58,236 research outputs found
The Family SU(2)_l x SU(2)_h x U(1) Model
We consider extension of the standard model where the first two families of quarks and leptons transform according to
the group and the third family according to the group. In
this approach, the largeness of top-quark mass is associated with the large
vacuum expectation value of the corresponding Higgs field. The model predicts
almost degenerate heavy and bosons with non-universal couplings, and
extra Higgs bosons. We present in detail the symmetry breaking mechanism, and
carry out the subsequent phenomenology of the gauge sector. We compare the
model with electroweak precision data, and conclude that the extra gauge bosons
and the Higgs bosons whose masses lie in the TeV range, can be discovered at
the LHC.Comment: Latex 18 pages. No figure. Some references added. Version appeared in
PR
Two-body Cabibbo-suppressed Decays of Charmed Baryons into Vector Mesons and into Photons
The heavy quark effective theory and the factorization approximation are used
to treat the Cabibbo-suppressed decays of charmed baryons to vector mesons,
,
and . The input from two recent experimental results on
decays allows the estimation of the branching ratios for these modes, which
turn out to be between and . The long distance contribution
of these transitions via vector meson dominance to the radiative weak processes
, and
leads to quite small branching ratios,
; the larger value holds if a sum rule between the coupling
constants of the vector mesons is broken.Comment: 11 pages, latex, no figure
Radiative Kaon Decays and Direct CP Violation
It is stressed that a measurement of the electric dipole amplitude for direct
photon emission in \kpm decays through its interference with inner
bremsstrahlung is important for differentiating among various models. Effects
of amplitude CP violation in the radiative decays of the charged kaon are
analyzed in the Standard Model in conjunction with the large approach. We
point out that gluon and electromagnetic penguin contributions to the
CP-violating asymmetry between the Dalitz plots of \kpm are of equal weight.
The magnitude of CP asymmetry ranges from to when the photon energy in the kaon rest frame varies from 50 MeV to
170 MeV.Comment: Latex, 11 pages, ITP-SB-93-36, IP-ASTP-22-9
Eigenmodes of Decay and Discrete Fragmentation Processes
Linear rate equations are used to describe the cascading decay of an initial
heavy cluster into fragments. This representation is based upon a triangular
matrix of transition rates. We expand the state vector of mass multiplicities,
which describes the process, into the biorthonormal basis of eigenmodes
provided by the triangular matrix. When the transition rates have a scaling
property in terms of mass ratios at binary fragmentation vertices, we obtain
solvable models with explicit mathematical properties for the eigenmodes. A
suitable continuous limit provides an interpolation between the solvable
models. It gives a general relationship between the decay products and the
elementary transition rates.Comment: 6 pages, plain TEX, 2 figures available from the author
Micromagnetic understanding of stochastic resonance driven by spin-transfertorque
In this paper, we employ micromagnetic simulations to study non-adiabatic
stochastic resonance (NASR) excited by spin-transfer torque in a
super-paramagnetic free layer nanomagnet of a nanoscale spin valve. We find
that NASR dynamics involves thermally activated transitions among two static
states and a single dynamic state of the nanomagnet and can be well understood
in the framework of Markov chain rate theory. Our simulations show that a
direct voltage generated by the spin valve at the NASR frequency is at least
one order of magnitude greater than the dc voltage generated off the NASR
frequency. Our computations also reproduce the main experimentally observed
features of NASR such as the resonance frequency, the temperature dependence
and the current bias dependence of the resonance amplitude. We propose a simple
design of a microwave signal detector based on NASR driven by spin transfer
torque.Comment: 25 pages 8 figures, accepted for pubblication on Phys. Rev.
Scaling Theory of Polyelectrolyte Adsorption on Repulsive Charged Surface
We studied polyelectrolyte adsorption on a repulsive charged surface by
scaling analysis. At low ionic strength and low surface charge density in which
a single polyelectrolyte is able to be adsorbed onto the surface, different
regimes in the phase diagram are identified. The possibility of multi-layer
structure formed by polyelectrolytes of like charge is also investigated.Comment: 4 pages, 2 figure
Measurement of a Sign-Changing Two-Gap Superconducting Phase in Electron-Doped Ba(Fe_{1-x}Co_x)_2As_2 Single Crystals using Scanning Tunneling Spectroscopy
Scanning tunneling spectroscopic studies of (x =
0.06, 0.12) single crystals reveal direct evidence for predominantly two-gap
superconductivity. These gaps decrease with increasing temperature and vanish
above the superconducting transition . The two-gap nature and the slightly
doping- and energy-dependent quasiparticle scattering interferences near the
wave-vectors and are consistent with
sign-changing -wave superconductivity. The excess zero-bias conductance and
the large gap-to- ratios suggest dominant unitary impurity scattering.Comment: 4 pages, 4 figures. Paper accepted for publication in Physical Review
Letters. Contact author: Nai-Chang Yeh ([email protected]
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