Mirjam Cvetic

Chiral Four-Dimensional N=1 Supersymmetric Type IIA Orientifolds from Intersecting D6-Branes

We construct N = 1 supersymmetric four-dimensional orientifolds of type IIA on T 6 /(Z2 × Z2) with D6-branes intersecting at angles. The use of D6branes not fully aligned with the O6-planes in the model allows for a construction of many supersymmetric models with chiral matter, including those with the Standard Model and grand unified gauge groups. We perform a search for realistic gauge sectors, and construct the first example of a supersymmetric type II orientifold with SU(3)C × SU(2)L × U(1)Y gauge group and three quark-lepton families. In addition to the supersymmetric Standard Model content, the model contains right-handed neutrinos, a (chiral but anomalyfree) set of exotic multiplets, and diverse vector-like multiplets. The general class of these constructions are related to familiar type II orientifolds by small instanton transitions, which in some cases change the number of generations, as discussed in specific models. These constructions are supersymmetric only for special choices of untwisted moduli. We briefly discuss the supersymmetry breaking effects away from that point. The M-theory lift of this general class of supersymmetric orientifold models should correspond to purely geometrical backgrounds admitting a singular G2 holonomy metric and leading to four-dimensional M-theory vacua with chiral fermions.

Three-Family Supersymmetric Standardlike Models from Intersecting Brane Worlds

We construct the first three family N = 1 supersymmetric string model with standard model gauge group SU(3)(C) x SU(2)(L) x U(1)(Y) from an orientifold of type IIA theory on T(6)/(Z(2) x 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.

Brane resolution through transgression

Modifications to the singularity structure of D3-branes that result from turning on a flux for the R–R and NS–NS 3-forms (fractional D3-branes) provide important gravity duals of four-dimensional N=1 super-Yang–Mills theories. We construct generalisations of these modified p-brane solutions in a variety of other cases, including heterotic 5-branes, dyonic strings, M2-branes, D2-branes, D4-branes and type IIA and type IIB strings, by replacing the flat transverse space with a Ricci-flat manifold Mn that admits covariantly constant spinors, and turning on a flux built from a harmonic form in Mn, thus obtaining deformations of the original solution. The construction makes essential use of the Chern–Simons or “transgression” terms in the Bianchi-identity or equation of motion of the field strength that supports the original undeformed solution. If the harmonic form is L2 normalisable, this can result in a deformation of the brane solution that is free of singularities, thus providing viable gravity duals of field theories in diverse dimensions that have less than maximal supersymmetry. We obtain examples of non-singular heterotic 5-branes, dyonic strings, M2-branes, type IIA strings, and D2-branes.

More supersymmetric standard-like models from intersecting D6-branes on type IIA orientifolds

We present new classes of supersymmetric Standard-like models from type IIA T 6 /(Z2 × Z2) orientifold with intersecting D6-branes. D6-branes can wrap general supersymmetric three-cycles of T 6 = T 2 × T 2 × T 2 , and any T 2 is allowed to be tilted. The models still suffer from additional exotics, however we obtained solutions with fewer Higgs doublets, as well as models with all three families of left-handed quarks and leptons arising from the same intersecting sector, and examples of a genuine left-right symmetric model with three copies of left-handed and right-handed families of quarks and leptons.

A three-family standard-like orientifold model: Yukawa couplings and hierarchy

Abstract We discuss the hierarchy of Yukawa couplings in a supersymmetric three family standard-like string model. The model is constructed by compactifying type IIA string theory on a Z2×Z2 orientifold in which the standard model matter fields arise from intersecting D6-branes. When lifted to M-theory, the model amounts to compactification of M-theory on a G2 manifold. While the actual fermion masses depend on the vacuum expectation values of the multiple Higgs fields in the model, we calculate the leading worldsheet instanton contributions to the Yukawa couplings and examine the implications of the Yukawa hierarchy.

Chiral type II orientifold constructions as M theory on G(2) holonomy spaces

We summarize some recent progress in constructing four-dimensional supersymmetric chiral models from Type II orientifolds. We present the construction a supersymmetric Standard-like Model and a supersymmetric GUT model to illustrate the new features of this approach and its connection to M theory on compact, singular G_2 holonomy spaces. The Standard-like model presented is the first example of a three-family supersymmetic orientifold model with the Standard Model as part of the gauge structure. We also discuss the connection of how chiral fermions arise in this class of models with recent results of M theory compactified on G_2 holonomy spaces.

Linearly-realised worldsheet supersymmetry in pp-wave backgrounds

Abstract We study the linearly-realised worldsheet supersymmetries in the “massive” type II light-cone actions for pp-wave backgrounds. The pp-waves have 16+ N sup Killing spinors, comprising 16 “standard” Killing spinors that occur in any wave background, plus N sup “supernumerary” Killing spinors (0⩽ N sup ⩽16) that occur only for special backgrounds. We show that only the supernumerary Killing spinors give rise to linearly-realised worldsheet supersymmetries after light-cone gauge fixing, while the 16 standard Killing spinors describe only non-linearly realised inhomogeneous symmetries. We also study the type II actions in the physical gauge, and we show that although in this case the actions are not free, there are now linearly-realised supersymmetries coming both from the standard and the supernumerary Killing spinors. In the physical gauge, there are no mass terms for any worldsheet degrees of freedom, so the masses appearing in the light-cone gauge may be viewed as gauge artefacts. We obtain type IIA and IIB supergravity solutions describing solitonic strings in pp-wave backgrounds, and show how these are related to the physical-gauge fundamental string actions. We study the supersymmetries of these solutions, and find examples with various numbers of Killing spinors, including total numbers that are odd.

Discrete Wilson lines in N=1 D=4 type IIB orientifolds: a systematic exploration for Z6 orientifold

We develop techniques to construct general discrete Wilson lines in four-dimensional N=1 type IIB orientifolds, their T-dual realization corresponds to branes positioned at the orbifold fixed points. The explicit order two and three Wilson lines along with their tadpole consistency conditions are given for D=4 N=1 Z6 type IIB orientifold. The systematic search for all models with general order three Wilson lines leads to a small class of inequivalent models. There are only two inequivalent classes of a potentially phenomenologically interesting model that has a possible SU(3)color×SU(2)L×SU(2)R×U(1)B–L gauge structure, arising from a set of branes located at the Z6 orbifold fixed point. We calculate the spectrum and Yukawa couplings for this model. On the other hand, introduction of anti-branes allows for models with three families and realistic gauge group assignment, arising from branes located at the Z3 orbifold fixed points.

Bent Bogomol’nyi-Prasad-Sommerfield domain walls of D = 5 , N = 2 gauged supergravity coupled to hypermultiplets

Within

How chiral are type-II superstrings?

D=5,