Über-naturalness: unexpectedly light scalars from supersymmetric extra dimensions

Standard lore asserts that quantum effects generically forbid the occurrence of light (non-pseudo-Goldstone) scalars having masses smaller than the Kaluza Klein scale, MKK, in extra-dimensional models, or the gravitino mass, M3/2, in supersymmetric situations. We argue that a hidden assumption underlies this lore: that the scale of gravitational physics, Mg, (e.g the string scale, Ms, in string theory) is of order the Planck mass, $$ {M_p} = …