Production of J/ψJ/\psi-pairs at HERA-N⃗\vec{{\rm N}}

The production of $J/\psi$-pairs as a possible measure of the polarized gluon distribution $\Delta G(x)$ is studied for proton--nucleon collisions at \sqrt{s} =40\;\mbox{GeV}^2 (HERA-$\vec{{\rm N}}$). Possibilities of reconstructing the helicity state of at least one of the $J/\psi$'s are critically reviewed. The observation of production asymmetries in the single polarized mode of HERA-$\vec{{\rm N}}$ is found to be not feasible.Comment: 8 pages, LATeX, 3 figures availabe as .uu-fil

Chandra Smells a RRAT: X-ray Detection of a Rotating Radio Transient

"Rotating RAdio Transients" (RRATs) are a newly discovered astronomical phenomenon, characterised by occasional brief radio bursts, with average intervals between bursts ranging from minutes to hours. The burst spacings allow identification of periodicities, which fall in the range 0.4 to 7 seconds. The RRATs thus seem to be rotating neutron stars, albeit with properties very different from the rest of the population. We here present the serendipitous detection with the Chandra X-ray Observatory of a bright point-like X-ray source coincident with one of the RRATs. We discuss the temporal and spectral properties of this X-ray emission, consider counterparts in other wavebands, and interpret these results in the context of possible explanations for the RRAT population.Comment: 5 pages, 2 b/w figures, 1 color figure. To appear in the proceedings of "Isolated Neutron Stars", Astrophysics & Space Science, in pres

Scalar Particle Contribution to Higgs Production via Gluon Fusion at NLO

We consider the gluon fusion production cross section of a scalar Higgs boson in models where fermion and scalar massive colored particles are present. We report analytic expressions for the matrix elements of $gg\to Hg$, $q\bar{q}\to Hg$, and $qg\to Hq$ processes completing the calculation of the NLO QCD corrections in these extended scenarios. The formulas are written in a complete general case, allowing a flexible use for different theoretical models. Applications of our results to two different models are presented: i) a model in which the SM Higgs sector is augmented by a weak doublet scalar in the $SU(N_c)$ adjoint representation. ii) The MSSM, in the limit of neglecting the gluino contribution to the cross section.Comment: 20 pages, 5 figures. Minor changes. Refs. adde

On the statistical significance of the conductance quantization

Recent experiments on atomic-scale metallic contacts have shown that the quantization of the conductance appears clearly only after the average of the experimental results. Motivated by these results we have analyzed a simplified model system in which a narrow neck is randomly coupled to wide ideal leads, both in absence and presence of time reversal invariance. Based on Random Matrix Theory we study analytically the probability distribution for the conductance of such system. As the width of the leads increases the distribution for the conductance becomes sharply peaked close to an integer multiple of the quantum of conductance. Our results suggest a possible statistical origin of conductance quantization in atomic-scale metallic contacts.Comment: 4 pages, Tex and 3 figures. To be published in PR

A note on second-order perturbations of non-canonical scalar fields

We study second-order perturbations for a general non-canonical scalar field, minimally coupled to gravity, on the unperturbed FRW background, where metric fluctuations are neglected a priori. By employing different approaches to cosmological perturbation theory, we show that, even in this simplified set-up, the second-order perturbations to the stress tensor, the energy density and the pressure display potential instabilities, which are not present at linear order. The conditions on the Lagrangian under which these instabilities take place are provided. We also discuss briefly the significance of our analysis in light of the possible linearization instability of these fields about the FRW background.Comment: 8 page, Revtex 4. Clarifications added, results unchanged; [v3] 10 pages, matches with the published version, Discussion for specific cases expanded and preliminary results including the metric perturbations discusse

Coherent propagation of interacting particles in a random potential: the Mechanism of enhancement

Coherent propagation of two interacting particles in $1d$ weak random potential is considered. An accurate estimate of the matrix element of interaction in the basis of localized states leads to mapping onto the relevant matrix model. This mapping allows to clarify the mechanism of enhancement of the localization length which turns out to be rather different from the one considered in the literature. Although the existence of enhancement is transparent, an analytical solution of the matrix model was found only for very short samples. For a more realistic situation numerical simulations were performed. The result of these simulations is consistent with l_{2}/l_1 \sim l_1^{\gamma} , where $l_1$ and $l_2$ are the single and two particle localization lengths and the exponent $\gamma$ depends on the strength of the interaction. In particular, in the limit of strong particle-particle interaction there is no enhancement of the coherent propagation at all ($l_{2} \approx l_1$).Comment: 23 pages, REVTEX, 3 eps figures, improved version accepted for publication in Phys. Rev.

The occurrence and characterization of Campylobacter jejuni and C. coli in organic pigs and their outdoor environment

The occurrence and species distribution of thermophilic Campylobacter was investigated in organic outdoor pigs. An increased exposure of outdoor pigs to C. jejuni from the environment may cause a shift from a normal dominance of C. coli to more C. jejuni, which may imply a concern of reduced food safety. Bacteriological methods for determination of Campylobacter excretion level were combined with colony-blot hybridization and real-time PCR for specific detection of C. jejuni in pigs. Campylobacter was isolated from pigs (n = 47), paddock environment (n = 126) and wildlife (n = 44), identified to species by real-time PCR and sub-typed by serotyping (Penner) and pulse-field gel electrophorsis (PFGE) genotyping. All pigs excreted Campylobacter (103–107 CFU g1 faeces) from the age of 8–13-weeks old. C. jejuni was found in 29% of pigs in three consecutive trials and always in minority to C. coli (0.3–46%). C. jejuni and C. coli were isolated from 10% and 29% of the environmental samples, respectively, while crow-birds and rats harboured C. jejuni. Individual pigs hosted several strains (up to nine serotypes). The paddock environment was contaminated with C. coli serotypes similar to pig isolates, while most of the C. jejuni serotypes differed. C. jejuni isolates of different origin comprised few similar serotypes, just one identical genotype was common between pigs, environment and birds. In conclusion, the occurrence of C. jejuni varied considerably between the three groups of outdoor pigs. Furthermore, transfer of C. jejuni to the outdoor pigs from the nearby environment was not predominant according to the subtype dissimilarities of the obtained isolates

Spacetime as a membrane in higher dimensions

By means of a simple model we investigate the possibility that spacetime is a membrane embedded in higher dimensions. We present cosmological solutions of d-dimensional Einstein-Maxwell theory which compactify to two dimensions. These solutions are analytically continued to obtain dual solutions in which a (d-2)-dimensional Einstein spacetime "membrane" is embedded in d-dimensions. The membrane solutions generalise Melvin's 4-dimensional flux tube solution. The flat membrane is shown to be classically stable. It is shown that there are zero mode solutions of the d-dimensional Dirac equation which are confined to a neighbourhood of the membrane and move within it like massless chiral (d-2)-dimensional fermions. An investigation of the spectrum of scalar perturbations shows that a well-defined mass gap between the zero modes and massive modes can be obtained if there is a positive cosmological term in (d-2) dimensions or a negative cosmological term in d dimensions.Comment: 30 pages, 4 figures in 10 files, epsf. This early brane world paper is being placed on the archive to make it more easily accessible, as its results are used in a new brane world construction in an accompanying submissio

Biliary effects of liraglutide and sitagliptin, a 12-week randomized placebo-controlled trial in type 2 diabetes patients

Aims: Treatment with glucagon-like peptide (GLP)-1 receptor agonists or dipeptidyl peptidase (DPP)-4 inhibitors might increase gallstone formation; however, the mechanisms involved are unknown. We aimed to assess the effects of these drugs on gallbladder volume and bile acid profile. Materials and methods: A total of 57 type 2 diabetes patients (mean±SD age, 62.8±6.9years; BMI, 31.8±4.1kg/m2; HbA1c, 7.3%±0.6%), treated with metformin and/or sulfonylureas, were included in this 12-week randomized, placebo-controlled, double-blind, single-centre trial between July 2013 and August 2015 at the VU University Medical Center, the Netherlands. Patients received the GLP-1 receptor agonist liraglutide, the DPP-4 inhibitor sitagliptin or matching placebo for 12weeks. Gallbladder fasting volume and ejection fraction were measured using ultrasonography after a high-fat meal. Serum bile acids were measured in the fasting and postprandial state and in faecal samples. The trial was registered at ClinicalTrials.gov (NCT01744236). Results: Neither liraglutide nor sitagliptin had an effect on gallbladder fast