Fractons, geometrically.

We initiate a systematic study of fracton physics within the geometric framework of Double Field Theory. We ascribe the immobility and large degeneracy of the former to the non-Riemannian backgrounds of the latter, via generalised geodesics and infinite-dimensional isometries. A doubled pure Yang--Mills or Maxwell theory reduces to an ordinary one interacting with a strain tensor theory, where the dual photon-phonon pair becomes fractonic. Minimally coupled to a charged particle, the immobility is lifted to a saturation velocity and the dispersion relation receives nontrivial corrections.