Bilinear embedding for real elliptic differential operators in   divergence form with potentials
  We present a simple Bellman function proof of a bilinear estimate for elliptic operators in divergence form with real coefficients and with nonnegative potentials. The constants are dimension-free. The $p$-range of applicability of this estimate is $(1,\infty)$ for any real accretive (nonsymmetric) matrix $A$ of coefficients. 
Oliver Dragi\v{c}evi\'c and Alexander Volberg
math.CA