Family Squarks Research Articles

Neutralino dark matter and other LHC predictions from quasi Yukawa unification

We explore the dark matter and LHC implications of t−b−τ quasi Yukawa unification in the framework of supersymmetric models based on the gauge symmetry G=SU(4)c×SU(2)L×SU(2)R. The deviation from exact Yukawa unification is quantified by a dimensionless parameter C (|C|≲0.2), such that the Yukawa couplings at MGUT are related by yt:yb:yτ=|1+C|:|1−C|:|1+3C|. In contrast to earlier studies which focused on universal gaugino masses, we consider non-universal gaugino masses at MGUT that are compatible with the gauge symmetry G. Our results reveal a variety of neutralino dark matter scenarios consistent with the observations. These include stau and chargino coannihilation scenarios, the A-resonance scenario, as well as Higgsino dark matter solutions which are more readily probed by direct detection searches. The gluino mass is found to be ≲4 TeV, the stop mass is ≳2 TeV, while the first two family squarks and sleptons are of order 4–5 TeV and 3 TeV respectively.

Nonuniversal supergravity at the LHC: Prospects and discovery potential

We explore supersymmetry (SUSY) parameter space with nonuniversal high scale parameters in a gravity mediated SUSY breaking (SUGRA) scenario that accommodates a Higgs mass of $(125\ifmmode\pm\else\textpm\fi{}2)\text{ }\text{ }\mathrm{GeV}$ while satisfying cold dark matter relic density and other low energy constraints. We indicate a few benchmark points consistent with different dark matter annihilation processes where third family squarks are lighter than the first two as a requirement to keep the Higgs mass within the limit. We show that bottom rich and leptonic final states have a better reach in such parameter space points and is the most likely scenario to discover SUSY at the upcoming run of LHC with center-of-mass energy 14 TeV.

Sensitivity of the squark flavor mixing to the CP violation of K, [formula omitted] and [formula omitted] mesons

We study the sensitivity of the squark flavor mixing to the CP violating phenomena of K, B0 and Bs mesons in the framework of the split-family scenario, where the first and second family squarks are very heavy, O(10) TeV, on the other hand, the third family squark masses are at O(1) TeV. In order to constrain the gluino-sbottom-quark mixing parameters, we input the experimental data of the CP violations of K, B0, and Bs mesons, that is ϵK, ϕd, and ϕs. The experimental upper bound of the chromo-EDM of the strange quark is also input. In addition, we take account of the observed values ΔMB0, ΔMBs, the CKM mixing |Vub|, and the branching ratio of b→sγ. The allowed region of the mixing parameters are obtained as |δ13dL(dR)|=0∼0.01 and |δ23dL(dR)|=0∼0.04. By using these values, the deviations from the SM are estimated in the CP violations of the B0 and Bs decays. The deviation from the SM one is tiny in the CP asymmetries of B0→ϕKS and B0→η′K0 due to the chromo-EDM of the strange quark. On the other hand, the CP asymmetries Bs→ϕϕ and Bs→ϕη′ could be largely deviated from the SM predictions. We also predict the time dependent CP asymmetry of B0→K0K¯0 and the semi-leptonic CP asymmetries of B0→μ−X and Bs→μ−X. We expect those precise measurements at Belle II, which will provide us interesting tests for the squark flavor mixing.

NONUNIVERSAL GAUGINO MASSES AND NATURAL SUPERSYMMETRY

We demonstrate that natural supersymmetry is readily realized in the framework of SU(4)c×SU(2)L×SU(2)Rwith nonuniversal gaugino masses. Focusing on ameliorating the little hierarchy problem, we explore the parameter space of this model which yields small fine-tuning measuring parameters (natural supersymmetry) at the electroweak scale (ΔEW) as well as at high scale (ΔHS). It is possible to have both ΔEWand ΔHSless than 100 in these models, (2% or better fine-tuning), while keeping the light CP-even (Standard Model-like) Higgs mass in the 123–127 GeV range. The light stop quark mass lies in the range [Formula: see text], and the range for the light stau lepton mass is [Formula: see text]. The first two family squarks are in the mass range [Formula: see text], and for the gluino we find [Formula: see text]. We do not find any solution with natural supersymmetry which yields significant enhancement for Higgs production and decay in the diphoton channel.

Higgs boson mass from t-b-τ Yukawa unification

We employ the Yukawa coupling unification condition, y_t= y_b= y_tau at M_GUT, inspired by supersymmetric SO(10) models, to estimate the lightest Higgs boson mass as well as masses of the associated squarks and gluino. We employ non-universal soft masses, dictated by SO(10) symmetry, for the gauginos. Furthermore, the soft masses for the two scalar Higgs doublets are set equal at M_GUT, and in some examples these are equal to the soft masses for scalars in the matter multiplets. For mu > 0, M_2 > 0, where M_2 denotes the SU(2) gaugino mass, essentially perfect t-b-tau Yukawa unification is possible, and it predicts a Higgs mass of 122 - 124 GeV with a theoretical uncertainty of about 3 GeV. The corresponding gluino and the first two family squarks have masses 3 TeV. We present some LHC testable benchmark points which also show the presence of neutralino-stau coannihilation in this scenario. The well-known MSSM parameter tan beta~47.

Constraints on supersymmetry with light third family from LHC data

We present a re-interpretation of the recent ATLAS limits on supersymmetry in channels with jets (with and without b-tags) and missing energy, in the context of light third family squarks, while the first two squark families are inaccessible at the 7 TeV run of the Large Hadron Collider (LHC). In contrast to interpretations in terms of the high-scale based constrained minimal supersymmetric standard model (CMSSM), we primarily use the low-scale parametrisation of the phenomenological MSSM (pMSSM), and translate the limits in terms of physical masses of the third family squarks. Side by side, we also investigate the limits in terms of high-scale scalar non-universality, both with and without low-mass sleptons. Our conclusion is that the limits based on 0-lepton channels are not altered by the mass-scale of sleptons, and can be considered more or less model-independent.

Neutralino-sbottom coannihilation in SU(5)

We identify within the SU(5) framework the minimum number of soft supersymmetry breaking parameters which can yield a bottom squrak (sbottom) as the next to lightest supersymmetric particle. We focus in particular on the neutralino-sbottom coannihilation scenario which gives rise to the desired neutralino dark matter relic density. We find solutions in which the sbottom mass is greater than or of order 210 GeV, while the gluino and the first two family squarks are heavier than 1 TeV. Some benchmark points which can be tested at the LHC are presented.

Light stop from b–τ Yukawa unification

We show that b–τ Yukawa unification can be successfully implemented in the constrained minimal supersymmetric model and it yields the stop co-annihilation scenario. The lightest supersymmetric particle is a bino-like dark matter neutralino, which is accompanied by a 10–20% heavier stop of mass ∼100–330 GeV. We highlight some benchmark points which show a gluino with mass ∼0.6–1.7 TeV, while the first two family squarks and all sleptons have masses in the multi-TeV range.

Signals of supersymmetry with inaccessible first two families at the Large Hadron Collider

We investigate the signals of supersymmetry in a scenario where only the third family squarks and sleptons can be produced at the Large Hadron Collider, in addition to the gluino, charginos, and neutralinos. The final states in such cases are marked by a multiplicity of top or bottom quarks. We study, in particular, the case when the top squark, bottom squark, and gluino masses are near the TeV scale due to which, the final state $t$'s and $b$'s are very energetic. We point out the difficulty in $b$ tagging and identifying energetic tops and suggest several event selection criteria which allow the signals to remain significantly above the standard model background. We show that such scenarios with gluino mass up to 2 TeV can be successfully probed at the Large Hadron Collider. Information on $\mathrm{tan}\ensuremath{\beta}$ can also be obtained by looking at associated Higgs production in the cascades of accompanying neutralinos. We also show that a combined analysis of event rates in the different channels and the effective mass distribution allows one to differentiate this scenario from the one where all three sfermion families are accessible.

Squark decays in MSSM under the cosmological bounds

We present the numerical investigation of the fermionic two-body decays of squarks in the minimal supersymmetric standard model with complex parameters. In the analysis, we particularly take into account the cosmological bounds imposed by Wilkinson Microwave Anisotropy Probe data. We find that the phase dependences of the decay widths of the third family squarks, as well as those of the first and second families, are quite significant which can provide viable probes of additional CP sources. We plot the CP-phase dependences for each fermionic two-body decay channel of squarks (i = 1, 2, q = u, d, c, s, t, b) and speculate about the branching ratios and total (two-body) decay widths.

Soft SUSY breaking and family symmetry

A spontaneously broken non-Abelian SU(3) family symmetry can generate a realistic form for quark, charged lepton and neutrino masses and mixing angles. It also gives a new solution to the SUSY flavour problem by ensuring near family degeneracy of the soft mass SUSY breaking terms. However the need to generate large third generation fermion masses means that the group must be strongly broken to SU(2) giving significant corrections to the third family squark and slepton masses. We investigate the phenomenological implications of such breaking and show that it leads to new solutions capable of fitting all present experimental measurements and bounds as well as the dark matter abundance.

Brane mediated supersymmetry breaking

We propose a mechanism for mediating supersymmetry breaking in Type I string constructions. The basic set-up consists of a system of three D-branes: two parallel D-branes, a matter D-brane and a source D-brane, with supersymmetry breaking communicated via a third D-brane, the mediating D-brane, which intersects both of the parallel D-branes. We discuss an example in which the first and second family matter fields correspond to open strings living on the intersection of the matter D-brane and mediating D-brane, while the gauge fields, Higgs doublets and third family matter fields correspond to open strings living on the mediating D-brane. As in gaugino mediated models, the gauginos and Higgs doublets receive direct soft masses from the source brane, and flavour-changing neutral currents are naturally suppressed since the first and second family squarks and sleptons receive suppressed soft masses. However, unlike the gaugino mediated model, the third family squarks and sleptons receive unsuppressed soft masses, resulting in a very distinctive spectrum with heavier stops, sbottoms and staus.