Modified Gravity

Modified gravity is one of the best frameworks that can alleviate cosmological tensions, due to the huge freedom one has to construct models. Gravitational modifications affect the late-time evolution of the universe through the new terms they bring in the Friedmann equations, namely in the effective dark-energy sector, as well as through the effective Newton’s constant they induce. If these effects lead to weaker gravity at suitable redshifts, or to more repulsive effective dark-energy (for instance exhibiting phantom behavior) then they can cause faster expansion comparing to \(\Lambda \) CDM paradigm, and thus lead to an increased \(H_0\) value. We present \(H_0\) -tension alleviations based on various subclasses of Horndeski/Generalized Galileon theories, such as Horndeski gravity with non-minimal derivative coupling, shift-symmetric Horndeski theories, Brans-Dicke theories, and minimal scalar-tensor theories. Then we provide alleviations based on torsional modifications of gravity, and in particular of f(T) gravity. Finally we present solutions based on f(R) gravity and bi-scalar modified theories of gravity. Such capabilities of gravitational modifications may be added in their other known advantages, and act as additional indication that modified gravity might be needed for the description of Nature.