1,360 research outputs found
Gauss-Bonnet assisted braneworld inflation in light of BICEP2 and Planck data
Motivated by the idea that quantum gravity corrections usually suppress the
power of the scalar primordial spectrum (E-mode) more than the power of the
tensor primordial spectrum (B-mode), in this paper we construct a concrete
gravitational theory in five-dimensions for which -type
inflation () generates an appropriate tensor-to-scalar ratio that may
be compatible with the BICEP2 and Planck data together. The true nature of
gravity is five-dimensional and described by the action where is
the five-dimensional Planck mass and is the Gauss-Bonnet (GB) term. The five-dimensional "bulk" spacetime
is anti-de Sitter () for which inflation ends naturally. The effects
of term on the magnitudes of scalar and tensor fluctuations and
spectral indices are shown to be important at the energy scale of inflation.
For GB-assisted -inflation, inflationary constraints from BICEP2 and
Planck, such as, , and
are all satisfied for .Comment: 5 pages, 4 figures, revtex4; v2: some additions to text in response
to comments, published versio
Natural Braneworld Inflation in Light of Recent Results from Planck and BICEP2
In this paper we report on a major theoretical observation in cosmology. We
present a concrete cosmological model for which inflation has natural beginning
and natural ending. Inflation is driven by a cosine-form potential, , which begins at and ends at
. The distance traversed by the
inflaton field is sub-Planckian. The Gauss-Bonnet term
arising as leading curvature corrections in the action
(where and are constants and is the five-dimensional
Planck mass) plays a key role to terminate inflation. The model generates
appropriate tensor-to-scalar ratio and inflationary perturbations that are
consistent with results from Planck and BICEP2. For example, for
and , the model predicts that and [ is the number of {\it
e}--folds of inflation and () is the scalar (tensor) spectrum
spectral index]. The ratio is (13% -- 24%) less than its value in 4D
Einstein gravity, . The upper bound on the energy scale of
inflation () implies that
and , which thereby rule out the case
(Randall-Sundrum model). The true nature of gravity is holographic as implied
by braneworld realization of string and M theory. The model correctly predicts
a late epoch cosmic acceleration with the dark energy equation of state .Comment: 13 pages, 14 figures; v2: minor changes, published versio
On applicability of inhomogeneous diffusion approach to localized transport through disordered waveguides
In this work we show analytically and numerically that wave transport through
random waveguides can be modeled as a diffusion with an inhomogeneous diffusion
coefficient (IDC). In localized regime, IDC retains the memory of the source
position. In an absorbing random medium, IDC becomes independent of the source.Comment: 5 pages, 3 figure
Warped brane-world compactification with Gauss-Bonnet term
In the Randall-Sundrum (RS) brane-world model a singular delta-function
source is matched by the second derivative of the warp factor. So one should
take possible curvature corrections in the effective action of the RS models in
a Gauss-Bonnet (GB) form. We present a linearized treatment of gravity in the
RS brane-world with the Gauss-Bonnet modification to Einstein gravity. We give
explicit expressions for the Neumann propagator in arbitrary D dimensions and
show that a bulk GB term gives, along with a tower of Kaluza-Klein modes in the
bulk, a massless graviton on the brane, as in the standard RS model. Moreover,
a non-trivial GB coupling can allow a new branch of solutions with finite
Planck scale and no naked bulk singularity, which might be useful to avoid some
of the previously known ``no--go theorems'' for RS brane-world
compactifications.Comment: 23 pages, typos in Secs. 5 & 6 corrected, expanded/published version
(IJMPA
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