31,790 research outputs found
Cosmological Vorticity in a Gravity with Quadratic Order Curvature Couplings
We analyse the evolution of the rotational type cosmological perturbation in
a gravity with general quadratic order gravitational coupling terms. The result
is expressed independently of the generalized nature of the gravity theory, and
is simply interpreted as a conservation of the angular momentum.Comment: 5 pages, revtex, no figure
Conserved cosmological structures in the one-loop superstring effective action
A generic form of low-energy effective action of superstring theories with
one-loop quantum correction is well known. Based on this action we derive the
complete perturbation equations and general analytic solutions in the
cosmological spacetime. Using the solutions we identify conserved quantities
characterizing the perturbations: the amplitude of gravitational wave and the
perturbed three-space curvature in the uniform-field gauge both in the
large-scale limit, and the angular-momentum of rotational perturbation are
conserved independently of changing gravity sector. Implications for
calculating perturbation spectra generated in the inflation era based on the
string action are presented.Comment: 5 pages, no figure, To appear in Phys. Rev.
A conserved variable in the perturbed hydrodynamic world model
We introduce a scalar-type perturbation variable which is conserved in
the large-scale limit considering general sign of three-space curvature (),
the cosmological constant (), and time varying equation of state. In a
pressureless medium is {\it exactly conserved} in all scales.Comment: 4 pages, no figure, To appear in Phys. Rev.
Second-order Perturbations of the Friedmann World Model
We consider instability of the Friedmann world model to the second-order in
perturbations. We present the perturbed set of equations up to the second-order
in the Friedmann background world model with general spatial curvature and the
cosmological constant. We consider systems with the completely general
imperfect fluids, the minimally coupled scalar fields, the electro-magnetic
field, and the generalized gravity theories. We also present the case of null
geodesic equations, and the one based on the relativistic Boltzmann equation.
In due stage a decomposition is made for the scalar-, vector- and tensor-type
perturbations which couple each other to the second-order. Gauge issue is
resolved to each order. The basic equations are presented without imposing any
gauge condition, thus in a gauge-ready form so that we can use the full
advantage of having the gauge freedom in analysing the problems. As an
application we show that to the second-order in perturbation the relativistic
pressureless ideal fluid of the scalar-type reproduces exactly the known
Newtonian result. As another application we rederive the large-scale conserved
quantities (of the pure scalar- and tensor-perturbations) to the second order,
first shown by Salopek and Bond, now from the exact equations. Several other
applications are made as well.Comment: 61 pages; published version in Phys. Rev.
Cosmological perturbations in a generalized gravity including tachyonic condensation
We present unified ways of handling the cosmological perturbations in a class
of gravity theory covered by a general action in eq. (1). This gravity includes
our previous generalized gravity and the gravity theory motivated
by the tachyonic condensation. We present general prescription to derive the
power spectra generated from vacuum quantum fluctuations in the slow-roll
inflation era. An application is made to a slow-roll inflation based on the
tachyonic condensation with an exponential potential.Comment: 5 page
Relativistic Hydrodynamic Cosmological Perturbations
Relativistic cosmological perturbation analyses can be made based on several
different fundamental gauge conditions. In the pressureless limit the variables
in certain gauge conditions show the correct Newtonian behaviors. Considering
the general curvature () and the cosmological constant () in the
background medium, the perturbed density in the comoving gauge, and the
perturbed velocity and the perturbed potential in the zero-shear gauge show the
same behavior as the Newtonian ones in general scales. In the first part, we
elaborate these Newtonian correspondences. In the second part, using the
identified gauge-invariant variables with correct Newtonian correspondences, we
present the relativistic results with general pressures in the background and
perturbation. We present the general super-sound-horizon scale solutions of the
above mentioned variables valid for general , , and generally
evolving equation of state. We show that, for vanishing , the
super-sound-horizon scale evolution is characterised by a conserved variable
which is the perturbed three-space curvature in the comoving gauge. We also
present equations for the multi-component hydrodynamic situation and for the
rotation and gravitational wave.Comment: 16 pages, no figure, To appear in Gen. Rel. Gra
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