Vacuum Energy Cancellation in a Non-supersymmetric String

TL;DR

This work constructs a nonsupersymmetric asymmetric orbifold of type II strings and demonstrates perturbative vanishing of the cosmological constant $\oldmath{\Lambda}$ at 1- and 2-loop orders, with heuristic arguments for higher-genus cancellation. The authors rely on bose–fermi degeneracy without spacetime supersymmetry, modular invariance, and careful gauge fixing of worldsheet gravitini to show the spin-structure dependent contributions cancel and boundary terms vanish. They focus on the genus-2 amplitude with the $(1,1,f,g)$ twist and use theta-function identities to show no finite contributions arise, supporting a potentially all-genus cancellation. The paper also discusses connections to AdS/CFT ideas about conformal fixed lines and dilaton potentials, and contemplates implications for nonsupersymmetric vacua with vanishing or stabilized cosmological constant and possible extensions to lower-dimensional models.

Abstract

We present a nonsupersymmetric orbifold of type II string theory and show that it has vanishing cosmological constant at the one and two loop level. We argue heuristically that the cancellation persists at higher loops.