Bahar Nikbakht

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

Non-Gaussianity consistency relations and their consequences for the peaks

Abstract: Strong deviations from scale invariance and the appearance of high peaks in the primordial power spectrum have been extensively studied for generating primordial black holes (PBHs) or gravitational waves (GWs). It is also well-known that the effect of non-linearities can be significant in both phenomena. In this study, we introduce a general single-field consistency relation that relates the amplitude of non-Gaussianity in the squeezed limit  to the power spectrum and remains valid when almost all other consistency relations are violated.

Then we discuss the general and model-independent consequences of the consistency relation on the behavior of  at different scales.

As an implication of our results, we argue that non-linearities can shift or extend the range of scales responsible for the production of PBHs or GWs, relative to the window as determined by the largest peak of the power spectrum, and may also open up new windows for both phenomena.

یکشنبه 26 فروردین 1403، ساعت 17:00

Sunday 14 April 2024 – 17:00 Tehran Time

Hybrid Seminar

دانشکده فیزیک – طبقه اول – کلاس فیزیک 3 /Physics Department – first floor – Room Physics 3   

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

گزینه ورود به صورت مهمان – Enter as a Guest

Samaneh Sarbaz

Department of Physics, Sharif University of Technology

Seminar 1: Radio Astronomy: A brief report on the topics covered in the I_HOW/IAU radio astronomy workshop

Zahra Tabatabaee

Department of Physics, Sharif University of Technology

Seminar 2: The dynamics of FRW universe in scalar-Tensor-Vector gravity

Abstract 1: Today, radio astronomy is one of the best methods for observing the universe. A wide range of topics, such as star and planet formation, galaxy formation and evolution and interstellar and intergalactic medium can be ideally studied using these radio data. In September 2023,IAU/I-HOW Radio Astronomy was held at Erciyes University, Kayseri, Türkiye. One of the objectives of this Workshop was to prepare young researchers to learn how to analyse radio data from radio telescopes such as ALMA and VLA. In our upcoming talk, I will discuss radio astronomy. I am going to talk about the introduction of radio telescopes and analyzing radio data. This talk will be a brief report on the topics covered in the I_HOW/IAU radio astronomy workshop. 

Abstract 2: The Scalar-Tensor-Vector-Gravity (STVG), also known as MOG (Modified Gravity), has been proposed as a solution to the dark matter problem. In this talk, a gauge-invariant theory for MOG will be introduced through a symmetry-breaking mechanism at low temperatures, where gravitational attraction is governed by an effective gravitational constant. The modified Friedmann equation and scale factor evolution for this theory will be discussed. Finally, it will be mentioned that this theory has the potential to alter the dynamics of the early and late Universe.

یکشنبه 20 اسفند 1402، ساعت 17:00

Sunday 10 March 2024 – 17:00 Tehran Time

Hybrid Seminar

دانشکده فیزیک – طبقه اول – کلاس فیزیک 3 Physics Department – first floor – Room Physics 3  / 

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

گزینه ورود به صورت مهمان – Enter as a Guest

Samira Cheraghchi

Department of Physics, University of Tehran

Four-dimensional SO(3)-spherically symmetric Berwald Finsler spaces

Abstract: Besides having an introduction to Finslerian geometry and its application in Physics, We locally classify all SO(3)-invariant four-dimensional pseudo-Finsler Berwald structures. These are Finslerian geometries which are closest to (spatially, or SO(3))-spherically symmetric pseudo-Riemannian ones — and serve as ansatz to find solutions of Finsler gravity equations which generalize the Einstein equations. We find that there exist five classes of non-pseudo-Riemannian (i.e. non-quadratic in the velocities) SO(3)-spherically symmetric pseudo-Finsler Berwald functions, which have either a heavily constrained dependence on the velocities, or, up to a suitable choice of the tangent bundle coordinates, no dependence at all on the “time” and “radial” coordinates. Also, we will present that in the cosmological symmetric case, the Finsler function only can have one non-trivial (non-Riemannian) form.

یکشنبه 13 اسفند 1402، ساعت 17:00

Sunday 3 March 2024 – 17:00 Tehran Time

Hybrid Seminar

دانشکده فیزیک – طبقه اول – کلاس فیزیک 3 Physics Department – first floor – Room Physics 3    /

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

گزینه ورود به صورت مهمان – Enter as a Guest

Sadra Jazayeri

Department of Physics, Imperial College London

Cosmological Phonon Collider 

Abstract: The expansion of the universe spontaneously breaks time translation by selecting a preferred time foliation. As a consequence, very much like a superfluid at zero temperature, the low-energy description of single-field inflation can be organised in terms of the associated Goldstone mode of the broken symmetry (aka the phonon). Similar to particle colliders, if we were to scatter sound waves, the presence of additional heavy fields coupled to the medium would manifest as distinct peaks in the cross-section of the phonons. In this talk, I introduce a cosmological version of this idea, in which the imprints of additional heavy particles during inflation are encoded in the late time boundary correlators of the Goldstone boson. I discuss various phenomenological consequences of this setup for the primordial bispectrum and trispectrum.

یکشنبه  29 بهمن 1402، ساعت 17:00

Sunday 18 February 2023 – 17:00 Tehran Time

Hybrid Seminar

دانشکده فیزیک – طبقه اول – کلاس فیزیک 3 Physics Department – first floor – Room Physics 3   /

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

گزینه ورود به صورت مهمان – Enter as a Guest

Reza Rezaei

Department of Physics, Sharif University of Technology

Radio telescopes and the ongoing project in the Physics Department

Abstract: We will resume our seminar at the beginning of the second semester with a talk by Dr Reza Rezaei on Radio telescopes and the ongoing project in the Physics Department of Sharif University for building radio antennas.

The M.Sc. and B.Sc. Students interested in knowing more and being involved in this project, please attend the seminar.

یکشنبه 15 بهمن 1402، ساعت 17:00

Sunday 4 February 2024 – 17:00 Tehran Time

Hybrid Seminar

دانشکده فیزیک – طبقه اول – کلاس فیزیک 3 Physics Department – first floor – Room Physics 3   /

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

گزینه ورود به صورت مهمان – Enter as a Guest

Hamed Manouchehri Kousha

Department of Physics, Sharif University of Technology

The Effective Field Theory of Large-Scale Structures  of a Fuzzy Dark Matter Universe

Abstract: Ultra-light scalar fields and their non-interacting class, the so-called fuzzy dark matter (FDM), are candidates for dark matter, introduced to solve the small-scale problems of the standard cold dark matter. In this talk, after reviewing FDM and its main effects, I address whether the small-scale effects of FDM, specifically the quantum pressure, could leave sizable imprints on the large-scale statistics of the matter. For this purpose, we utilized the effective field theory of large-scale structures wherein small-scale physics is integrated and represented on large scales by only a set of free parameters. These parameters can be determined by fitting to the cosmological simulations. We performed three FDM simulations with different masses and compared their sound speed with the standard cold dark matter (CDM) simulation. We found that the FDM sound speed is slightly higher than CDM’s. We conclude that the impact of the FDM is not limited to the small scales alone, and we can search for them by studying the matter on large scales. Though it is beyond the observations’ scope today, it is possible to discriminate it with upcoming observations.

یکشنبه 10 دی 1402، ساعت 17:15

Sunday 31 December 2023 – 17:15 Tehran Time

Hybrid Seminar

دانشکده فیزیک – طبقه اول – کلاس فیزیک 3 Physics Department – first floor – Room Physics 3  / 

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

گزینه ورود به صورت مهمان – Enter as a Guest

Mohammad Hassanshahi

Department of Physics and Astronomy, University College London, UK

The use of quantum computers in machin  learning algorithms and its application in physics

استفاده از کامپیوترهای کوانتومی در الگوریتم­های یادگیری ماشین و کاربرد آن در فیزیک

 چکیده: «در این ارائه ابتدا برخی مفاهیم و روش­های یادگیری ماشین را مرور می­کنم. سپس با ذکر چند مثال نشان می­دهم که کامپیوترهای کوانتومی پتانسیل این را دارند که به بهبود این روش ها کمک کنند. الگوریتم ­هایی وجود دارند که اجرای آن­ها در کامپیوترهای کوانتومی سریع اما در کامپیوترهای غیر کوانتومی (کلاسیکی) بسیار زمانگیر است. آیا می­توان از این الگوریتم­ها در روش­های یادگیری ماشین استفاده کرد؟ در انتها به برخی چالش­ها در این الگوریتم­ها اشاره کرده و در نهایت مثال­هایی می­زنم از کاربرد این الگوریتم­ها در برخی حوزه­ های فیزیک (مثل ذرات بنیادی و نجوم)».

یکشنبه  3 دی 1402، ساعت 17:15

Sunday 24 December 2023 – 17:15 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

Amin Farhang

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

How heavy molecules are living in ISM?

Abstract: In the study of heavy molecular formation and evolution, we aim to understand the processes involved in the creation and development of complex molecules in various interstellar environments. The interstellar medium (ISM) is a vast and dynamic region that contains a wide range of elements and compounds, including carbon-based molecules. Through our recent research conducted as part of the VLT large survey, we have been able to investigate the interaction of unknown molecules with carbon in different environments within the ISM. By analyzing spectroscopic data obtained from the VLT, we can identify and characterize these molecules, shedding light on their properties and behavior. One particular aspect of interest is the correlation relationships between these unknown molecules. By studying the patterns and connections between different molecular species, we can gain insights into their mutual influences and the underlying mechanisms that govern their presence and distribution. Our ongoing research efforts also involve investigating the formation mechanisms of these molecules in planetary nebulae. We plan to explore the role of various environmental factors, such as temperature, pressure, and radiation, in shaping the molecular composition of the ISM. Additionally, we aim to investigate the influence of specific astrophysical events, such as gas depletion, on the formation and evolution of these complex molecules.

یکشنبه 12 آذر 1402، ساعت 17:15

Sunday 3 December 2023 – 17:15 Tehran Time

Hybrid Seminar

دانشکده فیزیک – طبقه اول – کلاس فیزیک 3 Physics Department – first floor – Room Physics 3/   

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

گزینه ورود به صورت مهمان – Enter as a Guest

Parisa Arabameri

Department of Physics, Shahid Beheshti University

k−Dependent Dark Matter 

Abstract: With the emersion of precise cosmology and the emergence of cosmic tensions, we are faced with the question of whether the simple model of Cold Dark Matter needs to be extended and whether doing so can alleviate the tensions and improve our understanding of the properties of dark matter. In this talk, first, I will briefly review Cold Dark Matter challenges, and Warm and Mixed Dark Matter models as solutions to some of these challenges. Then, I will introduce a new model that examines whether Dark Matter has any scale-dependent behavior. This model is one of the generalized models of dark matter with the non-zero equation of state (w) so that the behavior of this dark matter changes according to the scale of (k). In large scales (small (k)’s), the dark matter is cold (w = 0), while it becomes warm (w \neq 0) for small scales (large k’s). This behavior is modeled phenomenologically for two different cases:(I) the sound speed behaves independently of (k) as a constant parameter and (II) it changes depending on (k).

یکشنبه 5 آذر 1402، ساعت 17:15

Sunday 26 November 2023 – 17:15 Tehran Time

Hybrid Seminar

دانشکده فیزیک – طبقه اول – کلاس فیزیک 3/ Physics Department – first floor – Room Physics 3   

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

گزینه ورود به صورت مهمان – Enter as a Guest

Maryam Zeinali

Research Center for High Energy Physics, Department of Physics,

Sharif University of Technology

Luminosity at LHC  

Abstract: Luminosity, along with the center of mass energy, is the most important figure of merit of any particle collider. It quantifies the power of a machine to squeeze particles through a given space in a given time. The precision luminosity measurement is crucial as it directly affects the other physics parameters like physics process’s production cross section. In this talk the luminosity is first introduced. Then the technique used to measure this quantity is presented, which yields in determining a calibration constant; so-called \sig_{visible}, via some specific van-der-Meer (vdM) scans. Finally, the contribution from several sources of systematic uncertainties on the measurement of the luminosity is discussed.

یکشنبه  28 آبان 1402، ساعت 17:15

Sunday 19 November 2023 – 17:15 Tehran Time

Hybrid Seminar

دانشکده فیزیک، طبقه اول – کلاس فیزیک 3 Physics Department – first floor – Room Physics 3   / 

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

گزینه ورود به صورت مهمان – Enter as a Guest