How can I minimize the following term taking alpha and beta as variables

When I was trying to taking an object of the form showed in the picture, it always shown "Matrix dimensions must agree.
". Can I minimize this term taking alpha and beta as variables?

The Hessian is indefinite. So this is non-convex and can not be accepted by CVX.

Read Why isn’t CVX accepting my model? READ THIS FIRST! and read the CVX User’s Guide http://web.cvxr.com/cvx/doc/ .