μ-distortion around stupendously large primordial black holes

In a variety of mechanisms generating primordial black holes, each black hole is expected to form along with a surrounding underdense region that roughly compensates the black hole mass. This region will propagate outwards and expand as a shell at the speed of sound in the homogeneous background. Dissipation of the shell due to Silk damping could lead to detectable mu-distortion in the CMB spectrum: if black holes are rare on the last scattering surface, the signal(s) would be pointlike; whereas if there are a sufficient number of them, we could have a uniform distortion in the CMB sky. While the current bound on the average it-distortion is vertical bar(mu) over bar vertical bar less than or similar to 10(-4), the standard ACDM model predicts vertical bar(mu) over bar vertical bar similar to 10(-8), which could possibly be detected in future missions. It is shown in this work that the nonobservation of (mu) over bar beyond ACDM can place a new upper bound on the density of supermassive primordial black holes within the mass range 10(6) M-circle dot less than or similar to M less than or similar to 10(15) M-circle dot. Furthermore, black holes with initial mass M greater than or similar to 10(12)m(circle dot) could leave a pointlike distortion with mu greater than or similar to 10(-8 )at an angular scale similar to 1 degrees in CMB, and its non-observation would impose an even more stringent bound on the population of these stupendously large primordial black holes.

Automated summary

In various mechanisms generating primordial black holes, each black hole is expected to form along with a surrounding underdense region. The dissipation of this region could lead to detectable mu-distortion in the CMB spectrum. Current bounds suggest the potential for detection of mu-distortion, with the possibility of stringent limitations on the population of large primordial black holes.