1,379 research outputs found
Constraining the neutrino magnetic moment with anti-neutrinos from the Sun
We discuss the impact of different solar neutrino data on the
spin-flavor-precession (SFP) mechanism of neutrino conversion. We find that,
although detailed solar rates and spectra allow the SFP solution as a
sub-leading effect, the recent KamLAND constraint on the solar antineutrino
flux places stronger constraints to this mechanism. Moreover, we show that for
the case of random magnetic fields inside the Sun, one obtains a more stringent
constraint on the neutrino magnetic moment down to the level of \mu_\nu \lsim
few \times 10^{-12}\mu_B, similar to bounds obtained from star cooling.Comment: 4 pages, 3 figures. Final version to appear in Phys. Rev. Let
Fluctuations effects in high-energy evolution of QCD
Recently, Iancu and Triantafyllopoulos have proposed a hierarchy of evolution
equations in QCD at high energy which generalises previous approaches by
including the effects of gluon number fluctuations and thus the pomeron loops.
In this paper, we present the first numerical simulations of the Langevin
equation which reproduces that hierarchy. This equation is formally the
Balitsky-Kovchegov equation supplemented with a noise term accounting for the
relevant fluctuations. In agreement with theoretical predictions, we find that
the effects of the fluctuations is to reduce the saturation exponent and to
induce geometric scaling violations at high energy.Comment: 12 pages, 7 figures, minor corrections, version appeared in Phys.
Rev.
Lyapunov-like Conditions of Forward Invariance and Boundedness for a Class of Unstable Systems
We provide Lyapunov-like characterizations of boundedness and convergence of
non-trivial solutions for a class of systems with unstable invariant sets.
Examples of systems to which the results may apply include interconnections of
stable subsystems with one-dimensional unstable dynamics or critically stable
dynamics. Systems of this type arise in problems of nonlinear output
regulation, parameter estimation and adaptive control.
In addition to providing boundedness and convergence criteria the results
allow to derive domains of initial conditions corresponding to solutions
leaving a given neighborhood of the origin at least once. In contrast to other
works addressing convergence issues in unstable systems, our results require
neither input-output characterizations for the stable part nor estimates of
convergence rates. The results are illustrated with examples, including the
analysis of phase synchronization of neural oscillators with heterogenous
coupling
Space-Time Complexity in Hamiltonian Dynamics
New notions of the complexity function C(epsilon;t,s) and entropy function
S(epsilon;t,s) are introduced to describe systems with nonzero or zero Lyapunov
exponents or systems that exhibit strong intermittent behavior with
``flights'', trappings, weak mixing, etc. The important part of the new notions
is the first appearance of epsilon-separation of initially close trajectories.
The complexity function is similar to the propagator p(t0,x0;t,x) with a
replacement of x by the natural lengths s of trajectories, and its introduction
does not assume of the space-time independence in the process of evolution of
the system. A special stress is done on the choice of variables and the
replacement t by eta=ln(t), s by xi=ln(s) makes it possible to consider
time-algebraic and space-algebraic complexity and some mixed cases. It is shown
that for typical cases the entropy function S(epsilon;xi,eta) possesses
invariants (alpha,beta) that describe the fractal dimensions of the space-time
structures of trajectories. The invariants (alpha,beta) can be linked to the
transport properties of the system, from one side, and to the Riemann
invariants for simple waves, from the other side. This analog provides a new
meaning for the transport exponent mu that can be considered as the speed of a
Riemann wave in the log-phase space of the log-space-time variables. Some other
applications of new notions are considered and numerical examples are
presented.Comment: 27 pages, 6 figure
Approximated maximum likelihood estimation in multifractal random walks
We present an approximated maximum likelihood method for the multifractal
random walk processes of [E. Bacry et al., Phys. Rev. E 64, 026103 (2001)]. The
likelihood is computed using a Laplace approximation and a truncation in the
dependency structure for the latent volatility. The procedure is implemented as
a package in the R computer language. Its performance is tested on synthetic
data and compared to an inference approach based on the generalized method of
moments. The method is applied to estimate parameters for various financial
stock indices.Comment: 8 pages, 3 figures, 2 table
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