A new entropy based on a group-theoretical structure

Abstract

A multi-parametric version of the nonadditive entropy S_q is introduced. This new entropic form, denoted by S_a,b,r, possesses many interesting statistical properties, and it reduces to the entropy S_q for b=0, a=r:=1−q (hence Boltzmann–Gibbs entropy S_BG for b=0, a=r→0). The construction of the entropy S_a,b,r is based on a general group-theoretical approach recently proposed by one of us, Tempesta (2016). Indeed, essentially all the properties of this new entropy are obtained as a consequence of the existence of a rational group law, which expresses the structure of S_a,b,r with respect to the composition of statistically independent subsystems. Depending on the choice of the parameters, the entropy S_a,b,r can be used to cover a wide range of physical situations, in which the measure of the accessible phase space increases say exponentially with the number of particles NN of the system, or even stabilizes, by increasing NN, to a limiting value. This paves the way to the use of this entropy in contexts where the size of the phase space does not increase as fast as the number of its constituting particles (or subsystems) increases.