Nonadditive entropy: The Concept and its use

May 20, 2009
10 pages
Published in:
  • Eur.Phys.J.A 40 (2009) 257-266
e-Print:

Citations per year

200920132017202120250246810
Abstract: (arXiv)
The entropic form SqS_q is, for any q1q \neq 1, {\it nonadditive}. Indeed, for two probabilistically independent subsystems, it satisfies Sq(A+B)/k=[Sq(A)/k]+[Sq(B)/k]+(1q)[Sq(A)/k][Sq(B)/k]Sq(A)/k+Sq(B)/kS_q(A+B)/k=[S_q(A)/k]+[S_q(B)/k]+(1-q)[S_q(A)/k][S_q(B)/k] \ne S_q(A)/k+S_q(B)/k. This form will turn out to be {\it extensive} for an important class of nonlocal correlations, if qq is set equal to a special value different from unity, noted qentq_{ent} (where entent stands for entropyentropy). In other words, for such systems, we verify that Sqent(N)N(N>>1)S_{q_{ent}}(N) \propto N (N>>1), thus legitimating the use of the classical thermodynamical relations. Standard systems, for which SBGS_{BG} is extensive, obviously correspond to qent=1q_{ent}=1. Quite complex systems exist in the sense that, for them, no value of qq exists such that SqS_q is extensive. Such systems are out of the present scope: they might need forms of entropy different from SqS_q, or perhaps -- more plainly -- they are just not susceptible at all for some sort of thermostatistical approach. Consistently with the results associated with SqS_q, the qq-generalizations of the Central Limit Theorem and of its extended L\'evy-Gnedenko form have been achieved. These recent theorems could of course be the cause of the ubiquity of qq-exponentials, qq-Gaussians and related mathematical forms in natural, artificial and social systems. All of the above, as well as presently available experimental, observational and computational confirmations -- in high energy physics and elsewhere --, are briefly reviewed. Finally, we address a confusion which is quite common in the literature, namely referring to distinct physical mechanisms {\it versus} distinct regimes of a single physical mechanism.
Note:
  • Brief review to appear in "Statistical Power-Law Tails in High Energy Phenomena", ed. T.S. Biro, Eur. Phys. J. A (2009);10 pages including 3 figures
  • 05.90.+m
  • 05.70.-a
  • 02.50.Cw
  • 05.20.-y
  • entropy
  • thermodynamics
  • statistical mechanics