Weak type estimates for the absolute value mapping

Abstract: We prove that if A and B are bounded self-adjoint operators such that A-B belongs to the trace class, then |A| -|B| belongs to the principal ideal L_{1,\infty} in the algebra L(H) of all bounded operators on an infinite-dimensional Hilbert space generated by an operator whose sequence of eigenvalues is {1, 1/2, 1/3, 1/4, ...}. Moreover, \mu(j;|A| -|B|)\leq const(1 + j)^{-1}|A-B|_1. We also obtain a semifinite version of this result, as well as the corresponding commutator estimates.