1,012 research outputs found
Inflation driven by scalar field with non-minimal kinetic coupling with Higgs and quadratic potentials
We study a scalar field with non-minimal kinetic coupling to itself and to
the curvature. The slow rolling conditions allowing an inflationary background
have been found. The quadratic and Higgs type potentials have been considered,
and the corresponding values for the scalar fields at the end of inflation
allows to recover the connection with particle physics.Comment: 16 pages, to appear in JCA
Estimating the abundance of clustered and cryptic marine macro-invertebrates in the Galápagos with particular reference to sea cucumbers
Estimating the abundance of marine macro-invertebrates
is complicated by a variety of factors: 1) human
factors, such as diver efficiency and diver error; and 2)
biological factors, such as aggregation of organisms,
crypsis, and nocturnal emergence behavior. Diver efficiency
varied according to the detectability of an organism
causing under-estimation of density by up to 50% in some
species. All common species were aggregated at scales
from 10-50 m. Transects need to be long enough to transcend
the scale of patchiness to improve accuracy. Some
species of sea urchins and sea cucumbers (pepinos) which
are cryptic by day emerged at night so that daytime
censuses underestimated their abundance by up to 10
times. In the sea cucumber fishery, estimates of abundance
need to be made at the scale of the population, i.e. at
hundreds of km. A strategy for this is proposed
Dark energy from scalar field with Gauss Bonnet and non-minimal kinetic coupling
We study a model of scalar field with a general non-minimal kinetic coupling
to itself and to the curvature, and additional coupling to the Gauss Bonnet
4-dimensional invariant. The model presents rich cosmological dynamics and some
of its solutions are analyzed. A variety of scalar fields and potentials giving
rise to power-law expansion have been found. The dynamical equation of state is
studied for two cases, with and without free kinetic term . In both cases
phenomenologically acceptable solutions have been found. Some solutions
describe essentially dark energy behavior, and and some solutions contain the
decelerated and accelerated phases.Comment: 21 page
Exact solutions in a scalar-tensor model of dark energy
We consider a model of scalar field with non minimal kinetic and Gauss Bonnet
couplings as a source of dark energy. Based on asymptotic limits of the
generalized Friedmann equation, we impose restrictions on the kinetic an
Gauss-Bonnet couplings. This restrictions considerable simplify the equations,
allowing for exact solutions unifying early time matter dominance with
transitions to late time quintessence and phantom phases. The stability of the
solutions in absence of matter has been studied.Comment: 30 pages, 2 figures, to appear in JCA
Age problem in holographic dark energy
We study the age problem of the universe with the holographic DE model
introduced in [21], and test the model with some known old high redshift
objects (OHRO). The parameters of the model have been constrained using the
SNIa, CMB and BAO data set. We found that the age of the old quasar APM 08
279+5255 at z = 3.91 can be described by the model.Comment: 13 page
Scalar wormholes with nonminimal derivative coupling
We consider static spherically symmetric wormhole configurations in a
gravitational theory of a scalar field with a potential and
nonminimal derivative coupling to the curvature describing by the term
in the
action. We show that the flare-out conditions providing the geometry of a
wormhole throat could fulfilled both if (phantom scalar) and
(ordinary scalar). Supposing additionally a traversability, we
construct numerical solutions describing traversable wormholes in the model
with arbitrary , and (no potential). The
traversability assumes that the wormhole possesses two asymptotically flat
regions with corresponding Schwarzschild masses. We find that asymptotical
masses of a wormhole with nonminimal derivative coupling could be positive
and/or negative depending on . In particular, both masses are positive
only provided , otherwise one or both wormhole masses are
negative. In conclusion, we give qualitative arguments that a wormhole
configuration with positive masses could be stable.Comment: 17 pages, 8 figure
Renormalization Group Flow of Quantum Gravity in the Einstein-Hilbert Truncation
The exact renormalization group equation for pure quantum gravity is used to
derive the non-perturbative \Fbeta-functions for the dimensionless Newton
constant and cosmological constant on the theory space spanned by the
Einstein-Hilbert truncation. The resulting coupled differential equations are
evaluated for a sharp cutoff function. The features of these flow equations are
compared to those found when using a smooth cutoff. The system of equations
with sharp cutoff is then solved numerically, deriving the complete
renormalization group flow of the Einstein-Hilbert truncation in . The
resulting renormalization group trajectories are classified and their physical
relevance is discussed. The non-trivial fixed point which, if present in the
exact theory, might render Quantum Einstein Gravity nonperturbatively
renormalizable is investigated for various spacetime dimensionalities.Comment: 58 pages, latex, 24 figure
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