Additivity of minimal entropy output for a class of covariant channels
  Additivity of minimal entropy output is proven for the class of quantum channels $\Lambda_t (A):=t A^{T}+(1-t)\tau (A)$ in the parameter range $-2/(d^2-2)\le t \le 1/(d+1)$. 
M. Fannes, B. Haegeman, M. Mosonyi and D. Vanpeteghem