Sparticle Masses Research Articles

Tiny neutrino mass from SUSY and lepton number breaking sector

We suggest a new setup where SUSY breaking spurion F-term possesses lepton number. This setup not only modifies sparticle mass spectra but also realizes several new models, where neutrino mass is naturally induced through radiative corrections. We here suggest two new models; the first one is (i): pseudo-Dirac/Schizophrenic neutrino model, and the second one is (ii): pure Majorana neutrino model. We will also show this setup can naturally apply to the supersymmetric Zee–Babu model.

GAUGE MEDIATION OF SUPERSYMMETRY BREAKING AND THE FROGGATT–NIELSEN MECHANISM

In the model of gauge mediation of SUSY breaking in the presence of tree-level mediation, the Froggatt–Nielsen mechanism provides a different hierarchy of sparticle masses. We study the spectra and show the results to be like those in an effective supersymmetric model.

Implications of initial LHC searches for supersymmetry

The CMS and ATLAS Collaborations have recently published the results of initial direct LHC searches for supersymmetry analyzing ∼35/pb of data taken at 7 TeV in the centre of mass. We incorporate these results into a frequentist analysis of the probable ranges of parameters of simple versions of the minimal supersymmetric extension of the Standard Model (MSSM), namely the constrained MSSM (CMSSM), a model with common non-universal Higgs masses (NUHM1), the very constrained MSSM (VCMSSM) and minimal supergravity (mSUGRA). We present updated predictions for the gluino mass, \(m_{\tilde{g}}\), the light-Higgs boson mass, M h , BR(B s →μ + μ −) and the spin-independent dark matter scattering cross section, \(\sigma^{\mathrm{SI}}_{p}\). The CMS and ATLAS data make inroads into the CMSSM, NUHM1 and VCMSSM (but not mSUGRA) parameter spaces, thereby strengthening previous lower limits on sparticle masses and upper limits on \(\sigma^{\mathrm{SI}}_{p}\) in the CMSSM and VCMSSM. The favoured ranges of BR(B s →μ + μ −) in the CMSSM, VCMSSM and mSUGRA are close to the Standard Model, but considerably larger values of BR(B s →μ + μ −) are possible in the NUHM1. Applying the CMS and ATLAS constraints improves the consistency of the model predictions for M h with the LEP exclusion limits.

Metastability bounds on flavor-violating trilinear soft terms in the MSSM

The vacuum stability bounds on flavour-violating trilinear soft terms are revisited from the viewpoint that one should not ban a standard-model-like false vacuum as long as it is long-lived on a cosmological timescale. The vacuum transition rate is evaluated numerically by searching for the bounce configuration. Like stability, a metastability bound does not decouple even if sfermion masses grow. Apart from being more generous than stability, the new bounds are largely independent of Yukawa couplings except for the stop trilinears. With vacuum longevity imposed on otherwise arbitrary LR insertions, it is found that a super flavour factory has the potential to probe sparticle masses up to a few TeV through B and tau physics whereas the MEG experiment might cover a far wider range. In the stop sector, metastability is more restrictive than any existing experimental constraint such as from electroweak precision data. Also discussed are dependency on other parameters and reliability under radiative corrections.

Discrimination of supersymmetric grand unified models in gaugino mediation

We consider supersymmetric grand unified theory (GUT) with the gaugino mediated supersymmetry breaking and investigate a possibility to discriminate different GUT models in terms of predicted sparticle mass spectra. Taking two example GUT models, the minimal SU(5) and simple SO(10) models, and imposing a variety of theoretical and experimental constraints, we calculate sparticle masses. Fixing parameters of each model so as to result in the same mass of neutralino as the lightest supersymmetric particle (LSP), giving the observed dark matter relic density, we find sizable mass differences in the left-handed slepton and right-handed down-type squark sectors in two models, which can be a probe to discriminate the GUT models realized at the GUT scale far beyond the reach of collider experiments.

Frequentist analysis of the parameter space of minimal supergravity

We make a frequentist analysis of the parameter space of minimal supergravity (mSUGRA), in which, as well as the gaugino and scalar soft supersymmetry-breaking parameters being universal, there is a specific relation between the trilinear, bilinear and scalar supersymmetry-breaking parameters, A_0 = B_0 + m_0, and the gravitino mass is fixed by m_{3/2} = m_0. We also consider a more general model, in which the gravitino mass constraint is relaxed (the VCMSSM). We combine in the global likelihood function the experimental constraints from low-energy electroweak precision data, the anomalous magnetic moment of the muon, the lightest Higgs boson mass M_h, B physics and the astrophysical cold dark matter density, assuming that the lightest supersymmetric particle (LSP) is a neutralino. In the VCMSSM, we find a preference for values of m_{1/2} and m_0 similar to those found previously in frequentist analyses of the constrained MSSM (CMSSM) and a model with common non-universal Higgs masses (NUHM1). On the other hand, in mSUGRA we find two preferred regions: one with larger values of both m_{1/2} and m_0 than in the VCMSSM, and one with large m_0 but small m_{1/2}. We compare the probabilities of the frequentist fits in mSUGRA, the VCMSSM, the CMSSM and the NUHM1: the probability that mSUGRA is consistent with the present data is significantly less than in the other models. We also discuss the mSUGRA and VCMSSM predictions for sparticle masses and other observables, identifying potential signatures at the LHC and elsewhere.

Quirks in supersymmetry with gauge coupling unification

I investigate the phenomenology of supersymmetric models with extra vectorlike supermultiplets that couple to the standard model gauge fields and transform as the fundamental representation of a new confining non-Abelian gauge interaction. If perturbative gauge coupling unification is to be maintained, the new group can be $SU(2)$, $SU(3)$, or $SO(3)$. The impact on the sparticle mass spectrum is explored, with particular attention to the gaugino mass dominated limit in which the supersymmetric flavor problem is naturally solved. The new confinement length scale is astronomical for $SO(3)$, so the new particles are essentially free. For the $SU(2)$ and $SU(3)$ cases, the new vectorlike fermions are quirks; pair production at colliders yields quirk-antiquirk states bound by stable flux tubes that are microscopic but long compared to the new confinement scale. I study the reach of the Tevatron and LHC for the optimistic case that in a significant fraction of events the quirk-antiquirk bound state will lose most of its energy before annihilating as quirkonium.

Low mass gluino within the sparticle landscape, implications for dark matter, and early discovery prospects at LHC-7

We analyze supergravity models that predict a low mass gluino within the landscape of sparticle mass hierarchies. The analysis includes a broad class of models that arise in minimal and in nonminimal supergravity unified frameworks and in extended models with additional $U(1{)}_{X}^{n}$ hidden sector gauge symmetries. Gluino masses in the range (350--700) GeV are investigated. Masses in this range are promising for early discovery at the LHC at $\sqrt{s}=7\text{ }\text{ }\mathrm{TeV}$ (LHC-7). The models exhibit a wide dispersion in the gaugino-Higgsino eigencontent of their lightest supersymmetric particles and in their associated sparticle mass spectra. A signature analysis is carried out and the prominent discovery channels for the models are identified with most models needing only $\ensuremath{\sim}1\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ for discovery at LHC-7. In addition, significant variations in the discovery capability of the low mass gluino models are observed for models in which the gluino masses are of comparable size due to the mass splittings in different models and the relative position of the light gluino within the various sparticle mass hierarchies. The models are consistent with the current stringent bounds from the Fermi-LAT, CDMS-II, XENON100, and EDELWEISS-2 experiments. A subclass of these models, which include a mixed--$w$-ino lightest supersymmetric particle and a Higgsino lightest supersymmetric particle, are also shown to accommodate the positron excess seen in the PAMELA satellite experiment.

Dynamical R-parity breaking at the LHC

In a class of extensions of the minimal supersymmetric standard model with (B-L)/left-right symmetry that explains the neutrino masses, breaking R-parity symmetry is an essential and dynamical requirement for successful gauge symmetry breaking. Two consequences of these models are: (i) a new kind of R-parity breaking interaction that protects proton stability but adds new contributions to neutrinoless double beta decay and (ii) an upper bound on the extra gauge and parity symmetry breaking scale which is within the large hadron collider (LHC) energy range. We point out that an important prediction of such theories is a potentially large mixing between the right-handed charged lepton ($e^c$) and the superpartner of the right-handed gauge boson ($\widetilde W_R^+$), which leads to a brand new class of R-parity violating interactions of type $\widetilde{\mu^c}^\dagger\nu_\mu^c e^c$ and $\widetilde{d^c}^\dagger\u^c e^c$. We analyze the relevant constraints on the sparticle mass spectrum and the LHC signatures for the case with smuon/stau NLSP and gravitino LSP. We note the "smoking gun" signals for such models to be lepton flavor/number violating processes: $pp\to \mu^\pm\mu^\pm e^+e^-jj$ (or $\tau^\pm\tau^\pm e^+e^-jj$) and $pp\to\mu^\pm e^\pm b \bar{b} jj$ (or $\tau^\pm e^\pm b \bar{b} jj$) without significant missing energy. The predicted multi-lepton final states and the flavor structure make the model be distinguishable even in the early running of the LHC.

Superpartner spectrum of minimal gaugino-gauge mediation

We evaluate the sparticle mass spectrum in the minimal four-dimensional construction that interpolates between gaugino and ordinary gauge mediation at the weak scale. We find that even in the hybrid case -- when the messenger scale is comparable to the mass of the additional gauge particles -- both the right-handed as well as the left-handed sleptons are lighter than the bino in the low-scale mediation regime. This implies a chain of lepton production and, consequently, striking signatures that may be probed at the LHC already in the near future.

Controlling initial state radiation in sparticle mass reconstruction

Use of inclusive MT2 distribution for sparticle mass determination is discussed. We define new parameters MT2(min) and MT2mod(min), which are a kind of minimum of sub-systerm MT2 values. Their endpoints are less affected by initial state radiations. We demonstrate that both masses of squark and gluino can be extracted from the endpoints of the distributions in the wide region of parameter space expected in CMSSM. We also present a comparison with MTGen distributions.

A common source for neutrino and sparticle masses

We discuss supersymmetric scenarios in which neutrino masses arise from effective d = 6 operators in the Kähler potential (including SUSY-breaking insertions). Simple explicit realizations of those Kähler operators are presented in the context of the type II seesaw. An appealing scenario emerges upon identifying the seesaw mediators with SUSY-breaking messengers

Precision superpartner spectroscopy in the inclusive same-sign dilepton channel at the LHC

The inclusive same-sign dilepton channel is already recognized as a promising discovery signature for supersymmetry in the early days of the LHC. We point out that it can also be used for precision measurements of sparticle masses after the initial discovery. As an illustration, we consider the LM6 CMS study point in minimal supergravity, where the same-sign leptons most often result from chargino decays to sneutrinos. We discuss three different techniques for determining the chargino and sneutrino masses in an inclusive manner, i.e., using only the two well measured lepton momenta, while treating all other upstream objects in the event as a single entity of total transverse momentum ${\stackrel{\ensuremath{\rightarrow}}{P}}_{T}$. This approach takes full advantage of the large production rates of colored superpartners, but does not rely on the poorly measured hadronic jets, and avoids any jet combinatorics problems.

Sparticle masses from transverse mass kinks at the LHC: the case of Yukawa-unified SUSY GUTs

We explore, in a concrete example, to which extent new particle mass determinations are practicable with LHC data. Our chosen example is that of Yukawa-unified SUSY GUTs, whose viability has been recently studied for two general patterns of soft SUSY-breaking terms. We note that both patterns of SUSY spectra do not admit long decay chains, which would make it possible to determine the masses of the SUSY particles involved using endpoints or mass relations. We thus take the so-called mT2-kink method as our key strategy, since it does not rely on the presence of long decay chains. We then discuss a procedure allowing to determine the masses of the gluino, of the lightest chargino as well as of the first two neutralinos and, for the scenario where a stop is lighter than the gluino, the mass of the light stop too. Our worked example of Yukawa-unified SUSY GUTs may offer a useful playground for dealing with other theories which predict similar patterns of SUSY spectra.

Interplay of LFV and slepton mass splittings at the LHC as a probe of the SUSY seesaw

We study the impact of a type-I SUSY seesaw concerning lepton flavour violation (LFV) both at low-energies and at the LHC. The study of the di-lepton invariant mass distribution at the LHC allows to reconstruct some of the masses of the different sparticles involved in a decay chain. In particular, the combination with other observables renders feasible the reconstruction of the masses of the intermediate sleptons involved in \( \chi_2^0 \to \tilde{\ell }\ell \to \ell \ell \chi_1^0 \) decays. Slepton mass splittings can be either interpreted as a signal of non-universality in the SUSY soft breaking-terms (signalling a deviation from constrained scenarios as the cMSSM) or as being due to the violation of lepton flavour. In the latter case, in addition to these high-energy processes, one expects further low-energy manifestations of LFV such as radiative and three-body lepton decays. Under the assumption of a type-I seesaw as the source of neutrino masses and mixings, all these LFV observables are related. Working in the framework of the cMSSM extended by three right-handed neutrino superfields, we conduct a systematic analysis addressing the simultaneous implications of the SUSY seesaw for both high-and low-energy lepton flavour violation. We discuss how the confrontation of slepton mass splittings as observed at the LHC and low-energy LFV observables may provide important information about the underlying mechanism of LFV.

The sparticle spectrum in minimal gaugino-gauge mediation

We compute the sparticle mass spectrum in the minimal four-dimensional construction that interpolates between gaugino mediation and ordinary gauge mediation.

Predicting Supersymmetry

We review the result of SUSY parameter fits based on frequentist analyses of experimental constraints from electroweak precision data, (g-2)_mu, B-physics and cosmological data. We investigate the parameters of the constrained MSSM (CMSSM) with universal soft supersymmetry-breaking mass parameters, and a model with common non-universal Higgs mass parameters in the superpotential (NUHM1). Shown are the results for the SUSY and Higgs spectrum of the models. Many sparticle masses are highly correlated in both the CMSSM and NUHM1, and parts of the regions preferred at the 68% C.L. are accessible to early LHC running. The best-fit points could be tested even with 1/fb at sqrt[s] = 7 Tev.

Beyond the standard seesaw: neutrino masses from Kähler operators and broken supersymmetry

We investigate supersymmetric scenarios in which neutrino masses are generated by effective d=6 operators in the Kahler potential, rather than by the standard d=5 superpotential operator. First, we discuss some general features of such effective operators, also including SUSY-breaking insertions, and compute the relevant renormalization group equations. Contributions to neutrino masses arise at low energy both at the tree level and through finite threshold corrections. In the second part we present simple explicit realizations in which those Kahler operators arise by integrating out heavy SU(2)_W triplets, as in the type II seesaw. Distinct scenarios emerge, depending on the mechanism and the scale of SUSY-breaking mediation. In particular, we propose an appealing and economical picture in which the heavy seesaw mediators are also messengers of SUSY breaking. In this case, strong correlations exist among neutrino parameters, sparticle and Higgs masses, as well as lepton flavour violating processes. Hence, this scenario can be tested at high-energy colliders, such as the LHC, and at lower energy experiments that measure neutrino parameters or search for rare lepton decays.

Long-lived stops in MSSM scenarios with a neutralino LSP

This work investigates the possibility of a long-lived stop squark in supersymmetric models with the neutralino as the lightest supersymmetric particle (LSP). We study the implications of meta-stable stops on the sparticle mass spectra and the dark matter density. We find that in order to obtain a sufficiently long stop lifetime so as to be observable as a stable R-hadron at an LHC experiment, we need to fine tune the mass degeneracy between the stop and the LSP considerably. This increases the stop-neutralino co-anihilation cross section, leaving the neutralino relic density lower than what is expected from the WMAP results for stop masses ≲1.5 TeV/c 2. However, if such scenarios are realised in nature we demonstrate that the long-lived stops will be produced at the LHC and that stop-based R-hadrons with masses up to 1 TeV/c2 can be detected after one year of running at design luminosity.

What if supersymmetry breaking unifies beyond the GUT scale?

We study models in which soft supersymmetry-breaking parameters of the MSSM become universal at some unification scale, $M_{in}$, above the GUT scale, $\mgut$. We assume that the scalar masses and gaugino masses have common values, $m_0$ and $m_{1/2}$ respectively, at $M_{in}$. We use the renormalization-group equations of the minimal supersymmetric SU(5) GUT to evaluate their evolutions down to $\mgut$, studying their dependences on the unknown parameters of the SU(5) superpotential. After displaying some generic examples of the evolutions of the soft supersymmetry-breaking parameters, we discuss the effects on physical sparticle masses in some specific examples. We note, for example, that near-degeneracy between the lightest neutralino and the lighter stau is progressively disfavoured as $M_{in}$ increases. This has the consequence, as we show in $(m_{1/2}, m_0)$ planes for several different values of $\tan \beta$, that the stau coannihilation region shrinks as $M_{in}$ increases, and we delineate the regions of the $(M_{in}, \tan \beta)$ plane where it is absent altogether. Moreover, as $M_{in}$ increases, the focus-point region recedes to larger values of $m_0$ for any fixed $\tan \beta$ and $m_{1/2}$. We conclude that the regions of the $(m_{1/2}, m_0)$ plane that are commonly favoured in phenomenological analyses tend to disappear at large $M_{in}$.