Comment on the linear mirror instability near the threshold

A linear threshold condition of the mirror instability in a homogeneous, multispecies collisionless plasma with a general class of distribution functions is obtained in the low-frequency, long-wavelength limit of the Vlasov-Maxwell equation. In the case of one cold species, the conditions of the validity of the threshold condition and the behavior of the instability near threshold are also presented. It is confirmed that finite Larmor radius effects do not change the threshold condition. The linear threshold condition is extended to the case of hot species with a general class of distribution functions. In this case the conditions of the validity of the threshold condition or the behavior of the instability near threshold are hard to get analytically. Previous analytical and numerical results are discussed