Weak Chaos Detection in the FERMIPASTAULAMα System Using qGAUSSIAN Statistics
Abstract
We study numerically statistical distributions of sums of orbit coordinates, viewed as independent random variables in the spirit of the Central Limit Theorem, in weakly chaotic regimes associated with the excitation of the first ($k=1$) and last ($k=N$) linear normal modes of the FermiPastaUlam$\alpha$ system under fixed boundary conditions. We show that at low energies ($E=0.19$), when the $k=1$ linear mode is excited, chaotic diffusion occurs characterized by distributions that are well approximated for long times ($t>10^9$) by a $q$Gaussian QuasiStationary State (QSS) with $q\approx1.4$. On the other hand, when the $k=N$ mode is excited at the same energy, diffusive phenomena are \textit{absent} and the motion is quasiperiodic. In fact, as the energy increases to $E=0.3$, the distributions in the former case pass through \textit{shorter} $q$Gaussian states and tend rapidly to a Gaussian (i.e. $q\rightarrow 1$) where equipartition sets in, while in the latter we need to reach to E=4 to see a \textit{sudden transition} to Gaussian statistics, without any passage through an intermediate QSS. This may be explained by different energy localization properties and recurrence phenomena in the two cases, supporting the view that when the energy is placed in the first mode weak chaos and "sticky" dynamics lead to a more gradual process of energy sharing, while strong chaos and equipartition appear abruptly when only the last mode is initially excited.
 Publication:

International Journal of Bifurcation and Chaos
 Pub Date:
 2011
 DOI:
 10.1142/S0218127411029781
 arXiv:
 arXiv:1105.1465
 Bibcode:
 2011IJBC...21.2285A
 Keywords:

 Nonlinear Sciences  Chaotic Dynamics
 EPrint:
 12 pages, 3 figures, submitted for publication to International Journal of Bifurcation and Chaos. In honor of Prof. Tassos Bountis' 60th birthday