Routing protocol

Physics

Cosmic microwave background

Slow roll

Computer network

Mathematics

Black hole (networking)

Link-state routing protocol

Scalar field

Statistics

Spectral density

Inflaton

Primordial black hole

Gravitational wave

Inflation (cosmology)

Geometry

Theoretical physics

Computer science

Astrophysics

Quantum mechanics

Routing (electronic design automation)

Anisotropy

Binary black hole

Scalar (mathematics)

Classical mechanics

Journal of Cosmology and Astroparticle Physics

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.

Primordial black holes from a tiny bump/dip in the inflaton potential