19 research outputs found
Reduction formalism for dimensionally regulated one-loop N-point integrals
We consider one-loop scalar and tensor integrals with an arbitrary number of
external legs relevant for multi-parton processes in massless theories. We
present a procedure to reduce N-point scalar functions with generic
4-dimensional external momenta to box integrals in (4-2\epsilon) dimensions. We
derive a formula valid for arbitrary N and give an explicit expression for N=6.
Further a tensor reduction method for N-point tensor integrals is presented.
We prove that generically higher dimensional integrals contribute only to order
\epsilon for N>=5. The tensor reduction can be solved iteratively such that any
tensor integral is expressible in terms of scalar integrals. Explicit formulas
are given up to N=6.Comment: 21 pages Latex, 1 eps figur
Calculation of 1-loop Hexagon Amplitudes in the Yukawa Model
We calculate a class of one-loop six-point amplitudes in the Yukawa model.
The construction of multi-particle amplitudes is done in the string inspired
formalism and compared to the Feynman diagrammatic approach. We show that there
exists a surprisingly efficient way of calculating such amplitudes by using
cyclic identities of kinematic coefficients and discuss in detail cancellation
mechanisms of spurious terms. A collection of formulas which are useful for the
calculation of massless hexagon amplitudes is given.Comment: 15 pages Late
Inelastic production in polarized photon-hadron collisions
Presented here is a calculation of inelastic production in polarized
photon-hadron collisions under the framework of NRQCD factorization formalism.
We consider the photoproduction of \jpsi in the energy range relevant to
HERA. The Weizs\"acker-Williams approximation is adopted in the evaluation of
the cross sections for collisions. We found that this process can give
another independent test for the color-octet mechanism, and the different
features for the two color-octet processes may provide further informations on
the mechanism for inelastic \jpsi photoproduction. And the discrepancy on the
production asymmetry between various sets of polarized gluon distribution
functions is also found to be distinctive.Comment: 14pages, 6 PS figure
Polarized Parton Distributions in the Nucleon
The distribution of the spin of the nucleon among its constituents can be
parametrized in the form of polarized parton distribution functions for quarks
and gluons. Using all available data on the polarized structure function
, we determine these distributions both at leading and
next-to-leading order in perturbation theory. We suggest three different,
equally possible scenarios for the polarized gluon distribution, which is found
to be only loosely constrained by current experimental data. We examine various
possibilities of measuring polarized parton distributions at future
experiments.Comment: 18 pages, LATEX, 6 figures available as .uu fil
A novel method to compute one loop 4 point functions
International audienceWe present a part of an ongoing work initiated by Prof. Shimizu on a method to compute numerically two loop scalar integrals as a sum of two dimensional integrals of generalized scalar one loop four point functions. This implies to have a formula for the one loop scalar four point functions which is valid outside the physical domain, this is the object of the present work
A subtraction scheme for processes involving fragmentation functions at NLO
International audienceWe present a novel subtraction method to remove the soft and collinear divergences at next-to-leading order for processes involving an arbitrary number of fragmentation functions, where this method acts directly in the hadronic centre-of-mass frame. We provide the analytical formulae of the subtraction terms in the general case where all the final state partons fragment to hadrons and for the two special cases when one of the partons of the final state does not fragment, i.e. it is a photon or involved in a jet
Towards an efficient method to compute two-loop scalar amplitudes
International audienceWe report on an ongoing work initiated by Prof. Shimizu, proposing a method to numerically compute two-loop scalar integrals as sums of two-dimensional integrals of generalised one-loop N-point functions analytically computed and integrated over some simple weight functions. The analytic computation of the generalised one-loop N-point functions in a systematic way motivates a novel approach sketched in this talk
A subtraction scheme for processes involving fragmentation functions at NLO
International audienceWe present a novel subtraction method to remove the soft and collinear divergences at next-to-leading order for processes involving an arbitrary number of fragmentation functions, where this method acts directly in the hadronic centre-of-mass frame. We provide the analytical formulae of the subtraction terms in the general case where all the final state partons fragment to hadrons and for the two special cases when one of the partons of the final state does not fragment, i.e. it is a photon or involved in a jet