Evidence for Nonvanishing Cosmological Constant in NonSusy Superstring Models

TL;DR

This paper investigates the two-loop cosmological constant in non-supersymmetric superstring models, finding it to be nonzero in models with explicit supersymmetry breaking, which challenges the construction of realistic superstring models.

Contribution

It provides a detailed analysis of the two-loop cosmological constant in non-supersymmetric superstring models using both theta-function and hyperelliptic formalisms, revealing nonvanishing results.

Findings

The cosmological constant is nonzero in models with broken supersymmetry.

The analysis confirms the difficulty in constructing realistic superstring models.

The results are consistent across different computational formalisms.

Abstract

We reanalyse the computation of the cosmological constant $\Lambda$ at two loops in recently proposed Superstring models without massless gravitini, both in the theta-function based formalism and by a detailed computation in the more explicit hyperelliptic description of the underlying genus two Riemann surface. $\Lambda$ is expressed as the integral over the surface moduli of an amplitude which is zero if susy is not completely broken, but we find it to be nonvanishing in the susy breaking models which can be given an explicitly workable fermionic formulation. Thus unfortunately the issue of getting realistic and perturbatively viable models from Superstring Theory remains open.