Modern Physics Letters A

The proton spin puzzle has challenged our understanding of QCD for the last 20 years. New measurements of polarized glue, valence and sea quark polarization, including strange quark polarization, are available. What is new and exciting in the data, and what might this tell us about the structure of the proton? The proton spin puzzle seems to be telling us about the interplay of valence quarks with the complex vacuum structure of QCD.

We discuss how the reflective scattering would affect elastic scattering in the region of small and moderate values of -t, in particular, we demonstrate that diffractive pattern in the angular distribution will be kept in a modified form.

We discuss the effects of non-inertial motion in reactions occurring in laboratory, stars, and elsewhere. It is demonstrated that non-inertial effects due to large accelerations during nuclear collisions might have appreciable effects nuclear and atomic transitions. We also explore the magnitude of the corrections induced by strong gravitational fields on nuclear reactions in massive, compact stars, and the neighborhood of black holes.

A set of scaling laws, based on the stochastic motions of the granular components of astronomical systems, is applied to a cosmological model with a positive cosmological constant. It follows that the mass of the dominant particle in the observable universe must be proportional to the sixth root of the cosmological constant and of order near the nucleon mass, which is consistent with the Zel'dovich scaling law. The approach is a natural way to solve the "cosmic coincidence" problem. On the other hand, the observed value of the cosmological constant emerges as the result of a scaling law induced by the stochastic mechanism which gives rise to the gravitationally bound systems.

We calculate the charged scalar particle creation in the presence of gravitational and electromagnetic fields in two models of spatially flat Robertson–Walker spacetimes: de Sitter space and asymptotically radiation dominated model. We used the Bogoliubov transformation to compute the rate of production of the particles. Possibility of creation of massless charged particles is also discussed.

Since the discovery of accelerated expansion of the universe, it was necessary to introduce a new component of matter distribution called dark energy. The standard cosmological model considers isotropy of the pressure and assumes an equation of state p = ωρ, relating the pressure p and the energy density ρ. The interval of the parameter ω defines the kind of matter of the universe, related to the fulfillment, or not, of the energy conditions of the fluid. The recent interest in this kind of fluid with anisotropic pressure, in the scenario of the gravitational collapse and star formation, imposes a careful analysis of the energy conditions and the role of the components of the pressure. Here, in this work, we show an example where the classification of dark energy for isotropic pressure fluids is used incorrectly for anisotropic fluids. The correct classification and its consequences are presented.

As two generalizations of Einstein's general relativity, the nontrivial spacetime torsion and the compact extra dimensions have been largely studied in the literature. In this paper, by combining a torsioned Kaluza–Klein scheme and the field-theory cosmic string theory, we discuss that a higher-dimensional torsion component can be expressed in terms of the usual four-dimensional field strength two-form, and this torsion form can then get trapped into the cores of the cosmic strings and further relate to the intrinsic spins of the strings.

Recent research on Hawking radiations of the Rindler spacetime and spherically symmetric uncharged spacetime shows that the Hawking temperature can be obtained by fermions tunnelling method. In this paper, we extend this work to the charged rotating spacetime and review the Hawking radiation of the Kerr–Sen dilaton–axion black hole by fermions tunnelling. The Hawking temperature is recovered and is exactly the same as that obtained by other methods.