Mohammad Reza Ebrahimi

Department of Physics, Sharif University of Technology

Simulation of Structure Formation in the presence of Fuzzy Dark Matter using Gevolution Code 

Supervisor: Ali Akbar Abolhasani

 Abstract: In this thesis, the formation of cosmic structures in the presence of fuzzy dark matter (FDM) is investigated using the Gevolution code. In the FDM model, dark matter is composed of ultralight bosons. In fact, the mentioned bosons are the remnants of a scalar field present in the early universe. Simulations of structure formation in the presence of FDM that have been carried out so far (for example with Gadget and RAMSES) are based on Newtonian gravity, which have a number of limitations. The Gevolution code is an N-Body simulation that, unlike other existing simulations, is based on General Relativity, which can lead to interesting results. In fact, in this simulation, the weak field limit in General Relativity is looked at and metric degrees of freedom are calculated. Other advantages of Gevolution code are higher simulation speed and less hardware limitations. In addition, in this code, a number of theories can be studied.

 یکشنبه  26 بهمن 1401، ساعت 17:00

Sunday 19 February 2023 – 17:00 Tehran Time

تالار جناب  – آمفی تئاتر دانشکده فیزیک

Melika Sarrami

Department of Physics, Sharif University of Technology

Non-linear Structure formation and halo statistics in the fuzzy dark matter model 

Supervisor: Shant Baghram

 Abstract: Fuzzy dark matter ( FDM ) or wave dark matter is an alternative theory designed to solve small-scale problems faced by the standard cold dark matter, such as the missing satellites problem, core cusp problem, and too big to fail problem. FDM is made up of ultra-light axions having mass ∼  that typically have de Broglie wavelength of several kpc, so in small-scales behave like a wave.

For this thesis, I aim to explore how the sub-halo structure and its features change with FDM particles masses which may be able to solve small-scale problems. We derived the halo mass function for FDM by solving the excursion set problem with a mass-dependent barrier function; then, we compared the approach and results of the ΛCDM model and halo statistics that stem from it with the FDM model. FDM model suppresses the small-scale structure of dark matter that results in a cut-off at the lower end of the halo mass function. Markovian processes have an analytical solution, but most are non markov, meaning steps are correlated. Then for this problem, we can approximate it using up-crossing in large mass structure. This approach could be intelligent because Non-Markov trajectories are more smooth than Markovian trajectories, which makes it possible to use this approximation. At the end of the project, we conduct progenitor history for FDM in different redshifts with various mass ranges using the top hat window function.

چهارشنبه  26 بهمن 1401، ساعت 10:00

Wednesday 15 February 2023 – 10:00 Tehran Time

تالار پرتوی  – دانشکده فیزیک

Elahe Khalouei

Research Center for Gravitational-Wave Universe (GWUniverse), Seoul National University

Primordial Black Holes and Gravitational waves

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

Abstract: Detection of Gravitational waves is a new tracer to search Primordial Black Holes (PBHs). In this talk, I will overview the primordial black holes, focusing on gravitational waves.

یکشنبه 2 بهمن 1401، ساعت 17:00

Sunday 22 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

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