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:
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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
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**
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
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
فرنیک نیک اختر
Farnik Nikakhtar
Department of Physics and Astronomy University of Pennsylvania
**لطفا به ساعت نامتعارف سمینار توجه فرمایید**
Abstract: The baryon acoustic oscillation feature can be used as a standard cosmological ruler. In practice, for sub-percent level accuracy on the distance scale, it must be standardized. The physical reason why is understood, so we use this to develop an algorithm that improves the estimated scale. Tests of the method in numerical simulations show that it delivers the sub percent precision that is needed if future datasets are to deliver unbiased constraints from observations of tracers whose bias may be scale-dependent. Our algorithm provides a simple and fast reconstruction of the full shape of the BAO feature, as well as sub percent precision reconstruction of the linear point in the correlation function of biased tracers.
یکشنبه 1 تیر 1399، ساعت 17:00
Sunday 21 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
رویا مهیایی
Roya Mohayaee
Sorbonne Universites, UPMC Universite Paris 06, CNRS,
Institut d’Astrophysique de Paris, France
**لطفا به ساعت و مکان نامتعارف سمینار توجه فرمایید**
Abstract: The cosmic microwave background provides strong evidence for the global isotropy of the Universe. On the other hand, its dipole implies that locally our Universe is highly anisotropic. A cross-over to isotropy is expected within the standard model of cosmology. However, observational data seem to suggest that the scale of such cross-over is larger than that predicted by the model. I shall discuss the question of isotropy by using the observational data from SNe Ia surveys, the space-based infrared WISE survey, and at higher redshift through radio galaxies. The isotropy is studied through bulk flow measurements and also by measuring the effects of aberration and Doppler boosting. I shall then discuss results from numerical N-body simulation to show in better detail the theoretical expectation and highlight the discrepancies between the theory and the observations, and the implications for LCDM.
یکشنبه 25 خرداد 1399، ساعت 13:30
Sunday 14 June, 2020 – 13:30 Tehran Time
اتاق سمینار مجازی –Virtual Seminar Room
https://vclass.ecourse.sharif.edu/ch/langari
گزینه ورود به صورت مهمان – Enter as a Guest
نیایش افشردی
Niayesh Afshordi
Department of Physics and Astronomy, University of Waterloo
Waterloo Centre for Astrophysics, University of Waterloo
Perimeter Institute of Theoretical Physics
Abstract: I will introduce a novel way to measure mass in Astronomy, based on maximizing clustering in the space of the integrals of motion. This novel method is now made possible using Gaia observations of stars in our galaxy, and I will present its first application of this method to constrain the Galactic potential: https://arxiv.org/abs/1908.02336
یکشنبه 18 خرداد 1399، ساعت 17:00
Sunday 7 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
**لطفا به ساعت نامتعارف سمینار توجه فرمایید**
ماریکا عسگری
Marika Asgari
Institute for Astronomy, University of Edinburgh
Abstract: Cosmology is a new and fast growing field, owing this growth to both new technology and statistical methods in imaging and data processing. It is believed that we can explain the cosmology of the entire Universe using a handful of parameters through the standard cosmological model. This model has been very successful in predicting the distribution of galaxies and matter, as well as very early measurements of cosmic microwave background radiation. As the volume of data is growing we are starting to see cracks in this simple picture of the Universe, through tensions between the results of different observational analyses. In this talk I will focus on the analysis of the data from the kilo degree survey (KiDS). KiDS is a purpose-built gravitational lensing survey with high quality images and a wide photometric coverage, resulting in very high fidelity data. This dataset, therefore, provides an excellent playground where we can test our methods in preparation for future weak lensing surveys. Already the first 450 degrees of the KiDS data shows a mild tension with CMB results from the Planck satellite, which has sparked both skepticism and excitement within the community. I will go through the systematics that can affect the results and methods to mitigate them. I will also show results from the combination of KiDS and the dark energy survey (DES). Combining probes of cosmology can break degeneracies in the parameter space, resulting in tighter constraints. I will finally show results for the combination of KiDS with spectroscopic galaxy surveys.
یکشنبه 11 خرداد 1399، ساعت 17:00
Sunday 31 May, 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
محمد حسین ژولیده حقیقی
Mohammad Hossein Zhoolideh Haghighi
School of Astronomy – Institute for Research in Fundamental Sciences (IPM)
Abstract: Characterizing the relaxation state of galaxy systems is a necessary step for probing the role of environment and halo dynamics in the evolution of galaxies. In this presentation, we will provide an assessment of the reliability of both the photometric and spectroscopic probes. We quantify the correlations between the halo relaxation or the dynamical age, which is defined based on the halo mass assembly in the cosmological simulations, with two spectroscopic indicators, namely the Anderson Darling statistic of the galaxy velocity distribution, A2, and the velocity-segregation, ∆V. We also talk about the correlation of the halo relaxation with photometric indicators, which are, primarily, the luminosity gap between the two most luminous galaxies within half the virial radius of a group, complemented with the off-set between brightest group galaxies and the luminosity centroid. We will explain how a combination of ∆m12 and off-set, correlates more strongly with the dynamical age of the halo than the A2, thus offering a reliable yet fast and economical method of quantifying the relaxation of galaxy systems.
یکشنبه 28 اردیبهشت 1399، ساعت 15:00
Sunday 17 May, 2020 – 15:00 Tehran Time
اتاق سمینار مجازی –Virtual Seminar Room
https://vclass.ecourse.sharif.edu/ch/cosmology
گزینه ورود به صورت مهمان – Enter as a Guest