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Register a new userPrimordial Black Holes from a tiny bump/dip in the Inflaton potential
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Added by
Swagat Saurav Mishra
Publication date
2019
fields
Physics
and research's language is
English
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Scalar perturbations during inflation can be substantially amplified by tiny features in the inflaton potential. A bump-like feature behaves like a local speed-breaker and lowers the speed of the scalar field, thereby locally enhancing the scalar power spectrum. A bump-like feature emerges naturally if the base inflaton potential $V_b(phi)$ contains a local correction term such as $V_b(phi)left[1+varepsilon(phi)right]$ at $phi=phi_0$. The presence of such a localised correction term at $phi_0$ leads to a large peak in the curvature power spectrum and to an enhanced probability of black hole formation. Remarkably this does not significantly affect the scalar spectral index $n_{_S}$ and tensor to scalar ratio $r$ on CMB scales. Consequently such models can produce higher mass primordial black holes ($M_{rm PBH}geq 1 M_{odot}$) in contrast to models with `near inflection-point potentials in which generating higher mass black holes severely affects $n_{_S}$ and $r$. With a suitable choice of the base potential - such as the string theory based (KKLT) inflation or the $alpha$-attractor models - the amplification of primordial scalar power spectrum can be as large as $10^7$ which leads to a significant contribution of primordial black holes (PBHs) to the dark matter density today, $f_{rm PBH} = Omega_{0,rm PBH}/Omega_{0,rm DM} sim O(1)$. Interestingly, our results remain valid if the bump is replaced by a dip. In this case the base inflaton potential $V_b(phi)$ contains a negative local correction term such as $V_b(phi)left[1-varepsilon(phi)right]$ at $phi=phi_0$ which leads to an enhanced probability of PBH formation. We conclude that primordial black holes in the mass range $10^{-17} M_{odot} leq M_{rm PBH} leq 100, M_{odot}$ can easily form in single field inflation in the presence of small bump-like and dip-like features in the inflaton potential.
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