Minimal Supersymmetric Standard Model Parameter Research Articles

Search for Neutral Higgs Bosons in Multi-b-Jet Events inpp¯Collisions ats=1.96 TeV

Data recorded by the D0 experiment at the Fermilab Tevatron Collider are analyzed to search for neutral Higgs bosons produced in association with b quarks. This production mode can be enhanced in the minimal supersymmetric standard model (MSSM). The search is performed in the three b quark channel using multijet triggered events corresponding to an integrated luminosity of 1 fb(-1). No statistically significant excess of events with respect to the predicted background is observed and limits are set in the MSSM parameter space.

Triplet extended supersymmetric standard model

We revisit an extension of the minimal supersymmetric standard model (MSSM) by adding a hypercharge-neutral, $SU(2)$-triplet chiral superfield. Similar to the next-to-minimal supersymmetric standard model , the triplet gives an additional contribution to the quartic coupling in the Higgs potential, and the mass of the lightest $CP$-even Higgs boson can be greater than ${M}_{Z}$ at tree level. In addition to discussing the perturbativity, fine-tuning, and decoupling issues of this model, we compute the dominant 1-loop corrections to the mass of the lightest $CP$-even Higgs boson from the triplet sector. When the Higgs-Higgs-Triplet coupling in the superpotential is comparable to the top Yukawa coupling, we find that the Higgs mass can be as heavy as 140 GeV even without the traditional contributions from the top--s-top sector, and at the same time consistent with the precision electroweak constraints. At the expense of having Landau poles before the grand unified theory scale, this opens up a previously forbidden region in the MSSM parameter space where both s-tops are light. In addition to having relatively small fine-tuning (about one part in 30), this leads to a gluophilic Higgs boson whose production via gluon-gluon fusion at the CERN LHC can be twice as large as the standard model prediction.

Lepton flavor violating leptonic and semileptonic decays of charged leptons in the minimal supersymmetric standard model

We consider the leptonic and semileptonic (SL) lepton-flavor violating (LFV) decays of the charged leptons in the minimal supersymmetric standard model (MSSM) with right-handed neutrinos. The parameters of the MSSM model are determined in the framework of the minimal supersymmetric SO(10) GUT model assuming the minimal supergravity model of supersymmetry breaking. The free parameters of the model are constrained adopting the WMAP cold dark matter constraint and adjusting the neutrino oscillation data. So constrained, the SO(10) GUT model gives a definite prediction for the Dirac-neutrino Yukawa matrix, which induces all LFV effects in the MSSM model through renormalization group equations of soft SUSY breaking parameters. A very detailed numerical analysis has been made to define numerically all MSSM parameters necessary for the evaluation of the LFV amplitudes. The basic LFV amplitudes in MSSM were rederived and improved. The formalism for the evaluation of all SL LFV amplitudes is given. Numerical results for dominant SL LFV branching ratios, the anomalous magnetic moment of the muon and the l→l’γ branching ratios are given.

Di-photon Higgs decay in the MSSM with explicit CP violation

The Minimal Supersymmetric Standard Model (MSSM) with explicit CP violation is studied with the help of the di-photon decay channel of the lightest neutral Higgs boson. Effects of CP violation, entering via the scalar/pseudo-scalar mixing at higher order as well as through the Higgs-sfermion-sfermion couplings at tree-level, are analyzed in the MSSM with and without light sparticles. A light stop may have a strong impact on the decay width and Branching Ratio (BR) of the decay process H1 → γγ, whereas other light sparticles have only little influence. In some regions of the MSSM parameter space with large CP-violating phase ϕμ ∼ 90° a light stop can change the BR by more than 50%.

Exploring the di-photon decay of a light Higgs boson in the MSSM with explicit CP violation

The di-photon decay channel of the lightest Higgs boson is considered as a probe to explore CP violation in the minimal supersymmetric standard model (MSSM). The scalar/pseudo-scalar mixing is considered along with CP violation entering through the Higgs–sfermion–sfermion couplings, with and without light sparticles. The impact of a light stop on the decay width and branching ratio (BR) is established through a detailed study of the amplitude of the process H1→γγ. The other sparticles have little influence even when they are light. With a suitable combination of other MSSM parameters, a light stop can change the BR by more than 50% with a CP-violating phase φμ∼90°, while the change is almost nil with a heavy stop.

Impact of slepton generation mixing on the search for sneutrinos

We perform a systematic study of sneutrino production and decays in the Minimal Supersymmetric Standard Model (MSSM) with slepton generation mixing. We study both fermionic decays like ν˜→ℓ−χ˜+, νχ˜0 and bosonic decays such as ν˜→ℓ˜−H+, ℓ˜−W+. We show that the effect of slepton generation mixing on the sneutrino production cross sections and its decay branching ratios can be quite large in a significant part of the MSSM parameter space despite the very strong experimental limits on lepton flavour violating processes. This could have an important impact on the search for sneutrinos and the determination of the MSSM parameters at future colliders, such as LHC, ILC, CLIC and muon collider.

CP violation in Charged Higgs Bosons decays H± → W± (γ, Z) in the Minimal Supersymmetric Standard Model (MSSM)

One loop mediated charged Higgs bosons decays H± → W±V, V = Z, γ are studied in the Minimal Supersymmetric Standard Model (MSSM) with and without CP violating phases. We evaluate the MSSM contributions to these processes taking into account B → Xsγ constraint as well as experimental constraints on the MSSM parameters. In the MSSM, we found that in the intermediate range of tan β ≲ 10 and for large At and large μ, where the lightest top squark becomes very light and hence non-decoupled, the branching ratio of H± → W±Z can be of the order 10−3 while the branching ratio of H± → W±γ is of the order 10−5. We found also that the CP violating phases of soft SUSY parameters can modify the branching ratio by about one order of magnitude. We also show that MSSM with CP violating phases lead to CP-violating asymmetry in the decays H+ → W+V and H− → W−V. Such CP asymmetry can be rather large and can reach 80% in some region of parameter space.

Single top-quark production by strong and electroweak supersymmetric flavor-changing interactions at the LHC

We report on a complete study of the single top-quark production by direct supersymmetric flavor-changing neutral-current (FCNC) processes at the LHC. The total cross section, σ(pp(gg) → + ), is computed at the 1-loop order within the unconstrained Minimal Supersymmetric Standard Model (MSSM). The present study extends the results of the supersymmetric strong effects (SUSY-QCD), which were advanced by some of us in a previous work, and includes the computation of the full supersymmetric electroweak corrections (SUSY-EW). Our analysis of σ(pp(gg) → + ) in the MSSM has been performed in correspondence with the stringent low-energy constraints from b → sγ. In the most favorable scenarios, the SUSY-QCD contribution can give rise to production rates of around 105 events per 100 fb−1 of integrated luminosity. Furthermore, we show that there exist regions of the MSSM parameter space where the SUSY-EW correction becomes sizeable. This could be important, especially if the SUSY-QCD effects would be suppressed. In the SUSY-EW favored regions, one obtains lower, but still appreciable, event production rates that can reach the 103 level for the same range of integrated luminosity. We study also the possible reduction in the maximum event rate obtained from the full MSSM contribution if we additionally include the constraints from the B0s−0s. However, we treat these restrictions at a different level from the b → sγ ones, due to the higher uncertainties inherent in the calculation of the matrix element associated to that mixing. In view of the fact that the FCNC production of heavy quark pairs of different flavors, such as or , is extremely suppressed in the SM, the detection of a significant number of these events could lead to evidence of new physics — of likely supersymmetric origin.

On MSSM charged Higgs-boson production in association with an electroweak W boson at electron–positron colliders

We present a calculation of the cross section for the process e+ e- --> W+/- H-/+ in the minimal supersymmetric standard model (MSSM) and the Two Higgs Doublet Model (THDM). We study the basic features of the MSSM prediction for some distinctive parameter scenarios. We find large effects from virtual squarks for scenarios with large mixing in the stop sector which can lead to a cross section vastly different from a THDM with identical Higgs sector parameters. We investigate this interesting behaviour in more detail by thoroughly scanning the MSSM parameter space for regions of large cross section. For a charged Higgs boson too heavy to be pair-produced at such a machine, it turns out that a large MSSM cross section with a good chance of observation is linked to a squark mass scale below 600 GeV and a considerable amount of mixing in either the stop and sbottom sector.

CP asymmetries in chargino production and decay: the three-body decay case

We study CP violation in chargino production and decay in the minimal supersymmetric standard model (MSSM) with complex parameters at an e+e- linear collider with longitudinally polarised beams. We investigate CP-sensitive asymmetries by means of triple product correlations and study their dependence on the complex parameters M1 and μ. We give numerical predictions for the asymmetries and their measurability at the future International Linear Collider. Our results show that the CP asymmetries can be measured in a large region of the MSSM parameter space.

A collider signature of the supersymmetric golden region

Null results of experimental searches for the Higgs boson and the superpartners imply a certain amount of fine-tuning in the electroweak sector of the Minimal Supersymmetric Standard Model (MSSM). The "golden region" in the MSSM parameter space is the region where the experimental constraints are satisfied and the amount of fine-tuning is minimized. In this region, the stop trilinear soft term is large, leading to a significant mass splitting between the two stop mass eigenstates. As a result, the decay of the heavier stop into the lighter stop and a Z boson is kinematically allowed throughout the golden region. We propose that the experiments at the Large Hadron Collider (LHC) can search for this decay through an inclusive signature, Z+2jb+missing Et+X. We evaluate the Standard Model backgrounds for this channel, and identify a set of cuts that would allow detection of the supersymmetric contribution at the LHC for the MSSM parameters typical of the golden region. We also discuss other possible interpretations of a signal for new physics in the Z+2jb+missing Et+X channel, and suggest further measurements that could be used to distinguish among these interpretations.

Charged Higgs boson decays H± → W±(γ, Z) revisited

We study the complete one-loop contribution to H± → W±V, V = Z, γ, both in the minimal supersymmetric standard model (MSSM) and in the two Higgs doublet model (2HDM). We evaluate the MSSM contributions and compare them with the 2HDM one, taking into account the B → Xsγ constraint, vacuum stability and unitarity constraints in the case of 2HDM as well as experimental constraints on the MSSM and 2HDM parameters. In the MSSM, we found that in the intermediate range of tan β ≲ 10 and for large At, the branching ratio of H± → W±Z can be of the order 10−3 while the branching ratio of H± → W±γ is of the order 10−5. We also study the effects of the CP violating phases of soft SUSY parameters, and found that they can modify the branching ratio by about one order of magnitude. However, in 2HDM where the Higgs sector is less constrained as compared to the MSSM Higgs sector, the branching ratio can be enhanced. For charged Higgs mass of the order 180–200 GeV, which can accommodate B → Xsγ constraint if one takes into account large theoretical uncertainties, the branching ratio of both modes H± → W±Z, W±γ can be of the order 10−2.

Left–right squarks mixings effects in charged Higgs bosons decays H±→W±(γ,Z) in the MSSM

We study the complete one loop contribution to H±→W±V, V=Z,γ, in the Minimal Supersymmetric Standard Model (MSSM). We evaluate the MSSM contributions taking into account B→Xsγ constraint as well as experimental constraints on the MSSM parameters. In the MSSM, we found that in the intermediate range of tanβ≲10 and for large At and large μ, where lightest stop becomes very light and hence squarks contribution is not decoupling, the branching ratio of H±→W±Z can be of the order 10−3 while the branching ratio of H±→W±γ is of the order 10−5. We also study the effects of the CP violating phases of soft SUSY parameters and found that they can modify the branching ratio by about one order of magnitude.

ProbingCP-violating Higgs contributions inγγ→ff¯through fermion polarization

We discuss the use of fermion polarization for studying neutral Higgs bosons at a photon collider. To this aim we construct polarization asymmetries which can isolate the contribution of a Higgs boson {phi} in {gamma}{gamma}{yields}ff, f={tau}/t, from that of the QED continuum. This can help in getting information on the {gamma}{gamma}{phi} coupling in case {phi} is a CP eigenstate. We also construct CP-violating asymmetries which can probe CP mixing in case {phi} has indeterminate CP. Furthermore, we take the minimal supersymmetric standard model (MSSM) with CP violation as an example to demonstrate the potential of these asymmetries in a numerical analysis. We find that these asymmetries are sensitive to the presence of a Higgs boson as well as its CP properties over a wide range of MSSM parameters. In particular, the method suggested can cover the region where a light Higgs boson may have been missed by LEP due to CP violation in the Higgs sector, and may be missed as well at the LHC.

Natural implementation of neutralino dark matter

The prediction of neutralino dark matter is generally regarded as one of the successes of the Minimal Supersymmetric Standard Model (MSSM). However the successful regions of parameter space allowed by WMAP and collider constraints are quite restricted. We discuss fine-tuning with respect to both dark matter and Electroweak Symmetry Breaking (EWSB) and explore regions of MSSM parameter space with non-universal gaugino and third family scalar masses in which neutralino dark matter may be implemented naturally. In particular allowing non-universal gauginos opens up the bulk region that allows Bino annihilation via t-channel slepton exchange, leading to ``supernatural dark matter'' corresponding to no fine-tuning at all with respect to dark matter. By contrast we find that the recently proposed ``well tempered neutralino'' regions involve substantial fine-tuning of MSSM parameters in order to satisfy the dark matter constraints, although the fine tuning may be ameliorated if several annihilation channels act simultaneously. Although we have identified regions of ``supernatural dark matter'' in which there is no fine tuning to achieve successful dark matter, the usual MSSM fine tuning to achieve EWSB always remains.

Search for neutral MSSM Higgs bosons at LEP

The four LEP collaborations, ALEPH, DELPHI, L3 and OPAL, have searched for the neutral Higgs bosons which are predicted by the Minimal Supersymmetric standard model (MSSM). The data of the four collaborations are statistically combined and examined for their consistency with the background hypothesis and with a possible Higgs boson signal. The combined LEP data show no significant excess of events which would indicate the production of Higgs bosons. The search results are used to set upper bounds on the cross-sections of various Higgs-like event topologies. The results are interpreted within the MSSM in a number of “benchmark” models, including CP-conserving and CP-violating scenarios. These interpretations lead in all cases to large exclusions in the MSSM parameter space. Absolute limits are set on the parameter cosβ and, in some scenarios, on the masses of neutral Higgs bosons.

Baryogenesis, electric dipole moments and dark matter in the MSSM

We study the implications for electroweak baryogenesis (EWB) within the minimal supersymmetric Standard Model (MSSM) of present and future searches for the permanent electric dipole moment (EDM) of the electron, for neutralino dark matter, and for supersymmetric particles at high energy colliders. We show that there exist regions of the MSSM parameter space that are consistent with both present two-loop EDM limits and the relic density and that allow for successful EWB through resonant chargino and neutralino processes at the electroweak phase transition. We also show that under certain conditions the lightest neutralino may be simultaneously responsible for both the baryon asymmetry and relic density. We give present constraints on chargino/neutralino-induced EWB implied by the flux of energetic neutrinos from the Sun, the prospective constraints from future neutrino telescopes and ton-sized direct detection experiments, and the possible signatures at the Large Hadron Collider and International Linear Collider.

Yukawa and triscalar processes in electroweak baryogenesis

We derive the contributions to the quantum transport equations for electroweak baryogenesis due to decays and inverse decays induced by triscalar and Yukawa interactions. In the minimal supersymmetric standard model (MSSM), these contributions give rise to couplings between Higgs and fermion supermultiplet densities, thereby communicating the effects of $CP$-violation in the Higgs sector to the baryon sector. We show that the decay and inverse decay-induced contributions that arise at zeroth order in the strong coupling, ${\ensuremath{\alpha}}_{s}$, can be substantially larger than the $\mathcal{O}({\ensuremath{\alpha}}_{s})$ terms that are generated by scattering processes and that are usually assumed to dominate. We revisit the often-used approximation of fast Yukawa-induced processes and show that for realistic parameter choices it is not justified. We solve the resulting quantum transport equations numerically with special attention to the impact of Yukawa rates and study the dependence of the baryon-to-entropy ratio ${Y}_{B}$ on MSSM parameters.

Full one-loop supersymmetric electroweak corrections tott¯h0associated production ine+e−annihilation

We present a precise calculation of the lightest neutral Higgs boson production associated with top-quark pair at a linear collider. The full one-loop electroweak $\mathcal{O}({\ensuremath{\alpha}}_{ew})$ contributions to the process ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}t\overline{t}{h}^{0}$ within the minimal supersymmetric standard model (MSSM) are included. We analyze the dependence of the electroweak corrections on the MSSM parameters such as ${M}_{{A}^{0}}$, $\mathrm{tan}\ensuremath{\beta}$, ${M}_{2}$ ${A}_{f}$, ${M}_{SUSY}$ and $\ensuremath{\mu}$. The results show that the full one-loop electroweak radiative corrections turn out to be about $\ensuremath{-}20%$ quantitatively and thus are important for future ${e}^{+}{e}^{\ensuremath{-}}$ linear colliders.

Associated production of a light Higgs boson and a chargino pair in the MSSM at linear colliders

In the minimal supersymmetric standard model (MSSM), we study the light Higgs boson radiation off a light-chargino pair in the process $ e^{ + } e ^{-} \to h\tilde{\chi }^{ + }_{1} \tilde{\chi }^{ - }_{1} $ at linear colliders with $ {\sqrt s } = 500\;{\text{Gev}} $ GeV. We analyze cross sections in the regions of the MSSM parameter space where the process $ e^{ + } e ^{-} \to h\tilde{\chi }^{ + }_{1} \tilde{\chi }^{ - }_{1} $ cannot proceed via on-shell production and subsequent decay of either heavier charginos or the pseudoscalar Higgs boson A. Cross sections up to a few fb are allowed, according to present experimental limits on the Higgs boson, chargino and sneutrino masses. We also show how a measurement of the $ e^{ + } e ^{-} \to h\tilde{\chi }^{ + }_{1} \tilde{\chi }^{ - }_{1} $ production rate could provide a determination of the Higgs boson couplings to charginos.