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

Improved constraint on primordial gravitational waves with delensing

Kimmy Wu Stanford University

Inflation generically predicts a background of primordial gravitational waves, which generate a primordial B-mode component in the polarization of the cosmic microwave background (CMB). The measurement of such a B-mode signature would lend significant support to the paradigm of inflation. Observed B modes also contain a component from the gravitational lensing of primordial E modes, which can obscure the measurement of the primordial B modes.

Precision cosmology with the next generation of CMB and optical surveys

Mathew Madhavacheril Perimeter Institute for Theoretical Physics

Ground-based cosmic microwave background (CMB) experiments are now pushing into discovery space where new insights on inflation, dark matter, dark energy and neutrino physics will be obtained by unraveling signatures buried beneath the primordial fluctuations. I will present new results from the Atacama Cosmology Telescope (ACT) that exemplify the power of high-resolution measurements of the microwave sky, including high-fidelity maps of dark matter through gravitational lensing.

Black hole archaeology with gravitational waves

The growing gravitational wave dataset makes black hole population studies possible. In this talk I will demonstrate how such studies can be used to study particle and nuclear physics. The key insight is that a wide range of initial stellar masses leave no compact remnant, due to the physics of pair-instability; the unpopulated space in the stellar graveyard is known as the black hole mass gap (BHMG). New physics can dramatically alter the late stages of stellar evolution and shift the BHMG, when it acts as an additional source of energy (loss) or modifies the equation of state.

Precision Cosmology from the Clustering of Galaxies

Marcel Schmittfull Institute for Advanced Study (IAS)

Large surveys of the positions of galaxies in the Universe are becoming increasingly powerful to shed light on some of the unsolved problems of cosmology, including the question of what caused the early Universe to expand. The analysis of the data is challenging, however, because the signal is small, the data is difficult to model, and its probability distribution is not fully known. I will present some recent ideas to approach these challenges.


Spinning black holes as cosmic string factories

Yuri Levin Columbia University

I will discuss what happens when a black hole captures a much larger in
size cosmic string loop. In some cosmological scenarios, such encounters
are not unlikely for supermassive black holes in galactic nuclei, and
for primordial black holes. The talk will feature some fun physics and
geometry: non-flat quadrilaterals, black-hole superradiance,
one-dimensional geometric flows, and persistent ultra-relativistic
gravitational-wave whips.

Insights into searches for the nanohertz gravitational-wave background with a Fisher analysis

Yacine Ali-Haimoud Johns Hopkins University

Within the next several years pulsar timing arrays (PTAs) are positioned to detect the stochastic gravitational-wave background (GWB) likely produced by the collection of inspiralling supermassive black holes binaries, and potentially constrain some exotic physics. Searches for a GWB in real PTA data rely on Markov-Chain Monte Carlo (MCMC) analyses, which are computationally demanding and not easily accessible to non-experts.

Uptunneling to de Sitter

Mehrdad Mirbabayi Institute for Advanced Study (IAS)

Motivated by the question of how inflation started, we propose a Euclidean preparation of an asymptotically AdS2 spacetime that contains an inflating dS2 bubble. The setup can be embedded in a four dimensional theory with a Minkowski vacuum and a false vacuum. AdS2 times 2-sphere approximate the near horizon geometry of a 4d near-extremal RN wormhole. Likewise, in the false vacuum the near-horizon geometry of a near-extremal black hole is approximately dS2 times 2-sphere.

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.