This series consists of talks in the areas of Cosmology, Gravitation and Particle Physics.
The nature of dark matter is a fundamental problem in cosmology and particle physics. Many particle candidates have been devised over the course of the last decades, and are still at stake to be soon discovered or rejected. However, astronomical observations, in conjunction with the phenomenological efforts in astrophysical modeling, as well as in particle theories to explain them, have helped to pin down several key properties which any successful candidate has to have.
Fluctuations of the 21 cm brightness temperature before the formation of the first stars hold the promise of becoming a high-precision cosmological probe in the future. The growth of over densities is very well described by perturbation theory at that epoch and the signal can in principle be predicted to arbitrary accuracy for given cosmological parameters.
We observe a finite subvolume of the universe, so CMB and large scale structure data may give us either a representative or a biased sample of statistics in the larger universe. Mode coupling (non-Gaussianity) in the primordial perturbations can introduce a bias of parameters measured in any subvolume due to coupling to superhorizon background modes longer than the size of the subvolume. This leads to a "cosmic variance" of statistics on smaller scales, as the long-wavelength background modes vary around the global mean.
Systems in which the local gravitational attraction is coupled to the expansion of the Universe have been studied since the early stages of General Relativity as the pioneering works of McVittie show. In this talk I start reviewing the McVittie black hole solution and its variable mass generalization from a classical fluid approach to understand its properties. I then move to a field theoretical analysis to investigate the scalar theories that support such black holes.
The theory of eternal inflation in an inflaton potential with multiple vacua predicts that our universe is one of many bubble universes nucleating and growing inside an ever-expanding false vacuum. The collision of our bubble with another could provide an important observational signature to test this scenario. In this talk I will describe an algorithm for accurately computing the cosmological observables arising from bubble collisions directly from the Lagrangian of a single scalar field.
The large-scale structure of the universe suggests that the physics underlying its early evolution is scale-free. In this talk, using a hydrodynamic approach, I will discuss how the scale-free principle restores predictive power and makes it possible to evaluate inflationary models and to compare them with alternative cosmologies.
We study the dynamics of a 2+1 dimensional relativistic viscous conformal fluid in Minkowski spacetime. Such fluid solutions arise as duals, under the "gravity/fluid correspondence", to 3+1 dimensional asymptotically anti-de Sitter (AAdS) black brane solutions to the Einstein equation. We examine stability properties of shear flows, which correspond to hydrodynamic quasinormal modes of the black brane. We find that, for sufficiently high Reynolds number, the solution undergoes an inverse turbulent cascade to long wavelength modes.
Recently there has been a successful non-linear covariant ghost-free generalization of Fierz-Pauli massive gravity theory, the dRGT theory. I will explore the cosmology in the decoupling limit of this theory. Furthermore, I will construct a Proxy theory to dRGT from the decoupling limit and study the cosmology there as well and compare the results. Finally, I will discuss the quantum consistency of the theory.
Within the Minimal Supersymmetric Standard Model (MSSM), LHC bounds suggest that scalar superpartner masses are far above the electroweak scale. Given a high superpartner mass, nonthermal dark matter is a viable alternative to WIMP dark matter generated via freezeout. In the presence of moduli fields nonthermal dark matter production is associated with a long matter dominated phase, modifying the spectral index and primordial tensor amplitude relative to those in a thermalized primordial universe.