Abstract
We evaluate abundance anomalies generated in patches of the universe where the baryon-to-photon ratio was locally enhanced by possibly many orders of magnitude in the range $\eta = 10^{-10} - 10^{-1}$. Our study is motivated by the possible survival of rare dense regions in the early universe, the most extreme of which, above a critical threshold, collapsed to form primordial black holes. If this occurred, one may expect there to also be a significant population of early-forming stars that formed in similar but subthreshold patches. We derive a range of element abundance signatures by performing BBN simulations at high values of the baryon-to-photon ratio that may be detectable in any surviving first generation stars of around a solar mass. Our predictions apply to metal-poor galactic halo stars, to old globular star clusters and to dwarf galaxies, and we compare with observations in each of these cases.
Highlights
Big bang nucleosynthesis (BBN) is a fundamental probe of the first few minutes of the Universe
When η is larger than the standard BBN (SBBN) value η0 ∼ 6 × 10−10, we find that groups of elements in addition to helium are overproduced compared to the solar abundances
While the horizon size is of order 105 M⊙ at the onset of BBN, when the neutron abundance is frozen in an epoch of T ∼ 1 MeV, Ref. [22] notes that extreme curvature fluctuations on horizon scales could form rare primordial black holes (PBHs) in this mass range provided the initial conditions are highly nonGaussian, so that extreme perturbations that affect BBN only occur in rare inhomogeneous patches of the universe
Summary
Big bang nucleosynthesis (BBN) is a fundamental probe of the first few minutes of the Universe. Our study is motivated by the possible survival of rare dense regions in the early Universe that collapsed to form primordial black holes (PBHs), a subject of intense current scrutiny for its role in contributing to the dark matter abundance and/or seeding early supermassive black hole formation. Such regions are commonly thought to derive from primordial isocurvature perturbations, where the initial baryon-to-photon ratio is considerably enhanced relative to the standard model. These overdense regions might have later formed stars that retained a memory of inhomogeneous BBN
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