Modern Physics Letters A

Since the first "string revolution" of 1984, the weakly coupled E₈⊗E₈ heterotic string theory has been a promising candidate for the underlying theory of the Standard Model. The particle spectrum and the issue of dilaton stabilization are reviewed. Specific models for hidden sector condensation and supersymmetry breaking are described and their phenomenological and cosmological implications are discussed. The importance of T-duality is emphasized. Theoretical challenges to finding a satisfactory vacuum, as well as constraints from LHC data are addressed.

Here we investigate the effects of first-order correction to eikonal approximation in the analysis of longitudinal momentum distribution (LMD) data of outgoing core fragment ¹⁰Be coming from ⁹Be(¹¹Be, ¹⁰Be+n)⁹Be stripping reaction at 60 MeV/A incident energy. It is found that the inclusion of first-order correction term alters the tail region significantly which in turn improves matching between the data and prediction.

Noncommutative space which is rotationally invariant is considered. The hydrogen atom is studied in this space. We exactly find the leading term in the asymptotic expansion of the corrections to the ns energy levels over the small parameter of noncommutativity.

We discuss metric perturbations of the relativistic diffusion equation around the homogeneous Jüttner equilibrium of massless particles in a homogenous expanding universe. We describe the perturbations corresponding to the gravitational wave background. We show that the lowest order perturbation can be treated as a variation of temperature. We derive a formula expressing temperature fluctuations in terms of the diffusion and tensor power spectrum. We discuss the multipole expansion of the fluctuations in the presence of diffusion.

This paper is devoted to investigate the dynamics of the self-gravitating adiabatic and anisotropic source in 5D Einstein Gauss–Bonnet gravity. To this end, the source has been taken as Tolman–Bondi model which preserve inhomogeneity in nature. The field equations, Misner–Sharp mass and dynamical equations have formulated in Einstein Gauss–Bonnet gravity in 5D. The junction conditions have been explored between the anisotropic source and vacuum solution in Gauss–Bonnet gravity in detail. The Misner and Sharp approach has been applied to define the proper time and radial derivatives. Further, these helps to formulate general dynamical equations. The equations show that the mass of the collapsing system increases with the same amount as the effective radial pressure increases. The dynamical system preserves retardation which implies that system under-consideration goes to gravitational collapse.

We impose perfect fluid concept along with slow expansion approximation to derive new solutions which, considering non-static spherically symmetric metrics, can be treated as Black Holes (BHs). We will refer to these solutions as Quasi BHs. Mathematical and physical features such as Killing vectors, singularities, and mass have been studied. Their horizons and thermodynamic properties have also been investigated. In addition, relationship with other related works (including McVittie's) are described.

We consider spin- particles on the background of general accelerating black holes and the C-metric. The Rarita–Schwinger equations of spin- particles are analyzed on these backgrounds. The emission and absorption probabilities of these particles on these spacetimes are calculated. These backgrounds which we analyze contain both black hole horizon and acceleration horizon, and have general electric and magnetic charges, rotation, and acceleration parameter. Other physical quantities of the spin- field near the acceleration horizon are also computed.

We reconsider a recent perturbative calculation [M. A. Băloi, Mod. Phys. Lett. A29, 1450138 (2014)] of particle production in the expanding de Sitter space in an external electromagnetic field and apply it to the case of a constant uniform electric field in two dimensions. We show that perturbative number of created particles significantly differs from the existing nonperturbative result based on the Bogoliubov transformation method. We also point out that for a physically meaningful perturbative amplitude one should restrict to external potentials A_μ which in conformal coordinates vanish at infinite times. Potentials which do not respect this condition lead to gauge-dependent amplitudes, which also show close similarities with amplitudes in flat space in the unphysical case when the external potential suddenly vanishes. These problems are intimately linked with the finite upper limit of the conformal time in the de Sitter space and most probably a similar restriction should be imposed in perturbative calculations in FRW spacetimes with the same property.