Precession of spheroids under Lorentz violation and observational consequences for neutron stars

The Standard-Model Extension (SME) is an effective-field-theoretic framework that catalogs all Lorentz-violating field operators. The anisotropic correction from the minimal gravitational SME to Newtonian gravitational energy for spheroids is studied, and the rotation of rigid spheroids is solved with perturbation method and numerical approach. The well-known forced precession solution given by Nordtvedt in the parameterized post-Newtonian formalism is recovered and applied to two observed solitary millisecond pulsars to set bounds on the coefficients for Lorentz violation in the SME framework. A different solution, which describes the rotation of an otherwise free-precessing star in the presence of Lorentz violation, is found, and its consequences on pulsar signals and continuous gravitational waves (GWs) emitted by neutron stars (NSs) are investigated. The study provides new possible tests of Lorentz violation once free-precessing NSs are firmly identified in the future.