A geometrical approach to degenerate scalar-tensor theories

Understand

Degenerate scalar-tensor theories are recently proposed covariant theories of gravity coupled with a scalar field.

• Despite being characterised by higher order equations of motion, they do not propagate more than three degrees of freedom, thanks to the existence of constraints.
• We discuss a geometrical approach to degenerate scalar-tensor systems, and analyse its consequences.
• We show that some of these theories emerge as a certain limit of DBI Galileons.