摘要: We perform a Markov Chain Monte Carlo (MCMC) analysis of a simple yet generic
multifield inflation model characterized by two scalar fields coupled to each
other and nonminimally coupled to gravity, fit to Planck 2018 cosmic microwave
background (CMB) data. In particular, model parameters are constrained by data
on the amplitude of the primordial power spectrum of scalar curvature
perturbations on CMB scales $A_s$, the spectral index $n_s$, and the ratio of
power in tensor to scalar modes $r$, with a prior that the primordial power
spectrum should also lead to primordial black hole (PBH) production sufficient
to account for the observed dark matter (DM) abundance. We find that $n_s$ in
particular controls the constraints on our model. Whereas previous studies of
PBH formation from an ultra-slow-roll phase of inflation have highlighted the
need for at least one model parameter to be highly fine-tuned, we identify a
degeneracy direction in parameter space such that shifts by $\sim 10\%$ of one
parameter can be compensated by comparable shifts in other parameters while
preserving a close fit between model predictions and observations. Furthermore,
we find this allowed parameter region produces observable gravitational wave
(GW) signals in the frequency ranges to which upcoming experiments are
projected to be sensitive, including Advanced LIGO and Virgo, the Einstein
Telescope (ET), DECIGO, and LISA.
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