Gravity seminar - Davide Gerosa Seminar

Although Solar System and binary-pulsar experiments test General Relativity to remarkable accuracy, the strong-field regime of the theory is still untested and lies in the realm of gravitational-wave astronomy. Testing General Relativity requires developing signatures in alternative theories of gravity, to be tested against future observations. The simplest and most famous of these models are scalar-tensor theories, where the spacetime metric is coupled to one or more scalar fields. I present new fully non-linear numerical simulations of core collapse and neutron-star formation in scalar-tensor theories. The presence of a non-perturbative effect called “spontaneous scalarization” (somewhat similar to spontaneous magnetization in ferromagnets) makes the dynamics of the collapse and formation of such objects qualitatively different from General Relativity thus providing an ideal way to constrain the parameters of the theory. We are able to simulate for the first time collapse of realistic stars using state-of-the-art microphysics and advanced shock-capturing numerical techniques. I also present the first investigation of spontaneous scalarization for relativistic stars in tensor-multi-scalar theories. Theories with more than one scalar field are remarkably interesting because the scalar fields are free to interact with each other in their own “target-space” manifold.