Modern Physics Letters A

We shall consider the general problem of causal propagation for spinor fields, focus attention in particular on the case constituted by ELKO fields and will show that the problem of causal propagation for ELKO fields is always solvable.

In this note, we apply a special metric ansatz to simplify the equations of motion for gravitational systems. Then we construct charged brane solutions in D = n+p+2 dimensions which have spherical symmetry of Sⁿ and translational symmetry along p directions. They are characterized by mass density, uniform tension and electric/magnetic charges, and nonsingular only for specific tension. In particular, we find the limits and the coordinate transformations which reduce the charged brane solutions to M2- and M5-branes. We also obtain the regularity condition for an electrically charged two-brane solution which has two tensions.

We consider a locally scale invariant extension of the Standard Model of particle physics and argue that it fits both the particle and cosmological observations. The model is scale invariant both classically and quantum mechanically. The scale invariance is broken (or hidden) by a mechanism which we refer to as cosmological symmetry breaking. This produces all the dimensionful parameters in the theory. The cosmological constant or dark energy is a prediction of the theory and can be calculated systematically order by order in perturbation theory. It is expected to be finite at all orders. The model does not suffer from the hierarchy problem due to the absence of scalar particles, including the Higgs, from the physical spectrum.

We revisit the extended Feynman formula for the harmonic oscillator beyond and at caustics. The extension has been made by some authors, however, it is not obtained by the discrete formulation of path integral, which we consider the most reliable regularization of it. We derive the result by, especially at caustics, more rigorous method than previous.

It has been shown recently that phantom-like effect can be realized on the normal branch of the DGP setup without introduction of any phantom matter in the bulk or on the brane and therefore without violation of the null energy condition. Inclusion of the Gauss–Bonnet term in the bulk action modifies this picture via curvature effects. Based on the Lue–Starkman conjecture on the dynamical screening of the brane cosmological constant in the DGP scenario, we extend this proposal to a general DGP-inspired f(R, ϕ) model that stringy effects in the ultraviolet sector of the theory are taken into account by inclusion of the Gauss–Bonnet term in the bulk action. We study cosmological dynamics of this setup, especially its phantom-like behavior and possible crossing of the phantom divide line. In this setup, scalar field and curvature quintessence are treated in a unified framework.

In this paper, on the basis of Ref. 24 we will further study the new agegraphic dark energy (NADE) model with interaction term Γ = 3b²Hρ_c. Concretely, not only can the evolutions of some related cosmological quantities be described, but also the two geometrical diagnostic approaches are performed to this model, i.e. statefinder and Om diagnostics. By illustrating the evolutionary trajectories in r-s, r-q, w'-w and Om planes, we find that the constant n and coupling intensity b² play very important roles in the NADE model, and the Om curves of the NADE model are more sensitive to the constants than ones of the OADE model. In addition, we also plot the LCDM horizonal lines in Om diagrams, and show the discrimination among the NADE, OADE and LCDM models.

The conserved quantities, that are, gravitational energy–momentum and its relevant quantities are investigated for cylindrical and spherical gravitational waves in the framework of teleparallel equivalent of General Relativity using the Hamiltonian approach. For both cylindrical and spherical gravitational waves, we obtain definite energy and constant momentum. The constant momentum shows consistency with the results available in General Relativity and teleparallel gravity. The angular momentum for cylindrical and spherical gravitational waves also turn out to be constant. Further, we evaluate their gravitational energy–momentum fluxes and gravitational pressure.