8,878 research outputs found
Comment on the frozen QCD coupling
The frozen QCD coupling is a parameter often used as an effective fixed
coupling. It is supposed to mimic both the running coupling effects and the
lack of knowledge of alpha_s in the infrared region. Usually the value of the
frozen coupling is fixed from the analysis of the experimental data. We present
a novel way to define such coupling(s) independently of the experiments. We
argue that there are different frozen couplings which are used in the double-
(DL) and single- logarithmic (SL) Approximations. We introduce four kinds of
the frozen couplings: the coupling used in DLA with a time-like argument (i.e.
the coupling present in the non-singlet scattering amplitudes and DIS structure
functions) which we find 0.24 approximately; the DLA coupling with a space-like
argument (in e+e- -annihilation, in DY processes and in any scattering
amplitude in the hard or backward kinematics) which is a factor two larger,
namely 0.48. We also show that the frozen coupling in the SL evolution
equations like BFKL has to be defined in a way less accurate compared to DLA,
and our estimate for this coupling is 0.1. Our estimates for the singlet and
non-singlet intercepts are also in a good agreement with the results available
in the literature.Comment: 11 pages, 3 figure
Singlet structure function g_1 at small x and small Q^2
Explicit expressions for the singlet g_1 at small x and small Q^2 are
obtained with the total resummation of the leading logarithmic contributions.
It is shown that g_1 practically does not depend on Q^2 in this kinematic
region. In contrast, it would be interesting to investigate its dependence on
the invariant energy 2pq because, being g_1 positive at small 2pq, it can turn
negative at greater values of this variable. The position of the turning point
is sensitive to the ratio between the initial quark and gluon densities, so its
experimental detection would enable to estimate this ratioComment: Section 2 is totally changed, one more ref adde
Small -x behavior of the non-singlet and singlet structure functions g_1
Explicit expressions for the non-singlet and singlet structure functions g_1
at the small -region are obtained. They include the total resummation of
double-logarithmic contributions and accounting for the running QCD coupling
effects. We predict that both the non-singlet and singlet g_1 asymptotically ~
x^{- \Delta}, with the singlet intercept
= 0.86 and being more than twice larger than the non-singlet intercept = 0.4.
The impact of the initial quark and gluon densities on the sign of g_1 at x <<
1 is discussed.Comment: Talk given at Xth Workshop on high energy spin physics, Dubna,
Russia, September,16-20, 2003. LateX 9pp, 4 fig
Impact of the running QCD coupling on the value of the intercept of the structure function singlet
The running QCD coupling effects for singlet are studied. We predict
that asymptotically , with the singlet intercept
.Comment: Talk given at the "XI International Workshop on Deep Inelastic
Scattering (DIS2003)", Saint Petersburg, 23-27 April 2003; 6 page
Synthesis of DGLAP and total resummation of leading logarithms for the non-singlet spin structure function g_1
The explicit expressions for the non-singlet DIS structure function g_1 at
small are obtained by resumming the leading logarithmic contributions. The
role played by the fits for the initial parton densities currently used in the
DGLAP on the small-x behavior of the non-singlet g_1 is discussed. Explicit
expressions combining DGLAP with our results are presented.Comment: Talk given at XIII International Workshop on Deep Inelastic
Scattering, April,27 - May,1, 2005, Madison, Wisconsin, USA, 3 pages, no
figure
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