21,003 research outputs found
Tests of non-standard electroweak couplings of right-handed quarks
The standard model can be interpreted as the leading order of a Low-Energy
Effective Theory (LEET) invariant under a higher non linearly realized symmetry
equipped with a systematic power
counting. Within the minimal version of this ``not quite decoupling'' LEET, the
dominant non-standard effect appears at next-to-leading order (NLO) and is a
modification of the couplings of fermions to W and Z. In particular, the
coupling of right-handed quarks to Z is modified and a direct coupling of
right-handed quarks to W emerges. Charged right-handed lepton currents are
forbidden by an additional discrete symmetry in the lepton sector originally
designed to suppress Dirac neutrino masses. A complete NLO analysis of
experimental constraints on these modified couplings is presented. Concerning
couplings of light quarks, the interface of the electroweak tests with QCD
aspects is discussed in detail.Comment: 56 pages, 14 figures, v2: references added, minor modifications in
the text, accepted for publication in JHE
Photon breeding mechanism in relativistic jets: astrophysical implications
Photon breeding in relativistic jets involves multiplication of high-energy
photons propagating from the jet to the external environment and back with the
conversion into electron-positron pairs. The exponential growth of the energy
density of these photons is a super-critical process powered by the bulk energy
of the jet. The efficient deceleration of the jet outer layers creates a
structured jet morphology with the fast spine and slow sheath. In initially
fast and high-power jets even the spine can be decelerated efficiently leading
to very high radiative efficiencies of conversion of the jet bulk energy into
radiation. The decelerating, structured jets have angular distribution of
radiation significantly broader than that predicted by a simple blob model with
a constant Lorentz factor. This reconciles the discrepancy between the high
Doppler factors determined by the fits to the spectra of TeV blazars and the
low apparent velocities observed at VLBI scales as well as the low jet Lorentz
factors required by the observed statistics and luminosity ratio of
Fanaroff-Riley I radio galaxies and BL Lac objects. Photon breeding produces a
population of high-energy leptons in agreement with the constraints on the
electron injection function required by spectral fits of the TeV blazars.
Relativistic pairs created outside the jet and emitting gamma-rays by inverse
Compton process might explain the relatively high level of the TeV emission
from the misaligned jet in the radio galaxies. The mechanism reproduces basic
spectral features observed in blazars including the blazar sequence (shift of
the spectral peaks towards lower energies with increasing luminosity). The
mechanism is very robust and can operate in various environments characterised
by the high photon density.Comment: 6 pages, 3 figures, to appear in the proceedings of the HEPRO
conference, September 24-28, 2007, Dublin, Irelan
Juncture stress fields in multicellular shell structures. Volume III - Stresses and deformations on fixed-edge segmental conical shells Final report
Equations for thin elastic conical shells and digital program for analysis of stress and deformation on fixed edge segmental conical shells - solution by finite difference techniqu
Monopole and Dyon Bound States in N=2 Supersymmetric Yang-Mills Theories
We study the existence of monopole bound states saturating the BPS bound in
N=2 supersymmetric Yang-Mills theories. We describe how the existence of such
bound states relates to the topology of index bundles over the moduli space of
BPS solutions. Using an index theorem, we prove the existence of certain
BPS states predicted by Seiberg and Witten based on their study of the vacuum
structure of N=2 Yang-Mills theories.Comment: 34 pages, harvma
Interaction Effects in Conductivity of Si Inversion Layers at Intermediate Temperatures
We compare the temperature dependence of resistivity \rho(T) of Si MOSFETs
with the recent theory by Zala et al. This comparison does not involve any
fitting parameters: the effective mass m* and g*-factor for mobile electrons
have been found independently. An anomalous increase of \rho with temperature,
which has been considered a signature of the "metallic" state, can be described
quantitatively by the interaction effects in the ballistic regime. The in-plane
magnetoresistance \rho(B) is qualitatively consistent with the theory; however,
the lack of quantitative agreement indicates that the magnetoresistance is more
susceptible to the sample-specific effects than \rho(T).Comment: 4 pages, 5 figures. References update
Interplane magnetic coupling effects in the multilattice compound Y_2Ba_4Cu_7O_{15}
We investigate the interplane magnetic coupling of the multilattice compound
Y_2Ba_4Cu_7O_{15} by means of a bilayer Hubbard model with inequivalent planes.
We evaluate the spin response, effective interaction and the intra- and
interplane spin-spin relaxation times within the fluctuation exchange
approximation. We show that strong in-plane antiferromagnetic fluctuations are
responsible for a magnetic coupling between the planes, which in turns leads to
a tendency of the fluctuation in the two planes to equalize.
This equalization effect grows whit increasing in-plane antiferromagnetic
fluctuations, i. e., with decreasing temperature and decreasing doping, while
it is completely absent when the in-layer correlation length becomes of the
order of one lattice spacing. Our results provide a good qualitative
description of NMR and NQR experiments in Y_2Ba_4Cu_7O_{15}.Comment: Final version, to appear. in Phys. Rev. B (Rapid Communications),
sched. Jan. 9
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