Supersymmetric Standard Model Research Articles

Global LHC constraints on electroweak-inos with SModelS v2.3

Electroweak-inos, superpartners of the electroweak gauge and Higgs bosons, play a special role in supersymmetric theories. Their intricate mixing into chargino and neutralino mass eigenstates leads to a rich phenomenology, which makes it difficult to derive generic limits from LHC data. In this paper, we present a global analysis of LHC constraints for promptly decaying electroweak-inos in the context of the minimal supersymmetric standard model, exploiting the SMODELS software package. Combining up to 16 ATLAS and CMS searches for which electroweak-ino efficiency maps are available in SMODELS, we study which combinations maximise the sensitivity in different regions of the parameter space, how fluctuations in the data in individual analyses influence the global likelihood, and what is the resulting exclusion power of the combination compared to the analysis-by-analysis approach.

B 0— B¯0 mixing in the U(1) X SSM

U(1) X SSM is a non-universal Abelian extension of the Minimal Supersymmetric Standard Model and its local gauge group is extended to SU(3) C × SU(2) L × U(1) Y × U(1) X . Based on the latest data of neutral meson mixing and experimental limitations, we investigate the process of B0−B0¯ mixing in U(1) X SSM. Using the effective Hamiltonian method, the Wilson coefficients and mass difference Δm B are derived. The abundant numerical results verify that vS,MD2,λC,μ,M2,tanβ,gYX,M1 and λ H are sensitive parameters to the process of B0−B0¯ mixing. With further measurement in the experiment, the parameter space of the U(1) X SSM will be further constrained during the mixing process of B0−B0¯ .

Precision predictions for dark matter with DM@NLO in the MSSM

We present DM@NLO, a Fortran 77 based program with a C++ interface dedicated to precision calculations of dark matter (DM) (co)annihilation cross-sections and elastic dark matter-nucleon scattering amplitudes in the minimal supersymmetric (SUSY) Standard Model (MSSM) at next-to-leading order (NLO) in perturbative (SUSY) QCD. If the annihilating initial particles carry an electric or colour charge, the Sommerfeld enhanced cross section is included as well and can be matched to the NLO cross section. We review these calculations including technical details relevant for using the code. We illustrate their impact by applying DM@NLO to an example scenario in the constrained MSSM.

Comparative analysis on the validity of golden ratio, tri-bimaximal, hexagonal and bimaximal neutrino mixing patterns under the radiative corrections

We study the comparative analysis on the validity of four popular leptonic mixing patterns viz, golden ratio (GR), tri-bimaximal (TBM), hexagonal mixing (HM) and bimaximal (BM), which are assumed to be defined at high energy scale, M R = 1016 GeV. We perform numerical analysis of low energy neutrino oscillation parameters through the renormalisation group equations (RGEs) in both standard model (SM) and minimal supersymmetric standard model (MSSM) with the inclusion of scale dependent vacuum expectation value (VEV). The sum of three absolute neutrino mass eigenvalues obtained from the latest Planck cosmological data, ∑∣m i ∣ < 0.12 eV, is used as a constraint in the analysis of these four leptonic mixing patterns. We consider both normal hierarchical (NH) model and inverted hierarchical (IH) model in the analysis of these four leptonic mixing patterns, with SUSY breaking scale at m s = 1 TeV and tanβ=67 . Among the four mixing patterns, GR is found to satisfy the latest Planck cosmological data, ∑∣m i ∣ < 0.12 eV. Further analysis on the effect of the variation of SUSY breaking scale 1 TeV ≤ m s ≤ 14 TeV is also studied for GR neutrino mixing pattern in NH.

Precise estimate of charged Higgsino/Wino decay rate

Higgsinos and Winos in the supersymmetric Standard Model are prime candidates for dark matter due to their weakly interacting nature. The mass differences between their charged components (charginos) and neutral components (neutralinos) become degenerate when other superparticles are heavy, resulting in long-lived charginos. In the case of the Winos, the mass difference is approximately 160 MeV across a wide range of the parameter space. Consequently, the chargino decays into the lightest neutralino, emitting a single charged pion. For Higgsinos, however, mass differences ranging from O(0.1) GeV to O(1) GeV are possible, leading to a variety of decay channels. In this paper, we extend our previous analysis of Wino decay to the chargino with a larger mass difference. We emphasize characterizing its decay signatures through leptonic and hadronic modes. By utilizing the latest experimental data, we perform a comprehensive study of the decay rate calculations incorporating these hadronic modes to determine the impact on the predicted chargino lifetime. Additionally, we conduct next-to-leading order (NLO) calculations for the leptonic decay modes. Our NLO results can be applied to the case of more general fermionic electroweak multiplets, e.g., quintuplet dark matter.

Generating the μ-term and Neutrino Mass via the Clockwork Mechanism in the Supersymmetric Standard Model

Generating the μ-term and Neutrino Mass via the Clockwork Mechanism in the Supersymmetric Standard Model

(g-2)μ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$(g-2)_\\mu $$\\end{document} and stau coannihilation: dark matter and collider analysis

Slepton coannihilation is one of the most promising scenarios that can bring the predicted Dark Matter (DM) abundance in the the Minimal Supersymmetric Standard Model (MSSM) into agreement with the experimental observation. In this scenario, the lightest supersymmetric particle (LSP), usually assumed to be the lightest neutralino, χ~10\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ ilde{\\chi }_{1}^0$$\\end{document} can serve as a Dark Matter (DM) candidate while the sleptons as the next-to-LSPs (NLSPs) lie close in mass. In our previous studies analyzing the electroweak sector of MSSM, a degeneracy between the three generations of sleptons was assumed for the sake of simplicity. In case of slepton coannihilation this directly links the smuons involved in the explanation for (g-2)μ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$(g-2)_\\mu $$\\end{document} to the coannihilating NLSPs required to explain the DM content of the universe. On the other hand, in well-motivated top-down models such degeneracy do not hold, and often the lighter stau turns out to be the NLSP at the electroweak (EW) scale, with the smuons (and selectrons) somewhat heavier. In this paper we analyze such a scenario at the EW scale assuming non-universal slepton masses where the first two generations of sleptons are taken to be mass-degenerate and heavier than the staus, enforcing stau coannihilation. We analyze the parameter space of the electroweak MSSM in the light of a variety of experimental data namely, the DM relic density and direct detection limits, LHC data and especially, the discrepancy between the experimental result for the anomalous magnetic moment of the muon, (g-2)μ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$(g-2)_\\mu $$\\end{document}, and its Standard Model (SM) prediction. We find an upper limit on the lightest neutralino mass, the lighter stau mass and the mass of the tau sneutrino of about ∼550GeV\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sim 550 \\,\\, {\ extrm{GeV}}$$\\end{document}. In contrast to the scenario with full degeneracy among the three families of sleptons, the upper limit on the light smuon/selectron mass moves up by ∼200GeV\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sim 200 \\,\\, {\ extrm{GeV}}$$\\end{document}. We analyze the DD prospects as well as the physics potential of the HL-LHC and a future high-energy e+e-\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$e^+e^-$$\\end{document} collider to investigate this scenario further. We find that the combination DD experiments and e+e-\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$e^+e^-$$\\end{document} collider searches with center of mass energies up to s∼1100GeV\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sqrt{s} \\sim 1100 \\,\\, {\ extrm{GeV}}$$\\end{document} can fully cover this scenario.

Lepton flavor violating decays lj → liγγ

In this paper, we study the lepton flavor violating decays of the lj→liγγ (j=2, 3; i=1, 2) processes under the U(1)XSSM. The U(1)XSSM is the addition of three singlet new Higgs superfields and right-handed neutrinos to the minimal supersymmetric standard model (MSSM). Based on the latest experimental constraints of lj→liγγ, we analyze the effects of different sensitive parameters on the results and made reasonable predictions for future experimental development. Numerical analysis shows that many parameters have a greater or lesser effect on lepton flavor violation (LFV), but the main sensitive parameters and sources leading to LFV are the non-diagonal elements involving the initial and final leptons. This work could provide a basis for the discovery of the existence of new physics (NP).

Supersymmetric U(1) B-L flat direction and NANOGrav 15 year data

We show that, when connected with monopoles, the flat D-flat direction breaking the local U(1) B-L symmetry as an extension of the minimal supersymmetric standard model can be responsible for the signal of a stochastic gravitational wave background recently reported by NANOGrav collaborations, while naturally satisfying constraints at high frequency band.Thanks to the flatness of the direction, a phase of thermal inflation arises naturally.The reheating temperature is quite low, and suppresses signals at frequencies higher than the characteristic frequency set by the reheating temperature.Notably, forthcoming spaced based experiments such as LISA can probe the cutoff frequency, providing an indirect clue of the scale of soft SUSY-breaking mass parameter.

Invisible dark matter decays of a non-Standard Model like CP-even scalar boson

We investigate two extensions of the standard model that include particle dark matter candidates: the Next-to-Two Higgs Doublet Model and the Next-to-minimal Supersymmetric Standard Model. These models feature a non-Standard Model like CP-even scalar with a sub-TeV mass, denoted by H2, among other particles. At a 13 TeV proton–proton collider, the primary production channel for such scalars is via the fusion of a pair of gluons. Subsequently, these scalars can decay invisibly into a pair of dark matter candidates, which can be dominant. In the supersymmetric model, it is possible for the Lightest Supersymmetric Particle (LSP) and Next-to Lightest Supersymmetric Particle (NLSP) to be mass degenerate, leading to quasi-invisible H2 decays to LSP+NLSP and NLSP+NLSP. We present the predictions of both models for this challenging scenario while ensuring compatibility with recent experimental constraints.

Non-thermal WIMP production from higher order moduli decay

In a non-standard cosmological scenario heavy, long-lived particles, which we call moduli, dominate the energy density prior to Big Bang Nucleosynthesis. Weakly Interacting Massive Particles (WIMPs) may be produced non-thermally from moduli decays. The final relic abundance then depends on additional parameters such as the branching ratio of moduli to WIMPs and the modulus mass. This is of interest for WIMP candidates, such as a bino-like neutralino, where thermal production in standard cosmology leads to an overdensity. Previous works have shown that the correct dark matter (DM) relic density can then still be obtained if the moduli, with mass less than 107 GeV, decay to WIMPs with a branching ratio of less than 10-4. This upper bound could easily be violated once higher order corrections, involving final states with more than two particles, are included. We compute the branching ratios of three- and four-body decays of a modulus into final states involving two DM particles for general couplings. We then apply these expressions to sparticle production within the Minimal Supersymmetric Standard Model (MSSM) with neutralino DM. We find that this upper bound on the branching ratio can be satisfied in simplified models through an appropriate choice of as yet undetermined couplings. However, in the MSSM, it requires sparticle masses to be very close to half the modulus mass, in contrast to the idea of weak-scale supersymmetry.

Hunting ewinos and a light scalar of Z3-NMSSM with a bino-like dark matter in top squark decays at the LHC

We explore a possible signal of the presence of relatively light electroweakinos (ewinos) and a singlet-like scalar (aS) of the Z3-symmetric Next-to-Minimal Supersymmetric Standard Model (Z3-NMSSM) in the cascade decays of not so heavy top squarks ( {m}_{{tilde{t}}_1} ≲ 1.5 TeV) that may be produced in pairs at the Large Hadron Collider LHC. We work in a scenario where the lightest (next-to-lightest) SUSY particle is bino (singlino)-like with its mass below 100 GeV and is mildly tempered with higgsino and singlino admixtures. The singlet-like scalar provides an annihilation funnel for the bino-like states such that the latter could act as a viable dark matter candidate, unlike what is now highly constrained in the MSSM. We consider a pair of immediately heavier neutralinos and the lighter chargino which all are higgsino-like with masses in the range ~ 0.5–1 TeV and are still compatible with all experimental constraints. While these states may not be accessible in their direct searches at the LHC in our present scenario, such ewinos could still be traced in the decays of the top squarks of the above-mentioned kind. We consider the signal final state at the LHC. We find that while a usual cut-based analysis (CBA) of LHC data worth 300 fb−1 would be unable to discover such excitations, a multivariate analysis (MVA) can be reasonably sensitive to higgsino-like ewinos having masses ≳ 650 GeV when {m}_{{tilde{t}}_1} ≳ 1 TeV. On the other hand, with 3000 fb−1 of data, these masses become accessible in a CBA while even an MVA on such a data set is unlikely to find these ewinos with masses around 1 TeV when {m}_{{tilde{t}}_1} hits ∼ 1.5 TeV.

Lighting up the LHC with Dark Matter

We show that simultaneously explaining dark matter and the observed value of the muon’s magnetic dipole moment may lead to yet unexplored photon signals at the LHC. We consider the Minimal Supersymmetric Standard Model with electroweakino masses in the few-to-several hundred GeV range, and opposite sign of the Bino mass parameter with respect to both the Higgsino and Wino mass parameters. In such region of parameter space, the spin-independent elastic scattering cross section of a Bino-like dark matter candidate in direct detection experiment is suppressed by cancellations between different amplitudes, and the observed dark matter relic density can be realized via Bino-Wino co-annihilation. Moreover, the observed value of the muon’s magnetic dipole moment can be explained by Bino and Wino loop contributions. Interestingly, “radiative” decays of Wino-like neutralinos into the lightest neutralino and a photon are enhanced, whereas decays into leptons are suppressed. While these decay patterns weaken the reach of multi-lepton searches at the LHC, the radiative decay opens a new window for probing dark matter at the LHC through the exploration of parameter space regions beyond those currently accessible. To complement the current electroweakino searches, we propose searching for a single (soft) photon plus missing transverse energy, accompanied by a hard initial state radiation jet.

Stability of electroweak vacuum and supersymmetric contribution to muon g − 2

We study the stability of the electroweak vacuum in the supersymmetric (SUSY) standard model (SM), paying particular attention to its relation to the SUSY contribution to the muon anomalous magnetic moment aμ. If the SUSY contribution to aμ is sizable, the electroweak vacuum may become unstable because of enhanced trilinear scalar interactions. With aμ being fixed, larger slepton masses require more enhanced trilinear couplings, which make the electroweak vacuum more unstable. Thus, assuming SUSY contribution to aμ being sizable, an upper bound on the slepton masses is obtained. We give a detailed prescription to perform a full one-loop calculation of the decay rate of the electroweak vacuum for the case that the SUSY contribution to aμ is enhanced. We also give an upper bound on the slepton masses as a function of the SUSY contribution to aμ.

SModelS v2.3: Enabling global likelihood analyses

We present version 2.3 of SModelS, a public tool for the fast reinterpretation of LHC searches for new physics on the basis of simplified-model results. The main new features are a database update with the latest available experimental results for full Run 2 luminosity, comprising in particular a large variety of electroweak-ino searches, and the ability to combine likelihoods from different analyses. This enables statistically more rigorous constraints and opens the way for global likelihood analyses for LHC searches. The physics impact is demonstrated for the electroweak-ino sector of the minimal supersymmetric standard model.

Cosmology with a supersymmetric local B - L model

We propose a minimal gauged U(1) B-L extension of the minimal supersymmetric Standard Model (MSSM) which resolves the cosmological moduli problem via thermal inflation, and realizes late-time Affleck-Dine leptogensis so as to generate the right amount of baryon asymmetry at the end of thermal inflation. The present relic density of dark matter can be explained by sneutrinos, MSSM neutralinos, axinos, or axions. Cosmic strings from U(1) B-L breaking are very thick, and so the expected stochastic gravitational wave background from cosmic string loops has a spectrum different from the one in the conventional Abelian-Higgs model, as would be distinguishable at least at LISA and DECIGO. The characteristic spectrum is due to a flat potential, and may be regarded as a hint of supersymmetry. Combined with the resolution of moduli problem, the expected signal of gravitational waves constrains the U(1) B-L breaking scale to be 𝒪(1012–13) GeV. Interestingly, our model provides a natural possibility for explaining the observed ultra-high-energy cosmic rays thanks to the fact that the core width of strings in our scenario is very large, allowing a large enhancement of particle emissions from the cusps of string loops. Condensation of LHu flat-direction inside of string cores arises inevitably and can also be the main source of the ultra-high-energy cosmic rays accompanied by ultra-high-energy lightest supersymmetric particles.

The absence of observable proton decay in a global SU(5) F-theory model

We begin with an E8× E8 Heterotic model broken to an SU(5)gauge× U(1)X and a twin SU(5)gauge× U(1)X, where one SU(5) and its spectrum is identified as the visible sector while the other can be identified as a hidden twin sector. In both cases we obtain the minimal supersymmetric standard model (MSSM) spectrum after Wilson-line symmetry-breaking enhanced by a low energy R-parity and ℤ4R\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {\\mathbb{Z}}_4^R $$\\end{document} symmetry. We argue that there will not be any observable proton decay in this model.

A novel probe of supersymmetry in light of nanohertz gravitational waves

A new era of exploring the early Universe may have begun with the recent strong evidence for the stochastic gravitational wave (GW) background from the data reported by NANOGrav, EPTA (including InPTA data), PPTA, and CPTA. Inspired by this, we propose a new potential source of stochastic GWs in the minimal supersymmetric standard model (MSSM), which could be the theory at a very high energy scale. This source is the “axion” field in the Higgs multiplets when the Higgs field takes a large value along the D-flat direction in the early Universe, for example, during inflation. The axion motion triggers the instability of the standard model U(1) and/or SU(3) gauge fields, producing stochastic GWs during the inflation. This scenario can be seen as a simple UV completion of the commonly studied models where an axion spectator/inflaton is coupled to a hidden U(1) or SU(N) gauge field without matter fields. Thus the nanohertz GWs may be a sign of supersymmetry. Primordial magnetic field production is also argued. In addition, we point out the simple possibility that this axion within the MSSM drives inflation.

Automated choice for the best renormalization scheme in BSM models

The explorations of models beyond the Standard Model (BSM) naturally involve scans over the unknown BSM parameters. On the other hand, high precision predictions require calculations at the loop-level and thus a renormalization of (some of) the BSM parameters. Often many choices are possible for the renormalization scheme (RS). This concerns the choice of the set of to-be-renormalized parameters out of a larger set of BSM parameters, but can also concern the type of renormalization condition which is chosen for a specific parameter. A given RS can be well suited to yield “stable” and “well behaved” higher-order corrections in one part of the BSM parameter space, but can fail completely in other parts, which may not even be noticed numerically if an isolated parameter point is investigated, or when the higher-order BSM calculations are performed in an automated, not supervised set-up. Consequently, the (automated) exploration of BSM models requires a choice of a good RS before the calculation is performed. We propose a new method with which such a choice can be performed. We demonstrate the feasibility of our new method in the chargino/neutralino sector of the Minimal Supersymmetric Standard Model (MSSM), but stress the general applicability of our method to all types of BSM models.

Light Higgs boson in the NMSSM confronted with the CMS di-photon and di-tau excesses* *Supported by the National Natural Science Foundation of China (12275066, 11605123, 11547103, 12074295)

In 2018, the CMS collaboration reported a di-photon excess at approximately 95.3 GeV with a local significance of 2.8 σ. Interestingly, the CMS collaboration also recently reported a di-tau excess at GeV with a local significance of . In addition, a excess at 98 GeV with a local significance of 2.3 σ was reported from LEP data approximately twenty years ago. In this study, we addressed the interpretation of these excesses together with a light Higgs boson in the next-to-minimal supersymmetric standard model (NMSSM). We conclude that, in the NMSSM, the GeV excesses are difficult to be satisfied simultaneously (not possible globally at the level or simultaneously at the level). We analyzed two partially-satisfied scenarios: global and small di-photon. An approximate equation of global fit to the three excesses was derived, and two representative types of surviving samples were analyzed in detail. Given that the mass regions of these excesses are near the Z boson, we also checked the light Higgs boson in the -associated channels. The detailed results may be useful for further checking the low-mass-region excesses in the future.