Speakers: Norihiro Tanahashi and Seiju Ohashi
Horndeski theory is the most general scalar-tensor theory with second-order field equations, and recently it is attracting attention in the context of cosmology. We discuss extension of this theory to the multi-scalar field case. As the first step, we focus on a candidate of the most general theory, the generalized covariant multi-galileons, and study cosmological perturbations in this theory. Comparing it to the multi-field DBI galileon inflation, we find that the theory must be extended to be the most general one. We explain our attempt toward construction of the most general theory based on Horndeski’s strategy.