Galactic halos of fluid dark matter

Dwarf spiral galaxies - and in particular the prototypical DDO 154 - areknown to be completely dominated by an unseen component. The putativeneutralinos - so far the favored explanation for the astronomical dark matter -fail to reproduce the well measured rotation curves of those systems becausethese species tend to form a central cusp whose presence is not supported byobservation. We have considered here a self-coupled charged scalar field as analternative to neutralinos and investigated whether a Bose condensate of thatfield could account for the dark matter inside DDO 154 and more generallyinside dwarf spirals. The size of the condensate turns out to be preciselydetermined by the scalar mass m and self-coupling lambda of the field. We findactually that for m^4 / lambda = 50 - 75 eV^4, the agreement with themeasurements of the circular speed of DDO 154 is impressive whereas it lessensfor larger systems. The cosmological behavior of the field is also found to beconsistent - yet marginally - with the limits set by BBN on the effectivenumber of neutrino families. We conclude that classical configurations of ascalar and self-coupled field provide a possible solution to the astronomicaldark matter problem and we suggest further directions of research.Comment: 20 pages, 7 figures; one reference added, version to be published in PR