**Collection Number**S004

**Collection Type**Series

## Formation and evolution of dark matter substructure: Semi-analytic approach

Although cold dark matter (CDM) has been established, this is only the case for measurements at large scales, which are larger than galaxy-sized structures. Even though we need to understand the important role of baryonic components, matter distribution at small scales can be the key to distinguishing different particle dark matter candidates. In fact, warm dark matter, self-interacting dark matter, and fuzzy dark matter have been proposed, yielding different matter distributions at sub-galactic scales. These small-scale distributions have been studied with numerical simulations.

## Physical modelling of patchy reionization

The epoch of cosmic reionization can be probed using the secondary anisotropies imprinted on the cosmic microwave background (CMB) temperature and polarization field. I will discuss the imprints of patchy reionization on the kSZ power spectrum and CMB B-mode polarization. I will introduce two new scaling relations to connect the kSZ and secondary B-mode power spectrum with the physics of reionization.

## Improved constraint on primordial gravitational waves with delensing

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

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.

## The problem of time meets the problem of constants: could Quantum Cosmology be happening now?

Abstract: TBD

## 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

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

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

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

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.