34 research outputs found
Resolution of cosmological singularity in Ho\v{r}ava-Lifshitz cosmology
The standard CDM model despite its agreement with observational data
still has some issues unaddressed, lie the problem of initial singularity.
Solving that problem usually requires modifications of general relativity.
However, there appeared the Ho\v{r}ava-Lifshitz (HL) theory of gravity, in
which equations governing cosmological evolution include a new term scaling
similarly as dark radiation term in the Friedmann equations, enabling a bounce
of the universe instead of initial singularity. This review describes past
works on a stability of such a bounce in different formulations of HL theory,
initial detailed balance scenario and further projectable versions containing
higher than quadratic term to the original action.Comment: Submitted to Universe. Rewritten in order to remove repetitions from
the previous paper
Comparing the dynamics of diagonal and general Bianchi IX spacetime
We make comparison of the dynamics of the diagonal and nondiagonal Bianchi IX
models in the evolution towards the cosmological singularity. Apart from the
original variables, we use the Hubble normalized ones commonly applied in the
examination of the dynamics of homogeneous models. Applying the dynamical
systems method leads to the result that in both cases the continuous space of
critical points is higher dimensional and they are of the nonhyperbolic type.
This is a generic feature of the dynamics of both cases and seems to be
independent on the choice of phase space variables. The topologies of the
corresponding critical spaces are quite different. We conjecture that the
nondiagonal case may carry a new type of chaos different from the one specific
to the usually examined diagonal one.Comment: 25 pages, 2 figures, version including numerical simulations of
dynamic
Nonadiabatic bounce and an inflationary phase in the quantum mixmaster universe
Following our previous paper, Bergeron et al, Smooth quantum dynamics of the
mixmaster universe, Phys. Rev. D 92, 061302(R) (2015), concerning the
quantization of the vacuum Bianchi IX model and the Born-Huang-Oppenheimer
framework, we present a further analysis of the dynamical properties of the
model. Consistently with the deep quantum regime, we implement the harmonic
approximation of the anisotropy potential. We thus obtain manageable dynamical
equations. We study the quantum anisotropic oscillations during the bouncing
phase of the universe. Neglecting the backreaction from transitions between
quantum anisotropy states we obtain analytical results. In particular, we
identify a parameter which is associated with dynamical properties of the
quantum model and describes a sort of phase transition. Once the parameter
exceeds its critical value, the Born-Huang-Oppenheimer approximation breaks
down. The application of the present result to a simple model of the Universe
indicates that the parameter indeed exceeds its critical value and that there
takes place a huge production of anisotropy at the bounce. This in turn must
lead to a sustained phase of accelerated expansion, an inflationary phase. The
quantitative inclusion of backreaction shall be examined in a follow-up paper
based on the vibronic approach.Comment: 32 pages, 9 figure
Vibronic framework for quantum mixmaster universe
Following our previous papers concerning the quantization of the vacuum
Bianchi-IX model within or beyond the Born-Oppenheimer and adiabatic
approximation, we develop a more elaborate analysis of the dynamical properties
of the model based the vibronic approach utilized in molecular physics. As in
the previous papers, we restrict our approach to the harmonic approximation of
the anisotropy potential in order to obtain resoluble analytical expressions.Comment: 29 pages, 12 figure
On the energy flow of in Ho\v{r}ava-Lifshitz cosmology
Ho\v{r}ava-Lifshitz gravity has been proposed as a ghost-free quantum gravity
model candidate with an anisotropic UV-scaling between space and time. We
present here a cosmological background analysis of two different formulations
of the theory, with particular focus on the running of the parameter .
Using a large dataset consisting of Cosmic Microwave Background data from {\it
Planck}, Pantheon+ supernovae catalogue, SH0ES Cepheid variable stars, Baryon
acoustic oscillations (BAO), Cosmic Chronometers, and gamma-ray bursts (GRB),
we arrive at new bounds on the cosmological parameters, in particular
, which describes deviation from classical general relativity. For the
detailed balance scenario we arrive at the bound ,
and for beyond detailed balance the limit reads
. We also study the influence of different
data sets and priors, and we find that removing low-redshift data generally
moves closer towards UV values, whilst simultaneously widening the
error bars. In the detailed balance scenario, this effect is more noticeable,
and takes on values that are significantly below unity, which
corresponds to the infrared limit of the theory.Comment: 16 pages, 2 tables, 1 figur