Collection Number S004
Collection Type Series
This series consists of talks in the area of Cosmology and Gravitation.

Constraining Early Dark Energy with Large Scale Structure

Evan McDonough University of Chicago

The Hubble tension is conventionally viewed as that between the cosmic microwave background (CMB) and the SH0ES measurement. A prominent proposal for a resolution of this discrepancy is to introduce a new component in the early universe, which initially acts as "early dark energy" (EDE), thus decreasing the physical size of the sound horizon imprinted in the CMB and increasing the inferred H_0, bringing it into near agreement with SH0ES.

Tackling the challenges of galaxy-dark matter connection modeling and new insights into secondary (assembly) biases

Sihan Yuan Harvard University

Modeling galaxy-dark matter connection is essential in deriving unbiased cosmological constraints from galaxy clustering observations. We show that a more physically motivated galaxy-dark matter incorporating secondary (assembly) biases results in more accurate predictions of galaxy clustering, yields novel insights into effects such as baryonic feedback, and significantly reduces the tension in galaxy lensing.

Stellar streams in the Gaia era

Vasily Belokurov University of Cambridge

Stellar streams are a powerful tool for mapping of the Galactic matter distribution. Thanks to Gaia we now have full 6D (complete phase-space) view of a quickly growing subset of the Milky Way streams. These stars are precious as they can shed light not only on the broad-brush structure of the Galaxy, but also reveal small time-evolving perturbations of the Galactic potential. I will use the Sagittarius and the Orphan streams to present the most recent measurements of the dark matter halo of the Milky Way and one of its sub-halos.

A 2020s Vision of CMB Lensing

Marius Millea University of California

With much of the cosmological information in the primary CMB having already been mined, the next decade of CMB observations will revolve around the secondary CMB lensing effect, which will touch nearly all aspects of observation in some way. At the same time, the increasingly low noise levels of these future observations will render existing "quadratic estimator" methods for analyzing CMB lensing obsolete. This leaves us in an exciting place where new methods need to be developed to fully take advantage of the upcoming generation of CMB data just on our doorstep.

Probing angular-dependent primordial non-Gaussianity from galaxy intrinsic alignments

Kazuyuki Akitsu Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU)

The primordial non-Gaussianity (PNG) is a key feature to screen various inflationary models and it is one of the main targets in the next generation galaxy surveys. In particular, the local-type of PNG makes the galaxy bias scale-dependent in large-scales, which is known as the scale-dependent bias, allowing to constrain the local-type PNG from galaxy surveys. In this talk, I will present the galaxy shape correlation, called the ``intrinsic alignment'', can explore the angular-dependent PNG.

Mapping the Cosmos Using Multi-Messenger Observations

Suvodip Mukherjee Institut d’Astrophysique de Paris

The discovery of astrophysical gravitational waves has opened a new avenue to explore the cosmos using transients. I will discuss a few new frontiers in the field of physical cosmology and fundamental physics that can be explored using gravitational waves from the current generation gravitational wave detectors such as LIGO/Virgo, and in the future from gravitational wave detectors such as LISA, Einstein Telescope, and Cosmic Explorer.

Cosmological tensions and how to ease them

Nils Schöneberg Rheinisch-Westfälische Technische Hochschule (RWTH Aachen University)

Tensions between measurements in the early and the late universe could be the first hint of new physics beyond the cosmological standard model. In particular, the clustering of large scale structure and the current value of the Hubble parameter show intriguing discrepancies between measurements in the early and late universe. In this talk, I review the most common ways of easing these two tensions and focus specifically on parameter extensions and various models of dark matter, such as warm dark matter, cannibalistic dark matter, dark matter interactions, and dark radiation.

Testing the standard cosmological model with the Dark Energy Survey

Jessica Muir University of Michigan

The Dark Energy Survey (DES) is a photometric galaxy survey which, using measurements of distortions to galaxy shapes from weak gravitational lensing and other observables, we can use to test the validity of our standard cosmological model, LambdaCDM. As an example of this, I will motivate and discuss a recent analysis of the DES Year 1 data (described in https://arxiv.org/abs/2010.05924) in which we use a "growth-geometry split" parameterization to check the consistency of constraints from structure growth and expansion history.

Torsion cosmology and beyond

William Barker Kavli Institute for Cosmology Cambridge

Torsion is a popular ingredient in gravity, yet fraught with quantum and classical pathologies. I develop a novel torsion theory, consistent with power-counting and unitarity. The Friedmann equations emerge (with dark energy and radiation), as do pp waves and the Schwarzschild vacuum, all without an Einstein-Hilbert term. I show that cosmology sees torsion as a non-canonical scalar, revealing a rich phenomenology of conformal or waterfall inflatons, and cuscutons. I finally argue that future work will be driven less by toy-models, and more by computer surveys.

Challenges for large-scale structure theory and data analysis

Mikhail Ivanov New York University (NYU)

In the first part of the talk I will review some recent progress in large-scale structure theory and show how it can be used to measure cosmological parameters from current and future redshift surveys. Then I will discuss some ongoing challenges in the modeling of galaxy clsutering data and covariance matrices. Finally, I will present a systematic calculation of the probability distribution function for the dark matter density field and discuss its potential as a cosmological probe.