  We construct realistic supersymmetric theories in which the correct scale for
electroweak symmetry breaking is obtained without significant fine-tuning. We
consider two classes of models. In one class supersymmetry breaking is
transmitted to the supersymmetric standard model sector through Dirac gaugino
mass terms generated by a D-term vacuum expectation value of a U(1) gauge
field. In the other class the supersymmetry breaking sector is separated from
the supersymmetric standard model sector in an extra dimension, and the
transmission of supersymmetry breaking occurs through gauge mediation. In both
these theories the Higgs sector contains two Higgs doublets and a singlet, but
unlike the case for the next-to-minimal supersymmetric standard model the
singlet field is not responsible for generating the supersymmetric or
supersymmetry breaking mass for the Higgs doublets. These masses, as well as
the mass for the singlet, are generated through gravitational-strength
interactions. The scale at which the squark and slepton masses are generated is
of order (1-100) TeV, and the generated masses do not respect the unified mass
relations. We find that electroweak symmetry breaking in these theories is
caused by an interplay between the top-stop radiative correction and the
holomorphic supersymmetry breaking mass for the Higgs doublets and that the
fine-tuning can be reduced to the level of 20%. The theories have rich
phenomenology, including a variety of possibilities for the lightest
supersymmetric particle.
