Three-Family Supersymmetric Standardlike Models from Intersecting Brane Worlds

Abstract

We construct the first three family N 1 supersymmetric string model with standard model gauge group SU͑3͒ C 3 SU͑2͒ L 3 U͑1͒ Y from an orientifold of type IIA theory on T 6 ͑͞Z 2 3 Z 2 ͒ and D6-branes intersecting at angles. In addition to the minimal supersymmetric standard model particles, the model contains right-handed neutrinos, a chiral (but anomaly-free) set of exotic multiplets, and extra vectorlike multiplets. We discuss some phenomenological features of this model. DOI: 10.1103/PhysRevLett.87.201801 PACS numbers: 11.10.Kk, 11.25.Mj, 12.60.Jv, 98.80.Cq The space of classical string vacua is highly degenerate, and at present we are unable to make definitive statements about how the string vacuum describing our universe is selected. Nonetheless, one can use phenomenological constraints as guidelines to construct semirealistic string models and explore, with judicious assumptions, the resulting phenomenology. The purpose of such explorations is, of course, not to find the model which would fully describe our world, but to examine the generic features of these string derived solutions.Until a few years ago, such explorations were carried out mainly in the framework of weakly coupled heterotic string theory. Indeed, a number of semirealistic string models have been constructed and analyzed [1]. However, an important lesson from string duality is that these models represent only a corner of M theory -the string vacuum describing our world may well be in a completely different regime in which the perturbative description of heterotic string theory breaks down [2]. Fortunately, the advent of D-branes allows for the construction of semirealistic string models in another calculable regime, as illustrated by the various four-dimensional N 1 supersymmetric type II orientifolds ([3-12] and references therein) constructed using conformal field theory techniques. However, the constraints on supersymmetric fourdimensional models are rather restrictive, leading to not fully realistic gauge sectors and matter contents. Motivated by the search for standard model-like solutions, several discrete or continuous deformations of this class of models have been explored. They include the following: (i) blowing-up of orientifold singularities [13,14], (ii) locating the branes at different points in the internal space (see, e.g., [9,12,15]) which in a T -dual picture corresponds to turning on continuous or discrete Wilson lines, (iii) introduction of discrete values for the Neveu-Schwarz -Neveu-Schwarz (NS-NS) B field [7,16] which in the T-dual picture corresponds to tilting the compactification tori, (iv) introduction of gauge fluxes in the D-brane world volumes (see [17] for an earlier discussion, and [18,19] for supersymmetric D 6 models), which in the T -dual version corresponds to D-branes intersecting at angles (hence closely related to models in [20,21]).An appealing feature of (iv) is that generically, there exists chiral fermions where D-branes intersect [22]. Their multiplicity is hence determined by a topological q...

Chiral D-brane Models with Frozen Open String Moduli

“…The first orbifold employed in constructing N = 1 chiral vacua of intersecting D6-branes was Z 2 × Z 2 [27,28], usually referred to as Z 2 × Z 2 without vector structure. As can be seen from table 1 this orbifold has eight independent 3-cycles, all of them inherited from the covering space T 6 .…”

“…Compared to the model building difficulties of intersecting D6-branes on the Z 2 ×Z 2 orientifold with the opposite discrete torsion, the main new ingredient here comes from the RR twisted tadpoles (30) that have now to be imposed. Roughly speaking, since the Z 2 × Z ′ 2 orbifold possesses plenty of collapsed 3-cycles that D6-branes can wrap, the variety of RR charges (and thus the RR tadpoles constraints) greatly increases as compared to the Z 2 × Z 2 constructions in [27,28]. Hence, it will prove useful to take some extra working assumptions, which will greatly simplify the twisted tadpole conditions but nevertheless allow us to construct a rich variety of models.…”

“…In particular, important issues, such as the pattern of soft SUSY breaking terms [11][12][13][14][15] and the signatures and stability of cosmic strings (see [16][17][18] for some reviews) formed at the end of brane inflation [19,20], depend critically on how the Standard Model (SM) is embedded. In the past few years, the intersecting brane (and, in the T-dual picture, magnetized D-brane) world scenario [21][22][23][24][25][26] has proven to be a promising framework to construct semi-realistic, D = 4, N = 1 chiral string models [27][28][29][30][31][32]. 1 More importantly, it has recently been realized [11,37,38] that by turning on background NSNS and RR fluxes in magnetized D-branes models, SUSY can be softly broken while satisfying the supergravity equation of motion (hence the usual problem of the classical instability in non-supersymmetric models due to non-vanishing NSNS tadpoles is absent).…”

Constraining the string scale: from Planck to weak and back again

“…The first models containing just the SM were presented in [28]. Since then, a great deal of effort has gone into into the study of the consistency and stability [29] and phenomenological implications of intersecting brane models, from the construction of supersymmetric models [23], gauge symmetry breaking [30], GUT or realistic SM constructions [31,32] to cosmological implications [33]. In the following we will review some of these developments paying particular attention to their flavour structure [34,35,36] and its profound experimental implications.…”

“…Therefore we seem to be forced back to high string scales solely on experimental grounds. A great deal of effort has been dedicated to the study of realistic supersymmetric models (in order to protect the hierarchy of scales) with a high string scale, of the order of the Planck or GUT scales [23,31] and it seems likely that it is to these that we must now turn.…”