Minimal four-family supergravity model

Abstract

In this work, we investigate the phenomenology of minimal four-family MSSM supergravity theories containing an additional generation (t', b', T', ~'1 of heavy fermions along with their superpartuers. We constrain the models by demanding gauge coupling constant unification at high energy scales, perturbative values for all Yukawa couplings for energy scales up to the grand-unification scale, radiative electroweak (EW) symmetry breaking via renormalization group evolution down from the grand-unification scale, a neutral LSP, and consistency with constraints from direct searches for new particles and precision electroweak data. The perturbative constraints imply a rather light fourth-family quark and lepton spectrum, and tanp < 3. The lightest CP-even Higgs boson mass receives fourth-family loop corrections that can result in as much as a 30% increase over the corresponding three-family ~BSS value. Significant fourth-family Yukawa coupling contributions to the evolution of scalar masses,lead to unexpected mass hierarchies among the sparticles. For example, the il is generally the lightest slepton and the lightest squark is the g,. A significant lower bound is placed on the gluino mass by the simple requirement that the i; uat be the LSP. Sleptons of the first two families are much more massive compared to the LSP and other neutralinos and charginos than in the three-family models; in particular, all sleptons belonging to the first three families could easily lie beyond the reach of a & = 500 GeV e+e-collider. Consistency tests of the RG equations via mass sum rules and relations are explored. Relations between slepton masses and gaugino masses are shown to be very sensitive to the presence of a fourth generation. The most important near-future experimental probes of the four-family models are reviewed. A scenario with mt -mw and t + i,g? is shown to be inconsistent with universal soft-SUSY-breaking boundary conditions. Full four-family evolution of a, is shown to lead to a significant enhancement in inclusive jet and dijet spectra at Fermilab Tevatron energies when all sparticle masses are near their lower bounds. PACS number(s): 12.6O.Jv, 04.65.+e, .14.8O.Ly MINIMAL ,FOUR-FAMILY SUPERGRAVITY MODEL 1617

Electroweak phase transition in the minimal supersymmetric standard model with four generations

“…In principle, the SM, as well as the MSSM, can accomodate any number of generations. In various contexts, the MSSM with four generations has been studied [8,9,10]. Our study shows that the fourth generation is found to enhance the strength of the first-order electroweak phase transition, while the scalar Higgs boson mass is calculated to be larger than the experimental lower bound, and the scalar quarks of the third generations are comparable to the supersymmetry breaking scale (M SUSY = 1 TeV), in a reasonably wide region of parameter space in the MSSM.…”

“…[8] where the upper bound on the lightest Higgs boson mass is obtained as 152 GeV for small tan β and 96 ≤ m t ′ , m b ′ ≤ 125 GeV in the MSSM with four generations of quarks. If the mass difference between t ′ and b ′ is small, they may have smaller masses [9]. Now, let us study other regions of the parameter space.…”

Simple approach to fourth generation effects inB→Xsl+Solmaz1 2004Phys. Rev. D11010View full textAdd to dashboardCite

“…Generalizations of the SM can be used to introduce a new family, which was performed previously [18]. Using similar techniques, one can search fourth generation effects in B meson decays.…”

Higgs masses in the four generation minimal supersymmetric standard model

“…Some early works exploring four generation supersymmetry models [15] did not really address the possibility of fourth generation quarks above 300 GeV. More recently, an exploration of the electroweak phase transition in the four generation MSSM appeared [16], but it used a value of tan β which put the b ′ Yukawa coupling far outside the region of perturbative validity.…”