Title: Spatially covariant gravity and unifying framework for scalar-tensor theories

Speaker: Dr. Xian Gao(高显) (Tokyo Institute of Technology，Japan)

Time: 10:00AM, Dec. 4th (Thursday)

Place: Library Building，319

Abstact:

We investigate gravity theories that are invariant under spatial diffeomorphism. In a spacetime covariant point of view, such theories describe dynamical spacelike hypersurfaces in a general background. Comparing with general relativity, an additional scalar mode arises, which encodes the fluctuation of the hypersurfaces. Therefore such spatially covariant gravity can also be viewed as scalar tensor theories, in which various scalar tensor theories in the literature could get unified. Our framework also extends the popular Horndeski theory in the sense that it propagates the correct number of degrees of freedom, although the equations of motion are generally higher order.