Failure of the collinear expansion in calculation of the induced gluon emission
P. Aurenche, B. G. Zakharov+, H. Zaraket*
Laboratoire d'Annecy-le-Vieux de Physique Théorique LAPTH, F-74941 Annecy-le-Vieux Cedex, France
+L.D. Landau Institute for Theoretical Physics RAS, 117940 GSP-1, 117334 Moscow, Russia
*Lebanese University Faculty of Sciences (I), Hadeth-Beirut, Lebanon
PACS: 12.38.Bx, 12.39.St, 13.87.Ce
We demonstrate that the collinear expansion fails in the case of
gluon emission from a fast quark produced
in eA DIS. In this approximation the N!=!1 rescattering contribution
to the gluon spectrum vanishes.
We show that
the higher-twist approach by Guo, Wang and Zhang [11aur-W1,11aur-W2]
based on the collinear expansion is wrong.
The nonzero gluon spectrum obtained in [11aur-W1,11aur-W2]
is a consequence of unjustified neglecting some important terms
in the collinear expansion.