Analogous projections with less supersymmetry

Construct analogous amplitude projections in theories with less supersymmetry that can eliminate regular higher-point contributions and produce nontrivial constraints on lower-point amplitudes.

Background

The paper shows that, in maximally supersymmetric Yang–Mills theory and supergravity, a single discrete R-symmetry combined with scalar parity produces a projection that removes the unknown regular six-point contribution in a special collinear limit. This mechanism is essential for deriving the master equations.

The authors explicitly identify the extension of such projections to theories with less supersymmetry as unresolved. A successful construction would test how much of the infrared consistency mechanism survives when the strong Ward identities and R-symmetry structure of maximal supersymmetry are weakened.

References

Several questions remain open. Firstly, one should explore the constraint of maximal supersymmetry for gauge-gravity coupled system. Recent analysis has found non-linear constraints that mixes the single- and double-trace Wilson coefficients in the gluon sector, with promising numeric bounds that isolate Heterotic and IST. It will be interesting to find the exact form of identity that gives rise to these non-linear constraints. Scalar parity is imposed as a condition on selected six-point components; it would be useful to understand whether it follows from a more general physical principle or can be replaced by a weaker condition. The reduction of the R-symmetry requirement to a single discrete transformation also motivates a search for analogous projections in theories with less supersymmetry.

— Infrared Consistency and the Uniqueness of String Amplitudes  (2610.02124 - Huang et al., 1 Oct 2026) in Section 7, Summary and discussion