  The very existence of a phase transition for spin glasses in an external
magnetic field is controversial, even in high dimensions. We carry out massive
simulations of the Ising spin-glass in a field, in six dimensions (which,
according to classical -- but not generally accepted -- field-theoretical
studies, is the upper critical dimension). We obtain results compatible with a
second-order phase transition and estimate its critical exponents for the
simulated lattice sizes. The detailed analysis performed by other authors of
the replica symmetric Hamiltonian, under the hypothesis of critical behavior,
predicts that the ratio of the renormalized coupling constants remain bounded
as the correlation length grows. Our numerical results are in agreement with
this expectation.
