Hall 123

New second derivative theories of gravity for spherically symmetric spacetimes and emergent spacetime

Rakesh Tibrewala

Center for High Energy Physics, IISc, Bengaluru

Symmetry reduced or the so called mini/midisuperspace models
play an important role in the investigation of various approaches to
quantum gravity. Motivated by certain loop quantum gravity (LQG) inspired
corrections, it is shown that for spherically symmetric midisuperspace
models infinitely many second derivative classical theories of gravity
exist and not just those allowed by spherical symmetry reduction of
general relativity. This infinity of classical theories is revealed by the
presence of certain arbitrary functions in the Hamiltonian. Since quantum
corrections will lead to a modification of general relativity, these new
theories can be thought of as providing the freedom to accommodate these
corrections without requiring higher curvature/derivative modifications.
Conversely, the freedom in the arbitrary functions can possibly be used to
simplify the Hamiltonian constraint of the symmetry reduced theory which
can then aid in the quantization of the theory. We also use these new
theories to explicitly show that use of symmetry reduced models imply that
one loses the information about the dimensionality of spacetime and show
that these new theories have sufficient freedom to accommodate (at the
semiclassical level) scenarios of emergent spacetime dimensions (as is
suggested by certain theories like causal dynamical triangulation).