Positivity constraints in QCD
نویسنده
چکیده
The density matrix positivity is a natural counterpart of unitarity. The resulting constraints for various parton distribution and correlations are considered. Their compatibility with leading order QCD evolution is guaranteed by the probabilistic interpretation of the latter. In the case of non-forward distributions the positivity constraints naturally imply the symmetric form of the evolution equation. The positivity of density matrix is just the positivity of its eigenvalues λi ≥ 0, (1) required, together with the normalization condition
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