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Register a new userTransient Pulses from Exploding Primordial Black Holes as a Signature of an Extra Dimension
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An evaporating black hole in the presence of an extra spatial dimension would undergo an explosive phase of evaporation. We show that such an event, involving a primordial black hole, can produce a detectable, distinguishable electromagnetic pulse, signaling the existence of an extra dimension of size $Lsim10^{-18}-10^{-20}$ m. We derive a generic relationship between the Lorentz factor of a pulse-producing fireball and the TeV energy scale. For an ordinary toroidally compactified extra dimension, transient radio-pulse searches probe the electroweak energy scale ($sim$0.1 TeV), enabling comparison with the Large Hadron Collider.
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We show that the number of primordial black holes (PBHs) which is originated from primordial density perturbations with moderately-tilted power spectrum fluctuates following the log-normal distribution, while it follows the Poisson distribution if the spectrum is steeply blue. The log-normal, as well as the Poisson, fluctuation of the PBH number behaves as an isocurvature mode and affects the matter power spectrum and the halo mass function in a different way from those for the Poisson case. The future 21cm observation can potentially put a stronger constraint on the PBH fraction than the current one in a wide mass range, $10^{-5}M_odot$--$10M_odot$.
We investigate the clustering property of primordial black holes (PBHs) in a scenario where PBHs can explain the existence of supermassive black holes (SMBHs) at high redshifts. We analyze the angular correlation function of PBHs originating from fluctuations of a spectator field which can be regarded as a representative model to explain SMBHs without conflicting with the constraint from the spectral distortion of cosmic microwave background. We argue that the clustering property of PBHs can give a critical test for models with PBHs as the origin of SMBHs and indeed show that the spatial distribution of PBHs in such a scenario is highly clustered, which suggests that those models may be disfavored from observations of SMBHs although a careful comparison with observational data would be necessary.
An observable stochastic background of gravitational waves is generated whenever primordial black holes are created in the early universe thanks to a small-scale enhancement of the curvature perturbation. We calculate the anisotropies and non-Gaussianity of such stochastic gravitational waves background which receive two contributions, the first at formation time and the second due to propagation effects. The former contribution can be generated if the distribution of the curvature perturbation is characterized by a local and scale-invariant shape of non-Gaussianity. Under such an assumption, we conclude that a sizeable magnitude of anisotropy and non-Gaussianity in the gravitational waves would suggest that primordial black holes may not comply the totality of the dark matter.
We study the dynamics of a spectator Higgs field which stochastically evolves during inflation onto near-critical trajectories on the edge of a runaway instability. We show that its fluctuations do not produce primordial black holes (PBHs) in sufficient abundance to be the dark matter, nor do they produce significant second-order gravitational waves. First we show that the Higgs produces larger fluctuations on CMB scales than on PBH scales, itself a no-go for a viable PBH scenario. Then we track the superhorizon perturbations nonlinearly through reheating using the delta N formalism to show that they are not converted to large curvature fluctuations. Our conclusions hold regardless of any fine-tuning of the Higgs field for both the Standard Model Higgs and for Higgs potentials modified to prevent unbounded runaway.
The NANOGrav Collaboration has recently published a strong evidence for a stochastic common-spectrum process that may be interpreted as a stochastic gravitational wave background. We show that such a signal can be explained by second-order gravitational waves produced during the formation of primordial black holes from the collapse of sizeable scalar perturbations generated during inflation. This possibility has two predictions: $i$) the primordial black holes may comprise the totality of the dark matter with the dominant contribution to their mass function falling in the range $(10^{-15}div 10^{-11}) M_odot$ and $ii$) the gravitational wave stochastic background will be seen as well by the LISA experiment.
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