Deeply virtual Compton scattering amplitude at the tree level: Transversality, twist-3, and factorization
We study the virtual Compton amplitude in the generalized Bjorken region (q{sup 2}{yields}{infinity}, t small) in QCD by means of a light-cone expansion of the product of EM currents in string operators in coordinate space. Electromagnetic gauge invariance (transversality) is maintained by including in addition to the twist-2 operators ''kinematical'' twist-3 operators which appear as total derivatives of twist-2 operators. The non-forward matrix elements of the elementary twist-2 operators are parametrized in terms of two-variable spectral functions (double distributions), from which twist-2 and 3 skewed distributions are obtained through reduction formulas. Our approach is equivalent to a Wandzura-Wilczek--type approximation for the twist-3 skewed distributions. The resulting Compton amplitude is manifestly transverse up to terms of order t/q{sup 2}. We find that in this approximation the tensor amplitude for longitudinal polarization of the virtual photon is finite, while the one for transverse polarization contains a divergence already at the tree level. However, this divergence has zero projection on the polarization vector of the final photon, so that the physical helicity amplitudes are finite.
- Sponsoring Organization:
- (US)
- OSTI ID:
- 40205135
- Journal Information:
- Physical Review D, Vol. 63, Issue 11; Other Information: DOI: 10.1103/PhysRevD.63.114012; Othernumber: PRVDAQ000063000011114012000001; 004111PRD; PBD: 1 Jun 2001; ISSN 0556-2821
- Publisher:
- The American Physical Society
- Country of Publication:
- United States
- Language:
- English
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