Narrow Results

We discuss the implications of a purely classical (instead of quantum) theory of gravity for the primordial gravitational wave spectrum generated during inflation. We argue that for a scalar field driven inflation in a classical gravity the amplitude of the gravitational wave will be too small, irrespective of its primordial seed, to be detected in any forthcoming experiments. Therefore, a positive detection of the B-mode polarizations in the Cosmic Microwave Background (CMB) spectrum will naturally confirm the quantum nature of gravity itself. Furthermore there will be no upper limit on the scale of inflation in the case of classical gravity, and a high-scale model of inflation can easily bypass the observational constraints.

We describe the equation of motion of two charged spherical shells with tangential pressure in the field of a central Reissner–Nordstrom (RN) source. We solve the problem of determining the motion of the two shells after the intersection by solving the related Einstein–Maxwell equations and by imposing a physical continuity condition on the shells' velocities.

In addition, we consider four applications: post-Newtonian and ultrarelativistic approximations, a test-shell case, and the ejection mechanism of one shell.

This work is a direct generalization of Barkov–Belinski–Bisnovati–Kogan paper.

We prove the stability of a spacetime with a naked singularity under scalar field perturbations, where the perturbations are regular at the singularity. This spacetime, found by Janis, Newman and Winicour and independently by Wyman, is sourced by a massless scalar field and also arises as a certain limit of a class of charged dilatonic solutions in string theory. This stability result opens up specific questions for investigation related to the cosmic censorship conjecture and the mechanism by which it is implemented in nature.