# Astroparticles & Cosmology

## Oriol Pujolàs

## The Astroparticles and Cosmology group studies on the cosmology-particle physics interplay, such as extracting information on the nature of the fundamental interactions from astrophysical and cosmological environments. This is a valuable and complementary approach because cosmological and astrophysical systems probe conditions that are very difficult to reproduce in the laboratory. We are interested in: axion physics, phase transitions in the early universe, dark matter, dark energy, neutrinos (atmospherical and solar) and modifications of gravity. Additionally, we are interested in using particle physics techniques for condensed matter problems.

## Introduction

Astroparticle physics and particle cosmology are recent fields of research at the intersection between particle physics, astrophysics, and cosmology. The main research goal is to exploit our knowledge of astrophysical and cosmological phenomena to answer fundamental physics questions. The main research lines in this area include early universe cosmology, dark matter, axion-like particles, dark matter, gravitation and the application of the AdS/CFT correspondence to condensed matter systems.

During 2018, the work done by the members of the Theory Division in this research area concern early universe cosmology, the role of black holes as dark matter, and the application of the AdS/CFT and Effective Field Theory methods for solid state physics. Among these works, we highlight the following.

## Applications to Condensed Matter

In collaboration with M. Ammon (Jena U, Germany) A. Jimenez-Alba (Jena U, Germany), L. Alberte (ICTP Trieste, Italy) and M. Baggioli (Crete U., Greece), O. Pujolas showed that the holographic models of solids (with a finite static shear modulus and propagating transverse phonons) accommodate for an explicit breaking of translations, and showed that its effect is to give the phonons a mass term in a fashion very similar to how the quark masses give the pions a mass. Moreover, we showed that the phonon mass obeys a Gell-Mann-Oakes-Renner-like relation. This opens a new approach to understand the effects of disorder on the phonons in solids.

In collaboration with L. Alberte (ICTP, Trieste) and M. Baggioli (Crete U.), PhD student Victor Cancer-Castillo and O. Pujolas have studied how the Effective Field Theory methods can be used to study consistently the nonlinear elastic response of materials, and in particular to obtain universal bounds on the elasticity (the degree of reversible deformation) attainable by materials.