Color Triplet Research Articles

Variety ofSO(10)GUTs with natural doublet-triplet splitting via the missing partner mechanism

We present a new class of unified $SO(10)$ models where the grand unified theory symmetry breaking down to the standard model gauge group involves just one scale, in contrast to the conventional $SO(10)$ models which require two scales. Further, the models we discuss possess a natural doublet-triplet splitting via the missing partner mechanism without fine-tuning. Such models involve $560+\overline{560}$ pair of heavy Higgs fields along with a set of light fields. The $560+\overline{560}$ are the simplest representations of $SO(10)$ besides the $126+\overline{126}$ which contain an excess of color triplets over $SU(2{)}_{L}$ doublets. We discuss several possibilities for realizing the missing partner mechanism within these schemes. With the $126+\overline{126}$ multiplets, three viable models are found with additional fields belonging to ${210+2\ifmmode\times\else\texttimes\fi{}10+120}$, ${45+10+120}$, or ${210+16+\overline{16}+10+120}$. With the $560+\overline{560}$, a unique possibility arises for the missing partner mechanism, with additional ${2\ifmmode\times\else\texttimes\fi{}10+320}$ fields. These models are developed in some detail. It is shown that fully realistic fermion masses can arise in some cases, while others can be made realistic by addition of vectorlike representations. Naturally large neutrino mixing angles, including sizable ${\ensuremath{\theta}}_{13}$, can emerge in these models. The couplings of the ${H}_{u}({H}_{d})$ Higgs doublets of the minimal supersymmetric standard model which give masses to the up quarks (down quarks and leptons) are not necessarily equal at the grand unification scale and would lead to a new phenomenology at the low-energy scales.

The μνSSM with an extra U(1)

The $\mu\nu$SSM solves the $\mu$ problem of the MSSM and generates correct neutrino masses by simply using right-handed neutrinos. This mechanism implies that only dimensionless trilinear terms, breaking R-parity, are present in the superpotential. We present an extension of the $\mu\nu$SSM with an extra U(1) gauge symmetry. We use the extra U(1) charges of the matter fields to forbid the presence in the superpotential of renormalizable and non-renormalizable baryon number violating operators, the trilinear operator producing a domain wall problem, and bilinear operators such as the $\mu$ term and the Majorana masses. We apply the anomaly cancellation conditions associated to the extra U(1), to constrain the values of the U(1) charges. We find that six assignments of the U(1) charges to the matter fields are viable, once extra matter is introduced. In particular, three generations of vector-like color triplets and $SU(2)_L$ doublets, as well as six Standard Model singlets are necessary. Electroweak symmetry breaking is viable in the model, with wide regions of the parameter space fulfilling the experimental constraints on the existence of a new gauge boson $Z'$. Neutrinos and the extra gaugino mix with the MSSM neutralinos, producing a generalized see-saw matrix that can reproduce the experimental results on neutrino masses. Finally, we have estimated the tree-level upper bound on the lightest Higgs mass, finding that it can be as large as about 120 GeV.

Testing new physics models by top charge asymmetry and polarization at the LHC

As a top quark factory, the LHC can test new physics models used to explain the top quark forward-backward asymmetry ${A}_{\mathrm{FB}}^{t}$ measured at the Tevatron. In this work we perform a comparative study for two such models: the ${W}^{\ensuremath{'}}$ model and the color triplet diquark ($\ensuremath{\phi}$) model. Requiring these models to explain ${A}_{\mathrm{FB}}^{t}$ and also satisfy the top pair production rate measured at the Tevatron, we examine their contributions to the LHC observables such as the polarizations and charge asymmetries in top quark productions and the charge asymmetry in ${W}^{\ensuremath{'}}$ (or $\ensuremath{\phi}$) pair production. We find that these observables can be enhanced to their observable levels and current LHC measurement on the top charge asymmetry has already tightly constrained the ${W}^{\ensuremath{'}}$ model. We also find that each observable shows different characteristics in different models, which can be utilized to discriminate the models.

Heavy flavor simplified models at the LHC

Abstract We consider a comprehensive set of simplified models that contribute to final states with top and bottom quarks at the LHC. These simplified models are used to create minimal search strategies that ensure optimal coverage of new heavy flavor physics involving the pair production of color octets and triplets. We provide a set of benchmarks that are representative of model space, which can be used by experimentalists to perform their own optimization of search strategies. For data sets larger than 1 fb−1, same-sign dilepton and 3b search regions become very powerful. Expected sensitivities from existing and optimized searches are given.

Color & weak triplet scalars, the dimuon asymmetry in B s decay, the top forward-backward asymmetry, and the CDF dijet excess

The new physics required to explain the anomalies recently reported by the D0 and CDF collaborations, namely the top forward-backward asymmetry (FBA), the like-sign dimuon charge asymmetry in semileptonic b decay, and the CDF dijet excess, has to feature an amount of flavor symmetry in order to satisfy the severe constrains arising from flavor violation. In this paper we show that, once baryon number conservation is imposed, color & weak triplet scalars with hypercharge $Y=1/3$ can feature the required flavor structure as a consequence of standard model gauge invariance. The color & weak triplet model can simultaneously explain the top FBA and the dimuon charge asymmetry or the dimuon charge asymmetry and the CDF dijet excess. However, the CDF dijet excess appears to be incompatible with the top FBA in the minimal framework. Our model for the dimuon asymmetry predicts the observed pattern $h_d\ll h_s$ in the region of parameter space required to explain the top FBA, whereas our model for the CDF dijet anomaly is characterized by the absence of beyond the SM b-quark jets in the excess region. Compatibility of the color & weak triplet with the electroweak constraints is also discussed. We show that a Higgs boson mass exceeding the LEP bound is typically favored in this scenario, and that both Higgs production and decay can be significantly altered by the triplet. The most promising collider signature is found if the splitting among the components of the triplet is of weak scale magnitude.

LHC signatures of the constrained exceptional supersymmetric standard model

We discuss two striking Large Hadron Collider (LHC) signatures of the constrained version of the exceptional supersymmetric standard model (cE6SSM), based on a universal high energy soft scalar mass m_0, soft trilinear coupling A_0 and soft gaugino mass M_{1/2}. The first signature we discuss is that of light exotic colour triplet charge 1/3 fermions, which we refer to as D-fermions. We calculate the LHC production cross section of D-fermions, and discuss their decay patterns. Secondly we discuss the E6 type U(1)_N spin-1 Z' gauge boson and show how it may decay into exotic states, increasing its width and modifying the line shape of the dilepton final state. We illustrate these features using two representative cE6SSM benchmark points, including an "early LHC discovery" point, giving the Feynman rules and numerical values for the relevant couplings in order to facilitate further studies.

Quirks at the Tevatron and beyond

We consider the physics and collider phenomenology of quirks that transform nontrivially under QCD color, SU(2)_W as well as an SU(N)_{ic} infracolor group. Our main motivation is to show that the recent Wjj excess observed by CDF naturally arises in quirky models. The basic pattern is that several different quirky states can be produced, some of which beta-decay during or after spin-down, leaving the lightest electrically neutral quirks to hadronize into a meson that subsequently decays into gluon jets. We analyze LEP II, Tevatron, UA2, and electroweak precision constraints, identifying the simplest viable models: scalar quirks ("squirks") transforming as color triplets, SU(2)_W triplets and singlets, all with vanishing hypercharge. We calculate production cross sections, weak decay, spin-down, meson decay rates, and estimate efficiencies. The novel features of our quirky model includes: quirkonium decay proceeds into a pair of gluon jets, without a b-jet component; there is essentially no associated Zjj or gamma+jj signal; and there are potentially new (parameter-dependent) contributions to dijet production, multi-W production plus jets, W+gamma, gamma+gamma resonance signals, and monojet signals. There may be either underlying event from low energy QCD deposition resulting from quirky spin-down, and/or qualitatively modified event kinematics from infraglueball emission.

NEW BOUND STATES OF HEAVY QUARKS AT LHC AND TEVATRON

The present paper is based on the assumption that heavy quarks bound states exist in the Standard Model (SM). Considering New Bound States (NBS) of top–antitop quarks (named T-balls) we have shown that: (1) there exists the scalar 1S-bound state of [Formula: see text]; (2) the forces which bind the top-quarks are very strong and almost completely compensate the mass of the twelve top–antitop-quarks in the scalar NBS; (3) such strong forces are produced by the Higgs–top-quarks interaction with a large value of the top-quark Yukawa coupling constant gt≃1. Theory also predicts the existence of the NBS [Formula: see text], which is a color triplet and a fermion similar to the t'-quark of the fourth generation. We have also considered the "b-quark-replaced" NBS, estimated the masses of the lightest fermionic NBS: M NBS ≳300 GeV , and discussed the larger masses of T-balls. We have developed a theory of the scalar T-ball's condensate and predicted the existence of three SM phases. Searching for heavy quark bound states at the Tevatron and LHC is discussed. We have constructed the possible form-factors of T-balls, and estimated the charge multiplicity coming from the T-ball's decays.

No like-sign tops at Tevatron: Constraints on extended models and implications for the [formula omitted] asymmetry

We use a recent upper limit from CDF on like-sign top pair production to place constraints on general new vector bosons and scalars mediating uu→tt. The possible vector bosons comprise neutral colour singlets or octets, and charge 4/3 colour triplets or sextets, whereas the new scalars can be neutral colour singlets or octets and charge 4/3 colour sextets. We also estimate the expected bounds from like-sign top pair production at LHC in the near future. Then, we address the implications of these limits for the forward–backward asymmetry in tt¯ production measured at Tevatron. In particular, we find that models explaining the observed asymmetry by the exchange of a single t-channel heavy Z′ boson are already excluded. On the other hand, light Z′ bosons with a mass MZ′≃150 GeV, which could also account for a recent CDF dijet excess in W+jet production, are barely allowed.

Searching singlet extensions of the supersymmetric standard model in Z 6−II orbifold compactification of heterotic string

We search for supersymmetric standard model realizations with extra singlets and extra U(1) using the heterotic string compactification on the Z 6−II orbifold with two Wilson lines. The effective superpotential produced through the vacuum restabilization mechanism is examined for three representative Pati–Salam string models obtained in the literature. An automated selection of semi-realistic vacua along flat directions in the non-Abelian singlet modes field space is performed by requiring the presence of massless pairs of electroweak Higgs bosons having trilinear superpotential couplings with massless singlet modes and the decoupling of color triplet exotic modes needed to suppress B and L number violating processes.

Characterization, Delineation and Visualization of Agro- Ecozones Using Multivariate Geographical Clustering

Agro-ecozoning is a delineation of landscape into relatively homogeneous regions of expected similar crop performance. Past classifications have been subjective, crop specific and did not take into account spatial correlation. A quantitative approach is proposed to unambiguously locate, characterise and visualise agro-ecozones and their boundaries which can be allied to different environmental conditions. In this study the environmental parameters, including climatic and soil characteristics, hypothesized to be generally relevant to many crops in Capitanata-Foggia (South Italy), were used. Cokriged environmental estimates at 500 m scale were used in a clustering algorithm based on non-parametric multivariate density estimation. A 3D map of density estimation and red-green-blue colour triplet were used for visualisation of agro-ecozones as a unique combination of environmental factors. The proposed approach produced the delineation of the study area in five compact classes in the space of environmental attributes that were also contiguous in geographic space. The resulting agro-ecozones may provide a framework for useful application in land use decision making.

Solving the flavour problem in supersymmetric Standard Models with three Higgs families

We show how a non-Abelian family symmetry Δ27 can be used to solve the flavour problem of supersymmetric Standard Models containing three Higgs families such as the Exceptional Supersymmetric Standard Model (E6SSM). The three 27-dimensional families of the E6SSM, including the three families of Higgs fields, transform in a triplet representation of the Δ27 family symmetry, allowing the family symmetry to commute with a possible high energy E6 symmetry. The Δ27 family symmetry here provides a high energy understanding of the Z2H symmetry of the E6SSM, which solves the flavour changing neutral current problem of the three families of Higgs fields. The main phenomenological predictions of the model are tri-bi-maximal mixing for leptons, two almost degenerate LSPs and two almost degenerate families of colour triplet D-fermions, providing a clear prediction for the LHC. In addition the model predicts PGBs with masses below the TeV scale, and possibly much lighter, which appears to be a quite general and robust prediction of all models based on the D-term vacuum alignment mechanism.

Color triplet diquarks at the LHC

We consider a class of supersymmetric models containing baryon number violating processes such as observable n–n¯ oscillations that are mediated by color triplet diquark fields. For plausible values of the diquark–quark couplings, the scalar diquark with mass between a few hundred GeV and one TeV or so can be produced in the s-channel at the LHC and detected through its decay into a top quark and a hadronic jet.

Explorations of the top quark forward-backward asymmetry at the Tevatron

We consider the recent measurement of the top quark forward-backward asymmetry at the Fermilab Tevatron, which shows a discrepancy of slightly more than $2\ensuremath{\sigma}$ compared to the standard model prediction. We find that $t$-channel exchange of a color sextet or triplet scalar particle can explain the measurement, while leaving the cross section for $t\overline{t}$ production within measured uncertainties. Such particles have good discovery prospects by study of the kinematic structure of $t\overline{t}+\mathrm{\text{jets}}$ at the LHC.

Predictions of the constrained exceptional supersymmetric standard model

We discuss the predictions of a constrained version of the exceptional supersymmetric standard model (cE6SSM), based on a universal high energy soft scalar mass m0, soft trilinear coupling A0 and soft gaugino mass M1/2. We predict a supersymmetry (SUSY) spectrum containing a light gluino, a light wino-like neutralino and chargino pair and a light bino-like neutralino, with other sparticle masses except the lighter stop being much heavier. In addition, the cE6SSM allows the possibility of light exotic colour triplet charge 1/3 fermions and scalars, leading to early exotic physics signals at the LHC. We focus on the possibility of a Z′ gauge boson with mass close to 1 TeV, and low values of (m0,M1/2), which would correspond to an LHC discovery using “first data”, and propose a set of benchmark points to illustrate this.

Standard model on a domain-wall brane?

We propose a $4+1$-dimensional action that is a candidate for realizing a standard-model-like effective theory for fields dynamically localized to a domain-wall brane. Our construction is in part based on the conjecture that the Dvali-Shifman mechanism for dynamically localizing gauge bosons to a domain wall works correctly in $4+1\mathrm{\text{\ensuremath{-}}}\mathrm{d}$. Assuming this to be so, we require the gauge symmetry to be SU(5) in the bulk, spontaneously breaking to $\mathrm{SU}(3)\ensuremath{\bigotimes}\mathrm{SU}(2)\ensuremath{\bigotimes}\mathrm{U}(1)$ inside the domain wall, thus dynamically localizing the standard-model gauge bosons provided that the SU(5) theory in the bulk exhibits confinement. The wall is created jointly by a real singlet-Higgs field $\ensuremath{\eta}$ configured as a kink, and an SU(5) adjoint-Higgs field $\ensuremath{\chi}$ that takes nonzero values inside the wall. Chiral $3+1$-dimensional quarks and leptons are confined and split along the bulk direction via their Yukawa couplings to $\ensuremath{\eta}$ and $\ensuremath{\chi}$. The Higgs doublet and its color triplet SU(5) partner are similarly localized and split. The splittings can suppress colored-Higgs-induced proton decay and, because of the different localization profiles, the usual SU(5) mass relation ${m}_{e}={m}_{d}$ does not arise. Localized gravity is generated via the Randall-Sundrum alternative to compactification.

Exceptional supersymmetric standard models with non-abelian discrete family symmetry

We introduce a non-Abelian discrete $\Delta_{27}$ family symmetry into the recently proposed classes of Exceptional Supersymmetric Standard Model ($E_6$SSM) based on a broken $E_6$ Grand Unified Theory (GUT) in order to solve the flavour problem in these models and in particular to account for tri-bimaximal neutrino mixing. We consider both the minimal version of the model (the ME$_6$SSM) with gauge coupling unification at the string scale and the E$_6$SSM broken via the Pati-Salam chain with gauge coupling unification at the conventional GUT scale. In both models there are low energy exotic colour triplets with couplings suppressed by the symmetries of the model, including the family symmetry. This leads to suppressed proton decay and long lived TeV mass colour triplet states with striking signatures at the LHC. We also present a dynamical solution to the $\mu'$ problem (where $\mu'$ is the mass of the additional pair of electroweak doublets in the E$_6$SSM).

Perturbative SO(10) GUT and the minimal Higgs sector

The breaking of SO(10) to SU(3)C×U(1)EM can be accomplished by just four Higgs fields: the symmetric rank-two tensor, S(54); a pair of spinors, C(16) and C¯(16¯); and a vector, T(10). This setup is also able to generate realistic fermion masses. The heavy color triplets in the vector and spinor fields mediate proton decay via dimension-five operators. The experimental bounds on proton decay constrain the structure and size of the Yukawa operators.

Suppression of Higgsino mediated proton decay by cancellations in grand unified theories and strings

A mechanism for the enhancement for proton lifetime in supersymmetric/supergravity (SUSY/SUGRA) grand unified theories and in string theory models is discussed where Higgsino mediated proton decay arising from color triplets (antitriplets) with charges $Q=\ensuremath{-}1/3(1/3)$ and $Q=\ensuremath{-}4/3(4/3)$ is suppressed by an internal cancellation due to contributions from different sources. We exhibit the mechanism for an $SU(5)$ model with ${45}_{H}+{\overline{45}}_{H}$ Higgs multiplets in addition to the usual Higgs structure of the minimal model. This model contains both $Q=\ensuremath{-}1/3(1/3)$ and $Q=\ensuremath{-}4/3(4/3)$ Higgs color triplets (antitriplets) and simple constraints allow for a complete suppression of Higgsino mediated proton decay. Suppression of proton decay in an $SU(5)$ model with Planck scale contributions is also considered. The suppression mechanism is then exhibited for an $SO(10)$ model with a unified Higgs structure involving ${144}_{H}+{\overline{144}}_{H}$ representations. The $SU(5)$ decomposition of ${144}_{H}+{\overline{144}}_{H}$ contains ${5}_{H}+{\overline{5}}_{H}$ and ${45}_{H}+{\overline{45}}_{H}$ and the cancellation mechanism arises among these contributions which mirror the $SU(5)$ case. The cancellation mechanism appears to be more generally valid for a larger class of unification models. Specifically the cancellation mechanism may play a role in string model constructions to suppress proton decay from dimension five operators. The mechanism allows for the suppression of proton decay consistent with current data allowing for the possibility that proton decay may be visible in the next round of nucleon stability experiment.

Origin of matter in the universe

We extend the Standard Model with two iso-singlet color triplet scalars, one singlet real scalar and one singlet fermion. The new fields are odd under an unbroken Z2 discrete symmetry while the Standard Model particles are even. The decays of the singlet real scalar into three Standard Model quarks (antiquarks) with three singlet antifermions (fermions), which explicitly violate the baryon number, will become effective after the electroweak phase transition and then produce the observed baryon asymmetry in the universe through the loop diagram involving the exchange of the W gauge boson. The singlet fermion can serve as the candidate for cold dark matter. In our model, all new particles with masses below the TeV scale can be detected by the forthcoming collider experiments or the next generation experiments for neutron–antineutron oscillations.