Modern Physics Letters A

The descriptions of Reissner–Nordström and Kerr–Newman dilatonic black holes in the Einstein frame are compared to those in the string frame. We describe various physical measurements in the two frames and show which experiments can distinguish between the two frames. In particular we discuss the gyromagnetic ratios of black holes, the decay law via Hawking radiation and the propagation of light on black hole backgrounds.

We present here three new exact solutions of Brans–Dicke theory for a stationary geometry with cylindrical symmetry in the presence of matter in rigid rotation with . All the solutions have eternal closed timelike curves in some region of space–time which has a size that depends on ω. Moreover, two of them do not go over a solution of general relativity in the limit ω→∞.

We propose an infinite family of difference equations, which are derived from the first principle that they are invariant with respect to the Schrödinger algebra. The first member of this family is a difference analogue of the free Schrödinger equation. These equations are obtained via a purely algebraic construction from a corresponding family of singular vectors in Verma modules over the Schrödinger algebra. The crucial moment in the construction is the realization of the Schrödinger algebra through additive difference vector fields, i.e. vector fields with difference operators instead of differential operators. Our method produces also differential-difference equations in which only space- or time-differentiation is replaced with the corresponding difference operators.

We attempt to construct new superstring actions with a D-plet of Majorana fermions , where ℬ is the D-dimensional space–time index and A is the two-dimensional spinor index, by deforming the Schild action. As a result, we propose three kinds of actions: the first is invariant under N=1 (the worldsheet) supersymmetry transformation and the area-preserving diffeomorphism. The second contains the Yukawa type interaction. The last possesses some nonlocality because of bilinear terms of . The reasons why completing a Schild type superstring action with is difficult are finally discussed.

The uniqueness of the hypercharge assignments in the three-fermion families leptoquark–bilepton SU(3)_C× SU(4)_L×U(1)_N model is established. Although the gauge group contains an explicit U(1) factor, freedom from triangle anomalies combined with the requirement of nonvanishing charged fermion masses uniquely fix the electric charges of all fermions independently of the neutrinos being massless or not. The electric-charge quantization, flavor family replication, and the existence of three colors are interwoven.

We construct the anti-de Sitter supergravity in three dimensions associated with the supergroup SU(1,1|2)×SU(1,1|2). The field content and the action are inferred using the fact that AdS supergravity theories in three dimensions are Chern–Simons theories.

Supersymmetry in quantum optical models is pointed out here by dealing with differential realizations of the generators of the nonlinear Higgs algebra, when this algebra is seen as the spectrum generating algebra subtending the multi-boson Hamiltonians of such models.