Multi-Higgs-boson production in gluon fusion at 100 TeV

We carry out a detailed study of multi-Higgs production processes in the gluon fusion channel in the high-energy regime relevant to future circular hadron colliders and in the high-Higgs-multiplicity limit (>= 20). Our results are based on the computation of the leading polygons-the triangles, boxes, pentagons and hexagons-to the scattering processes, further combined with the subsequent branchings to reach high final-state multiplicities. The factorial growth of the number of diagrams leads to an exponential enhancement of such large-multiplicity cross sections and, ultimately, to the breaking of perturbativity. We find that the characteristic energy and multiplicity scales where these perturbative rates become highly enhanced and grow with increasing energy are within the 100 TeV regime, on the order of 130 Higgses (or more) in the final state. We also show that already for a 50 TeV hadron collider, the perturbative cross sections for 140 bosons are at the picobarn level.