Constraints on primordial black holes: The importance of accretion

We consider the constraints on the fraction of dark matter in the universe in the form of primordial black holes taking into account the crucial role of accretion which may change both their mass and mass function. We show that accretion may drastically weaken the constraints at the present epoch for primordial black holes with masses larger than a few solar masses.

Figure 1

Final mass $M_{\mathrm{f}}$ at a given redshift $z$ obtained from the evolution of an initial mass $M_{\mathrm{i}}$ in the various scenarios with cutoff redshift $z_{\text{cut-off}}=15$, 10 and 7.

Figure 2

Evolution of the mass function from formation (solid lines) to redshift $z=10$ (dashed lines), for an initial lognormal shape with width $\sigma =0.5$ at different values of $M_c$.

Figure 3

Ratio between the initial and late time PBH abundance depending on $⟨M(z=0)⟩$ for an initial lognormal mass function with $\sigma =0.5$, away from the saturation happening when $f_{\mathrm{PBH}}$ approaches unity.

Figure 4

Combined constraints on the fraction of DM composed by PBHs today in terms of $⟨M(z=0)⟩$ for the different accretion models corresponding to $z_{\text{cut-off}}=15$, 10 and 7 compared to the case in which accretion is neglected (“No Evolution”). Left: monochromatic case. Right: lognormal mass function with width $\sigma =0.5$ at formation.