A nonminimally coupled, conformally extended Einstein-Maxwell theory of pp-waves

Abstract

A nonminimal coupling of Weyl curvatures to electromagnetic fields is considered in Brans-Dicke-Maxwell theory. The gravitational field equations are formulated in a Riemannian spacetime where the spacetime torsion is constrained to zero by the method of Lagrange multipliers in the language of exterior differential forms. The significance and ramifications of nonminimal couplings to gravity are examined in a pp-wave spacetime.

Compatibility of the Dimensional Reduction and Variation Procedures for a Quadratic Curvature Model with a Kaluza-Klein Ansatz

“…As for the equations governing the electromagnetic field, one may be tempted to take the variation directly with respect to F mn [12]. As it is clear in that article, in order to get the proper equations in regard to the electromagnetic equations, one should take an additional derivative.…”

“…The Kaluza-Klein (KK) theory unifies electromagnetism with gravitation. Unifying gravity with electromagnetism by some suitable trivial and/or non-trivial couplings with the generic F n , (DF ) n and RF 2 terms in the action is shown to be interesting [10,11,12]. They account for photon graviton oscillations [13] and also drew attention from an astrophysical point of view [14].…”