115685696
Fermion masses and mixings in a - symmetric SO(10)
The {mu}-{tau} symmetry imposed on the neutrino mass matrix in the flavor basis is known to be quite predictive. We integrate this very specific neutrino symmetry into a more general framework based on the supersymmetric SO(10) grand unified theory. As in several other models, the fermion mass spectrum is determined by Hermitian mass matrices resulting from the renormalizable Yukawa couplings of the 16-plet of fermions with the Higgs fields transforming as 10, 126, and 120 representations of the SO(10) group. The {mu}-{tau} symmetry is spontaneously broken through the 120-plet. Consequences of this scheme are considered for fermion masses using both a type-I and a type-II seesaw mechanism. This scenario is shown to lead to a generalized CP invariance of the mass matrices and vanishing CP violating phases if the Yukawa couplings are invariant under the {mu}-{tau} symmetry. Small explicit breaking of the {mu}-{tau} symmetry is then shown to provide a very good understanding of all of the fermion masses and mixing. Detailed fits to the fermion spectrum are presented in several scenarios. One obtains a very good fit to all observables in the context of the type-I seesaw mechanism, but the type-II seesaw model also provides a good description exceptmore » for the overall scale of the neutrino masses. Three major predictions on the leptonic mixing parameters in the type-I seesaw case are (i) the atmospheric mixing angle {theta}{sub 23}{sup l} close to maximal, (ii) {theta}{sub 13}{sup l} close to the present upper bound, and (iii) a negative but very small Dirac CP violating phase in the neutrino oscillations.« less
118568742
Yukawa coupling unification in SO(10) with positive \mu\ and a heavier gluino
The t-b-tau unification with positive Higgs mass parameter \mu\ in the minimal supersymmetric standard model prefers "just so" Higgs splitting and a light gluino < 500 GeV which appears to be ruled out by the recent LHC searches. We reanalyze constraints on soft supersymmetry breaking parameters in this scenario allowing independent splittings among squarks and Higgs doublets at the grand unification scale and show that it is possible to obtain t-b-tau unification and satisfy experimental constraints on gluino mass without raising supersymmetry breaking scale to very high value ~ 20 TeV. We discuss the origin of independent squark and Higgs splittings in realistic SO(10) models. Just so Higgs splitting can be induced without significantly affecting the t-b-tau unification in SO(10) models containing Higgs fields transforming as 10+\bar{126}+126+210. This splitting arises in the presence of non-universal boundary conditions from mixing between 10 and other Higgs fields. Similarly, if additional matter fields are introduced then their mixing with the matter multiplet 16 is shown to generate the squark splitting required to raise the gluino mass within the t-b-tau unified models with positive \mu.
120224041
Unified description of fermion masses with quasi‐degenerate neutrinos in SO(10)
Obtaining a unified description of the quasi‐degenerate neutrino mass spectrum together with the hierarchical charged fermions is a challenging task. In this talk, we discuss two distinct possible scenarios leading to such spectra in the supersymmetric SO(10) grand unified framework. Consistency of both scenarios is demonstrated through detailed fits to fermion masses and mixing angles, all of which can be explained with reasonable accuracy in a model with the most general Yukawa sector of SO(10). The origin of large neutrino mixing angles is linked to neutrino mass degeneracy in both the scenarios.
26745596
A massless neutrino and lepton mixing patterns from finite discrete subgroups of U(3)
A bstractFinite discrete subgroups of U(3) as possible flavour symmetries Gf for a massless neutrino with predictive mixing angles are studied. This is done by assuming that a residual symmetry Sν appropriate for describing a massless neutrino is contained in Gf. It is shown that all the groups Gf admitting three dimensional faithful irreducible representation and generated from a specific set of 3×3 matrices imply only one of the three flavour compositions for the massless state namely, unmixed, maximally mixed with equal probabilities and bimaximally mixed with probabilities (0, 1/2, 1/2) and their permutations. This result holds irrespective of the order of Gf and the choice of Sν within it. All of these lead to unfavorable leading order prediction for the solar mixing angle. Neutrino mixing pattern is then numerically investigated in case of subgroups of U(3) with order less than 512 and it is found that only one of these can lead to a massless neutrino and leading order predictions for all the mixing angles close to their experimental values. Ways to correct for the solar angle prediction are proposed and two concrete examples giving the observed mixing pattern are discussed.
25504271
Cytochrome rC552, formed during expression of the truncated, Thermus thermophilus cytochrome c552 gene in the cytoplasm of Escherichia coli, reacts spontaneously to form protein-bound 2-formyl-4-vinyl (Spirographis) heme.
Expression of the truncated (lacking an N-terminal signal sequence) structural gene of Thermus thermophilus cytochrome c(552) in the cytoplasm of Escherichia coli yields both dimeric (rC(557)) and monomeric (rC(552)) cytochrome c-like proteins [Keightley, J. A., et al. (1998) J. Biol. Chem. 273, 12006-12016], which form spontaneously without the involvement of cytochrome c maturation factors. Cytochrome rC(557) is comprised of a dimer and has been structurally characterized [McRee, D., et al. (2001) J. Biol. Chem. 276, 6537-6544]. Unexpectedly, the monomeric rC(552) transforms spontaneously to a cytochrome-like chromophore having, in its reduced state, the Q(oo) transition (alpha-band) at 572 nm (therefore called p572). The X-ray crystallographic structure of rC(552), at 1.41 A resolution, shows that the 2-vinyl group of heme ring I is converted to a [heme-CO-CH(2)-S-CH(2)-C(alpha)] conjugate with cysteine 11. Electron density maps obtained from isomorphous crystals of p572 at 1.61 A resolution reveal that the 2-vinyl group has been oxidized to a formyl group. This explains the lower energy of the Q(oo)() transition, the presence of a new, high-frequency band in the resonance Raman spectra at 1666 cm(-1) for oxidized and at 1646 cm(-1) for reduced samples, and the greatly altered, paramagnetically shifted (1)H NMR spectrum observed for this species. The overall process defines a novel mechanism for oxidation of the 2-vinyl group to a 2-formyl group and adds to the surprising array of chemical reactions that occur in the interaction of heme with the CXXCH sequence motif in apocytochromes c.