Quantized Temperatures Spectra in Curved Spacetimes

We consider the thermal properties of a scalar field theory on curved spacetimes. In particular, we argue for the existence in the de Sitter, Kruskal and Rindler manifolds of a discrete spectrum of allowed temperatures (the odd multiples of a fundamental one). For each temperature we give an explicit construction of the relative two point function in terms of the lowest temperature one. These results are actually valid for a wider class of static metrics with bifurcate Killing horizons, originally studied by Sewell. Some comments on the interpretation of our results are given.