Modern Physics Letters A

Comparisons between the redshifts of spectral lines from cosmologically-distant galaxies can be used to probe temporal changes in low-energy fundamental constants like the fine structure constant and the proton–electron mass ratio. Here, we review the results from, and the advantages and disadvantages of, the best techniques using this approach, before focussing on a new method, based on conjugate satellite OH lines, that appears to be less affected by systematic effects and hence holds much promise for the future.

The classical confinement condition of test particles to a brane universe in the absence of non-gravitational forces is transformed using the Hamilton–Jacobi formalism. The transformed condition provides a direct criterion for selecting in a cosmological scenario 5D bulk manifolds wherein it is possible to obtain confinement of trajectories to 4D hypersurfaces purely due to classical gravitational effects.

We show that the gluon fusion amplitude in the gauge-Higgs unification scenario is finite in any dimension regardless of its nonrenormalizability. This result is supported by the fact that the local operator describing the gluon fusion process is forbidden by the higher dimensional gauge invariance. We explicitly calculate the gluon fusion amplitude in an arbitrary dimensional gauge-Higgs unification model and indeed obtain the finite result.

From several neutrino oscillation experiments, we understand now that neutrinos have mass. However, we really do not know what mechanism is responsible for producing this neutrino mass. Current or planned neutrino experiments utilize neutrino beams and long-baseline detectors to explore flavor mixing but do not address the question of the origin of neutrino mass. In order to begin answering that question, neutrino interactions need to be explored at much higher energies. This paper outlines a program to explore neutrinos and their interactions with various particles through a series of experiments involving colliding neutrino beams.

Recently, W. A. Hiscock⁴ studied the semi classical gravitational effects around global monopole. He obtained the vacuum expectation value of the stress–energy tensor of an arbitrary collection of conformal mass less free quantum fields (scalar, spinor and vectors) in the spacetime of a global monopole. With this stress–energy tensor, we study the semiclassical gravitational effects of a global monopole in the context of Brans–Dicke theory of gravity.

In this work we calculate the neutrino self-energy in the presence of a magnetized medium. The magnetized medium consists of electrons, positrons, neutrinos and a uniform classical magnetic field. The calculation is done assuming that the background magnetic field is weak compared to the W-boson mass squared, as a consequence of which only linear order corrections in the field are included in the W-boson propagator. The electron propagator consists of all order corrections in the background field. Although the neutrino self-energy in a magnetized medium in various limiting cases has been calculated previously, in this paper we produce the most general expression of the self-energy in the absence of the Landau quantization of the charged gauge fields. We calculate the effect of the Landau quantization of the charged leptons on the neutrino self-energy in the general case. Our calculation is specifically suited for situations where the background plasma may be CP symmetric.

Null Energy Condition (NEC) requires the equation of state (EoS) of the universe w_u satisfy w_u ≥ -1, which implies, for instance in a universe with matter and dark energy dominating w_u = w_mΩ_m + w_deΩ_de = w_deΩ_de ≥ -1. In this paper we study constraints on the dark energy models from the requirement of the NEC. We will show that with Ω_de ~ 0.7, w_de < -1 at present epoch is possible. However, NEC excludes the possibility of w_de < -1 forever as happened in the Phantom model, but if w_de < -1 stays for a short period of time as predicted in the Quintom theory, NEC can be satisfied. We take three examples of Quintom models of dark energy, namely the phenomenological EoS, the two-scalar-field model and the single scalar model with a modified Dirac–Born–Infeld (DBI) Lagrangian to show how this happens.