Higgs Representations Research Articles

Fermion masses in supersymmetric SO(10) with type II seesaw mechanism: A nonminimal predictive scenario

A predictive framework for fermion masses and mixing is given by the supersymmetric SO(10) model with one 10{sub H}, one 126-bar{sub H}, one 126{sub H}, and one 210{sub H} Higgs representations, and type-II seesaw dominating the neutrino mass matrix. We investigate the origin of the tension between this model and lepton mixing data and refine previous numerical analyses. We discuss an extension of the minimal model that includes one 120{sub H} chiral superfield representation. This exhausts the possible renormalizable contributions to the Yukawa sector. In spite of the increase in the number of parameters the predictivity of the minimal setting is not spoiled. We argue that the contributions to fermion masses due to the doublet components of 120{sub H} can be naturally small compared to those of 10{sub H} and 126{sub H}-bar, thus acting as a perturbation in the fermion mass generation. The antisymmetric nature of the 120{sub H} Yukawa coupling affects at leading order the determination of the mixing angles and it allows to remove the inconsistencies between predictions and data on the neutrino parameters. An improvement in the experimental bound on U{sub e3} can tell this scenario from the minimal model.

Antisymmetric Higgs representation in SO(10) for neutrinos

A Model based on SO(10) grand unified theory (GUT) and supersymmetry is presented to describe observed phenomena for neutrinos. The large mixing angles among different generations, together with the small masses, are attributed to the Higgs boson structure at the GUT energy scale. Quantitative discussions for these observables are given, taking into account their energy evolution.

Intersecting branes flip SU(5)

Within a toroidal orbifold framework, we exhibit intersecting brane-world constructions of flipped SU(5)× U(1) GUT models with various numbers of generations, other chiral matter representations and Higgs representations. We exhibit orientifold constructions with integer winding numbers that yield 8 or more conventional SU(5) generations, and orbifold constructions with fractional winding numbers that yield flipped SU(5)× U(1) models with just 3 conventional generations. Some of these models have candidates for the 5 and 5 Higgs representations needed for electroweak symmetry breaking, but not for the 10 and 10 representations needed for GUT symmetry breaking. We have also derived models with complete GUT and electroweak Higgs sectors, but these have undesirable extra chiral matter.

Gaugino mass nonuniversality and dark matter in supergravity, strings, and D-brane models

The effects of nonuniversality of gaugino masses on dark matter are examined within supersymmetric grand unification, and in string and D-brane models with R parity invariance. In SU(5) unified models nonuniversality in the gaugino sector can be generated via the gauge kinetic energy function which may depend on the 24, 75 and 200 dimensional Higgs representations. We also consider string models which allow for nonuniversality of gaugino masses and D-brane models where nonuniversality arises from embeddings of the standard model gauge group on five-branes and nine-branes. It is found that with gaugino mass nonuniversality the range of the LSP mass can be extended much beyond the range allowed in the universal SUGRA case, up to about 600 GeV even without coannihilation effects in some regions of the parameter space. The effects of coannihilation are not considered and inclusion of these effects may further increase the allowed neutralino mass range. Similarly with the inclusion of gaugino mass nonuniversality, the neutralino-proton $(\ensuremath{\chi}\ensuremath{-}p)$ cross section can increase by as much as a factor of 10 in some regions of the parameter space. An analysis of the uncertainties in the quark density content of the nucleon is given and their effects on the $\ensuremath{\chi}\ensuremath{-}p$ cross section are discussed. The predictions of our analysis including nonuniversality are compared with the current limits from dark matter detectors and implications for future dark matter searches are discussed.

Grand unification of the sterile neutrino

The simplest way to simultaneously understand all existing indications of neutrino oscillations from solar and atmospheric neutrino deficits and the LSND experiment, seems to be to postulate a sterile neutrino. We present a realistic grand unified model based on the gauge group SO(10)×SO(10) ′ that leads to the desired masses and mixings for the sterile and the known neutrinos needed to understand the above observations while fitting those of the known charged fermions. The model is a grand unified realization of the recently proposed idea that the sterile neutrino is the lightest neutrino of a mirror sector of the universe which has identical matter and gauge content as the standard model. The two SO(10)'s operate on the two sectors in a mirror symmetric way and are connected by a mixed Higgs representations whose net effect is to connect the superheavy right handed neutrinos of the two sectors.

Group-theoretic evidence for SO(10) grand unification

The hypercharges of the fermions are not uniquely determined in SO(10) grand unification, but rather depend upon which linear combination of the two U(1) subgroups of SO(10) > SU(3) X SU(2) X U(1) X U(1) remains unbroken. We show that, in general, a given hypercharge assignment can be obtained only with very high-dimensional Higgs representations. The observation that the standard model is obtained with low-dimensional Higgs representations can therefore be regarded as further evidence for SO(10) grand unification. This evidence is independent of the fact that SO(10) > SU(5).

Quark and lepton masses and mixing angles in a supersymmetric 422 model

We discuss a specific supersymmetric model based on the gauge group SU(4) ⊗ SU(2)L ⊗ SU(2)R. In this model the gauge group is broken to that of the standard model at 1016 GeV, and supersymmetry is broken at low-energy. The model may be regarded as a “surrogate SUSY GUT”, and has several advantages over the SU(5) and SO(10) SUSY GUTs, such as the absence of the doublet-triplet splitting problem, and a simpler Higgs sector which does not involve any large Higgs representations. The model predicts full quadruple Yukawa unification (top-bottom-tau-tau neutrino), leading to the prediction of large top mass and tan β. An operator analysis leads to schemes where the strange and down mass are predicted.

GUTs with exclusively ΔB = 1, ΔL = 0 R-parity violation

We study R-parity violation in the framework of GUTs, focusing on the case that R-parity is broken exclusively through ΔB = 1, ΔL = 0 effective interactions. We construct two such model, an SU(5) and an SU(5) × U(1) x model, in which R-parity breaking is induced through interactions with extra supermassive fields. The presence of only the baryon number violating operators d c d c u c requires an asymmetry between quarks and leptons, which is achieved either by virtue of the Higgs representations used or by modifications in the matter multiplets. The latter possibility is realized in the second of the above models, where the left-handed leptons have been removed from the representation in which they normally cohabit with the right-handed up quarks and enter as a combination of the isodoublets in ( 5 , −3 ) and ( 5, −2) representations. In both models the particle content below the GUT scale is unaffected by the introduced R-parity breaking sector.

Grand unification with three generations in free fermionic string models.

We examine the problem of constructing three generation free fermionic string models with grand unified gauge groups. We attempt the construction of $G\times G$ models, where $G$ is a grand unified group realized at level 1. This structure allows those Higgs representations to appear which are necessary to break the symmetry down to the standard model gauge group. For $G=SO(10)$, we find only models with an even number of generations. However, for $G=SU(5)$ we find a number of 3 generation models.

PROBING LEPTON-NUMBER-VIOLATING COUPLINGS OF DOUBLY-CHARGED HIGGS BOSONS AT AN e−e− COLLIDER

The doubly charged Higgs bosons Δ−− that are present in exotic Higgs representations can have lepton-number-violating couplings to e−e−. We discuss general constraints and phenomenology for the Δ−− and demonstrate that extremely small values for the e−e−→Δ−− coupling-squared (some 8 orders of magnitude smaller than the current limit) would produce observable signals for Δ−− production in direct s-channel production at an e−e− collider.

AN EXPLICIT SO(10)×U(1)F MODEL OF THE YUKAWA INTERACTIONS

We construct an explicit SO (10)× U (1)F model of the Yukawa interactions by using as a guide previous phenomenological results obtained from a bottom-up approach to quark and lepton mass matrices. The U (1)F family symmetry group sets the textures for the Majorana and generic Dirac mass matrices by restricting the type and number of Higgs diagrams which can contribute to each matrix element, while the SO(10) group relates each particular element of the up, down, neutrino and charged lepton Dirac matrices. The Yukawa couplings and vacuum expectation values associated with pairs of 1, 45, 10 and 126 Higgs representations successfully correlate all the quark and lepton masses and mixings in the scenario incorporating the nonadiabatic solar neutrino and atmospheric neutrino depletion effects.

Construction of an SO(10) x U(1)F model of the Yukawa interactions.

We construct a supersymmetric $SO(10) \times U(1)_F$ model of the Yukawa interactions at the grand unification scale from knowledge of a phenomenological set of mass matrices obtained by a previous bottom-up approach. The $U(1)_F$ family symmetry determines the textures for the Majorana and generic Dirac mass matrices, while the $SO(10)$ symmetry relates each particular element of the up, down, neutrino and charged lepton Dirac matrices. The dominant second and third family contributions in the Dirac sector are renormalizable, while the remaining contributions to the Dirac mass matrices are of higher order, restricted by the $U(1)_F$ family symmetry to a small set of tree diagrams, and mainly complex-symmetric. The tree diagrams for the Majorana mass matrix are all non-renormalizable and of progressively higher-order, leading to a nearly geometrical structure. Pairs of ${\bf 1, 45, 10}$ and ${\bf 126}$ Higgs representations enter with those having large vacuum expectation values breaking the symmetry down to $SU(3)_c \times SU(2)_L \times U(1)_Y$ near the grand unification scale. In terms of 12 parameters expressed as the Yukawa couplings times vacuum expectation values for the Higgs representations employed, a realistic set of 15 quark and lepton masses (including those for the 3 heavy righthanded Majorana neutrinos) and 8 mixing parameters emerges for the neutrino scenario involving the non-adiabatic conversion of solar neutrinos and the depletion of atmospheric muon-neutrinos through oscillations into tau-neutrinos.

Signatures of Higgs-triplet representations at TeVe+e−colliders

We investigate the potential of future TeV linear e^+e^- colliders to observe singly-charged Higgs bosons ($H^\pm$) via the coupling $H^\pm W^\mp Z$, which would signal the existence of exotic Higgs representations. In the context of a Higgs-triplet model compatible with the electroweak oblique parameters, we estimate the cross section for pro- ducing charged Higgs-triplet bosons that couple predominantly to $W$ and $Z$ bosons in 0.5--2 TeV-$e^+e^-$ colliders. The principal backgrounds are evaluated and the viability of the signal is discussed and illustrated.

Automatically R-conserving supersymmetric SO(10) models and mixed light Higgs doublets.

In automatic R-parity conserving SO(10) models, the simplest way to accomodate realistic fermion masses is to demand that that the light Higgs doublets be linear combinations of the {10} and {126}-bar grand unified Higgs representations. We study the realization of this mixed light Higgs property consistent with doublet-triplet splitting in a minimal model and discuss its predictions for neutrino masses and implications for proton decay.

Natural doublet-triplet splitting in supersymmetric SO(10) models

We construct a supersymmetric SO(10) model, where the Dimopoulos-Wilczek mechanism for doublet-triplet splitting is stable under the addition of Higgs superfields belonging to 126 + 126 often used to implement the see-saw mechanism for neutrino masses and where the charged fermion and neutrino mass spectra arise from a single set of 10 and 126 Higgs representations.

Higgs scalar in the grand desert with observable proton lifetime in SU(5) and small neutrino masses in SO(10).

We find that the presence of a real scalar in the grand desert transforming as $\ensuremath{\zeta}(3, 0, 8)$ under $\mathrm{SU}{(2)}_{L}\ifmmode\times\else\texttimes\fi{}\mathrm{U}{(1)}_{Y}\ifmmode\times\else\texttimes\fi{}\mathrm{SU}{(3)}_{C}$ ensures the agreement of the GUT predictions with the data from CERN LEP and proton lifetime (${\ensuremath{\tau}}_{p}$). The mass of $\ensuremath{\zeta}$ is predicted to be close to the Peccei-Quinn symmetry-breaking scale. The computation of the threshold effects in SU(5) with Higgs representations 24, 5, and 75 shows that the maximum allowed ${\ensuremath{\tau}}_{p}$ for reasonable superheavy Higgs boson masses is accessible to experimental tests at low energies. The additional predictions in SO(10) are small neutrino masses compatible with solutions to the solar-neutrino problem and the dark matter of the Universe.

Constraints on additional Z bosons.

$Z$-pole, $W$-mass, and weak neutral-current (WNC) data as well as direct collider limits are used to constrain the mass and mixing of possible heavy ${Z}_{2}$ bosons with couplings expected in grand unified theories and ${\mathrm{SU}(2)}_{L}\ifmmode\times\else\texttimes\fi{}{\mathrm{SU}(2)}_{R}\ifmmode\times\else\texttimes\fi{}\mathrm{U}(1)$ models. The data now enable the top-quark mass and ${Z}_{2}$ properties to be limited simultaneously. The indirect ($Z$-pole, ${M}_{W}$, WNC) data stringently constrain the ${Z}_{1}^{0}\ensuremath{-}{Z}_{2}^{0}$ mixing angle $\ensuremath{\theta}$ ($|\ensuremath{\theta}|l0.01$ in most cases). For models with arbitrary Higgs representations, the limits on the ${Z}_{2}$ mass ${M}_{2}$ from indirect and direct constraints are rather weak (typically 160-400 GeV), but in specific models in which ${M}_{2}$ and $\ensuremath{\theta}$ are correlated, the constraints are much stronger (${M}_{2}g500\ensuremath{-}1000$ GeV). The weak angle in the modified minimal subtraction scheme is well determined even allowing for extra $Z'\mathrm{s}$ and an arbitrary Higgs structure: ${sin}^{2}{\stackrel{^}{\ensuremath{\theta}}}_{W}({M}_{Z})={0.2334}_{\ensuremath{-}0.0011}^{+0.0008}$, for the models considered, where the uncertainties include ${m}_{t}$, compared to the SU(2)\ifmmode\times\else\texttimes\fi{}U(1) model value 0.2333\ifmmode\pm\else\textpm\fi{}0.0008. The 95%-C.L. upper limits on ${m}_{t}$ (${m}_{t}l182$ GeV for Higgs doublets and singlets only, and ${m}_{t}l310$ GeV for arbitrary Higgs representations) continue to hold in the presence of the extra $Z'\mathrm{s}$ considered. The implications of these results for ordinary and supersymmetric grand unification, atomic parity violation, charged-current universality, $R$ (${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$, hadrons) below the $Z$ pole, and superstring theories are discussed. A nongauge model in which the ${Z}_{2}$ has the same couplings as the ordinary $Z$ is included for comparison.

SU (5) unification revisited

>Model-independent criteria for unification in the SU (5) framework are studied. These are applied to the minimal supersymmetric standard model and to the standard model with a split 45 Higgs representation. Although the former is consistent with SU (5) unification, the superpartner masses can vary over a wide range, and may even all lie well beyond the reach of planned colliders. Adding a split 45 to the standard model can also satisfy the unification criteria, so supersymmetric SU (5) is far from unique. Furthermore, we learn that separate Higgs doublets must couple to the top and bottom quarks in order to give a correct mb/mτ prediction.

Implications of precision electroweak experiments for mt, rho 0, sin2 theta W, and grand unification.

The implications of precision $Z$-pole, $W$-mass, and weak-neutral-current data for SU(2)\ifmmode\times\else\texttimes\fi{}U(1) models are described. Within the minimal model one finds ${{sin}^{2}\stackrel{^}{\ensuremath{\theta}}}_{W}({M}_{Z})=0.2334\ifmmode\pm\else\textpm\fi{}0.0008$ in the modified minimal subtraction scheme or ${{sin}^{2}\ensuremath{\theta}}_{W}\ensuremath{\equiv}1\ensuremath{-}\frac{{M}_{W}^{2}}{{M}_{Z}^{2}}=0.2291\ifmmode\pm\else\textpm\fi{}0.0034$ in the on-shell scheme, where the uncertainties include the ${m}_{t}$ and ${M}_{H}$ dependence. The top-quark mass is predicted to be ${124}_{\ensuremath{-}34\ensuremath{-}15}^{+28+20}$ GeV, where the second uncertainty is from ${M}_{H}$, with ${m}_{t}<174(182)$ GeV at 90 (95)% C.L. For the first time subleading effects and vertex corrections allow a significant separation of ${m}_{t}$ and ${\ensuremath{\rho}}_{0}$ in models with a nonminimal Higgs structure. Allowing arbitrary ${m}_{t}$ and Higgs representations one obtains ${{sin}^{2}\stackrel{^}{\ensuremath{\theta}}}_{W}({M}_{Z})=0.2333\ifmmode\pm\else\textpm\fi{}0.0008$, ${\ensuremath{\rho}}_{0}=0.992\ifmmode\pm\else\textpm\fi{}0.011$, and ${m}_{t}<294(310)$ GeV. The implications of these results for ordinary and supersymmetric grand unified theories are considered. Supersymmetric theories with a grand desert between the supersymmetry and unification scales are in striking agreement with data for ${M}_{\mathrm{SUSY}}$ in the ${M}_{Z}\ensuremath{-}1$ TeV range. Ordinary grand unified theories breaking to the standard model in more than one step are also discussed.

ONE LOOP-INDUCED WZH COUPLING IN THE TWO HIGGS DOUBLET MODEL

Although absent at the tree level in models with only doublet and singlet Higgs representations, the WZH coupling can be induced at the one-loop level. We examine the size of this induced coupling in the two Higgs doublet model due to fermion as well as Higgs/gauge boson loops. Such couplings could provide a new mechanism for charged Higgs production at colliders and are ‘backgrounds’ to new physics beyond the Standard Model. We find, however, that these couplings are very weak for all regions of the parameter space explored.