The Linear Point standard ruler for galaxy survey data: Reconstruction

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

?Is our Universe isotropic

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

A New Way to Measure Mass

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**

Understanding the dark Universe with observational cosmology

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

On the reliability of photometric and spectroscopic tracers of halo relaxation

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

Quantum Black Holes in the Sky

جاهد عابدی

Jahed Abedi

Max Planck Institute for Gravitational Physics (Albert Einstein Institute)

Abstract: Black Holes are possibly the most enigmatic objects in our Universe. From their detection in gravitational waves upon their mergers, to their snapshot eating at the centers of galaxies, black hole astrophysics has undergone an observational renaissance in the past 4 years. Nevertheless, they remain active playgrounds for strong gravity and quantum effects, where novel aspects of the elusive theory of quantum gravity may be hard at work. In this review article, we provide an overview of the strong motivations for why “Quantum Black Holes” may be radically different from their classical counterparts in Einstein’s General Relativity. We then discuss the observational signatures of quantum black holes, focusing on gravitational wave echoes as smoking guns for quantum horizons (or exotic compact objects), which have led to significant recent excitement and activity. We review the theoretical underpinning of gravitational wave echoes and critically examine the seemingly contradictory observational claims regarding their (non-)existence. Finally, we discuss the future theoretical and observational landscape for unraveling the “Quantum Black Holes in the Sky”.

یکشنبه 21 اردیبهشت 1399، ساعت 15:00

Sunday 10 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

Berkeley SETI  Seminar series

Searching ETI: possibility of follow-up observations of microlensing events with the radio telescopes

Sohrab Rahvar

Physics Department Sharif University of Technology

Abstract: In this talk, I will give a brief review of gravitational microlensing and history of detecting exoplanets with the microlensing method. Then, we discuss the theoretical basis of caustic crossing in the binary lenses. Assuming the extraterrestrial intelligence (ETI) uses the same radio stations on his/her planet as we have on the Earth, we study the possibility of follow-up microlensing observation as the natural amplifiers to magnify the radio signals from the ETIs. We investigate wave optics effects in the magnification factor for the radio waves. Finally, we will discuss the feasibility of this observation with the present radio telescope surveys.

NOTE: Professor Sohrab Rahvar is invited by  the research center of “The Search for Extraterrestrial Intelligence (SETI) At UC Berkeley” for the seminar.

پنجشنبه 18 اردیبهشت 1399، ساعت 22:30

Thursday 7  May, 2020 – 22:30 Tehran Time

  اتاق سمینار مجازی –Virtual Seminar Room

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

گزینه ورود به صورت مهمان – Enter as a Guest

Cuscuton Bounce

غزال گشنیزجانی

Ghazal Geshnizjani

Department of Applied Mathematics,

Waterloo Centre for Astrophysics University of Waterloo

Affiliate and PSI Fellow, Perimeter Institute for Theoretical Physics

**لطفا  به ساعت نامتعارف سمینار توجه فرمایید**

Abstract: In general relativity producing a regular bounce entails violation of Null Energy Condition for a dynamical source in the model. That generically indicates the existence of ghosts or other instabilities. However, in cuscuton modification of gravity, the correspondence between a background bounce and violation of Null Energy Condition for dynamical sources is broken. Cuscuton action modifies equations of motion in InfraRed limit allowing the background to go through a regular bounce phase. At the same time, since it does not contain any dynamical degrees of freedom, it does not lead to ghosts or other instabilities. Here, I present a toy scenario of a regular bouncing cosmology and prove this claim.

یکشنبه 7 اردیبهشت 1399، ساعت 17:00

Sunday 26 April, 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

H_0 Tension: New Physics vs Systematics

آرمان شفیعلو

Arman Shafieloo

Faculty of Theoretical Astrophysics, Cosmology Group

Korea Astronomy and Space Science Institute [KASI]

یکشنبه 31 فروردین 1399، ساعت 15:00

  اتاق سمینار مجازی

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

Primordial Black Holes

انسیه عرفانی (دانشکده فیزیک – دانشگاه تحصیلات تکمیلی زنجان )

Abstract: With the discovery of gravitational waves (GW) from merging pairs of massive black holes, the interest in the question of whether Primordial Black Holes (PBHs) could constitute the Dark Matter (DM) has been revived. In this talk, I will review the different mechanisms for (DM) PBHs formation with a special focus on inflation which can source the required large density fluctuations for PBHs formation. I will explain in detail the possibility of PBHs as a candidate for DM. I will review the cosmological constraints on the abundance of PBHs after the discovery of GWs and the ways to distinguish PBHs from astronomical BHs.

یکشنبه 24 فروردین 1399، ساعت 15:00

  اتاق سمینار مجازی

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

گزینه ورود به صورت مهمان