Radiative Electroweak Symmetry Breaking Research Articles

Radiative effects in the scalar sector of vector leptoquark models

Gauge models with massive vector leptoquarks at the TeV scale provide a successful framework for addressing the B-physics anomalies. Among them, the 4321 model has been considered as the low-energy limit of some complete theories of flavor. In this work, we study the renormalization group evolution of this model, laying particular emphasis on the scalar sector. We find that, despite the asymptotic freedom of the gauge couplings, Landau poles can arise at relatively low scales due to the fast running of quartic couplings. Moreover, we discuss the possibility of radiative electroweak symmetry breaking and characterize the fine-tuning associated with the hierarchy between the electroweak scale and the additional TeV-scale scalars. Finally, the idea of scalar fields unification is explored, motivated by ultraviolet embeddings of the 4321 model.

Muon g \u2212 2 in Higgs-anomaly mediation

A simple model for the explanation of the muon anomalous magnetic moment was proposed by the present authors within the context of the minimal supersymmetric standard model [1, 2]: Higgs-anomaly mediation. In the setup, squarks, sleptons, and gauginos are massless at tree-level, but the Higgs doublets get large negative soft supersymmetry (SUSY) breaking masses squared {m}_{H_u}^2simeq {m}_{H_d}^2<0 at a certain energy scale, Minp. The sfermion masses are radiatively generated by anomaly mediation and Higgs-loop effects, and gaugino masses are solely determined by anomaly mediation. Consequently, the smuons and bino are light enough to explain the muon g − 2 anomaly while the third generation sfermions are heavy enough to explain the observed Higgs boson mass. The scenario avoids the SUSY flavor problem as well as various cosmological problems, and is consistent with the radiative electroweak symmetry breaking. In this paper, we show that, although the muon g − 2 explanation in originally proposed Higgs-anomaly mediation with Minp∼ 1016 GeV is slightly disfavored by the latest LHC data, the muon g − 2 can still be explained at 1σ level when Higgs mediation becomes important at the intermediate scale, Minp∼ 1012 GeV. The scenario predicts light SUSY particles that can be fully covered by the LHC and future collider experiments. We also provide a simple realization of {m}_{H_u}^2simeq {m}_{H_d}^2<0 at the intermediate scale.

On the tuning in the (mh,mt) plane: Standard Model criticality vs. high-scale SUSY

We analyse the predictions of both Higgs and top masses in a generic MSSM satisfying gauge-coupling unification, radiative electroweak symmetry breaking, with a natural (non-splitted) spectrum of soft-breaking terms, and an arbitrary soft-breaking scale (above a few TeV). This procedure allows us to identify a relatively narrow SUSY-allowed region in the (mh,mt) plane. We argue that the compatibility of the measured values of Higgs and top masses with this SUSY-allowed region is not less surprising than the corresponding compatibility with the narrow SM metastability region. As such, it provides a non-trivial signal of the compatibility of present data with a supersymmetric completion of the SM.

The Constrained NMSSM with right-handed neutrinos

In this article, we demonstrate that the inclusion of right-handed neutrino superfields in the Next-to-Minimal Supersymmetric Standard Model (NMSSM) makes it possible to impose universality conditions on the soft supersymmetry-breaking parameters at the Grand Unification scale, alleviating many of the problems of the so-called Constrained NMSSM. We have studied the renormalization group equations of this model, showing that right-handed neutrinos greatly contribute to driving the singlet Higgs mass-squared parameter negative, which makes it considerably easier to satisfy the conditions for radiative electroweak symmetry breaking. The new fields also lead to larger values of the Standard Model Higgs mass, thus making it easier to reproduce the measured value. As a consequence, all bounds from colliders and low-energy observables can be fulfilled in wide areas of the parameter space. However, the relic density in these regions is generally too high requiring some form of late entropy production to dilute the density of the lightest supersymmetric particle.

Radiative electroweak symmetry breaking in standard model extensions

We study the possibility of radiative electroweak symmetry breaking where loop corrections to the mass parameter of the Higgs boson trigger the symmetry breaking in various extensions of the Standard Model (SM). Although the mechanism fails in the SM, it is shown to be quite successful in several extensions which share a common feature of having an additional scalar around the TeV scale. The positive Higgs mass parameter at a high energy scale is turned negative in the renormalization group flow to lower energy by the cross couplings between the scalars in the Higgs potential. The type-II seesaw model with a TeV scale weak scalar triplet, a two-loop radiative neutrino mass model with new scalars at the TeV scale, the inert doublet model, scalar singlet dark matter model, and a universal seesaw model with an additional U(1) broken at the TeV scale are studied and shown to exhibit successful radiative electroweak symmetry breaking.

Electroweak symmetry breaking and collider signatures in the next-to-minimal composite Higgs model

We conduct a detailed numerical analysis of the composite pseudo-Nambu-Goldstone Higgs model based on the next-to-minimal coset SO(6)/SO(5) ≅ SU(4)/Sp(4), featuring an additional SM singlet scalar in the spectrum, which we allow to mix with the Higgs boson. We identify regions in parameter space compatible with all current exper-imental constraints, including radiative electroweak symmetry breaking, flavour physics, and direct searches at colliders. We find the additional scalar, with a mass predicted to be below a TeV, to be virtually unconstrained by current LHC data, but potentially in reach of run 2 searches. Promising indirect searches include rare semi-leptonic B decays, CP violation in Bs mixing, and the electric dipole moment of the neutron.

Natural supersymmetry from extra dimensions

We show that natural supersymmetry can be embedded in a five-dimensional theory with supersymmetry breaking \`a la Scherk-Schwarz (SS). There is no 'gluino-sucks' problem for stops localized in the four-dimensional brane and gluinos propagating in the full five-dimensional bulk, and sub-TeV stops are easily accommodated. The $\mu / B_\mu$ problem is absent as well; the SS breaking generates a Higgsino Dirac mass and no bilinear Higgs mass parameter in the superpotential is required. Moreover, for non-maximal SS twists leading to $\tan \beta \simeq 1$, the Higgs spectrum is naturally split, in agreement with LHC data. The 125-GeV Higgs mass and radiative electroweak symmetry breaking can be accommodated by minimally extending the Higgs sector with $Y=0$ $SU(2)_L$ triplets.

WW scattering in a radiative electroweak symmetry breaking scenario

A classically scale invariant (CSI) extension of the standard model (SM) induces radiative electroweak symmetry breaking and predicts anomalously large Higgs self-interactions. Hence, $W_LW_L$ scattering processes can be a good probe of the symmetry breaking mechanism. We develop a theoretical framework for perturbative computation and calculate $WW$ scattering amplitudes in a CSI model. It is shown that $W_LW_L$ scattering amplitudes satisfy the equivalence theorem, and that a large deviation of $W_LW_L$ differential cross sections from the SM predictions is predicted depending on the c.m. energy and scattering angle. The results are more accurate than those based on the effective-potential approach. A prescription to implement predictions of the CSI model to Monte Carlo event generators is also presented.

Minimal but non-minimal inflation and electroweak symmetry breaking

We consider the most minimal scale invariant extension of the standard model that allows for successful radiative electroweak symmetry breaking and inflation. The framework involves an extra scalar singlet, that plays the rôle of the inflaton, and is compatibile with current experimental bounds owing to the non-minimal coupling of the latter to gravity. This inflationary scenario predicts a very low tensor-to-scalar ratio r ≈ 10−3, typical of Higgs-inflation models, but in contrast yields a scalar spectral index ns ≃ 0.97 which departs from the Starobinsky limit. We briefly discuss the collider phenomenology of the framework.

Vacuum stability and radiative electroweak symmetry breaking in an SO(10) dark matter model

Vacuum stability in the Standard Model is problematic as the Higgs quartic self-coupling runs negative at a renormalization scale of about $10^{10}$ GeV. We consider a non-supersymmetric SO(10) grand unification model for which gauge coupling unification is made possible through an intermediate scale gauge group, $G_{\text{int}}=\text{SU}(3)_C\otimes \text{SU}(2)_L\otimes \text{SU}(2)_R \otimes \text{U}(1)_{B-L}$. $G_{\text{int}}$ is broken by the vacuum expectation value of a 126 of SO(10) which not only provides for neutrino masses through the seesaw mechanism but also preserves a discrete $\mathbb{Z}_2$ that can account for the stability of a dark matter candidate, here taken to be the Standard Model singlet component of a bosonic 16. We show that in addition to these features the model insures the positivity of the Higgs quartic coupling through its interactions to the dark matter multiplet and 126. We also show that the Higgs mass squared runs negative triggering electroweak symmetry breaking. Thus, the vacuum stability is achieved along with radiative electroweak symmetry breaking and captures two more important elements of supersymmetric models without low-energy supersymmetry. The conditions for perturbativity of quartic couplings and for radiative electroweak symmetry breaking lead to tight upper and lower limits on the dark matter mass, respectively, and this dark matter mass region (1.35-2 TeV) can be probed in future direct detection experiments.

20pAL-11 輻射補正により電弱対称性が破られる模型のWボソン縦波散乱による間接探索

20pAL-11 輻射補正により電弱対称性が破られる模型のWボソン縦波散乱による間接探索

Direct and indirect signals of natural composite Higgs models

We present a comprehensive numerical analysis of a four-dimensional model with the Higgs as a composite pseudo-Nambu-Goldstone boson that features a calculable Higgs potential and protective custodial and flavour symmetries to reduce electroweak fine-tuning. We employ a novel numerical technique that allows us for the first time to study constraints from radiative electroweak symmetry breaking, Higgs physics, electroweak precision tests, flavour physics, and direct LHC bounds on fermion and vector boson resonances in a single framework. We consider four different flavour symmetries in the composite sector, one of which we show to not be viable anymore in view of strong precision constraints. In the other cases, all constraints can be passed with a sub-percent electroweak fine-tuning. The models can explain the excesses recently observed in $WW$, $WZ$, $Wh$ and $\ell^+\ell^-$ resonance searches by ATLAS and CMS and the anomalies in angular observables and branching ratios of rare semi-leptonic $B$ decays observed by LHCb. Solving the $B$ physics anomalies predicts the presence of a dijet or $t\bar t$ resonance around 1 TeV just below the sensitivity of LHC run 1. We discuss the prospects to probe the models at run 2 of the LHC. As a side product, we identify several gaps in the searches for vector-like quarks at hadron colliders, that could be closed by reanalyzing existing LHC data.

Radiative electroweak symmetry breaking models

The possibility of electroweak symmetry breaking radiatively with Coleman-Weinberg mechanism is examined. New mixed quartic coupling of the Higgs boson with an extra scalar field allows radiative electroweak symmetry breaking but it comes with a Landau pole very near the weak scale.

Non-thermal CMSSM with a 125 GeV Higgs

We study the phenomenology of the CMSSM/mSUGRA with non-thermal neutralino dark matter. Besides the standard parameters of the CMSSM we include the reheating temperature as an extra parameter. Imposing radiative electroweak symmetry breaking with a Higgs mass around 125 GeV and no dark matter overproduction, we contrast the scenario with dierent experimental bounds from colliders (LEP, LHC), cosmic microwave background (Planck), direct (LUX, XENON100, CDMS, IceCube) and indirect (Fermi) dark matter searches. The allowed parameter space is characterised by a Higgsino- like LSP with a mass around 300 GeV. The observed dark matter abundance can be saturated for reheating temperatures around 2 GeV while larger temperatures require extra non-neutralino dark matter candidates and extend the allowed parameter space. Sfermion and gluino masses are in the few TeV region. These scenarios can be achieved in string models of sequestered supersymmetry breaking which avoid cosmological moduli problems and are compatible with gauge coupling unication. Astrophysics and particle physics experiments will fully investigate this non-thermal scenario in the near future.

Light Higgsinos in pure gravity mediation

Pure gravity mediation (PGM), with two free parameters, is a minimalistic approach to supergravity models, yet is capable of incorporating radiative electroweak symmetry breaking, a Higgs mass in agreement with the experimental measurement, without violating any phenomenological constraints. The model may also contain a viable dark matter candidate in the form of a wino. Here, we extend the minimal model by allowing the $\mu$-term to be a free parameter (equivalent to allowing the two Higgs soft masses, $m_1$ and $m_2$, to differ from other scalar masses) which are set by the gravitino mass. In particular, we examine the region of parameter space where $\mu \ll m_{3/2}$ in which case, the Higgsino becomes the lightest supersymmetric particle (LSP) and a dark matter candidate. We also consider a generalization of PGM which incorporates a Peccei-Quinn symmetry which determines the $\mu$-term dynamically. In this case, we show that the dark matter may either be in the form of an axion and/or a neutralino, and that the LSP may be either a wino, bino, or Higgsino.

Universality in pure gravity mediation with vector multiplets

We consider models of pure gravity mediation in which scalar mass universality is imposed at the grand unified scale and gaugino masses are generated through loops. The minimal model requires a very restricted range for $\mathrm{tan}\ensuremath{\beta}\ensuremath{\approx}2--3$ and scalar masses (set by the gravitino mass) of order 300 TeV--1.5 PeV in order to obtain a Higgs mass near 126 GeV. Here we augment the minimal model with one or more sets of vector multiplets (either a $\mathbf{10}$ and $\overline{\mathbf{10}}$ pair or one or more $\mathbf{5}$ and $\overline{\mathbf{5}}$ pairs). If coupled to the minimal supersymmetric standard model Higgs, these allow for radiative electroweak symmetry breaking over a significantly larger range of $\mathrm{tan}\ensuremath{\beta}\ensuremath{\approx}2--40$ and can fit the Higgs mass with much smaller values of the gravitino mass. In these models, the lightest supersymmetric particle is often the bino, and in order to satisfy the relic density constraint, the bino must be nearly degenerate with either the wino or gluino. In the models considered here, bino gluino coannihilations determine the relic density and since the two are nearly degenerate, LHC limits on the gluino mass are greatly relaxed allowing light relatively gravitinos and gluino masses well within the reach of the LHC.

Higgs partner searches and dark matter phenomenology in a classically scale invariant Higgs boson sector

In a previous work, a classically scale invariant extension of the standard model was proposed, as a potential candidate for resolving the hierarchy problem, by minimally introducing a complex gauge singlet scalar, and generating radiative electroweak symmetry breaking by means of the Coleman- Weinberg Mechanism. Postulating the singlet sector to respect the CP-symmetry, the existence of a stable pseudoscalar dark matter candidate with a mass in the TeV range was demonstrated. More- over, the model predicted the presence of another physical CP-even Higgs boson (with suppressed tree-level couplings), in addition to the 125 GeV scalar discovered by the LHC. The viable region of the parameter space was determined by various theoretical and experimental considerations. In this work, we continue to examine the phenomenological implications of the proposed minimal sce- nario by considering the constraints from the dark matter relic density, as determined by the Planck collaboration, as well as the direct detection bounds from the LUX experiment. Furthermore, we investigate the implications of the collider Higgs searches for the additional Higgs boson. Our results are comprehensively demonstrated in unified exclusion plots, which analyze the viable region of the parameter space from all relevant angles, demonstrating the testability of the proposed scenario.

Peccei–Quinn symmetric pure gravity mediation

Successful models of Pure Gravity Mediation (PGM) with radiative electroweak symmetry breaking can be expressed with as few as two free parameters which can be taken as the gravitino mass and $\tan \beta$. These models easily support a 125-126 GeV Higgs mass at the expense of a scalar spectrum in the multi-TeV range and a much lighter wino as the lightest supersymmetric particle. In these models, it is also quite generic that the Higgs mixing mass parameter, $\mu$, which is determined by the minimization of the Higgs potential is also in the multi-TeV range. For $\mu > 0$, the thermal relic density of winos is too small to account for the dark matter. The same is true for $\mu < 0$ unless the gravitino mass is of order 500 TeV. Here, we consider the origin of a multi-TeV $\mu$ parameter arising from the breakdown of a Peccei-Quinn (PQ) symmetry. A coupling of the PQ-symmetry breaking field, $P$, to the MSSM Higgs doublets, naturally leads to a value of $\mu \sim \langle P \rangle^2 /M_P \sim \mathcal{O}(100)$ TeV and of order that is required in PGM models. In this case, axions make up the dark matter or some fraction of the dark matter with the remainder made up from thermal or non-thermal winos. We also provide solutions to the problem of isocurvature fluctuations with axion dark matter in this context.

Next-to-minimal SOFTSUSY

We describe an extension to the SOFTSUSY program that provides for the calculation of the sparticle spectrum in the Next-to-Minimal Supersymmetric Standard Model (NMSSM), where a chiral superfield that is a singlet of the Standard Model gauge group is added to the Minimal Supersymmetric Standard Model (MSSM) fields. Often, a Z3 symmetry is imposed upon the model. SOFTSUSY can calculate the spectrum in this case as well as the case where general Z3 violating (denoted as ▪) terms are added to the soft supersymmetry breaking terms and the superpotential. The user provides a theoretical boundary condition for the couplings and mass terms of the singlet. Radiative electroweak symmetry breaking data along with electroweak and CKM matrix data are used as weak-scale boundary conditions. The renormalisation group equations are solved numerically between the weak scale and a high energy scale using a nested iterative algorithm. This paper serves as a manual to the NMSSM mode of the program, detailing the approximations and conventions used. Program SummaryProgram title: SOFTSUSYCatalogue identifier: ADPM_v4_0Program summary URL:http://cpc.cs.qub.ac.uk/summaries/ADPM_v4_0.htmlProgram obtainable from: CPC Program Library, Queen’s University, Belfast, N. IrelandLicensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.htmlNo. of lines in distributed program, including test data, etc.: 154886No. of bytes in distributed program, including test data, etc.: 1870890Distribution format: tar.gzProgramming language: C++, fortran.Computer: Personal computer.Operating system: Tested on Linux 3.x.Word size: 64 bitsClassification: 11.1, 11.6.Does the new version supersede the previous version?: YesCatalogue identifier of previous version: ADPM_v3_0Journal reference of previous version: Comput. Phys. Comm. 183 (2012) 785Nature of problem: Calculating supersymmetric particle spectrum and mixing parameters in the next-to-minimal supersymmetric standard model. The solution to the renormalisation group equations must be consistent with boundary conditions on supersymmetry breaking parameters, as well as on the weak-scale boundary condition on gauge couplings, Yukawa couplings and the Higgs potential parameters.Solution method: Nested iterative algorithm and numerical minimisation of the Higgs potential.Reasons for new version: Major extension to include the next-to-minimal supersymmetric standard model.Summary of revisions: Added additional supersymmetric and supersymmetry breaking parameters associated with the additional gauge singlet. Electroweak symmetry breaking conditions are significantly changed in the next-to-minimal mode, and some sparticle mixing changes. An interface to NMSSMTools has also been included. Some of the object structure has also changed, and the command line interface has been made more user friendly.Restrictions: SOFTSUSY will provide a solution only in the perturbative regime and it assumes that all couplings of the model are real (i.e. CP-conserving). If the parameter point under investigation is non-physical for some reason (for example because the electroweak potential does not have an acceptable minimum), SOFTSUSY returns an error message.Running time: A few seconds per parameter point.

Viable dark matter via radiative symmetry breaking in a scalar singlet Higgs portal extension of the standard model.

We consider the generation of dark matter mass via radiative electroweak symmetry breaking in an extension of the conformal standard model containing a singlet scalar field with a Higgs portal interaction. Generating the mass from a sequential process of radiative electroweak symmetry breaking followed by a conventional Higgs mechanism can account for less than 35% of the cosmological dark matter abundance for dark matter mass M(s)>80 GeV. However, in a dynamical approach where both Higgs and scalar singlet masses are generated via radiative electroweak symmetry breaking, we obtain much higher levels of dark matter abundance. At one-loop level we find abundances of 10%-100% with 106 GeV<M(s)<120 GeV. However, when the higher-order effects needed for consistency with a 125 GeV Higgs mass are estimated, the abundance becomes 10%-80% for 80 GeV<M(s)<96 GeV, representing a significant decrease in the dark matter mass. The dynamical approach also predicts a small scalar-singlet self-coupling, providing a natural explanation for the astrophysical observations that place upper bounds on dark matter self-interaction. The predictions in all three approaches are within the M(s)>80 GeV detection region of the next generation XENON experiment.