Quadratic $A_1$ bounds for commutators of singular integrals with BMO   functions
  For commutators of the form [b,T] where T is any Calderon--Zygmund operator and b is any BMO function we derive weighted quadratic type estimates in term of the A1 constant of the weight both in the Lp context or of LlogL type at the endpoint 
Carmen Ortiz-Caraballo
math.CA