Multiplicity Fluctuations and Correlations in Limited Momentum Space Bins in Relativistic Gases

Multiplicity fluctuations and correlations are calculated within thermalized relativistic ideal quantum gases. These are shown to be sensitive to the choice of statistical ensemble as well as to the choice of acceptance window in momentum space. It is furthermore shown that global conservation laws introduce non-trivial correlations between disconnected regions in momentum space, even in the absence of any dynamics.