High-colour and mass hierarchies

We present a model based on the gauge group G = G_HC × G_S × SU(2)_L × U(1), where the hypercolour gauge group G_HC is responsible for the dynamical breaking of the strong group G_S to SU(3)_C of QCD. Chiral symmetry breaking of high-colour representations produces dynamical breaking of the electroweak SU(2)_L × U(1) gauge group. Fermion masses and flavour mixing are dynamically generated from the condensations of high-colour representations. A phenomenological analysis of the model is also presented.     

Renormalization-group analysis of supersymmetric mass hierarchies

A renormalization-group analysis is performed for supersymmetric models of the O'Raifeartaigh type coupled to a Yang-Mills supermultiplet. For an appropriate range of coupling constants, we find that large mass ratios can be naturally generated by one-loop corrections to the effective potential. The results confirm Witten's recent observation that these models provide a potential solution to the gauge hierarchy problem. The general renormalization-group analysis of symmetry breaking developed in this paper is applicable in contexts other than supersymmetry. We also give a simple argument that the canonical form of the supersymmetric Ward identities can be maintained in the presence of quantum effects.     

Gauge hierarchies of SU(N) grand unification

The structure of spontaneous breaking of SU(N) gauge symmetry for grand unification is investigated. The results obtained are applied to the analysis of SU(8) symmetry for which possible ways of breaking and intermediate symmetries are considered. It is assumed that the SU(8) group unifies the subgroups of colour, standard electroweak and horizontal symmetries. We find conditions which it is necessary to impose on the vacuum expectation values of Higgs multiplets to provide an arbitrary breaking pattern of SU(N) symmetry and conserve any intermediate symmetry. If in the SU(8) models considered fermions and mirror fermions do not violate the (V-A) and (V+A) structure of weak interactions, then their masses should not be greater than ～10² GeV. It is also shown that the contributions of fermion and Higgs multiplets to the renormalization group equation for the coupling constant of any subgroup of SU(N) are identical. Renormalization group identities for the case of arbitrary SU(N) breaking are given where the contribution of Higgs multiplets have been taken into account (but they cancel each other). Using these identities one can calculate the mass values for the breaking of the intermediate symmetries in the SU(8) models, and also exclude part of the possible breaking patterns.     

Bolometric bounds on the antineutrino mass

High statistics calorimetric measurements of the beta spectrum of 187Re are being performed with arrays of silver perrhenate crystals operated at low temperature. After a substantial modification of the experimental setup, a new measurement with ten silver perrhenate microbolometers has been running since July 2002. The crystals have masses around 300 microg and their average FWHM energy resolution is of 28.3 eV at the beta end point. The Kurie plot collected during 4485 h x mg effective running time has an end-point energy of 2466.1+/-0.8(stat)+/-1.5(syst) eV, while the half lifetime of the decay is found to be 43.2+/-0.2(stat)+/-0.1(syst) Gy. These values are the most precise obtained so far for 187Re. The best fit value for m(2)(nu(e)) is 147+/-237(stat)+/-90(syst) eV(2), which corresponds to an upper limit for the electron antineutrino mass m(nu(e))< or =21.7 eV at 90% C.L.     

Upper bounds on superpartner masses from upper bounds on the Higgs boson mass

The LHC is putting bounds on the Higgs boson mass. In this Letter we use those bounds to constrain the minimal supersymmetric standard model (MSSM) parameter space using the fact that, in supersymmetry, the Higgs mass is a function of the masses of sparticles, and therefore an upper bound on the Higgs mass translates into an upper bound for the masses for superpartners. We show that, although current bounds do not constrain the MSSM parameter space from above, once the Higgs mass bound improves big regions of this parameter space will be excluded, putting upper bounds on supersymmetry (SUSY) masses. On the other hand, for the case of split-SUSY we show that, for moderate or large tanβ, the present bounds on the Higgs mass imply that the common mass for scalars cannot be greater than 10(11) GeV. We show how these bounds will evolve as LHC continues to improve the limits on the Higgs mass.     

Neutrino mass bounds from neutrinoless double beta-decays and cosmological probes

We investigate the way the total mass sum of neutrinos can be constrained from the neutrinoless double beta-decay and cosmological probes with cosmic microwave background (CMBR), large-scale structures including 2dFGRS and SDSS datasets. First we discuss, in brief, the current status of neutrino mass bounds from neutrino beta decays and cosmic constraint within the flat ΛCMD model. In addition, we explore the interacting neutrino dark-energy model, where the evolution of neutrino masses is determined by quintessence scalar field, which is responsible for cosmic acceleration. Assuming the flatness of the Universe, the constraint we can derive from the current observation is \(\sum m_{\nu } < 0.87\) eV at 95% confidence level, which is consistent with \(\sum m_{\nu } < 0.68\) eV in the flat ΛCDM model without Lyman alpha forest data. In the presence of Lyman- α forest data, interacting dark-energy models prefer a weaker bound \(\sum m_{\nu } < 0.43\) eV to \(\sum m_{\nu } < 0.17\) eV (Seljark et al). Finally, we discuss the future prospect of the neutrino mass bound with weak-lensing effects.     

Stability of triviality mass bounds in the standard model

The perturbative consistency and triviality mass bounds at the two-loop level are discussed in the framework of the standard model.     

Gauge coupling and fermion mass relations in low string scale brane models

We analyze the gauge coupling evolution in brane inspired models with U(3) x U(2) x U(1)^N symmetry at the string scale. We restrict our work to the case of brane configurations with two and three abelian factors (N = 2,3) and where only one Higgs doublet is coupled to down quarks and leptons and only one to the up quarks. We find that the correct hypercharge assignment of the standard model particles is reproduced for six viable models distinguished by different brane configurations. We investigate the third generation fermion mass relations and find that the correct low energy m_b/m_τ ratio can be obtained for b-τ Yukawa coupling equality at a string scale as low as M_S~10³ TeV. Received: 30 August 2005, Published online: 16 November 2005 PACS: 11.25.Wx, 11.25.Uv, 12.10.Kt     

Gauge independence of subleading contributions to the operator product pole mass

We prove that the mass-shell gauge independence of the quark condensate contribution to the quark self-energy is not accidental: the same phenomenon is shown to occur for the mixed condensate contribution. This allows one to conclude that the pole mass is gauge-independent in the operator product expansion.