1,286 research outputs found
A_4 flavour symmetry breaking scheme for understanding quark and neutrino mixing angles
We propose a spontaneous A_4 flavour symmetry breaking scheme to understand
the observed pattern of quark and neutrino mixing. The fermion mass eigenvalues
are arbitrary, but the mixing angles are constrained in such a way that the
overall patterns are explained while also leaving sufficient freedom to fit the
detailed features of the observed values, including CP violating phases. The
scheme realises the proposal of Low and Volkas to generate zero quark mixing
and tribimaximal neutrino mixing at tree-level, with deviations from both
arising from small corrections after spontaneous A_4 breaking. In the neutrino
sector, the breaking is A_4 --> Z_2, while in the quark and charged-lepton
sectors it is A_4 --> Z_3 = C_3. The full theory has A_4 completely broken, but
the two different unbroken subgroups in the two sectors force the dominant
mixing patterns to be as stated above. Radiative effects within each sector are
shown to deviate neutrino mixing from tribimaximal, while maintaining zero
quark mixing. Interactions between the two sectors -- "cross-talk" -- induce
nonzero quark mixing, and additional deviation from tribimaximal neutrino
mixing. We discuss the vacuum alignment challenge the scenario faces, and
suggest three generic ways to approach the problem. We follow up one of those
ways by sketching how an explicit model realising the symmetry breaking
structure may be constructed.Comment: 14 pages, no figures; v3: Section 5 rewritten to correct an error;
new section added to the appendix; added references; v4: minor change to
appendix C, version to be published by JHE
System-size scan of dihadron azimuthal correlations in ultra-relativistic heavy ion collisions
System-size dependence of dihadron azimuthal correlations in
ultra-relativistic heavy ion collision is simulated by a multi-phase transport
model. The structure of correlation functions and yields of associated
particles show clear participant path-length dependences in collision systems
with a partonic phase. The splitting parameter and root-mean-square width of
away-side correlation functions increase with collision system size from
N+N to Au+Au collisions. The double-peak
structure of away-side correlation functions can only be formed in sufficient
"large" collision systems under partonic phase. The contrast between the
results with partonic phase and with hadron gas could suggest some hints to
study onset of deconfinment.Comment: 8 pages, 4 figures, 1 table; Nucl. Phys. A (accepted
One-dimensional semiconductor in a polar solvent: Solvation and low-frequency dynamics of an excess charge carrier
Due to solvation, excess charge carriers on 1d semiconductor nanostructures
immersed in polar solvents undergo self-localization into polaronic states.
Using a simplified theoretical model for small-diameter structures, we study
low-frequency properties of resulting 1d adiabatic polarons. The combined
microscopic dynamics of the electronic charge density and the solvent leads to
macroscopic Langevin dynamics of a polaron and to the appearance of local
dielectric relaxation modes. Polaron mobility is evaluated as a function of
system parameters. Numerical estimates indicate that the solvated carriers can
have mobilities orders of magnitude lower than the intrinsic values.Comment: Typo in Eq.(12) has been correcte
TeV-scale seesaw from a multi-Higgs model
We suggest new simple model of generating tiny neutrino masses through a
TeV-scale seesaw mechanism without requiring tiny Yukawa couplings. This model
is a simple extension of the standard model by introducing extra one Higgs
singlet, and one Higgs doublet with a tiny vacuum expectation value.
Experimental constraints, electroweak precision data and no large flavor
changing neutral currents, are satisfied since the extra doublet only has a
Yukawa interaction with lepton doublets and right-handed neutrinos, and their
masses are heavy of order a TeV-scale. Since active light neutrinos are
Majorana particles, this model predicts a neutrinoless double beta decay.Comment: 21 pages, 8 figure
Semisolid processing characteristics of AM series Mg alloys by rheo-diecasting
The official published version of this Article can be found at the link below - Copyright @ 2006 ASM InternationalAn investigation has been made into the solidification behavior and microstructural evolution of AM50, AM70, and AM90 alloys during rheo-diecasting, their processibility, and the resulting mechanical properties. It was found that solidification of AM series alloys under intensive melt shearing in the unique twin-screw slurry maker during rheo-diecasting gave rise to numerous spheroidal primary magnesium (Mg) particles that were uniformly present in the microstructure. As a result, the network of the beta-Mg17Al12 phase was consistently interrupted by these spheroidal and ductile particles. Such a microstructure reduced the obstacle of deformation and the harmfulness of the beta-Mg17Al12 network on ductility, and therefore improved the ductility of rheo-diecast AM alloys. It was shown that, even with 9 wt pct Al, the elongation of rheo-diecast AM90 still achieved (9 +/- 1.2) pct. Rheodiecasting thus provides an attractive processing route for upgrading the alloy specification of AM series alloys by increasing the aluminum (Al) content while ensuring ductility. Assessment of the processibility of AM series alloys for semisolid processing showed that high Al content AM series alloys are more suitable for rheo-diecasting than low Al content alloys, because of the lower sensitivity of solid fraction to temperature, the lower liquidus temperature, and the smaller interval between the semisolid processing temperature and the complete solidification temperature.This work is supported by the EPSR
Reexamining nonstandard interaction effects on supernova neutrino flavor oscillations
Several extensions of the standard electroweak model allow new four-fermion
interactions (nu_a nu_b * ff) with strength eps_ab*G_F, where (a,b) are flavor
indices. We revisit their effects on flavor oscillations of massive
(anti)neutrinos in supernovae, in order to achieve, in the region above the
protoneutron star, an analytical treatment valid for generic values of the
neutrino mixing angles (omega,phi,psi)=(theta_12,theta_13,theta_23). Assuming
that eps_ab<<1, we find that the leading effects on the flavor transitions
occurring at high (H) and low (L) density along the supernova matter profile
can be simply embedded through the replacements phi-->phi+eps_H and
omega-->omega+eps_L, respectively, where eps_H and eps_L are specific linear
combinations of the eps_ab's. Similar replacements hold for eventual
oscillations in the Earth matter. From a phenomenological point of view, the
most relevant consequence is a possible uncontrolled bias (phi-->phi+eps_H) in
the value of the mixing angle phi inferred by inversion of supernova neutrino
data. Such a drawback, however, does not preclude the discrimination of the
neutrino mass spectrum hierarchy (direct or inverse) through supernova neutrino
oscillations.Comment: Text clarified, one figure added. To appear in PR
Di-hadron azimuthal correlation and Mach-like cone structure in parton/hadron transport model
In the framework of a multi-phase transport model (AMPT) with both partonic
and hadronic interactions, azimuthal correlations between trigger particles and
associated scattering particles have been studied by the mixing-event
technique. The momentum ranges of these particles are
GeV/ and GeV/ (soft), or 4
GeV/ and GeV/ (hard) in Au + Au collisions at
= 200 GeV. A Mach-like structure has been observed in
correlation functions for central collisions. By comparing scenarios with and
without parton cascade and hadronic rescattering, we show that both partonic
and hadronic dynamical mechanisms contribute to the Mach-like structure of the
associated particle azimuthal correlations. The contribution of hadronic
dynamical process can not be ignored in the emergence of Mach-like correlations
of the soft scattered associated hadrons. However, hadronic rescattering alone
cannot reproduce experimental amplitude of Mach-like cone on away-side, and the
parton cascade process is essential to describe experimental amplitude of
Mach-like cone on away-side. In addition, both the associated multiplicity and
the sum of decrease, whileas the increases, with the impact
parameter in the AMPT model including partonic dynamics from string melting
scenario.Comment: 9 pages, 5 figures; Physics Letters B 641, 362-367 (2006
Effects of new physics in neutrino oscillations in matter
A new flavor changing electron neutrino interaction with matter would always
dominate the nu_e oscillation probability at sufficiently high neutrino
energies. Being suppressed by theta_{13}, the energy scale at which the new
effect starts to be relevant may be within the reach of realistic experiments,
where the peculiar dependence of the signal with energy could give rise to a
clear signature in the nu_e --> nu_tau channel. The latter could be observed by
means of a coarse large magnetized detector by exploiting tau --> mu decays. We
discuss the possibility of identifying or constraining such effects with a high
energy neutrino factory. We also comment on the model independent limits on
them.Comment: 11 pages, 5 figure
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