Effective field theories and Cosmology

Cosmology represents a very interesting and wide research field. The standard cosmological model is in agreement with most of our observations at a high level of accuracy. However, some important questions are still to be answered. The Dark matter and the Baryon Asymmetry in the Universe represent two of the main open problems. The connection between Cosmology and Particle Physics plays an important role for the fundamental comprehension of Dark Matter and Baryogenesis as well. Different models have been proposed to solve these compelling open issues. The common feature of most of them is the following: the particle production, either Dark Matter or heavy particles relevant for the Baryogenesis, might have occurred in a high temperature and density environment, namely our Universe in its early stage. Hence a combination of Cosmology, Particle Physics and Statistical Physics techniques is needed. At T30f, building on QCD thermal field theory methods, we define and apply effective field theories (EFTs) which are useful to make systematic and accurate computations in the case a hierarchy of scales appears in the problem.

Baryogenesis via Leptogenesis represents an elegant way to explain the observed Baryon Asymmetry in the Universe. Very accurate measurements of the Cosmic Microwave Background provides the experimental evidences to be understood within some theoretical models. In most of the Leptogenesis scenarios, heavy right-handed Majorana neutrinos produce an imbalance between leptons and anti-leptons in their decays, violating the CP symmetry. Later on such lepton asymmetry is partially converted in a baryon asymmetry via the sphaleron process already present in the standard model of Particle Physics. It is expected the generation of the baryon asymmetry to take place when the heavy Majorana neutrinos are non-relativistic. In this situation a hierarchy of scales appears that may be exploited by using EFTs techniques to obtain accurate predictions for particle dynamics in medium, such as neutrino production rate and lepton asymmetry generation.

The Dark Matter existence is inferred by many astrophysical and cosmological observations. It has to be non baryonic and does not interact with light. However, no direct detection for Dark Matter has been successful so far, neither at big accelerator facilities nor in underground laboratories. From the Particle Physics point of view it is necessary to provide an identikit of this elusive and weakly interacting particle to help the experimental searches. Being the Dark Matter necessary for baryonic matter clumping and galaxies formation, it is likely produced in the early stages of the Universe evolution. In our group we aim to address and explore the thermal production of Dark Matter in a hot and dense medium by using EFT techniques.

Written by S. Biondini.

People

Nora Brambilla, Antonio Vairo, Simone Biondini

Some related publications

S. Biondini, N. Brambilla, M. A. Escobedo and A. Vairo,
An effective field theory for non-relativistic Majorana neutrinos,
JHEP 1312 (2013) 028
[arXiv:1307.7680].