Thermalization of gluons at RHIC: Dependence on initial conditions

We investigate how thermalization of gluons depends on the initial conditions assumed in ultrarelativistic heavy ion collisions at RHIC. The study is based on simulations employing the pQCD inspired parton cascade solving the Boltzmann equation for gluons. We consider independently produced minijets with $p_T > p_0=1.3 \sim 2.0$ GeV and a color glass condensate as possible initial conditions for the freed gluons. It turns out that full kinetic equilibrium is achieved slightly sooner in denser system and its timescale tends to saturate. Compared with the kinetic equilibration we find a stronger dependence of chemical equilibration on the initial conditions.Comment: 8 pages, 4 figures; Contribution to Proceedings of the Quark-Gluon Plasma Thermalization workshop, Vienna, Austria, August 10-12, 200

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

Possible influence of the two string events on the hadron formation in a nuclear environment

One of the basic assumptions of the string model is that as a result of a DIS in nucleus a single string arises, which then breaks into hadrons. However the pomeron exchange considered in this work, leads to the production of two strings in the one event. The hadrons produced in these events have smaller formation lengths, than those with the same energy produced in the single string events. As a consequence, they undergo more substantial absorption in the nuclear matter

Higgs production with large transverse momentum in hadronic collisions at next-to-leading order

Inclusive associated production of a light Higgs boson (m_H < m_t) with one jet in pp collisions is studied in next-to-leading order QCD. Transverse momentum (p_T < 30 GeV) and rapidity distributions of the Higgs boson are calculated for the LHC in the large top-quark mass limit. It is pointed out that, as much as in the case of inclusive Higgs production, the K-factor of this process is large (~1.6) and depends weakly on the kinematics in a wide range of transverse momentum and rapidity intervals. Our result confirms previous suggestions that the production channel p+p -> H+jet -> gamma+gamma+jet gives a measurable signal for Higgs production at the LHC in the mass range 100-140 GeV, crucial also for the ultimate test of the Minimal Supersymmetric Standard Model.Comment: 7 pages, 3 eps figures include

The Q2Q^2 dependence of the measured asymmetry A1A_1: the test of the Bjorken sum rule

We analyse the proton and deutron data on spin dependent asymmetry $A_1(x,Q^2)$ supposing the DIS structure functions $g_1(x,Q^2)$ and $F_3(x,Q^2)$ have the similar $Q^2$-dependence. As a result, we have obtained that $\Gamma_1^p - \Gamma_1^n = 0.190 \pm 0.038$ at $Q^2= 10 GeV^2$ and $\Gamma_1^p - \Gamma_1^n = 0.165 \pm 0.026$ at $Q^2= 3 GeV^2$, what is in the best agreement with the Bjorken sum rule predictions.Comment: LaTeX, 5 pages, no figures, to be published in JETP Letter

Wannier functions of elliptic one-gap potentials

Wannier functions of the one dimensional Schroedinger equation with elliptic one gap potentials are explicitly constructed. Properties of these functions are analytically and numerically investigated. In particular we derive an expression for the amplitude of the Wannier function in the origin, a power series expansion valid in the vicinity of the origin and an asymptotic expansion characterizing the decay of the Wannier function at large distances. Using these results we construct an approximate analytical expression of the Wannier function which is valid in the whole spatial domain and is in good agreement with numerical results.Comment: 24 pages, 5 figure

Production and Two-photon Decay of the MSSM Scalar Higgs Bosons at the LHC

We consider the production and two-photon decay of the $CP$-even Higgs bosons ($h^0$ and $H^0$) of the Minimal Supersymmetric Standard Model (MSSM) at the Large Hadron Collider. We study in detail the dependence of the cross section on various parameters of the MSSM, especially the dependence on the mixing effects in the squark sector due to the Higgs bilinear parameter $\mu$ and the soft supersymmetry breaking parameter $A$. We find that the cross section for the production of these Higgs bosons has a significant dependence on the parameters which determine the chiral mixing in the squark sector. The cross section times the two-photon branching ratio of $h^0$ is of the order of 15--25~fb in much of the parameter space that remains after imposing the present experimental constraints. For the $H^0$ the two-photon branching ratio is only significant if the $H^0$ is light, but then the cross section times the branching ratio may exceed 200~fb. The QCD corrections due to quark loop contributions are known to increase the cross section by 50\%. We find the dependence of the cross section on the gluon distribution function used to be rather insignificant.Comment: 16 pages, LaTex, plus 9 uuencoded figures attached Full ps file available at ftp://vsfys1.fi.uib.no/anonymous/pub/ as nordita-9548.ps or nordita-9548.ps-gz or via http://vsfys1.fi.uib.no/thpubl/publications.htm

Parton coalescence and antiproton/pion anomaly at RHIC

Coalescence of minijet partons with the partons from the quark-gluon plasma formed in relativistic heavy ion collisions is suggested as the mechanism for production of hadrons with intermediate transverse momentum. The resulting enhanced antiproton and pion yields at intermediate transverse momentum gives a plausible explanation for the observed large antiproton to pion ratio. With further increasing momentum, the ratio is predicted to decrease and approach the small value given by independent fragmentations of minijet partons after their energy loss in the quark-gluon plasma.Comment: 4 pages, 3 figures, version to appear in Phys. Rev. Let

Charm quark and D^* cross sections in deeply inelastic scattering at DESY HERA

A next-to-leading order Monte Carlo program for the calculation of heavy quark cross sections in deeply inelastic scattering is described. Concentrating on charm quark and D^*(2010) production at HERA, several distributions are presented and their variation with respect to charm quark mass, parton distribution set, and renormalization-factorization scale is studied.Comment: 15 pages including 8 figures. Uses Latex, Revtex, and psfig. References added - others updated. Several sentences/words added for clarity. Results/conclusions unchanged. To appear in Phys. Rev.

Factorization and soft-gluon divergences in isolated-photon cross sections

We study the production of isolated photons in $e^+e^-$ annihilation and give the proof of the all-order factorization of the collinear singularities. These singularities are absorbed in the standard fragmentation functions of partons into a photon, while the effects of the isolation are consistently included in the short-distance cross section. We compute this cross section at order \as and show that it contains large double logarithms of the isolation parameters. We explain the physical origin of these logarithms and discuss the possibility to resum them to all orders in \as.Comment: 18 pages, LaTex, 2 eps figures, few modifications in the text, results unchange