Observational evidence for primordial black holes: A positivist perspective

Big Bang Nucleosynthesis (BBN) is a strong probe for constraining new physics including gravitation. f(R) gravity theory is an interesting alternative to general relativity which introduces additional degrees of freedom known as scalarons. In this work we demonstrate the existence of black hole solutions in f(R) gravity and develop a relation between scalaron mass and black hole mass. We have used observed bound on the freezeout temperature to constrain scalaron mass range by modifying the cosmic expansion rate at the BBN epoch. The mass range of primordial black holes (PBHs) which are astrophysical dark matter candidates is deduced. The range of scalaron mass which does not spoil the BBN era is found to be 10-16–104 eV for both relativistic and non-relativistic scalarons. The window 10-16–10-14 eV of scalaron mass obtained from solar system constraint on PPN parameter is compatible with the BBN bound derived in this work. The PBH mass range is obtained as 106–10-14 M ⊙. Scalarons constrained by BBN are also eligible to accommodate axion like dark matter particles. The problem of ultra-light PBHs (M ≤ 10-24 M ⊙) not constrained by the present study of BBN is still open. Estimation of deuterium (D) fraction and relative D+3He abundance in the f(R) gravity scenario shows that the BBN history mimics that of general relativity. While the PBH mass range is eligible for non-baryonic dark matter, the BBN bounded scalarons provide with an independent strong field test of f(R) gravity. The PBH mass range obtained in the study is discussed in relation to future astronomical measurements.

Section: Resultsmentioning

confidence: 99%

Constraining primordial black hole masses through f(R) gravity scalarons in Big Bang Nucleosynthesis

Talukdar,

Kalita,

Das

et al. 2024

“…Recent and future advances in astrophysical and cosmological observations are opening new observational windows at small scales that may allow us to test the inflationary history at later times than those presently probed by Cosmic Microwave Background (CMB) and Large Scale Structure (LSS) observations. A number of physical processes in act during these times can lead to enhanced scalar and/or tensor fluctuations, that in turn could lead to the production of primordial black holes (PBH) [1,2], with a number of observational prospects [3][4][5][6][7], and/or the generation of a detectable stochastic background of gravitational waves (SGWB) [8][9][10].…”

Section: Introductionmentioning

confidence: 99%

One-loop infrared rescattering by enhanced scalar fluctuations during inflation

Fumagalli,

Bhattacharya,

Peloso

et al. 2024

We show that, whenever the perturbations of some field are excited during inflation by a physical process on sub-horizon scales, they unavoidably generate, even through gravitational interactions alone, a significant resonant IR cascade of power down to scales that are of the order of the horizon at that time (we denote these scales as near IR). We provide general analytic one-loop results for the enhancement of the IR power of the curvature perturbation generated by this effect, highlighting the role played by the resonance. We then study a number of examples in which the excited state is: (i) an isocurvature field, (ii) the curvature perturbation itself, (iii) a mixture of curvature and isocurvature fluctuations driven to an excited state by their coupled dynamics. In the cases shown, the cascade significantly modifies the near IR part of the power spectrum of the curvature perturbation with respect to the linear theory, indicating that this effect can impact the phenomenology associated with a variety of mechanisms considered in the literature, notably concerning primordial black holes and gravitational waves.

“…As such, these models can make more probable the extreme objects of our universe [11]. Further observational prospects for these non-perturbative PNG include the search for primordial black holes [21], that could also represent a fraction of dark matter [22,23], the gravitational waves cosmological background [24], or ultracompact minihalos [25].…”

Section: Introductionmentioning

confidence: 99%

From inflation to dark matter halo profiles: the impact of primordial non-Gaussianities on the central density cusp

Stahl,

Mai,

Famaey

et al. 2024

It has recently been shown that local primordial non-Gaussianities (PNG) with significant amplitude (|f NL| ∼ 1000), at small (Mpc) scales, can help in forming simulated galaxies with more disky baryonic kinematics than in the Gaussian case, while generating matter power spectra that can differ by up to 20% from the Gaussian case at non-linear scales. Here, we explore in detail the consequences of such small-scale PNG on the dark matter halo profiles. We show in particular that, for negative f NL, dark matter halos formed in collisionless simulations are not always well described by the traditional Navarro-Frenk-White (NFW) profiles, as supported by their sparsity distribution. We conclude that NFW profiles are not as clear attractors for the density profiles of dark matter halos in the presence of PNG than in the case of a Gaussian contrast density field. We show how alternatives to the NFW profile can describe halos both in the Gaussian and non-Gaussian cases. From the combination of our sparsity analysis and the quality of the adjustments of the density profiles with a minimal extension to NFW, we conclude that z = 1 halos carry the most interesting information about PNG.