68 research outputs found
Field localization on a brane intersection in anti-de Sitter spacetime
We discuss the localization of scalar, fermion, and gauge field zero modes on
a brane that resides at the intersection of two branes in
six-dimensional anti-de Sitter space. This set-up has been introduced in the
context of brane world models and, higher-dimensional versions of it, in string
theory. In both six- and ten-dimensional cases, it has been shown that
four-dimensional gravity can be reproduced at the intersection, due to the
existence of a massless, localized graviton zero-mode. However, realistic
scenarios require also the Standard Model to be localized on the brane. In
this paper, we discuss under which conditions a higher-dimensional field
theory, propagating on the above geometry, can have a zero-mode sector
localized at the intersection and find that zero modes can be localized only if
masses and couplings to the background curvature satisfy certain relations. We
also consider the case when other 4-branes cut the bulk at some distance from
the intersection and argue that, in the probe brane approximation, there is no
significant effect on the localization properties at the brane. The case of
bulk fermions is particularly interesting, since the properties of the geometry
allow localization of chiral modes independently.Comment: 13 pages, 3 figures, the version to be published in PR
A Kinematically Complete Analysis of the CLAS data on the Proton Structure Function in a Regge-Dual model
The recently measured inclusive electron-proton cross section in the nucleon
resonance region, performed with the CLAS detector at the Thomas Jefferson
Laboratory, has provided new data for the nucleon structure function with
previously unavailable precision. In this paper we propose a description of
these experimental data based on a Regge-dual model for . The basic inputs
in the model are nonlinear complex Regge trajectories producing both isobar
resonances and a smooth background. The model is tested against the
experimental data, and the dependence of the moments is calculated. The
fitted model for the structure function (inclusive cross section) is a limiting
case of the more general scattering amplitude equally applicable to deeply
virtual Compton scattering (DVCS). The connection between the two is discussed.Comment: 21 pages, 12 figures, revtex style. Misprints in eqs. (15,17) are
corrected. To appear in Phys. Rev.
Quantum self-consistency of brane models
Continuing on our previous work, we consider a class of higher dimensional
brane models with the topology of , where
is a one-parameter compact manifold and two branes of codimension 1 are located
at the orbifold fixed points. We consider a set-up where such a solution arises
from Einstein-Yang-Mills theory and evaluate the one-loop effective potential
induced by gauge fields and by a generic bulk scalar field. We show that this
type of brane models resolves the gauge hierarchy between the Planck and
electroweak scales through redshift effects due to the warp factor . The value of is then fixed by minimizing the effective potential. We
find that, as in the Randall Sundrum case, the gauge field contribution to the
effective potential stabilises the hierarchy without fine-tuning as long as the
laplacian on has a zero eigenvalue. Scalar fields can
stabilise the hierarchy depending on the mass and the non-minimal coupling. We
also address the quantum self-consistency of the solution, showing that the
classical brane solution is not spoiled by quantum effects.Comment: 10 page
Casimir effect of electromagnetic field in Randall-Sundrum spacetime
We study the finite temperature Casimir effect on a pair of parallel
perfectly conducting plates in Randall-Sundrum model without using scalar field
analogy. Two different ways of interpreting perfectly conducting conditions are
discussed. The conventional way that uses perfectly conducting condition
induced from 5D leads to three discrete mode corrections. This is very
different from the result obtained from imposing 4D perfectly conducting
conditions on the 4D massless and massive vector fields obtained by decomposing
the 5D electromagnetic field. The latter only contains two discrete mode
corrections, but it has a continuum mode correction that depends on the
thicknesses of the plates. It is shown that under both boundary conditions, the
corrections to the Casimir force make the Casimir force more attractive. The
correction under 4D perfectly conducting condition is always smaller than the
correction under the 5D induced perfectly conducting condition. These
statements are true at any temperature.Comment: 20 pages, 4 figure
Quantum Back Reaction to asymptotically AdS Black Holes
We analyze the effects of the back reaction due to a conformal field theory
(CFT) on a black hole spacetime with negative cosmological constant. We study
the geometry numerically obtained by taking into account the energy momentum
tensor of CFT approximated by a radiation fluid. We find a sequence of
configurations without a horizon in thermal equilibrium (CFT stars), followed
by a sequence of configurations with a horizon. We discuss the thermodynamic
properties of the system and how back reaction effects alter the space-time
structure. We also provide an interpretation of the above sequence of solutions
in terms of the AdS/CFT correspondence. The dual five-dimensional description
is given by the Karch-Randall model, in which a sequence of five-dimensional
floating black holes followed by a sequence of brane localized black holes
correspond to the above solutions.Comment: 13 pages, 10 figure
Explicit Model Realizing Parton-Hadron Duality
We present a model that realizes both resonance-Regge (Veneziano) and
parton-hadron (Bloom-Gilman) duality. We first review the features of the
Veneziano model and we discuss how parton-hadron duality appears in the
Bloom-Gilman model. Then we review limitations of the Veneziano model, namely
that the zero-width resonances in the Veneziano model violate unitarity and
Mandelstam analyticity. We discuss how such problems are alleviated in models
that construct dual amplitudes with Mandelstam analyticity (so-called DAMA
models). We then introduce a modified DAMA model, and we discuss its
properties. We present a pedagogical model for dual amplitudes and we construct
the nucleon structure function F2(x,Q2). We explicitly show that the resulting
structure function realizes both Veneziano and Bloom-Gilman duality.Comment: 11 pages, 8 figure
Wightman function and vacuum densities for a Z_2-symmetric thick brane in AdS spacetime
Positive frequency Wightman function, vacuum expectation values of the field
square and the energy-momentum tensor induced by a Z_{2}-symmetric brane with
finite thickness located on (D+1)- dimensional AdS background are evaluated for
a massive scalar field with general curvature coupling parameter. For the
general case of static plane symmetric interior structure the expectation
values in the region outside the brane are presented as the sum of free AdS and
brane induced parts. For a conformally coupled massless scalar the brane
induced part in the vacuum energy-momentum tensor vanishes. In the limit of
strong gravitational fields the brane induced parts are exponentially
suppressed for points not too close to the brane boundary. As an application of
general results a special model is considered in which the geometry inside the
brane is a slice of the Minkowski spacetime orbifolded along the direction
perpendicular to the brane. For this model the Wightman function, vacuum
expectation values of the field square and the energy-momentum tensor inside
the brane are evaluated as well and their behavior is discussed in various
asymptotic regions of the parameters. It is shown that for both minimally and
conformally coupled scalar fields the interior vacuum forces acting on the
brane boundaries tend to decrease the brane thickness.Comment: 25 pages, 6 figures, discussion adde
- …