Singlet extensions of the MSSM in the quiver landscape

We map out possible extensions of the MSSM in the context of type II string theory. We systematically investigate three-stack and four-stack quivers which realize the MSSM spectrum with the addition of a single MSSM singlet S with an allowed SHuHd term, which can lead to a dynamical electroweak-scale μ-term. We present the three quivers which satisfy stringent string-theoretic and phenomenological constraints, including the presence of non-zero masses for all three families of quarks and leptons, the perturbative and non-perturbative absence of R-parity violating couplings and rapid dimension-five proton decay, and a mechanism for small neutrino masses. We find that these quivers can realize many models in the class of singlet-extended (supersymmetric) standard models, as D-instanton effects can in principle generate a superpotential of the form f(S), where f is a polynomial. Finally, we address the issue of the stabilization and decoupling of charged moduli which generically appear in D-instanton corrections to the superpotential.

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title: Neutrino Majorana masses from string theory instanton effects
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title: Instanton Induced Neutrino Majorana Masses in CFT Orientifolds with MSSM-like spectra
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title: INSTANTON INDUCED CHARGED FERMION AND NEUTRINO MASSES IN A MINIMAL STANDARD MODEL SCENARIO FROM INTERSECTING D-BRANES
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title: TOWARD REALISTIC INTERSECTING D-BRANE MODELS
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title: Varieties of Baryon and Lepton Nonconservation
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title: The μ-problem and the strong CP-problem
abstract: We investigate a possible connection of a solution of the strong CP-problem and the generation of a mass term μ in the low energy Higgs superpotential of supersymmetric models. This possibility comes from the fact that both supersymmetry and the Peccei-Quinn symmetry (to give an acceptable invisible axion) are broken at the same scale.

title: New minimal extension of MSSM
abstract: We construct a new minimal extension of the minimal supersymmetric standard model (MSSM) by promoting the μ-parameter to a singlet superfield. The resulting renormalizable superpotential is enforced by a Z5 R-symmetry which is imposed on the non-renormalizable operators as well. The proposed model provides a natural solution to the μ-problem and is free from phenomenological and cosmological problems.

title: Higgs scalars in the minimal nonminimal supersymmetric standard model
abstract: We consider the simplest and most economic version among the proposed nonminimal supersym. models, in which the m parameter is promoted to a singlet superfield, whose self-couplings are all absent from the renormalizable superpotential. Such a particularly simple form of the renormalizable superpotential may be enforced by discrete R symmetries which are extended to the gravity-induced non-renormalizable operators as well. We show explicitly that within the supergravity-mediated supersymmetry-breaking scenario, the potentially dangerous divergent tadpoles assocd. with the presence of the gauge singlet first appear at loop levels higher than 5 and therefore do not destabilize the gauge hierarchy. The model provides a natural explanation for the origin of the m term, without suffering from the visible axion or the cosmol. domain-wall problem. Focusing on the Higgs sector of this minimal nonminimal supersym. std. model, we calc. its effective Higgs potential by integrating out the dominant quantum effects due to top squarks. We then discuss the phenomenol. implications of the Higgs scalars predicted by the theory for the present and future high-energy colliders. In particular, we find that our new minimal nonminimal supersym. model can naturally accommodate a relatively light charged Higgs boson, with a mass close to the present exptl. lower bound. [on SciFinder (R)]

title: Higgs bosons in a nonminimal supersymmetric model.
abstract: The minimal supersymmetric standard model contains two Higgs doublets which must mix via a mass parameter whose magnitude remains to be explained. We explore an extension of the minimal model to include a singlet Higgs field whose vacuum expectation value determines the mixing. We study the spectrum and couplings of Higgs bosons in this extended model and compare them with those in the minimal model. We examine a number of limiting cases analytically and also make numerical studies of the extended model both with and without constraints from the renormalization-group analysis of a parent superstring-inspired grand-unified-theory model. We establish the conditions for there to be a charged Higgs boson lighter than the W/sup +- / and the circumstances under which there is no light neutral Higgs boson. With a particularly simple set of boundary conditions at the unification scale, the renormalization-group equations imply that one or more Higgs bosons are light enough to be found at the CERN LEP or SLAC Linear Collider and that many supersymmetric particles should be accessible to these accelerators and the Fermilab Tevatron; relatively few would require the Superconducting Super Collider, Large Hadron Collider, or a TeV-scale e/sup +/e/sup -/ collider for discovery. Finally, wemore » analyze the possible production mechanisms and phenomenological signatures of the different Higgs bosons at these machines.« less

title: Radiative Symmetry Breaking in a Supersymmetric Model with an Extra $U(1)$
abstract: Radiative symmetry breaking is studied in a superstring-inspired supersymmetric model which is extended with a low energy extra U(1) symmetry. In this model the μ problem is radiatively solved in an automatic way. The right-handed neutrino can be heavy and the seesaw mechanism will produce the small neutrino mass which makes the MSW solution applicable to the solar neutrino problem. We search a parameter region which has the favorable feature for the radiative symmetry breaking at the weak scale. A rather wide parameter region is found to be allowed. Although there are certain dependences on the soft supersymmetry breaking parameters in the estimation of masses of various fields, the upper bound of the extra Z boson mass is estimated to be mZ2≤2000 GeV for a top mass range 150 GeV≤mt≤190 GeV within a suitable parameter region (m0<1 TeV and m1/2<200 GeV). Some phenomenological features of the extra Z boson are also presented.

title: Implications of Abelian extended gauge structures from string models.
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title: Electroweak breaking and the mu problem in supergravity models with an additional U(1)
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title: Nonstandard Higgs Boson Decays
abstract: This review summarizes the motivations for and the phenomenological consequences of nonstandard Higgs boson decays, with an emphasis on final states containing a pair of non–standard model particles that subsequently decay to standard model particles. Typically these non–standard model particles form part of a “hidden” sector, for example a pair of neutral Higgs bosons or a pair of unstable neutralinos. We emphasize that such decays allow for a Higgs substantially below the standard model Higgs Large Electron-Positron Collider limit of 114 GeV. A Higgs with standard model WW, ZZ, and top couplings and a mass near 100 GeV eliminates the fine-tuning problems of many beyond the standard model theories, in particular supersymmetric models, and leads to excellent consistency with precision electroweak data.

title: Higgs Sector in Extensions of the MSSM
abstract: Extensions of the Minimal Supersymmetric Standard Model (MSSM) with additional singlet scalar fields solve the important mu-parameter fine tuning problem of the MSSM. We compute and compare the neutral Higgs boson mass spectra, including one-loop corrections, of the following MSSM extensions: Next-to-Minimal Supersymmetric Standard Model (NMSSM), the nearly-Minimal Supersymmetric Standard Model (nMSSM), and the U(1)'-extended Minimal Supersymmetric Standard Model (UMSSM) by performing scans over model parameters. We find that the Secluded U(1)'-extended Minimal Supersymmetric Standard Model (sMSSM) is identical to the nMSSM if three of the additional scalars decouple. The dominant part of the one-loop corrections are model-independent since the singlet field does not couple to MSSM particles other than the Higgs doublets. Thus, model-dependent parameters enter the masses only at tree-level. We apply constraints from LEP bounds on the Standard Model and MSSM Higgs boson masses and the MSSM chargino mass, the invisible Z decay width, and the Z-Z' mixing angle. Some extended models permit a Higgs boson with mass substantially below the SM LEP limit or above theoretical limits in the MSSM. Ways to differentiate the models via masses, couplings, decays and production of the Higgs bosons are discussed.

title: Workshop on CP Studies and Non-Standard Higgs Physics
abstract: There are many possibilities for new physics beyond the Standard Model that feature non-standard Higgs sectors. These may introduce new sources of CP violation, and there may be mixing between multiple Higgs bosons or other new scalar bosons. Alternatively, the Higgs may be a composite state, or there may even be no Higgs at all. These non-standard Higgs scenarios have important implications for collider physics as well as for cosmology, and understanding their phenomenology is essential for a full comprehension of electroweak symmetry breaking. This report discusses the most relevant theories which go beyond the Standard Model and its minimal, CP-conserving supersymmetric extension: two-Higgs-doublet models and minimal supersymmetric models with CP violation, supersymmetric models with an extra singlet, models with extra gauge groups or Higgs triplets, Little Higgs models, models in extra dimensions, and models with technicolour or other new strong dynamics. For each of these scenarios, this report presents an introduction to the phenomenology, followed by contributions on more detailed theoretical aspects and studies of possible experimental signatures at the LHC and other colliders.

title: TeV physics and the Planck scale
abstract: Supersymmetry is one of the best motivated possibilities for new physics at the TeV scale. However, both concrete string constructions and phenomenological considerations suggest the possibility that the physics at the TeV scale could be more complicated than the minimal supersymmetric standard model (MSSM), e.g. due to extended gauge symmetries, new vector-like supermultiplets with non-standard SU(2)× U(1) assignments, and extended Higgs sectors. We briefly comment on some of these possibilities, and discuss in more detail the class of extensions of the MSSM involving an additional standard model singlet field. The latter provides a solution to the μ problem, and allows significant modifications of the MSSM in the Higgs and neutralino sectors, with important consequences for collider physics, cold dark matter, and electroweak baryogenesis.

title: Getting just the standard model at intersecting branes
abstract: We present what we believe are the first specific string (D-brane) constructions whose low-energy limit yields just a three generation SU(3) × SU(2) × U(1) standard model with no extra fermions nor U(1)'s (without any further effective field theory assumption). In these constructions the number of generations is given by the number of colours. The Baryon, Lepton and Peccei-Quinn symmetries are necessarily gauged and their anomalies cancelled by a generalized Green-Schwarz mechanism. The corresponding gauge bosons become massive but their presence guarantees automatically proton stability. There are necessarily three right-handed neutrinos and neutrino masses can only be of Dirac type. They are naturally small as a consequence of a PQ-like symmetry. There is a Higgs sector which is somewhat similar to that of the MSSM and the scalar potential parameters have a geometric interpretation in terms of brane distances and intersection angles. Some other physical implications of these constructions are discussed.

title: The NMSSM and string theory
abstract: We study the possibility of constructing the NMSSM from the heterotic string. String-derived NMSSMs are much more rare than MSSMs due to the extra requirement that there exist a light singlet which couples to the Higgs pairs. They share the common feature that the singlet self-interactions are typically suppressed, leading to either the “decoupling” or the Peccei–Quinn limit of the NMSSM. In the latter case, the spectrum contains a light pseudoscalar which may be relevant to the MSSM fine-tuning problem. We provide a Z 6 heterotic orbifold example of the NMSSM with approximate Peccei–Quinn symmetry, whose origin lies in the string selection rules combined with our choice of the vacuum configuration.

title: Dynamical supersymmetry breaking in standardlike models with intersecting D6-branes
abstract: We address dynamical supersymmetry breaking within a N=1 supersymmetric Standard-like Model based on a Z_2 x Z_2 Type IIA orientifold with intersecting D6-branes. The model possesses an additional, confining gauge sector with the USp(2)_A x USp(2)_B x USp(4) gauge group, where the gaugino condensation mechanism allows for the breaking of supersymmetry and stabilizes moduli. We derive the leading contribution to the non-perturbative effective superpotential and determine numerically the minima of the supergravity potential. These minima break supersymmetry and fix two undetermined moduli, which in turn completely specify the gauge couplings at the string scale. For this specific construction the minima have a negative cosmological constant. We expect that for other supersymmetric Standard-like models with intersecting D6-branes, which also possess confining gauge sectors, the supersymmetry breaking mechanism would have qualitatively similar features.

title: A new mechanism of Kähler moduli stabilization in type IIB theory
abstract: We study the scalar potential in supersymmetric (orientifolded) Calabi Yau flux compactifications of Type IIB theory. We present a new mechanism to stabilize all closed string moduli at leading order in ?' by consistently introducing fluxes. As usual we consider the dilaton and the complex structure moduli stabilized by turning on three-form fluxes that couple to the F-part of the scalar potential. The Kahler moduli get fixed by the combined action of the flux-induced scalar masses with the magnetic fields of the open string sector, and Fayet-Illiopoulos terms. For supersymmetric three-form fluxes the model is N = 1, otherwise the mass terms are the scalar soft breaking terms of the MSSM fields. For the case of imaginary self dual three-form fluxes (ISD), the mass terms are positive and the minimum of the potential is at exactly zero energy. We argue that, under generic assumptions, this is a general mechanism for the full stabilization of closed string moduli. The vacua depend explicitly on the fluxes introduced in the manifold. A concrete realization of this mechanism for type IIB on a (T6/Z2 ? Z2) orientifold is provided.