NORDITA-98/51 HE hep-ph/9808229 HANDBOOK OF HIGHER TWIST DISTRIBUTION AMPLITUDES OF VECTOR MESONS IN QCD

We give a summary of existing results on higher twist distribution amplitudes of vector mesons in QCD. Special attention is payed to meson mass corrections which turn out to be large. A \shopping list" is presented of most important nonperturbative parameters which enter distribution amplitudes. The notion of distribution amplitudes refers to momentum fraction distributions of partons in the meson in a particular Fock state with xed number of components. For the minimal number of constituents, the distribution amplitude is related to the Bethe-Salpeter wave function BS by The standard approach to distribution amplitudes, which is due to Brodsky and Lepage 1 , considers the hadron's parton decomposition in the innnite momentum frame. A conceptually diierent, but mathematically equivalent formalism is the light-cone quantization 2. Either way, power suppressed contributions to exclusive processes in QCD, which are commonly referred to as higher twist corrections, are thought to originate from three diierent sources: contributions of \bad" components in the wave function and in particular of those with \wrong" spin projection; contributions of transverse motion of quarks (antiquarks) in the leading twist components, given for instance by integrals as above with additional factors of k 2 ? ; contributions of higher Fock states, with additional gluons and/or quark-antiquark pairs.