On the fate of singularities and horizons in higher derivative gravity

We study static spherically symmetric solutions of high derivative gravity theories, with 4, 6, 8 and even 10 derivatives. Except for isolated points in the space of theories with more than 4 derivatives, only solutions that are nonsingular near the origin are found. But these solutions cannot smooth out the Schwarzschild singularity without the appearance of a second horizon. This conundrum, and the possibility of singularities at finite r, leads us to study numerical solutions of theories truncated at four derivatives. Rather than two horizons we are led to the suggestion that the original horizon is replaced by a rapid nonsingular transition from weak to strong gravity. We also consider this possibility for the de Sitter horizon.Comment: 15 pages, 3 figures, improvements and references added, to appear in PR

Properties of charmed and bottom hadrons in nuclear matter: A plausible study

Changes in properties of heavy hadrons with a charm or a bottom quark are studied in nuclear matter. Effective masses (scalar potentials) for the hadrons are calculated using quark-meson coupling model. Our results also suggest that the heavy baryons containing a charm or a bottom quark will form charmed or bottom hypernuclei, which was first predicted in mid 70's. In addition a possibility of $B^-$-nuclear bound (atomic) states is briefly discussed.Comment: Latex, 11 pages, 3 figures, text was expanded substantially, version to appear in Phys. Lett.

The cosmological background of vector modes

We investigate the spectrum of vector modes today which is generated at second order by density perturbations. The vector mode background that is generated by structure formation is small but in principle it contributes to the integrated Sachs-Wolfe effect, to redshift-space distortions and to weak lensing. We recover, clarify and extend previous results, and explain carefully why no vorticity is generated in the fluid at second order. The amplitude of the induced vector mode in the metric is around 1% that of the first-order scalars on small scales. We also calculate the power spectrum and the energy density of the vector part of the shear at second order.Comment: 9 pages, 2 figures. Version to appear in JCAP; minor improvements and additional reference

Exact soliton solution and inelastic two-soliton collision in spin chain driven by a time-dependent magnetic field

We investigate dynamics of exact N-soliton trains in spin chain driven by a time-dependent magnetic field by means of an inverse scattering transformation. The one-soliton solution indicates obviously the spin precession around the magnetic field and periodic shape-variation induced by the time varying field as well. In terms of the general soliton solutions N-soliton interaction and particularly various two-soliton collisions are analyzed. The inelastic collision by which we mean the soliton shape change before and after collision appears generally due to the time varying field. We, moreover, show that complete inelastic collisions can be achieved by adjusting spectrum and field parameters. This may lead a potential technique of shape control of soliton.Comment: 5 pages, 5 figure

Combined constraints on modified Chaplygin gas model from cosmological observed data: Markov Chain Monte Carlo approach

We use the Markov Chain Monte Carlo method to investigate a global constraints on the modified Chaplygin gas (MCG) model as the unification of dark matter and dark energy from the latest observational data: the Union2 dataset of type supernovae Ia (SNIa), the observational Hubble data (OHD), the cluster X-ray gas mass fraction, the baryon acoustic oscillation (BAO), and the cosmic microwave background (CMB) data. In a flat universe, the constraint results for MCG model are, $\Omega_{b}h^{2}=0.02263^{+0.00184}_{-0.00162}$ ($1\sigma$) $^{+0.00213}_{-0.00195}$ $(2\sigma)$, $B_{s}=0.7788^{+0.0736}_{-0.0723}$ ($1\sigma$) $^{+0.0918}_{-0.0904}$ $(2\sigma)$, $\alpha=0.1079^{+0.3397}_{-0.2539}$ ($1\sigma$) $^{+0.4678}_{-0.2911}$ $(2\sigma)$, $B=0.00189^{+0.00583}_{-0.00756}$ ($1\sigma$) $^{+0.00660}_{-0.00915}$ $(2\sigma)$, and $H_{0}=70.711^{+4.188}_{-3.142}$ ($1\sigma$) $^{+5.281}_{-4.149}$ $(2\sigma)$.Comment: 12 pages, 1figur

Low energy and dynamical properties of a single hole in the t-Jz model

We review in details a recently proposed technique to extract information about dynamical correlation functions of many-body hamiltonians with a few Lanczos iterations and without the limitation of finite size. We apply this technique to understand the low energy properties and the dynamical spectral weight of a simple model describing the motion of a single hole in a quantum antiferromagnet: the $t-J_z$ model in two spatial dimension and for a double chain lattice. The simplicity of the model allows us a well controlled numerical solution, especially for the two chain case. Contrary to previous approximations we have found that the single hole ground state in the infinite system is continuously connected with the Nagaoka fully polarized state for $J_z \to 0$. Analogously we have obtained an accurate determination of the dynamical spectral weight relevant for photoemission experiments. For $J_z=0$ an argument is given that the spectral weight vanishes at the Nagaoka energy faster than any power law, as supported also by a clear numerical evidence. It is also shown that spin charge decoupling is an exact property for a single hole in the Bethe lattice but does not apply to the more realistic lattices where the hole can describe closed loop paths.Comment: RevTex 3.0, 40 pages + 16 Figures in one file self-extracting, to appear in Phys. Rev

Bianchi Type I Cosmology in Generalized Saez-Ballester Theory via Noether Gauge Symmetry

In this paper, we investigate the generalized Saez-Ballester scalar-tensor theory of gravity via Noether gauge symmetry (NGS) in the background of Bianchi type I cosmological spacetime. We start with the Lagrangian of our model and calculate its gauge symmetries and corresponding invariant quantities. We obtain the potential function for the scalar field in the exponential form. For all the symmetries obtained, we determine the gauge functions corresponding to each gauge symmmetry which include constant and dynamic gauge. We discuss cosmological implications of our model and show that it is compatible with the observational data.Comment: 13 pages, 2 figures, accepted for publication in 'European Physical Journal C

The generalized second law for the interacting generalized Chaplygin gas model

We investigate the validity of the generalized second law (GSL) of gravitational thermodynamics in a non-flat FRW universe containing the interacting generalized Chaplygin gas with the baryonic matter. The dynamical apparent horizon is assumed to be the boundary of the universe. We show that for the interacting generalized Chaplygin gas as a unified candidate for dark matter (DM) and dark energy (DE), the equation of state parameter can cross the phantom divide. We also present that for the selected model under thermal equilibrium with the Hawking radiation, the GSL is always satisfied throughout the history of the universe for any spatial curvature, independently of the equation of state of the interacting generalized Chaplygin gas model.Comment: 8 page

Upregulation of Haploinsufficient Gene Expression in the Brain by Targeting a Long Non-coding RNA Improves Seizure Phenotype in a Model of Dravet Syndrome

AbstractDravet syndrome is a devastating genetic brain disorder caused by heterozygous loss-of-function mutation in the voltage-gated sodium channel gene SCN1A. There are currently no treatments, but the upregulation of SCN1A healthy allele represents an appealing therapeutic strategy. In this study we identified a novel, evolutionary conserved mechanism controlling the expression of SCN1A that is mediated by an antisense non-coding RNA (SCN1ANAT). Using oligonucleotide-based compounds (AntagoNATs) targeting SCN1ANAT we were able to induce specific upregulation of SCN1A both in vitro and in vivo, in the brain of Dravet knock-in mouse model and a non-human primate. AntagoNAT-mediated upregulation of Scn1a in postnatal Dravet mice led to significant improvements in seizure phenotype and excitability of hippocampal interneurons. These results further elucidate the pathophysiology of Dravet syndrome and outline a possible new approach for the treatment of this and other genetic disorders with similar etiology

Quest for Localized 4-D Black Holes in Brane Worlds

We investigate the possibility of obtaining localized black hole solutions in brane worlds by introducing a dependence of the four-dimensional line--element on the extra dimension. An analysis, performed for the cases of an empty bulk and of a bulk containing either a scalar or a gauge field, reveals that no conventional type of matter can support such a dependence. Considering a particular ansatz for the five-dimensional line--element that corresponds to a black hole solution with a ``decaying'' horizon, we determine the bulk energy--momentum tensor capable of sustaining such a behaviour. It turns out that an exotic, shell-like distribution of matter is required. For such solutions, the black hole singularity is indeed localized near the brane and the spacetime is well defined near the AdS horizon, in contrast to the behaviour found in black string type solutions.Comment: 17 pages, RevTex, 3 figures, version to appear in Physical Review D, comments and references added, typos correcte