Is it possible to tell the difference between fermionic and bosonic hot dark matter?

Abstract

We study the difference between thermally produced fermionic and bosonic hot darkmatter in detail. In the linear regime of structure formation, their distinct free-streamingbehaviours can lead to pronounced differences in the matter power spectrum. Whilenot detectable with current cosmological data, such differences will be clearlyobservable with upcoming large scale weak lensing surveys for particles as light asmHDM∼0.2 eV. In the nonlinear regime, bosonic hot dark matter is not subject to the same phasespace constraints that severely limit the amount of fermionic hot dark matter infall intocold dark matter halos. Consequently, the overdensities in fermionic and bosonic hot darkmatter of equal particle mass can differ by more than a factor of five in the central part of ahalo. However, this unique manifestation of quantum statistics may prove very difficult todetect unless the mass of the hot dark matter particle and its decoupling temperature fallwithin a very narrow window, and . In this case, hot dark matter infall may have some observable consequences for thenonlinear power spectrum and hence the weak lensing convergence power spectrum at at the per cent level.