Nonconservative unimodular gravity: Gravitational waves

Abstract: Unimodular gravity is characterized by an extra condition with respect to General Relativity: the determinant of the metric is constant. This extra condition leads to a more restricted class of invariance by coordinate transformation. Even though, if the conservation of the energy-momentum tensor is imposed in unimodular gravity, the General Relativity theory is recovered with an additional integration constant which is associated to the cosmological term $\Lambda$. However, if the energy-momentum tensor does not conserve separately, a new geometric structure appears with potentially observational signatures. In this text, we consider the evolution of gravitational waves in the nonconservative unimodular gravity, showing how it differs from the usual signatures in the standard model.