Diffractive charged meson pair production

We investigate the possibility to measure the nonforward gluon distribution function by means of diffractively produced \pi^+\pi^- and K^+K^- pairs in polarized lepton nucleon scattering. The resulting cross sections are small and are dominated by the gluonic contribution. We find relatively large spin asymmetries, both for \pi^+\pi^- and for K^+K^- pairs.Comment: 15 pages, version with changed kinematical cuts, to be pubished in Phys.Lett.

Low-momentum Hyperon-Nucleon Interactions

We present a first exploratory study for hyperon-nucleon interactions using renormalization group techniques. The effective two-body low-momentum potential V_low-k is obtained by integrating out the high-momentum components from realistic Nijmegen YN potentials. A T-matrix equivalence approach is employed, so that the low-energy phase shifts are reproduced by V_low-k up to a momentum scale Lambda ~ 500 MeV. Although the various bare Nijmegen models differ somewhat from each other, the corresponding V_low-k interactions show convergence in some channels, suggesting a possible unique YN interaction at low momenta.Comment: 4 pages, 6 figure

QCD critical region and higher moments for three flavor models

One of the distinctive feature of the QCD phase diagram is the possible emergence of a critical endpoint. The critical region around the critical point and the path dependency of the critical exponents is investigated within effective chiral (2+1)-flavor models with and without Polyakov-loops. Results obtained in no-sea mean-field approximations where a divergent vacuum part in the fermion-loop contribution is neglected, are confronted to the renormalized ones. Furthermore, the modifications caused by the back-reaction of the matter fluctuations on the pure Yang-Mills system are discussed. Higher order, non-Gaussian moments of event-by-event distributions of various particle multiplicities are enhanced near the critical point and could serve as a probe to determine its location in the phase diagram. By means of a novel derivative technique higher order generalized quark-number susceptibilities are calculated and their sign structure in the phase diagram is analyzed.Comment: 12 pages, 11 figures. Final PRD version (references and one more equation added

Near-infrared studies of the 2010 outburst of the recurrent nova U Scorpii

We present near-infrared (near-IR) observations of the 2010 outburst of U Sco. JHK photometry is presented on 10 consecutive days starting from 0.59 d after outburst. Such photometry can gainfully be integrated into a larger data base of other multiwavelength data which aim to comprehensively study the evolution of U Sco. Early near-IR spectra, starting from 0.56 d after outburst, are presented and their general characteristics discussed. Early in the eruption, we see very broad wings in several spectral lines, with tails extending up to ∼10 000 km s−1 along the line of sight; it is unexpected to have a nova with ejection velocities equal to those usually thought to be exclusive to supernovae. From recombination analysis, we estimate an upper limit of [inline image] for the ejected mass

Modeling the allocation and economic evaluation of PV panels and wind turbines in urban areas

A model for allocating PV panels and wind turbines in urban areas is developed. Firstly, it examines the spatial and technical requirements for the installation of PV panels and wind turbines and then evaluates their economic feasibilities in order to generate the cost effective electricity neutral plan. The model is applied on a residential district in the municipality of Eindhoven, the Netherlands and simulates the electricity generation of allocated renewable energy technologies to satisfy the demand of the area in hourly time-steps over a one year. The allocation model runs for different combinations of PV panels and wind turbines. Accordingly, four scenarios based on the different technical and economic assumptions are conducted and energy and economic indicators are compared. Results show that in the current situation without subsidies, PV panels are not economic, compared with wind turbines, but if appropriate subsidies are devised, they become comparable. The analyses also show that the allocation model help planners and policy makers to examine the influence of different energy policy tools for the promotion of renewable energy technologies in urban areas

Severe New Limits on the Host Galaxies of Gamma Ray Bursts

The nature of Gamma Ray Bursts (GRBs) remains a complete mystery, despite the recent breakthrough discovery of low energy counterparts, although it is now generally believed that at least most GRBs are at cosmological distances. Virtually all proposed cosmological models require bursters to reside in ordinary galaxies. This can be tested by looking inside the smallest GRB error boxes to see if ordinary galaxies appear at the expected brightness levels. This letter reports on an analysis of the contents of 26 of the smallest regions, many from the brightest bursts. These events will have $z < 0.4$ and small uncertainties about luminosity functions, K corrections and galaxy evolutions; whereas the recent events with optical transients are much fainter and hence have high redshifts and grave difficulties in interpretation. This analysis strongly rejects the many models with peak luminosities of $10^{57} photons \cdot s^{-1}$ as deduced from the $LogN-LogP$ curve with no evolution. Indeed, the lower limit on acceptable luminosities is $6 \times 10^{58} photons \cdot s^{-1}$. The only possible solution is to either place GRBs at unexpectedly large distances (with $z > 5.9$ for the faint BATSE bursts) or to require bursters to be far outside any normal host galaxy.Comment: 17 pages, to be published by ApJ

From X-ray dips to eclipse: Witnessing disk reformation in the recurrent nova USco

The 10th recorded outburst of the recurrent eclipsing nova USco was observed simultaneously in X-ray, UV, and optical by XMM-Newton on days 22.9 and 34.9 after outburst. Two full passages of the companion in front of the nova ejecta were observed, witnessing the reformation of the accretion disk. On day 22.9, we observed smooth eclipses in UV and optical but deep dips in the X-ray light curve which disappeared by day 34.9, then yielding clean eclipses in all bands. X-ray dips can be caused by clumpy absorbing material that intersects the line of sight while moving along highly elliptical trajectories. Cold material from the companion could explain the absence of dips in UV and optical light. The disappearance of X-ray dips before day 34.9 implies significant progress in the formation of the disk. The X-ray spectra contain photospheric continuum emission plus strong emission lines, but no clear absorption lines. Both continuum and emission lines in the X-ray spectra indicate a temperature increase from day 22.9 to day 34.9. We find clear evidence in the spectra and light curves for Thompson scattering of the photospheric emission from the white dwarf. Photospheric absorption lines can be smeared out during scattering in a plasma of fast electrons. We also find spectral signatures of resonant line scattering that lead to the observation of the strong emission lines. Their dominance could be a general phenomenon in high-inclination systems such as Cal87.Comment: Submitted to ApJ. 16 pages, 16 figure

A lattice evaluation of four-quark operators in the nucleon

Nucleon matrix elements of various four-quark operators are evaluated in quenched lattice QCD using Wilson fermions. Some of these operators give rise to twist-four contributions to nucleon structure functions. Furthermore, they bear valuable information about the diquark structure of the nucleon. Mixing with lower-dimensional operators is avoided by considering appropriate representations of the flavour group. We find that for a certain flavour combination of baryon structure functions, twist-four contributions are very small. This suggests that twist-four effects for the nucleon might be much smaller than m_p^2/Q^2.Comment: 17 pages, 3 figure

Applied lattice gauge calculations: diquark content of the nucleon

As an example of an application of lattice QCD we describe a computation of four-quark operators in the nucleon. The results are interpreted in a diquark language.Comment: 6 pages, 1 figure, Invited talk given by M. G\"ockeler at the European Workshop on the QCD Structure of the Nucleon (QCD - N'02), Ferrara, Italy, 3-6 Apr 200

COBE Observations of the Microwave Counterparts of Gamma Ray Bursts

We have used the data from the COBE satellite to search for delayed microwave emission (31 - 90 GHz) from Gamma Ray Bursts (GRBs). The large $7^\circ$ beam of COBE is well matched to the large positional uncertainties in the GRB locations, although it also means that fluxes from (point source) GRB objects will be diluted. In view of this we are doing a statistical search of the GRBs which occurred during the currently released COBE DMR data (years 1990 and 1991), which overlap $\sim 200$ GRBs recorded by GRO. Here we concentrate on just the top 10 GRBs (in peak counts/second). We obtain the limits on the emission by comparing the COBE fluxes before and after the GRB at the GRB location. Since it is thought that the microwave emission should lag the GRB event, we have searched the GRB position for emission in the few months following the GRB occurrence.Comment: 5 pages, LaTE