Marginal tearing modes and stability threshold in presence of an anomalous electron viscosity

It is shown analytically that tearing modes in presence of an anomalous electron-like viscosity, that exist in the limit of no anomaly, is purely growing when ustable. Moreover the introduction of the 'viscosity' does not bring about any shift in the stability threshold. We derive an analytical dispersion relation for the marginal regime. The anomaly has an opposite effect on the marginal mode compared to modes away from the marginal regime, where it tends to destabilize the mode by enhancing the growth rate. Due to possible overlap these differences are indicating the existence of two different tearing modes. The growth rates has a continuous transition to the classical growth rate in the limit of vanishing 'viscosity', and thereby revealing the possibility of being branches of the same 'non-viscous' mode. (orig.)