Layering in the Ising model

We consider the three-dimensional Ising model in a half-space with a boundary field (no bulk field). We compute the low-temperature expansion of layering transition lines

Cosmological model with interactions in the dark sector

A cosmological model is proposed for the current Universe consisted of non-interacting baryonic matter and interacting dark components. The dark energy and dark matter are coupled through their effective barotropic indexes, which are considered as functions of the ratio between their energy densities. It is investigated two cases where the ratio is asymptotically stable and their parameters are adjusted by considering best fits to Hubble function data. It is shown that the deceleration parameter, the densities parameters, and the luminosity distance have the correct behavior which is expected for a viable present scenario of the Universe.Comment: 6 pages, 8 figure

Probing the time dependence of dark energy

A new method to investigate a possible time-dependence of the dark energy equation of state $w$ is proposed. We apply this methodology to two of the most recent data sets of type Ia supernova (Union2 and SDSS) and the baryon acoustic oscillation peak at $z = 0.35$. For some combinations of these data, we show that there is a clear departure from the standard $\Lambda$CDM model at intermediary redshifts, although a non-evolving dark energy component ($dw/dz = 0$) cannot be ruled out by these data. The approach developed here may be useful to probe a possible evolving dark energy component when applied to upcoming observational data.Comment: 6 pages, 3 figures, LaTe

Hartree-Fock-Bogoliubov theory versus local-density approximation for superfluid trapped fermionic atoms

We investigate a gas of superfluid fermionic atoms trapped in two hyperfine states by a spherical harmonic potential. We propose a new regularization method to remove the ultraviolet divergence in the Hartree-Fock-Bogoliubov equations caused by the use of a zero-range atom-atom interaction. Compared with a method used in the literature, our method is simpler and has improved convergence properties. Then we compare Hartree-Fock-Bogoliubov calculations with the semiclassical local-density approximation. We observe that for systems containing a small number of atoms shell effects, which cannot be reproduced by the semiclassical calculation, are very important. For systems with a large number of atoms at zero temperature the two calculations are in quite good agreement, which, however, is deteriorated at non-zero temperature, especially near the critical temperature. In this case the different behavior can be explained within the Ginzburg-Landau theory.Comment: 12 pages, 8 figures, revtex; v2: references and clarifying remarks adde

Saturation in heteronuclear photoassociation of 6Li7Li

We report heteronuclear photoassociation spectroscopy in a mixture of magneto-optically trapped 6Li and 7Li. Hyperfine resolved spectra of the vibrational level v=83 of the singlet state have been taken up to intensities of 1000 W/cm^2. Saturation of the photoassociation rate has been observed for two hyperfine transitions, which can be shown to be due to saturation of the rate coefficient near the unitarity limit. Saturation intensities on the order of 40 W/cm^2 can be determined.Comment: 5 pages, 3 figures, to appear in Phys. Rev. A (Rapid Communication

Constraints on accelerating universe using ESSENCE and Gold supernovae data combined with other cosmological probes

We use recently observed data: the 192 ESSENCE type Ia supernovae (SNe Ia), the 182 Gold SNe Ia, the 3-year WMAP, the SDSS baryon acoustic peak, the X-ray gas mass fraction in clusters and the observational $H(z)$ data to constrain models of the accelerating universe. Combining the 192 ESSENCE data with the observational $H(z)$ data to constrain a parameterized deceleration parameter, we obtain the best fit values of transition redshift and current deceleration parameter $z_{T}=0.632^{+0.256}_{-0.127}$, $q_{0}=-0.788^{+0.182}_{-0.182}$. Furthermore, using $\Lambda$CDM model and two model-independent equation of state of dark energy, we find that the combined constraint from the 192 ESSENCE data and other four cosmological observations gives smaller values of $\Omega_{0m}$ and $q_{0}$, but a larger value of $z_{T}$ than the combined constraint from the 182 Gold data with other four observations. Finally, according to the Akaike information criterion it is shown that the recently observed data equally supports three dark energy models: $\Lambda$CDM, $w_{de}(z)=w_{0}$ and $w_{de}(z)=w_{0}+w_{1}\ln(1+z)$.Comment: 18 pages, 8 figure

BPS Domain Wall Junctions in Infinitely Large Extra Dimensions

We consider models of scalar fields coupled to gravity which are higher-dimensional generalizations of four dimensional supergravity. We use these models to describe domain wall junctions in an anti-de Sitter background. We derive Bogomolnyi equations for the scalar fields from which the walls are constructed and for the metric. From these equations a BPS-like formula for the junction energy can be derived. We demonstrate that such junctions localize gravity in the presence of more than one uncompactified extra dimension.Comment: 17 pages, uses RevTeX, new references adde

Observational Constraints to Ricci Dark Energy Model by Using: SN, BAO, OHD, fgas Data Sets

In this paper, we perform a global constraint on the Ricci dark energy model with both the flat case and the non-flat case, using the Markov Chain Monte Carlo (MCMC) method and the combined observational data from the cluster X-ray gas mass fraction, Supernovae of type Ia (397), baryon acoustic oscillations, current Cosmic Microwave Background, and the observational Hubble function. In the flat model, we obtain the best fit values of the parameters in $1\sigma, 2\sigma$ regions: $\Omega_{m0}=0.2927^{+0.0420 +0.0542}_{-0.0323 -0.0388}$, $\alpha=0.3823^{+0.0331 +0.0415}_{-0.0418 -0.0541}$, $Age/Gyr=13.48^{+0.13 +0.17}_{-0.16 -0.21}$, $H_0=69.09^{+2.56 +3.09}_{-2.37 -3.39}$. In the non-flat model, the best fit parameters are found in $1\sigma, 2\sigma$ regions:$\Omega_{m0}=0.3003^{+0.0367 +0.0429}_{-0.0371 -0.0423}$, $\alpha=0.3845^{+0.0386 +0.0521}_{-0.0474 -0.0523}$, $\Omega_k=0.0240^{+0.0109 +0.0133}_{-0.0130 -0.0153}$, $Age/Gyr=12.54^{+0.51 +0.65}_{-0.37 -0.49}$, $H_0=72.89^{+3.31 +3.88}_{-3.05 -3.72}$. Compared to the constraint results in the $\Lambda \textmd{CDM}$ model by using the same datasets, it is shown that the current combined datasets prefer the $\Lambda \textmd{CDM}$ model to the Ricci dark energy model.Comment: 12 pages, 3 figure

Measurement of the Zero Crossing in a Feshbach Resonance of Fermionic 6-Li

We measure a zero crossing in the scattering length of a mixture of the two lowest hyperfine states of 6-Li. To locate the zero crossing, we monitor the decrease in temperature and atom number arising from evaporation in a CO2 laser trap as a function of magnetic field B. The temperature decrease and atom loss are minimized for B=528(4) G, consistent with no evaporation. We also present preliminary calculations using potentials that have been constrained by the measured zero crossing and locate a broad Feshbach resonance at approximately 860 G, in agreement with previous theoretical predictions. In addition, our theoretical model predicts a second and much narrower Feshbach resonance near 550 G.Comment: Five pages, four figure

The kk-essence scalar field in the context of Supernova Ia Observations

A $k$-essence scalar field model having (non canonical) Lagrangian of the form $L=-V(\phi)F(X)$ where $X=1/2g^{\mu\nu}\nabla_{\mu}\phi\nabla_{\nu}\phi$ with constant $V(\phi)$ is shown to be consistent with luminosity distance-redshift data observed for type Ia Supernova. For constant $V(\phi)$, $F(X)$ satisfies a scaling relation which is used to set up a differential equation involving the Hubble parameter $H$, the scale factor $a$ and the $k$-essence field $\phi$. $H$ and $a$ are extracted from SNe Ia data and using the differential equation the time dependence of the field $\phi$ is found to be: $\phi(t) \sim \lambda_0 + \lambda_1 t + \lambda_2 t^2$. The constants $\lambda_i$ have been determined. The time dependence is similar to that of the quintessence scalar field (having canonical kinetic energy) responsible for homogeneous inflation. Furthermore, the scaling relation and the obtained time dependence of the field $\phi$ is used to determine the $X$-dependence of the function $F(X)$.Comment: 8 pages, 5 figures, Late