A string-modified four-dimensional gravity theory (Q1120136)

A gravity theory generated by the Chapline-Manton ten-dimensional supergravity theory is discussed. It is conjectured that the supergravity action (derived in the lowest-order approximation) is reduced in the process of dimensional reduction to a simple action for 4-dimensional gravity and electromagnetic, dilaton and antisymmetric Kalb-Ramond fields. The resulting field equations for gravity are of third order due to the presence of the Chern-Simons term in the Kalb-Ramond field; also the field equation for the ``electromagnetic'' field is different from the Maxwell equations. In the static spherically symmetric case the field equations are of second order and can be explicitly integrated (in the absence of the electromagnetic field). The analogue of the Schwarzschild solution in general relativity is specified here by values of three free parameters: dilaton and Kalb-Ramond charges and a mass parameter. It is also shown that in the case of spherical symmetry the Kalb-Ramond field does not disturb the geodesic motion of test particles, thus the theory makes the same predictions as general relativity for solar system tests. The stability problems are not discussed.