Title: A New Unified Theory of Electromagnetic and Gravitational Interactions

Speaker: Prof. Li-Xin Li （李立新）(Peking University)

Time: 10:00AM, July 11st (Monday)

Place: Theoretical Physics Division，319

Abstract:In this talk we present a new unified theory of electromagnetic and gravitational interactions. By considering a four-dimensional spacetime as a hypersurface embedded in a five dimensional bulk spacetime, we derive the complete set of field equations in the four-dimensional spacetime from the five-dimensional Einstein field equation. We show that, besides the Einstein field equation in the four-dimensional spacetime, a new electromagnetic field equation is derived: ?aFab?xRbaAa = ?4pJb with x = ?2, where Fab is the antisymmetric electromagnetic field tensor defined by the potential vector Aa, Rab is the Ricci curvature tensor of the hypersurface, and Ja is the electric current vector. The new electromagnetic field equation differs from the Einstein-Maxwell equation by a curvature-coupled term x RbaAa, which addresses the problem of incompatibility of the Einstein-Maxwell equation with a universe containing a uniformly distributed net charge as discussed in a previous paper by the author. Hence, the new theory is physically different from the Kaluza-Klein theory and its variants where the Einstein-Maxwell equation is derived. In the four-dimensional Einstein field equation derived in the new theory, the source term includes the stress-energy tensor of electromagnetic fields as well as the stress-energy tensor of other unidentified matter. We show that, under some conditions the unidentified matter can be interpreted as a cosmological constant in the four-dimensional spacetime. We argue that, the new electromagnetic field equation and hence the new unified theory can be tested in an environment with a high mass density, e.g., inside a neutron star or a white dwarf, and in the early epoch of the universe.