Continuous-spin degrees of freedom in non-perturbative string theory

Determine whether continuous-spin particles play a role in non-perturbative formulations of string theory, including whether a fully non-perturbative formulation of M-theory requires continuous-spin degrees of freedom.

Background

The paper establishes that continuous-spin representations are absent from the massless spectrum of perturbative superstring theories, including open, closed, Type IIA, Type IIB, and heterotic constructions. The authors emphasize that this conclusion is intrinsically perturbative and therefore does not settle the status of continuous-spin particles in non-perturbative string theory.

The authors identify M-theory as a natural framework in which to investigate the unresolved issue. Although its low-energy limit is eleven-dimensional supergravity with a known perturbative massless field content, the authors leave open whether a complete non-perturbative formulation could involve continuous-spin degrees of freedom.

References

Since our result is intrinsically perturbative, it leaves open the question of whether CSPs play a role in non-perturbative formulations of string theory. M-theory offers a natural setting in which to pose this question: its low-energy limit, eleven-dimensional supergravity, is governed by the couplings among just three massless fields (the graviton, a three-form gauge potential, and the gravitino) and these couplings are well understood perturbatively. We may speculate, however, that a fully non-perturbative formulation of M-theory could require continuous-spin degrees of freedom.

— Absence of Continuous Spin Particles in Superstring Theory  (2610.00745 - Alabbasi et al., 30 Sep 2026) in Section Conclusions