Causal Set Theory and Cosmology

Yasaman Yazdi

Theoretical Physics Group, Blackett Laboratory, Imperial College London

Abstract: Causal sets are fundamentally discrete structures proposed to underlie spacetime. A causal set is made of ‘atoms’ of spacetime related according to the causal relations between them. Causal structure, discreteness, covariance, and nonlocality play a prominent role in the physics described by causal sets, including cosmology. Causal set theory has touched on a number of fundamental cosmological questions. These range from the cosmological constant problem to the origin of cosmological horizon entropy. In this talk I will review some of these studies and highlight how the unique features of causal sets come into play.

یکشنبه 2 شهریور 1399، ساعت 19:00

Sunday 23 August 2020 – 19:00 Tehran Time

اتاق سمینار مجازی –Virtual Seminar Room

https://vclass.ecourse.sharif.edu/ch/cosmology

گزینه ورود به صورت مهمان – Enter as a Guest

The Cosmological principle and the frame that never was

Mohamed Rameez

Niels Bohr Institute, University of Copenhagen

Abstract: The largest anisotropic feature of the Cosmic Microwave Background is the dipole, believed to originate from the relative motion of the heliocentric frame with a velocity of ~369 km/s with respect to the ‘rest frame of the Universe’ in standard cosmology. This should cause a dipolar modulation in the number counts of distant sources, through special relativistic aberration and Doppler boosting effects. We test this with various all-sky catalogues: NVSS and SUMSS radio galaxies, WISE galaxies and AGNs as well as GAIA-unWISE AGNs and consistently find a significantly larger dipole than expected, implying velocities > 1000 km/s at conservative statistical significances as high as 3.3 sigma. These and other observations hint at a bulk flow of matter in the local Universe, extending out to scales larger than is typical in \Lambda CDM N-body simulations. Convergence to the CMB rest frame has never been demonstrated. An observational effect of such a bulk flow would be a scale dependent dipolar modulation in the deceleration parameter. We look for this in the SDSS-II/SNLS-III Joint lightcurve analysis compilation of SN1a data and find such a modulation at ~3.9 sigma statistical significance, while the evidence for any isotropic acceleration of the Universe simultaneously drops to <1.4 sigma. These observations suggest that dark energy is an artefact of our idealized cosmological model.

یکشنبه 26 مرداد 1399، ساعت 19:00

Sunday 16 August, 2020 – 19:00 Tehran Time

اتاق سمینار مجازی –Virtual Seminar Room

https://vclass.ecourse.sharif.edu/ch/cosmology

گزینه ورود به صورت مهمان – Enter as a Guest

Loop quantum gravity and black hole interior

سعید راستگو

Saeed Rastgoo

Department of Physics and Astronomy, University of York

Abstract: Loop Quantum Gravity (LQG) is one of the few main top-down approaches to the quantization of spacetime that originated from the gravitation community.  It has various predictions regarding quantum cosmology and quantum black holes. This talk is divided into two parts. In the first part I will briefly explain what  LQG is all about and what are its main general predictions. In the second part, I will concentrate on black holes and sketch how this theory quantizes the interior of the Schwarzschild black hole and predicts the resolution of its classical singularity and a bounce to a white hole.

یکشنبه 19 مرداد 1399، ساعت 19:00

Sunday 9 August, 2020 – 19:00 Tehran Time

اتاق سمینار مجازی –Virtual Seminar Room

https://vclass.ecourse.sharif.edu/ch/cosmology

گزینه ورود به صورت مهمان – Enter as a Guest

Late time universe as a probe of cosmic origins

آزاده مرادی نژاد دیزگاه

Azadeh Moradinezhad Dizgah

Department of theoretical physics, University of Geneva

**لطفا  به ساعت نامتعارف سمینار توجه فرمایید** 

Abstract: The non-Gaussianity of the initial conditions leaves its imprints on the large scale structure. While the upcoming galaxy surveys will provide data with an unprecedented volume and precision, a novel observational technique referred to as line intensity mapping is also attracting significant amount of attention, given its unique potential to probe the universe at the range of scales and redshifts not accessible to galaxy surveys. In this talk, I will discuss a few different aspects of using these two observational windows to constrain primordial non-Gaussianity. In particular, I’ll discuss (a) the prospects of intensity mapping with CO and [CII] emission lines and its synergies with galaxy surveys, (b) the impact of modes larger than the size of a given survey on the measurement of clustering statistics within the survey, (c) the optimal estimators to extract information from clustering bispectrum.

یکشنبه 12 مرداد 1399، ساعت 19:00

Sunday 2 August, 2020 – 19:00 Tehran Time

اتاق سمینار مجازی –Virtual Seminar Room

https://vclass.ecourse.sharif.edu/ch/cosmology

گزینه ورود به صورت مهمان – Enter as a Guest

The dark matter distribution from simulations and observations

نسیم بزرگنیا

Nassim Bozorgnia

Department of Physics and Astronomy University of York

**لطفا  به ساعت نامتعارف سمینار توجه فرمایید**

Abstract: High resolution cosmological simulations of galaxy formation are powerful tools, which provide important information on the properties of the dark matter halo. Combined with the information obtained from the second data release of the Gaia satellite, simulations can significantly improve our understanding of the dark matter distribution in the Solar neighborhood. Determining the local dark matter velocity distribution is crucial for the correct analysis and interpretation of data from dark matter direct detection experiments. I will discuss the local dark matter distribution of Milky Way-like galaxies extracted from state-of-the-art hydrodynamic simulations, and present an analysis of direct detection data using this distribution. I will also discuss the properties of the dark matter component of the radially anisotropic stellar population recently discovered in the Gaia data, using the Auriga simulations. In particular, I will present the local dark matter density and velocity distributions of the simulated Milky Way-like galaxies with and without the anisotropic substructure, and discuss their implications for dark matter direct detection.

یکشنبه 5 مرداد 1399، ساعت 19:00

Sunday 26 July, 2020 – 19:00 Tehran Time

اتاق سمینار مجازی –Virtual Seminar Room

https://vclass.ecourse.sharif.edu/ch/cosmology

گزینه ورود به صورت مهمان – Enter as a Guest

کارگاه مجازی تارکیهان و شبیه‌سازی‌های کیهانی

دکتر علی اکبر ابوالحسنی
دکتر شانت باغرام
محمد انصاری فرد
احسان ابراهیمان
حامد منوچهری
سینا هوشنگی
سینا تاملی
زهرا باغخانی
لعیا قدسی

زمان : پنج‌شنبه  ۲ مرداد ماه ۱۳۹۹
https://vclass.ecourse.sharif.edu/ch/cosmology 

در خواست جهت ثبت نام در کارگاه و اطلاعات بیشتر:

m.ansari1373=AT=gmail.com

برنامه کارگاه

چکیده سخنرانی‌ها

Gravitational microlensing and pulsing stars

صدیقه سجادیان

Sedighe Sajadian

Department of physics, Isfahan University of Technology (IUT)

Abstract: Gravitational microlensing refers to the temporary enhancement in the stellar brightness due to the gravitational effect of a collinear massive object. In this talk, I will explain the microlensing of pulsing stars. Discerning and characterizing the properties of distant, faint pulsating stars are achievable through high-cadence microlensing observations. Mutually, combining stellar variability period with microlensing gives the source distance, type, and radius and helps better determine the lens parameters. For radial pulsing stars, considering periodically variations in their radius and surface temperature, their microlensing light curves are resulted from multiplication of the magnification factor with variable finite size effect by the intrinsic brightness curves of the pulsing source. Whereas, for non-radial pulsing stars, the light curve is not a simple multiplication of the magnification curve and the interstice luminosity curve of the source star, unless the effect of finite source size can be ignored. Other properties of microlensing light curves from pulsing stars will be discussed in the talk.

یکشنبه 29 تیر 1399، ساعت 17:00

Sunday 19 July, 2020 – 17:00 Tehran Time

اتاق سمینار مجازی –Virtual Seminar Room

https://vclass.ecourse.sharif.edu/ch/cosmology

گزینه ورود به صورت مهمان – Enter as a Guest

From de Sitter to Planck: Searches for new physics with Stage IV cosmological surveys

یاشار اکرمی

Yashar Akrami

International Center for Fundamental Physics,

 École Normale Supérieure (ENS), Paris, France

**لطفا  به ساعت نامتعارف سمینار توجه فرمایید**

Abstract: In the era of precision cosmology, various large-scale cosmological collaborations have been formed with the ambitious objective of mapping the entire observable Universe. Not only has this provided us with detailed understanding of the Universe and its evolution, but it has also made it possible to search for new physics beyond our standard models of particle physics and gravity. This new physics is expected to show up at extremely high energies (close to the Planck scale) and/or extremely low energies (the scale of vacuum energy today), the two ends of the spectrum that can be probed by cosmic evolution at earliest and latest times, respectively. Cosmological observations, therefore, have played and will continue to play essential roles in developing fundamental theories, in the quest for understanding the nature of fundamental interactions and answering basic questions about the structure of spacetime.  In this seminar, I will review some of these unsolved fundamental questions, and will explain how they are expected to be answered in the coming years using the wealth of cosmological data that will be provided by a large number of upcoming surveys across all wavelengths in combination with future theoretical developments in cosmology and high energy physics. I will focus on the synergistic science that will be provided by Stage IV cosmological surveys, in particular Euclid, LiteBIRD and the Square Kilometre Array (SKA). I will also introduce a powerful machinery based on advanced inference techniques and artificial intelligence that is currently being developed and is expected to significantly facilitate searches for new physics beyond the standard frameworks.

یکشنبه 22 تیر 1399، ساعت 17:00

Sunday 12 July, 2020 – 17:00 Tehran Time

  اتاق سمینار مجازی –Virtual Seminar Room

https://vclass.ecourse.sharif.edu/ch/cosmology

گزینه ورود به صورت مهمان – Enter as a Guest

**لطفا  به ساعت نامتعارف سمینار توجه فرمایید**

Dwarf galaxies and the small scale problems of the standard model of cosmology

آزاده فتاحی

Azadeh Fattahi

Institute for Computational Cosmology,

 Department of Physics, Durham University

Abstract: Despite its large success in explaining the large scale structure of the Universe, the standard model of cosmology (LCDM) has faced a number of challenges in explaining the observations of dwarf galaxies in the local universe. I will discuss the main problems and show how/whether these “small scale problems” are resolved in the state-of-the-art LCDM hydrodynamical simulations. I will particularly focus on the dark matter content of dwarfs galaxies, the too-big-to-fail and the core-cusp problem.

 یکشنبه 15 تیر 1399، ساعت 17:00

Sunday 5 July, 2020 – 17:00 Tehran Time

  اتاق سمینار مجازی –Virtual Seminar Room

https://vclass.ecourse.sharif.edu/ch/cosmology

گزینه ورود به صورت مهمان – Enter as a Guest

کیهان‌شناسی بدون زمان! 

صدرا جزایری

Sadra Jazayeri

Department of Applied Mathematics and Theoretical Physics, University of Cambridge

**لطفا  به ساعت نامتعارف سمینار توجه فرمایید**

چکیده: در کیهان شناسی مدرن در پی این هستیم، که از روی مشاهده‌ها الگوهایی که در افت و خیزهای اختلالات کیهان در جهان متاخر  می بینیم تصویری سازگار از گذشته کیهان، بالاخص از تاریخچه جهان اولیه در دوره تورم بیابیم. اما سوال این جاست که چه قوانینی به این الگوها-یا به طور معادل به تابع موج کیهان- در یک لحظه از زمان (به خصوص انتهای دوره تورم) حکمفرماست؟ قوانین مکانیک کوانتومی، مثل یکانیت، و تقارن‌های سیستم چطور روی تابع موج کیهان (روی مرز فضای دوسیته)  تجلی پیدا می‌کنند؟ سوال مشابهی در فیزیک ذرات بنیادی در آزمایش‌های پراکندگی ذرات (در فضای تخت) قابل طرح است: آیا بدون توجه به تحول یکانی سیستم در زمان می‌توان دامنه‌های پراکندگی درون-بیرون را به طور یکتا معین کرد؟ در فضای تخت، تقارن‌های پوانکاره به همراه اصول مکانیک کوانتومی (یکانیت)، موضعیت و نهایتا علیت ساختار نظریه‌های سازگار را بسیار مقید می‌کنند. به طور مثال تنها نظریه‌ی سازگار برای توصیف برهم‌کنش گرویتون (ذره اسپین دو بدون جرم) نظریه‌ی نسبیت عام اینشتین خواهد بود. این نوع نتایج از نقطه نگاه بوت‌استرپ (boostrap) با اعمال مستقیم تقارن‌های پوانکاره، یکانیت، موضعیت و علیت بر دامنه‌های پراکندگی به دست می‌آیند-با توسل حداقلی به مفاهیمی چون لاگرانژی و نمودا‌ر‌های فاینمن. اخیرا برنامه‌ی بوت‌استرپ برای محاسبه‌ی توابع همبستگی (یا تابع موج کیهان) در کیهان‌شناسی با انگیزه‌های مشابهی دنبال شده که در این ارائه به طور خلاصه مرور می‌شود. در ادامه با صرف نظر از تقارن خیز در فضای دوسیته، تعدادی از توابع همبستگی در قالب نظریه میدان موثر تورمی با میدان‌های اضافی ارائه می‌گردد. در ادامه در راستای یافتن ردپای یکانیت بر روی تابع موج کیهان، قضیه‌ای شبیه قضیه‌ی اپتیکی در فضای تخت برای توابع همبستگی روی مرز فضای دوسیته به دست می‌آید و نتایج این قضیه برای برنامه‌ی بوت‌استرپ بررسی می‌شود.

یکشنبه 8  تیر 1399، ساعت 17:00

Sunday 28 June, 2020 – 17:00 Tehran Time

  اتاق سمینار مجازی –Virtual Seminar Room

https://vclass.ecourse.sharif.edu/ch/cosmology

گزینه ورود به صورت مهمان – Enter as a Guest