128 research outputs found
Zeta Functions in Brane World Cosmology
We present a calculation of the zeta function and of the functional
determinant for a Laplace-type differential operator, corresponding to a scalar
field in a higher dimensional de Sitter brane background, which consists of a
higher dimensional anti-de Sitter bulk spacetime bounded by a de Sitter
section, representing a brane. Contrary to the existing examples, which all
make use of conformal transformations, we evaluate the zeta function working
directly with the higher dimensional wave operator. We also consider a generic
mass term and coupling to curvature, generalizing previous results. The
massless, conformally coupled case is obtained as a limit of the general result
and compared with known calculations. In the limit of large anti-de Sitter
radius, the zeta determinant for the ball is recovered in perfect agreement
with known expressions, providing an interesting check of our result and an
alternative way of obtaining the ball determinant.Comment: 14 pages, 1 figur
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
Quark-antiquark contribution to the BFKL kernel
The quark-antiquark contribution to the BFKL kernel is calculated. Using the
effective vertex for the pair production in the Reggeon-Reggeon
collision we find this contribution by integrating the square of this vertex
over relative transverse momenta and fractions of longitudinal momenta of
produced particles.Comment: 12 pages, Late
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.
Branes and Black holes in Collision
We study the collision of a brane with a black hole. Our aim is to explore
the topology changing process of perforation of a brane. The brane is described
as a field theoretical domain wall in the context of an axion-like model
consisting of a complex scalar effective field theory with approximate U(1)
symmetry. We simulate numerically the dynamics of the collision and illustrate
the transition from the configuration without a hole to the pierced one with
the aid of a phase diagram. The process of perforation is found to depend on
the collisional velocity, and, contrary to our expectation, we observe that
above a critical value of the velocity, the black hole has no chance to
perforate the wall. That is: high energy collisions do not assist piercing. We
also show that, only when the model parameters are fine-tuned so that the
energy scale of the string is very close to that of the domain wall, the
collision of the wall with the black hole has a possibility to provide a
mechanism to erase domain walls, if the hole expands. However, in such cases,
domain walls will form with many holes edged by a string and therefore
disappear eventually. Therefore this mechanism is unlikely to be a solution to
the cosmological domain wall problem, although it may cause some minor effects
on the evolution of a domain wall network.Comment: 14 pages; 9 figure
Quantized bulk scalar fields in the Randall-Sundrum brane-model
We examine the lowest order quantum corrections to the effective action
arising from a quantized real scalar field in the Randall-Sundrum background
spacetime. The leading term is the familiar vacuum, or Casimir, energy density.
The next term represents an induced gravity term that can renormalize the
4-dimensional Newtonian gravitational constant. The calculations are performed
for an arbitrary spacetime dimension. Two inequivalent boundary conditions,
corresponding to twisted and untwisted field configurations, are considered. A
careful discussion of the regularization and renormalization of the effective
action is given, with the relevant counterterms found. It is shown that the
requirement of self-consistency of the Randall-Sundrum solution is not simply a
matter of minimizing the Casimir energy density. The massless, conformally
coupled scalar field results are obtained as a special limiting case of our
results. We clarify a number of differences with previous work.Comment: 31 pages, 1 figur
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