116037266
Revisiting lepton flavor violation in a supersymmetric type II seesaw mechanism
In view of the recent measurement of reactor mixing angle 13 and updated limit on BR( ! e ) by the MEG experiment, we re-examine the charged lepton avor violations in a framework of supersymmetric type II seesaw mechanism. Supersymmetric type II seesaw predicts strong correlation between BR( ! e ) and BR( ! ) mainly in terms of the neutrino mixing angles. We show that such a correlation can be determined accurately after the measurement of 13. We compute dierent factors which can aect this correlation and show that the mSUGRA-like scenarios, in which slepton masses are taken to be universal at the high scale, predicts 3:5 . BR( ! )=BR( ! e ) . 30 for normal hierarchical neutrino masses. Any experimental indication of deviation from this prediction would rule out the minimal models of supersymmetric type II seesaw. We show that the current MEG limit puts severe constraints on the light sparticle spectrum in mSUGRA model if the seesaw scale lies within 10 13 -10 15 GeV. It is shown that these constraints can be relaxed and relatively light sparticle spectrum can be obtained in a class of models in which the soft mass of triplet scalar is taken to be non-universal at the high scale.
119259182
Quasidegenerate neutrinos in SO(10)
We propose a specific ansatz for the structure of Yukawa matrices in SO(10) models that lead to quasidegenerate neutrinos through the type-I seesaw mechanism. Consistency of this ansatz is demonstrated through detailed fits to fermion masses and mixing angles, all of which can be explained with reasonable accuracy in a model that uses the Higgs fields transforming as 10, 120, and 126 representations of SO(10). The proposed ansatz is shown to follow from an extended model based on the three generations of the vectorlike fermions and an O(3) flavor symmetry. Successful numerical fits are also discussed in earlier proposed models, which used a combination of the type-I and type-II seesaw mechanisms for obtaining quasidegenerate neutrinos. Large neutrino mixing angles emerge as a consequence of neutrino mass degeneracy in both these cases.
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
119107787
TESTING TIMES FOR SUPERSYMMETRY: LOOKING UNDER THE LAMP POST
We make a critical study of two highly-constrained models of supersymmetry — the constrained minimal supersymmetric standard model (cMSSM), and the nonuniversal Higgs mass (NUHM) model — in the light of the 125–126 GeV Higgs boson, the first observation of Bs→μμ at the LHCb, and the updated B → τν branching ratio at BELLE. It turns out that these models are still allowed by the experimental data, even if we demand that there be a light stop with mass less than 1.5 TeV. The only significant effects of all these constraints are to push the mass of the light stop above ~500 GeV, and to prefer the universal trilinear coupling A0 to be large and negative. We calculate the Higgs boson branching ratios to WW, ZZ, ττ and γγ in these models and show that improved experimental limits on these could put them to the most stringent experimental tests yet.
119247811
Horizontal symmetries of leptons with a massless neutrino
Abstract Residual symmetry G ν of neutrino mass matrix with a massless neutrino and embedding of G ν and the residual symmetry G l of the charged lepton mass matrix into finite discrete groups G is discussed. Massless neutrino results if G ν and hence G are subgroups of U ( 3 ) rather than of SU ( 3 ) . Structure of the resulting leptonic mixing matrix U PMNS is discussed in three specific examples based on groups (a) Σ ( 3 N 3 ) , (b) Σ ( 2 N 2 ) and (c) S 4 ( 2 ) ≡ A 4 ⋊ Z 4 . Σ ( 3 N 3 ) groups are able to reproduce either the second or the third column of U PMNS correctly. Σ ( 2 N 2 ) groups lead to prediction θ 13 = 0 , θ 23 = π 4 for the reactor and atmospheric mixing angles respectively if neutrino mass hierarchy is inverted. Solar angle remains undetermined in this case. This also gets determined when G = S 4 ( 2 ) which can give bi-maximal mixing for inverted hierarchy. Examples (b) and (c) provide a good zeroth order approximation to realistic leptonic mixing with a massless neutrino. We also present an example of the specific model based on S 4 ( 2 ) symmetry in which a massless neutrino and viable leptonic mixing angles are obtained.
119213437
Discrete flavor symmetries for degenerate solar neutrino pair and their predictions
Flavour symmetries appropriate for describing a neutrino spectrum with degenerate solar pair and a third massive or massless neutrino are discussed. We demand that the required residual symmetries of the leptonic mass matrices be subgroups of some discrete symmetry group $G_f$. $G_f$ can be a subgroup of SU(3) if the third neutrino is massive and we derive general results on the mixing angle predictions for various discrete subgroups of SU(3). The main results are: (a) All the SU(3) subgroups of type C fail in simultaneously giving correct $\theta_{13}$ and $\theta_{23}$. (b) All the groups of type D can predict a relation $\cos^2\theta_{13} \sin^2\theta_{23}=\frac{1}{3}$ among the mixing angles which appears to be a good zeroth order approximation. Among these, various $\Delta(6n^2)$ groups with $n\geq 8$ can simultaneously lead also to $\sin^2 \theta_{13}$ in agreement with global fit at 3$\sigma$. (c) The group $\Sigma(168)\cong PSL(2,7)$ predicts near to the best fit value for $\theta_{13}$ and $\theta_{23}$ within the 1$\sigma$ range. All discrete subgroups of U(3) with order $<512$ and having three dimensional irreducible representation are considered as possible $G_f$ when the third neutrino is massless. Only seven of them are shown to be viable and three of these can correctly predict $\theta_{13}$ and/or $\theta_{23}$. The solar angle remains undetermined at the leading order in all the cases due to degeneracy in the masses. A class of general perturbations which can correctly reproduce all the observables are discussed in the context of several groups which offer good leading order predictions.
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.