Spectral statistics

For classically integrable systems the spectral statistics are expected to follow a Poissonian random process. In contrast, for classically chaotic systems random matrix statistics are expected.
One of the simplest statistics is the level spacing distribution, i.e. the distribution of the spacings between neighboured eigenvalues. For the integrable circular billiard and the strongly chaotic cardioid billiard one gets:

level spacing, circular billiard level spacing, cardioid billiard

However, both for integrable and chaotic systems exceptions are known.

Mode fluctuation distribution

The distribution for the (suitably) normalized fluctuations of the spectral staircase function around its mean behaviour has been conjectured to be Gaussian for strongly chaotic systems and non-Gaussian otherwise. The figure shows the mode fluctuation distribution for the cardioid billiard and a rectangular billiard:
mode fluctuation distribution, 
cardioid billiard mode fluctuation distribution, torus

References:


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