  We derive the action and symmetries of the bosonic sector of non-Lorentzian
IIB supergravity by taking the non-relativistic string limit. We find that the
bosonic field content is extended by a Lagrange multiplier that implements a
restriction on the Ramond-Ramond fluxes. We show that the SL(2,R)
transformation rules of non-Lorentzian IIB supergravity form a novel, nonlinear
polynomial realization. Using classical invariant theory of polynomial
equations and binary forms, we will develop a general formalism describing the
polynomial realization of SL(2,R) and apply it to the special case of
non-Lorentzian IIB supergravity. Using the same formalism, we classify all the
relevant SL(2,R) invariants. Invoking other bosonic symmetries, such as the
local boost and dilatation symmetry, we show how the bosonic part of the
non-Lorentzian IIB supergravity action is formed uniquely from these SL(2,R)
invariants. This work also points towards the concept of a non-Lorentzian
bootstrap, where bosonic symmetries in non-Lorentzian supergravity are used to
bootstrap the bosonic dynamics in Lorentzian supergravity, without considering
the fermions.
