Gravitational induced particle production in modified gravity

Tese de mestrado, Física (Física Nuclear e Partículas), 2023, Universidade de Lisboa, Faculdade de Ciências ; In this thesis, we investigate the possibility of gravitationally generated particle production in modified gravity. To accomplish this objective, we consider the equivalent scalar-tensor representation of f(R,T) gravity, a modified theory of gravity in which the matter energy-momentum tensor may not be conserved due to a non-minimal curvature-matter coupling. By recurring to the formalism of irreversible thermodynamics of open systems, such non-conservation can be interpreted as an irreversible flow of energy from the gravitational sector to the matter sector, which, in particular, could result in particle creation. Hence, we explore the physical and cosmological consequences of this feature by using the referred formalism. Subsequently, we obtain and discuss the expressions for the particle creation rate, the creation pressure, and the entropy and temperature evolutions. Applied together with the modified field equations of scalar-tensor f(R,T) gravity, the thermodynamics of open systems lead to a generalization of the standard ΛCDM cosmological paradigm, in which the particle creation rate and pressure are considered effectively as components of the cosmological fluid energy-momentum tensor. Furthermore, we also consider specific functional models and compare the scalar-tensor f(R,T) cosmology with the ΛCDM scenario and the observational data for the Hubble function. The properties of the particle creation rate through gravitational matter production are further investigated in both the low and high redshift limits.