Modern Physics Letters A

It is now well established and accepted that roughly 25% of the total mass-energy density of the Universe is in the form of non-relativistic particles. That these particles, referred to as Dark Matter, have remained a mystery has served as motivation for the design and implementation of increasingly ingenious and far reaching experiments in an attempt to identify and understand them. This paper will review various ongoing Dark Matter searches with focus on the variety of techniques and implementation used to both detect the rare Dark Matter interactions as well as reject the vast number of background events.

The Newtonian solid-mechanical theory of non-compressional spheroidal and torsional nodeless elastic vibrations in the homogenous crust model of a quaking neutron star is developed and applied to the modal classification of the quasi-periodic oscillations (QPOs) of X-ray luminosity in the aftermath of giant flares in SGR 1806-20 and SGR 1900+14. Particular attention is given to the low-frequency QPOs in the data for SGR 1806-20 whose physical origin has been called into question. Our calculations suggest that unspecified QPOs are due to nodeless dipole torsional and dipole spheroidal elastic shear vibrations.

Intersecting spacelike braneworld cosmologies are investigated. The time axis is set on the scale parameter of extra space, which may include more than one timelike metric. We obtain the eternally inflating (i.e. undergoing late-time inflation) Robertson–Walker spacetime and extra space with a constant scale factor. In the case of multibrane solutions, some dimensions are static or shrink. The fact that the largest supersymmetry algebra contains 32 supercharges in four dimensions imposes a restriction on the geometry of extra space.

We describe various nonrelativistic contractions of two classes of twisted Poincaré algebra: canonical one (θ_μν-deformation) and the one leading to Lie-algebraic models of noncommutative spacetimes. The cases of contraction-independent and contraction-dependent twist parameters are considered. We obtain five models of noncommutative nonrelativistic spacetimes, in particular, two new Lie-algebraic nonrelativistic deformations of spacetime, respectively, with quantum time/classical space and with quantum space/classical time.

We investigate the degree of spin polarization of single top quarks in the eγ collision via the process with center-of-mass energies , 1 and 1.5 TeV of the parental linear e⁺e^- collider. Dominant spin fractions and spin asymmetries for the various top quark spin bases are investigated. We show that e⁺-beam direction is the favorite top quark spin decomposition axis. It is found to be comparable with the ones in pp and ep collisions.

The constituent quark model (CQM) has recently been widely used for the description of the internal structure of baryons. The baryon spectrum is usually well described, although various models are quite different. However, the study of baryon spectroscopy is not sufficient to distinguish among the various forms of quark dynamics. It would be interesting to consider the effect of an extra residual interaction among the quarks, which contains a dependence on isospin (or flavor). In the chiral constituent quark model the non-confining part of the potential is provided by the interaction with the Goldstone bosons, giving rise to a spin- and isospin-dependent part which is crucial for the description of the spectrum for energies lower than 1.7 GeV. In this work we have introduced an improved form of the hyperfine interaction and isospin dependent quark potential. The resulting description of the baryon spectrum was found to be satisfactory and we not only have included confinement potential at large separations, but also color charge and non-confining hyperfine interaction potentials. This combination of potentials yields spectra which are very close to the ones obtained in experiments.

Hawking radiation viewed as a semiclassical tunneling process of particles from the event horizon of general static black holes is investigated by taking the back-reaction of the emitted particles into account. In a general static spacetime, the emission rates of massless, massive and massive charged particles are computed respectively and the tunneling probabilities are obtained. Our results show that when energy and charge conservation are incorporated into the radiation process, the emission rate of the tunneling particles is related to changes of the Bekenstein-Hawking entropies of the black hole before and after the emission, thus it is consistent with an underlying unitary theory. The present results are obtained in a general way, no matter what the special static metric function is, and hence a generalization for the results found in the literature is given. Some remarks on the tunneling method are presented.