Modern Physics Letters A

Between the well-known adiabatic and radiative stages of the Supernova remnant (SNR) evolution there is, in fact, a transition stage with a duration comparable to the duration of adiabatic one. Physical existence of the transition stage is motivated by cooling of some part of the downstream hot gas with formation of a thin cold shell that is joined to a shell of swept up interstellar medium (ISM). We give an approximate analytical method for full hydrodynamical description of the transition stage. On its base we investigate the evolution of X-ray and γ-ray radiation during this stage. It is shown that formation of a dense shell during the transition stage is accompanied by the decrease of X-ray luminosity because of hot gas cooling and increase of gamma-ray flux according to the increase of target proton density and CR energy in the newly born shell. The role of nonuniformity of ISM and its influence on the high energy fluxes from the SNRs is also discussed.

We investigate a model of brane cosmology to find a unified description of the radiation-matter-dark energy universe. It is of the interacting holographic dark energy with a bulk-holographic matter χ. This is a five-dimensional cold dark matter, which plays a role of radiation on the brane. Using the effective equations of state instead of the native equations of state ω_Λ, we show that this model cannot accommodate any transition from the dark energy with to the phantom regime . Furthermore, the case of interaction between four-dimensional cold dark matter and five-dimensional cold dark matter is considered for completeness. Here we find that the redshift of matter-radiation equality z_eq is the same order as . Finally, we obtain a general decay rate Γ which is suitable for describing all interactions.

A stochastic background of relic gravitational waves is achieved by the so-called adiabatically-amplified zero-point fluctuations process derived from early inflation. In principle, it provides a distinctive spectrum of relic gravitational waves. In the framework of scalar–tensor gravity, we discuss the scalar modes of gravitational waves and the primordial production of this scalar component which is generated besides tensorial one. We also discuss the upper limit for such a relic scalar component with respect to the WMAP constraints.

For the confining phase of SU(2) Yang–Mills thermodynamics, we show that the asymptotic series representing the pressure is Borel summable for negative (unphysical) values of a suitably defined coupling constant. The inverse Borel transform is meromorphic except for a branch cut along the positive-real axis. The physical pressure is precisely nil at vanishing and acquires a small imaginary admixture at small temperature, the latter indicating violations of thermal equilibrium (turbulences).

Spatial noncommutativity removes the degeneracy of nonrelativistic electron gas. In particular one can interpret the noncommutativity parameter appearing in the second-order correlation term, as a new temperature reference. We investigate the effect of the noncommutativity of space on a many-particle system composed of locally interacting nonrelativistic fermions. We calculate the first-order energy shift of the system up to the second order in noncommutativity parameter and as a result the noncommutativity of space eliminates the degeneracy of the model. Thus, as the case of electron gas, one may interpret the noncommutativity parameter as a new reference temperature.

In this work the conditions appearing in the so-called WKB approximation formalism of quantum mechanics are analyzed. It is shown that, in general, a careful definition of an approximation method requires the introduction of two length parameters, one of them always considered in the textbooks on quantum mechanics, whereas the other is usually neglected. Afterwards we define a particular family of potentials and prove, resorting to the aforementioned length parameters, that we may find an energy which is a lower bound to the ground energy of the system. The idea is applied to the case of a harmonic oscillator and also to a particle freely falling in a homogeneous gravitational field, and in both cases the consistency of our method is corroborated. This approach, together with the so-called Rayleigh–Ritz formalism, allows us to define an energy interval in which the ground energy of any potential, belonging to our family, must lie.

We consider the possibility of observing the onset of the late time inflation of our patch of the Universe. The Hubble size criterion and the event horizon criterion are applied to several dark energy models to discuss the problem of future inflation of the Universe. We find that the acceleration has not lasted long enough to confirm the onset of inflation by present observations for the dark energy model with constant equation of state, the holographic dark energy model and the generalized Chaplygin gas (GCG) model. For the flat ΛCDM model with Ω_m0 = 0.3, we find that if we use the Hubble size criterion, we need to wait until the a_v which is the scale factor at the time when the onset of inflation is observed reaches 3.59 times of the scale factor a_T when the Universe started acceleration, and we need to wait until a_v = 2.3a_T to see the onset of inflation if we use the event horizon criterion. For the flat holographic dark energy model with d = 1, we find that a_v = 3.46a_T with the Hubble horizon and a_v = 2.34a_T with the event horizon, respectively. For the flat GCG model with the best supernova fitting parameter α = 1.2, we find that a_v = 5.50a_T with the Hubble horizon and a_v = 2.08a_T with the event horizon, respectively.