Virtual photon structure functions and positivity constraints

We study the three positivity constraints among the eight virtual photon structure functions, derived from the Cauchy-Schwarz inequality and which are hence model-independent. The photon structure functions obtained from the simple parton model show quite different behaviors in a massive quark or a massless quark case, but they satisfy, in both cases, the three positivity constraints. We then discuss an inequality which holds among the unpolarized and polarized photon structure functions $F_1^\gamma$, $g_1^\gamma$ and $W_{TT}^\tau$, in the kinematic region $\Lambda^2\ll P^2 \ll Q^2$, where $-Q^2 (-P^2)$ is the mass squared of the probe (target) photon, and we examine whether this inequality is satisfied by the perturbative QCD results.Comment: 24 pages, 13 eps figure

Binary optical communication in single-mode and entangled quantum noisy channels

We address binary optical communication in single-mode and entangled quantum noisy channels. For single-mode we present a systematic comparison between direct photodetection and homodyne detection in realistic conditions, i.e. taking into account the noise that occurs both during the propagation and the detection of the signals. We then consider entangled channels based on twin-beam state of radiation, and show that with realistic heterodyne detection the error probability at fixed channel energy is reduced in comparison to the single-mode cases for a large range of values of quantum efficiency and noise parameters

Parton distributions in the virtual photon target up to NNLO in QCD

Parton distributions in the virtual photon target are investigated in perturbative QCD up to the next-to-next-to-leading order (NNLO). In the case $\Lambda^2 \ll P^2 \ll Q^2$, where $-Q^2$ ($-P^2$) is the mass squared of the probe (target) photon, parton distributions can be predicted completely up to the NNLO, but they are factorisation-scheme-dependent. We analyse parton distributions in two different factorisation schemes, namely $\bar{\rm MS}$ and ${\rm DIS}_{\gamma}$ schemes, and discuss their scheme dependence. We show that the factorisation-scheme dependence is characterised by the large-$x$ behaviours of quark distributions. Gluon distribution is predicted to be very small in absolute value except in the small-$x$ region.Comment: 28 pages, 5 figures, version to appear in Eur. Phys. J.

BRS Cohomology of Zero Curvature Systems II. The Noncomplete Ladder Case

The Yang-Mills type theories and their BRS cohomology are analysed within the zero curvature formalism.Comment: 14 pages, latex, no figures, latex improve

Evaluation of design recommendations for the development of wheelchair rugby sports-wear

Currently, wheelchair rugby athletes face the challenges of playing the sport without specifically designed sports-wear kit. A few designs and recommendations have already been proposed by researchers but none have made it to market yet. The purpose of this study was to evaluate a set of design recommendations for the development of wheelchair rugby sports-wear. This was done so that the products to be created are developed in collaboration with their potential users, responding to their particular needs and requirements. The evaluation was done through an online survey, where the athletes were presented with a visual representation of the design recommendations. The results indicate that the people questioned agree with the majority of the proposed designs and would be happy to have these improvements made to their current sports-wear. The most criticised recommendations were for the gloves, as they are the most important part of the kit, so it is important that they are adequate and allow for a good performance

Vector-axialvector mixing from a chiral effective field theory at finite temperature

We study the vector-axialvector mixing in a hot medium and its evolution toward the chiral phase transition using different symmetry restoration scenarios based on the generalized hidden local symmetry framework. We show that the presence of the $a_1$ meson reduces the vector spectral function around $\rho$ meson mass and enhances it around $a_1$ meson mass. The coupling strength of $a_1$ to $\rho$ and $\pi$ vanishes at the critical temperature due to the degenerate $\rho$-$a_1$ masses. This feature holds rigorously in the chiral limit and still stays intact to good approximation for the physical pion mass.Comment: v2:11 pages, 6 figures, reorganized and expanded the text, new plots and references added, main result and conclusions unchange

Target Mass Effects in Polarized Virtual Photon Structure Functions

We study target mass effects in the polarized virtual photon structure functions $g_1^\gamma (x,Q^2,P^2)$, $g_2^\gamma (x,Q^2,P^2)$ in the kinematic region $\Lambda^2\ll P^2 \ll Q^2$, where $-Q^2 (-P^2)$ is the mass squared of the probe (target) photon. We obtain the expressions for $g_1^\gamma (x,Q^2,P^2)$ and $g_2^\gamma (x,Q^2,P^2)$ in closed form by inverting the Nachtmann moments for the twist-2 and twist-3 operators. Numerical analysis shows that target mass effects appear at large $x$ and become sizable near $x_{\rm max}(=1/(1+\frac{P^2}{Q^2}))$, the maximal value of $x$, as the ratio $P^2/Q^2$ increases. Target mass effects for the sum rules of $g_1^\gamma$ and $g_2^\gamma$ are also discussed.Comment: 24 pages, LaTeX, 9 eps figure