Theory of incompressible MHD turbulence with cross-helicity

(Abridged) An anisotropic theory of MHD turbulence with nonvanishing cross-helicity is constructed based on Boldyrev's alignment hypothesis and probabilities p and q for fluctuations v and b to be positively or negatively aligned. Guided by observations suggesting that the normalized cross-helicity and the probability p are approximately constant in the inertial range, a generalization of Boldyrev's theory is derived that depends on the three ratios w+/w-, epsilon+/epsilon-, and p/q. The theory reduces to Boldyrev's original theory when w+ = w-, epsilon+ = epsilon-, and p = q.