A strong regularity result for parabolic equations (Q1418326)

The paper deals with the regularity of solutions of the following equation \[ \Delta u(x,t)+b(x,t)\cdot \nabla u(x,t)-u_t(x,t)=0,\qquad (x,t)\in {\mathbb R}^n\times(0,\infty), \] under the condition \(\operatorname{div} b=0.\)