2 research outputs found
Spherically symmetric Einstein-Maxwell theory and loop quantum gravity corrections
Effects of inverse triad corrections and (point) holonomy corrections,
occuring in loop quantum gravity, are considered on the properties of
Reissner-Nordstr\"om black holes. The version of inverse triad corrections with
unmodified constraint algebra reveals the possibility of occurrence of three
horizons (over a finite range of mass) and also shows a mass threshold beyond
which the inner horizon disappears. For the version with modified constraint
algebra, coordinate transformations are no longer a good symmetry. The
covariance property of spacetime is regained by using a \emph{quantum} notion
of mapping from phase space to spacetime. The resulting quantum effects in both
versions of these corrections can be associated with renormalization of either
mass, charge or wave function. In neither of the versions, Newton's constant is
renormalized. (Point) Holonomy corrections are shown to preclude the undeformed
version of constraint algebra as also a static solution, though
time-independent solutions exist. A possible reason for difficulty in
constructing a covariant metric for these corrections is highlighted.
Furthermore, the deformed algebra with holonomy corrections is shown to imply
signature change.Comment: 38 pages, 9 figures, matches published versio
Modified general relativity as a model for quantum gravitational collapse
We study a class of Hamiltonian deformations of the massless
Einstein-Klein-Gordon system in spherical symmetry for which the Dirac
constraint algebra closes. The system may be regarded as providing effective
equations for quantum gravitational collapse. Guided by the observation that
scalar field fluxes do not follow metric null directions due to the
deformation, we find that the equations take a simple form in characteristic
coordinates. We analyse these equations by a unique combination of numerical
methods and find that Choptuik's mass scaling law is modified by a mass gap as
well as jagged oscillations. Furthermore, the results are universal with
respect to different initial data profiles and robust under changes of the
deformation.Comment: 22 pages, 4 figure