3,980 research outputs found
Braneworld Cosmological Perturbation Theory at Low Energy
Homogeneous cosmology in the braneworld can be studied without solving bulk
equations of motion explicitly. The reason is simply because the symmetry of
the spacetime restricts possible corrections in the 4-dimensional effective
equations of motion. It would be great if we could analyze cosmological
perturbations without solving the bulk. For this purpose, we combine the
geometrical approach and the low energy gradient expansion method to derive the
4-dimensional effective action. Given our effective action, the standard
procedure to obtain the cosmological perturbation theory can be utilized and
the temperature anisotropy of the cosmic background radiation can be computed
without solving the bulk equations of motion explicitly.Comment: 10 pages, Based on a talk presented at ACRGR4, the 4th Australasian
Conference on General Relativity and Gravitation, Monash University,
Melbourne, January 2004. To appear in the proceedings, in General Relativity
and Gravitatio
Vector Field and Inflation
We have investigated if the vector field can give rise to an accelerating
phase in the early universe. We consider a timelike vector field with a general
quadratic kinetic term in order to preserve an isotropic background spacetime.
The vector field potential is required to satisfy the three minimal conditions
for successful inflation: i) , ii) and iii) the slow-roll
conditions. As an example, we consider the massive vector potential and small
field type potential as like in scalar driven inflation.Comment: 1+7pages, 3figures, To appear in the Proceedings of the CospA 2008,
Kore
Towards musical interaction : 'Schismatics' for e-violin and computer.
This paper discusses the evolution of the Max/MSP
patch used in schismatics (2007, rev. 2010) for electric
violin (Violectra) and computer, by composer Sam
Hayden in collaboration with violinist Mieko Kanno.
schismatics involves a standard performance paradigm
of a fixed notated part for the e-violin with sonically unfixed
live computer processing. Hayden was unsatisfied
with the early version of the piece: the use of attack
detection on the live e-violin playing to trigger stochastic
processes led to an essentially reactive behaviour in the
computer, resulting in a somewhat predictable one-toone
sonic relationship between them. It demonstrated
little internal relationship between the two beyond an
initial e-violin âactionâ causing a computer âeventâ. The
revisions in 2010, enabled by an AHRC Practice-Led
research award, aimed to achieve 1) a more interactive
performance situation and 2) a subtler and more
âmusicalâ relationship between live and processed
sounds. This was realised through the introduction of
sound analysis objects, in particular machine listening
and learning techniques developed by Nick Collins. One
aspect of the programming was the mapping of analysis
data to synthesis parameters, enabling the computer
transformations of the e-violin to be directly related to
Kannoâs interpretation of the piece in performance
Low Energy Effective Action for Horava-Witten Cosmology
As a supersymmetric extension of the Randall-Sundrum model, we consider a
5-dimensional Horava-Witten type theory, and derive its low energy effective
action. The model we consider is a two-brane system with a bulk scalar field
satisfying the BPS condition. We solve the bulk equations of motion using a
gradient expansion method, and substitute the solution into the original action
to get the 4-dimensional effective action. The resultant effective theory can
be casted into the form of Einstein gravity coupled with two scalar fields, one
arising from the radion, the degree of freedom of the inter-brane distance, and
the other from the bulk scalar field. We also clarify the relation between our
analysis and the moduli approximation.Comment: 11 page
A study of longitudinal oscillations of propellant tanks and wave propagations in feed lines. Part 1 - Propagating pressure waves in a fluid-filled cylindrical shell
Theory and equations for propagating pressure waves in liquid filled cylindrical shell
Anisotropic Power-law Inflation
We study an inflationary scenario in supergravity model with a gauge kinetic
function. We find exact anisotropic power-law inflationary solutions when both
the potential function for an inflaton and the gauge kinetic function are
exponential type. The dynamical system analysis tells us that the anisotropic
power-law inflation is an attractor for a large parameter region.Comment: 14 pages, 1 figure. References added, minor corrections include
Anisotropic Inflation with Non-Abelian Gauge Kinetic Function
We study an anisotropic inflation model with a gauge kinetic function for a
non-abelian gauge field. We find that, in contrast to abelian models, the
anisotropy can be either a prolate or an oblate type, which could lead to a
different prediction from abelian models for the statistical anisotropy in the
power spectrum of cosmological fluctuations. During a reheating phase, we find
chaotic behaviour of the non-abelian gauge field which is caused by the
nonlinear self-coupling of the gauge field. We compute a Lyapunov exponent of
the chaos which turns out to be uncorrelated with the anisotropy.Comment: 16 pages, 4 figure
Anisotropic Inflation from Charged Scalar Fields
We consider models of inflation with U(1) gauge fields and charged scalar
fields including symmetry breaking potential, chaotic inflation and hybrid
inflation. We show that there exist attractor solutions where the anisotropies
produced during inflation becomes comparable to the slow-roll parameters. In
the models where the inflaton field is a charged scalar field the gauge field
becomes highly oscillatory at the end of inflation ending inflation quickly.
Furthermore, in charged hybrid inflation the onset of waterfall phase
transition at the end of inflation is affected significantly by the evolution
of the background gauge field. Rapid oscillations of the gauge field and its
coupling to inflaton can have interesting effects on preheating and
non-Gaussianities.Comment: minor changes, references added, figures are modified, conforms JCAP
published versio
Black String Perturbations in RS1 Model
We present a general formalism for black string perturbations in
Randall-Sundrum 1 model (RS1). First, we derive the master equation for the
electric part of the Weyl tensor . Solving the master equation
using the gradient expansion method, we give the effective Teukolsky equation
on the brane at low energy. It is useful to estimate gravitational waves
emitted by perturbed rotating black strings. We also argue the effect of the
Gregory-Laflamme instability on the brane using our formalism.Comment: 14 pages, Based on a talk presented at ACRGR4, the 4th Australasian
Conference on General Relativity and Gravitation, Monash University,
Melbourne, January 2004. To appear in the proceedings, in General Relativity
and Gravitatio
Modified Friedmann Equation and Inflation in Warped Codimension-two Braneworld
We study the Friedmann equation for the warped codimension-two braneworld
background which most closely resembles the Randall-Sundrum model. Extra matter
on the (Planck) 4-brane, with equation of state p_\theta=(\alpha-1)\rho for the
azimuthal pressure, is required to satisfy the junction conditions. For 1 <
\alpha < 5, we show that there are two static solutions to the Einstein
equations for given values of the brane stress-energies. Close to the static
solutions, the relation between Hubble expansion rate H and brane tension
reproduces the standard 4D result for small H, but exhibits unusual deviations
when H is of order the AdS curvature scale. The two static branches for 1
<\alpha < 5 are shown to come together smoothly at a maximum value of H;
however the radion is shown to be unstable in the branch with higher H. This
remains true even with a mechanism for stabilization of the radion, i.e., the
Goldberger-Wise (GW) mechanism, since large enough H overcomes the force of
stabilization. Even in the unstabilized case, cosmological constraints on the
time and spatial variation of Newton's constant are typically satisfied; only
fifth force constraints require the stabilization. For \alpha > 5 the model is
intrinsically stable, without the need for a GW field, and in this case we show
that inflationary predictions can be modified by the nonstandard Friedmann
equation; in particular it is possible to get an upper limit on the spectral
index, large deviations from the consistency condition between the tensor
spectrum and ratio r, and large running of the spectral index even though the
slow roll parameters remain small.Comment: 29 pages, 23 figure
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