Physics Letters B 734 (2014) 377–382
Contents lists available at ScienceDirect
Physics Letters B
www.elsevier.com/locate/physletb
Brans–Dicke gravity theory from topological gravity
C. Inostroza, A. Salazar, P. Salgado
∗
Departamento de Física, Universidad de Concepción, Casilla 160-C, Concepción, Chile
a r t i c l e i n f o a b s t r a c t
Article history:
Received
28 December 2013
Received
in revised form 26 May 2014
Accepted
28 May 2014
Available
online 2 June 2014
Editor:
M. Cveti
ˇ
c
We consider a model that suggests a mechanism by which the four dimensional Brans–Dicke gravity
theory may emerge from the topological gravity action.
To
achieve this goal, both the Lie algebra and the symmetric invariant tensor that define the topological
gravity Lagrangian are constructed by means of the Lie algebra S-expansion procedure with an
appropriate abelian semigroup S.
© 2014 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license
(http://creativecommons.org/licenses/by/3.0/). Funded by SCOAP
3
.
1. Introduction
It has been known for a long time that in General Relativity the
spacetime is a dynamical object which has independent degrees
of freedom, and is governed by dynamical equations, namely the
Einstein field equations. This means that in General Relativity the
geometry is dynamically determined. Therefore, the construction of
a gauge theory of gravity requires an action that does not consider
a fixed space-time background. An action for gravity fulfilling these
conditions was proposed long ago by Chamseddine [1,2].
A.H.
Chamseddine [1,2] constructed actions for topological grav-
ity
in all dimensions. In these references it was shown that
the odd-dimensional theories are based on Chern–Simons forms
with the gauge groups taken to be ISO(2n, 1) or SO(2n + 1, 1) or
SO(2n, 2) depending on the sign of the cosmological constant. The
use of the Chern–Simons form was essential so as to have a gauge
invariant action without constraints.
The
even-dimensional theories use, in addition to the gauge
fields, a scalar multiplet in the fundamental representation of the
gauge group. For even-dimensional spaces there is no natural geo-
metric
candidate such as the Chern–Simons form. The wedge prod-
uct
of n of the field strengths can made the required 2n-form in
a 2n-dimensional space-time. To form a group invariant 2n-form,
the n-product of the field strength is not enough, but will require
in addition the introduction of a scalar field φ
a
in the fundamental
representation.
If
topological gravity theories are to provide the appropri-
ate
gauge-theory framework for the gravitational interaction, then
these theories must satisfy the correspondence principle, namely
they must be related to General Relativity or to Brans–Dicke the-
ory.
*
Corresponding author.
It is the purpose of this paper to show that Brans–Dicke the-
ory
emerges as the → 0 limit of a topological gravity theory
invariant under the so called AdS-Lorentz algebra (AdS L
4
) [3,4]
(see
also [5]). Here is a length scale—a coupling constant that
characterizes different regimes within the theory. The AdS-Lorentz
algebra, on the other hand, is constructed from the AdS algebra and
a particular semigroup S by means of the S-expansion procedure
introduced in Refs. [6,9]. The field content induced by AdS-Lorentz
includes the vielbein e
a
, the spin connection ω
ab
and the extra
bosonic fields k
ab
, φ
ab
, h
ab
, φ
a
.
This
paper is organized as follows: In Section 2 we briefly re-
view
some aspects of (i) topological gravity, (ii) the S-expansion
procedure and (iii) the Brans–Dicke gravity theory. An explicit
action for four-dimensional gravity is considered in Section 3
where
the Lie algebra S-expansion procedure is used to obtain an
AdS
L
4
-invariant topological gravity action. The weak coupling con-
stant
limit of this action is then shown to yield the Brans–Dicke
action.
The work concludes with a comment and with Appen-
dices A
and B, where the case of a topological gravity invariant
under the B
5
algebra [10] is considered.
2. Topological gravity, S-expansion method and Brans–Dicke
gravity theor y
In this section we shall review some aspects of (i) topological
gravity, (ii) the S-expansion procedure and (iii) the Brans–Dicke
gravity theory.
2.1. Topological gravity
In Refs. [1,2] Chamseddine constructed actions for topological
gravity in all dimensions. For odd dimensions, the action is given
by
http://dx.doi.org/10.1016/j.physletb.2014.05.080
0370-2693/
© 2014 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/3.0/). Funded by
SCOAP
3
.