In the AdS/CFT correspondence, a spatial subregion of a conformal field theory allows for the recovery of a corresponding subregion of the bulk known as its entanglement wedge. In some cases, an entanglement wedge contains a locally but not globally minimal surface homologous to the CFT subregion, in which case it is said to contain a python's lunch. It has been proposed that python's...
It is widely anticipated that a quantized theory of gravity will admit quantum spacetime configurations that are described by a superposition of semiclassical spacetimes. However, in the absence of such a complete theory of quantum gravity, can we learn anything about how such states might behave?
Recent developments led by Foo et al., propose an operational approach to this problem by...
The effect of black holes on entanglement harvesting--the process of extracting entanglement from the quantum vacuum--has been of considerable interest over the past decade. Research involving stationary Unruh-DeWitt (UDW) detectors in a (2+1)-dimensional black hole spacetime (the BTZ black hole) has uncovered phenomena such as entanglement shadows, entanglement amplification through black...
Both freeze-in of very weakly coupled dark matter and freeze-out of initially thermalized dark matter from the primordial heat bath provide interesting possibilities for dark matter creation in the early universe. Both scenarios allow for a calculation of baryon-dark matter coupling constants as a function of dark matter mass $m_\chi$, $g=g(m_\chi)$, due to the constraint that freeze-in or...
We point out a pathology with a canonical approach to the semiclassical Einstein equation. To be precise, it is shown that such a theory, subjected to the Dirac constraint analysis, renders itself empty, that is, devoid of any nontrivial degrees of freedom. The reason is identified to be the diffeomorphism invariance.
The equivalent formulations of gravity will be introduced as General relativity (GR), Teleparallel Equivalent of General Relativity (TEGR), Symmetric Teleparallel Equivalent of General Relativity (STEGR) with a basis toward teleparallel gravity. Mathematical models of theses theories will be introduced with a emphasis on physical differences and mathematical differences. A brief section on the...
In the ultralocal limit along timelike geodesics, any geometry is perceived as Bianchi I. It is shown that, in general, this limit does not extend to non-geodesic timelike observers. We discuss exceptions, including particles with variable mass, test particles in Einstein frame scalar-tensor gravity, and self-interacting dark matter.
[Based on R. Saadati, L. Valsan & V. Faraoni 2025, Eur....
