33,293 research outputs found
Brane induced gravity from asymmetric warped compactification
We show that brane induced gravity can be realized as a low energy effective
theory of brane worlds with asymmetric warped compactification. A
self-accelerating universe without cosmological constant on the brane can be
realized in a model where one side of the bulk has finite volume, but the other
side has infinite volume. The spin-2 perturbations for brane induced gravity
and asymmetric warped compactification models have the same spectrum at low
energies. For a de Sitter brane, the spin-2 graviton has mass in the range
, with in the self-accelerating universe.Comment: 4 pages, 3 figures, typos corrected, a reference adde
A Review on the Cognitive Neuroscience of Autism
With increased recognition in the media, heightened prevalence, and advances in research technologies, investigation into the causes of autism has broadened in recent years. Studies at the molecular, structural, and behavioral levels have resulted in significant findings, linking autism to qualitative differences in neurological function and an alteration of early development. Familial aggregation of autism demonstrate a strong genetic factor, although genetics can not completely account for its pathogenesis. Studies show autism having one of the most complex pathologies among neurodevelopmental disorders. Future studies applying sophisticated methodologies in new areas may shed light on current mysteries surrounding the disorder
Epilepsy – A Brief Overview
Epilepsy is a neurological condition in which an individual experiences chronic abnormal bursts of electrical discharge in the brain. These seizures can cause a variety symptoms depending on the areas of the brain affected. Symptoms can vary from mild to severe and can include complete or partial loss of consciousness, loss of speech, uncontrollable motor behavior, and/or unusual sensory experiences. From various studies worldwide6, approximately 0.5% of the population is reported to be affected by active epilepsy
Structure formation in modified gravity models alternative to dark energy
We study structure formation in phenomenological models in which the
Friedmann equation receives a correction of the form
, which realize an accelerated expansion without
dark energy. In order to address structure formation in these model, we
construct simple covariant gravitational equations which give the modified
Friedmann equation with where is an integer. For , the
underlying theory is known as a 5D braneworld model (the DGP model). Thus the
models interpolate between the DGP model () and the LCDM model
in general relativity (). Using the covariant
equations, cosmological perturbations are analyzed. It is shown that in order
to satisfy the Bianchi identity at a perturbative level, we need to introduce a
correction term in the effective equations. In the DGP model,
comes from 5D gravitational fields and correct conditions on
can be derived by solving the 5D perturbations. In the general
case , we have to assume the structure of a modified theory of gravity to
determine . We show that structure formation is different from a
dark energy model in general relativity with identical expansion history and
that quantitative features of the difference crucially depend on the conditions
on , that is, the structure of the underlying theory of modified
gravity. This implies that it is essential to identify underlying theories in
order to test these phenomenological models against observational data and,
once we identify a consistent theory, structure formation tests become
essential to distinguish modified gravity models from dark energy models in
general relativity.Comment: 12 pages, 3 figure
Radion and Large Scale Anisotropy on the Brane
We investigate the effect of the radion on cosmological perturbations in the
brane world. The S^1/Z_2 compactified 5D Anti-de Sitter spacetime bounded by
positive and negative tension branes is considered. The radion is the relative
displacement of the branes in this model. We find two different kinds of the
radion at the linear perturbation order for a cosmological brane. One describes
a "fluctuation" of the brane which does not couple to matter on the brane. The
other describes a "bend" of the brane which couples to the matter. The bend
determines the curvature perturbation on the brane. At large scales, the radion
interacts with anisotopic perturbations in the bulk. By solving the bulk
anisotropic perturbations, large scale metric perturbations and anisotropies of
the Cosmic Microwave Background (CMB) on the positive tension brane are
calculated. We find an interesting fact that the radion contributes to the CMB
anisotropies. The observational consequences of these effects are discussed.Comment: Improved version to appear in PRD, Results and conclusions unchange
Non-Gaussianity of quantum fields during inflation
In this review, we discuss how non-Gaussianity of cosmological perturbations
arises from inflation. After introducing the in-in formalism to calculate the
-point correlation function of quantum fields, we present the computation of
the bispectrum of the curvature perturbation generated in general single field
inflation models. The shapes of the bispectrum are compared with the local-type
non-Gaussianity that arises from non-linear dynamics on super-horizon scales.Comment: 17 pages, 2 figures, references added, matches published version,
invited review for CQG issue on non-linear cosmolog
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