Modern Physics Letters A

We review the status of a certain (infinite) class of four-dimensional generally covariant gravity theories propagating two degrees of freedom that are formulated without any direct mention of the metric. General relativity itself (in its Plebański formulation) belongs to the class, so these theories are examples of modified gravity. We summarize the current understanding of the nature of the modification, of the renormalizability properties of these theories, of their coupling to matter fields, and describe some of their physical properties.

We discuss the relation between N = 2 Volkov–Akulov model and the spontaneously broken linear supersymmetry (LSUSY) interacting gauge theory for N = 2 vector and N = 2 scalar supermultiplets in two-dimensional spacetime (d = 2). The local gauge interaction of LSUSY is induced by the specific composite structure of the auxiliary fields and the consequent transformations.

The existence of degenerated quantum vacua (coherent states of zero modes), for N-level quantum systems, leads to a breakdown of the original unitary U(N) symmetry in the many-particle theory. The action of some spontaneously broken symmetry transformations destabilize these pseudo-vacua and make them radiate. We study the structure of this thermal radiation, which turns out to be of Fermi–Dirac type.

Using N = 1+1 supersymmetric extension of the three-dimensional gravity with torsion, we show that a generic black hole has no exact supersymmetries, the extremal black hole has only one, while the zero-energy black hole has two. Combining these results with the asymptotic supersymmetry algebra, we are naturally led to interpret the zero-energy black hole as the ground state of the Ramond sector, and analogously, the anti-de Sitter solution as the ground state of the Neveu–Schwarz sector.

We apply the conical singularity method to the two-dimensional version of the Schwarzschild metric to obtain the Kruskal coordinates of the black hole in a very simple and direct way. Then we make use of this metric in an approximated version and calculate the expected value of energy–momentum tensor of a massless quantum field near the horizon, resulting in regular expressions for its components.

The long and short gamma-ray bursts are believed to be produced due to collapse of massive stars and merger of compact binaries respectively. All these objects are rich in neutron and the jet outflow from these objects must have a neutron component in it. By postulating the oscillation in the gamma-ray burst fireball, we show that, 19–38 GeV neutrinos and anti-neutrinos can be produced due to annihilation of anti-neutrons with the background neutrons. These neutrinos and anti-neutrinos will be produced before the 5–10 GeV neutrinos due to dynamical decoupling of neutrons from the rest of the fireball. Observation of these neutrinos will shed more light on the nature of the GRB progenitors and also be a unique signature of physics beyond the standard model. A possible way of detecting these neutrinos in future is also discussed.

In this paper, we regard dilaton in Weyl-scaled induced gravitational theory as coupled quintessence, which is called DCQ model by us. Parametrization of the dark energy model is a good method by which we can construct the scalar potential directly from the effective equation of state function ω_σ(z) describing the properties of the dark energy. Applying this method to the DCQ model, we consider four parametrizations of ω(z) and investigate the features of the constructed DCQ potentials, which possess two different evolutive behaviors called "O" mode and "E" mode. Lastly, we comprise the results of the constructed DCQ model with those of quintessence model numerically.