Eur. Phys. J. C (2016) 76:21
DOI 10.1140/epjc/s10052-015-3873-z
Regular Article - Theoretical Physics
The stability and gravitational Newtonian limit of a modified
Randall–Sundrum model
Shahrokh Parvizi
a
, Mojtaba Shahbazi
b
Department of Physics, School of Sciences, Tarbiat Modares University, P.O. Box 14155-4838, Tehran, Iran
Received: 14 October 2015 / Accepted: 29 December 2015 / Published online: 19 January 2016
© The Author(s) 2016. This article is published with open access at Springerlink.com
Abstract For a modified Randall–Sundrum model (Jones
et al. in Phys. Rev. D 88:025048, 2013), the graviton equa-
tions are derived and the mass spectrum found. The latter
includes a massless graviton and a continuum mass with a
gap. There is no negative mass-squared in the spectrum, so the
model is stable. The gravitational Newtonian limit is obtained
with an exponentially suppressed modification from the extra
dimension.
1 Introduction
Extra dimensional brane-world models were first introduced
in [1] and then in [2](seealso[3]) to solve the hierarchy prob-
lem in fundamental interactions including gauge fields and
gravity. The basic idea of these models and their followers is
an assumption that matter and gauge fields are confined on a
three-dimensional brane embedded in a higher dimensional
spacetime, while the gravity, by definition, can travel in all
dimensions. This is compatible with observations, provided
either the extra dimension volume is of the order of the TeV
scale as suggested in [1] or somehow warped over the brane
as in [2].
The mentioned assumption is supported by string theory
in which (D-)branes are defined to be where open strings
ended. The latter correspond to the standard model fields in
the low energy limit. In contrast, closed strings can propagate
into extra dimension(s) off the brane and in the low energy
limit correspond to gravitons. Despite this justification, it is
important to understand the mechanism of field localization
on the brane in the low energy scales and independent of the
string theory. This was not very satisfactory and all Standard
Model’s particles could not be trapped into the brane in the
original five-dimensional version of this model, though there
are successes by using some six-dimensional models [4–7].
a
e-mail: parvizi@modares.ac.ir
b
e-mail: Mojtaba.Shahbazi@modares.ac.ir
In this regard, in [8], a five-dimensional modified Randall–
Sundrum (MRS) model was proposed and shown that it
improves the field localization behavior on the brane. This
model, locally, looks very similar to the original RS, but it
was shown that they differ globally [8]. An important differ-
ence is that, in contrast to the RS model, the new one does
not contain any five-dimensional cosmological constant.
Regarding progress in the field localization by propos-
ing [8], it is worth examining the effective four-dimensional
gravitational behavior of this model. In this article, we inves-
tigate the gravitational perturbation of the background and
find the graviton spectrum. We show that it excludes negative
mass modes which signing stability of the model. Moreover,
its Newtonian gravity limit is studied.
The organization of this paper is as follows. In Sect. 2 we
introduce the metric and recall its differences with the RS.
In Sect. 3, we perturb the background and find the graviton
mass spectrum. In Sect. 4, we study the Newtonian limit and
conclude in Sect. 5.
2 The background metric
Consider the five-dimensional Einstein–Hilbert gravity act-
ion, which reads as follows:
S
g
=
1
2κ
2
d
5
x
|g
(5)
|R + S
brane
+ S
matter
(1)
in which S
brane
is a localized action of brane(s) and S
matter
is
the action for any matter in the system. In the next section it
will be shown that μν-component of energy-momentum ten-
sor comprises two terms, a delta Dirac term which indicates
the brane and a constant term which could emanate from a
scalar source field [8].
Based on this action, the following metric can be introduced
as a solution to the equations of motion which contains a
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