Primordial Black Holes Fraction Research Articles

Calculating the mass fraction of primordial black holes

We reinspect the calculation for the mass fraction of primordial black holes (PBHs) which are formed from primordial perturbations, finding that performing the calculation using the comoving curvature perturbation ℛc in the standard way vastly overestimates the number of PBHs, by many orders of magnitude. This is because PBHs form shortly after horizon entry, meaning modes significantly larger than the PBH are unobservable and should not affect whether a PBH forms or not—this important effect is not taken into account by smoothing the distribution in the standard fashion. We discuss alternative methods and argue that the density contrast, Δ, should be used instead as super-horizon modes are damped by a factor k2. We make a comparison between using a Press-Schechter approach and peaks theory, finding that the two are in close agreement in the region of interest. We also investigate the effect of varying the spectral index, and the running of the spectral index, on the abundance of primordial black holes.

Constraints on primordial black holes as dark matter candidates from capture by neutron stars

We investigate constraints on primordial black holes (PBHs) as dark matter candidates that arise from their capture by neutron stars (NSs). If a PBH is captured by a NS, the star is accreted onto the PBH and gets destroyed in a very short time. Thus, mere observations of NSs put limits on the abundance of PBHs. High DM densities and low velocities are required to constrain the fraction of PBHs in DM. Such conditions may be realized in the cores of globular clusters if the latter are of a primordial origin. Assuming that cores of globular clusters possess the DM densities exceeding several hundred $\mathrm{GeV}/{\mathrm{cm}}^{3}$ would imply that PBHs are excluded as comprising all of the dark matter in the mass range $3\ifmmode\times\else\texttimes\fi{}{10}^{18}\ensuremath{\lesssim}{m}_{\mathrm{BH}}\ensuremath{\lesssim}{10}^{24}\text{ }\text{ }\mathrm{g}$. At the DM density of $2\ifmmode\times\else\texttimes\fi{}{10}^{3}\text{ }\text{ }\mathrm{GeV}/{\mathrm{cm}}^{3}$ that has been found in simulations in the corresponding models, less than 5% of the DM may consist of PBH for these PBH masses.

Searching for Primordial Black Hole Dark Matter with Pulsar Timing Arrays

We discuss the possibility of detecting the presence of primordial black holes (PBHs), such as those that might account for galactic dark matter, using modification of pulsar timing residuals when PBHs pass within ~1000 AU and impart impulse accelerations to the Earth. With this technique, PBHs with masses around 10^{25} g (~0.1 lunar mass) can be detected. Currently, the constraints on the abundance of such dark matter candidates are weak. A 30 year-long monitoring campaign with the proposed Square Kilometer Array (SKA) can rule out a PBH fraction more than ~1/10 in the solar neighborhood in the form of dark matter with mass ~10^{25} g.

New calculation of the mass fraction of primordial black holes

We revisit the calculation of the abundance of primordial black holes (PBHs) formed from primordial density perturbations, using a formation criterion derived by Shibata and Sasaki which refers to a metric perturbation variable rather than the usual density contrast. We implement a derivation of the PBH abundance which uses peaks theory, and compare it to the standard calculation based on a Press-Schechter-like approach. We find that the two are in reasonable agreement if the Press-Schechter threshold is in the range Δth≃0.3 to 0.5, but advocate use of the peaks theory expression which is based on a sounder theoretical footing.