Gaugino Mass Parameters Research Articles

Light Higgsino scenario confronted with the muon g−2

Light higgsinos below several hundred GeV are favored or required by the naturalness of low energy supersymmetry. If only higgsinos are light while other sparticles are sufficiently heavy, we have the so-called light higgsino scenario. Confronted with the muon $g-2$ data, this scenario is examined in this work. Since in this scenario the LSP (lightest sparticle) is higgsino-like, we need to also consider the dark matter constraints. Assuming a light higgsino mass parameter $\mu$ in the range of 100-400 GeV while gaugino mass parameters above TeV, we explore the parameter space under the muon $g-2$ data and the dark matter constraints. We find that, to explain the muon $g-2$ anomaly at $2\sigma$, the winos and sleptons are respectively upper bounded by 3 TeV and 800 GeV. In this case, we find that the light higgsino-like dark matter can sizably scatter with nucleon and thus the allowed parameter space can be covered almost fully by the future LZ dark matter detection project. We also perform a Monte Carlo simulation to figure out the potential of HL-LHC to detect the light sleptons in this scenario. It turns out that compared with the current LHC limits, the HL-LHC can further cover a part of the parameter space.

Higgs information in Split-SUSY at the LHC

Information theory turns out to be an interesting tool for studying the consequences of Higgs observations to various new physics candidate theories by means of the information measure as the entropy of Higgs-Boson through its various detection modes at the Large Hadron Collider. The present article investigates the parameter space of a supersymmetric scenario where sfermions and one of the Higgs superfields are decoupled, while the gauginos, Higgsinos, and the remaining Higgs doublet are still allowed to be lighter. Our analysis reveals that this is quite a viable choice in the light of LHC discovery of a Higgs which resembles the SM Higgs-Boson and nothing else so far. While the supersymmetry breaking scale MS could be as high as 1011 GeV or so, the most preferred values of the MS and tan⁡β are found to be around 3.6×107 GeV and 41 respectively, which is also consistent with the relic abundance of the neutralino dark matter. The corresponding value of neutralino (mχ˜10) LSP is estimated to be around 1.01 TeV. The preferred values of other parameters, namely, the Higgsino mass (μ) and gaugino mass parameters (M1 and M2) are found to be about 1.05 TeV, 1.74 TeV, and 2.57 TeV, respectively.

Discovery potential for split supersymmetry with thermal dark matter

Supersymmetric extensions of the Standard Model with scalar superpartners above 10 TeV are well motivated since the Higgs boson mass can be explained by quantum corrections while maintaining gauge coupling unification. If supersymmetry breaking is transmitted to gauginos via anomaly mediation, the gaugino masses are loop suppressed compared to scalar masses, and the lightest supersymmetric particle is the Higgsino or wino, which can be the dark matter. In this setup, we identify the regions of parameter space that reproduce the observed Higgs boson mass and the thermal abundance of dark matter. We analyze the effects of complex phases in the gaugino mass parameters on the electron electric dipole moment (EDM) and the dark matter scattering cross section. We find that, for scalar masses up to 10 PeV and any size of the complex phases, the model with Higgsino dark matter is within reach of planned experiments -- Advanced ACME via electron EDM and LUX-ZEPLIN via dark matter direct detection -- with complementary discovery potentials, and the model with wino dark matter is within reach of future electron EDM experiments.

Electric dipole moments and dark matter in a CP violating MSSM

We investigate electric dipole moments (EDMs) in a CP-violating minimal supersymmetric standard model with the Bino-like neutralino dark matter (DM) annihilating through the heavy Higgs funnel. Motivated by the current experimental results, in particular, the measured mass of the standard model-like Higgs boson, we consider a mass spectrum with stop masses of about 10 TeV. For the other sfermions, we consider masses of about 100 TeV. We show that CP-violating phases of the order of ten degrees in gaugino and Higgsino mass parameters are consistent with the current bound by EDMs of the electron, the neutron, and the mercury. They are within the reach of future experiments. We also show that effects of CP-violating phases induce a difference in DM-nucleon scattering cross section by a factor.

SU(5) with nonuniversal gaugino masses

We explore the sparticle spectroscopy of the supersymmetric SU(5) model with nonuniversal gaugino masses in light of latest experimental searches. We assume that the gaugino mass parameters are independent at the GUT scale. We find that the observed deviation in the anomalous magnetic moment of the muon can be explained in this model. The parameter space that explains this deviation predicts a heavy colored sparticle spectrum whereas the sleptons can be light. We also find a notable region of the parameter space that yields the desired relic abundance for dark matter. In addition, we analyze the model in light of latest limits from direct detection experiments and find that the parameter space corresponding to the observed deviation in the muon anomalous magnetic moment can be probed at some of the future direct detection experiments.

Study of dark matter physics in non-universal gaugino mass scenario

We study dark matter physics in the Minimal Supersymmetric Standard Model with non-universal gaugino masses at the unification scale. In this scenario, the specific ratio of wino and gluino masses realizes the electro-weak scale naturally and achieves 125 GeV Higgs boson mass. Then, relatively light higgsino is predicted and the lightest neutral particle, that is dominantly given by the neutral component of higgsino, is a good dark matter candidate. The direct detection of the dark matter is sensitive to not only a higgsino mass but also gaugino masses significantly. The upcoming XENON1T experiment excludes the parameter region where bino or gluino is lighter than about 2.5 TeV if the higgsino and the gaugino mass parameters have same signs. We see that the direct detection of dark matter gives stronger bound than the direct search at the LHC experiment when higgsino gives sizable contribution to the dark matter abundance.

Constraints on supersymmetric dark matter for heavy scalar superpartners

We study the constraints on neutralino dark matter in minimal low energy supersymmetry models and the case of heavy lepton and quark scalar superpartners. For values of the Higgsino and gaugino mass parameters of the order of the weak scale, direct detection experiments are already putting strong bounds on models in which the dominant interactions between the dark matter candidates and nuclei are governed by Higgs boson exchange processes, particularly for positive values of the Higgsino mass parameter mu. For negative values of mu, there can be destructive interference between the amplitudes associated with the exchange of the standard CP-even Higgs boson and the exchange of the non-standard one. This leads to specific regions of parameter space which are consistent with the current experimental constraints and a thermal origin of the observed relic density. In this article we study the current experimental constraints on these scenarios, as well as the future experimental probes, using a combination of direct and indirect dark matter detection and heavy Higgs and electroweakino searches at hadron colliders.

Low-mass neutralino dark matter in supergravity scenarios: phenomenology and naturalness

The latest experimental results from the LHC and dark matter (DM) searches suggest that the parameter space allowed in supersymmetric theories is subject to strong reductions. These bounds are especially constraining for scenarios entailing light DM particles. Previous studies have shown that light neutralino DM in the Minimal Supersymmetric Standard Model (MSSM), with parameters defined at the electroweak scale, is still viable when the low energy spectrum of the model features light sleptons, in which case, the relic density constraint can be fulfilled. In view of this, we have investigated the viability of light neutralinos as DM candidates in the MSSM, with parameters defined at the grand unification scale. We have analysed the optimal choices of non-universalities in the soft supersymmetry-breaking parameters for both, gauginos and scalars, in order to avoid the stringent experimental constraints. We show that light neutralinos, with a mass as low as 25 GeV, are viable in supergravity scenarios if the gaugino mass parameters at high energy are very non universal, while the scalar masses can remain of the same order. These scenarios typically predict a very small cross section of neutralinos off protons and neutrons, thereby being very challenging for direct detection experiments. However, a potential detection of smuons and selectrons at the LHC, together with a hypothetical discovery of a gamma-ray signal from neutralino annihilations in dwarf spheroidal galaxies could shed light on this kind of solutions. Finally, we have investigated the naturalness of these scenarios, taking into account all the potential sources of tuning. Besides the electroweak fine-tuning, we have found that the tuning to reproduce the correct DM relic abundance and that to match the measured Higgs mass can also be important when estimating the total degree of naturalness.

CP-violating phenomenological MSSM

We investigate the sensitivity of the next generation of flavor-based low-energy experiments to probe the supersymmetric parameter space in the context of the phenomenological MSSM (pMSSM), and examine the complementarity with direct searches for Supersymmetry at the 13 TeV LHC in a quantitative manner. To this end, we enlarge the previously studied pMSSM parameter space to include all physical non-zero CP-violating phases, namely those associated with the gaugino mass parameters, Higgsino mass parameter, and the tri-linear couplings of the top quark, bottom quark and tau lepton. We find that future electric dipole moment and flavor measurements can have a strong impact on the viability of these models even if the sparticle spectrum is out of reach of the 13 TeV LHC. In particular, the lack of positive signals in future low-energy probes would exclude values of the phases between ${\cal O}(10^{-2})$ and ${\cal O}(10^{-1})$. We also find regions of parameter space where large phases remain allowed due to cancellations. Most interestingly, in some rare processes, such as BR($B_s \to \mu^+ \mu^-$ ), we find that contributions arising from CP-violating phases can bring the potentially large SUSY contributions into better agreement with experiment and Standard Model predictions.

CP-safe gravity mediation and muong − 2

We propose a CP-safe gravity mediation model, where the phases of the Higgs B parameter, scalar trilinear couplings and gaugino mass parameters are all aligned. Since all dangerous CP violating phases are suppressed, we are now safe to consider low-energy SUSY scenarios. As an application, we consider a gravity mediation model explaining the observed muon $g-2$ anomaly. The CP-safe property originates in two simple assumptions: SUSY breaking in the K\"ahler potential and a shift symmetry of a SUSY breaking field $Z$. As a result of the shift symmetry, the imaginary part of $Z$ behaves as a QCD axion, leading to an intriguing possibility: the strong CP problem in QCD and the SUSY CP problem are solved simultaneously.

Invisible decays of the heavier Higgs boson in the minimal supersymmetric standard model

We consider the possibility that the heavier CP-even Higgs boson~($H^0$) in the minimal supersymmetric standard model (MSSM) decays invisibly into neutralinos in the light of the recent discovery of the 126 GeV resonance at the CERN Large Hadron Collider (LHC). For this purpose we consider the minimal supersymmetric standard model with universal, non-universal and arbitrary boundary conditions on the supersymmetry breaking gaugino mass parameters at the grand unified scale. Typically, scenarios with universal and nonuniversal gaugino masses do not allow invisible decays of the lightest Higgs boson~($h^0$), which is identified with the $126$ GeV resonance, into the lightest neutralinos in the MSSM. With arbitrary gaugino masses at the grand unified scale such an invisible decay is possible. The second lightest Higgs boson can decay into various invisible final states for a considerable region of the MSSM parameter space with arbitrary gaugino masses as well as with the gaugino masses restricted by universal and nonuniversal boundary conditions at the grand unified scale.The possibility of the second lightest Higgs boson of the MSSM decaying into invisible channels is more likely for arbitrary gaugino masses at the grand unified scale. The heavier Higgs boson decay into lighter particles leads to the intriguing possibility that the entire Higgs boson spectrum of the MSSM may be visible at the LHC even if it decays invisibly, during the searches for an extended Higgs boson sector at the LHC. In such a scenario the nonobservation of the extended Higgs sector of the MSSM may carefully be used to rule out regions of the MSSM parameter space at the LHC.

Natural SUSY with a bino- or wino-like LSP

In natural SUSY models higgsinos are always light because \mu^2 cannot be much larger than M_Z^2, while squarks and gluinos may be very heavy. Unless gluinos are discovered at LHC13, the commonly assumed unification of gaugino mass parameters will imply correspondingly heavy winos and binos, resulting in a higgsino-like LSP and small inter-higgsino mass splittings. The small visible energy release in higgsino decays makes their pair production difficult to detect at the LHC. Relaxing gaugino mass universality allows for relatively light winos and binos without violating LHC gluino mass bounds and without affecting naturalness. In the case where the bino mass M_1<~ \mu, then one obtains a mixed bino-higgsino LSP with instead sizable w_1-z_1 and z_2-z_1 mass gaps. The thermal neutralino abundance can match the measured dark matter density in contrast to models with a higgsino-like LSP where WIMPs (weakly interacting massive particles) are underproduced by factors of 10-15. If instead M_2<~ \mu, then one obtains a mixed wino-higgsino LSP with large z_2-z_1 but small w_1-z_1 mass gaps with still an under-abundance of thermally-produced WIMPs. Portions of the light wino parameter space may already be excluded by the IceCube upper bound on the spin-dependent neutralino-nucleon cross section. We discuss dark matter detection in other direct and indirect detection experiments and caution that the bounds from these must be interpreted with care. Finally, we show that LHC13 experiments should be able to probe these non-universal mass scenarios via a variety of channels including multi-lepton + etmiss events, WZ+etmiss events, Wh+etmiss events and W^\pm W^\pm +etmiss events from electroweak chargino and neutralino production.

General focus point in the MSSM

The minimal supersymmetric extension of the Standard Model (SM) is a well motivated scenario for physics beyond the SM, which allows a perturbative description of the theory up to scales of the order of the Grand Unification scale, where gauge couplings unify. The Higgs mass parameter is insensitive to the ultraviolet physics and is only sensitive to the scale of soft supersymmetry breaking parameters. Present collider bounds suggest that the characteristic values of these parameters may be significantly larger than the weak scale. Large values of the soft breaking parameters, however, induce large radiative corrections to the Higgs mass parameter and therefore the proper electroweak scale may only be obtained by a fine tuned cancellation between the square of the holomorphic \mu-parameter and the Higgs supersymmetry breaking square mass parameter. This can only be avoided if there is a correlation between the scalar and gaugino mass parameters, such that the Higgs supersymmetry breaking parameter remains of the order of the weak scale. The scale at which this happens is dubbed as focus point. In this article, we define the general conditions required for this to happen, for different values of the messenger scale at which supersymmetry breaking is transmitted to the observable sector, and for arbitrary boundary conditions of the sfermion, gaugino, and Higgs mass parameters. Specific supersymmetry breaking scenarios in which these correlations may occur are also discussed.

Electroweakinos in the light of the Higgs boson

Given the increasingly more stringent bounds on Supersymmetry (SUSY) from the LHC searches, we are motivated to explore the situation in which the only accessible SUSY states are the electroweakinos (charginos and neutralinos). In the minimal SUSY framework, we systematically study the three general scenarios classified by the relative size of the gaugino mass parameters M_1, M_2 and the Higgsino mass parameter \mu, with six distinctive cases, four of which would naturally result in a compressed spectrum of nearly degenerate LSPs. We present the relevant decay branching fractions and provide insightful understanding about the decay modes in connection with the Goldstone-boson Equivalence Theorem. We show the cross sections for electroweakino pair production at the LHC and ILC, and emphasize the unique signals involving the Standard Model-like Higgs boson as a new search reference. The electroweakino signal from pair production and subsequent decay to Wh/Zh (h to b\bar{b}) final state may yield a sensitivity of 95% C.L. exclusion (5sigma discovery) to the mass scale M_2, \mu ~ 350-400 GeV (220-270 GeV) at the 14 TeV LHC with an luminosity of 300 fb^{-1}. Combining with all the other decay channels, the 95% C.L. exclusion (5sigma discovery) may be extended to M_2, \mu ~ 480-700 GeV (320-500 GeV). At the ILC, the electroweakinos could be readily discovered once the kinematical threshold is crossed, and their properties could be thoroughly studied.

Tackling light higgsinos at the ILC

In supersymmetric extensions of the Standard Model, higgsino-like charginos and neutralinos are preferred to have masses of the order of the electroweak scale by naturalness arguments. Such light $\widetilde{\chi}^{0}_{1}$ , $\widetilde{\chi}^{0}_{2}$ and $\widetilde{\chi}^{\pm}_{1}$ states can be almost mass degenerate, and their decays are then difficult to observe at colliders. In addition to the generic naturalness argument, light higgsinos are well motivated from a top-down perspective. For instance, they arise naturally in certain models of hybrid gauge-gravity mediation. In the present analysis, we study two benchmark points which have been derived in the framework of such a model, which exhibit mass differences of $\mathcal {O}(\mathrm {GeV})$ in the higgsino sector. For chargino-pair and neutralino associated production with initial-state photon radiation, we simulate the detector response and determine how accurately the small mass differences, the absolute masses and the cross sections can be measured at the International Linear Collider. Assuming that 500 fb−1 has been collected at each of two beam-polarisations P(e +,e −)=(±30 %,∓80 %), we find that the mass differences can be measured to 40–300 MeV, the cross sections to 2–5 %, and the absolute masses to 1.5–3.3 GeV, where the range of values correspond to the different scenarios and channels. Based on these observables we perform a parameter fit in the MSSM, from which we infer that the higgsino mass parameter μ can be measured to a precision of about Δμ=2–7 GeV. For the electroweak gaugino mass parameters M 1, M 2, which are chosen in the multi-TeV range, a narrow region is compatible with the measurements. For both parameters independently, we can determine a lower bound.

Implication of a Higgs boson at 125 GeV within the stochastic superspace framework

We revisit the issue of considering stochasticity of Grassmannian coordinates in $N=1$ superspace, which was analyzed previously by Kobakhidze et al. In this stochastic supersymmetry (SUSY) framework, the soft SUSY breaking terms of the minimal supersymmetric Standard Model (MSSM) such as the bilinear Higgs mixing, trilinear coupling, as well as the gaugino mass parameters are all proportional to a single mass parameter $\ensuremath{\xi}$, a measure of supersymmetry breaking arising out of stochasticity. While a nonvanishing trilinear coupling at the high scale is a natural outcome of the framework, a favorable signature for obtaining the lighter Higgs boson mass ${m}_{h}$ at 125 GeV, the model produces tachyonic sleptons or staus turning to be too light. The previous analyses took $\ensuremath{\Lambda}$, the scale at which input parameters are given, to be larger than the gauge coupling unification scale ${M}_{G}$ in order to generate acceptable scalar masses radiatively at the electroweak scale. Still, this was inadequate for obtaining ${m}_{h}$ at 125 GeV. We find that Higgs at 125 GeV is highly achievable, provided we are ready to accommodate a nonvanishing scalar mass soft SUSY breaking term similar to what is done in minimal anomaly mediated SUSY breaking (AMSB) in contrast to a pure AMSB setup. Thus, the model can easily accommodate Higgs data, LHC limits of squark masses, WMAP data for dark matter relic density, flavor physics constraints, and XENON100 data. In contrast to the previous analyses, we consider $\ensuremath{\Lambda}={M}_{G}$, thus avoiding any ambiguities of a post-grand unified theory physics. The idea of stochastic superspace can easily be generalized to various scenarios beyond the MSSM.

The Higgs boson mass in a natural minimal supersymmetric standard model with nonuniversal gaugino masses at the grand unification theory scale

We identify a parameter region where the mass of the lightest CP-even Higgs boson resides in $124.4-126.8$ GeV, and at the same time the degree of tuning a Higgsino-mass parameter (so-called $\mu$-parameter) is relaxed above 10% in the minimal supersymmetric standard model (MSSM) with soft supersymmetry breaking terms, by solving the full set of one-loop renormalization group equations numerically. It is found that certain nonuniversal values of gaugino-mass parameters at the so-called grand unification theory (GUT) scale $\sim 10^{16}$ GeV are important ingredients for the MSSM to predict, without a severe fine-tuning, the Higgs boson mass $\sim 125$ GeV indicated by recent observations at the Large Hadron Collider. We also show a typical superparticle spectrum in this parameter region.

Magic messengers in gauge mediation and signal for 125 GeV boosted Higgs boson

We consider a renormalizable messenger sector with magic messenger fields instead of usual SU(5) complete multiplets. We derive the soft supersymmetry breaking terms and show that the gaugino sector can be parameterized by only two parameters. These parameters can be chosen appropriately to obtain various patterns of gaugino masses and different ratios among them. The sfermion sector can also be characterized by two independent parameters which can be adjusted to change the relative masses of squarks and sleptons. A judicious choice of parameters also allows us to achieve the lightest Higgs boson mass about 125 GeV. In this paper we focus on a scenario where a comparatively large hierarchy exists between the U(1) and SU(2) gaugino mass parameters. In such a case, the lightest Higgs boson originating from the decay of the next-to-lightest neutralino, following the direct production of chargino neutralino pair, can be considerably boosted. We show that a boosted Supersymmetric Higgs signal with a decent signal to background ratio can be obtained using the jet substructure technique at LHC with 8 TeV (14 TeV) center of mass energy and an integrated luminosity of about 30 fb$^{-1}$ (15 fb$^{-1}$).

Closing in on supersymmetric electroweak baryogenesis with dark matter searches and the Large Hadron Collider

We study the impact of recent direct and indirect searches for particle dark matter on supersymmetric models with resonant neutralino- or chargino-driven electroweak baryogenesis (EWB) and heavy sfermions. We outline regions of successful EWB on the planes defined by gaugino and higgsino mass parameters, and calculate the portions of those planes excluded by dark matter search results, and the regions soon to be probed by current and future experiments. We conclude that dark matter searches robustly exclude a wino-like lightest supersymmetric particle in successful EWB regions. Bino-like dark matter is still a possibility, although one that will be probed with a modest improvement in the sensitivity of current direct and indirect detection experiments. We also calculate the total production cross section of chargino and neutralino pairs at the Large Hadron Collider, with a center of mass energy of 7 and 14 TeV.

Statistical coverage for supersymmetric parameter estimation: a case study with direct detection of dark matter

Models of weak-scale supersymmetry offer viable dark matter (DM) candidates. Their parameter spaces are however rather large and complex, such that pinning down the actual parameter values from experimental data can depend strongly on the employed statistical framework and scanning algorithm. In frequentist parameter estimation, a central requirement for properly constructed confidence intervals is that they cover true parameter values, preferably at exactly the stated confidence level when experiments are repeated infinitely many times. Since most widely-used scanning techniques are optimised for Bayesian statistics, one needs to assess their abilities in providing correct confidence intervals in terms of the statistical coverage. Here we investigate this for the Constrained Minimal Supersymmetric Standard Model (CMSSM) when only constrained by data from direct searches for dark matter. We construct confidence intervals from one-dimensional profile likelihoods and study the coverage by generating several pseudo-experiments for a few benchmark sets of pseudo-true parameters. We use nested sampling to scan the parameter space and evaluate the coverage for the benchmarks when either flat or logarithmic priors are imposed on gaugino and scalar mass parameters. The sampling algorithm has been used in the configuration usually adopted for exploration of theBayesian posterior. We observe both under- and over-coverage, which in some cases vary quite dramatically when benchmarks or priors are modified. We show how most of the variation can be explained as the impact of explicit priors as well as sampling effects, where the latter are indirectly imposed by physicality conditions. For comparison, we also evaluate the coverage for Bayesian credible intervals, and observe significant under-coverage in those cases.