Anisotropic quantum universe in Ho\v{r}ava-Lifshitz gravity

TL;DR

This paper quantizes a Bianchi IX universe within Hořava-Lifshitz gravity, analyzing quantum states and anisotropies in both large and small universe regimes, revealing unique behaviors from classical General Relativity.

Contribution

It provides the first detailed quantum analysis of anisotropic universes in Hořava-Lifshitz gravity, including wave functions, tunneling probabilities, and bounds on coupling parameters.

Findings

Wave function of the universe derived with semi-classical and analytic methods.

Distinct anisotropy behavior in UV limit due to higher-dimensional operators.

Bound on Hořava-Lifshitz coupling parameters from wave function normalizability.

Abstract

We quantize a Bianchi IX universe in Ho\v{r}ava-Lifshitz theory. For analytical tractability, we consider the small anisotropy limit of the Bianchi IX, that is, a perturbative anisotropic deformation of a closed, homogeneous and isotropic universe. In the case of the projectable theory we further set the ``dark matter as integration constant'' to zero by assuming that the space consists of only one connected piece. In that limit and under the assumption, we first study the semi-classical WKB solutions to the Wheeler-DeWitt equation. We find the wave function of the universe, up to an overall normalization, and estimate the semi-classical tunneling probability for the emergence of an expanding universe. We establish a dictionary of correspondence between the WKB wave functions in General Relativity and Ho\v{r}ava-Lifshitz theory in the large-scale factor (or IR) limit. For a small universe (UV limit), on the other hand, due to contributions from higher-dimensional operators, the anisotropies decouple from the scale factor, a behavior significantly different from General Relativity, and analytic solutions to the Wheeler-DeWitt equation beyond the WKB approximation can be found. The wave function of the scale factor satisfies the DeWitt criterion, whereas the wave functions of anisotropies resemble those of quantum harmonic oscillators. The quantum prediction for the initial condition of anisotropies is obtained in terms of the coupling parameters of Ho\v{r}ava-Lifshitz theory. We find a bound on the coupling parameters from the normalizability of the wave functions of anisotropies. Further, we calculate the expectation values for squared anisotropic shear and squared anisotropies in both the large universe and small universe limits.