Modified Gravity in Cosmology and Astroparticle Physics
Details

Call:
PTCERN Call 2021/2

Academic Year:
2021

Domain:
Astroparticle Physics

Supervisor:
Francisco Lobo

CoSupervisor:
Pedro Avelino

Institution:
FCUL (Universidade de Lisboa)

Host Institution:
IA  Instituto de Astrofísica e Ciências do Espaço

Abstract:
General Relativity (GR) is facing many theoretical and experimental challenges and this might be indicative of a need for new gravitational physics. Renormalization approaches to GR clearly showed that counterterms must be introduced, which alter the theory significantly and transform the general relativistic second order field equations to higher order. This implies that extra degrees of freedom,besides the spintwo massless graviton, need to be introduced. In a more general approach, when one tries to explore gravity from the highenergy regime and obtain lowenergy physics, one does not recover GR. Adopting string theory as a full theory of quantum gravity, one gets a low energy limit that does not reproduce GR but instead provides a scalartensor theory of gravity. Indeed, dilaton fields and their couplings to the spacetime curvature are unavoidable features of string and scalartensor theories. It seems that attempts to fully quantize gravity introduce significant deviations from GR and extra degrees of freedom. In highenergy astroparticle physics, modified gravity could shed light on several outstanding problems, e.g. the nature of dark matter as its production in the early universe may give rise to a relic density of the same order of magnitude of the present dark matter density. Modified gravity theories and GR predict different thermal evolution of the universe. Fundamental issues in modified gravity, and particle physics, relate to the origin of the matterantimatter asymmetry and Leptogenesis. Other issues to be explored are mixing fields, vacuum fluctuations, neutrino oscillations, WIMPS, gravitational waves and the absolute value of the neutrino mass, which could be important tools to probe modified gravity. The ultimate goal of the proposed research program is to devise viable modified gravity models that pass local tests, explain the dynamics of the Universe and be consistent with constraints from highenergy astroparticle physics.