Modern Physics Letters A

We review the recent programme undertaken to construct, systematically and algorithmically, large classes of heterotic vacua, as well as the search for the MSSM therein. Specifically, we outline the monad construction of vector bundles over complete intersection Calabi–Yau threefolds, their classification, stability, equivariant cohomology and subsequent relevance to string phenomenology. It is hoped that this top–down algorithmic approach will isolate special corners in the heterotic landscape.

An equivalence of total angular momentum operator of charge–monopole system to the momentum operator of a symmetrical quantum top is observed. This explicitly shows the string independence of Dirac's quantization condition leading to disappearance of Schwinger's string and reveals some properties of diatomic molecule for this system.

Ever since the first observations that we are living in an accelerating universe, it has been asked what dark energy is. There are various explanations, all of which have various drawbacks or inconsistencies. Here we show that using a dark spinor field it is possible to have an equation of state that crosses the phantom divide, becoming a dark phantom spinor which evolves into dark energy. This type of equation of state has been mildly favored by experimental data, however, in the past there were hardly any theories that satisfied this crossing without creating ghosts or causing a singularity which results in the universe essentially ripping. The dark spinor model converges to dark energy in a reasonable time frame avoiding the big rip and without attaining negative kinetic energy as it crosses the phantom divide.

The effect of cosmic string on the quasinormal modes (QNMs) of massless Dirac field perturbations were studied in different black hole spacetimes. Quasi-normal mode frequencies of massless Dirac field in Schwarzschild, RN extremal, SdS and near extremal SdS black hole spacetimes with cosmic string are obtained using WKB approximation. Our study shows a clear deviation in QNMs due to presence of cosmic string from those in the absence of string. The influence of cosmic string coded in the form of an increase in the oscillation frequency and damping time of QNMs.

The Mansouri–Sexl theory is a well-known test theory of relativity. In the following paper we demonstrate a novel way of detecting second-order effects in terms of both lab and ion speed for light speed anisotropy detection. Prior literature^15,18–21 has shown the way of constraining the Mansouri–Sexl parameter "a" via the Ives–Stilwell experiment, however, the prior approaches have proven to be incomplete in managing to constrain only one parameter, the "a" parameter. In the current paper we will take the unprecedented step of reconstructing the Mansouri–Sexl formalism for the Ives–Stilwell experiment and by showing how to improve on the theoretical and experimental bases such as to constrain both the parameter "a" and the parameter "b". Our paper is organized as follows: in the first section we give a new and more complete derivation of the Mansouri–Sexl Doppler effect. In the second part, we apply the newly expanded Mansouri–Sexl Doppler formalism in order to revise the principles of the Ives–Stilwell experiment. We continue by showing how the revised experiment is to be used in order to constrain both the parameter "a" and the parameter "b" in a measurement of light speed isotropy. This turns the Mansouri–Sexl Ives–Stilwell experiment into a very powerful tool for constraining light speed anisotropy.

Motivated by the Hamilton–Jacobi approach of constrained systems, we analyze the classical structure of a four-dimensional superstring. The equations of motion for a singular system are obtained as total differential equations in many variables. The path integral quantization based on Hamilton–Jacobi approach is applied to quantize the system, and the integration is taken over the canonical phase space coordinates.

Two monitoring proportional counters (MPCs), installed at the inlet and outlet of the gas system of BESIII drift chamber (DC), were used to monitor the operation of the BESIII DC successfully and effectively as reported in this paper. The ratio of G_out/G_in (full energy photoelectron peak position of ⁵⁵Fe 5.9 keV X-ray in inlet MPC as G_in and outlet MPC as G_out) is used as the main monitoring parameter. The MPC method is very useful for the gas detector system.