Extended Massive Ambitwistor String II

TL;DR

This work extends the massive ambitwistor string by introducing an auxiliary gauge sector that embeds a Super-Yang-Mills component on the Coulomb branch, yielding an anomaly-free, modular-invariant framework. It provides a detailed construction of all-multiplicity loop amplitudes, proving that vacuum partitions and the cosmological constant vanish at all orders, and demonstrates factorization on both non-separating and separating degenerations. Loop amplitudes are shown to be modular-invariant and UV-finite at least at one loop for even spin structures, with odd spin structures decoupling; the formalism reduces cleanly to tree-level results and aligns with unitarity expectations. The results position the model as a compelling modular-invariant, unitary N=8 supergravity theory in twistor space with embedded SYM, while highlighting avenues to tighten UV bounds and address IR issues via potential off-shell formulations.

Abstract

This article continues previous work done in arXiv:2406.01907. It is shown in more detail how vacuum partition functions and the cosmological constant vanish at all orders of perturbation theory. Further, all-multiplicity higher-loop amplitudes are given and shown to be modular invariant, to have proper factorization, and to be UV-finite at least up to one-loop level, formally even to all levels. Therefore, the model provides a modular invariant and unitary N=8 supergravity theory in twistor space with embedded Super-Yang-Mills and promising UV-finiteness behavior.