Cosmology News & Events

Abstract: In this talk, I will first discuss the challenges one faces when trying to explain the observed late-time acceleration of our Universe, due to the obstacles which the yet unkown physics of dark energy and dark matter place when we try to understand the true theory of gravity at large scales. In this context, I will further explain how model-independent observables have the potential to reveal whether gravity is truly modified at large scales, and will describe a fundamental, underlying relation between large-scale modifications of gravity and the (non-trivial) propagation of gravitational waves, as well as its observational implications for cosmology and astrophysics.

Abstract: Inflationary cosmology is the most successful explanation of the large scale features of our universe, such as the uniform tempertaure distribution of the Cosmic microwave background radiation (CMB) and the near flat global geometry of the universe. Satellite based measurements of the CMB in the past 2 decades by COBE, WMAP, and Planck have shown the predictions of inflation to be consistent with data. The most recent of these, the Planck Satellite, has provided the most precise measurement of the CMB ever and offers the best possibility to learn details about the dynamics during the early universe. I will first explain what sort of information can be obtained from measuring the CMB for understanding large scale structure and then review the results of measurement of the CMB made by these satellite experiments. Included in this discussion will be a summary on polarization and non-gaussianity measurements. I will then discuss the two dynamical descriptions of inflation, warm and cold, and present various models in both cases and their predictions for the CMB. I will then discuss how well CMB data has been able to discriminate between the different inflation models.

Abstract: The amplitude of primordial curvature perturbations is enhanced when a radiation bath at a temperature T>H is sustained during inflation by dissipative particle production, which is particularly significant when a non-trivial statistical ensemble of inflaton fluctuations is also maintained. This can be achieved during warm inflation, where the interactions of the inflaton field with other light degrees of freedom give rise to dissipative processes. We will review in this talk the basic of warm inflation, and how dissipation and viscous effects affect the spectrum of primordial fluctuations. Since gravitational modes are oblivious to dissipative dynamics, those generically lowers the tensor-to-scalar ratio and yields a modified consistency relation for warm inflation, as well as changing the tilt of the scalar spectrum. We show that this alters the landscape of observationally allowed inflationary models, with for example the quartic chaotic potential being in very good agreement with the Planck results for nearly-thermal inflaton fluctuations, whilst essentially ruled out for an underlying vacuum state.

Abstract: I will give an overview of the program to use AdS/CFT techniques to explore the classical and quantum dynamics near cosmological singularities.

Abstract: The recent discovery of the accelerated cosmic expansion suggests that our universe may be endowed with a positive cosmological constant Λ. In addition, even though general relativity (GR) is a very successful and well-tested theory, it could be that it is not the final theory of gravity. Brans-Dicke theory is the one of the first and simplest modifications of Einstein’s theory. In this seminar, I will present the study of cosmic structures in Brans-Dicke like scalar-tensor theories in the presence of a positive cosmological constant. I will discuss the validity of the no-hair theorem in the context of such theories. Moreover, I will show that, the black hole solutions in these theories are no different from those in GR and also that the presence of a stationary cosmological event horizon rules out any regular spherical stationary solution, appropriate for the description of a star.

link to paper