Speaker
Andrea Dapor
Description
We present a new perspective on QFT on quantum
cosmological space-times. Naively, the semiclassical limit
of a quantum space-time can be taken by averaging the
gravitational operators on a semiclassical state of
geometry. The result is an effective classical metric
(which in general does not obey Einstein equation). We
show that, once quantum matter is taken into account, a
new possibility arises: the dynamics of matter on
quantum space-time can be equivalently described by
standard QFT on a classical space-time, whose geometry
is encoded in a so-called "dressed metric", a classical
metric which is different than the naive semiclassical
one. Such matter-dependent dressed metric can be
thought of as the metric "seen" by the matter field.
We explore this interpretation and its consequences in
various instances, such as scalar field on quantum
cosmological space-times, addressing the question of
observable effects on the propagation of matter.
Indeed, since the dressed metric depends on the
matter, Lorentz-violating phenomena are expected (such
as deformation of dispersion relations). We prove that
for massless field on FRW [1] or Bianchi I [2] quantum
geometries, no violation takes place at test-field level.
We present a way to take into account the matter back-
reaction (in which case a deformation in the dispersion
relation is present). Finally, we address the case of a
massive field on FRW quantum geometry [3], and show
that an isotropy-breaking is present already at the test-
field level, since the dressed metric depends on the
direction of propagation of the mode of the field.
References:
[1] A. Ashtekar, W. Kaminski, J. Lewandowski -
"Quantum field theory on a cosmological, quantum
space-time", Phys. Rev. D 79, 064030 (2009)
[2] A. Dapor, J. Lewandowski, Y. Tavakoli - "Lorentz
Symmetry in QFT on Quantum Bianchi I Space-Time",
Phys. Rev. D 86, 064013 (2012)
[3] A. Dapor, J. Lewandowski - "Isotropy-Breaking in
Quantum Cosmology", in preparation
