سمینار هفتگی گروه کیهانشناسی

سمینار 1 : Investigation of Fuzzy Dark Matter Theory II

 

علیرضا مالکی (دانشکده فیزیک دانشگاه صنعتی شریف )

سمینار 2 : Emergence of Life on Earth

 A key to search for extraterrestrial life

 

سعیده هاشمی (دانشکده فیزیک دانشگاه صنعتی شریف )

درفصل تابستان سمینارها 10 صبح برگزار خواهد شد!

Abstract of Seminar 1:  In this talk, we will discuss about the cosmological standard model’s problems in small scales and introduce the Fuzzy Dark Matter theory as a possible solution to these problems. Finally we will discuss about observational methods to investigate this theory.

Abstract of Seminar 2: The holy grail of astrobiologists is to find life elsewhere in the universe. This goal needs several areas of research including simulating of early Earth’s condition, looking for footprints of life on our own planet and biosignatures out there in the universe. This could not be done but by having a clear definition of life on Earth, looking for where and how it happened and searching for this kind of life in other places. In this talk, I will give a brief review of the efforts done so far to reach this goal including emergence of building blocks of life on Earth and the consequences.

 

یکشنبه 18 تیر ماه 1396، ساعت 10:00

دانشکده فیزیک، طبقه اول، کلاس فیزیک 3

سمینار 1 : Investigation of Fuzzy Dark Matter Theory

 

علیرضا مالکی (دانشکده فیزیک دانشگاه صنعتی شریف )

سمینار 2 : GW170104: Observation of a 50-Solar-Mass Binary Black Hole Coalescence at Redshift 0.2

 

عباس خان بیگی (دانشکده فیزیک دانشگاه صنعتی شریف )

درفصل تابستان سمینارها 10 صبح برگزار خواهد شد!

Abstract of Seminar 1:   In this talk, we will discuss about the cosmological standard model’s problems in small scales and introduce the Fuzzy Dark Matter theory as a possible solution to these problems. Finally we will discuss about observational methods to investigate this theory.

Abstract of Seminar 2: On January 4, 2017 at 10:11:58.6 the twin detectors of LIGO, observed a signal which was calculated to belong to the coalescence of two stellar-mass black holes with roughly 31 and 19 solar masses. The resulting black hole was roughly 2 solar masses lighter than combined masses, emitting the difference as the energy carried out by gravitational radiation. The signal to noise ratio was 13 and the signal travelled through universe roughly about 3 billion years which is two times further than the first detection. The significant point about this detection, which is considered to be the third official announcement, is that the spin configurations in which the spin of both constituent black holes are positively aligned with the orbital angular momentum are disfavored which provides hints about how this binary was formed. Consistency with General Relativity and the constrains on the mass of graviton is also discussed.

 یکشنبه 11 تیر ماه 1396، ساعت 10:00

دانشکده فیزیک، طبقه اول، کلاس فیزیک 3

هندسه و توپولوژی نظریه گرانش و کوانتیزه کردن آن

هندسه و توپولوژی نظریه گرانش و کوانتیزه کردن آن

فرهاد قابوسی (University of Konstanz – Germany) 

چکیده: از آنجایی که نظریه گرانش اینشتین بصورت فعلی آن قابل کوانتیزاسیون نیست. لذا پس از تحلیل ساختار هندسی کنش اینشتین ـ هیلبرت در نظریه گرانش و وردش آن که منجر به معادله اینشتین می شود، نتایج هندسی و توپولوژیک این تحلیل ارزیابی می شوند. تا با توجه به ساختمان کیفی معادلات دیفرانسیل سه اثر اساسی نظریه گرانش اینشتین بر اساس هندسه دیفرانسیل مدلی برای نظریه گرانش پیشنهاد شود که قابل کوانتیزاسیون است.

 

 یکشنبه 31 اردیبهشت ماه 1396، ساعت 15:00

دانشکده فیزیک، طبقه اول، کلاس فیزیک 3

The Jubilee ISW Project (simulated ISW) and using it to study voids

The Jubilee ISW Project (simulated ISW) and using it to study voids

امیر ملازاده (دانشکده فیزیک دانشگاه خوارزمی )

Abstract: What are the properties of dark energy? To answer this question, the late-time integrated Sachs-Wolfe (ISW) effect (Sachs & Wolfe 1967; Rees & Sciama1968; Hu & Sugiyama 1994) can be a useful cosmological probe, since it is sensitive to the dynamical effects of dark energy and may thus be used to discriminate between different cosmological models (Crittenden & Turok 1996; Afshordi et al. 2004). The Jubilee project consists of two of the largest N-body simulations done up to date. Two volumes of 3072 Mpc and 6000 Mpc respectively with same mass and spatial resolution. These simulations were intended to be used primarily to compute an all-sky map of the Integrated Sachs-Wolfe effect (or ISW) but also to produce catalogs of luminous red galaxies (or LRG), radio and IR galaxies as well as all sky maps of the Sunyaev-Zel’dovich (or SZ) and lensing effects.

 یکشنبه 24 اردیبهشت ماه 1396، ساعت 15:00

دانشکده فیزیک، طبقه اول، کلاس فیزیک 3

GW & FRB and Matter quantum fluctuation correction to BHs

سمینار 1 : Gravitational waves and fast radio bursts 

الهه خالویی (دانشکده فیزیک دانشگاه صنعتی شریف )

سمینار 2 : Matter quantum fluctuation correction to black holes 

وحید تومانی (دانشکده فیزیک دانشگاه صنعتی شریف )

Abstract of Seminar 1:     Fast radio bursts (FRB) are perhaps the most mysterious phenomena detected in radio wavelengths with the duration of only a few milliseconds. A variety of models have been proposed to explain their origin. In this talk I will present the possible scenario for the formation of fast radio bursts accompanied by the gravitational-wave signal.

Abstract of Seminar 2:

This talk is based on a paper written by Jahed Abedi & Dr. Arfaei  arxiv:1506.5844 [gr-qc]. In this paper they have calculated the trace anomaly to the spin 1 and 1/2 and 2 matter field and the corrections to metric then they’ve discussed its effect on geodesics and star collapse and they concluded the singularity could not be formed.

 

 یکشنبه 17 اردیبهشت ماه 1396، ساعت 15:00

دانشکده فیزیک، طبقه اول، کلاس فیزیک 3

Cosmic flows: testing gravity and the matter power spectrum on very large scales

پخش فیلم سمینار “

Cosmic flows: testing gravity and the matter power spectrum on very large scales

 Mike Hudson

Department of Physics and Astronomy – University of Waterloo and Perimeter Institute for Theoretical Physics

Seminar in Perimeter Institute –  16 September 2014

 

Abstract:  Peculiar velocities – deviations from Hubble expansion – are the only practical probe of the growth of matter density fluctuations on very large scales in the nearby Universe. I will discuss recent measurements of quantities of cosmological interest from our group and others. One is the “bulk” flow of nearby galaxies with respect to the frame defined by the Cosmic Microwave Background, and what this tells us about fluctuations on large very spatial scales. The second is the measurement of the growth rate of fluctuations, a critical test of Lambda CDM and modified gravity models.

یکشنبه 10 اردیبهشت ماه 1396، ساعت 15:00

    دانشکده فیزیک، طبقه اول کلاس فیزیک 3

Quasar host galaxies revealed by eclipsing damped Lyman alpha systems

Quasar host galaxies revealed by eclipsing damped Lyman alpha systems

حسن فتحی واوسری (پژوهشکده نجوم پژوهشگاه دانش های بنیادی IPM)

 

Abstract:  Damped Lyman alpha absorption systems (DLAs) with the same redshift as their background quasars, can act as natural coronagraphs, blocking the blazing radiation from the broad line region (BLR) of the quasar, and as a result revealing to us the much fainter emission from the quasar host galaxy. This constitutes a new way to have direct access to the quasar host galaxy, and possibly to the very center of the active galactic nucleus (AGN). We searched the SDSS database and found ~ 200 such eclipsing DLAs that exhibit narrow Lyman-alpha emission in their DLA troughs. We obtained high-resolution echelle spectra of six of these systems using the MagE spectrograph. Remarkably, the 2-dimentional spectra of all these systems reveal that the narrow Lyman-alpha emission in the DLA trough are also spatially extended. In this seminar, I will present the results of our study of these extended Lyman-alpha emission and their eclipsing DLAs.

 

یکشنبه 3 اردیبهشت ماه 1396، ساعت 15:00

دانشکده فیزیک، طبقه اول کلاس فیزیک 3

کیهانشناسی پس-واکنشی

 کیهانشناسی پس-واکنشی

مجاهد پارسی مود  (دانشکده فیزیک دانشگاه صنعتی شریف)

 

چکیده: یکی از پرسش‌های قدیمی و مهم در کیهانشناسی تاثیر تشکیل ساختارهای بزرگ مقیاس بر دینامیک کیهان بوده است. پس از کشف انبساط تند شونده عالم، یکی از راه حل‌های پیشنهادی برای مساله انرژی تاریک؛ رهیافت پس-واکنش کیهانی بوده است. در این سمینار ابتدا مروری می‌کنم بر روش محاسبه پس-واکنش با استفاده از میانگین‌گیری معادلات کیهانی، سپس گزارشی می‌دهم از تلاش برای محاسبه پس-واکنش کیهانی با استفاده ازحدسی که بر اساس قضیه برهمنهی در معادلات گرانش استوار است. در نهایت هم اشاره‌ای به مساله ناهنجاری در اندازه‌گیری پارامتر هابل خواهم داشت.

 

 

 

یکشنبه 27 فروردین ماه 1396، ساعت 15:00

دانشکده فیزیک، طبقه اول کلاس فیزیک 3

Energy-Momentum Squared Gravity

 Energy-Momentum squared gravity (EMSG)

محمود روشن  (گروه فیزیک دانشکده علوم دانشگاه فردوسی مشهد)

 

Abstract:  In this talk I review a covariant generalization of Einstein’s general relativity which allows the existence of a term proportional to T_{\alpha\beta} T^{\alpha\beta} in the action functional of the theory ( T_{\alpha\beta} is the energy-momentum tensor). This simple generalization leads to interesting consequences in the early universe. Applying this theory to a homogeneous and isotropic spacetime, we find that there is a maximum energy density ρ_{max}, and correspondingly a minimum length a_{min}, in the thermal history of the universe. This means that there is a bounce at early times, and this theory avoids the existence of an early-time singularity. Also I review the possible consequences of this theory in the dynamics of compact objects like Neutron stars. More specifically I discuss the mass-radius relation for Neutron stars in this model.

The talk is based on the following paper:Roshan and Shojai PRD 2016: 10.1103/PhysRevD.94. 044002

 

 

یکشنبه 20 فروردین ماه 1396، ساعت 15:00

دانشکده فیزیک، طبقه اول کلاس فیزیک 3