Gravity with explicit spacetime symmetry breaking and the Standard-Model Extension

Understand

The Standard-Model Extension (SME) is the general phenomenological framework used to investigate Lorentz violation at the level of effective field theory.

• It has been used to obtain stringent experimental bounds on Lorentz violation in a wide range of tests.
• In the gravity sector of the SME, it is typically assumed that the spacetime symmetry breaking occurs spontaneously in order to avoid potential conflicts with the Bianchi identities.
• A post-Newtonian limit as well as matter-gravity couplings in the SME have been developed and investigated based on this assumption.