Modern Physics Letters A

The problem of constructing global models describing isolated axially symmetric rotating bodies in equilibrium is analyzed. It is claimed that, whenever the global space–time is constructed by giving boundary data on the limiting surface of the body and integrating Einstein's equations on both inside and outside the body, the problem becomes overdetermined. Similarly, when the space–time describing the interior of the body is explicitly given, the problem of finding the exterior vacuum solution becomes overdetermined. We discuss in detail the procedure to be followed in order to construct the exterior vacuum field created by a given but arbitrary distribution of matter. Finally, the uniqueness of the exterior vacuum gravitational field is proven by exploiting the harmonic map formulation of the vacuum equations and the boundary conditions prescribed from the matching.

We give a microscopic description of extreme and near-extreme Reissner–Nordström black holes in four dimensions in terms of fundamental strings in a background of magnetic five branes and monopoles. The string oscillator numbers and tension are rescaled due to the Rindler space background with the string mass fixed. The entropy of the black holes is reproduced correctly by that of the string by taking into account the tension rescaling.

We study the vacuum polarization of supersymmetric toroidal D-brane placed in the constant electromagnetic field. Explicit calculation of the one-loop effective potential is performed for membrane with constant magnetic or electric background. We find that the one-loop potentials vanish as the effect of supersymmetry.

The possibility of generating the observed baryon asymmetry of the universe in an SO(10) gauge model with spontaneous symmetry breaking pattern is studied. We find it possible to generate a , converting the leptonic number produced at the B- L breaking scale via the B+L violating processes mediated by sphalerons at the electroweak scale. The resulting picture is tested against the limit coming from experimental data: proton lifetime and neutrino oscillations.

We calculate the spectrum of separations between nucleation sites of hadron bubbles formed during the first-order cosmic QCD phase transition considered within the Lee–Wick model, an effective QCD model. On the basis of the separation spectrum, we construct a naive model mass spectrum of quark nuggets. Using this mass spectrum and the microlensing event statistics of the MACHO group, we place an upper limit on the mass density of quark nuggets in the galactic halo.

In this letter we show that an uncharged black hole moving superluminally in a transparent dielectric medium violates Hawking's area theorem. The violation can be overcome through the emission of radiation. Since modes cannot emerge from the black hole itself, this radiation must originate from a collective effect in the medium, in complete analogy with the Vavilov–Cherenkov effect. However, because the black hole is uncharged, the emission mechanism must be different. We discuss the physical origin of the effect and obtain a Newtonian estimation. Then we obtain the appropriate equations in the relativistic case and show that the field which is radiated away is a combination of gravitational and electromagnetic degrees of freedom. Possible astrophysical relevance for the detection of primordial black holes and binary systems is discussed.

A longstanding conjecture by Belinskii, Khalatnikov and Lifshitz that the singularity in generic gravitational collapse is spacelike, local and oscillatory is explored analytically and numerically in spatially inhomogeneous cosmological space–times. With a convenient choice of variables, it can be seen analytically how nonlinear terms in Einstein's equations control the approach to the singularity and cause oscillatory behavior. The analytic picture requires the drastic assumption that each spatial point evolves toward the singularity as an independent spatially homogeneous universe. In every case, detailed numerical simulations of the full Einstein evolution equations support this assumption.

In this letter, we assume that negative mass objects can exist in the extragalactic space and analyze the consequences of their microlensing on light from distant active galactic nuclei. We find that such events have very similar features to some observed gamma ray bursts and use recent satellite data to set an upper bound to the amount of negative mass in the universe.

This letter elucidates recent achievements of the "nongravitating vacuum energy (NGVE) theory" which has the feature that a shift of the Lagrangian density by a constant does not affect dynamics. In the first-order formalism, a constraint appears that enforces the vanishing of the cosmological constant Λ. Standard dynamics of gauge unified theories (including fermions) and their SSB appear if a four-index field strength condensate is present. At the vacuum state, there is exact balance (to zero) of the gauge fields condensate and the original scalar fields potential. As a result it is possible to combine the solution of the Λ problem with inflation and transition to a Λ=0 phase without fine tuning after a reheating period. The model opens new possibilities for a solution of the hierarchy problem.