New phenomena in the standard no-scale supergravity model

Abstract

We revisit the no-scale mechanism in the context of the simplest no-scale supergravity extension of the Standard Model. This model has the usual five-dimensional parameter space plus an additional parameter ${\xi }_{3/2}\equiv m_{3/2}/m_{1/2}$. We show how predictions of the model may be extracted over the whole parameter space. A necessary condition for the potential to be stable is $\mathrm{Str}{\mathcal{M}}^4>0$, which is satisfied if ${\mathbf{m}}_{3/2}\text{lsim}2{\mathbf{m}}_{\tilde{\mathbf{q}}}$. Order of magnitude calculations reveal a no-lose theorem guaranteeing interesting and potentially observable new phenomena in the neutral scalar sector of the theory which would constitute a ``smoking gun'' of the no-scale mechanism. This new phenomenology is model-independent and divides into three scenarios, depending on the ratio of the weak scale to the vev at the minimum of the no-scale direction. We also calculate the residual vacuum energy at the unification scale ($C_0{m}_{3/2}^4$), and find that in typical models one must require $C_0>10$. Such constraints should be important in the search for the correct string no-scale supergravity model. We also show how specific classes of string models fit within this framework.

Comments: 11pages, LaTeX, 1 figure (included), CERN-TH.7433/94