Nonvanishing Cosmological Constant of Flat Universe in Brane-World Scenario

The finite temperature effect is examined in Randall-Sundrum brane-world scenario with inclusion of the matter fields on the brane. At zero temperature it is found that the theory on the brane is conformally invariant, which guarantees $AdS$/CFT. At 4d effective action we derived a temperature-dependent nonvanishing cosmological constant at the flat spacetime limit of brane worldvolume. At the cosmological temperature $3 {\bf K}$ the cosmological constant is roughly $(0.0004 eV)^4$ which is within the upper bound of the recent experimental value $(0.01 eV)^4$Comment: 10 pages, 1 figure; V2 12 pages, figure removed, the contribution of matter to the cosmological constant is added, will appear in PL

Field theory models for variable cosmological constant

Anthropic solutions to the cosmological constant problem require seemingly unnatural scalar field potentials with a very small slope or domain walls (branes) with a very small coupling to a four-form field. Here we introduce a class of models in which the smallness of the corresponding parameters can be attributed to a spontaneously broken discrete symmetry. We also demonstrate the equivalence of scalar field and four-form models. Finally, we show how our models can be naturally embedded into a left-right extension of the standard model.Comment: A reference adde

Is employment status in adults over 25 years old associated with nonmedical prescription opioid and stimulant use?

Purpose: Nonmedical use of prescription opioid and stimulants (NMUPO and NMUPS, respectively) has declined in recent years, but remains an important public health problem. Evidence regarding their relationships with employment status remains unclear. We determined the relationship between employment status and NMUPO and NMUPS. Methods: We analyzed a cross-sectional, nationally representative, weighted sample of 58,486 adults, ages 26 years and older, using combined 2011–2013 data from the National Survey on Drug Use and Health (NSDUH). We fit two crude and two adjusted multivariable logistic regression models to assess the relationship between our two different outcomes of interest: (1) past-year NMUPO and (2) past-year NMUPS, and our exposure of interest: employment status, categorized as (1) full time, (2) part time, (3) unemployed, and (4) not in the workforce. Our adjusted models featured the following covariates: sex, race, age, marital status, and psychological distress, and other nonmedical use. Results: Prevalence of NMUPO was higher than NMUPS (3.48 vs. 0.72%). Unemployed participants had the highest odds of NMUPO [aOR 1.45, 95% CI (1.15–1.82)], while those not in the workforce had the highest odds of NMUPS [aOR 1.71, 95% CI (1.22–2.37)]. Additionally, part-time and unemployed individuals had increased odds of NMUPS [aORs, 95% CI 1.59 (1.09–2.31) and 1.67 (1.11–2.37) respectively], while those not in the workforce had decreased odds of NMUPO [aOR 0.82, 95% CI (0.68–0.99)] relative to full-time participants. Conclusions: There is a need for adult prevention and deterrence programs that target nonmedical prescription drug use, especially among those unemployed or not in the workforce

Quintessence and variation of the fine structure constant in the CMBR

We study dependence of the CMB temperature anisotropy spectrum on the value of the fine structure constant $\alpha$ and the equation of state of the dark energy component of the total density of the universe. We find that bounds imposed on the variation of $\alpha$ from the analysis of currently available CMB data sets can be significantly relaxed if one also allows for a change in the equation of state.Comment: 5 pages, 3 figures. Several references added and a few minor typos corrected in the revised versio

An inhomogeneous universe with thick shells and without cosmological constant

We build an exact inhomogeneous universe composed of a central flat Friedmann zone up to a small redshift $z_1$, a thick shell made of anisotropic matter, an hyperbolic Friedmann metric up to the scale where dimming galaxies are observed ($z\simeq 1.7$) that can be matched to a hyperbolic Lema\^{i}tre-Tolman-Bondi spacetime to best fit the WMAP data at early epochs. We construct a general framework which permits us to consider a non-uniform clock rate for the universe. As a result, both for a uniform time and a uniform Hubble flow, the deceleration parameter extrapolated by the central observer is always positive. Nevertheless, by taking a non-uniform Hubble flow, it is possible to obtain a negative central deceleration parameter, that, with certain parameter choices, can be made the one observed currently. Finally, it is conjectured a possible physical mechanism to justify a non-uniform time flow.Comment: Version published in Class. Quantum gra

On likely values of the cosmological constant

We discuss models in which the smallness of the effective vacuum energy density \rho_\L and the coincidence of the time of its dominance t_\L with the epoch of galaxy formation $t_G$ are due to anthropic selection effects. In such models, the probability distribution for \rho_\L is a product of an {\it a priori} distribution {\cal P}_*(\rho_\L) and of the number density of galaxies at a given \rho_\L (which is proportional to the number of observers who will detect that value of \rho_\L). To determine ${\cal P}_*$, we consider inflationary models in which the role of the vacuum energy is played by a slowly-varying potential of some scalar field. We show that the resulting distribution depends on the shape of the potential and generally has a non-trivial dependence on \rho_\L, even in the narrow anthropically allowed range. This is contrary to Weinberg's earlier conjecture that the {\it a priori} distribution should be nearly flat in the range of interest. We calculate the (final) probability distributions for \rho_\L and for t_G/t_\L in simple models with power-law potentials. For some of these models, the agreement with the observationally suggested values of \rho_\L is better than with a flat {\it a priori} distribution. We also discuss quantum-cosmological approach in which \rho_\L takes different values in different disconnected universes and argue that Weinberg's conjecture is not valid in this case as well. Finally, we extend our analysis to models of quintessence, with similar conclusions.Comment: 24 pages, 2 figures; replaced with published versio

Prescription opioid use disorder and heroin use among 12-34 year-olds in the United States from 2002 to 2014

Trend analyses of prescription opioids in the U.S. indicate use, especially use of prescription opioids stronger than morphine, has more than doubled among adults since the early 1990's (Frenk, Porter, & Paulozzi, 2015). Prescription opioids, like Oxycontin®, are effective pharmacological treatments for acute and chronic pain (Fitzcharles and Shir, 2009 ; Gallagher and Rosenthal, 2008). When used as indicated, these medications can be an important component of pain management. However, their high abuse potential presents concerns regarding their nonmedical use, which can be defined as ‘use of a prescription opioid that was not prescribed, or taken for the experience or feeling it caused’ (SAMHSA, 2014). In the United States, nonmedical use of prescription opioids (NMPO) is increasingly recognized as a serious public health problem among adults (Blanco et al., 2007; Han et al., 2015 ; Huang et al., 2006). Nonmedical prescription drug use, specifically nonmedical use of prescription opioids, is also a growing problem in other countries such as Canada (Fischer et al., 2014 ; Fischer et al., 2013) and Australia (Degenhardt et al., 2006 ; Rintoul et al., 2011)

Can the Chaplygin gas be a plausible model for dark energy?

In this note two cosmological models representing the flat Friedmann Universe filled with a Chaplygin fluid, with or without dust, are analyzed in terms of the recently proposed "statefinder" parameters. Trajectories of both models in the parameter plane are shown to be significantly different w.r.t. "quiessence" and "tracker" models. The generalized Chaplygin gas model with an equation of state of the form $p = -A/\rho^{\alpha}$ is also analyzed in terms of the statefinder parameters.Comment: 6 pages, 2 figure

Dynamical System Approach to Cosmological Models with a Varying Speed of Light

Methods of dynamical systems have been used to study homogeneous and isotropic cosmological models with a varying speed of light (VSL). We propose two methods of reduction of dynamics to the form of planar Hamiltonian dynamical systems for models with a time dependent equation of state. The solutions are analyzed on two-dimensional phase space in the variables $(x, \dot{x})$ where $x$ is a function of a scale factor $a$. Then we show how the horizon problem may be solved on some evolutional paths. It is shown that the models with negative curvature overcome the horizon and flatness problems. The presented method of reduction can be adopted to the analysis of dynamics of the universe with the general form of the equation of state $p=\gamma(a)\epsilon$. This is demonstrated using as an example the dynamics of VSL models filled with a non-interacting fluid. We demonstrate a new type of evolution near the initial singularity caused by a varying speed of light. The singularity-free oscillating universes are also admitted for positive cosmological constant. We consider a quantum VSL FRW closed model with radiation and show that the highest tunnelling rate occurs for a constant velocity of light if $c(a) \propto a^n$ and $-1 < n \le 0$. It is also proved that the considered class of models is structurally unstable for the case of $n < 0$.Comment: 18 pages, 5 figures, RevTeX4; final version to appear in PR

Electromagnetic waves in an axion-active relativistic plasma non-minimally coupled to gravity

We consider cosmological applications of a new self-consistent system of equations, accounting for a nonminimal coupling of the gravitational, electromagnetic and pseudoscalar (axion) fields in a relativistic plasma. We focus on dispersion relations for electromagnetic perturbations in an initially isotropic ultrarelativistic plasma coupled to the gravitational and axion fields in the framework of isotropic homogeneous cosmological model of the de Sitter type. We classify the longitudinal and transversal electromagnetic modes in an axionically active plasma and distinguish between waves (damping, instable or running), and nonharmonic perturbations (damping or instable). We show that for the special choice of the guiding model parameters the transversal electromagnetic waves in the axionically active plasma, nonminimally coupled to gravity, can propagate with the phase velocity less than speed of light in vacuum, thus displaying a possibility for a new type of resonant particle-wave interactions.Comment: 19 pages, 9 figures, published versio