HIP Theory Program: Cosmophysics

Motivation

Recent advances in observational astrophysics have transformed cosmology into a precision science. As a result, modern cosmology provides a useful testing ground for effective theories of particle physics and gravity and it may also be our best hope for testing the Fundamental Theory of nature. Modern cosmology still holds many challenges and unanswered questions including the nature of the dark energy, or the source of the apparent acceleration, what is the dark matter, when did inflation take place and what is inflaton in the field theory context and what is the origin of the matter-antimatter asymmetry.

Research Plan

The standard Lambda-CDM-model postulates an ad hoc dark energy fluid, a cosmological constant, to explain the apparent acclerated expansion. We are studying alternative explanations for the acceleration, including effects of inhomogeneities to the light propagation due to weak gravitational lensing, back reaction, ``swiss cheese" and Lemaitre-Tolman-Bondi models, and extensions of Einsteins gravity to scalar tensor models and f(R)-gravity theories. We are also considering bounds on these extensions from the precision measurements in the Solar system, and from the structure of compact stars. On the other hand, we are working on models with eternal inflation that may provide a natural explanation for the smallness of the actual cosmological constant.

A new class of "walking" technicolour models, are currently providing a viable alternative for supersymmetry, as they can explain both the hierarchy problem as well as for gauge coupling unification. They may also provide an explanation for the dark matter in the universe. We are currently working, in collaboration with the ``laws of nature and condensed particle matter phenomenology" group, on both the cosmological consequences as well as the collider phenomenology of a possible tecnicolour dark matter sector of the theory.

The most important element of the inflationary scenario is the formation of primordial perturbations. We investigate both the multi-field inflationary models and the curvaton as a mechansim for creating the inflationary perturbation spectrum, and in particular the nonlinearity parameters f_NL and g_NL. characterizing the nongaussian signatures of the perturbation. We also investigate the means to probe the curvaton potential and the equation of state of the background fluid using these parameteres. It is also possile that inflation may be associated with a relatively low energy phase transition involving supersymmetry. In this case the inflaton would be a gauge invariant combination of squark or slepton fields. We are continuing our work on a class of MSSM inflatory models originating from supergravity. Inflation will also be addressed in the stochastic formulation. Loop corrections to CMB correlators will be studied together with the infra-red properties of the non-linearity parameters.

Baryon asymmetry may have formed via CP-violating out-of-equilibrium interactions during the electroweak phase transition. We are focussing on developing quantum transport equations for baryogenesis including nonlocal quantum reflection effects. We are currently working to extend our recently developed quantum transport theory for temporally varying, but spatially homogeonous systems, to the stationary planar symmetric problems. These results will pave way for a later application to baryogenesis via chargino and neutralino interactions in the MSSM.