Exceptional Supersymmetric Standard Model Research Articles

TeV-scale leptoquark searches at the LHC and their E6SSM interpretation

We perform a model-independent search for leptoquarks (LQs) at the Large Hadron Collider through their pair-production and subsequent decay into toverline{t}tau tau intermediate states. We show that, assuming full luminosity of the Run 2, a fully hadronic signal emerging from this intermediate state can surpass in sensitivity the established searches relying on leptons in the final state. Our conclusion is supported by a thorough Monte-Carlo analysis, and we advocate the deployment of our proposed search channel in the proper experimental setting of the Run 3. Furthermore, in order to highlight the full scope of this approach for constraining LQ theories, we interpret our results in the context of the string-inspired Exceptional Supersymmetric Standard Model, which naturally predicts the S1-type scalar LQ states that we analyse here.

A combined approach to the analysis of space and ground experimental data within a simplified E_6SSM

Within the Exceptional Supersymmetric Standard Model (E_6SSM), we investigate signatures at the Large Hadron Collider (LHC) for a long-lived charged inert higgsino, which is degenerate with the inert neutralino at tree level and a small mass splitting is generated at the loop level, resulting in a lifetime mathcal{O}(0.02) nanoseconds. We focus on the most sensitive search for long-lived charged inert higgsino decays to the lightest neutral inert higgsino dark matter and very soft charged leptons, which are eventually stopped in the detector resulting in a disappearing-track signal. Furthermore, we study the displaced vertex signature of the inert chargino in the case where it is produced via the Z^{prime } portal. We illustrate how difficult it is to construct displaced vertices in this class of models, though some evidence could be gained at the High Luminosity LHC. Finally, we compare the spin independent and spin dependent cross sections of the lightest inert higgsino DM to those of current direct detection experiments, proving that it is possible to gain sensitivity to the active DM component of this scenario in the near future. The combination of these signatures with the one emerging from Z' production and decay via Drell–Yan, which can be characterised as belonging to the E_6SSM via both the cross section and Forward–Backward Asymmetry, could point uniquely to this non-minimal realisation of Supersymmetry.

Multicomponent dark matter in a simplified E6SSM

We study Dark Matter (DM) in the Exceptional Supersymmetric Standard Model (E$_6$SSM). The model has both active and inert Higgs superfields and by imposing discrete symmetries one can generate two DM candidates. We show that the lightest higgsinos of the active and inert sectors give a viable setup for two-component DM. We also illustrate the scope of both direct and indirect detection experiments in extracting such a DM sector. Future experiments of the former kind have a good chance of finding the active component while the inert higgsino will be very hard to detect while those of the latter kind will have no sensitivity to either candidate.

A Review of the Exceptional Supersymmetric Standard Model

Local supersymmetry (SUSY) provides an attractive framework for the incorporation of gravity and unification of gauge interactions within Grand Unified Theories (GUTs). Its breakdown can lead to a variety of models with softly broken SUSY at low energies. In this review article, we focus on the SUSY extension of the Standard Model (SM) with an extra U ( 1 ) N gauge symmetry originating from a string-inspired E 6 GUTs. Only in this U ( 1 ) extension of the minimal supersymmetric standard model (MSSM) can the right-handed neutrinos be superheavy, providing a mechanism for the baryon asymmetry generation. The particle content of this exceptional supersymmetric standard model (E 6 SSM) includes three 27 representations of the E 6 group, to ensure anomaly cancellation. In addition it also contains a pair of S U ( 2 ) W doublets as required for the unification of gauge couplings. Thus, E 6 SSM involves exotic matter beyond the MSSM. We consider symmetries that permit suppressing flavor changing processes and rapid proton decay, as well as gauge coupling unification, the gauge symmetry breaking and the spectrum of Higgs bosons in this model. The possible Large Hadron Collider (LHC) signatures caused by the presence of exotic states are also discussed.

Dark matter candidates in the constrained exceptional supersymmetric standard model

The Exceptional Supersymmetric Standard Model (E$_6$SSM) is a low energy alternative to the MSSM with an extra $U(1)$ gauge symmetry and three generations of matter filling complete 27-plet representations of $E_6$. This provides both new D and F term contributions that raise the Higgs mass at tree level, and a compelling solution to the $\mu$-problem of the MSSM by forbidding such a term with the extra $U(1)$ symmetry. Instead, an effective $\mu$-term is generated from the VEV of an SM singlet which breaks the extra $U(1)$ symmetry at low energies, giving rise to a massive $Z^\prime$. We explore the phenomenology of the constrained version of this model (cE$_6$SSM) in substantially more detail than has been carried out previously, performing a ten dimensional scan that reveals a large volume of viable parameter space. We classify the different mechanisms for generating the measured relic density of dark matter found in the scan, including the identification of a new mechanism involving mixed bino/inert-Higgsino dark matter. We show which mechanisms can evade the latest direct detection limits from the LUX 2016 experiment. Finally we present benchmarks consistent with all the experimental constraints and which could be discovered with the XENON1T experiment.

750 GeV diphoton resonance from singlets in an exceptional supersymmetric standard model

Abstract The 750-760 GeV diphoton resonance may be identified as one or two scalars and/or one or two pseudoscalars contained in the two singlet superfields S1,2 arising from the three 27-dimensional representations of E6. The three 27s also contain three copies of colour-triplet charge ∓1/3 vector-like fermions D,$$ \overline{D} $$ D ¯ and two copies of charged inert Higgsinos $$ {\tilde{H}}^{+} $$ H ˜ + ,$$ {\tilde{H}}^{-} $$ H ˜ − to which the singlets S1,2 may couple. We propose a variant of the E6SSM where the third singlet S3 breaks a gauged U(1)N above the TeV scale, predicting Z N ′ , D,$$ \overline{D} $$ D ¯ , $$ {\tilde{H}}^{+} $$ H ˜ + ,$$ {\tilde{H}}^{-} $$ H ˜ − at LHC Run 2, leaving the two lighter singlets S1,2 with masses around 750 GeV. We calculate the branching ratios and cross-sections for the two scalar and two pseudoscalar states associated with the S1,2 singlets, including possible degeneracies and maximal mixing, subject to the constraint that their couplings remain perturbative up to the unification scale.

Electroweak baryogenesis in the exceptional supersymmetric standard model

We study electroweak baryogenesis in the E6 inspired exceptional supersymmetric standard model (E6SSM). The relaxation coefficients driven by singlinos and the new gaugino as well as the transport equation of the Higgs supermultiplet number density in the E6SSM are calculated. Our numerical simulation shows that both CP-violating source terms from singlinos and the new gaugino can solely give rise to a correct baryon asymmetry of the Universe via the electroweak baryogenesis mechanism.

Fine tuning in the constrained exceptional supersymmetric standard model

Supersymmetric unified models in which the ${Z}^{\ensuremath{'}}$ couples to the Higgs doublets, as in the ${E}_{6}$ class of models, have large fine tuning dominated by the experimental mass limit on the ${Z}^{\ensuremath{'}}$. To illustrate this, we investigate the degree of fine tuning throughout the parameter space of the constrained exceptional supersymmetric standard model (${\mathrm{cE}}_{6}\mathrm{SSM}$) that is consistent with a Higgs mass ${m}_{h}\ensuremath{\sim}125\text{ }\text{ }\mathrm{GeV}$. Fixing $\mathrm{tan}\ensuremath{\beta}=10$, and taking specific values of the mass of the ${Z}^{\ensuremath{'}}$ boson, with ${M}_{{Z}^{\ensuremath{'}}}\ensuremath{\sim}2--4\text{ }\text{ }\mathrm{TeV}$, we find that the minimum fine tuning is set predominantly from the mass of ${Z}^{\ensuremath{'}}$ and varies from $\ensuremath{\sim}200$ to 400 as we vary ${M}_{{Z}^{\ensuremath{'}}}$ from $\ensuremath{\sim}2$ to 4 TeV. However, this is significantly lower than the fine tuning in the constrained minimal supersymmetric standard model, of $\mathcal{O}(1000)$, arising from the large stop masses required to achieve the Higgs mass.

Threshold corrections in the exceptional supersymmetric standard model

We calculate threshold corrections to the running gauge and Yukawa couplings in the Exceptional Supersymmetric Standard Model (E6SSM) and analyse the more precise and reliable mass spectra in a constrained model (CE6SSM). Full expressions for the corrections are provided and the implementation into a spectrum generator is described. We find a dramatic reduction in the matching scale dependency of the masses of many states and observe a significant adjustment of the correlation of low-scale physical masses and high-scale parameters. Still, in substantial regions of parameter space the mass of the lightest Higgs is compatible with the new boson discovered at the LHC and the model satisfies limits from collider searches for squark, gluinos and Z' bosons. We study the implications for gauge coupling unification from a new dependency of the spectrum on so-called survival Higgs fields which cannot be addressed without the inclusion of the threshold corrections.

Constrained exceptional supersymmetric standard model with a Higgs signal near 125 GeV

We study the parameter space of the constrained exceptional supersymmetric standard model (${\mathrm{cE}}_{6}\mathrm{SSM}$) consistent with a Higgs signal near 125 GeV and the LHC searches for squarks, gluinos and ${Z}^{\ensuremath{'}}$. The ${\mathrm{cE}}_{6}\mathrm{SSM}$ parameter space, consistent with correct electroweak symmetry breaking, is represented by scans in the $({m}_{0},{M}_{1/2})$ plane for fixed ${Z}^{\ensuremath{'}}$ mass and $\mathrm{tan}\ensuremath{\beta}$, with squark, gluino and Higgs masses plotted as contours in this plane. We find that a 125 GeV Higgs mass only arises for a sufficiently large ${Z}^{\ensuremath{'}}$ mass, mostly above current limits, and for particular regions of squark and gluino masses corresponding to multi-TeV squark masses, but with lighter gluinos typically within reach of the LHC 8 TeV or forthcoming 14 TeV runs. Successful dark matter relic abundance may be achieved over all the parameter space, assuming a binolike lightest supersymmetric particle with a nearby heavier inert Higgsino doublet and decoupled inert singlinos, resulting in conventional gluino decay signatures. A set of typical benchmark points with a Higgs near 125 GeV is provided which exemplifies these features.

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.

Novel Higgs decays and dark matter in the exceptional supersymmetric standard model

The Exceptional Supersymmetric (SUSY) Standard Model predicts three families of Higgs doublets plus three Higgs singlets, where one family develops vacuum expectation values (VEVs), while the remaining two which do not are called Inert. The model can account for the dark matter relic abundance if the two lightest Inert neutralinos, identified as the (next-to) lightest SUSY particles ((N)LSPs), have masses close to half the Z mass. In this case we find that the usual SM-like Higgs boson decays more than 95% of the time into either LSPs or NLSPs. The latter case produces a final state containing two leptons l^{+}l^{-} with an invariant mass less than or about 10 GeV. We illustrate this scenario with a set of benchmark points satisfying phenomenological constraints and the WMAP dark matter relic abundance. This scenario also predicts other light Inert chargino and neutralino states below 200 GeV, and large LSP direct detection cross-sections close to current limits and observable soon at XENON100.

An exceptional SSM from E 6 orbifold GUTs with intermediate LR symmetry

We propose a class of E 6-based local orbifold Grand Unified Theories (GUTs) which yield an exceptional supersymmetric standard model as their low energy theory including leptoquark and un-Higgs exotics and a Z’ at the TeV scale. Unification is achieved in two steps through an intermediate scale symmetry breaking at a unified coupling which is enhanced due to the contributions of leptoquarks to the QCD beta function.

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.

Aspects of the Exceptional Supersymmetric Standard Model

The existence of weak scale supersymmetry (SUSY) is theoretically well motivated, because of its ability to stabilise the electro-weak symmetry breaking (EWSB) scale. One of the benefits of weak scale SUSY with conserved R-parity is that the lightest supersymmetric particle (LSP) is absolutely stable and provides a weakly interacting massive particle (WIMP) candidate capable of accounting for the observed cold dark matter (CDM) relic density ΩCDMh ≈ 0.1. In particular, the lightest neutralino in SUSY models is an excellent such candidate, providing its mass, composition and interactions are suitably tuned to result in the correct value of ΩCDMh. The Minimal Supersymmetric Standard Model (MSSM) [1] provides the simplest supersymmet-

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.

Constrained exceptional supersymmetric standard model

We propose and study a constrained version of the exceptional supersymmetric standard model (E6SSM), which we call the cE6SSM, based on a universal high energy scalar mass m0, trilinear scalar coupling A0 and gaugino mass M1/2. We derive the renormalization group (RG) Equations for the cE6SSM, including the extra U(1)N gauge factor and the low-energy matter content involving three 27 representations of E6. We perform a numerical RG analysis for the cE6SSM, imposing the usual low-energy experimental constraints and successful electroweak symmetry breaking. Our analysis reveals that the sparticle spectrum of the cE6SSM involves a light gluino, two light neutralinos, and a light chargino. Furthermore, although the squarks, sleptons, and Z? boson are typically heavy, the exotic quarks and squarks can also be relatively light. We finally specify a set of benchmark points, which correspond to particle spectra, production modes, and decay patterns peculiar to the cE6SSM, altogether leading to spectacular new physics signals at the Large Hadron Collider.

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).

Leptogenesis in the E6SSM

We investigate leptogenesis in the E6 inspired Exceptional Supersymmetric Standard Model (E6SSM). Right-handed (RH) neutrinos are singlets under the Standard Model gauge groups and the extra U1 gauge group of the E6SSM at low energies and are therefore not involved in gauge interactions. This allows them to have Majorana mass large enough for the seesaw mechanism and leptogenesis. In addition to canonical leptogenesis, the RH neutrinos may decay into exotic leptons and leptoquarks, the subsequent decays of which lead to extra lepton asymmetries. We find that the lepton asymmetry can be drastically enhanced as compared with that in the SM and MSSM?

Electroweak symmetry breaking in the E6SSM

The Exceptional Supersymmetric Standard Model (E6SSM) is an E6 inspired model with an extra gauged U(1) symmetry, which solves the μ-problem in a similar way to the NMSSM but without the accompanying problems of singlet tadpoles or domain walls. It predicts new exotic particles at the TeV scale. We investigate the Renormalisation Group Evolution of the model and test electroweak symmetry breaking for a selection of interesting scenarios with non-universal Higgs masses at the GUT scale. We present a detailed particle spectrum that could be observed at the LHC.