289,647 research outputs found
Inclusive Decays of Heavy Quarkonium to Light Particles
We derive the imaginary part of the potential NRQCD Hamiltonian up to order
1/m^4, when the typical momentum transfer between the heavy quarks is of the
order of Lambda_{QCD} or greater, and the binding energy E much smaller than
Lambda_{QCD}. We use this result to calculate the inclusive decay widths into
light hadrons, photons and lepton pairs, up to O(mv^3 x
(Lambda_{QCD}^2/m^2,E/m)) and O(mv^5) times a short-distance coefficient, for
S- and P-wave heavy quarkonium states, respectively. We achieve a large
reduction in the number of unknown non-perturbative parameters and, therefore,
we obtain new model-independent QCD predictions. All the NRQCD matrix elements
relevant to that order are expressed in terms of the wave functions at the
origin and six universal non-perturbative parameters. The wave-function
dependence factorizes and drops out in the ratio of hadronic and
electromagnetic decay widths. The universal non-perturbative parameters are
expressed in terms of gluonic field-strength correlators, which may be fixed by
experimental data or, alternatively, by lattice simulations. Our expressions
are expected to hold for most of the charmonium and bottomonium states below
threshold. The calculations and methodology are explained in detail so that the
evaluation of higher order NRQCD matrix elements in this framework should be
straightforward. An example is provided.Comment: 61 pages, 9 figures. Minor change
Reliable random error estimation in the measurement of line-strength indices
We present a new set of accurate formulae for the computation of random
errors in the measurement of atomic and molecular indices. The new expressions
are in excellent agreement with numerical simulations. We have found that, in
some cases, the use of approximated equations can give misleading line-strength
index errors. It is important to note that accurate errors can only be achieved
after a full control of the error propagation throughout the data reduction
with a parallel processing of data and error frames. Finally, simple recipes
for the estimation of the required signal-to-noise ratio to achieve a fixed
index error are presented.Comment: 9 pages, LaTeX file + 5 PostScript figures, psfig.sty and laa-s.sty
required, to be published in Astronomy & Astrophysics Supplement Serie
The Two-Loop Finite-Temperature Effective Potential of the MSSM and Baryogenesis
We construct an effective three dimensional theory for the MSSM at high
temperatures in the limit of large-. We analyse the two-loop effective
potential of the 3D theory for the case of a light right handed stop to
determine the precise region in the - plane for which
the sphaleron constraint for preservation of the baryon asymmetry is satisfied.
We also compare with results previously obtained usind 3D and 4D calculations
of the effective potential. A two-stage phase transition still persists for a
small range of values of . The allowed region requires a
value of m_{\tilde{t}_{R}} \lsi m_{t} and m_{h} \lsi 100 (110) GeV for
GeV (1 TeV).Comment: 40 pages, 6 Postcsript figures, uses eps
Vortex tilt modulus in Fulde-Ferrell-Larkin-Ovchinnikov state
Vortex tilt response in Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) vortex
lattice is theoretically examined as a probe reflecting the spatial structure
of this state. In the FFLO state with nodal planes perpendicular to the
magnetic field in a quasi 2D material under a parallel field, the tilt modulus
E_{2} {\it of the nodal planes} decreases as the paramagnetic effect is
effectively enhanced, and this reduction of E_{2} in turn reduces the vortex
tilt modulus. This reduction of vortex tilt modulus, more remarkable in more
anisotropic systems, accompanying the FFLO transition may be an origin of the
monotonous reduction of sound velocity detected upon cooling in a ultrasound
measurement for CeCoIn5.Comment: 14 pages, 5 figures. Accepted for publication in Phys. Rev.
On the strength of the nonlinearity in isotropic turbulence
Turbulence governed by the Navier-Stokes equations shows a tendency to evolve
towards a state in which the nonlinearity is diminished. In fully developed
turbulence this tendency can be measured by comparing the variance of the
nonlinear term to the variance of the same quantity measured in a Gaussian
field with the same energy distribution. In order to study this phenomenon at
high Reynolds numbers, a version of the Direct Interaction Approximation is
used to obtain a closed expression for the statistical average of the
mean-square nonlinearity. The wavenumber spectrum of the mean-square nonlinear
term is evaluated and its scaling in the inertial range is investigated as a
function of the Reynolds number. Its scaling is dominated by the sweeping by
the energetic scales, but this sweeping is weaker than predicted by a random
sweeping estimate. At inertial range scales, the depletion of nonlinearity as a
function of the wavenumber is observed to be constant. At large it is observed
that the mean-square nonlinearity is larger than its Gaussian estimate, which
is shown to be related to the non-Gaussianity of the Reynolds-stress
fluctuations at these scales.Comment: Accepted for publication in J. Fluid Mec
System Measure for Persistence in Holographic Recording and Application to Singly-Doped and Doubly-Doped Lithium Niobate
We define a measure for persistence in holographic recording. Using this measure and the known measures for dynamic range and sensitivity, we compare the performance of singly-doped and doubly-doped LiNbO3 crystals. We show that the range of performance that can be obtained using doubly-doped crystals is much larger than that obtained using singly-doped ones
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