Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

Primordial Black Holes from Kinetic Preheating

Peter Adshead, Eve Currens, John T. Giblin

TL;DR

The paper shows that violent kinetic preheating after $\alpha$-attractor inflation, driven by derivative couplings between a dilaton inflaton and an axion reheaton, can seed nonlinear gravitational collapse and form micro-black holes at sub-horizon scales. Using fully nonlinear 3+1 general-relativistic lattice simulations with the BSSN formalism, the authors demonstrate black-hole formation with masses of order tens of grams within a few inflaton oscillations, without relying on large primordial curvature perturbations. The resulting PBHs evaporate rapidly via Hawking radiation, reheating the Universe to $T_{\rm reh}^{\rm (PBH)}$ of order $10^{8-10}$ GeV well before BBN, and contributing negligibly to $\Delta N_{\rm eff}$ unless extra light species are present. These results establish kinetic preheating as a robust channel for PBH production and connect inflationary symmetries to strong-gravity phenomena during reheating, offering a compelling reheating mechanism through PBH evaporation.

Abstract

We demonstrate that violent kinetic preheating following inflation can lead to the formation of black holes in the early Universe. In $α$-attractor models with derivative inflaton couplings, nonlinear amplification of field fluctuations drives large spacetime curvature and gravitational collapse shortly after inflation ends. Using fully general-relativistic lattice simulations, we find that these dynamics produce black holes with masses of order tens of grams at sub-horizon scales, without requiring large primordial curvature perturbations. Although such micro-black holes evaporate rapidly via Hawking radiation, their formation modifies the post-inflationary equation of state and their evaporation can successfully reheat the Universe before Big Bang nucleosynthesis. These results identify kinetic preheating as a new, efficient channel for black-hole production and establish a direct connection between inflationary symmetries and strong-gravity phenomena at reheating.

Primordial Black Holes from Kinetic Preheating

TL;DR

The paper shows that violent kinetic preheating after -attractor inflation, driven by derivative couplings between a dilaton inflaton and an axion reheaton, can seed nonlinear gravitational collapse and form micro-black holes at sub-horizon scales. Using fully nonlinear 3+1 general-relativistic lattice simulations with the BSSN formalism, the authors demonstrate black-hole formation with masses of order tens of grams within a few inflaton oscillations, without relying on large primordial curvature perturbations. The resulting PBHs evaporate rapidly via Hawking radiation, reheating the Universe to of order GeV well before BBN, and contributing negligibly to unless extra light species are present. These results establish kinetic preheating as a robust channel for PBH production and connect inflationary symmetries to strong-gravity phenomena during reheating, offering a compelling reheating mechanism through PBH evaporation.

Abstract

We demonstrate that violent kinetic preheating following inflation can lead to the formation of black holes in the early Universe. In -attractor models with derivative inflaton couplings, nonlinear amplification of field fluctuations drives large spacetime curvature and gravitational collapse shortly after inflation ends. Using fully general-relativistic lattice simulations, we find that these dynamics produce black holes with masses of order tens of grams at sub-horizon scales, without requiring large primordial curvature perturbations. Although such micro-black holes evaporate rapidly via Hawking radiation, their formation modifies the post-inflationary equation of state and their evaporation can successfully reheat the Universe before Big Bang nucleosynthesis. These results identify kinetic preheating as a new, efficient channel for black-hole production and establish a direct connection between inflationary symmetries and strong-gravity phenomena at reheating.

Paper Structure

This paper contains 5 sections, 12 equations, 5 figures.

Table of Contents

  1. Introduction
  2. The Model
  3. Results
  4. Reheating from Primordial Black-Hole Evaporation
  5. Discussion and Conclusion

Figures (5)

  • Figure 1: The variances of the inflation (black), $\varphi$, and the axion (red), $\chi$ over time for the run presented here (solid) and a corresponding FLRW simulation (dashed). The rise of the variance of the axion represents the phase of kinetic preheating which extends from $\approx 0.5 \,H_*^{-1}$ until $t\approx 1.25\,H_*^{-1}$.
  • Figure 2: Two-dimensional slices of the density, $\rho/\langle \rho\rangle$ over several slices from the end of the tachyonic resonance period until the gravitational collapse begins. From left to right, these are at $t\approx 1.3730 \,H_*^{-1},1.5332 \,H_*^{-1},1.5904\, H_*^{-1},$ and $1.6705 \,H_*^{-1}$. Note the increasing scale of the vertical axis over these four slices.
  • Figure 3: The lapse, $\alpha$, at $t\approx 1.7050 H_*^{-1}$ right before gravitational collapse begins.
  • Figure 4: The density contrast (top panels) and the scaled lapse, $\log_{10}(1-\alpha)$, (bottom panels) during the time when the over-dense region is collapsing. We scale the lapse to emphasize that it is departing significantly from one and we plot only the region surrounding the emerging black hole.
  • Figure 5: The density contrast at the time of the horizon formation, $t\approx 1.7063 \,H_*^{-1}$. The black circle indicates the apparent horizon.