I would like to consider how to solve the following optimization problem:
$\max x^{T}\mathbf{a}-b\sqrt{x^{T}\Sigma x}\;s.t.x^{T}\mathbf{1}=1$, provided that $b>0$ and $\Sigma$ is positive definite.
I want to solve KKT condition to solve the problem, however, I do not obtain a nice result.