Magnetized Branes and the Six-Torus (original) (raw)

More about branes on a general magnetized torus

Journal of High Energy Physics, 2012

In the framework of low-energy effective actions of branes compactified on magnetized extra-dimensions, we determine Yukawa couplings for the chiral matter described by open strings attached to D9 branes having different oblique magnetization and living on a general torus T 6 with an arbitrary complex structure. These results generalize the ones existing in literature.

String Techniques for the Computation of the Effective Action in Brane World Models

2007

The present thesis contains the development of new techniques to compute the Yukawa couplings for the fundamental matter in the context of string theoretic Brane World Models. Exploiting the unitarity of String Theory these couplings are derived by means of factorisation of the classical limit of the two-loop twisted partition function in generic toroidal compactifications. In fact by taking the Schwinger time of the strings propagating in the loops to infinity, the string theoretic diagram is reduced to a field theoretic interaction involving the low-lying states of oscillations of the so-called twisted strings. These are strings stretched between two D-Branes either intersecting at angles or with different magnetic fields turned on in their world-volumes and they reproduce four dimensional chiral fermions in the low energy limit of the theory. The models involving intersecting or magnetised D-Branes are related to one another by means of T-Duality. The factorisation of the resulti...

Kähler metrics and Yukawa couplings in magnetized brane models

Journal of High Energy Physics, 2009

Using the field theoretical approach introduced by Cremades, Ibáñez and Marchesano for describing open strings attached to D9 branes having different magnetizations, we give a procedure for determining the Kähler metrics of those open strings in toroidal compactifications. Work partially supported by the European Community's Human Potential Programme under contract MRTN-CT-2004-005104 "Constituents, Fundamental Forces and Symmetries of the Universe". Contents 1 Introduction 1 2 The KK reduction of the relevant terms of the action 3 3 The Kähler metrics 9 4 Yukawa couplings 11 5 Fixing the Kähler metrics 15 6 Conclusions and outlook 16 A The torus T 2 18 B Solving the eigenvalue equations 20 C Evaluating the Yukawa couplings 26 D Supersymmetry transformations 31

Yukawa coupling structure in intersecting D-brane models

The European Physical Journal C, 2005

The structure of Yukawa coupling matrices is investigated in type IIA T 6 /(Z2 × Z2) orientifold models with intersecting D-branes. Yukawa coupling matrices are difficult to be realistic in the conventional models in which the generation structure emerges by the multiple intersection of D-branes in the factorized T 6 = T 2 × T 2 × T 2. We study the new type of flavor structure, where Yukawa couplings are dynamically generated, and show this type of models lead to nontrivial structures of Yukawa coupling matrices, which can be realistic.

Realistic Yukawa couplings through instantons in intersecting brane worlds

Journal of High Energy Physics, 2007

The Yukawa couplings of the simpler models of D-branes on toroidal orientifolds suffer from the so-called "rank one" problem-there is only a single nonzero mass and no mixing. We consider the one-loop contribution of E2-instantons to Yukawa couplings on intersecting D6-branes, and show that they can solve the rank one problem. In addition they have the potential to provide a geometric explanation for the hierarchies observed in the Yukawa coupling. In order to do this we provide the necessary quantities for instanton calculus in this class of background.

Wave functions and Yukawa couplings in local string compactifications

Journal of High Energy Physics, 2008

We consider local models of magnetised D7 branes in IIB string compactifications, focussing on cases where an explicit metric can be written for the local 4-cycle. The presence of an explicit metric allows analytic expressions for the gauge bundle and for the chiral matter wavefunctions through solving the Dirac and Laplace equations. The triple overlap of the normalised matter wavefunctions generates the physical Yukawa couplings. Our main examples are the cases of D7 branes on P 1 × P 1 and P 2 . We consider both supersymmetric and non-supersymmetric gauge backgrounds and both Abelian and non-Abelian gauge bundles. We briefly outline potential phenomenological applications of our results.

Dynamical Generation of mu-terms and Yukawa Couplings in Intersecting D-brane Models

2004

We construct a supersymmetric composite model in type IIA T 6 /(Z 2 ×Z 2) orientifold with intersecting D6-branes. Four generations of quarks and leptons are naturally emerged as composite fields at low energies. Two pairs of light electroweak Higgs doublets are also naturally obtained. The hierarchical Yukawa couplings for the quark-lepton masses can be generated by the interplay between the string-level higher dimensional interactions among "preons" and the dynamics of the confinement of "preons". Besides having four generations of quarks and leptons, the model is not realistic in some points: some exotic particles, one additional U(1) gauge symmetry, no explicit mechanism for supersymmetry breaking, and so on. This model is a toy model to illustrate a new mechanism of dynamical generation of Yukawa couplings for the masses and mixings of quarks and leptons.

N=1 Locally Supersymmetric Standard Models from Intersecting branes

We construct four dimensional intersecting D6-brane models that have locally the spectrum of the N=1 Supersymmetric Standard Model. All open visible string sectors share the same N=1 supersymmetry. As expected in these supersymmetric classes of models, where the D6-branes wrap a toroidal orientifold of type IIA, the hierarchy may be stabilized if the string scale is low, e.g. below 30 TeV. We analyze the breaking of supersymmetry in the vicinity of the supersymmetric point by turning on complex structure deformations as Fayet-Iliopoulos terms. Positive masses for all squarks and sleptons, to avoid charge/colour breaking minima, may be reached when also two loop contributions may be included. In the ultimate version of the present models N=1 supersymmetry may be broken by gauge mediation. The constructions with four, five and six stacks of D6-branes at M s are build directly. Next by the use of brane recombination we are able to show that there is a continuous, RR homology flow, between six, five and four stack models. Moreover, we examine the gauge coupling constants of the Standard Model SU(3) C , SU(2) L , U(1) Y at the string scale in the presence of a non-zero antisymmetric NS B-field.

Branes and six-dimensional supersymmetric theories

We consider configurations of six-branes, five-branes and eight-branes in various superstring backgrounds. These configurations give rise to (0, 1) supersymmetric theories in six dimensions. The condition for RR charge conservation of a brane configuration translates to the condition that the corresponding field theory is anomaly-free. Sets of infinitely many models with non-trivial RG fixed points at strong coupling are demonstrated. Some of them reproduce and generalise the world-volume theories of SO(32) and E 8 × E 8 small instantons. All the models are shown to be connected by smooth transitions. In particular, the small instanton transition for which a tensor multiplet is traded for 29 hypermultiplets is explicitly demonstrated. The particular limit in which these theories can be considered as six-dimensional string theories without gravity are discussed. New fixed points (string theories) associated with E n global symmetries are discovered by taking the strong string coupling limit.