NGC 4945 is one of the brightest Seyfert galaxies on the sky at 100 keV, but is completely absorbed below 10 keV, implying an optical depth of the absorber to electron scattering of a few; its absorption column is probably the largest which still allows a direct view of the nucleus at hard X–ray energies. Our observations of it with the Rossi X–ray Timing Explorer (RXTE) satellite confirm the l...

Recently a new approach to wide-angle Compton scattering off protons has been proposed [1,2] where, for Mandelstam variables s,−t,−u that are large as compared to a typical hadronic scale, Λ of the order of 1 GeV, the process amplitudes factorize into a hard parton-level subprocess, Compton scattering off quarks, and in soft form factors which represent 1/xmoments of generalized parton distribu...

I present a systematic approach to calculating soft-gluon corrections through next-to-next-to-nextto-leading order for arbitrary hard-scattering cross sections. Using a unified approach, master formulas are derived for processes with both simple and complex color flows. Applications and numerical results are given for some processes of interest, including charged Higgs production and top quark ...

We study the origin of the non-thermal emission from the intracluster medium, including the excess hard X-ray emission and cluster-wide radio haloes, through fitting two representative models to the Coma cluster. If the synchrotron emitting relativistic electrons are accelerated in situ from the vast pool of thermal electrons, then a quasi-stationary solution of the kinetic equation with partic...

The hard pomeron component needed to reproduce small-x data seems to be present in elastic scattering at moderate energy. If this is the case, it is likely that the total cross section at the LHC will be appreciably larger than previously expected. 1 The effective trajectory Historically, hadronic exchanges have been remarkably well described by the simple-pole model of Donnachie and Landshoff ...

The rules of soft-collinear effective theory can be used naı̈vely to write hard scattering cross-sections as convolutions of separate hard, jet, and soft functions. One condition required to guarantee the validity of such a factorization is the infrared safety of these functions in perturbation theory. Using e+e− angularity distributions as an example, we propose and illustrate an intuitive meth...

In the context of hard hadronic reactions diquarks are a useful phenomenological device to model non-perturbative effects still observable in the kinematic range accessible by present-day experiments. In the following we present diquark-model predictions for γγ → pp̄ and ΛΛ̄. We also sketch how the (pure quark) hard-scattering formalism for exclusive reactions involving baryons can be reformulate...