Shear viscosity of hadronic gas mixtures

We investigate the effects of baryon chemical potential \mu on the shear viscosity coefficient \eta and the viscosity to entropy density ratio \eta/s of a pion-nucleon gas mixture. We find that \eta is an increasing function of T and \mu, while the ratio \eta/s turns to a decreasing function in a wide region of T-\mu plane. In the kinematical region we studied, the smallest value of \eta/s is about 0.3.