41 research outputs found
Non-singular inflationary universe from polymer matter
We consider a polymer quantization of a free massless scalar field in a
homogeneous and isotropic cosmological spacetime. This quantization method
assumes that field translations are fundamentally discrete, and is related to
but distinct from that used in loop quantum gravity. The semi-classical
Friedman equation yields a universe that is non-singular and non-bouncing,
without quantum gravity. The model has an early de Sitter-like inflationary
phase with sufficient expansion to resolve the horizon and entropy problems,
and a built in mechanism for a graceful exit from inflation.Comment: 4 pages, 1 figure; v2 clarifications added, reference update
Background independent quantization and wave propagation
We apply a type of background independent "polymer" quantization to a free
scalar field in a flat spacetime. Using semi-classical states, we find an
effective wave equation that is both nonlinear and Lorentz invariance
violating. We solve this equation perturbatively for several cases of physical
interest, and show that polymer corrections to solutions of the Klein-Gordon
equation depend on the amplitude of the field. This leads to an effective
dispersion relation that depends on the amplitude, frequency and shape of the
wave-packet, and is hence distinct from other modified dispersion relations
found in the literature. We also demonstrate that polymer effects tend to
accumulate with time for plane-symmetric waveforms. We conclude by discussing
the possibility of measuring deviations from the Klein-Gordon equation in
particle accelerators or astrophysical observations.Comment: 15 pages, minor revision to match PRD versio
Genericness of inflation in isotropic loop quantum cosmology
Non-perturbative corrections from loop quantum cosmology (LQC) to the scalar
matter sector is already known to imply inflation. We prove that the LQC
modified scalar field generates exponential inflation in the small scale factor
regime, for all positive definite potentials, independent of initial conditions
and independent of ambiguity parameters. For positive semi-definite potentials
it is always possible to choose, without fine tuning, a value of one of the
ambiguity parameters such that exponential inflation results, provided zeros of
the potential are approached at most as a power law in the scale factor. In
conjunction with generic occurrence of bounce at small volumes, particle
horizon is absent thus eliminating the horizon problem of the standard Big Bang
model.Comment: 4 pages, revtex4, one figure. Only e-print archive numbers correctedi
in the second version. Reference added in the 3rd version. Final version to
appear in Phys. Rev. Lett. Explanations improve
Aerobic and anaerobic biosynthesis of nano-selenium for remediation of mercury contaminated soil
Monitoring Movement Behaviour of Caenorhabditis elegans in Response to Formaldehyde at Low Concentrations
Abstract.-This study describes a new approach for assessing toxic response behaviour of Caenorhabditis elegans by automatic recognition of line movement through an image-processing system. The movement behaviour of this nematode is different even at low concentrations of formaldehyde. A comparison of the response behaviour of this animal at different concentrations of formaldehyde has shown concentration-dependent toxicity. This study has identified some sequential line-movements on nematodes that confirmed the toxicological effect on nematode behaviour
Anomaly freedom in perturbative loop quantum gravity
A fully consistent linear perturbation theory for cosmology is derived in the
presence of quantum corrections as they are suggested by properties of inverse
volume operators in loop quantum gravity. The underlying constraints present a
consistent deformation of the classical system, which shows that the
discreteness in loop quantum gravity can be implemented in effective equations
without spoiling space-time covariance. Nevertheless, non-trivial quantum
corrections do arise in the constraint algebra. Since correction terms must
appear in tightly controlled forms to avoid anomalies, detailed insights for
the correct implementation of constraint operators can be gained. The
procedures of this article thus provide a clear link between fundamental
quantum gravity and phenomenology.Comment: 54 pages, no figure
Background independent quantization and the uncertainty principle
It is shown that polymer quantization leads to a modified uncertainty
principle similar to that obtained from string theory and non-commutative
geometry. When applied to quantum field theory on general background
spacetimes, corrections to the uncertainty principle acquire a metric
dependence. For Friedmann-Robertson-Walker cosmology this translates to a scale
factor dependence which gives a large effect in the early universe.Comment: 6 page
Cosmological vector modes and quantum gravity effects
In contrast to scalar and tensor modes, vector modes of linear perturbations
around an expanding Friedmann--Robertson--Walker universe decay. This makes
them largely irrelevant for late time cosmology, assuming that all modes
started out at a similar magnitude at some early stage. By now, however,
bouncing models are frequently considered which exhibit a collapsing phase.
Before this phase reaches a minimum size and re-expands, vector modes grow.
Such modes are thus relevant for the bounce and may even signal the breakdown
of perturbation theory if the growth is too strong. Here, a gauge invariant
formulation of vector mode perturbations in Hamiltonian cosmology is presented.
This lays out a framework for studying possible canonical quantum gravity
effects, such as those of loop quantum gravity, at an effective level. As an
explicit example, typical quantum corrections, namely those coming from inverse
densitized triad components and holonomies, are shown to increase the growth
rate of vector perturbations in the contracting phase, but only slightly.
Effects at the bounce of the background geometry can, however, be much
stronger.Comment: 20 page
Using Energy Conditions to Distinguish Brane Models and Study Brane Matter
Current universe (assumed here to be normal matter on the brane) is
pressureless from observations. In this case the energy condition is
and . By using this condition, brane models can be
distinguished. Then, assuming arbitrary component of matter in DGP model, we
use four known energy conditions to study the matter on the brane. If there is
nonnormal matter or energy (for example dark energy with ) on the
brane, the universe is accelerated.Comment: 5pages, no figures; Accepted by Communications in Theoretical Physic
Hubble operator in isotropic loop quantum cosmology
We present a construction of the Hubble operator for the spatially flat
isotropic loop quantum cosmology. This operator is a Dirac observable on a
subspace of the space of physical solutions. This subspace gets selected
dynamically, requiring that its action be invariant on the physical solution
space. As a simple illustrative application of the expectation value of the
operator, we do find a generic phase of (super)inflation, a feature shown by
Bojowald from the analysis of effective Friedmann equation of loop quantum
cosmology.Comment: 20 pages, 3 eps figures, few comments and clarifications added to
match with the published versio