Thermodynamic limit in number theory: Riemann-Beurling gases

We study the grand canonical version of a solved statistical model, the Riemann gas: a collection of bosonic oscillators with energies the logarithms of the prime numbers. The introduction of a chemical potential μ amounts to multiply each prime by e-μ, the corresponding gases could be called Beurling gases because they are defined by the choice of appropriate generalized primes when considered as canonical ensembles; one finds generalized Hagedorn singularities in the temperature. The discrete spectrum can be treated as continuous in its high energy region; this approximation allows us to study the high energy level density and is applied to Beurling gases. It is expected to be accurate for the high temperature behaviour. One model (the logarithmic gases) will be studied in more detail, it corresponds to the choice of all the integers strictly larger than one as Beurling primes; we give an explicit formula for its grand canonical thermodynamic potential F - μN in terms of a hypergeometric function and check the approximation on the Hagedorn phenomenon. Related physical situations include string theories and quark deconfinement where one needs a better understanding of the nature of the Hagedorn transitions.