70,480 research outputs found
Diffusion limited mixing rates in passive scalar advection
We are concerned with flow enhanced mixing of passive scalars in the presence
of diffusion. Under the assumption that the velocity gradient is suitably
integrable, we provide upper bounds on the exponential rates of mixing and of
enhanced dissipation. Our results suggest that there is a crossover from
advection dominated to diffusion dominated mixing, and we observe a slow down
in the exponential decay rates by (some power of) a logarithm of the
diffusivity.Comment: Generalized resul
Sterile neutrinos in tau lepton decays
We study possible contributions of heavy sterile neutrinos to the
decays . From the experimental
upper bounds on their rates we derive new constraints on the
mixing in the mass region MeV. We discuss
cosmological and astrophysical status of in this mass region and
compare our constraints with those recently derived by the NOMAD collaboration.Comment: 17 pages, 2 figure
Signal Propagation, with Application to a Lower Bound on the Depth of Noisy Formulas
We study the decay of an information signal propagating through a series of noisy channels. We obtain exact bounds on such decay, and as a result provide a new lower bound on the depth of formulas with noisy components. This improves upon previous work of N. Pippenger and significantly decreases the gap between his lower bound and the classical upper bound of von Neumann. We also discuss connections between our work and the study of mixing rates of Markov chains
The effect of large-decoherence on mixing-time in Continuous-time quantum walks on long-range interacting cycles
In this paper, we consider decoherence in continuous-time quantum walks on
long-range interacting cycles (LRICs), which are the extensions of the cycle
graphs. For this purpose, we use Gurvitz's model and assume that every node is
monitored by the corresponding point contact induced the decoherence process.
Then, we focus on large rates of decoherence and calculate the probability
distribution analytically and obtain the lower and upper bounds of the mixing
time. Our results prove that the mixing time is proportional to the rate of
decoherence and the inverse of the distance parameter (\emph{m}) squared.
This shows that the mixing time decreases with increasing the range of
interaction. Also, what we obtain for \emph{m}=0 is in agreement with
Fedichkin, Solenov and Tamon's results \cite{FST} for cycle, and see that the
mixing time of CTQWs on cycle improves with adding interacting edges.Comment: 16 Pages, 2 Figure
Bounds on neutrino magnetic moment tensor from solar neutrinos
Solar neutrinos with non-zero magnetic moments will contribute to the
electron scattering rates in the Super-Kamiokande experiment. The magnetic
moment scattering events in Super-K can be accommodated in the standard VO or
MSW solutions by a change of the parameter space of mass square difference and
mixing angle-but the shifted neutrino parameters obtained from Super-K will
(for some values of neutrino magnetic moments) become incompatible with the
fits from SNO, Gallium and Chlorine experiments. We compute the upper bounds on
the Dirac and Majorana magnetic moments of solar neutrinos by simultaneously
fitting all the observed solar neutrino rates. The bounds the magnetic moment
matrix elements are of the order of 10^{-10} Bohr magnetron.Comment: 9 pages latex file with 6 figures; References added, typos corrected,
matches version to appear in Phys Rev
Nonparametric regression with martingale increment errors
We consider the problem of adaptive estimation of the regression function in
a framework where we replace ergodicity assumptions (such as independence or
mixing) by another structural assumption on the model. Namely, we propose
adaptive upper bounds for kernel estimators with data-driven bandwidth
(Lepski's selection rule) in a regression model where the noise is an increment
of martingale. It includes, as very particular cases, the usual i.i.d.
regression and auto-regressive models. The cornerstone tool for this study is a
new result for self-normalized martingales, called ``stability'', which is of
independent interest. In a first part, we only use the martingale increment
structure of the noise. We give an adaptive upper bound using a random rate,
that involves the occupation time near the estimation point. Thanks to this
approach, the theoretical study of the statistical procedure is disconnected
from usual ergodicity properties like mixing. Then, in a second part, we make a
link with the usual minimax theory of deterministic rates. Under a beta-mixing
assumption on the covariates process, we prove that the random rate considered
in the first part is equivalent, with large probability, to a deterministic
rate which is the usual minimax adaptive one
B decays dominated by omega-phi mixing
Recently Belle has established the 90% confidence level (CL) upper limit \b
< 9.4 \times 10^{-7} for the branching ratio for , a
process expected to be suppressed by the Okubo-Zweig-Iizuka (OZI) rule
disfavoring disconnected quark diagrams. We use information on --
mixing to establish likely lower bounds on this and related processes. We find
that the Belle result is about a factor of five above our limit, while other
decays such as and , for which
upper limits have been obtained by BaBar, could be observable with similar
improvements in data. We argue that a significant enhancement of our predicted
decay rates by rescattering is unlikely.Comment: paragraph added, submitted to Physics Letters
Neutrino mixing and masses in a left-right model with mirror fermions
In the framework of a left-right model containing mirror fermions with gauge
group SU(3),
we estimate the neutrino masses, which are found to be consistent with their
experimental bounds and hierarchy. We evaluate the decay rates of the Lepton
Flavor Violation (LFV) processes , and . We obtain upper limits for the
flavor-changing branching ratios in agreement with their present experimental
bounds. We also estimate the decay rates of heavy Majorana neutrinos in the
channels , and , which are roughly equal for large values of the heavy
neutrino mass. Starting from the most general Majorana neutrino mass matrix,
the smallness of active neutrino masses turns out from the interplay of the
hierarchy of the involved scales and the double application of seesaw
mechanism. An appropriate parameterization on the structure of the neutrino
mass matrix imposing a symmetric mixing of electron neutrino with muon and tau
neutrinos leads to Tri-bimaximal mixing matrix for light neutrinos.Comment: Accepted by European Physical Journal
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