Monte-Carlo Event Generators at NLO

A method to construct Monte-Carlo event generators at arbitrarily non-leading order is explained for the case of a non-gauge theory. A precise and correct treatment of parton kinematics is provided. Modifications of the conventional formalism are required: parton showering is not exactly the same as DGLAP evolution, and the external line prescription for the hard scattering differs from the LSZ prescription. The prospects for extending the results to QCD are discussed.Comment: 57 pages, 16 eps figures, revtex

Three-dimensional flux states as a model for the pseudogap phase of transition metal oxides

We propose that the pseudogap state observed in the transition metal oxides can be explained by a three-dimensional flux state, which exhibits spontaneously generated currents in its ground state due to electron-electron correlations. We compare the energy of the flux state to other classes of mean field states, and find that it is stabilized over a wide range of $t$ and $\delta$. The signature of the state will be peaks in the neutron diffraction spectra, the location and intensity of which are presented. The dependence of the pseudogap in the optical conductivity is calculated based on the parameters in the model.Comment: submitted to Phys. Rev. B on January 8, 200

Factorization and infrared properties of non-perturbative contributions to DIS structure functions

In this paper we present a new derivation of the QCD factorization. We deduce the k_T- and collinear factorizations for the DIS structure functions by consecutive reductions of a more general theoretical construction. We begin by studying the amplitude of the forward Compton scattering off a hadron target, representing this amplitude as a set of convolutions of two blobs connected by the simplest, two-parton intermediate states. Each blob in the convolutions can contain both the perturbative and non-perturbative contributions. We formulate conditions for separating the perturbative and non-perturbative contributions and attributing them to the different blobs. After that the convolutions correspond to the QCD factorization. Then we reduce this totally unintegrated (basic) factorization first to the k_T- factorization and finally to the collinear factorization. In order to yield a finite expression for the Compton amplitude, the integration over the loop momentum in the basic factorization must be free of both ultraviolet and infrared singularities. This obvious mathematical requirement leads to theoretical restrictions on the non-perturbative contributions (parton distributions) to the Compton amplitude and the DIS structure functions related to the Compton amplitude through the Optical theorem. In particular, our analysis excludes the use of the singular factors x^{-a} (with a > 0) in the fits for the quark and gluon distributions because such factors contradict to the integrability of the basic convolutions for the Compton amplitude. This restriction is valid for all DIS structure functions in the framework of both the k_T- factorization and the collinear factorization if we attribute the perturbative contributions only to the upper blob.Comment: 19 pages, 6 figure

Single-Inclusive Jet Production in Polarized pp Collisions at O(alpha_s^3)

We present a next-to-leading order QCD calculation for single-inclusive high-p_T jet production in longitudinally polarized pp collisions within the ``small-cone'' approximation. The fully analytical expressions obtained for the underlying partonic hard-scattering cross sections greatly facilitate the analysis of upcoming BNL-RHIC data on the double-spin asymmetry A_{LL}^{jet} for this process in terms of the unknown polarization of gluons in the nucleon. We simultaneously rederive the corresponding QCD corrections to unpolarized scattering and confirm the results existing in the literature. We also numerically compare to results obtained with Monte-Carlo methods and assess the range of validity of the ``small-cone'' approximation for the kinematics relevant at BNL-RHIC.Comment: 23 pages, 8 eps-figure

Towards a global analysis of polarized parton distributions

We present a technique for implementing in a fast way, and without any approximations, higher-order calculations of partonic cross sections into global analyses of parton distribution functions. The approach, which is set up in Mellin-moment space, is particularly suited for analyses of future data from polarized proton-proton collisions, but not limited to this case. The usefulness and practicability of this method is demonstrated for the semi-inclusive production of hadrons in deep-inelastic scattering and the transverse momentum distribution of ``prompt'' photons in pp collisions, and a case study for a future global analysis of polarized parton densities is presented.Comment: 20 pages, LaTeX, 6 eps figures, final version to appear in PRD (minor changes

Next-to-leading order QCD corrections to A_TT for prompt photon production

We present a next-to-leading order QCD calculation of the cross section for isolated large-p_T prompt photon production in collisions of transversely polarized protons. We devise a simple method of dealing with the phase space integrals in dimensional regularization in the presence of the cos(2 phi) azimuthal-angular dependence occurring for transverse polarization. Our results allow to calculate the double-spin asymmetry A_TT for this process at next-to-leading order accuracy, which may be used at BNL-RHIC to measure the transversity parton distributions of the proton.Comment: 19 pages, LaTeX, 2 figures as eps file

Recoil and Threshold Corrections in Short-distance Cross Sections

We identify and resum corrections associated with the kinematic recoil of the hard scattering against soft-gluon emission in single-particle inclusive cross sections. The method avoids double counting and conserves the flow of partonic energy. It reproduces threshold resummation for high-p_T single-particle cross sections, when recoil is neglected, and Q_T-resummation at low Q_T, when higher-order threshold logarithms are suppressed. We exhibit explicit resummed cross sections, accurate to next-to-leading logarithm, for electroweak annihilation and prompt photon inclusive cross sections.Comment: minor modifications of the text, some references added. 51 pages, LaTeX, 6 figures as eps file

Next-to-leading order QCD corrections to the polarized hadroproduction of heavy flavors

We present the complete next-to-leading order QCD corrections to the polarized hadroproduction of heavy flavors which soon will be studied experimentally in polarized pp collisions at the BNL Relativistic Heavy Ion Collider (RHIC) in order to constrain the polarized gluon density Δg. It is demonstrated that the dependence on unphysical renormalization and factorization scales is strongly reduced beyond the leading order. The sensitivity of the charm quark spin asymmetry to Δg is analyzed in some detail, including the limited detector acceptance for leptons from charm quark decays at the BNL RHIC.Ingo Bojak and Marco Stratman

Heavy quarkonium: progress, puzzles, and opportunities

A golden age for heavy quarkonium physics dawned a decade ago, initiated by the confluence of exciting advances in quantum chromodynamics (QCD) and an explosion of related experimental activity. The early years of this period were chronicled in the Quarkonium Working Group (QWG) CERN Yellow Report (YR) in 2004, which presented a comprehensive review of the status of the field at that time and provided specific recommendations for further progress. However, the broad spectrum of subsequent breakthroughs, surprises, and continuing puzzles could only be partially anticipated. Since the release of the YR, the BESII program concluded only to give birth to BESIII; the $B$-factories and CLEO-c flourished; quarkonium production and polarization measurements at HERA and the Tevatron matured; and heavy-ion collisions at RHIC have opened a window on the deconfinement regime. All these experiments leave legacies of quality, precision, and unsolved mysteries for quarkonium physics, and therefore beg for continuing investigations. The plethora of newly-found quarkonium-like states unleashed a flood of theoretical investigations into new forms of matter such as quark-gluon hybrids, mesonic molecules, and tetraquarks. Measurements of the spectroscopy, decays, production, and in-medium behavior of c\bar{c}, b\bar{b}, and b\bar{c} bound states have been shown to validate some theoretical approaches to QCD and highlight lack of quantitative success for others. The intriguing details of quarkonium suppression in heavy-ion collisions that have emerged from RHIC have elevated the importance of separating hot- and cold-nuclear-matter effects in quark-gluon plasma studies. This review systematically addresses all these matters and concludes by prioritizing directions for ongoing and future efforts.Comment: 182 pages, 112 figures. Editors: N. Brambilla, S. Eidelman, B. K. Heltsley, R. Vogt. Section Coordinators: G. T. Bodwin, E. Eichten, A. D. Frawley, A. B. Meyer, R. E. Mitchell, V. Papadimitriou, P. Petreczky, A. A. Petrov, P. Robbe, A. Vair

EuFe2_2As2_2 under high pressure: an antiferromagnetic bulk superconductor

We report the ac magnetic susceptibility $\chi_{ac}$ and resistivity $\rho$ measurements of EuFe$_2$As$_2$ under high pressure $P$. By observing nearly 100% superconducting shielding and zero resistivity at $P$ = 28 kbar, we establish that $P$-induced superconductivity occurs at $T_c \sim$~30 K in EuFe$_2$As$_2$. $\rho$ shows an anomalous nearly linear temperature dependence from room temperature down to $T_c$ at the same $P$. $\chi_{ac}$ indicates that an antiferromagnetic order of Eu$^{2+}$ moments with $T_N \sim$~20 K persists in the superconducting phase. The temperature dependence of the upper critical field is also determined.Comment: To appear in J. Phys. Soc. Jpn., Vol. 78 No.