[Paper Review] Regurgitated Dark Matter

TaeHun Kim, Philip Lu+2 more|arXiv (Cornell University)|Sep 11, 2023

Cosmology and Gravitation Theories4 citations

TL;DR

This paper proposes a novel dark matter (DM) production mechanism called Regurgitated Dark Matter (RDM), in which primordial black holes (PBHs) formed from DM particles evaporate to re-emit DM, thereby generating the observed relic abundance. The scenario allows for both fermionic and scalar DM in the 1 GeV to 10^16 GeV range, reopening parameter space previously excluded by conventional constraints.

ABSTRACT

We present a new paradigm for the production of the dark matter (DM) relic abundance based on the evaporation of early Universe primordial black holes (PBHs) themselves formed from DM particles. As a concrete realization, we consider a minimal model of the dark sector in which a first-order phase transition results in the formation of Fermiball remnants that collapse to PBHs, which then emit DM particles. We show that the regurgitated DM scenario allows for DM in the mass range $\sim1$ GeV $- \,10^{16}$ GeV, thereby unlocking parameter space considered excluded.

Motivation & Objective

• To address the long-standing challenge of explaining the observed dark matter relic abundance without relying on direct DM interactions.
• To explore a new paradigm in which DM particles form PBHs that subsequently evaporate to regenerate DM, thus bypassing traditional thermal freeze-out constraints.
• To demonstrate that both fermionic and scalar DM candidates can successfully account for the relic abundance within this framework.
• To identify viable parameter space—particularly in the WIMP and WIMPZilla mass ranges—previously considered excluded by collider and direct detection experiments.
• To propose a correlated gravitational wave signature from the first-order phase transition that forms Fermiballs and PBHs, offering a potential multi-messenger test.

Proposed method

• The model is based on a first-order phase transition (FOPT) in a dark sector with a scalar field $\phi$ and fermions $\chi$, where a Yukawa interaction and Higgs portal coupling $\kappa$ mediate interactions.
• Fermiball remnants form due to a dark matter asymmetry $\eta_\chi$, which collapses into primordial black holes (PBHs) when the phase transition completes.
• The PBHs then undergo Hawking evaporation, re-emitting DM particles (both $\phi$ and $\chi$) with altered energy and momentum distributions, independent of direct DM self-interactions.
• The relic abundance is computed by tracking the evaporation rate, PBH lifetime, and energy injection into the thermal bath, using the PBH number density and cooling timescale.
• The model uses the Higgs portal coupling $\kappa$ to mediate SM interactions, allowing constraints from invisible Higgs decays and direct detection to be applied.
• Gravitational wave (GW) signals from the FOPT are estimated using the peak frequency $f_{\rm GW} \sim \mathcal{O}(10^{-2})\,\text{mHz} \cdot (\beta/H_\star/100)(T_\star/1\,\text{GeV})$, potentially detectable by LISA and other future interferometers.

Experimental results

Research questions

• RQ1 Can the observed dark matter relic abundance be generated via PBH evaporation without relying on thermal freeze-out or direct DM interactions?
• RQ2 What is the viable mass range for DM particles (fermions or scalars) in this RDM scenario, and can it evade standard constraints from collider and direct detection experiments?
• RQ3 How does the inclusion of a first-order phase transition and Fermiball formation affect the PBH formation and subsequent DM regurgitation process?
• RQ4 What are the implications for gravitational wave signals from the FOPT and PBH evaporation, and can they serve as a correlated probe of the RDM mechanism?
• RQ5 Can the RDM scenario accommodate both WIMP-like and WIMPZilla-like DM masses, and how do cosmological overproduction bounds affect the parameter space?

Key findings

• The RDM scenario successfully produces the observed dark matter relic abundance across a broad mass range from ~1 GeV to ~10^16 GeV, including previously excluded regions.
• For scalar DM with $m_\phi \lesssim \text{TeV}$, the RDM mechanism avoids strong constraints from direct detection and invisible Higgs decays due to suppressed couplings and $\kappa$-dependence.
• In the WIMPZilla mass range ($10^{12} \lesssim m_\phi \lesssim 10^{16}$ GeV), the scenario evades gravitational overproduction by assuming low-scale inflation ($H_e \sim 10^{13}$ GeV), consistent with current bounds.
• Fermionic DM ($\chi$) can also constitute a significant fraction of the relic abundance, with indirect SM couplings via loop-level interactions involving $\phi$ and the Higgs portal.
• The scenario predicts a stochastic gravitational wave background from the first-order phase transition, with peak frequencies in the mHz band, potentially detectable by LISA, Einstein Telescope, and Cosmic Explorer.
• The PBH evaporation process scrambles the initial DM distribution, so the final relic abundance is not determined by standard thermal or annihilation cross-sections, enabling new production dynamics.