1pm AEST May 28

Link: https://macquarie.zoom.us/j/89267161769

Abstract: In linearized gravity, defining a local energy–momentum tensor for the gravitational field via variation of the action with respect to the metric is generally problematic. This difficulty arises from the principle of equivalence, which allows one to choose a local reference frame along any timelike curve in which the gravitational field vanishes, implying that any local gravitational energy density must also vanish there. Despite this limitation, certain local tensors can still characterize the strength of the gravitational field. In this talk, I will focus on the Bel–Robinson tensor, a four-index tensor that possesses many properties analogous to those of an energy–momentum tensor. Working in a de Sitter background spacetime, I will first demonstrate explicitly the non-negativity of the Bel–Robinson tensor when contracted with timelike vectors. I will then quantize the linearized gravitational perturbations and derive a quantum energy inequality, providing a lower bound on the timelike-averaged Bel–Robinson quantity along a timelike geodesic. Finally, I will discuss the bound in the Bunch–Davies vacuum of de Sitter spacetime.