Heavy quark production at HERA in k_t factorization supplemented with CCFM evolution

The application of k_t - factorization, supplemented with the CCFM small-x evolution equation, to heavy quark production is discussed. Differential cross sections of b-b_bar production and also inelastic J/psi production as measured at HERA are compared to the hadron level CCFM Monte Carlo generator CASCADE, using the unintegrated gluon density obtained within the CCFM evolution approach from a fit to HERA F_2 data.Comment: to appear in: Proceedings of Photon2001, Ascona, Switzerlan

Coupling of phonons and spin waves in triangular antiferromagnet

We investigate the influence of the spin-phonon coupling in the triangular antiferromagnet where the coupling is of the exchange-striction type. The magnon dispersion is shown to be modified significantly at wave vector (2pi,0) and its symmetry-related points, exhibiting a roton-like minimum and an eventual instability in the dispersion. Various correlation functions such as equal-time phonon correlation, spin-spin correlation, and local magnetization are calculated in the presence of the coupling.Comment: 6 pages, 5 figures; references added, minor text revisions, submitted to PR

Angular correlations in multi-jet final states from kt-dependent parton showers

We investigate parton-branching methods based on transverse-momentum dependent (TMD) parton distributions and matrix elements for the Monte Carlo simulation of multi-particle final states at high-energy colliders. We observe that recently measured angular correlations in ep final states with multiple hadronic jets probe QCD coherence effects in the space-like branching, associated with finite-angle gluon radiation from partons carrying small longitudinal momenta, and not included in standard shower generators. We present Monte Carlo calculations for azimuthal two-jet and three-jet distributions, for jet multiplicities and for correlations in the transverse-momentum imbalance between the leading jets. We discuss comparisons with current experimental multi-jet data, and implications of corrections to collinear-ordered showers for LHC final states.Comment: 25 pages. Discussion and references expanded; results unchanged. Additional calculations include