This series consists of talks in the areas of Cosmology, Gravitation and Particle Physics.
In this talk, I will review the main ideas underlying stochastic inflation, by introducing the formalism in two independent ways. First I will start from the intuitive picture stemming from the equations of motion of the system. I will then introduce a more rigorous approach based on the in-in formalism, and show how the usual set of Langevin equations can emerge from a path integral formulation. With this understanding, I will then formulate a new, recursive method which allows to solve consistently both in slow-roll parameters and in quantum corrections.
We propose a new way to search for (hidden) cool molecular hydrogen H2 in the Galaxy through diffractive and refractive effects: Stars twinkle because their light crosses the atmosphere. The same phenomenon is expected on a longer time scale when the light of a remote star crosses an interstellar turbulent molecular cloud, but it has never been observed at optical wavelengths.
Forthcoming 21cm intensity mapping surveys on the Square Kilometre Array (SKA) will be capable of probing unprecedentedly large volumes of the Universe. This will make it possible to detect effects beyond the matter-radiation equality peak in the power spectrum, including primordial non-Gaussianity, GR corrections, and possible signatures of modified gravity. I give an overview of the proposed SKA intensity mapping surveys, the science that they will be able to do, and some of the challenges that they face.
According to the Newtonian intuition, a constant gravitational field has no physical effect on a system since it can always be redefined, and a homogeneous gradient of the gravitational field (i.e. a homogeneous gravitational force) is equivalent to an accelerated reference frame. I will show how to extend this intuition to cosmological scales; in the presence of a single clock a constant curvature perturbation and its gradient can be set to zero through a coordinate transformation.
Velocity fields are a powerful probe of structure formation and the energy content of our Universe. Additionally, the motion of ionized gas on intermediate scales can be used to measure the clustering of baryons and shed light on galaxy formation and feedback mechanisms. I will discuss techniques that can be used to both constrain cosmology and measure baryon properties. I will also present some preliminary results.
A modified gravity (MOG) theory is explored that can explain current observational data in the present universe without detectable dark matter. This data includes galaxy rotation curves, cluster dynamics, gravitational lensing, globular clusters, the Bullet Cluster and solar system experiments. A vector field in the MOG action is a hidden, dark and massive photon that acts as a collisionless particle in the early universe and explains structure growth.
We are investigating modifications of general relativity that are operative at the largest observable scales. In this context, we are investigating the model of brane induced gravity in 6D, a higher dimensional generalization of the DGP model. As opposed to different claims in the literature, we have proven the quantum stability of the theory in a weakly coupling regime on a Minkowski background. In particular, we have shown that the Hamiltonian of the linear theory is bounded from below.
Quasars are highly biased tracers of the large-scale structure and therefore powerful probes of the initial conditions and the evolution of the universe. However, current spectroscopic catalogues are relatively small for studying the clustering of quasars on large-scales and over extended redshift ranges. Hence one must resort to photometric catalogues, which include large numbers of quasars identified using imaging data but suffer from significant stellar contamination and systematic uncertainties.
Cosmological perturbations are sourced by quantum fluctuations of the vacuum during inflation. In contrast, our observations of the Cosmic Microwave Background are classical. Can we test for the quantum origins of the perturbations? How much quantum information is lost when we make these observations? Have we totally screwed up by building PLANCK, and measured the correlations in the wrong basis and hence losing the primordial quantum information for good? I will talk about all these!