83,792 research outputs found
Estimating Form Factors of and their Applications to Semi-leptonic and Non-leptonic Decays
and weak transition
form factors are estimated for the whole physical region with a method based on
an instantaneous approximated Mandelstam formulation of transition matrix
elements and the instantaneous Bethe-Salpeter equation. We apply the estimated
form factors to branching ratios, CP asymmetries and polarization fractions of
non-leptonic decays within the factorization approximation. And we study the
non-factorizable effects and annihilation contributions with the perturbative
QCD approach. The branching ratios of semi-leptonic decays are also evaluated. We show that the calculated
decay rates agree well with the available experimental data. The longitudinal
polarization fraction of decays are when
denotes a light meson, and are when denotes a
() meson.Comment: Final version published in J Phys. G 39 (2012) 045002 (Title also
changed
The NLO QCD Corrections to Meson Production in Decays
The decay width of to meson is evaluated at the next-to-leading
order(NLO) accuracy in strong interaction. Numerical calculation shows that the
NLO correction to this process is remarkable. The quantum
chromodynamics(QCD)renormalization scale dependence of the results is obviously
depressed, and hence the uncertainties lying in the leading order calculation
are reduced.Comment: 14 pages, 7 figures; references added; expressions and typos ammende
Crystal orientation and thickness dependence of superconductivity on tetragonal FeSe1-x thin films
Superconductivity was recently found in the simple tetragonal FeSe structure.
Recent studies suggest that FeSe is unconventional, with the symmetry of the
superconducting pairing state still under debate. To tackle these problems,
clean single crystals and thin films are required. Here we report the
fabrication of superconducting beta-phase FeSe1-x thin films on different
substrates using a pulsed laser deposition (PLD) technique. Quite
interestingly, the crystal orientation, and thus, superconductivity in these
thin films is sensitive to the growth temperature. At 320C, films grow
preferably along c-axis, but the onset of superconductivity depends on film
thickness. At 500C, films grow along (101), with little thickness dependence.
These results suggest that the low temperature structural deformation
previously found is crucial to the superconductivity of this material
Multi-point observations of intermittency in the cusp regions
International audienceIn this paper we investigate the statistical properties of magnetic field fluctuations measured by the four Cluster spacecraft in the cusp and close to the interface with the magnetospheric lobes, magnetopause and magnetosheath. At lower altitudes along the outbound orbit of 26 February 2001, the magnetic field fluctuations recorded by all four spacecraft are random and their Probability Distribution Functions (PDFs) are Gaussian at all scales. The flatness parameter, F ? related to the kurtosis of the time series, is equal to 3. At higher altitudes, in the cusp and its vicinity, closer to the interface with the magnetopause and magnetosheath, the PDFs from all Cluster satellites are non-Gaussian and show a clear intermittent behavior at scales smaller than ?G? 61 s (or 170 km). The flatness parameter increases to values greater than 3 for scales smaller than ?G. A Haar wavelet transform enables the identification of the "events" that produce sudden variations of the magnetic field and of the scales that have most of the power. The LIM parameter (i.e. normalized wavelet power) indicates that events for scales below 65 s are non-uniformly distributed throughout the cusp passage. PDFs, flatness and wavelet analysis show that at coarse-grained scales larger than ?G the intermittency is absent in the cusp. Fluctuations of the magnetic energy observed during the same orbit in the magnetosheath show PDFs that tend toward a Gaussian at scales smaller than ?G found in the cusp. The flatness analysis confirms the decreasing of ?G from cusp to magnetosheath. Our analysis reveals the turbulent cusp as a transition region from a non-intermittent turbulent state inside the magnetosphere to an intermittent turbulent state in the magnetosheath that has statistical properties resembling the solar wind turbulence. The observed turbulent fluctuations in the cusp suggests a phenomenon of nonlinear interactions of plasma coherent structures as in contemporary models of space plasma turbulence
Top squark and neutralino decays in a R-parity violating model constrained by neutrino oscillation data
In a R-parity violating (RPV) model of neutrino mass with three bilinear
couplings and three trilinear couplings , where is
the lepton index, we find six generic scenarios each with a distinctive pattern
of the trilinear couplings consistent with the oscillation data. These patterns
may be reflected in direct RPV decays of the lighter top squark or in the RPV
decays of the lightest superparticle, assumed to be the lightest neutralino.
Typical signal sizes at the Tevatron RUN II and the LHC have been estimated
and the results turn out to be encouraging.Comment: 20 pages, 4 figures, LaTex,typos corrected and reference added for
section 2, a paragraph has been added in the conclusion par
Stable periodic waves in coupled Kuramoto-Sivashinsky - Korteweg-de Vries equations
Periodic waves are investigated in a system composed of a
Kuramoto-Sivashinsky - Korteweg-de Vries (KS-KdV) equation, which is linearly
coupled to an extra linear dissipative equation. The model describes, e.g., a
two-layer liquid film flowing down an inclined plane. It has been recently
shown that the system supports stable solitary pulses. We demonstrate that a
perturbation analysis, based on the balance equation for the field momentum,
predicts the existence of stable cnoidal waves (CnWs) in the same system. It is
found that the mean value U of the wave field u in the main subsystem, but not
the mean value of the extra field, affects the stability of the periodic waves.
Three different areas can be distinguished inside the stability region in the
parameter plane (L,U), where L is the wave's period. In these areas, stable
are, respectively, CnWs with positive velocity, constant solutions, and CnWs
with negative velocity. Multistability, i.e., the coexistence of several
attractors, including the waves with several maxima per period, appears at
large value of L. The analytical predictions are completely confirmed by direct
simulations. Stable waves are also found numerically in the limit of vanishing
dispersion, when the KS-KdV equation goes over into the KS one.Comment: a latex text file and 16 eps files with figures. Journal of the
Physical Society of Japan, in pres
Transport properties in FeSe0.5Te0.5 nanobridges
FeSeTe nanobridges of different widths have been fabricated on MgO substrates using focused ion beams. These nanobridges exhibit the Josephson effects. The current-voltage curves of junctions with 248–564 nm wide follow the resistively and capacitatively shunted junction model. Shapiro steps under microwave radiation were clearly observed in these nanobridges. The products of the critical current and normal state resistance (I c R n) are remarkably high. The temperature dependence of I c R n product followed the Ambegaokar-Baratoff (A-B) relation. The value of energy gap of FeSeTe calculated from the A-B relation is 3.5kBTc. The nanobridge junctions have a strong potential for high frequency applications
Theory of spin blockade, charge ratchet effect, and thermoelectrical behavior in serially coupled quantum-dot system
The charge transport of a serially coupled quantum dots (SCQD) connected to
the metallic electrodes is theoretically investigated in the Coulomb blockade
regime. A closed-form expression for the tunneling current of SCQD in the
{\color{red} weak interdot hopping} limit is obtained by solving an extended
two-site Hubbard model via the Green's function method. We use this expression
to investigate spin current rectification, negative differential conductance,
and coherent tunneling in the nonlinear response regime. The current
rectification arising from the space symmetry breaking of SCQD is suppressed by
increasing temperature. The calculation of SCQD is extended to the case of
multiple parallel SCQDs for studying the charge ratchet effect and SCQD with
multiple levels. In the linear response regime, the functionalities of spin
filter and low-temperature current filter are demonstrated to coexist in this
system. It is further demonstrated that two-electron spin singlet and triplet
states can be readily resolved from the measurement of Seebeck coefficient
rather than that of electrical conductance.Comment: 11 pages, 9 figures. Revised argument, results unchanged, added
reference
On a class of reductions of Manakov-Santini hierarchy connected with the interpolating system
Using Lax-Sato formulation of Manakov-Santini hierarchy, we introduce a class
of reductions, such that zero order reduction of this class corresponds to dKP
hierarchy, and the first order reduction gives the hierarchy associated with
the interpolating system introduced by Dunajski. We present Lax-Sato form of
reduced hierarchy for the interpolating system and also for the reduction of
arbitrary order. Similar to dKP hierarchy, Lax-Sato equations for (Lax
fuction) due to the reduction split from Lax-Sato equations for (Orlov
function), and the reduced hierarchy for arbitrary order of reduction is
defined by Lax-Sato equations for only. Characterization of the class of
reductions in terms of the dressing data is given. We also consider a waterbag
reduction of the interpolating system hierarchy, which defines
(1+1)-dimensional systems of hydrodynamic type.Comment: 15 pages, revised and extended, characterization of the class of
reductions in terms of the dressing data is give
- …