A Schr\"odinger approach to Newton-Cartan and Ho\v{r}ava-Lifshitz gravities

Understand

We define a `non-relativistic conformal method', based on a Schr\"odinger algebra with critical exponent z = 2, as the non-relativistic version of the relativistic conformal method.

• An important ingredient of this method is the occurrence of a complex compensating scalar field that transforms under both scale and central charge transformations.
• We apply this non-relativistic method to derive the curved space Newton-Cartan gravity equations of motion with twistless torsion.
• Moreover, we reproduce z = 2 Ho\v{r}ava-Lifshitz gravity by classifying all possible Schr\"odinger invariant scalar field theories of a complex scalar up to second order in time derivatives.