IIB Nine-branes

TL;DR

This work classifies half-BPS nine-branes in type IIB string theory by analyzing the coupling of branes to the RR ten-form sector and performing a detailed kappa-symmetry/SUSY variation analysis. It demonstrates that RR ten-forms split into SL(2,ℝ) doublets and quadruplets, yielding a linear and a nonlinear family of nine-branes, with explicit tension formulas and BPS projection conditions derived for each family. A key result is the existence of a solitonic S9-brane in the linear doublet and the identification of an SL(2,ℤ) orbit structure: all linear doublet nine-branes are connected to the D9-brane by duality, and the nonlinear doublet organizes around the D9 under the duality group. The findings illuminate the ten-form sector's role in IIB string theory, suggest avenues for non-perturbative open-string constructions, and motivate further study of the S9-brane's world-volume dynamics.

Abstract

We calculate the tensions of all half-supersymmetric nine-branes in IIB string theory. In particular, we point out the existence of a solitonic IIB nine-brane. We find that the D9-brane and its duality transformations parametrize a two-dimensional surface in a four-dimensional space.