Quasinormal Modes of a Black Hole with Quadrupole Moment

علیرضا الهیاری (پژوهشکده نجوم پژوهشگاه دانش های بنیادی – IPM )

Abstract:  We determine the quasinormal mode (QNM) frequencies of a black hole with quadrupole moment in the eikonal limit using the light-ring method. The generalized black holes that are discussed in this work possess arbitrary quadrupole and higher mass moments in addition to mass and angular momentum. Static collapsed configurations with mass and quadrupole moment are treated in detail and the QNM frequencies associated with two such configurations are evaluated to linear order in the quadrupole moment.  For a rotating system we consider the Hartle-Thorne spacetime. This collapsed system as well as its QNMs are characterized by mass M, quadrupole moment Q and angular momentum J. When the quadrupole moment is set equal to the relativistic quadrupole moment of the corresponding Kerr black hole, the Hartle-Thorne QNMs reduce to those of the Kerr black hole to second order in angular momentum J.

یکشنبه 21 مهر  1398، ساعت 15:00

دانشکده فیزیک، طبقه اول کلاس فیزیک 3

Trans-Planckian Censorship and the Swampland

آلک بدرویا

Alek Bedroya

Jefferson Physical Laboratory, Harvard University

Abstract: First, I am going to briefly review some of the Swampland conjectures which aim to find the common properties shared among all field theories consistent with quantum gravity. After that, I will talk about the motivations for, and consequences of a newly proposed conjecture, the Trans-Planckian Censorship Conjecture, and how it fits to the existing net of the Swampland conjectures. Finally, I am going to discuss the cosmological implications of this conjecture to inflationary models. This talk is based on arXiv preprints 1909.11063 and 1909.11106.

سه شنبه 16 مهر  1398، ساعت 15:00

دانشکده فیزیک

Three-dimensional map of the hot Local Bubble using diffuse interstellar bands

نقشه سه بعدی حباب محلی با استفاده از باندهای پخشی میان ستاره ای

امین فرهنگ (پژوهشکده نجوم پژوهشگاه دانش های بنیادی – IPM )

Abstract: Solar System is located within a low-density cavity, known as the Local Bubble, which appears to be filled with an X-ray emitting gas at a temperature of 10^6 K. Such conditions are too harsh for typical interstellar atoms and molecules to survive. There exists an enigmatic tracer of interstellar gas, known as Diffuse Interstellar Bands (DIB), which often appears as absorption features in stellar spectra. The carriers of these bands remain largely unidentified. Here we report the three-dimensional structure of the Local Bubble using two different DIB tracers (5780A and 5797A), which reveals that DIB carriers are present within the Bubble. The map shows low ratios of 5797A\5780A inside the Bubble compared to the outside. This finding proves that the carrier of the 5780A DIB can withstand X-ray photo-dissociation and sputtering by fast ions, where the carrier of the 5797A DIB succumbs. This would mean that DIB carriers can be more stable than hitherto thought and that the carrier of the 5780A DIB must be larger than that of the 5797A DIB. Alternatively, small-scale denser (and cooler) structures that shield some of the DIB carriers must be prevalent within the Bubble, implying that such structures may be an intrinsic feature of supernova-driven bubbles.

یکشنبه 7 مهر  1398، ساعت 15:00

دانشکده فیزیک، طبقه اول کلاس فیزیک 3

نسیبت عددی: فرمول بندی 3+1، استخراج عددی امواج گرانشی

Numerical Relativity: 3+1 Formalism, Numerical Extraction of Gravitational Waves

حسن خلوتی (دانشکده فیزیک دانشگاه صنعتی شریف )

استاد راهنما: سهراب راهوار

شنبه 30 شهریور 1398، ساعت 15:00

دانشکده فیزیک، تالار جناب (آمفی تئاتر دانشکده فیزیک)

بررسی داده های حاصل از گرفت تصویر پاریته منفی در ریزهمگرایی گرانشی ستارههای غول

Analysing microlensing data for Detecting signal from the eclipsing negative-parity Image by a giant lens star

نوید میرپوریان (دانشکده فیزیک دانشگاه صنعتی شریف )

استاد راهنما: سهراب راهوار

چهارشنبه 27 شهریور 1398، ساعت 16:00

    دانشکده فیزیک، تالار پرتوی – طبقه 4

مدل تورم گرم در نظریه موثراکسیون مونودرومی

 Warm inflation model in effective field theory of axion monodromy

 رضا قمی (دانشکده فیزیک دانشگاه صنعتی شریف )

استاد راهنما: علی اکبر ابوالحسنی

 چهارشنبه 27 شهریور 1398، ساعت 14:00

دانشکده فیزیک، تالار پرتوی – طبقه 4

سمینار 1: Footprints of gravitational grating in a strongly lensed quasar

فراز خالقی (دانشکده فیزیک دانشگاه صنعتی شریف )

سمینار 2 : Studying Spherical Collapse by N-Body Simulation On GPU

محمدجوادشاکرارانی ( دانشکده فیزیک دانشگاه صنعتی شریف )

درفصل تابستان سمینارها 10 صبح برگزار خواهد شد!

Abstract of Seminar 1: Interaction of the electromagnetic wave(EW), from a distant quasar with the gravitational wave, sourced by the binary stars can be a candidate for indirect detection of gravitational waves. While in the regime of geometric optics, the light bending due to this interaction is negligible, the phase shifting on the wavefront of an EW, playing the role of gravitational grating, can produce diffraction patterns on the observer plane. In this talk I will briefly explain the mechanics of phase shifting, due to gravitational grating. Then I will compare theory with the data from a doubly lensed system which is my candidate for detecting gravitational grating effect

چکیده سمینار 2: رمبش کروی (Spherical Collapse) یکی از ساده‌ترین مدل‌های تحلیلی برای مطالعه تشکیل هاله‌ها، به عنوان یکی از اجزای اصلی ساختارهای کیهانی است. برای بررسی بهتر و دقیق‌تر رمبش کروی و تشکیل هاله‌ها مطالعه تحلیلی کافی نیست و به ناچار باید سراغ روش‌های عددی و شبیه‌سازی رفت. با توجه به امکان پیاده‌سازی الگوریتم‌های پردازش موازی برای مسأله برهم‌کنش گرانشی بین ذرات استفاده از واحدهای پردازنده گرافیکی (GPU) می‌تواند هزینه و زمان این شبیه‌سازی‌ها را به طور قابل ملاحظه‌ای کاهش دهد.

یکشنبه 16 تیر  1398، ساعت 10:00

دانشکده فیزیک، طبقه اول کلاس فیزیک 3

سمینار 1: Fuzzy Dark Matter and its Effects on Halo Mass Function

حامد منوچهری کوشا (دانشکده فیزیک دانشگاه صنعتی شریف )

سمینار 2 : Inflation, Axions, Instantons, etc . . . 

پویان مینایی ( دانشکده فیزیک دانشگاه صنعتی شریف )

درفصل تابستان سمینارها 10 صبح برگزار خواهد شد!

Abstract of Seminar 1: Fuzzy Dark Matter (FDM) has recently become a hot candidate for Dark matter. According to this hypothesis, very light bosons (or axions) with rest mass of order 10^-22 ev, which results in a very long de Broglie wavelength can solve some small scale problems of cold dark matter paradigm, like “core-cusp” and “missing satellite” problems. This long de Broglie wavelength appears as the so called “quantum pressure” term in the Madelung fluid equations, which can suppress the small scale structure formation and accordingly change the shape of the halo mass function. In this talk, after reviewing some of the main theoretical features of FDM paradigm and showing some numerical results, I will discuss whether only the quantum pressure term is the source of change in the shape of halo mass function, or there is some other intrinsic differences between CDM and FDM which can probably change the shape of this function in larger scales.

Abstract of Seminar 2: In this talk, I will briefly review the idea of Inflation and its observational footprints. Then I will come back to field theory concepts like Effective Field Theories (EFTs), Instantons and Axions. These are some pieces of the puzzle to write the “Effective Field Theory of Axion Monodromy models with extra Light Degrees of Freedom”

یکشنبه 9 تیر  1398، ساعت 10:00

دانشکده فیزیک، طبقه اول کلاس فیزیک 3

کاوش در خاستگاه کیهانشناسی مبتنی بر مهبانگ 

شینگانگ چن (مرکز اخترفیزیک هاروارد-اسمیتسونیان)

Probing the Origin of the Big Bang Cosmology

Xingang Chen (Harvard-Smithsonian Center for Astrophysics)

 به همت انجمن علمی بین رشته‌ای ژرفا و پژوهشکده نجوم پژوهشگاه دانش‌های بنیادی

سه شنبه ۴ تیرماه ۱۳۹۸، ساعت ۱۳:۳۰

تالار جناب دانشکده فیزیک دانشگاه شریف

سمینار 1: Gravitational Lensing in Gamma Ray Bursts

زینب کلانتری (دانشکده فیزیک دانشگاه صنعتی شریف )

سمینار 2 : Gravitational Microlensing and Degeneracy Breaking

امیرحسین دهقانی ( دانشکده فیزیک دانشگاه صنعتی شریف )

درفصل تابستان سمینارها 10 صبح برگزار خواهد شد!

Abstract of Seminar 1: Gravitational lensing of gamma ray bursts (GRBs) by massive objects generates superimposed GRB images with a time delay. This could constrain compact dark matter in the intermediate mass range that has received a lot of attention following LIGO detection of merging black hole binaries. In this talk, I will review the basic astrophysical applications of gravitational lensing. Then, I will give a brief introduction on gravitational lensing as a probe of compact dark matter.

Abstract of Seminar 2: Detection of light blending in a gravitational field, previously predicted by general relativity, stimulated a new line of research for astronomers. In 1986 Paczynski introduced the modern formalism of microlensing which proposed the observation of lensing of a source star by 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 event. This parameter is related to physical properties of lens and source star which are their masses, distance and relative velocity. Here, there is a degeneracy problem that several methods have been proposed to overcome it. 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 for resolving the issue which is mainly based on Gaia observations.

یکشنبه 2 تیر  1398، ساعت 10:00

دانشکده فیزیک، طبقه اول کلاس فیزیک 3