19,949 research outputs found
Quantum fluctuations of Cosmological Perturbations in Generalized Gravity
Recently, we presented a unified way of analysing classical cosmological
perturbation in generalized gravity theories. In this paper, we derive the
perturbation spectrums generated from quantum fluctuations again in unified
forms. We consider a situation where an accelerated expansion phase of the
early universe is realized in a particular generic phase of the generalized
gravity. We take the perturbative semiclassical approximation which treats the
perturbed parts of the metric and matter fields as quantum mechanical
operators. Our generic results include the conventional power-law and
exponential inflations in Einstein's gravity as special cases.Comment: 5 pages, revtex, no figure
Analyses of decay constants and light-cone distribution amplitudes for s-wave heavy meson
In this paper, a study of light-cone distribution amplitudes (LCDAs) for
-wave heavy meson are presented in both general and heavy quark frameworks.
Within the light-front approach, the leading twist light-cone distribution
amplitudes, , and their relevant decay constants of heavy
pseudoscalar and vector mesons, , have simple relations. These relations
can be further simplified when the heavy quark limit is taken into
consideration. After fixing the parameters that appear in both Gaussian and
power-law wave functions, the corresponding decay constants are calculated and
compared with those of other theoretical approaches. The curves and the first
six -moments of are plotted and estimated. A conclusion is
drawn from these results: Even though the values of the decay constants of the
distinct mesons are almost equal, the curves of their LCDAs may have quite
large differences, and vice versa. Additionally, in the heavy quark limit, the
leading twist LCDAs, and , are compared
with the -meson LCDAs, , suggested by the other theoretical
groups.Comment: 25 pages, 3 figures, 4 tables, some typos are corrected, version to
be published in Phys. Rev.
Higher Fock sectors in Wick-Cutkosky model
In the Wick-Cutkosky model we analyze nonperturbatively, in light-front
dynamics, the contributions of two-body and higher Fock sectors to the total
norm and electromagnetic form factor. It turns out that two- and three-body
sectors always dominate. For maximal value of coupling constant ,
corresponding to zero bound state mass M=0, they contribute 90% to the norm.
With decrease of the two-body contribution increases up to 100%. The
form factor asymptotic is always determined by two-body sector.Comment: 4 pages, 2 figures, to appear in the proceedings of Light Cone 2004,
Amsterdam, August 16-20, 200
Gauge-invariant gravitational wave modes in pre-big bang cosmology
The t<0 branch of pre-big bang cosmological scenarios is subject to a
gravitational wave instability. The unstable behaviour of tensor perturbations
is derived in a very simple way in Hwang's covariant and gauge-invariant
formalism developed for extended theories of gravity. A simple interpretation
of this instability as the effect of an "antifriction" is given, and it is
argued that a universe must eventually enter the expanding phase.Comment: 4 pages, latex, to appear in Eur. Phys. J.
Base manifolds for fibrations of projective irreducible symplectic manifolds
Given a projective irreducible symplectic manifold of dimension , a
projective manifold and a surjective holomorphic map with
connected fibers of positive dimension, we prove that is biholomorphic to
the projective space of dimension . The proof is obtained by exploiting two
geometric structures at general points of : the affine structure arising
from the action variables of the Lagrangian fibration and the structure
defined by the variety of minimal rational tangents on the Fano manifold
Unified Analysis of Cosmological Perturbations in Generalized Gravity
In a class of generalized Einstein's gravity theories we derive the equations
and general asymptotic solutions describing the evolution of the perturbed
universe in unified forms. Our gravity theory considers general couplings
between the scalar field and the scalar curvature in the Lagrangian, thus
includes broad classes of generalized gravity theories resulting from recent
attempts for the unification. We analyze both the scalar-type mode and the
gravitational wave in analogous ways. For both modes the large scale evolutions
are characterized by the same conserved quantities which are valid in the
Einstein's gravity. This unified and simple treatment is possible due to our
proper choice of the gauges, or equivalently gauge invariant combinations.Comment: 4 pages, revtex, no figure
Cosmological perturbations in a gravity with quadratic order curvature couplings
We present a set of equations describing the evolution of the scalar-type
cosmological perturbation in a gravity with general quadratic order curvature
coupling terms. Equations are presented in a gauge ready form, thus are ready
to implement various temporal gauge conditions depending on the problems. The
Ricci-curvature square term leads to a fourth-order differential equation for
describing the spacetime fluctuations in a spatially homogeneous and isotropic
cosmological background.Comment: 5 pages, no figure, To appear in Phys. Rev.
Negative energy and stability in scalar-tensor gravity
Linearized gravitational waves in Brans-Dicke and scalar-tensor theories
carry negative energy. A gauge-invariant analysis shows that the background
Minkowski space is stable at the classical level with respect to linear scalar
and tensor inhomogeneous perturbations.Comment: 9 pages, latex, to appear in Phys. Rev.
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