Bahar Nosrati

Department of Physics, Shahid Beheshti University

Cosmic voids are emptier in the presence of symmetron’s domain walls

سمینار به صورت هیبریدی (حضوری و مجازی) برگزار می شود 

Abstract: The symmetron field has an environment (density) dependent behavior which is a common feature of the models with the screening mechanism and results in a rich phenomenology. This model can produce domain walls between regions with different densities. We consider this aspect and study the physics of domain walls in between (underdensity) voids and (overdensity) halo structures. The (spherical) domain walls exert a repulsive force on a test mass outside of the wall while a test mass inside of the wall sees no force. This makes the structures outside the voids go further to a larger radius. Effectively, this means the voids are becoming larger in this scenario in comparison to the standard model of cosmology. Interestingly, this makes voids emptier which may shed light on Peebles’ void phenomenon.

یکشنبه 25 دی 1401، ساعت 17:00

Sunday 15 January 2023 – 17:00 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

Javad Tabatabaei

Department of Physics, Sharif University of Technology

Local Limit of Nonlocal Gravity: A Teleparallel Extension of General Relativity

سمینار به صورت هیبریدی (حضوری و مجازی) برگزار می شود  

Abstract: In this talk we explore a general constitutive framework for a teleparallel extension of the general theory of relativity. This approach goes beyond the teleparallel equivalent of general relativity (TEGR) by broadening the analogy with the electrodynamics of media. This theory is a local constitutive extension of TEGR that is in fact the local limit of nonlocal gravity (NLG). We will also explore the cosmological implications of this theory for flat cosmology in background and perturbation levels. The observational problems we wish to approach using this theory are also discussed.

یکشنبه 11 دی 1401، ساعت 17:00

Sunday 1 January 2023 – 17:00 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

Borna Salehian

The Abdus Salam International Centre for Theoretical Physics (ICTP)

Dissipative effects during inflation 

سمینار به صورت هیبریدی (حضوری و مجازی) برگزار می شود

Abstract: I will talk about a model in which inflaton dissipates considerable amount of its energy into other fields with the expense of slowing down. In this scenario perturbations are dominated by the noise resulting from the extra fields rather than quantum fluctuations. I will also spend some time on comparison with different models that one can find in the literature.

یکشنبه 4 دی 1401، ساعت 17:00

Sunday 25 December 2022 – 17:00 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

Bahar Nikbakht

School of Astronomy, Institute for Research in Fundamental Sciences (IPM)

The Universe in the Hazelnut Shell

سمینار به صورت هیبریدی (حضوری و مجازی) برگزار می شود

Abstract: Today, we are in the middle of the golden age of cosmology. Many expensive and accurate terrestrial and space-based telescopes have opened new windows on the world and confronted us with many exciting questions and inconsistencies.
In this talk, we begin with a brief overview of the standard cosmology and then trace the history of the universe back to its very beginning. Then we examine one of the most prominent paradigms of the early universe, aka inflation, in which the universe undergoes an exponential expansion at the outset of its evolution. We then explore some observational and theoretical implications of this paradigm and its frontiers.

یکشنبه 20 آذر 1401، ساعت 17:00

Sunday 11 December 2022 – 17:00 Tehran Time

Hybrid Seminar

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

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

گزینه ورود به صورت مهمان – Enter as a Guest

Zahra Tabatabaee

Department of Physics, Sharif University of Technology;

Department of Physics, Ferdowsi University of Mashhad

Studying the Observational Appearance of the Planet With Eccentric Orbits in Protoplanetary Disk

سمینار به صورت هیبریدی (حضوری و مجازی) برگزار می شود

Abstract: Planets are by-products of star formation and when a sufficiently massive planet is embedded in a gaseous disk, that planet carves out a low-density annulus in the disk, also known as a gap. Gaps are important for a number of reasons; they might change the torques and accretion, but more importantly, gaps can be directly observed. In particular, the Atacama Large Millimeter Array has generated very detailed, resolved images of protoplanetary disks with distinct gap-like features. This provides a potential means of discovering exoplanets during the formation process.
In this work we used the 3D radiative transfer code RADMC-3D  to study the observational appearance of the planet with eccentric orbits. Then the effect of planetary mass change and eccentricity is investigated on the observational components such as density and temperature profile, spectral energy distribution and images.

یکشنبه13 آذر 1401، ساعت 17:00

Sunday 4 December 2022 – 17:00 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

Abdolali Banihashemi

Department of Physics, Shahid Beheshti University;

Department of Physics, Sharif University of Technology

Hubble tension as a hint for new models of dark energy

سمینار به صورت هیبریدی (حضوری و مجازی) برگزار می شود

Abstract: There is a ~5sigma discrepancy between the value of H0 measured from local standard candles and the one inferred from CMB in a LCDM-dependent way. In light of this so-called Hubble tension, many models have been proposed as alternatives to the standard model of cosmology; many of which are concerned with the physics of dark energy. In this session, we will have a review of the Hubble tension and then I’ll talk about Ginzburg-Landau theory of dark energy, which is based on the physics of critical phenomena.

یکشنبه 29 آبان 1401، ساعت 17:00

Sunday 20 November 2022 – 17:00 Tehran Time

Hybrid Seminar

دانشکده فیزیک-اتاق 626–Physics department Room 626  /

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

گزینه ورود به صورت مهمان – Enter as a Guest

Zeinab Kalantari

Department of Physics, Sharif University of Technology

Fermi-GBM Observation of GRB090717034: $\chi^2$ Test Confirms Evidence of Gravitational Lensing by a Supermassive Black Hole with a Million Solar Mass

سمینار به صورت هیبریدی برگزار می شود

Abstract: Gamma-ray bursts (GRBs) are one of the most luminous and prolific high-energy transients observed since their discovery in 1963. The theoretical investigations of gravitational lensing of GRBs have been carried out in the past half-century. In this talk, I will briefly review Gamma_Ray Bursts (GRBs) detections and progenitors. Next, I will give a general overview of gravitational microlensing and its observable signature on a GRB light curve for a point mass model of the lens. Then, I will highlight the results of our recent probe in the Fermi/GBM catalog and introduce one gravitationally lensed candidate which is discerned by the Autocorrelation method. Finally, we use the minimization of $\chi^2$ of the light curve of our candidate which confirms this candidate has a true lensing signature of a supermassive black hole with a redshifted mass of $\approx10^6 M_\odot$  and two peaks in this event is not a result of stochastic random fluctuations in the GRB light curve.

یکشنبه 22 آبان 1401، ساعت 17:00

Sunday 13 November 2022 – 17:00 Tehran Time

Hybrid Seminar

دانشکده فیزیک-اتاق 626–Physics department Room 626  /

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

گزینه ورود به صورت مهمان – Enter as a Guest

Mohammad Ansari

Department of Physics, Sharif University of Technology 

Cosmic web: excursion set of saddle points and nearest neighbor statistics

Supervisor: Shant Baghram 

Abstract: When we observe the universe on large scale, we see interwoven web, called the cosmic web. The cosmic web has different components and a lot of information is in it. In both cases, considering the cosmic web’s components as the environment of structure formation or considering them as structures, studying the cosmic web has advantages. But because of the non-linear nature of the cosmic web, extracting information from it has some challenges. The main challenge is that there are several ways of quantifying the cosmic web, in which there is no agreement between them. In this work, by introducing the excursion set of saddle points, we try to find a way for modelling cosmic filaments. By this model, which is an extension of the excursion of peaks, we calculate the critical density contrast of filaments with the help of the ellipsoidal collapse model and then we calculate the statistics of filaments with the help of up crossing approximation. The statistics and mass-to-length relation of filaments will help us to judge between different cosmic web finders. Finally, we calculate the number density of filaments concerning filament mass and length with this model. In the following of this work, we examine another approach to extracting information from the cosmic web. We calculate the spherical contact and nearest neighbor quantities for cosmological simulations and catalogs of galaxy groups. We report the behavior of these quantities for distance. Also by calculating the statistical modes of quantities, we show a linear relationship between the mean and variance of spherical contact distribution.

یکشنبه 27 شهریور 1401، ساعت 15:00

Sunday 18 September 2022 – 15:00 Tehran Time

تالار جناب  – آمفی تئاتر دانشکده فیزیک

Bahar Nikbakht

Department of Physics, Sharif University of Technology

Cosmic Inflation with Random Step-like Potentials and  Primordial Black Holes 

Supervisor: Ali Akbar Abolhasani 

Abstract: Recent observations of gravitational waves by the LIGO collaboration have returned attention to primordial black holes (PBHs). PBHs are also considered as candidates for dark matter. Furthermore, to be valid candidates, they must have extended mass distributions (EMD).

In this talk, we will show that modulation of the slow-roll potential with the local, sharp, and step-like noise can naturally produce primordial black holes in EMD. We first go to the long wavelength/low energy modes and show that some of these modes resonate with the noise, and hence their power spectrum is enhanced. Then we go to short wavelength/highly oscillating modes and define a correlation length for the stairs using them.

Finally, we calculate the probability of having at least two bursts of PBH for an arbitrary potential and show that this model may successfully explain the observations.

یکشنبه 27 شهریور 1401، ساعت 18:30

Sunday 18 September 2022 – 18:30 Tehran Time

تالار جناب  – آمفی تئاتر دانشکده فیزیک

پذیرش محقق پسادکتری در گروه کیهان شناسی دانشکده فیزیک دانشگاه صنعتی شریف

 بدین­وسیله به اطلاع می رساند: گروه کیهان شناسی دانشکده فیزیک دانشگاه صنعتی شریف از متقاضیان برای موقعیت محقق پسادکتری و همکاری با گروه کیهان­شناسی به مدت یکسال دعوت به عمل می آورد.

اعتبار مالی این برنامه یک ساله از سرآمدان علمی کشور به میزبانی دکتر سهراب راهوار تامین خواهد شد. علاقمندان می­توانند تقاضای خود را همراه شرح حال علمی و دو  توصیه نامه محرمانه تا تاریخ   15 مهر 1401 به رایانامه دکتر سهراب راهوار  با آدرس   rahvar@sharif.edu   ارسال فرمایند.

موضوع پژوهشی همکاری در زمینه سیاهچاله­‌های اولیه است.  فرایندهای تشکیل و تحول سیاهچاله­ های اولیه، ارتباط آن با تشکیل ساختار بزرگ مقیاس کیهانی و جنبه های مشاهداتی و کار با داده های تجربی مورد توجه این همکاری پژوهشی خواهد بود.

گروه کیهان شناسی

دانشکده فیزیک دانشگاه صنعتی شریف

21 شهریور 1401