Comment on paper by L. M. Malyshkin and S. Boldyrev, "Magnetic dynamo action at low magnetic Prandtl numbers", PRL 105, 215002 (2010)

英文摘要：

Is the scaling, λ\sim Rm^{1/2}, for the growth rate of small-scale dynamo instability at low magnetic Prandtl numbers and large magnetic Reynolds numbers, Rm, valid in the vicinity of the threshold? Our analysis and even numerical solution (Malyshkin and Boldyrev, 2010) of the dynamo equations for a Gaussian white-noise velocity field (the Kazantsev-Kraichnan model) imply that the answer is negative. Contrary to the claim by Malyshkin and Boldyrev (2010), there are two different asymptotics for the dynamo growth rate: in the vicinity of the threshold and far from the threshold.