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

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

https://vc.sharif.edu/ch/cosmology

گزینه ورود به صورت مهمان – Enter as a Guest

افزودن به تقویم گوگل-Add to Google Calendar

Large-N Random Matrix Gravity and the Double Hierarchy Problem

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

https://vc.sharif.edu/ch/cosmology

گزینه ورود به صورت مهمان – Enter as a Guest

افزودن به تقویم گوگل-Add to Google Calendar

سمینار مشترک گروه فیزیک انرژی بالا و گروه کیهانشناسی

علی اشتری اصفهانی

KArlsruhe TRItium Neutrino Experiment *

و

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

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

گزینه ورود به صورت مهمان – Enter as a Guest

افزودن به تقویم گوگل-Add to Google Calendar

Dust and Interstellar Medium of Galaxies at High Redshifts

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

https://vc.sharif.edu/ch/cosmology

گزینه ورود به صورت مهمان – Enter as a Guest

افزودن به تقویم گوگل-Add to Google Calendar

Presentations from the Advance Cosmology Class

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

https://vc.sharif.edu/ch/cosmology

گزینه ورود به صورت مهمان – Enter as a Guest

افزودن به تقویم گوگل-Add to Google Calendar

Cosmology with the Secondary CMB

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

https://vc.sharif.edu/ch/cosmology

گزینه ورود به صورت مهمان – Enter as a Guest

افزودن به تقویم گوگل-Add to Google Calendar

Tossin’ and Turnin’ in the Landscape

Amjad Ashoorioon

School of Physics, Institute for Research in Fundamental Sciences (IPM)

Tossin’ and Turnin’ in the Landscape: Primordial Black Holes and Gravitational Waves

Abstract: The landscape of String Theory could not only contain a lot of metastable vacua, but also a lot of troughs connecting them. These troughs are separated by barriers. Primordial inflation could have happened through rolling on one of these troughs.  While rolling slowly on the false vacuum trough during inflation, bubbles of true vacuum nucleate. These bubbles can collapse to primordial black holes (PBHs) after the end of slow-roll inflation. With this picture in mind, we explicitly construct double-field inflationary models at relatively small energy scales, which realizes this picture and satisfies the latest Planck constraints at the scales that contribute to the cosmic microwave background (CMB). We will show that the shape of the mass distribution of the PBHs is dependent on how inflation ends and the Universe settles from the false trough to the true one. The end of inflation can also be probed by examining the gravitational waves spectrum, which could be generated from both a first or second-order phase transition during or after the end of slow-roll inflation. The spectra that these two ways of settling to the true vacuum leave behind, could be distinguished from the shape, and sometimes from the amplitude. In particular, we apply this framework to PBHs in the mass range, 10^{-17}–10^{-13} M_{\odot}, which can constitute the whole dark matter budget and identify a correlated SGWB signal within the DECIGO and BBO sensitivity bands. Alternatively trying to interpret the recently claimed NANOGrav 12.5 year signal within this framework, lead us to LIGO mass and heavier PBHs. We discover that in the latter case, only a first-order phase transition can generate a signal as strong as NANOGrav.

یکشنبه 24  بهمن 1400، ساعت 19:00

Sunday 13 February 2022 – 19:00 Tehran Time

اتاق سمینار مجازی –Virtual Seminar Room

https://vc.sharif.edu/ch/cosmology

گزینه ورود به صورت مهمان – Enter as a Guest

Probing The Universe with Gravitational Waves

Valeri Vardanyan

Kavli Institute for the Physics and Mathematics of the Universe (WPI),

UTIAS, The University of Tokyo, Japan

Probing The Universe with Gravitational Waves

Abstract: In this talk, I will summarize several recent results about gravitational wave cosmology in the context of dark energy and inflation. In the first part of the talk, I will concentrate on astrophysical gravitational waves and will argue that the spatial clustering of gravitational wave sources provides a wealth of invaluable information. I will present a new powerful method and will demonstrate its applications for testing dark energy models, and for identifying the potentially primordial origin of gravitational-wave black holes. In the second part of the talk, I will discuss gravitational waves produced during inflation and will revisit the implications of their possible near-future detection for inflationary models. I will particularly present a working proposal of resonant gravitational wave production during inflation due to non-linear effects and will discuss the implications for the well-known Lyth bound.

یکشنبه 17 بهمن 1400، ساعت 19:00

Sunday 6 February 2022 – 19:00 Tehran Time

اتاق سمینار مجازی –Virtual Seminar Room

https://vc.sharif.edu/ch/cosmology

گزینه ورود به صورت مهمان – Enter as a Guest

Testing Large-Scale Structure Measurements Against Fisher Matrix Predictions

Setareh Foroozan

Waterloo Centre for Astrophysics, University of Waterloo

Department of Physics and Astronomy, University of Waterloo

Testing Large-Scale Structure Measurements Against Fisher Matrix Predictions

Abstract: We compare Baryonic Acoustic Oscillation (BAO) and Redshift Space Distortion (RSD) measurements from recent galaxy surveys with their Fisher matrix based predictions. Measurements of the position of the BAO signal lead to constraints on the comoving angular diameter distance DM and the Hubble distance DH that agree well with their Fisher matrix based expectations.

However, RSD-based measurements of the growth rate fσ8 do not agree with the predictions made before the surveys were undertaken, even when repeating those predictions using the actual survey parameters. We show that this is due to a combination of effects including degeneracies with the geometric parameters DM and DH, and optimistic assumptions about the scale to which the linear signal can be extracted. We show that measurements using current data and large-scale modelling techniques extract an equivalent amount of signal to that in the linear regime for k ~< 0.08 h/Mpc, remarkably independent of the sample properties and redshifts covered.

یکشنبه 10 بهمن 1400، ساعت 19:00

Sunday 30 January 2022 – 19:00 Tehran Time

اتاق سمینار مجازی –Virtual Seminar Room

https://vc.sharif.edu/ch/cosmology

گزینه ورود به صورت مهمان – Enter as a Guest

افزودن به تقویم گوگل-Add to Google Calendar

Handling Observational Challenges in the era of Big Data Cosmology

Mehdi Rezaie

Department of Physics, Kansas State University

Handling Observational Challenges in the era of Big Data Cosmology

Abstract: During four distinct phases, the Sloan Digital Sky Survey (SDSS) collected images and spectra of thousands to millions of astronomical objects and created the largest three-dimensional map of the cosmic web to date. As part of SDSS-IV, the extended Baryon Oscillation Spectroscopic Survey (eBOSS) was the final galaxy redshift survey proposed to measure the expansion history and energy contents of the Universe. In this talk, I will present a careful assessment of observational challenges in the final sample of quasars from eBOSS. Then, I will briefly present accompanying studies using the same dataset for constraining the local-type primordial non-Gaussianity and for exploring the impact of observational effects on Baryon Acoustic Oscillations measurements. Finally, I conclude with my ongoing work within the Dark Energy Spectroscopic Instrument (DESI).

یکشنبه 3 بهمن 1400، ساعت 19:00

Sunday 23 January 2022 – 19:00 Tehran Time

اتاق سمینار مجازی –Virtual Seminar Room

https://vc.sharif.edu/ch/cosmology

گزینه ورود به صورت مهمان – Enter as a Guest