Friedmann Robertson-Walker model in generalised metric space-time with weak anisotropy

A generalized model of space-time is given, taking into consideration the anisotropic structure of fields which are depended on the position and the direction (velocity).In this framework a generalized FRW-metric the Raychaudhouri and Friedmann equations are studied.A long range vector field of cosmological origin is considered in relation to the physical geometry of space-time in which Cartan connection has a fundamental role.The generalised Friedmann equations are produced including anisotropic terms.The variation of anisotropy $z_t$ is expressed in terms of the Cartan torsion tensor of the Finslerian space-time.A possible estimation of the anisotropic parameter $z_t$ can be achieved with the aid of the de-Sitter model of the empty flat universe with weak anisotropy. Finally a physical generalisation for the model of inflation is also studied.Comment: 21 pages- to appear in GR

Asymptotic behavior of w in general quintom model

For the quintom models with arbitrary potential $V=V(\phi,\sigma)$, the asymptotic value of equation of state parameter w is obtained by a new method. In this method, w of stable attractors are calculated by using the ratio (d ln V)/(d ln a) in asymptotic region. All the known results, have been obtained by other methods, are reproduced by this method as specific examples.Comment: 8 pages, one example is added, accepted for publication in Gen. Rel. Gra

Universality of the Lyapunov regime for the Loschmidt echo

The Loschmidt echo (LE) is a magnitude that measures the sensitivity of quantum dynamics to perturbations in the Hamiltonian. For a certain regime of the parameters, the LE decays exponentially with a rate given by the Lyapunov exponent of the underlying classically chaotic system. We develop a semiclassical theory, supported by numerical results in a Lorentz gas model, which allows us to establish and characterize the universality of this Lyapunov regime. In particular, the universality is evidenced by the semiclassical limit of the Fermi wavelength going to zero, the behavior for times longer than Ehrenfest time, the insensitivity with respect to the form of the perturbation and the behavior of individual (non-averaged) initial conditions. Finally, by elaborating a semiclassical approximation to the Wigner function, we are able to distinguish between classical and quantum origin for the different terms of the LE. This approach renders an understanding for the persistence of the Lyapunov regime after the Ehrenfest time, as well as a reinterpretation of our results in terms of the quantum--classical transition.Comment: 33 pages, 17 figures, uses Revtex

Geometric and thermodynamic properties in Gauss-Bonnet gravity

In this paper, the generalized second law (GSL) of thermodynamics and entropy is revisited in the context of cosmological models in Gauss-Bonnet gravity with the boundary of the universe is assumed to be enclosed by the dynamical apparent horizon. The model is best fitted with the observational data for distance modulus. The best fitted geometric and thermodynamic parameters such as equation of state parameter, deceleration parameter and entropy are derived. To link between thermodynamic and geometric parameters, the "entropy rate of change multiplied by the temperature" as a model independent thermodynamic state parameter is also derived. The results show that the model is in good agreement with the observational analysis.Comment: 13 pages, 13 figures, to be published in Astrophysics and Space Sc

On the distances between entangled pseudoscalar mesons states

Entangled states of pseudoscalar mesons represent a very interesting tool for studying foundations of quantum mechanics, e.g. for testing Bell inequalities. Recently, they also emerged as a test bench for quantum information protocols. On the other hand, from a quantum information point of view, the characterization of the distance between two quantum states is a topic of the utmost importance. In this letter, with the purpose of providing a useful tool for further investigations, we address the problem of which distance allows a better discrimination between density matrices appearing in pseudoscalar phenomenology

Role of bulk and of interface contacts in the behaviour of model dimeric proteins

Some dimeric proteins first fold and then dimerize (three--state dimers) while others first dimerize and then fold (two--state dimers). Within the framework of a minimal lattice model, we can distinguish between sequences obeying to one or to the other mechanism on the basis of the partition of the ground state energy between bulk than for interface contacts. The topology of contacts is very different for the bulk than for the interface: while the bulk displays a rich network of interactions, the dimer interface is built up a set of essentially independent contacts. Consequently, the two sets of interactions play very different roles both in the the folding and in the evolutionary history of the protein. Three--state dimers, where a large fraction of the energy is concentrated in few contacts buried in the bulk, and where the relative contact energy of interface contacts is considerably smaller than that associated with bulk contacts, fold according to a hierarchycal pathway controlled by local elementary structures, as also happens in the folding of single--domain monomeric proteins. On the other hand, two--state dimers display a relative contact energy of interface contacts which is larger than the corresponding quantity associated with the bulk. In this case, the assembly of the interface stabilizes the system and lead the two chains to fold. The specific properties of three--state dimers acquired through evolution are expected to be more robust than those of two--state dimers, a fact which has consequences on proteins connected with viral diseases

Transient Crossing of Phantom divide line wΛ=−1w_{\Lambda}=-1 under Gauss-Bonnet interaction

Smooth double crossing of the phantom barrier $w_{\Lambda} = -1$ has been found possible in cosmological model with Gauss-Bonnet-scalar interaction, in the presence of background cold dark matter. Such crossing has been observed to be a sufficiently late time phenomena and independent of the sign of Gauss-Bonnet-scalar interaction. The luminosity distance versus redshift curve shows a perfect fit with the $\Lambda CDM$ model up to $z=3.5$.Comment: 9 pages, 9 figure