Trackingk-essence

We derive a condition for converging a common evolutionary track for k-essence (a scalar field dark energy with noncanonical kinetic terms). For the Lagrangian density $V\left(\phi \right)W\left(X\right)\mathrm{}$ with $X={\dot{\phi }}^2/2,$ we find that tracker solutions with $w_{\phi }<w_B$ exist if $\Gamma \equiv V^{″}{V/(V}^{\prime }{)}^2>3/2.\mathrm{}$ Here $w_{\phi }{(w}_B)$ is the equation of state of the scalar field (background radiation or matter). Our condition may be useful for examining the existence of attractorlike behavior in cosmology with k-essence (for example, a rolling tachyon).