Stability of a class of scalar-tensor theories in the reheating period

• Grant number: 16/23655-0
• Support Opportunities: Research Grants - Visiting Researcher Grant - International
• Start date: March 04, 2017
• End date: March 31, 2017
• Field of knowledge: Physical Sciences and Mathematics - Physics - Elementary Particle Physics and Fields
• Principal Investigator: Elcio Abdalla
• Grantee: Elcio Abdalla
• Visiting researcher: Eleftherios Papantonopoulos
• Visiting researcher institution: National and Kapodistrian University of Athens, Greece
• Host Institution: Instituto de Física (IF). Universidade de São Paulo (USP). São Paulo , SP, Brazil
• Associated research grant: 11/18729-1 - Gravitation and cosmology: structural questions and applications, AP.TEM

Abstract

The present project aims to nd possible sources of instabilities in theories with non-minimal derivative couplings (NMDC), that can give us a new insight of inationary models. Scalar-tensor theories are non-trivial extensions of the Einstein gravity giving interesting modications to the standard theory in both small and large distances. We will consider a gravity theory which includes a term of a direct coupling of a scalar eld to Einstein tensor, belonging to the general class of Horndeski theories. This derivative coupling of the scalar eld to Einstein tensor introduces a new scale Ü M in the theory which has interesting implications on short distances for black hole physics and on large distances for ination. We are interested on large distance modications and it can be inferred that the reheating period may dierentiate the predictions of cosmological models with NMDC compared to models with the canonical coupling. It is crucial, however, that any model of scalar-tensor theories does not suer from instabilities. In this proposal we intend to study in detail a possible source of instabilities in theories with NMDC, i.e., the oscillating behavior between positive and negative values of the sound speed squared. (AU)