A global foliation of Einstein-Euler spacetimes with Gowdy-symmetry on T3

We investigate the initial value problem for the Einstein-Euler equations of general relativity under the assumption of Gowdy symmetry on T3, and we construct matter spacetimes with low regularity. These spacetimes admit, both, impulsive gravitational waves in the metric (for instance, Dirac mass curvature singularities propagating at light speed) and shock waves in the fluid (i.e., discontinuities propagating at about the sound speed). Given an initial data set, we establish the existence of a future development and we provide a global foliation in terms of a globally and geometrically defined time-function, closely related to the area of the orbits of the symmetry group. The main difficulty lies in the low regularity assumed on the initial data set which requires a distributional formulation of the Einstein-Euler equations.Comment: 24 page

J/psi production at the Tevatron and HERA: the effect of k_T smearing

We study the effects of intrinsic transverse momentum smearing on J/psi production both at the Tevatron and at HERA. For the case of large-p_T J/psi production at the Tevatron, the effects due to k_T smearing are mild. On the other hand, inelastic J/psi photoproduction at HERA is very sensitive to the k_T smearing and, in fact, with a reasonable value of it is possible to resolve the large-z discrepancy seen by comparing non-relativistic QCD (NRQCD) predictions with the HERA data. We conclude that, with the present kinematic cuts, photoproduction at HERA is not a good test of NRQCD.Comment: 11 pages, LaTeX, 2 figures, uses epsfi

Charge asymmetry in W + jets production at the LHC

The charge asymmetry in W + jets production at the LHC can serve to calibrate the presence of New Physics contributions. We study the ratio {\sigma}(W^+ + n jets)/{\sigma}(W^- + n jets) in the Standard Model for n <= 4, paying particular attention to the uncertainty in the prediction from higher-order perturbative corrections and uncertainties in parton distribution functions. We show that these uncertainties are generally of order a few percent, making the experimental measurement of the charge asymmetry ratio a particularly useful diagnostic tool for New Physics contributions.Comment: 13 pages, 7 figures. Reference added. Slightly modified tex

A model structure for coloured operads in symmetric spectra

We describe a model structure for coloured operads with values in the category of symmetric spectra (with the positive model structure), in which fibrations and weak equivalences are defined at the level of the underlying collections. This allows us to treat R-module spectra (where R is a cofibrant ring spectrum) as algebras over a cofibrant spectrum-valued operad with R as its first term. Using this model structure, we give suficient conditions for homotopical localizations in the category of symmetric spectra to preserve module structures.Comment: 16 page

Representation theory of super Yang-Mills algebras

We study in this article the representation theory of a family of super algebras, called the \emph{super Yang-Mills algebras}, by exploiting the Kirillov orbit method \textit{\`a la Dixmier} for nilpotent super Lie algebras. These super algebras are a generalization of the so-called \emph{Yang-Mills algebras}, introduced by A. Connes and M. Dubois-Violette in \cite{CD02}, but in fact they appear as a "background independent" formulation of supersymmetric gauge theory considered in physics, in a similar way as Yang-Mills algebras do the same for the usual gauge theory. Our main result states that, under certain hypotheses, all Clifford-Weyl super algebras \Cliff_{q}(k) \otimes A_{p}(k), for $p \geq 3$, or $p = 2$ and $q \geq 2$, appear as a quotient of all super Yang-Mills algebras, for $n \geq 3$ and $s \geq 1$. This provides thus a family of representations of the super Yang-Mills algebras

Relativistic graphene ratchet on semidisk Galton board

Using extensive Monte Carlo simulations we study numerically and analytically a photogalvanic effect, or ratchet, of directed electron transport induced by a microwave radiation on a semidisk Galton board of antidots in graphene. A comparison between usual two-dimensional electron gas (2DEG) and electrons in graphene shows that ratchet currents are comparable at very low temperatures. However, a large mean free path in graphene should allow to have a strong ratchet transport at room temperatures. Also in graphene the ratchet transport emerges even for unpolarized radiation. These properties open promising possibilities for room temperature graphene based sensitive photogalvanic detectors of microwave and terahertz radiation.Comment: 4 pages, 4 figures. Research done at Quantware http://www.quantware.ups-tlse.fr/. More detailed analysis is give

Virtual photon fragmentation functions

We introduce operator definitions for virtual photon fragmentation functions, which are needed for reliable calculations of Drell-Yan transverse momentum ($Q_T$) distributions when $Q_T$ is much larger than the invariant mass $Q$. We derive the evolution equations for these fragmentation functions. We calculate the leading order evolution kernels for partons to fragment into a unpolarized as well as a polarized virtual photon. We find that fragmentation functions to a longitudinally polarized virtual photon are most important at small $z$, and the fragmentation functions to a transversely polarized virtual photon dominate the large $z$ region. We discuss the implications of this finding to the J/$\psi$ mesons' polarization at large transverse momentum.Comment: Latex, 19 pages including 6 figures. An error in the first version has been corrected, and references update

W^+W^+ plus dijet production in the POWHEGBOX

We present an implementation of the calculation of the production of W^+W^+ plus two jets at hadron colliders, at next-to-leading order (NLO) in QCD, in the POWHEG framework, which is a method that allows the interfacing of NLO calculations to shower Monte Carlo programs. This is the first 2 -> 4 process to be described to NLO accuracy within a shower Monte Carlo framework. The implementation was built within the POWHEGBOX package. We discuss a few technical improvements that were needed in the POWHEGBOX to deal with the computer intensive nature of the NLO calculation, and argue that further improvements are possible, so that the method can match the complexity that is reached today in NLO calculations. We have interfaced our POWHEG implementation with PYTHIA and HERWIG, and present some phenomenological results, discussing similarities and differences between the pure NLO and the POWHEG+PYTHIA calculation both for inclusive and more exclusive distributions. We have made the relevant code available at the POWHEGBOX web site.Comment: 16 pages, 5 figure

The resummation of inter-jet energy flow for gaps-between-jets processes at HERA

We calculate resummed perturbative predictions for gaps-between-jets processes and compare to HERA data. Our calculation of this non-global observable needs to include the effects of primary gluon emission (global logarithms) and secondary gluon emission (non-global logarithms) to be correct at the leading logarithm (LL) level. We include primary emission by calculating anomalous dimension matrices for the geometry of the specific event definitions and estimate the effect of non-global logarithms in the large $N_c$ limit. The resulting predictions for energy flow observables are consistent with experimental data.Comment: 31 pages, 4 figures, 2 table

A new numerical method for obtaining gluon distribution functions G(x,Q2)=xg(x,Q2)G(x,Q^2)=xg(x,Q^2), from the proton structure function F2γp(x,Q2)F_2^{\gamma p}(x,Q^2)

An exact expression for the leading-order (LO) gluon distribution function $G(x,Q^2)=xg(x,Q^2)$ from the DGLAP evolution equation for the proton structure function $F_2^{\gamma p}(x,Q^2)$ for deep inelastic $\gamma^* p$ scattering has recently been obtained [M. M. Block, L. Durand and D. W. McKay, Phys. Rev. D{\bf 79}, 014031, (2009)] for massless quarks, using Laplace transformation techniques. Here, we develop a fast and accurate numerical inverse Laplace transformation algorithm, required to invert the Laplace transforms needed to evaluate $G(x,Q^2)$, and compare it to the exact solution. We obtain accuracies of less than 1 part in 1000 over the entire $x$ and $Q^2$ spectrum. Since no analytic Laplace inversion is possible for next-to-leading order (NLO) and higher orders, this numerical algorithm will enable one to obtain accurate NLO (and NNLO) gluon distributions, using only experimental measurements of $F_2^{\gamma p}(x,Q^2)$.Comment: 9 pages, 2 figure