Comment on ``Nonextensive theory of dark matter and gas density   profiles''
  Self-gravitating systems with nonlocal, long-range interactions are described by nonextensive statistics. Recently, Leubner demonstrated that the nonextensivity parameter $\kappa$ should be negative for self-gravitating, pressureless systems, such as dark matter halos. The equation for the spherically symmetric nonextensive dark matter halos has also been derived. Here we demonstrate that this equation is identical to the classical Lane-Emden equation describing the structure of self-gravitating polytropic spheres. This establishes an intimate connection between self-gravitating polytropes and nonextensive thermostatistics. Moreover, based on this fact and observational data, we put a stronger constraint on $\kappa$, namely $\kappa<-3.4$. 
Mikhail V. Medvedev (University of Kansas)