Bose-Fermi Degeneracy and Duality in Non-Supersymmetric Strings

Following Kachru, Kumar and Silverstein, we construct a set of nonsupersymmetric Type II string models which have equal numbers of bosons and fermions at each mass level. The models are asymmetric Z2 ⊗ Z ′ 2 orbifolds. We demonstrate that this bose-fermi degeneracy feature implies that both the one-loop and the two-loop contributions to the cosmological constant vanish. We conjecture and give a heuristic argument that the cosmological constant actually vanishes to all loops. We construct a strong-weak dual pair of models, both of which have bose-fermi degeneracy. This implies that their vanishing cosmological constants have no non-perturbative corrections. 11.25.-w Typeset using REVTEX ∗E-mail: [email protected] Address after September 1, 1998: Institute for Theoretical Physics, State University of New York at Stony Brook, Stony Brook, NY 11794. †E-mail: [email protected] 1