Breakdown of Conventional Factorization for Isolated Photon Cross Sections

Using $e^+e^-\rightarrow\gamma + X$ as an example, we show that the conventional factorization theorem in perturbative quantum chromodynamics breaks down for isolated photon cross sections in a well defined part of phase space. Implications and physical consequences are discussed.Comment: 11 pages, RevTex, 1 figure in postscrip

Nuclear enhanced power corrections to DIS structure functions

We calculate nuclear enhanced power corrections to structure functions measured in deeply inelastic lepton-nucleus scattering in Quantum Chromodynamics (QCD). We find that the nuclear medium enhanced power corrections at order of $O(\alpha_s/Q^2)$ enhance the longitudinal structure function $F_L$, and suppress the transverse structure function $F_1$. We demonstrate that strong nuclear effects in $\sigma_A/\sigma_D$ and $R_A/R_D$, recently observed by HERMES Collaboration, can be explained in terms of the nuclear enhanced power corrections.Comment: Latex, 10 pages including 3 figure

Isolated Prompt Photon Production

We show that the conventionally defined partonic cross section for the production of isolated prompt photons is not an infrared safe quantity. We work out the case of $e^+e^- \to \gamma + X$ in detail, and we discuss implications for hadron reactions such as $p \bar{p} \to \gamma + X$.Comment: 8 pages, latex2e, 2 figures, uses Moriond.sty; Invited paper presented by E. L. Berger at the XXXIInd Rencontres de Moriond, QCD and High Energy Hadronic Interactions, Les Arcs, Savoie, France, March 22 - 29, 199