832 research outputs found
Quark and Lepton Masses in 5D SO(10)
We construct a five dimensional supersymmetric SO(10)D grand
unified model with an orbifold as the extra
dimension. The orbifold breaks half of the supersymmetry and breaks the SO(10)
gauge symmetry down to . The Higgs mechanism is used to break the remaining gauge symmetry
the rest of the way to the Standard Model. We place matter fields variously in
the bulk and on the orbifold fixed points and the resulting massless fields are
mixtures between these brane and bulk fields. A chiral adjoint field in the
bulk gets a U(1) vacuum expectation value, resulting in an -dependent
localization of the bulk matter fields and the Standard Model Higgs field. This
Higgs field localization allows us to simultaneously explain the hierarchies
and . The model uses 11 parameters to fit the 13
independent low energy observables of the quark and charged lepton Yukawa
matrices. The model predicts the values of two quark mass combinations,
\f{m_u}{m_c} and , each of which are predicted to be
approximately above their experimental values. The remaining
observables are successfully fit at the 5% level.Comment: 52 pages, published version, includes more discussion of 6D version
of mode
F-term Induced Flavor Mass Spectrum
New mechanism of generating flavor mass spectrum is proposed by using an
O'Raifeartaigh-type supersymmetry breaking model. A desired bilinear form of
fermion mass spectrum is naturally realized through F-components of
gauge-singlet (nonet of SU(3) flavor symmetry) superfields, and the suitable
charged-lepton mass relation is reproduced. The charged-slepton mass spectrum
is non-degenerate in general, and can be even hierarchical (proportional to the
charged-lepton masses in the specific case). Flavor changing neutral processes
are suppressed since the charged-lepton and slepton (except for right-handed
sneutrino) mass matrices are diagonalized simultaneously in the flavor space.
The right-handed sneutrinos are light with the similar ratio to the lepton
sector (//).Comment: 12 pages, no figur
On the gluon content of the eta and eta' mesons
A phenomenological analysis of radiative and
decays is performed with the purpose of determining the gluonic content of the
and wave functions. Our results show that within our model
there is no evidence for a gluonium contribution in the ,
, or the , . In terms of a mixing angle description this corresponds to
and . In
addition, the - mixing angle is found to be if we don't allow for a gluonium component.Comment: 16 pages, 3 figures, JHEP style. First part of data fitting changed,
conclusions not modifie
Searching for Composite Neutrinos in the Cosmic Microwave Background
We analyze signals in the Cosmic Microwave Background (CMB) in theories where
the small Dirac neutrino masses arise as a consequence of the compositeness of
right-handed neutrinos. In such theories, the right-handed neutrinos are
massless ``baryons'' of a new strong gauge interaction. We find that the
results crucially depend on whether or not the new strong sector undergoes
chiral symmetry breaking. In the case with chiral symmetry breaking, we find
that there are indeed signals in the CMB, but none of them is a direct
consequence of neutrino compositeness. In contrast, if the underlying theory
does not undergo chiral symmetry breaking, the large scattering cross-section
among the composites gives rise to a sizable CMB signal over a wide region of
the parameter space, and it can potentially probe whether the neutrino mass
spectrum is hierarchical, inverse hierarchical, or degenerate. We also discuss
collider constraints on the compositeness in the context of the CMB signals.Comment: 26 pages. References and clarifying comments added. Version appearing
to JHE
Experimental Status of Exotic Mesons and the GlueX Experiment
One of the unanswered and most fundamental questions in physics regards the
nature of the confinement mechanism of quarks and gluons in QCD. Exotic hybrid
mesons manifest gluonic degrees of freedom and their spectroscopy will provide
the data necessary to test assumptions in lattice QCD and the specific
phenomenology leading to confinement. Within the past two decades a number of
experiments have put forth tantalizing evidence for the existence of exotic
hybrid mesons in the mass range below 2 GeV. This talk represents an overview
of the available data and what has been learned. In looking toward the future,
the GlueX experiment at Jefferson Laboratory represents a new initiative that
will perform detailed spectroscopy of the light-quark meson spectrum. This
experiment and its capabilities will be reviewed.Comment: 10 pages, 8 figures, 2nd Meeting of the APS Topical Group on Hadron
Physics GHP06, Nashville, TN (10/22-10/24/06
Inclusive Semi-leptonic B Decays to order 1/m_b^4
We give a systematic way to compute higher orders in the 1/m_b expansion in
inclusive semi-leptonic decays at tree level. We reproduce the known 1/m_b^3
terms and compute the 1/m_b^4 terms at tree level. The appearing
non-perturbative parameters and the impact on the determination of V_{cb} are
discussed.Comment: 23 pages, 3 figures, uses phystex.st
Composition of the Pseudoscalar Eta and Eta' Mesons
The composition of the eta and eta' mesons has long been a source of
discussion and is of current interest with new experimental results appearing.
We investigate what can be learnt from a number of different processes: V to P
gamma and P to V gamma (V and P are light vector and pseudoscalar mesons
respectively), P to gamma gamma, J/psi,psi' to P gamma, J/psi,psi' to P V, and
chi_{c0,2} to PP. These constrain the eta-eta' mixing angle to a consistent
value, phi approx 42 degrees; we find that the c cbar components are lesssim 5%
in amplitude. We also find that, while the data hint at a small gluonic
component in the eta', the conclusions depend sensitively on unknown form
factors associated with exclusive dynamics. In addition, we predict BR(psi' to
eta' gamma) approx 1 10^{-5} and BR(chi_{c0} to eta eta') approx 2 10^{-5} - 1
10^{-4}. We provide a method to test the mixing using chi_{c2} to eta eta, eta'
eta', and eta eta' modes and make some general observations on chi_{c0,2}
decays. We also survey the semileptonic and hadronic decays of bottom and
charmed mesons and find some modes where the mixing angle can be extracted
cleanly with the current experimental data, some where more data will allow
this, and some where a more detailed knowledge of the different amplitudes is
required.Comment: 34 pages, 11 figures. v2: version published in JHEP, added
substantial section on B and D meson electroweak decays, added comment on
psi' to eta(')/eta_c gamma, Figs 5 and 6 split and made clearer, added
references, other minor revisions which don't change conclusion
The Jacobi Polynomials QCD analysis for the polarized structure function
We present the results of our QCD analysis for polarized quark distribution
and structure function . We use very recently experimental data
to parameterize our model. New parameterizations are derived for the quark and
gluon distributions for the kinematic range , GeV^2. The analysis is based on the Jacobi polynomials
expansion of the polarized structure functions. Our calculations for polarized
parton distribution functions based on the Jacobi polynomials method are in
good agreement with the other theoretical models. The values of
and are determined.Comment: 23 pages, 8 figures and 4 table
Determination of the magnetic susceptibility of the quark condensate using radiative heavy meson decays
We use a light-cone sum rule (LCSR) analysis of the branching ratios of
radiative meson decays to contrain the value of the magnetic susceptibility of
the quark condensate . For the first time, we use a complete set of
three-particle distribution amplitudes that enables us to give a consistent
prediction for the branching ratios. Furthermore we will make use of a very
recent update of several non-perturbative parameters. Our final result for
(assuming asymptotic wave
functions) agrees with the currently used value of .Comment: 21 pages, 4 figures, references adde
Heavy Quarkonium States with the Holographic Potential
The quarkonium states in a quark-gluon plasma is examined with the heavy
quark potential implied by the holographic principle. Both the vanila
AdS-Schwarzschild metric and the one with an infrared cutoff are considered.
The dissociation temperature is calculated by solving the Schr\"o dinger
equation of the potential model. In the case of the AdS-Schwarzschild metric
with a IR cutoff, the dissociation temperatures for and
with the U-ansatz of the potential are found to agree with the lattice results
within a factor of two.Comment: 9 pages with 2 figues in Revte
- …