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Calendar of Physics Talks Vienna
| Stable, ghost-free solutions in UV non-local gravity |
| Speaker: | Shubham Maheshwari (Groningen U.) |
| Abstract: | I consider higher derivative, UV modifications to GR. In particular, I will focus on a specific kind of string theory-inspired higher derivative gravity where one includes derivatives to all orders in the action. First, I will discuss how such a non-local theory of gravity admits stable, non-singular bouncing solutions in the absence of matter. Moreover, around this bouncing background, there exists only one propagating (and ghost-free) scalar mode, and no vector or tensor modes. Next, I will discuss the general analysis of scalar-vector-tensor perturbations in non-local gravity - in particular, I will show how non-local gravity is ghost-free around (A)dS and certain non-maximally symmetric backgrounds, and how certain (A)dS backgrounds have special physical spectra in that the propagating degrees of freedom are different from usual expectations. |
| Date: | Thu, 22.10.2020 |
| Time: | 16:00 |
| Duration: | 60 min |
| Location: | https://tuwien.zoom.us/j/95482849369?pwd=SkU2WU5hMVJBQWsyVlFXRlRvQlIvdz09 |
| Contact: | Laura Donnay, Daniel Grumiller |
| Bartnik's quasi-local mass conjectures |
| Speaker: | Lan-Hsuan Huang (University of Connecticut) |
| Abstract: | Bartnik's quasi-local mass for a compact manifold with boundary is defined by minimizing the ADM masses among admissible extensions. Among several proposed conjectures, Bartnik's stationary conjecture asserts that a minimizing initial data set must be vacuum and admit a timelike Killing vector. We make partial progress toward this conjecture by showing that a minimizing initial data set must sit in a "null dust" spacetime carrying a global Killing vector. On the other hand, we find pp-wave counterexamples to Bartnik's stationary and strict positivity conjectures in dimensions greater than 8.
In our proof, we introduce the concept of improvability of the dominant energy scalar, and we derive strong consequences of non-improvability using a new infinite-dimensional family of deformation to the Einstein constraint operator. This talk is based on a joint work with Dan Lee. |
| Date: | Thu, 22.10.2020 |
| Time: | 16:00 |
| Duration: | 60 min |
| Location: | https://zoom.us/j/4200372900?pwd=c01vb0FNRU94V0JVdWlnaDE0eUwwQT09 |
| Contact: | Piotr Chrusciel, David Fajman |
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