Fermion Masses and Coupling Unification in E6. Life in the Desert

We present an $E_6$ Grand Unified model with a realistic pattern of fermion masses. All standard model fermions are unified in three fundamental 27-plets (i.e. supersymmetry is not invoked), which involve in addition right handed neutrinos and three families of vector like heavy quarks and leptons. The lightest of those can lie in the low TeV range, being accessible to future collider experiments. Due to the high symmetry, the masses and mixings of all fermions are closely related. The new heavy fermions play a crucial role for the quark and lepton mass matrices and the bilarge neutrino oscillations. In all channels generation mixing and ${\cal CP}$ violation arise from a single antisymmetric matrix. The $E_6$ breaking proceeds via an intermediate energy region with SU(3)_L\tm SU(3)_R\tm SU(3)_C gauge symmetry and a discrete left-right symmetry. This breaking pattern leads in a straightforward way to the unification of the three gauge coupling constants at high scales, providing for a long proton lifetime. The model also provides for the unification of the top, bottom and tau Yukawa couplings and for new interesting relations in flavor and generation space.Comment: RevTex4, three ps figures, some correction

Experimental cross sections of Ho 165 (α,n) Tm 168 and Er 166 (α,n) Yb 169 for optical potential studies relevant for the astrophysical γ process

Background: Optical potentials are crucial ingredients for the prediction of nuclear reaction rates needed in simulations of the astrophysical γ process. Associated uncertainties are particularly large for reactions involving α particles. This includes (γ,α) reactions which are of special importance in the γ process. Purpose: The measurement of (α,n) reactions allows for an optimization of currently used α-nucleus potentials. The reactions Ho165(α,n) and Er166(α,n) probe the optical model in a mass region where γ process calculations exhibit an underproduction of p nuclei which is not yet understood. Method: To investigate the energy-dependent cross sections of the reactions Ho165(α,n) and Er166(α,n) close to the reaction threshold, self-supporting metallic foils were irradiated with α particles using the FN tandem Van de Graaff accelerator at the University of Notre Dame. The induced activity was determined afterwards by monitoring the specific β-decay channels. Results: Hauser-Feshbach predictions with a widely used global α potential describe the data well at energies where the cross sections are almost exclusively sensitive to the α widths. Increasing discrepancies appear towards the reaction threshold at lower energy. Conclusions: The tested global α potential is suitable at energies above 14 MeV, while a modification seems necessary close to the reaction threshold. Since the γ and neutron widths show non-negligible impact on the predictions, complementary data are required to judge whether or not the discrepancies found can be solely assigned to the α width. © 2014 American Physical Society.Peer reviewedFinal Accepted Versio

Leading twist moments of the neutron structure function F2n

We perform a global analysis of neutron F2n structure function data, obtained by combining proton and deuteron measurements over a large range of kinematics. From these data the lowest moments (n <= 10) of the leading twist neutron F2n structure function are extracted. Particular attention is paid to nuclear effects in the deuteron, which become increasingly important for the higher moments. Our results for the nonsinglet, isovector (p - n) combination of the leading twist moments are used to test recent lattice simulations. We also determine the lowest few moments of the higher twist contributions, and find these to be approximately isospin independent, suggesting the possible dominance of ud correlations over uu and dd in the nucleon.Comment: 34 pages, 13 figures. Minor changes. Version to appear in NP

Quark mixing from softly broken symmetries

Quark flavor mixing may originate in the soft breaking of horizontal symmetries. Those symmetries, which in the simplest case are three family U(1) groups, are obeyed only by the dimension-4 Yukawa couplings and lead, when unbroken, to the absence of mixing. Their breaking may arise from the dimension-3 mass terms of SU(2)-singlet vector-like quarks. Those gauge-singlet mass terms break the horizontal symmetries at a scale much higher than the Fermi scale, yet softly, leading to quark mixing while the quark masses remain unsuppressed.Comment: 9 pages, plain Latex, no figure

Weak Hyperon Decays: Quark Sea and SU(3) Symmetry Breaking

An explanation of the difference in the values of the apparent $f/d$ ratios for the S- and P- wave amplitudes of nonleptonic hyperon decays is proposed. The argument is formulated in the framework of the standard pole model with $(56,0^{+})$ ground-state and $(70,1^{-})$ excited baryons as intermediate states for the P- and S- waves respectively. Under the assumption that the dominant part of the deviation of $(f/d)_{P-wave}$ from $-1$ is due to large quark sea effects, $SU(3)$ symmetry breaking in energy denominators is shown to lead to a prediction for $(f/d)_{S-wave}$ which is in excellent agreement with experiment. This corroborates our previous unitarity calculations which indicated that the matrix elements $$ of the parity conserving weak Hamiltonian between the ground-state baryons are characterized by $f_{0}/d_{0} \approx -1.6$ or more. A brief discussion of the problem of the relative size of S- and P- wave amplitudes is given. Finally, implications for weak radiative hyperon decays are also discussed.Comment: 26 pages, LATEX, 1647/PH IFJ Krako

The first direct measurement of ¹²C (¹²C,n) ²³Mg at stellar energies

Neutrons produced by the carbon fusion reaction ¹²C(¹²C,n)²³Mg play an important role in stellar nucleosynthesis. However, past studies have shown large discrepancies between experimental data and theory, leading to an uncertain cross section extrapolation at astrophysical energies. We present the first direct measurement that extends deep into the astrophysical energy range along with a new and improved extrapolation technique based on experimental data from the mirror reaction ¹²C(¹²C,p)²³Na. The new reaction rate has been determined with a well-defined uncertainty that exceeds the precision required by astrophysics models. Using our constrained rate, we find that ¹²C(¹²C,n)²³Mg is crucial to the production of Na and Al in Pop-III Pair Instability Supernovae. It also plays a non-negligible role in the production of weak s-process elements as well as in the production of the important galacti

Rare exclusive semileptonic b -> s transitions in the Standard Model

We study long-distance effects in rare exclusive semileptonic decays B -> (K, K*) (l+ l-, nu bar{nu}) and analyze dilepton spectra and asymmetries within the framework of the Standard Model. The form factors, describing the meson transition amplitudes of the effective Hamiltonian are calculated within the lattice-constrained dispersion quark model: the form factors are given by dispersion representations through the wave functions of the initial and final mesons, and these wave functions are chosen such that the B -> K* transition form factors agree with the lattice results at large q**2. We calculate branching ratios of semileptonic B -> K, K* transition modes and study the sensitivity of observables to the long-distance contributions. The shape of the forward-backward asymmetry and the longitudinal lepton polarization asymmetry are found to be independent of the long-distance effects and mainly determined by the values of the Wilson coefficients in the Standard Model.Comment: revtex, 17 pp., 5 figures with epsfig.st

Highly Pathogenic H5N1 Influenza Viruses Carry Virulence Determinants beyond the Polybasic Hemagglutinin Cleavage Site

Highly pathogenic avian influenza viruses (HPAIV) originate from avirulent precursors but differ from all other influenza viruses by the presence of a polybasic cleavage site in their hemagglutinins (HA) of subtype H5 or H7. In this study, we investigated the ability of a low-pathogenic avian H5N1 strain to transform into an HPAIV. Using reverse genetics, we replaced the monobasic HA cleavage site of the low-pathogenic strain A/Teal/Germany/Wv632/2005 (H5N1) (TG05) by a polybasic motif from an HPAIV (TG05poly). To elucidate the virulence potential of all viral genes of HPAIV, we generated two reassortants carrying the HA from the HPAIV A/Swan/Germany/R65/06 (H5N1) (R65) plus the remaining genes from TG05 (TG05-HAR65) or in reversed composition the mutated TG05 HA plus the R65 genes (R65-HATG05poly). In vitro, TG05poly and both reassortants were able to replicate without the addition of trypsin, which is characteristic for HPAIV. Moreover, in contrast to avirulent TG05, the variants TG05poly, TG05-HAR65, and R65-HATG05poly are pathogenic in chicken to an increasing degree. Whereas the HA cleavage site mutant TG05poly led to temporary non-lethal disease in all animals, the reassortant TG05-HAR65 caused death in 3 of 10 animals. Furthermore, the reassortant R65-HATG05poly displayed the highest lethality as 8 of 10 chickens died, resembling “natural” HPAIV strains. Taken together, acquisition of a polybasic HA cleavage site is only one necessary step for evolution of low-pathogenic H5N1 strains into HPAIV. However, these low-pathogenic strains may already have cryptic virulence potential. Moreover, besides the polybasic cleavage site, the additional virulence determinants of H5N1 HPAIV are located within the HA itself and in other viral proteins