گروه کیهان‌شناسی

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Ultralate transition of the strength of gravity as a resolution of the Hubble crisis

1 می 2022 Mojahed Parsi Mood دیدگاه‌تان را بنویسید:

Leandros Perivolaropoulos

Department of Physics, University of Ioannina, Greece

Ultralate transition of the strength of gravity as a resolution of the Hubble crisis: Observational hints and theoretical implications

Abstract: The 5σ mismatch of the measured value of the Hubble constant between observational probes calibrated at early times (sound horizon calibrated at z~1100) and late times (SnIa absolute magnitude calibrated at z<0.01) is currently the most significant challenge for the standard LCDM model. I discuss the potential of a sudden change of the strength of gravity occurring at some specific time during the last 150Myrs (z<0.01) to resolve this tension without affecting the other observational successes of the standard LCDM model. I also review the effects of such a transition on the growth rate of cosmological perturbations and show that the delay of this growth due to such a transition is consistent with indications for such a delayed growth coming from weak lensing and redshift space distortion cosmological observations. Finally, I discuss the consistency of such a transition with other astrophysical data including Tully-Fisher observations, galaxy survey data and solar system chronology. Theoretical models that are consistent with such a transition will also be discussed. Such models include an ultra-late decay of the false vacuum in the context of a scalar tensor modified gravity theory and a generalized symmetron screening mechanism based on an explicit symmetry breaking in addition to the standard spontaneous symmetry breaking mechanism.

یکشنبه 11 اردیبهشت 1401، ساعت 18:00

Sunday 1 May 2022 – 18:00 Tehran Time

اتاق سمینار مجازی –Virtual Seminar Room

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Statistics of the nearest neighbor and the cosmic web

24 آوریل 2022 Mojahed Parsi Mood دیدگاه‌تان را بنویسید:

Mohammad Ansari

Physics Department, Sharif University of Technology

Statistics of the nearest neighbor and the cosmic web

Abstract: The cosmic web is a rich source of information, which is appropriate to add a constraint on parameters of the standard model of cosmology or to study models beyond the standard model. On large scales, the two-point correlation function is a proper method to extract information. But in non-linear scales, the density field is non-Gaussian, so we need alternative approaches. In this presentation, we discuss these approaches. Specifically, we discuss the nearest neighbor statistics and show that one can study neutrino mass and fuzzy dark matter, using this method. Furthermore, we introduce the angle between nearest neighbors as a new probe for non-linear scales and the cosmic web.

یکشنبه 4 اردیبهشت 1401، ساعت 18:00

Sunday 24 April 2022 – 18:00 Tehran Time

اتاق سمینار مجازی –Virtual Seminar Room

گزینه ورود به صورت مهمان – Enter as a Guest

https://vc.sharif.edu/ch/physics-high-energy

سمینار مشترک گروه فیزیک انرژی بالا و گروه کیهانشناسی

18 آوریل 2022 Mojahed Parsi Mood دیدگاه‌تان را بنویسید:

Georges Obied

(Harvard University)

Inflation and light Dark Matter constraints from the Swampland

Abstracts: I will explore the interplay between Swampland conjectures and models of inflation and light Dark Matter. To that end, I will first review the weak gravity conjecture (WGC) and the related Festina Lente (FL) bound. These have implications for light darkly and milli-charged particles and can disfavor a large portion of parameter space. The FL bound also implies strong restrictions on the field content of our universe during inflation and presents an opportunity for inflationary model building. At the same time, it rules out some popular models like chromo-natural inflation and gauge-flation. Finally, I will review another Swampland conjecture related to Stückelberg photon masses and discuss its implications for astro-particle physics.

سه‌شنبه ۳۰ فروردین ۱۴۰۱، ساعت ۱۸

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A new picture of the cosmos: a two-sheeted, CPT-symmetric universe

16 آوریل 2022 Mojahed Parsi Mood دیدگاه‌تان را بنویسید:

Latham Boyle

Perimeter Institute for Theoretical Physics

A new picture of the cosmos: a two-sheeted, CPT-symmetric universe

Abstract: After reviewing some key hints and puzzles from the early universe, I will introduce recent work with Neil Turok suggesting a rigid and predictive new approach to addressing them.

Our universe seems to be dominated by radiation at early times, and positive vacuum energy at late times. Taking the symmetry and analyticity properties of such a universe seriously suggests a picture in which spacetime has two sheets, exchanged by a symmetry that, in turn, selects a preferred (CPT-symmetric) vacuum state for the quantum fields that live on the spacetime. In this picture, the Big Bang may be regarded as a kind of mirror.

I will explain how this line of thought suggests new explanations for a number of observed properties of the universe, including: its homogeneity, isotropy and flatness; the arrow of time; several properties of the primordial perturbations; the nature of dark matter (which, in this picture, is a right-handed neutrino, radiated from the Big Bang like Hawking radiation from a black hole); and even the existence of three generations of standard model fermions. I will also mention some observational predictions that will be tested in the coming decade, and some key open questions.

یکشنبه 28 فروردین 1401، ساعت 18:00

Sunday 17 April 2022 – 18:00 Tehran Time

اتاق سمینار مجازی –Virtual Seminar Room

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Large-N Random Matrix Gravity and the Double Hierarchy Problem

9 آوریل 2022 Mojahed Parsi Mood دیدگاه‌تان را بنویسید:

Nima Khosravi

Department of Physics, Shahid Beheshti University

Large-N Random Matrix Gravity and the Double Hierarchy Problem

Abstract: I will talk about my recent work 2004.01067 which is about connecting the electroweak hierarchy and the cosmological constant problem to each other. This happens as a result of thinking about the gravity sector including N randomly coupled massive gravitons. I also review some other byproducts of this model e.g. a chance to address the origin of dark matter.

یکشنبه 21 فروردین 1401، ساعت 18:00

Sunday 10 April 2022 – 18:00 Tehran Time

اتاق سمینار مجازی –Virtual Seminar Room

گزینه ورود به صورت مهمان – Enter as a Guest

https://vc.sharif.edu/ch/physics-high-energy

سمینار مشترک گروه فیزیک انرژی بالا و گروه کیهانشناسی

7 مارس 2022 Mojahed Parsi Mood ۳ دیدگاه

علی اشتری اصفهانی

KArlsruhe TRItium Neutrino Experiment *

محدثه خوش‌طینت

(دانشکده فیزیک دانشگاه صنعتی شریف)

The neutrino’s mass conundrum: Can cosmology resolve the mystery? **

*Abstract: Recently the KATRIN experiment made the cover of Nature physics by measuring the first sub-eV limit on the effective neutrino mass. In this talk, we first briefly present the neutrino mass question and the areas of physics in which we can search for an answer. Then we introduce the MAC-E filter technology used in the KATRIN experiment. Next, we explain the KATRIN beamline which includes the source, transport section, spectrometers, and detectors. Finally, the analysis method and the systematic effects of the recent result will be discussed.

**Abstract: After decoupling, neutrinos stream freely. But how? It depends on the mass Nature assigned to them. In this talk, we will follow the massive neutrinos timeline and explore the impacts their mass has on the evolution of the Universe, mainly on the Large Scale Structure (LSS). Then we will investigate what cosmological data sets could say about the neutrino’s properties, especially their mass. Inferring parameters from some of these data sets are straightforward – e.g., CMB-anisotropy, but the information in others needs to be deciphered – for example, the LSS data. Our journey will end with a summary of the methods used in the Cosmic Web Group to study the latter to find the neutrino’s footprint.

زمان: سه‌شنبه ۱۷ اسفند ۱۴۰۰، ساعت ۱۵

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Dust and Interstellar Medium of Galaxies at High Redshifts

4 مارس 2022 Mojahed Parsi Mood دیدگاه‌تان را بنویسید:

Irene Shivaei

Department of Astronomy and Steward Observatory at the University of Arizona

Dust and Interstellar Medium of Galaxies at High Redshifts

Abstract: Dust is one of the most mysterious components of galaxies. Although by mass it only represents ~1% of the interstellar medium, it has key roles in the physics and chemistry of the interstellar medium, has crucial roles in the star formation process, and hides a significant fraction of cosmic star formation across all redshifts. Despite its importance, our understanding of the properties of dust in galaxies at high redshifts is far from complete. In this talk, I will highlight our recent results using data from the Keck telescopes in Hawaii and the ALMA mm/submm array in Chile to set constraints on the dust attenuation and emission properties of galaxies at redshifts of z~1-3, the peak epoch of cosmic star formation activity known as Cosmic Noon. I will conclude the talk with a brief overview of the James Webb Space Telescope, its current state, and the revolutionary science that will be achieved by it in the near future, given its significantly higher sensitivity and resolution compared to those of its predecessors.

یکشنبه 15 اسفند 1400، ساعت 19:00

Sunday 6 March 2022 – 19:00 Tehran Time

اتاق سمینار مجازی –Virtual Seminar Room

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Presentations from the Advance Cosmology Class

27 فوریه 2022 Mojahed Parsi Mood ۲ دیدگاه

In this session, we will have five short presentations from the Advance Cosmology class held in Fall 2021 in the Physics Department of Sharif University.

Clustering of dark matter particles in stars

Hassan Khoshechin

Conformal Cyclic Cosmology

Masoud Molaei

Ultra slow-roll inflation and its consequences in PBHs

Amirhossein Samandar

Semiclassicality and decoherence of cosmological perturbations

Seyed Mohammad Javad Tabatabai

How does Gravitational Aether Theory, a solution to the Old Cosmological Constant problem, affect cosmological predictions?

Nooshin Torabi

یکشنبه 8 اسفند 1400، ساعت 19:00

Sunday 27 February 2022 – 19:00 Tehran Time

اتاق سمینار مجازی –Virtual Seminar Room

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Cosmology with the Secondary CMB

20 فوریه 2022 Mojahed Parsi Mood دیدگاه‌تان را بنویسید:

Matthew C. Johnson

Department of Physics and Astronomy, York University

Perimeter Institute for Theoretical Physics

Cosmology with the Secondary CMB

Abstract: Future CMB experiments will probe the high-resolution, low-noise frontier where secondary CMB anisotropies dominate the blackbody component of the observed temperature anisotropies. Secondary anisotropies arise due to the electromagnetic or gravitational scattering of CMB photons from structure, and encode a significant amount of astrophysical and cosmological information.

In this talk, I will illustrate how cosmological information is encoded in several CMB secondaries: the kinetic Sunyaev Zel’dovich effect, the moving lens effect, and the polarized Sunyaev Zel’dovich effect. I will outline how this information can be used to test early-Universe physics and the nature of gravity, and forecast constraints for upcoming surveys.

یکشنبه 1 اسفند 1400، ساعت 19:00

Sunday 20 February 2022 – 19:00 Tehran Time

اتاق سمینار مجازی –Virtual Seminar Room

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