# Edge modes and quantum reference frames in linearized gravity (Wolfgang Wieland, FAU) FAU^2 Talk

A common way to interpret the coordinate invariance of Einstein’s equations is to say that coordinates are a mere gauge redundancy and play no physical role themselves. This is no longer true when we restrict ourselves to subsystems localized in a compact but otherwise arbitrary domain. At the boundary of the domain, coordinate transformations are no longer gauge redundant. The then necessary boundary conditions brake the gauge symmetries of the theory in the bulk. Otherwise unphysical gauge redundancies take on physical meaning as physical boundary modes (edge modes). In my talk, I present two recent developments on this frontier. First of all, I will speak about how to connect the research on edge modes to the geometry of open systems, dissipation and entropy production via the framework of metriplectic geometry. The second part of the talk deals with perturbative gravity. Taking a decoupling limit, where the Newton constant is sent to zero, we characterize the local phase space of the gravitational field in a finite region. Phase space splits into radiation modes and additional edge modes that are dual to reference frames at the boundary. Taking the boundary to infinity, we obtain a new quantum representation of asymptotic symmetries in perturbative gravity. The resulting infinite-dimensional group of boundary symmetries is the group of asymptotic Bondi–Metzner–Sachs (BMS) transformations at spacelike infinity. In this way, our results extend the existing notions of quantum reference frames and make them applicable to the framework of asymptotic symmetries and weak fields.

The talk is based on [arXiv:2206.00029] and [arXiv:2302.11629].