Abstract
Intersecting D-brane models and their T-dual magnetic compactifications yield attractive models of particle physics where magnetic flux plays a twofold role, being the source of fermion chirality as well as supersymmetry breaking. A potential problem of these models is the appearance of tachyons which can only be avoided in certain regions of moduli space and in the presence of Wilson lines. We study the effective four-dimensional field theory for an orientifold compactification of type IIA string theory and the corresponding toroidal compactification of type I string theory. After determining the Kaluza-Klein and Landau-level towers of massive states in different sectors of the model, we evaluate their contributions to the one-loop effective potential, summing over all massive states, and we relate the result to the corresponding string partition functions. We find that the Wilson- line effective potential has only saddle points, and the theory is therefore driven to the tachyonic regime. There tachyon condensation takes place and chiral fermions acquire a mass of the order of the compactification scale. We also find evidence for a tachyonic behaviour of the volume moduli. More work on tachyon condensation is needed to clarify the connection between supersymmetry breaking, a chiral fermion spectrum and vacuum stability.
Highlights
An intriguing aspect of magnetic compactifications is the connection between fermion chirality and supersymmetry breaking [9], which occurs in compactifications of type I strings on tori and orbifolds [10,11,12] and in the related intersecting D-brane models [11, 13, 14]
In the Higgs sector branes are parallel in some tori and, knowing the spectrum of massive KK and LL states, we compute the effective potential as function of magnetic flux and Wilson lines
We have studied the effective field theory for an intersecting D-brane model and its T-dual magnetic compactification, which has all features wanted for extensions of the Standard Model with high-scale supersymmetry breaking: the model has a ‘matter sector’ with chiral fermions, broken supersymmetry and massive scalars, and a ‘Higgs sector’ with vector-like fermions
Summary
We are interested in a D-brane model with broken supersymmetry, which contains a ‘matter sector’ with chiral fermions and a ‘Higgs sector’ with vector-like fermions such that vacuum expectation values of Higgs fields can give mass to the chiral fermions. The branes intersect at angles determined by the wrapping numbers At these intersections fermions and scalars in bi-fundamental representations (Ne, Nf ) are localized. In the brane sector aa , bb and cc chiral fermions in symmetric and antisymmetric representations of the gauge group occur with multiplicities nsym,e =. Using eq (2.10) these angles yield the scalar mass spectrum at the various brane intersections which is listed in table 3. To compute the one-loop quantum correction to the potential is an essential goal of this paper To achieve this we first construct the Tdual type I string compactification on a magnetized torus, which allows a straightforward computation of the full mass spectrum of the model as well as Yukawa couplings
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