Cosmology News & Events

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

Abstract: I will discuss the relevance of the spins of massive black holes as probes of the coevolution of these objects with their host galaxies, as well as for the dynamics of binary systems and accretion disks, and for gravitational-wave emission. I will also present a semi-analytical model for the cosmological evolution of the spins of the massive black-hole population, and show that comparison of this model to existing spin measurements from relativistic iron lines allows one to put constraints on competing accretion scenarios. I will also comment on the prospects to test this model using future gravitational-wave space-based detectors.