Nonminimal Supersymmetric Model Research Articles

Stop-catalyzed baryogenesis beyond the MSSM

Non-minimal supersymmetric models that predict a tree-level Higgs mass above the Minimal Supersymmetric Standard Model (MSSM) bound are well motivated by naturalness considerations. Indirect constraints on the stop sector parameters of such models are significantly relaxed compared to the MSSM; in particular, both stops can have weak-scale masses. We revisit the stop-catalyzed electroweak baryogenesis (EWB) scenario in this context. We find that the LHC measurements of the Higgs boson production and decay rates already rule out the possibility of stop-catalyzed EWB. We also introduce a gauge-invariant analysis framework that may generalize to other scenarios in which interactions outside the gauge sector drive the electroweak phase transition.

Ширина распада бозона Хиггса на два фотона в однопетлевом приближении с учетом СР-нарушения в НМССМ

В статье рассматривается проблема расширения стандартной модели физики элементарных частиц. Основное внимание уделено неминимальной суперсимметричной модели. На сегодняшний день еe рассмотрение является наиболее приемлемым по сравнению с другими разрабатываемыми суперсимметричными теориями. Мы также рассматриваем нарушение СР-инвариантности в секторе Хиггса. При нахождении физических состояний бозонов Хиггса мы находим локальный минимум потенциала Хиггса. Эту процедуру необходимо выполнить для того, чтобы получить стабильное состояние вакуума. Далее произведены расчеты ширины распада бозона Хиггса на два фотона. Мы используем метод квантово-полевой теории возмущений совместно с фейнмановским диаграммным подходом. Результаты расчeтов представлены графически. Показано влияние СР-нарушающей фазы на величину ширины распада. Также приведены зависимости масс бозонов Хиггса от фазы СР-нарушения в древесном приближении. Некоторые параметры модели не определены на эксперименте, а заключены в некотором диапазоне значений, что дает возможность рассматривать различные сценарии нескольких бозонов Хиггса. В частности, в случае СР-нарушения возможно существование бозона Хиггса с массой меньше 125 ГэВ. Это объясняется отсутствием определенного СР-состояния этой частицы.

Lepton Flavor Violation beyond the MSSM

Most extensions of the Standard Model lepton sector predict large lepton flavor violating rates. Given the promising experimental perspectives for lepton flavor violation in the next few years, this generic expectation might offer a powerful indirect probe to look for new physics. In this review we will cover several aspects of lepton flavor violation in supersymmetric models beyond the Minimal Supersymmetric Standard Model. In particular, we will concentrate on three different scenarios: high-scale and low-scale seesaw models as well as models withR-parity violation. We will see that in some cases the LFV phenomenology can have characteristic features for specific scenarios, implying that dedicated studies must be performed in order to correctly understand the phenomenology in nonminimal supersymmetric models.

Charged lepton flavor violation beyond minimal supersymmetry

We discuss charged lepton flavor violation in supersymmetric models with extended leptonic sectors at low energies. Contrary to the usual high-scale realizations of the seesaw mechanism, these non-minimal supersymmetric models have new superfields and/or interactions at the supersymmetric scale. As a consequence of this, the resulting lepton flavor violating phenomenology may be very different from that of minimal models.

Electroweak baryogenesis and the Fermi gamma-ray line

Many particle physics models attempt to explain the 130 GeV gamma-ray feature that the Fermi large area telescope observes in the Galactic center. Neutralino dark matter in nonminimal supersymmetric models, such as the next-to-minimal supersymmetric standard Model (NMSSM), is an especially well-motivated theoretical setup that can explain the line. We explore the possibility that regions of the NMSSM consistent with the 130 GeV line can also produce the observed baryon asymmetry of the universe via electroweak baryogenesis. We find that such regions can, in fact, accommodate a strongly first-order electroweak phase transition (due to the singlet contribution to the effective potential), while also avoiding a light stop and producing a Standard Model (SM)-like Higgs in the observed mass range. Simultaneously, $CP$ violation from a complex phase in the wino-Higgsino sector can account for the observed baryon asymmetry through resonant sources at the electroweak phase transition, while satisfying current constraints from dark matter, collider, and electric dipole moment experiments. This result is possible by virtue of a relatively light pseudoscalar Higgs sector with a small degree of mixing, which yields efficient $s$-channel resonant neutralino annihilation consistent with indirect detection constraints, and of the moderate values of $\ensuremath{\mu}$ required to obtain a binolike lightest supersymmetric particle consistent with the line. The wino mass is essentially a free parameter that one can tune to satisfy electroweak baryogenesis. Thus, the NMSSM framework can potentially explain the origins of both baryonic and dark matter components in the Universe. The tightness of the constraints we impose on this scenario makes it extraordinarily predictive and conclusively testable in the near future by modest improvements in electric dipole moment and dark matter search experiments.

Unusual Higgs boson signal inR-parity violating nonminimal supersymmetric models at the LHC

We predict an unconventional background free signal of the Higgs boson in $R$-parity violating nonminimal supersymmetric models at the Large Hadron Collider (LHC). The signal comprises a dilepton plus four hadronic jets and two large displaced vertices. The displaced leptons and jets are coming from the decay of the lightest supersymmetric particle (LSP), which is predominantly a gauge-singlet neutrino. A pair of such LSPs can couple to a Higgs boson, created via gluon fusion. We have analyzed two cases--one corresponding to the tree-level Higgs boson mass and another with the one-loop corrected mass of the Higgs boson. A reliable Higgs mass reconstruction using this signal can lead to discovery at the LHC with center-of-mass energy $\sqrt{s}=14\text{ }\text{ }\mathrm{TeV}$ and $5\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ of integrated luminosity $(\mathcal{L})$. Even at $\sqrt{s}=7\text{ }\text{ }\mathrm{TeV}$ and $\mathcal{L}=5\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$, a reasonable number of events are expected. Besides, mass reconstruction of a gauge-singlet LSP can provide an estimate of the seesaw scale.

Effective two Higgs doublets in nonminimal supersymmetric models

The Higgs sectors of supersymmetric extensions of the Standard Model have two doublets in the minimal version (MSSM), and two doublets plus a singlet in two others: with (UMSSM) and without (NMSSM) an extra U(1)'. A very concise comparison of these three models is possible if we assume that the singlet has a somewhat larger breaking scale compared to the electroweak scale. In that case, the UMSSM and the NMSSM become effectively two-Higgs-doublet models (THDM), like the MSSM. As expected, the mass of the lightest CP-even neutral Higgs boson has an upper bound in each case. We find that in the NMSSM, this bound exceeds not very much that of the MSSM, unless tan(beta) is near one. However, the upper bound in the UMSSM may be substantially enhanced.

Neutrino masses and mixing in μνSSM

μνSSM is an R-parity violating non-minimal supersymmetric model which uses right chiral neutrino superfields to solve the μ-problem. The R-parity violation together with a TeV scale seesaw mechanism using right handed neutrinos are instrumental for the light neutrino mass generation in μνSSM. We show that it is possible to accommodate three flavour global neutrino data in μνSSM with three massive neutrinos at the tree level. Ingression of the one-loop corrections to neutrino masses and mixing shows certain variations over the tree level analysis depending on the specific hierarchy of neutrino masses involved. In μνSSM some of the R-parity violating decay branching ratios of the lightest neutralino show nice correlation with certain neutrino mixing angle. These correlations along with the presence of displaced vertices in the decay of the lightest neutralino can be further investigated as a test of μνSSM in collider experiments.

Single top production in a non-minimal supersymmetric model

We study single top production at the LHC in a SUSY-QCD model with a heavy Dirac gluino. The presence of a heavy Dirac gluino allows for notable top-up flavour changing neutral currents. In this scenario, we find that the process ug→tg gives the largest contribution to single top production via FCNCs at the LHC. The key features of this signal are that the top quark is produced very forward and that it is asymmetric to its anti-top counterpart, as the latter lacks a valence quark.

Electroweak phase transition in a nonminimal supersymmetric model

The Higgs potential of the minimal nonminimal supersymmetric standard model (MNMSSM) is investigated within the context of electroweak phase transition. We investigate the allowed parameter space yielding correct electroweak phase transitoin employing a high temperature approximation. We devote to phenomenological consequences for the Higgs sector of the MNMSSM for electron-positron colliders. It is observed that a future $e^+ e^-$ linear collider with $\sqrt{s} = 1000$ GeV will be able to test the model with regard to electroweak baryogenesis.

Spontaneous CP violation in non-minimal supersymmetric models

We study the possibilities of spontaneous CP violation in the Next-to-Minimal Supersymmetric Standard Model with an extra singlet tadpole term in the scalar potential. We calculate the Higgs boson masses and couplings with radiative corrections including dominant two loop terms. We show that it is possible to satisfy the LEP constraints on the Higgs boson spectrum with non-trivial spontaneous CP violating phases. We also show that these phases could account for the observed value of epsilonK.

Renormalization of parameters of a soft breakdown of supersymmetry in the regime of strong yukawa coupling within a nonminimal supersymmetric standard model

Within a nonminimal supersymmetric (SuSy) model, the renormalization of trilinear coupling constants A i(t) for scalar fields and of specific combinations \(\mathfrak{M}_i^2 (t)\) of the scalar-particle masses is investigated in the regime of strong Yukawa coupling. The dependence of these parameters on their initial values at the Grand Unification scale disappears as solutions to the renormalization-group equations approach infrared quasifixed points with increasing Y i(0). In the vicinities of quasifixed points for \(\tilde \alpha _{GUT} \ll Y_i (0) \ll 1\), all solutions A i(t) and \(\mathfrak{M}_i^2 (t)\) are concentrated near some straight lines or planes in the space of parameters of a soft breakdown of supersymmetry. This behavior of the solutions in question is explained by a sufficiently slow disappearance of the A i(0) and \(\mathfrak{M}_i^2 (t)\) dependence of the trilinear coupling constants and combinations of the scalar-particle masses. A method is proposed for deriving equations describing the aforementioned straight lines and planes, and the process of their formation is discussed by considering the example of exact and approximate solutions to the renormalization-group equations within a nonminimal supersymmetric standard model.

Higgs scalars in the minimal nonminimal supersymmetric standard model

We consider the simplest and most economic version among the proposed non-minimal supersymmetric models, in which the $\mu$-parameter is promoted to a singlet superfield, whose all self-couplings are 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 associated 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 $\mu$-term, without suffering from the visible axion or the cosmological domain-wall problem. Focusing on the Higgs sector of this minimal non-minimal supersymmetric standard model, we calculate its effective Higgs potential by integrating out the dominant quantum effects due to stop squarks. We then discuss the phenomenological 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 non-minimal supersymmetric model can naturally accommodate a relatively light charged Higgs boson, with a mass close to the present experimental lower bound.

Particle mass limits in minimal and nonminimal supersymmetric models

A review of the Higgs and neutralino sector of supersymmetric models is presented. This includes the upper limit on the mass of the lightest Higgs boson in the minimal supersymmetric standard model, as well as models based on the standard model gauge groupSU(2) L xU(l) Y with extended Higgs sectors. We then discuss the Higgs sector of left-right supersymmetric models, which conserveR-parity as a consequence of gauge invariance, and present a calculable upper bound on the mass of the lightest Higgs boson in these models. We also discuss the neutralino sector of general supersymmetric models based on the SM gauge group. We show that, as a consequence of gauge coupling unification, an upper bound on the mass of the lightest neutralino as a function of the gluino mass can be obtained.

Origins and renormalization of the superparticle spectrum

The importance of Yukawa contributions to the renormalization of the spectrum in non-minimal supersymmetric models is illustrated in the cases of explicit lepton number violation (leading to the possibility of singly produced sneutrinos at LEP energies), an intermediate scale singlet neutrino and negative mass squared parameters (possibly modifying fine-tuning considerations), and a grand-unified sector. The relevance of model-dependent renormalization to the supersymmetric flavor problem is emphasized. Sources of the flavor problem, some of which are newly identified, as well as possible solutions, are discussed and classified. It is then shown that gravitational interactions could lead (via a quadratically divergent singlet) to simple realizations of some of the low-energy frameworks that attempt to resolve the flavor problem.

HIGGS FACTORY μ+μ- COLLIDER AND THE SCALAR ELECTROWEAK SECTOR

We describe the concept of a Higgs factory μ+μ- collider and the process that will measure the particle width, particle spectrum, and normal and rare decay branching fractions. Such a factory would be able to distinguish between the standard, minimal supersymmetric, and nonminimal supersymmetric models. A μ+μ- collider with appropriate luminosity and energy spread will provide the Higgs factory. We describe the current design of such a collider and the higher energy multi-TeV collider development as well.

The dilaton-dominated supersymmetry breaking scenario in the context of the non-minimal supersymmetric model

The phenomenological consequences of the dilaton-type soft supersymmetry breaking terms in the context of the next to minimal supersymmetric standard model are investigated. We always find a very low top quark mass. As a consequence such string vacua are excluded by recent experimental results. The viability of the solution of the $\mu$ term through the introduction of a gauge singlet field is also briefly discussed.

Implications of a light stop for the spontanous CP breaking at finite temperature in a nonminimal supersymmetric model

We study the implications of a light stop for the spontaneous CP breaking at finite temperature in the Higgs sector of the Minimal Supersymmetric Standard Model with a gauge singlet. Assuming CP conservation at zero temperature, we show that the presence of a large mixing between the left- and the right-handed stops can trigger easily the spontaneous breaking of CP inside the bubbles nucleated during the electroweak phase transition. This allows to avoid the fine-tuning among the vacuum expectation values in the region of interest for the generation of the baryon asymmetry, namely the bubble walls, which has been recently analized.

Spontaneous CP breaking at finite temperature in a nonminimal supersymmetric model.

We study the spontaneous CP breaking at finite temperature in the Higgs sector in the Minimal Supersymmetric Standard Model with a gauge singlet. We consider the contribution of the standard model particles and that of stops, charginos, neutralinos, charged and neutral Higgs boson to the one-loop effective potential. Plasma effects for all bosons are also included. Assuming CP conservation at zero temperature, so that experimental constraints coming from, {\it e.g.}, the electric dipole moment of the neutron are avoided, and the electroweak phase transition to be of the first order and proceeding via bubble nucleation, we show that spontaneous CP breaking cannot occur inside the bubble mainly due to large effects coming from the Higgs sector. However, spontaneous CP breaking can be present in the region of interest for the generation of the baryon asymmetry, namely inside the bubble wall. The important presence of very tiny explicit CP violating phases is also commented.

Very light neutralino in nonminimal supersymmetric model

We show in the nonminimal supersymmetric model that there are parameter regions where a very light neutralino may exist without contradicting the present experimental data. We also investigate the possibility of its detection at the future 500 GeV e + e − collider.