Yukawa-unified Models Research Articles

Dark matter at the pseudoscalar Higgs resonance in the phenomenological MSSM and SUSY GUTs

We study dark matter at the MSSM pseudoscalar Higgs resonance (A-funnel), which is one of the few remaining MSSM thermal dark matter candidates in the $100-1000$ GeV range safe from direct detection constraints. To illustrate the various factors at play, this study is performed in two contrasting set-ups: a bottom-up phenomenological MSSM (pMSSM) approach that allows significant freedom, and the top-down, highly constrained Yukawa unified $SO(10)$ GUT model. In the pMSSM, for $\mu > 0$, the entire parameter space lies above the coherent neutrino background and mostly within reach of XENON1T and LZ, while blind spots exist at $m_A\,> \, 800\,$GeV for $\mu < 0$; the strongest constraints come from $A/H \rightarrow \tau \tau$ searches at the LHC. For Yukawa unified models, the confluence of $B_s \rightarrow \mu^+ \mu^-$ constraints, fits to the bottom quark and Higgs masses, and gluino mass bounds from the LHC result in a prediction: realizing the pseudoscalar resonance $requires$ gaugino mass non-universality, with a mass ratio that is determined to within a small range.

A heavier gluino from t–b–τ Yukawa-unified SUSY

Supersymmetric models with t–b–τ Yukawa coupling unification and unified gaugino masses at the GUT scale—with μ>0—show a mild preference for light gluino masses mg˜≲500 GeV. This range of mg˜ is now essentially ruled out by LHC searches. We show that a heavier gluino with mg˜∼0.5–3 TeV can also be compatible with excellent t–b–τ Yukawa coupling unification in supersymmetric models with non-universal Higgs masses (NUHM2). The gluino in such models is the lightest colored sparticle, while the squark sector displays an inverted mass hierarchy with mq˜∼5–20 TeV. We present some LHC testable benchmark points for which the lightest Higgs boson mass mh≃125 GeV. We also discuss LHC signatures of Yukawa-unified models with heavier gluinos. We expect gluino pair production followed by decay to final states containing four b-jets plus four W-bosons plus missing ET to occur at possibly observable rates at LHC.

LHC constraints on NLSP gluino and dark matter neutralino in Yukawa unified models

The ATLAS experiment has recently presented its search results for final states containing jets and/or b-jet(s) and missing transverse momentum, corresponding to an integrated luminosity of 165 pb−1. We employ this data to constrain a class of supersymmetric SU(4)c×SU(2)L×SU(2)R models with t−b−τ Yukawa unification, in which the gluino is the next to lightest supersymmetric particle (NLSP). The NLSP gluino is slightly (∼10–30%) heavier than the LSP dark matter neutralino, and it primarily decays into the latter and a quark–antiquark pair or gluon. We find that NLSP gluino masses below ∼300 GeV are excluded by the ATLAS data. For LSP neutralino mass ∼200–300 GeV and μ>0, where μ is the coefficient of the MSSM Higgs bilinear term, the LHC constraints in some cases on the spin-dependent (spin-independent) neutralino–nucleon cross section are significantly more stringent than the expected bounds from IceCube DeepCore (Xenon 1T/SuperCDMS). For μ<0, this also holds for the spin-dependent cross sections.

Suppression of lepton flavour violation from quantum corrections above M GUT

We study the predictions for sfermion masses and Lepton Flavour Violation (LFV) for the WMAP preferred parameter space in $b-\tau$ Yukawa-unified models with massive neutrinos. A soft term structure as predicted by an Abelian flavour symmetry combined with SU(5) RGEs for scales above $M_{GUT}$, results to an efficient suppression of the off-diagonal terms in the scalar soft matrices, particularly for $m_0< 100$ GeV. Using the WMAP bounds, this implies $35\le\tan\beta \le 45$, $350\,\mathrm{GeV}\le m_{1/2}\le 1\,\mathrm{TeV}$, with the higher $\tan\beta$ values being favored. Within this framework, SU(5) unification becomes compatible with the current experimental bounds, in contrast to the conventional case where the soft terms are postulated at the GUT scale.

Cosmological consequences of Yukawa-unified SUSY with mixed axion/axino cold and warm dark matter

Supersymmetric models with t−b−τ Yukawa unification at MGUTqualitatively predict a sparticle mass spectrum including first and second generation scalarsat the 3–15 TeV scale, third generation scalars at the (few) TeV scale and gluinos in the sub-TeV range. The neutralino relic density in these models typically turns out to lie far abovethe measured dark matter abundance, prompting the suggestion that instead dark matter is composed of an axion/axino mixture.We explore the axion and thermal and non-thermal axino dark matter abundance in Yukawa-unified SUSY models. We find in this scenario that (i) rather large values of Peccei-Quinn symmetry breaking scale fa ∼ 1012 GeV are favored and (ii) rather large values of GUT scale scalar masses ∼ 10−15 TeV allow for the re-heat temperature TR of the universe to be TR ⪆ 106 GeV. This allows in turn a solution to the gravitino/Big Bang Nucleosynthesis problem while also allowing for baryogenesis via non-thermal leptogenesis. The large scalar masses for Yukawa-unified models are also favored by data on b → sγ and Bs → μ+μ− decay.Testable consequences from this scenario include a possible axion detection at axion search experiments, but null results from direct and indirect WIMP search experiments.

Prospects for Yukawa unified SO(10) SUSY GUTs at the CERN LHC

The requirement of t − b − τ Yukawa coupling unification is common in simple grand unified models based on the gauge group SO(10), and it also places a severe con- straint on the expected spectrum of superpartners. For Yukawa-unified models with � > 0, the spectrum is characterized by three mass scales: i). first and second generation scalars in the multi-TeV range, ii). third generation scalars, � and mA in the few-TeV range and iii). gluinos in the ∼ 350 − 500GeV range with chargino masses around 100 − 160GeV. In such a scenario, gluino pair production should occur at large rates at the CERN LHC, followed by gluino three-body decays into neutralinos or charginos. Discovery of Yukawa- unified SUSY at the LHC should hence be possible with only 1fb −1 of integrated luminosity, by tagging multi-jet events with 2-3 isolated leptons, without relying on missing ET. A characteristic dilepton mass edge should easily be apparent above Standard Model back- ground. Combining dileptons with b-jets, along with the gluino pair production cross sec- tion information, should allow for gluino and neutralino mass reconstruction. A secondary corroborative signal should be visible at higher integrated luminosity in the ˜ χ ± ˜ χ 0 → 3l channel, and should exhibit the same dilepton mass edge as in the gluino cascade decay signal.

Dark matter allowed scenarios for Yukawa-unified SO(10) SUSY GUTs

Simple supersymmetric grand unified models based on the gauge group SO(10) require?in addition to gauge and matter unification?the unification of t-b-? Yukawa couplings. Owing to sparticle contributions to fermion self-energy diagrams, the Yukawa unification however only occurs for very special values of the soft SUSY breaking parameters. We perform a search using a Markov Chain Monte Carlo (MCMC) technique to investigate model parameters and sparticle mass spectra which occur in Yukawa-unified SUSY models, where we also require the relic density of neutralino dark matter to saturate the WMAP-measured abundance. For Yukawa unified models with 0$>?>0, the spectrum is characterizd by three mass scales: first and second generation scalars in the multi-TeV range, third generation scalars in the TeV range, and gauginos in the ~ 100 GeV range. Most solutions give far too high a relic abundance of neutralino dark matter. The dark matter discrepancy can be rectified by i). allowing for neutralino decay to axino plus photon, ii). imposing gaugino mass non-universality or iii). imposing generational non-universality. In addition, the MCMC approach finds a compromise solution where scalar masses are not too heavy, and where neutralino annihilation occurs via the light Higgs h resonance. By imposing weak scale Higgs soft term boundary conditions, we are also able to generate low ?,?mA solutions with neutralino annihilation via a light A resonance, though these solutions seem to be excluded by CDF/D0 measurements of the Bs ? ?+?? branching fraction. Based on the dual requirements of Yukawa coupling unification and dark matter relic density, we predict new physics signals at the LHC from pair production of 350?450 GeV gluinos. The events are characterized by very high b-jet multiplicity and a dilepton mass edge around m02?m01 ~ 50?75 GeV.

Yukawa coupling unification in supersymmetric models

We present an updated assessment of the viability of t-b-tau Yukawa coupling unification in supersymmetric models. For the superpotential Higgs mass parameter mu>0, we find unification to less than 1% is possible, but only for GUT scale scalar mass parameter m_{16}~8-20 TeV, and small values of gaugino mass m_{1/2}<400 GeV. Such models require that a GUT scale mass splitting exists amongst Higgs scalars with m_{H_u}^2<m_{H_d}^2. Viable solutions lead to a radiatively generated inverted scalar mass hierarchy, with third generation and Higgs scalars being lighter than other sfermions. These models have very heavy sfermions, so that unwanted flavor changing and CP violating SUSY processes are suppressed, but may suffer from some fine-tuning requirements. While the generated spectra satisfy b->s gamma and (g-2)_mu constraints, there exists tension with the dark matter relic density unless m_{16}<3 TeV. These models offer prospects for a SUSY discovery at the Fermilab Tevatron collider via the search for chargino_1 neutralino_2 -> 3 leptons events, or via gluino pair production. If mu<0, Yukawa coupling unification to less than 5% can occur for m_{16} and m_{1/2}>1-2 TeV. Consistency of negative mu Yukawa unified models with b->s gamma, (g-2)_mu, and relic density all imply very large values of m_{1/2} typically greater than about 2.5 TeV, in which case direct detection of sparticles may be a challenge even at the LHC.

Quadruple Yukawa unification in the minimal supersymmetric standard model

Predictions for m 1, tan β, m ν τ are calculated for quadruple third family t- b- τ- ν t Yukawa unified models in the MSSM. The renormalisation group equations for the 3 families of the MSSM, including the right-handed neutrino, are presented. For right-handed tau neutrino Majorana masses that are bigger than 10 11 GeV, the tau neutrino mass is consistent with present cosmological bounds. The m t , tan β predictions are approximately equivalent to those in triple third family Yukawa unified models.

Supercollider signatures of supergravity models with Yukawa unification.

We study the predictions of the simplest SU(5) grand unified model within the framework of minimal supergravity, including constraints from the radiative breaking of electroweak symmetry. As a consequence of the unification of the $b$-quark and $\tau$-lepton Yukawa couplings, the top quark mass is predicted to be close to its fixed point value. We delineate the regions of the supergravity parameter space allowed by constraints from the non-observation of proton decay and from the requirement that the LSP does not overclose the universe. These constraints lead to a definite pattern of sparticle masses: the feature unique to Yukawa unified models is that some of the third generation squarks are much lighter than those of the first two generations. Despite the fact that all sparticle masses and mixings are determined by just four SUSY parameters at the GUT scale (in addition to $m_t$), we find that the signals for sparticle production can vary substantially over the allowed parameter space. We identify six representative scenarios and study the signals from sparticle production at the LHC. We find that by studying the signal in various channels, these scenarios may be distinguished from one another, and also from usually studied ``minimal models'' where squarks and sleptons are taken to be degenerate. In particular, our studies allow us to infer that some third generation squarks are lighter than other squarks---a feature that could provide the first direct evidence of supergravity grand unification.