Topological modes in hydrodynamics and holography

In this talk I will show that gapless modes in relativistic hydrodynamics could become topologically nontrivial by weakly breaking the conservation of energy momentum tensor in a specific way. This system has topological semimetal-like crossing nodes in the spectrum of hydrodynamic modes that require the protection of a special combination of translational and boost symmetries in two spatial directions. One possible origin for the non-conservation terms of the energy momentum tensor is an external gravitational field which could be generated by a specific coordinate transformation from the flat spacetime. This suggests that topologically trivial modes could become topologically nontrivial by being observed in a special non-inertial reference frame. Finally a holographic realization of this system will be introduced.