264 research outputs found
Light-by-light scattering in Double-Logarithmic Approximation
In the present paper we consider the elastic 2 -> 2 -scattering of virtual
photons at high energies in the forward kinematics at zero and non-zero values
of t. Accounting for both gluon and quark double-logarithmic (DL) contributions
to all orders in the QCD coupling, we obtain explicit expressions for
amplitudes of this process in Double-Logarithmic Approximation (DLA). First we
keep the QCD coupling fixed and then account for running coupling effects.
Applying the saddle-point method to the obtained expressions for the scattering
amplitude, we calculate the high-energy asymptotics of the amplitude, which
proved to be of the Regge form. The Reggeon bears the vacuum quantum numbers
and therefore it is a new, DL contribution to Pomeron. Comparison of the DL
Pomeron to the BFKL Pomeron shows that contribution of the DL Pomeron to the
high-energy asymptotics is of the same order as contribution of the BFKL
Pomeron, so the DL Pomeron should be taken into account together with the BFKL
Pomeron. We estimate the applicability region for the asymptotics of the
light-by-light scattering amplitude, where the the DL Pomeron can reliably
represent the parent amplitude.Comment: 16 pages, 4 figures. Multiple errors are corrected, 2 figs are added,
comparizon to BFKL is done in more detai
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
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
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