بایگانی دسته: سمینارهای هفتگی

The importance of non-linearities in dark energy models

The importance of non-linearities in dark energy models

فربد حسنی

 (Department of Theoretical Physics of the University of Geneva)

Abstract: I’m going to introduce k-evolution, a relativistic N-body code, which includes clustering dark energy among its cosmological components. I’ll show the effect of dark energy non-linearities on the power spectrum of dark matter, dark energy and the gravitational potential using k-evolution results. I’ll also discuss about the importance of taking dark energy non-linearities into account for doing precision cosmology and I’ll show that for some choice of parameters the dark energy equation suffer from a new instability and blowup in finite time. My talk will be based on arXiv: 1910.01104, arXiv: 1910.01105 and arXiv:1906.04748.

  

یکشنبه 15 دی 1398، ساعت 15:00

دانشکده فیزیک، طبقه اول کلاس فیزیک 3

Beheshti-Sharif Joint Workshop on Structure Formation

We are pleased to announce a joint program between Sharif and Beheshti universities. Farnik Nikakhtar (University of Pennsylvania) will give four lectures on the topic of structure formation. This workshop is scheduled as follow:– Wednesday 11th Dey @ Shahid Beheshti University and– Wednesday 18th Dey @ Sharif University of Technology.
The poster is attached and please register if you like to participate.

روز کیهانشناسی

جای  بسی خرسندی است که برای دومین سال پیاپی روز کیهان شناسی را در شریف برگزار می کنیم. در فایل پیوست، لطفا برنامه روز کیهان شناسی  دانشکده فیزیک دانشگاه شریف را بیابید.
این برنامه روز یکشنیه 8 دی ماه 1398 / 29 دسامبر 2019 در آمفی تئاتر دانشکده فیزیک (تالار جناب) از ساعت 15:00 الی 18:30 برگزار می گردد.

Strong Lensing of Explosive Transients

Strong Lensing of Explosive Transients

زینب کلانتری (دانشکده فیزیک دانشگاه صنعتی شریف )

Abstract: Recent rapid progress in time domain surveys makes it possible to detect various types of explosive transients (Gamma-ray bursts, Gravitational wave, supernovae, and Fast radio bursts) in the Universe in large numbers, some of which will gravitationally lensed into multiple images. Although a large number of strongly lensed distant galaxies and quasars have already been discovered, strong lensing of explosive transients opens up new applications, including improved measurements of cosmological parameters and powerful probes of small scale structures of the Universe, thanks to their rapidly evolving light curves as well as their compact sizes. Recently we have witnessed first discoveries of strongly lensed supernovae, and strong lensing events of other types of explosive transients are expected to be observed soon. In this presentation, I will review a recent paper on the current state of research on strong gravitational lensing of explosive transients and discuss future prospects.

 

یکشنبه 24 آذر 1398، ساعت 15:00

دانشکده فیزیک، طبقه اول کلاس فیزیک 3

سمینار مشترک گروه ذرات و کیهان شناسی

Swampland Conjectures and Inflating Phases of the Universe (II)

مهدی ترابیان (دانشکده فیزیک دانشگاه صنعتی شریف )

Abstract: The swampland conjectures that are motivated by string theory offer a list of criteria that every field theory consistent with quantum gravity must admit. In particular, they constrain the inflating phases of the early and late universe. In this talk, we discuss the recently proposed trans-Planckian censorship conjecture and its consequences for inflationary cosmology. It excludes many models of inflation. Specifically, it implies that inflation must be low scale that implies severe fine-tuning of initial conditions and no primordial gravitation waves. We discuss how multiple inflationary models can explain the present horizon problem, alleviate the initial condition problem and accommodate possible detection of gravitational waves.

یکشنبه 17 آذر 1398، ساعت 15:00

    دانشکده فیزیک، طبقه اول کلاس فیزیک 3

سمینار مشترک گروه ذرات و کیهان شناسی

Swampland Conjectures and Inflating Phases of the Universe

مهدی ترابیان (دانشکده فیزیک دانشگاه صنعتی شریف )

Abstract: The swampland conjectures that are motivated by string theory offer a list of criteria that every field theory consistent with quantum gravity must admit. In particular, they constrain the inflating phases of the early and late universe. In this talk, we discuss the recently proposed trans-Planckian censorship conjecture and its consequences for inflationary cosmology. It excludes many models of inflation. Specifically, it implies that inflation must be low scale that implies severe fine-tuning of initial conditions and no primordial gravitation waves. We discuss how multiple inflationary models can explain the present horizon problem, alleviate the initial condition problem and accommodate possible detection of gravitational waves.

یکشنبه 10 آذر 1398، ساعت 15:00

    دانشکده فیزیک، طبقه اول کلاس فیزیک 3

Gravitational Microlensing and Degeneracy Problem

Gravitational Microlensing and Degeneracy Problem: New Method for Breaking the Degeneracy Using Gaia Catalogue

امیرحسین دهقانی (دانشکده فیزیک دانشگاه صنعتی شریف )

Abstract:  Detection of light blending in a gravitational field, previously predicted by general relativity, stimulated a new line of research for astronomers. In 1986, Paczynski, regarding the dark matter problem, investigated the possibility of observing lensing of a source star light by gravitational field of another star in the Milky Way galaxy. In a simple microlensing event, the only observable parameter that has physical information is the Einstein crossing time; a characteristic time scale of microlensing events. This parameter is a function of lens mass, lens and source distance and their relative velocity. Several methods have been proposed to overcome this degeneracy problem. In this talk, after presenting a brief review of basic formalism and physics, I will show different methods of microlensing degeneracy breaking and will finally present my proposal which is mainly based on Gaia observations. The results show a continuum in mass distribution of lenses with some candidates for neutron stars and black holes.

 

یکشنبه 3 آذر 1398، ساعت 15:00

دانشکده فیزیک، طبقه اول کلاس فیزیک 3

trans-Planckian Censorship

The trans-Planckian Censorship and the Initial Condition Problem

مهدی ترابیان (دانشکده فیزیک دانشگاه صنعتی شریف)

Abstract: The swampland picture that has been emerging from string theory offers a list of criteria that every field theory consistent with quantum gravity must admit. These conditions have interesting implications for the early Universe cosmology and strongly constrain cosmological models. In this talk, we discuss the trans-Planckian censorship conjecture and its consequences for inflationary cosmology.  In particular, it implies that the vanilla models of inflation are rather low scale and suffer from severe fine-tuning of initial conditions. We discuss how multiple inflationary models could alleviate the initial condition problem and accommodate a possible detection of gravitational waves in future. 

 

یکشنبه 26 آبان 1398، ساعت 15:00

    دانشکده فیزیک، طبقه اول کلاس فیزیک 3

Magnetic Penrose Process

50 years of energy extraction from rotating black hole: Magnetic Penrose Process

Naresh Dadhich

(Inter-University Center for Astronomy and Astrophysics (IUCAA), M.A. Ansari Chair in Theoretical Physics at Centre for Theoretical Physics, Jamia Millia Islamia, Delhi)

لطفا به مکان جدید سمینار توجه فرمایید!

Abstract: It is 50 years since Penrose proposed in 1969 the purely geometric process of extracting rotational energy from a rotating black hole. It was indeed a very novel and remarkable process but it was soon realized that it cannot be efficient enough for astrophysical application in powering high energy objects like quasars and AGNs. The difficulty was in the requirement that relative velocity between the two fragments must be greater half the velocity of light, which was astrophyically untenable. This difficulty was beautifully overcome by the speaker and his coworkers in 1985 when they considered magnetic version of the process and had shown that efficiency of energy extraction could even exceed 100%. Now the fully relativistic magnetohydrodynamics simulations wonderfully bear out this prediction and MPP is being considered the most favored process for powering the central engine of high energy objects. The speaker will review the fifty years journey.

یکشنبه ۱۹ آبان ۱۳۹۸، ساعت ۱۵:۰۰

دانشکده فیزیک، طبقه چهارم – تالار پرتوی