Cuspy dark matter haloes and the Galaxy

The microlensing optical depth to Baade's Window constrains the minimum total mass in baryonic matter within the Solar circle to be greater than ∼     , assuming the inner Galaxy is barred with viewing angle ∼20°. From the kinematics of solar neighbourhood stars, the local surface density of dark matter is ∼     . We construct cuspy haloes normalized to the local dark matter density and calculate the circular-speed curve of the halo in the inner Galaxy. This is added in quadrature to the rotation curve provided by the stellar and ISM discs, together with a bar sufficiently massive so that the baryonic matter in the inner Galaxy reproduces the microlensing optical depth. Such models violate the observational constraint provided by the tangent-velocity data in the inner Galaxy (typically at radii     . The high baryonic contribution required by the microlensing is consistent with implications from hydrodynamical modelling and the pattern speed of the Galactic bar. We conclude that the cuspy haloes favoured by the cold dark matter cosmology (and its variants) are inconsistent with the observational data on the Galaxy.     

Excursion set approach to the clustering of dark matter haloes in Lagrangian space

We present a stochastic approach to the spatial clustering of dark matter haloes in Lagrangian space. Our formalism is based on a local formulation of the 'excursion set' approach by Bond et al., which automatically accounts for the 'cloud-in-cloud' problem in the identification of bound systems. Our method allows us to calculate correlation functions of haloes in Lagrangian space using either a multidimensional Fokker–Planck equation with suitable boundary conditions, or an array of Langevin equations with spatially correlated random forces. We compare the results of our method with theoretical predictions for the halo autocorrelation function considered in the literature, and find good agreement with the results recently obtained within a treatment of halo clustering in terms of 'counting fields' by Catelan et al. Finally, the possible effect of spatial correlations on numerical simulations of halo merger trees is discussed.     

Profiles of dark matter haloes at high redshift

I study the evolution of halo density profiles as a function of time in the SCDM and ΛCDM cosmologies. Following Del Popolo, I calculate the concentration parameter c = r _v / a and study its time evolution. For a given halo mass, I find that c ( z ) ∝ 1/(1+ z ) in both the ΛCDM and SCDM cosmology, in agreement with the analytic model of Bullock et al. and N -body simulations. In both models, a ( z ) is roughly constant. The present model predicts a stronger evolution of c ( z ) with respect to the Navarro, Frenk & White model. Finally I show some consequences of the results on galaxy modelling.     

Cosmic strings with self-interacting hot dark matter

We compute the linear power spectrum of cosmic-string-seeded fluctuations in the context of neutrinos with a strong self-interaction and show that it is very similar to that obtained in the context of 'normal' neutrinos. We compare our results with observational data and show that for any value of the cosmological parameters h and Ω₀ the interacting hot dark matter power spectrum requires a scale-dependent biasing parameter.