SPEAKER: Dario Bettoni (Technion)
ABSTRACT: The Horndeski action is the most general one involving a metric and a scalar field that leads to second-order field equations in four dimensions. Being the natural extension of the well-known scalar-tensor theories, its structure and properties are worth analyzing along the experience accumulated in the latter context. In this talk I will discuss how disformal transformations play, for the Horndeski theory, a similar role to that of conformal transformations for scalar-tensor theories a la Brans-Dicke and introduce a method that allows to enligthen some physical properties of the scalar field equation without having to solve the full coupled system.