Alternatives to Seesaw

Abstract

The seesaw mechanism is attractive not only because it "explains'' small neutrino mass, but also because of its packaging with the SUSY-GUT, leptogenesis, Dark Matter, and electroweak symmetry breaking. However, this package has the flavor, CP, and gravitino problems. I discuss two alternatives to the seesaw mechanism. In one of them, the anomaly-mediated supersymmetry breaking solves these problems, while predicts naturally light Dirac neutrinos. In the other, the light Majorana neutrinos arise from supersymmetry breaking with right-handed neutrinos below TeV, and the Dark Matter and collider phenomenology are significantly different.