2,746 research outputs found
Gauges in the bulk
We present a general framework for nonparallel brane worlds and use it to
discuss the nonlinear radion problem. By imposing the Einstein frame as a gauge
condition we are able to give the effective action for both Minkowski and
(A)dS branes. In particular we find the nonlinear radion does not
disappear in the second Randall-Sundrum model.Comment: LaTeX file of 14 page
Black Holes and Black String-like Solutions in Codimension-2 Braneworlds
We discuss black hole solutions with a Gauss-Bonnet term in the bulk and an
induced gravity term on a thin brane of codimension-2. We show that these black
holes can be localized on the brane, and they can be extended further into the
bulk by a warp function. These solutions have regular horizons and no other
curvature singularities appear apart from the string-like ones. The projection
of the Gauss-Bonnet term on the brane imposes a constraint relation which
dictates the form of matter on the brane and in the bulk.Comment: 9 pages, no figures, plenary talk given at the 7th Friedmann
International Seminar on Gravitation and Cosmology, 29 June-5 July 2008, Joao
Pessoa, Brazil, to appear in the proceeding
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
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
Topological Gravity versus Supergravity on Manifolds with Special Holonomy
We construct a topological theory for euclidean gravity in four dimensions,
by enforcing self-duality conditions on the spin connection. The corresponding
topological symmetry is associated to the SU(2) X diffeomorphism X U(1)
invariance. The action of this theory is that of d=4, N=2 supergravity, up to a
twist. The topological field theory is SU(2) invariant, but the full SO(4)
invariance is recovered after untwist. This suggest that the topological
gravity is relevant for manifolds with special holonomy. The situation is
comparable to that of the topological Yang-Mills theory in eight dimensions,
for which the SO(8) invariance is broken down to Spin(7), but is recovered
after untwisting the topological theory.Comment: LateX file, 19 page
Symmetries and Observables for BF-theories in Superspace
The supersymmetric version of a topological quantum field theory describing
flat connections, the super BF-theory, is studied in the superspace formalism.
A set of observables related to topological invariants is derived from the
curvature of the superspace. Analogously to the non-supersymmetric versions,
the theory exhibits a vector-like supersymmetry. The role of the vector
supersymmetry and an additional new symmetry of the action in the construction
of observables is explained.Comment: 11 pages, LaTe
A Note on Gauss-Bonnet Holographic Superconductors
We present an analytic treatment near the phase transition for the critical
temperature of (3+1)-dimensional holographic superconductors in
Einstein-Gauss-Bonnet gravity with backreaction. We find that the backreaction
makes the critical temperature of the superconductor decrease and condensation
harder. This is consistent with previous numerical results.Comment: 6 pages, typos corrected, references added, published versio
Low energy effective action on a self-gravitating D-brane
Recently the study of braneworld on the self-gravitating D-brane has been
initiated and derived the gravitational equation on the brane by holographic
and geometrical projection methods. Surprisingly, in common with these two
methods, the matter on the brane cannot be the source of the gravity on the
brane at leading order. In this paper we will propose the low energy effective
action on the D-brane coupled with gravity which derives the same results.Comment: 8 pages, minor corrections, accepted for publication in Physical
Review
Indicators and trends of polar cold airmass
Trends and variations in the amount of cold airmass in the Arctic and the Northern Hemisphere are evaluated for the 60 year period, 1959â2018. The two indicators are (1) polar cold air mass (PCAM), which is the amount of air below a potential temperature threshold, and (2) negative heat content (NHC), which includes a weighting by coldness. Because the metrics of coldness are based on multiple layers in the atmosphere, they provide a more comprehensive framework for assessment of warming than is provided by surface air temperatures alone. The negative trends of PCAM and NHC are stronger (as a % per decade) when the threshold is 245 K rather than 280 K, indicating that the loss of extremely cold air is happening at a faster rate than the loss of moderately cold air. The loss of cold air has accelerated, as the most rapid loss of NHC has occurred in recent decades (1989â2018). The spatial patterns of the trends of PCAM and NHC provide another manifestation of Arctic amplification. Of the various teleconnection indices, the Atlantic Multidecadal Oscillation shows the strongest correlations with the spatially integrated metrics of moderate coldness. Several Pacific indices also correlate significantly with these indicators. However, the amount of extremely cold air mass does not correlate significantly with the indices of internal variability used here.publishedVersio
Pressure Dependence of Fragile-to-Strong Transition and a Possible Second Critical Point in Supercooled Confined Water
By confining water in nano-pores of silica glass, we can bypass the
crystallization and study the pressure effect on the dynamical behavior in
deeply supercooled state using neutron scattering. We observe a clear evidence
of a cusp-like fragile-to-strong (F-S) dynamic transition. Here we show that
the transition temperature decreases steadily with an increasing pressure,
until it intersects the homogenous nucleation temperature line of bulk water at
a pressure of 1600 bar. Above this pressure, it is no longer possible to
discern the characteristic feature of the F-S transition. Identification of
this end point with the possible second critical point is discussed.Comment: 4 pages, 3 figure
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