Abstract
Intersecting D-brane models and their T-dual magnetic compactifications provide an attractive framework for particle physics, allowing for chiral fermions and supersymmetry breaking. Generically, magnetic compactifications have tachyons that are usually removed by Wilson lines. However, quantum corrections prevent local minima for Wilson lines. We therefore study tachyon condensation in the simplest case, the magnetic compactification of type I string theory on a torus to eight dimensions. We find that tachyon condensation restores supersymmetry, which is broken by the magnetic flux, and we compute the Kaluza-Klein mass spectrum. The gauge group SO(32) is broken to USp(16). We give arguments that the vacuum reached by tachyon condensation corresponds to the unique 8d superstring theory already known in the literature, with discrete Bab background or, in the T-dual version, the type IIB orientifold with three O7−-planes, one O7+-plane and eight D7-branes coincident with the O7+-plane. The ground state after tachyon condensation is supersymmetric and has no chiral fermions.
Highlights
Example, we recently showed that quantum corrections render these vacua unstable and that the theory is always driven to the tachyonic regime [18], which represents a serious challenge to the known models
We find that tachyon condensation restores supersymmetry, which is broken by the magnetic flux, and we compute the Kaluza-Klein mass spectrum
We give arguments that the vacuum reached by tachyon condensation corresponds to the unique 8d superstring theory already known in the literature, with discrete Bab background or, in the T-dual version, the type IIB orientifold with three O7−-planes, one O7+-plane and eight D7-branes coincident with the O7+-plane
Summary
Let us consider the simplest system in which tachyon condensation occurs: intersecting D8-branes in type IIA string theory compactified on a toroidal orientifold with two compact dimensions, a setup very similar to the magnetic compactifications to six dimensions considered in [10]. The wrapping numbers we consider here are (n, m) = (1, k) for the D8-branes and (1, −k) for their mirrors At their intersection a massless chiral 8d N = 1 fermion in the antisymmetric representation 120 of U(16) is localized, together with massive fermions, vectors, scalars and tachyons, all in the antisymmetric representation. The mass spectrum of the intersection D8-branes is encoded in the magnetic deformation of the open string part of the type I partition function.1 This is the sum of annulus amplitude A and Moebius amplitude M, which can be compactly expressed in terms of standard modular functions and SO(8) characters [2], A=.
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