4 research outputs found
Einstein-aether as a quantum effective field theory
The possibility that Lorentz symmetry is violated in gravitational processes
is relatively unconstrained by experiment, in stark contrast with the level of
accuracy to which Lorentz symmetry has been confirmed in the matter sector. One
model of Lorentz violation in the gravitational sector is Einstein-aether
theory, in which Lorentz symmetry is broken by giving a vacuum expectation
value to a dynamical vector field. In this paper we analyse the effective
theory for quantised gravitational and aether perturbations. We show that this
theory possesses a controlled effective expansion within dimensional
regularisation, that is, for any process there are a finite number of Feynman
diagrams which will contribute to a given order of accuracy. We find that there
is no log-running of the two-derivative phenomenological parameters, justifying
the use of experimental constraints for these parameters obtained over many
orders of magnitude in energy scale. Given the stringent experimental bounds on
two-derivative Lorentz-violating operators, we estimate the size of matter
Lorentz-violation which arises due to loop effects. This amounts to an
estimation of the natural size of coefficients for Lorentz-violating
dimension-six matter operators, which in turn can be used to obtain a new bound
on the two-derivative parameters of this theory.Comment: 21 page
Noether Symmetry Approach in "Cosmic Triad" Vector Field Scenario
To realize the accelerations in the early and late periods of our universe,
we need to specify potentials for the dominant fields. In this paper, by using
the Noether symmetry approach, we try to find suitable potentials in the
"cosmic triad" vector field scenario. Because the equation of state parameter
of dark energy has been constrained in the range of by observations, we derive the Noether conditions for the vector field
in quintessence, phantom and quintom models, respectively. In the first two
cases, constant potential solutions have been obtained. What is more, a fast
decaying point-like solution with power-law potential is also found for the
vector field in quintessence model. For the quintom case, we find an
interesting constraint on the field potentials,
where and are constants related to the Noether symmetry.Comment: 15 pages, no figures, accepted by Classical and Quantum Gravity
Statistical Anisotropy from Anisotropic Inflation
We review an inflationary scenario with the anisotropic expansion rate. An
anisotropic inflationary universe can be realized by a vector field coupled
with an inflaton, which can be regarded as a counter example to the cosmic
no-hair conjecture. We show generality of anisotropic inflation and derive a
universal property. We formulate cosmological perturbation theory in
anisotropic inflation. Using the formalism, we show anisotropic inflation gives
rise to the statistical anisotropy in primordial fluctuations. We also explain
a method to test anisotropic inflation using the cosmic microwave background
radiation (CMB).Comment: 32 pages, 5 figures, invited review for CQG, published versio