1,609 research outputs found
Massive scalar states localized on a de Sitter brane
We consider a brane scenario with a massive scalar field in the
five-dimensional bulk. We study the scalar states that are localized on the
brane, which is assumed to be de Sitter. These localized scalar modes are
massive in general, their effective four-dimensional mass depending on the mass
of the five-dimensional scalar field, on the Hubble parameter in the brane and
on the coupling between the brane tension and the bulk scalar field. We then
introduce a purely four-dimensional approach based on an effective potential
for the projection of the scalar field in the brane, and discuss its regime of
validity. Finally, we explore the quasi-localized scalar states, which have a
non-zero width that quantifies their probability of tunneling from the brane
into the bulk.Comment: 14 pages; 5 figure
Scalar Kaluza-Klein modes in a multiply warped braneworld
The Kaluza-Klein (KK) modes of a massive scalar field on a 3-brane embedded
in six dimensional multiply warped spacetime are determined. Due to the
presence of warping along both the extra dimensions the KK mass spectrum splits
into two closely spaced branches which is a distinct feature of this model
compared to the five dimensional Randall-Sundrum model. This new cluster of the
KK mode spectrum is expected to have interesting phenomenological implications
for the upcoming collider experiments. Such a scenario may also be extended for
even larger number of orbifolded extra dimensions.Comment: 10 pages, Revte
Primordial gravitational waves in inflationary braneworld
We study primordial gravitational waves from inflation in Randall-Sundrum
braneworld model. The effect of small change of the Hubble parameter during
inflation is investigated using a toy model given by connecting two de Sitter
branes. We analyze the power spectrum of final zero-mode gravitons, which is
generated from the vacuum fluctuations of both initial Kaluza-Klein modes and
zero-mode. The amplitude of fluctuations is confirmed to agree with the
four-dimensional one at low energies, whereas it is enhanced due to the
normalization factor of zero-mode at high energies. We show that the
five-dimensional spectrum can be well approximated by applying a simple mapping
to the four-dimensional fluctuation amplitude.Comment: 16 pages, 4 figures, typos correcte
Exactly solvable model for cosmological perturbations in dilatonic brane worlds
We construct a model where cosmological perturbations are analytically solved
based on dilatonic brane worlds. A bulk scalar field has an exponential
potential in the bulk and an exponential coupling to the brane tension. The
bulk scalar field yields a power-law inflation on the brane. The exact
background metric can be found including the back-reaction of the scalar field.
Then exact solutions for cosmological perturbations which properly satisfy the
junction conditions on the brane are derived. These solutions provide us an
interesting model to understand the connection between the behavior of
cosmological perturbations on the brane and the geometry of the bulk. Using
these solutions, the behavior of an anisotropic stress induced on the
inflationary brane by bulk gravitational fields is investigated.Comment: 30 pages, typos corrected, reference adde
Geometry and cosmological perturbations in the bulk inflaton model
We consider a braneworld inflation model driven by the dynamics of a scalar
field living in the 5-dimensional bulk, the so-called ``bulk inflaton model'',
and investigate the geometry in the bulk and large scale cosmological
perturbations on the brane. The bulk gravitational effects on the brane are
described by a projection of the 5-dimensional Weyl tensor, which we denote by
. Focusing on a tachionic potential model, we take a perturbative
approach in the anti-de Sitter (AdS) background with a single de Sitter
brane. We first formulate the evolution equations for in the bulk.
Next, applying them to the case of a spatially homogeneous brane, we obtain two
different integral expressions for . One of them reduces to the
expression obtained previously when evaluated on the brane. The other is a new
expression that may be useful for analyzing the bulk geometry. Then we consider
superhorizon scale cosmological perturbations and evaluate the bulk effects
onto the brane. In the limit , where is the Hubble parameter
on the brane and is the bulk curvature radius, we find that the
effective theory on the brane is identical to the 4-dimensional Einstein-scalar
theory with a simple rescaling of the potential even under the presence of
inhomogeneities. % atleast on super-Hubble horizon scales. In particular, it is
found that the anticipated non-trivial bulk effect due to the spatially
anisotropic part of may appear only at %second order in the low
energy expansion, i.e., at .Comment: 21 pages including 6 pages for several appendixes, no figure
Braneworld reheating in the bulk inflaton model
In the context of the braneworld inflation driven by a bulk scalar field, we
study the energy dissipation from the bulk scalar field into the matter on the
brane in order to understand the reheating after inflation. Deriving the
late-time behavior of the bulk field with dissipation by using the Green's
function method, we give a rigorous justification of the statement that the
standard reheating process is reproduced in this bulk inflaton model as long as
the Hubble parameter on the brane and the mass of the bulk scalar field are
much smaller than the 5-dimensional inverse curvature scale. Our result
supports the idea that the brane inflation model caused by a bulk scalar field
is expected to be a viable alternative scenario of the early universe.Comment: 5 pages, no figures, final version to be published in PR
Bulk gravitational field and dark radiation on the brane in dilatonic brane world
We discuss the connection between the dark radiation on the brane and the
bulk gravitational field in a dilatonic brane world model proposed by Koyama
and Takahashi where the exact solutions for the five dimensional cosmological
perturbations can be obtained analytically. It is shown that the dark radiation
perturbation is related to the non-normalizable Kaluza-Klein (KK) mode of the
bulk perturbations. For the de Sitter brane in the anti-de Sitter bulk, the
squared mass of this KK mode is where is the Hubble parameter on
the brane. This mode is shown to be connected to the excitation of small black
hole in the bulk in the long wavelength limit. The exact solution for an
anisotropic stress on the brane induced by this KK mode is found, which plays
an important role in the calculation of cosmic microwave background radiation
anisotropies in the brane world.Comment: 11 page
Primordial fluctuations in bulk inflaton model
An inflationary brane model driven by a bulk inflaton with exponential
potential is proposed. We find a family of exact solutions that describe
power-law inflation on the brane. These solutions enable us to derive exact
solutions for metric perturbations analytically. By calculating scalar and
tensor perturbations, we obtain a spectrum of primordial fluctuations at the
end of the inflation. The amplitudes of scalar and tensor perturbations are
enhanced in the same way if the energy scale of the inflation is sufficiently
higher than the tension of the brane. Then the relative amplitude of scalar and
tensor perturbations is not suppressed even for high-energy inflation. This is
a distinguishable feature from the inflation model driven by inflaton on the
brane where tensor perturbations are suppressed for high-energy inflation. We
also point out that massive Kaluza-Klein modes are not negligible at
high-frequencies on 3-space of our brane.Comment: 16 pages, 3 figures, reference adde
Living on a dS brane: Effects of KK modes on inflation
We develop a formalism to study non-local higher-dimensional effects in
braneworld scenarios from a four-dimensional effective theory point of view and
check it against the well-known Garriga-Tanaka result in the appropriate limit.
We then use this formalism to study the spectrum of density perturbations
during inflation as seen from the lower-dimensional effective theory. In
particular, we find that the gravitational potential is greatly enhanced at
short wavelengths. The consequences to the curvature perturbations are
nonetheless very weak and will lead to no characteristic signatures on the
power spectrum.Comment: 21 pages, no figure
Then again, how often does the Unruh-DeWitt detector click if we switch it carefully?
The transition probability in first-order perturbation theory for an
Unruh-DeWitt detector coupled to a massless scalar field in Minkowski space is
calculated. It has been shown recently that the conventional
regularisation prescription for the correlation function leads to non-Lorentz
invariant results for the transition rate, and a different regularisation,
involving spatial smearing of the field, has been advocated to replace it. We
show that the non-Lorentz invariance arises solely from the assumption of
sudden switch-on and switch-off of the detector, and that when the model
includes a smooth switching function the results from the conventional
regularisation are both finite and Lorentz invariant. The sharp switching limit
of the model is also discussed, as well as the falloff properties of the
spectrum for large frequencies.Comment: 16 pages, v3. Final published version with section 5 expande
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