Speaker
Description
I will discuss the effects of adding a scalar spectator field to a primordial black hole (PBH) producing single-field inflation model. Such single field PBH models typically include a small-field feature that leads to a phase of ultra slow-roll inflation (USR). Scalar fields (including spectators—fields which are only coupled to gravity and have small masses and potentials, thus never driving the dynamics) are ubiquitous in Beyond Standard Model (BSM) theories and thus well motivated. I will show how, with the addition of a spectator, the slow-roll parameter is prevented from becoming extremely small, averting any USR phase. While this might suggest that PBH production is suppressed by adding a spectator field, I will further demonstrate that the overall change to the dynamics includes a period of tachyonic isocurvature coupled with a turn in field space. This allows for the transfer of power from isocurvature to adiabatic modes, enhancing the peak in the curvature power spectrum, and eventually leading to critical collapse post-inflation. I will also comment on the problem of fine-tuning in single field models and show that the addition of a spectator partially alleviates the need for such fine tuning while still simultaneously producing PBHs and satisfying the most recent CMB constraints.
