609 research outputs found
The impact factor for the virtual photon to light vector meson transition
We evaluate in the next-to-leading approximation the forward impact factor
for the virtual photon to light vector meson transition in the case of
longitudinal polarization. We find that in the hard kinematic domain, both in
the leading and in the next-to-leading approximation, the expression for the
impact factor factorizes, up to power suppressed corrections, into the
convolution of a perturbatively calculable hard-scattering amplitude and a
meson twist-2 distribution amplitude.Comment: 31 pages latex; few comments and one reference added; version to
appear in Eur. Phys. Journal
Radiative Corrections to QCD Amplitudes in Quasi-Multi-Regge Kinematics
Radiative corrections to QCD amplitudes in the quasi-multi-Regge kinematics
are interesting in particular since the Reggeized form of these amplitudes is
used in the derivation of the NLO BFKL. This form is a hypothesis which must be
at least carefully checked, if not proved. We calculate the radiative
corrections in the one-loop approximation using the s-channel unitarity.
Compatibility of the Reggeized form of the amplitudes with the s-channel
unitarity requires fulfillment of the set of nonlinear equations for the
Reggeon vertices. We show that these equations are satisfied.Comment: 28 pages,3 figure
The Quark Impact Factors
We calculate in the next-to-leading approximation the non-forward quark
impact factors for both singlet and octet color representation in the
-channel. The integral representation of the octet impact factor in the
general case of arbitrary space-time dimension and massive quark flavors is
used to check the so-called "second bootstrap condition" for the gluon
Reggeization at the next-to-leading logarithmic approximation in perturbative
QCD. We find that it is satisfied for both helicity conserving and
non-conserving parts. The integrations are then performed for the explicit
calculation of the impact factors in the massless quark case.Comment: 23 pages, LaTeX, 1 EPS figure, uses epsf.sty and axodraw.st
Calculation of Reggeon Vertices in QCD
The method of calculation of effective vertices of interaction of the
Reggeized gluon and quark with particles in QCD in the next-to-leading order is
developed. The method is demonstrated in the case of already known vertices of
both gluon-gluon and quark-quark transitions in the scattering of gluons and
quarks on the Reggeized gluon. It is used for the calculation of the
gluon-quark transition in the scattering on the Reggeized quark.Comment: 27 pages, LaTex, 1 figure, uses axodraw.st
Electroproduction of two light vector mesons in next-to-leading BFKL: study of systematic effects
The forward electroproduction of two light vector mesons is the first example
of a collision process between strongly interacting colorless particles for
which the amplitude can be written completely within perturbative QCD in the
Regge limit with next-to-leading accuracy. In a previous paper we have given a
numerical determination of the amplitude in the case of equal photon
virtualities by using a definite representation for the amplitude and a
definite optimization method for the perturbative series. Here we estimate the
systematic uncertainty of our previous determination, by considering a
different representation of the amplitude and different optimization methods of
the perturbative series. Moreover, we compare our result for the differential
cross section at the minimum momentum transfer with a different approach, based
on collinear kernel improvement.Comment: 17 pages, 11 figures; journal version, new figures and discussion
adde
The Gluon Impact Factors
We calculate in the next-to-leading approximation the non-forward gluon
impact factors for arbitrary color state in the -channel. In the case of the
octet state we check the so-called "second bootstrap condition" for the gluon
Reggeization in QCD, using the integral representation for the impact factors.
The condition is fulfilled in the general case of an arbitrary space-time
dimension and massive quark flavors for both helicity conserving and
non-conserving parts.Comment: 32 pages, LaTeX, 1 EPS figure, uses epsf.sty and axodraw.st
The quark part of the non-forward BFKL kernel and the ``bootstrap'' for the gluon Reggeization
We calculate the quark part of the kernel of the generalized non-forward BFKL
equation at non-zero momentum transfer in the next-to-leading logarithmic
approximation. Along with the quark contribution to the gluon Regge trajectory,
this part includes pieces coming from the quark-antiquark production and from
the quark contribution to the radiative corrections in one-gluon production in
the Reggeon-Reggeon collisions. The results obtained can be used for an
arbitrary representation of the colour group in the channel. Using the
results for the adjoint representation, we demonstrate explicitly the
fulfillment of the ``bootstrap'' condition for the gluon Reggeization in the
next-to-leading logarithmic approximation in the part concerning the quark
contribution.Comment: 26 pages, LaTeX, uses axodraw.sty; revised final comment; to appear
on Phys. Rev.
Photon-Reggeon Interaction Vertices in the Nla
We calculate the effective vertices for the quark-antiquark and the
quark-antiquark-gluon production in the virtual photon - Reggeized gluon
interaction. The last vertex is considered at the Born level; for the first one
the one-loop corrections are obtained. These vertices have a number of
applications; in particular, they are necessary for calculation of the virtual
photon impact factor in the next-to-leading logarithmic approximation.Comment: 20 pages, references adde
Minimal Subtraction vs. Physical Factorisation Schemes in Small-x QCD
We investigate the relationship of ``physical'' parton densities defined by
kt-factorisation, to those in the minimal subtraction scheme, by comparing
their small-x behaviour. We first summarize recent results on the above scheme
change derived from the BFKL equation at NLx level, and we then propose a
simple extension to the renormalisation-group improved (RGI) equation. In this
way we are able the examine the difference between resummed gluon distributions
in the Q_0 and MSbar schemes and also to show MSbar scheme resummed results for
P_gg and approximate ones for P_qg. We find that, due to the stability of the
RGI approach, small-x resummation effects are not much affected by the
scheme-change in the gluon channel, while they are relatively more sensitive
for the quark-gluon mixing.Comment: 14 pages, 8 figure
Heavy Pair Production Currents with General Quantum Numbers in Dimensionally Regularized NRQCD
We discuss the form and construction of general color singlet heavy
particle-antiparticle pair production currents for arbitrary quantum numbers,
and issues related to evanescent spin operators and scheme-dependences in
nonrelativistic QCD (NRQCD) in n=3-2epsilon dimensions. The anomalous
dimensions of the leading interpolating currents for heavy quark and colored
scalar pairs in arbitrary (2S+1)L_J angular-spin states are determined at
next-to-leading order in the nonrelativistic power counting.Comment: 39 pages, 2 tables, 10 figures; typos corrected, published versio
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