Title: Covariant effective dynamics, mimetic gravity,  generalized LTB condition and dust collapse in polymerized spherical symmetric models

Speaker: Dr. Honggang Liu (University of Erlangen-Nurmberg, Germany)

Spacetime Point:

A311 Science and Technology Building

Online (202.112.92.14)

10:00am-11:30am, Aug. 4th (Fri.)

Abstract: We first propose a method to construct mubar-scheme Hamiltonian effective dynamics in the spherical symmetric

spacetime (polymerized models), which is generally covariant as derived from a covariant Lagrangian. The Lagrangian

belongs to the class of extended mimetic gravity Lagrangians in 4 dimensions. We then derive compatible LTB conditions for polymerized models in this framework. Within this broader class of polymerizations there are effective models contained for which the classical LTB condition is a compatible one. Our results show that there exist a class of effective models for which the dynamics decouples completely along the radial direction. It turns out that this subsector is strongly linked to the property that in the

temporally gauge fixed model, the algebra of the geometric contribution to the Hamiltonian constraint and the spatial diffeomorphism constraint is closed. And this subsector of theories admit a Birkhoff-like theorem. Moreover, we can start from a given decoupled effective LQC model and construct the corresponding effective dust collapse model from it as well as the underlying spherically symmetric model which after implementing the LTB conditions yields exactly the given dust collapse model. We finally apply the formalism with some examples.

The talk will be based on 1712.03876, 2212.04605, and a series of papers which will appear on arxiv next week.