Seminários do Cosmo-ufes
Palestrante: Federico Scali
Título: A constructive approach to modified gravity
Resumo: The search of a fundamental explanation for the currently observed accelerated expansion of the universe is one of the greatest challenges in contemporary cosmology. The situation is worsened by the elusive nature of the dark energy and the spectacular failure of its most natural explanation as the vacuum energy of the quantum fields [1]. In this scenario, a promising avenue to move beyond the Λ-CDM is to modify or extend general relativity (GR) in such a way that the acceleration results from the large scale gravitational interaction of the known matter components. This is a non-trivial step because GR is extremely well tested at Solar-System scales.
In this talk, a novel constructive approach to f(R) gravity is presented [2]. A new family of
asymptotically Schwarzschild solutions is built inductively from solar system physics, and the
corresponding class of f(R) gravitational Lagrangians is reconstructed a posteriori. The latter
depends on a fundamental length scale which is fixed by the classical tests of the Solar System.
The applications of the model to galactic dynamics and cosmology are discussed eventually.
In passing, some formal aspects concerning the stationary action principle in f(R) gravity
are addressed [3]. Novel and more general boundary conditions are introduced – with respect to
known literature – which lead to a well posed action principle, and the corresponding Gibbons-
Hawking-York (GHY) boundary terms are computed. On the larger space of solutions allowed
by the new conditions, it is argued how the natural correspondence between f(R) gravity and
scalar-tensor theory ceases to hold. The Einstein frame mapping and the application of the new
GHY terms to black-hole thermodynamics are also discussed.
