Proof of the outage probability conjecture for MISO channels

In Telatar 1999, it is conjectured that the covariance matrices minimizing the outage probability for MIMO channels with Gaussian fading are diagonal with either zeros or constant values on the diagonal. In the MISO setting, this is equivalent to conjecture that the Gaussian quadratic forms having largest tale probability correspond to such diagonal matrices. We prove here the conjecture in the MISO setting.