47 research outputs found
Bounds on quantum gravity parameter from the NJL effective model of QCD
Existence of a minimal measurable length, as an effective cutoff in the
ultraviolet regime, is a common feature of all approaches to the quantum
gravity proposal. It is widely believed that this length scale will be of the
order of the Planck length , where
is a dimensionless parameter that should be
fixed only by the experiments. This issue can be taken into account through the
deformed momentum spaces with compact topologies. In this paper, we consider
minimum length effects on the physical quantities related to three parameters
of the Nambu-Jona-Lasinio effective model of QCD by means of the
deformed measure which is defined on compact momentum space with topology. This measure is suggested by the doubly special relativity
theories, Snyder deformed spaces, and the deformed algebra that is obtained in
the light of the stability theory of Lie algebras. Using the current
experimental data of the particle physics collaboration, we constraint quantum
gravity parameter and we compare our results with bounds that are
arisen from the other experimental setups.Comment: 10 pages, no figure, accepted for publication in Europhysics Letter
Horava-Lifshitz early universe phase transition beyond detailed balance
The early universe is believed to have undergone a QCD phase transition to
hadrons at about after the big bang. We study such a transition in
the context of the non-detailed balance Horava-Lifshitz theory by investigating
the effects of the dynamical coupling constant in a flat universe.
The evolution of the relevant physical quantities, namely the energy density
, temperature , scale factor and the Hubble parameter is
investigated before, during and after the phase transition, assumed to be of
first order. Also, in view of the recent lattice QCD simulations data, we study
a cross-over phase transition of the early universe whose results are based on
two different sets of lattice data.Comment: 14 pages, 11 figures, to appear in Eur. Phys. J. C. arXiv admin note:
text overlap with arXiv:0912.2541, arXiv:0807.3066, arXiv:1005.3508,
arXiv:1011.4230 by other author
On the Stability of Einstein Static Universe in Doubly General Relativity Scenario
By presenting a relation between average energy of the ensemble of probe
photons and energy density of the Universe, in the context of {\it gravity's
rainbow} or {\it doubly general relativity} scenario, we introduce a rainbow
FRW Universe model. By analyzing the fixed points in flat FRW model modified by
two well known rainbow functions, we find that the finite time singularity
avoidance (i.e. Big-Bang) may still remain as a problem. Then, we follow the
"Emergent Universe" scenario in which there is no beginning of time and
consequently there is no Big-Bang singularity. Moreover, we study the impact of
a high energy quantum gravity modifications related to the gravity's rainbow on
the stability conditions of an "Einstein static Universe" (ESU). We find that
independent of a particular rainbow function, the positive energy condition
dictates a positive spatial curvature for the Universe. In fact, without
raising a nonphysical energy condition in the quantum gravity regimes, we can
address an agreement between gravity's rainbow scenario and basic assumption of
modern version of "Emergent Universe". We show that in the absence and presence
of an energy-dependent cosmological constant , a stable
Einstein static solution is available versus the homogeneous and linear scalar
perturbations under the variety of obtained conditions. Also, we explore the
stability of ESU against the vector and tensor perturbations.Comment: 18 pages, Revisio