Roberto Fiore

Gluon Reggeization in QCD in the next to leading order

Abstract Gluon Reggeization can significantly simplify the calculation of subleading terms for parton distributions at small x , where x is the longitudinal momentum fraction carried by a parton. We check the Reggeization in elastic scattering processes of QCD at large energy and fixed momentum transfer . For amplitudes of these processes with gluon quantum numbers and negative signature in the t channel s -channel discontinuities are calculated in the two-loop approximation. The two-loop correction to the gluon trajectory is expressed in terms of these discontinuities. Remarkable cancellations lead to the independence of the trajectory on the properties of the scattered particles, confirming the gluon Reggeization.

Gluon Regge trajectory in the two-loop approximation☆

Abstract Evaluating two-loop integrals in the transverse momentum space we obtain the trajectory of the Reggeized gluon in QCD in an explicit form in the two-loop approximation. It is presented as an expansion in powers of ( D − 4) for the space-time dimension D tending to the physical value D = 4. As the result of a remarkable cancellation the third order pole in D − 4 disappears in the trajectory and the expansion starts with ( D − 4) −2 .

String effects in the Wilson loop: A High precision numerical test

Abstract We test numerically the effective string description of the infrared limit of lattice gauge theories in the confining regime. We consider the 3D Z 2 lattice gauge theory, and we define ratios of Wilson loops such that the predictions of the effective string theory do not contain any adjustable parameters. In this way we are able to obtain a degree of accuracy high enough to show unambiguously that the flux-tube fluctuations are described, in the infrared limit, by an effective bosonic string theory.

Quark contribution to the reggeon - reggeon - gluon vertex in QCD

The quark loop contribution to the Reggeon-Reggeon-gluon vertex is calculated in QCD, where the Reggeon is the Reggeized gluon. Compared with the vertex in the Born approximation, this contribution exhibits a new spin structure as well as the gluon loop one. A remarkable but not complete cancellation between gluon and quark contributions to this new spin structure takes place for the case of three massless quark flavors.

QUARK-ANTIQUARK CONTRIBUTION TO THE BFKL KERNEL

Abstract The quark-antiquark contribution to the BFKL kernel is calculated. Using the effective vertex for the q q pair production in the Reggeon-Reggeon collision we find this contribution by integrating the square of this vertex over relative transverse momenta and fractions of longitudinal momenta of produced particles.

Proof of the multi-Regge form of QCD amplitudes with gluon exchanges in the NLA

The multi-Regge form of QCD amplitudes with gluon exchanges is proved in the next-to-leading approximation. The proof is based on the bootstrap relations, which are required for the compatibility of this form with the s-channel unitarity. We show that the fulfillment of all these relations ensures the reggeized form of energy dependent radiative corrections order by order in perturbation theory. Then we prove that all these relations are fulfilled if several bootstrap conditions on the reggeon vertices and trajectory hold true. Now all these conditions are checked and proved to be satisfied.

Reggeization of the quark-quark scattering amplitude in QCD.

{ital s}-channel discontinuity of the quark-quark scattering amplitude with gluon quantum numbers in the {ital t} channel and a negative signature is calculated in the Regge kinematical region in the two-loop approximation. Using this discontinuity and assuming that the Regge asymptotic behavior is given by the Reggeized gluon contribution, we calculate the gluon trajectory in the two-loop approximation. Remarkable cancellations lead to the independence of the trajectory on properties of the scattered quarks, confirming the gluon Reggeization. {copyright} {ital 1996 The American Physical Society.}

Gribov's theorem on soft emission and the Raggeon-Reggeon-gluon vertex at small transverse momentum

Abstract In spite of the fact that the Gribovs theorem about the region of applicability of the soft emission factorization cannot be referred literally to the case of massless charged particles, it can be used for the calculation of soft emission amplitudes in such a case also. We demonstrate this for the gluon production amplitude in the multi-Regge kinematics with small transverse momentum.

Rough interfaces beyond the Gaussian approximation

Abstract We compare predictions of the Capillary Wave Model beyond its gaussian approximation with Monte Carlo results for the energy gap and the surface energy of the 3D Ising model in the scaling region. Our study reveals that the finite-size effects of these quantities are well described by the Capillary Wave Model, expended to two-loop order (one order beyond the gaussian approximation).

Quark contribution to the gluon-gluon-reggeon vertex in QCD☆

Abstract The quark loop contribution to the gluon-gluon-reggeon vertex is calculated in QCD, where the reggeon is the reggeized gluon. This contribution exhibits helicity non-conservation as well as a gluon loop contribution. We find an exact cancellation between these two contributions in the case of three massless quark flavours.