Speaker
Description
Scalar-tensor theories are modified theories of gravity in which one introduces one or more scalar degrees of freedom in addition to the dynamical metric. Phenomenologically, scalar-tensor theories provide models for cosmological inflation and dark energy, and form a theoretical framework for black holes and other astrophysical objects beyond general relativity. Extending the theory space of scalar-tensor gravity and clarifying its structure are important for exploring the fundamental nature of gravity.
When one extends a theory by adding higher-order derivative terms, Ostrogradsky ghosts typically propagate, which is physically undesirable. Therefore, one must impose appropriate conditions to eliminate ghost instabilities.
This talk is based on our paper, arXiv:2601.09164, and discusses the motivation for constructing ghost-free scalar-tensor theories with third-order derivatives, as well as the method used to achieve this.