Abstract
We investigate interactions between branes of various dimensions, both charged and uncharged, in three non-supersymmetric string models. These include the USp(32) and U(32) orientifold projections of the type IIB and type 0B strings, as well as the SO(16)×SO(16) projection of the exceptional heterotic string. The resulting ten-dimensional spectra are free of tachyons, and the combinations of branes that they contain give rise to rich and varied dynamics. We compute static potentials for parallel stacks of branes in three complementary regimes: the probe regime, in which one of the two stacks is parametrically heavier than the other, the string-amplitude regime, in which both stacks are light, and the holographic regime. Whenever comparisons are possible, we find qualitative agreement despite the absence of supersymmetry. For charged branes, our analysis reveals that the Weak Gravity Conjecture is satisfied in a novel way via a renormalization of the effective charge-to-tension ratio.
Highlights
At any rate, in order to elucidate deeper features of supersymmetry breaking it appears paramount to go beyond the EFT regime
One can consider the dynamics of branes, which manifest themselves in various guises in different regimes of string theory, ranging from soliton solutions of space-time field equations to conformal field theory (CFT) boundary states to world-volume gauge theories
Branes with the same charges always repel, corroborating the Weak Gravity Conjecture (WGC) [19] in a non-supersymmetric context. This behavior stems from a novel renormalization of the effective charge-to-tension ratio due to the supersymmetry-breaking gravitational tadpoles [13], while in the world-volume gauge theory it stems from the absence of the fermionic contribution to the one-loop effective potential
Summary
We briefly review the three non-supersymmetric string models that we shall investigate on in this paper, focusing on their brane content. One can obtain the USp(32) model of [5] introducing an O9-plane with positive tension and charge together with D9-branes, yielding a vanishing R-R tadpole. Since the residual tension in the NS-NS tadpole does not cancel, the low-energy physics of this model includes the string-frame runaway exponential potential. In the string-frame low-energy effective action it appears as a cosmological constant, and as a runaway exponential potential (2.3). The low-energy manifestation of gravitational tadpoles in both the orientifold models and in the SO(16) × SO(16) heterotic model can be encompassed by the same type of exponential potential for the dilaton
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