Higher-twist contributions to F_L and F_2 from instantons

Abstract

We study the twist-4 contribution to the unpolarized nucleon structure functions, F_L and F_2, in an approach where the vacuum structure of QCD is described by a dilute medium of instantons ($\bar{\rho }/\bar{R}\ll 1$). The dominant power corrections come from the twist-4 quark-gluon operators and are of the order $1/({\bar{\rho }}^2{Q}^2)$. The contributions from four-quark operators are suppressed. The approach predicts large 1/Q^2-corrections to F_L, in agreement with the results of QCD fits to the data.

Comments: 4 pages, LaTeX, uses sprocl.sty. Contribution to Proceedings of DIS 2000, Liverpool, April 25 - 30, 2000