direction normal to that of mean order and traveling along the direction of broken symmetry. These bands have been observed in simulations of the Vicsek model [@Gregoire2004; @Chate2008], as well as in numerical solutions of the nonlinear hydrodynamic equations for polar fluids  [@Bertin2006; @Bertin2009; @Mishra2010]. We have shown here that active nematics exhibit a similar instability, controlled by the interplay of of curvature currents ($\overline{D}_Q$) and the self-regulation due to the density dependence of $\alpha $. The instability occurs even for $\overline{v}=0$, i.e., is present in both active and self-propelled nematics. It occurs for wavevectors perpendicular to the direction of broken nematic symmetry and the mode that goes unstable is a diffusive one. It is therefore tempting to associate it with the emergence of the stationary bands consisting of alternating ordered (nematic) and disorders regions that have been seems in simulations of active systems with apolar interactions  [@Chate2006] and physical excluded volume interactions [@Yang2010],[@Sam2012]. Finally, but most importantly, this instability mechanism is *generic*, in the sense that it does not depend on microscopic parameters, but only on the presence of a dynamical feedback between density and active currents.

Curvature Induced Flux {#subsec:curvature}
----------------------

Next we consider the region of small 