Five-Dimensional QED, Muon Pair Production and Correction to the Coulomb Potential

We consider QED in five dimensions in a configuration where matter is localized on a 3-brane while foton propagates in the bulk. The idea is to investigate the effects of the Kaluza-Klein modes of the photon in the relativistic regime, but in low energy, and in the nonrelativistic regime. In the relativistic regime, we calculate the cross section for the reaction $e^+ + e^- \to \mu^+ + \mu^-$. We compare our theoretical result with a precise measurement of this cross section at $\sqrt{s}=57.77$ GeV. As result, we extract a lower bound on the size of the extra dimension. In the nonrelativistic regime, we derive the contribution for the Coulomb potential due to the whole tower of the Kaluza-Klein excited modes of the photon. We use the modified potential to calculate the Rutherford scattering differential cross section.Comment: minor changes, three new refs. added, to appear in IJMP

Universality of weakly bound dimers and Efimov trimers close to Li-Cs Feshbach resonances

We study the interspecies scattering properties of ultracold Li-Cs mixtures in their two energetically lowest spin channels in the magnetic field range between 800 G and 1000 G. Close to two broad Feshbach resonances we create weakly bound LiCs dimers by radio-frequency association and measure the dependence of the binding energy on the external magnetic field strength. Based on the binding energies and complementary atom loss spectroscopy of three other Li-Cs s-wave Feshbach resonances we construct precise molecular singlet and triplet electronic ground state potentials using a coupled-channels calculation. We extract the Li-Cs interspecies scattering length as a function of the external field and obtain almost a ten-fold improvement in the precision of the values for the pole positions and widths of the s-wave Li-Cs Feshbach resonances as compared to our previous work [Pires \textit{et al.}, Phys. Rev. Lett. \textbf{112}, 250404 (2014)]. We discuss implications on the Efimov scenario and the universal geometric scaling for LiCsCs trimers

Singular diffusion and criticality in a confined sandpile

We investigate the behavior of a two-state sandpile model subjected to a confining potential in one and two dimensions. From the microdynamical description of this simple model with its intrinsic exclusion mechanism, it is possible to derive a continuum nonlinear diffusion equation that displays singularities in both the diffusion and drift terms. The stationary-state solutions of this equation, which maximizes the Fermi-Dirac entropy, are in perfect agreement with the spatial profiles of time-averaged occupancy obtained from model numerical simulations in one as well as in two dimensions. Surprisingly, our results also show that, regardless of dimensionality, the presence of a confining potential can lead to the emergence of typical attributes of critical behavior in the two-state sandpile model, namely, a power-law tail in the distribution of avalanche sizes.Comment: 5 pages, 5 figure

XMM-Newton observations of the low-luminosity cataclysmic variable V405 Pegasi

V405 Peg is a low-luminosity cataclysmic variable (CV) that was identified as the optical counterpart of the bright, high-latitude ROSAT all-sky survey source RBS1955. The system was suspected to belong to a largely undiscovered population of hibernating CVs. Despite intensive optical follow-up its subclass however remained undetermined. We want to further classify V405 Peg and understand its role in the CV zoo via its long-term behaviour, spectral properties, energy distribution and accretion luminosity. We perform a spectral and timing analysis of \textit{XMM-Newton} X-ray and ultra-violet data. Archival WISE, HST, and Swift observations are used to determine the spectral energy distribution and characterize the long-term variability. The X-ray spectrum is characterized by emission from a multi-temperature plasma. No evidence for a luminous soft X-ray component was found. Orbital phase-dependent X-ray photometric variability by $\sim50\%$ occurred without significant spectral changes. No further periodicity was significant in our X-ray data. The average X-ray luminosity during the XMM-Newton observations was L_X, bol simeq 5e30 erg/s but, based on the Swift observations, the corresponding luminosity varied between 5e29 erg/s and 2e31 erg/son timescales of years. The CV subclass of this object remains elusive. The spectral and timing properties show commonalities with both classes of magnetic and non-magnetic CVs. The accretion luminosity is far below than that expected for a standard accreting CV at the given orbital period. Objects like V405 Peg might represent the tip of an iceberg and thus may be important contributors to the Galactic Ridge X-ray Emission. If so they will be uncovered by future X-ray surveys, e.g. with eROSITA.Comment: A&A, in pres

On the width of the last scattering surface

We discuss the physical effects of some accelerated world models on the width of the last scattering surface (LSS) of the cosmic microwave background radiation (CMBR). The models considered in our analysis are X-matter (XCDM) and a Chaplygin type gas. The redshift of the LSS does not depend on the kind of dark energy (if XCDM of Chaplygin). Further, for a Chaplygin gas, the width of the LSS is also only weakly dependent on the kind of scenario (if we have dark energy plus cold dark matter or the unified picture).Comment: 10 pages, 1 figure, 2 tables, accepted to IJMP

Universal three-body recombination and Efimov resonances in an ultracold Li-Cs mixture

We study Efimov resonances via three-body loss in an ultracold two-component gas of fermionic $^6$Li and bosonic $^{133}$Cs atoms close to a Feshbach resonance at 843~G, extending results reported previously [Pires \textit{et al.}, Phys. Rev. Lett. 112, 250404 (2014)] to temperatures around 120~nK. The experimental scheme for reaching lower temperatures is based upon compensating the gravity-induced spatial separation of the mass-imbalanced gases with bichromatic optical dipole traps. We observe the first and second excited Li-Cs-Cs Efimov resonance in the magnetic field dependence of the three-body event rate constant, in good agreement with the universal zero-range theory at finite temperature [Petrov and Werner, Phys. Rev. A 92, 022704 (2015)]. Deviations are found for the Efimov ground state, and the inelasticity parameter $\eta$ is found to be significantly larger than those for single-species systems

Surface properties of extracts from cork black condensate

The insulation corkboard production generates black condensate (BC), a paste-like solid waste. It is hydrophobic and has the potential to be used as protective coating. To evaluate this potential, coatings were prepared from BC extracts and their surface behavior was evaluated by contact angle (CA) measurements. The CA dynamics were recorded as a function of time; advancing CAs were also registered; the approaches were applied according to Fowkes, Owens- Wendt-Rabel-Kaelble (OWRK), and Van Oss to determine the surface energy (SE) for each coating. Depending on the liquid probe, three phenomena were observed: water evaporation, diiodomethane diffusion into the coating, and rearrangement of the chemical groups on the coating surface, when glycerol was dropped onto the surface. Based on the results from the CA dynamics, the applicability of the coatings against hydrophobic environments was limited owing to its affinity to apolar compounds. The results show that the coating prepared by the toluene BC extract was the best coating. The key data were: water CA of 99.38, total SE (between 37.4 mN m-1 and 40.1 mN m-1), SE polar component (0.1 mN m-1), and the acidic and basic characters were negligible. It can be concluded that the BC extracts have potential for coatings.R.P. acknowledges a post-doc research grant BPD/39333/2007 from the Portuguese Foundation for Science and Technology (FCT). We gratefully acknowledge Amorim Isolamentos S.A. for the supply of black condensate