We calculate the strength of the electroweak phase transition in a supersymmetric model with four chiral generations. The additional chiral fermions (and scalar partners) lower the critical temperature and thus strengthen the first-order phase transition. The scalar partners stabilize the potential, leading to an effective theory that is bounded from below. We identify the ensemble of parameters where φc/Tc > ∼ 1 simultaneous with obtaining a large enough Higgs mass. Our calculations focus on a subset of the full four generational supersymmetric parameter space: We take the pseudoscalar heavy, tan β = 1, and neglect all subleading contributions to the effective potential. We find that the region of parameter space with a strong first-order phase transition requires mq /m q < ∼ 1.1 while the constraint on the lightest Higgs mass requires mq /m q > ∼ 1 with m q > ∼ 300 GeV. We are led to an intriguing prediction of quarks and squarks just beyond the current Tevatron direct search limits that are poised to be discovered quickly at the LHC.
The new particle X recently discovered by the ATLAS and CMS Collaborations in searches for the Higgs boson has been observed to decay into γγ, ZZ * and W W * , but its spin and parity, J P , remain a mystery, with J P = 0 + and 2 + being open possibilities. We use PYTHIA and Delphes to simulate an analysis of the angular distribution of gg → X → γγ decays in a full 2012 data set, including realistic background levels. We show that this angular distribution should provide strong discrimination between the possibilities of spin zero and spin two with graviton-like couplings: ∼ 3σ if a conservative symmetric interpretation of the log-likelihood ratio (LLR) test statistic is used, and ∼ 6σ if a less conservative asymmetric interpretation is used. The W W and ZZ couplings of the Standard Model Higgs boson and of a 2 + particle with graviton-like couplings are both expected to exhibit custodial symmetry. We simulate the present ATLAS and CMS search strategies for X → W W * using PYTHIA and Delphes, and show that their efficiencies in the case of a spin-two particle with graviton-like couplings are a factor 1.9 smaller than in the spin-zero case. On the other hand, the ratio of X 2 + → W W * and ZZ * branching ratios is larger than that in the 0 + case by a factor 1.3. We find that the current ATLAS and CMS results for X → W W * and X → ZZ * decays are compatible with custodial symmetry under both the spin-zero and -two hypotheses, and that the data expected to become available during 2012 are unlikely to discriminate significantly between these possibilities.
We calculate the two-body decay rates of "quirkonium" states formed from quirks that acquire mass solely through electroweak symmetry breaking. We consider SU (N )ic infracolor with two flavors of quirks transforming under the electroweak group (but not QCD) of the Standard Model. In one case, the quirks are in a chiral representation of the electroweak group, while in the other case, a vector-like representation. The differences in the dominant decay channels between "chiral quirkonia" versus "vector-like quirkonia" are striking. Several chiral quirkonia states can decay into the unique two-body resonance channels W H, ZH, tt, tb/bt, and γH, which never dominate for vector-like quirkonia. Additionally, the channels W W , W Z, ZZ, and W γ, are shared among both chiral and vector-like quirkonia. Resonances of dileptons or light quarks (dijets) can dominate for some vector-like quirkonia states throughout their mass range, while these modes never dominate for chiral quirkonia unless the decays into pairs of gauge or Higgs bosons are kinematically forbidden.
We compute the one-loop corrections to the Z → b ¯ b vertex in the U (1) R symmetric minimal supersymmetric extension of the standard model. We find that the predicted value of R b is consistent with experiment if the mass of the lighter top squark is no more than 180 GeV. Furthermore, other data combines to place a lower bound of 88 GeV on the mass of the light top squark. A top squark in this mass range should be accessible to searches by experiments at FNAL and LEP. 1
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