgsless approach to simulate the plasma dynamics and to predict the stochastic GW spectrum from PTs. I will explain how the Higgsless simulations can produce fully nonlinear results and extend the current predictions to strong PTs, one of the most exciting scenarios to be explored by LISA. Finally, I will discuss two non-conventional scenarios and how they affect the GW spectrum: first-order phase transitions seeded by domain wall networks or by temperature fluctuations.

یکشنبه 24 اردیبهشت 1402، ساعت 17:30

Sunday 14 May 2023 – 17:30 Tehran Time

Hybrid Seminar

آمفی تئاتر دانشکده فیزیک-تالار جنابPhysics Department – Amphitheater- Jenab Hall/

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

گزینه ورود به صورت مهمان – Enter as a Guest