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We present a Next-to-Leading Order calculation of the cross section for the leptoproduction of large-E ⊥ hadrons and we compare our predictions with H1 data on the forward production of π 0 . We find large higher order corrections and an important sensitivity to the renormalization and factorization scales. These large corrections are shown to arise in part from BFKL-like diagrams at the lowest order.

The associated production of J/ϩ␥ at the CERN LHC is studied within the NRQCD framework. The signal we focus on is the production of a J/ and an isolated photon produced back to back, with their transverse momenta balanced. It is shown that even for very large values of transverse momentum (p T ϳ50 GeV) the dominant contribution to this process is not fragmentation. This is because of the fact that fragmentation-type contributions to the cross section come from only a qq initial state, which is suppressed at the LHC. We identify gg-initiated diagrams higher-order in ␣ s which do have fragmentation-type vertices. We find, however, that the contribution of these diagrams is negligibly small. ͓S0556-2821͑99͒03613-9͔

We develop various complementary concepts and techniques for handling quantum fluctuations of Goldstone bosons. We emphasize that one of the consequences of the masslessness of Goldstone bosons is that the longitudinal fluctuations also have a diverging susceptibility characterized by an anomalous dimension (d-2) in space–time dimensions 2<d<4. In d=4 these fluctuations diverge logarithmically in the infrared region. We show the generality of this phenomenon on the basis of (i) Renormalization group flows, (ii) Ward identities, and (iii) Schwinger–Dyson equations. We also obtain an explicit form for the generating functional of one-particle irreducible vertices of the O(N) (non)linear σ models in the leading 1/N approximation. We show that this incorporates all infrared behavior correctly both in linear and nonlinear σ models. Some consequences are discussed briefly.

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