Non-Gaussianity and secondary gravitational waves from primordial black holes production in $$\alpha $$-attractor inflation

Abstract

We study the non-Gaussianity and secondary Gravitational Waves (GWs) in the process of the Primordial Black Holes (PBHs) production from inflation. In our work, we focus on the $$\alpha $$ α -attractor inflation model in which a tiny bump in the inflaton potential enhances the amplitude of the curvature perturbations at some scales and consequently leads to the PBHs production with different mass scales. We implement the computational code BINGO which calculates the non-Gaussianity parameter in different triangle configurations. Our examination implies that in this setup, the non-Gaussianity gets amplified significantly in the equilateral shape around the scales in which the power spectrum of the scalar perturbations undergoes a sharp declination. The imprints of these non-Gaussianities can be probed in the scales corresponding to the BBN and $$\mu $$ μ -distortion events, or in smaller scales, and detection of such signatures in the future observations may confirm the idea of our model for the generation of PBHs or rule it out. Moreover, we investigate the secondary GWs in this framework and show that in our model, the peak of the present fractional energy density is obtained as $$\Omega _{\mathrm{GW0}} \sim 10^{-8}$$ Ω GW 0 ∼ 10 - 8 at different frequencies which depends on the model parameters. These results lie well within the sensitivity region of some GWs detectors at some frequencies, and therefore the observational compatibility of our model can be evaluated by the forthcoming data from these detectors. We further provide some estimations for the tilts of the induced GWs spectrum in the different intervals of frequency, and demonstrate that the spectrum obeys the power-law relation $$\Omega _{\mathrm{GW0}}\sim f^{n}$$ Ω GW 0 ∼ f n in those frequency bands.

Ruling Out Primordial Black Hole Formation From Single-Field Inflation

“…Models with an extremely flat feature fall in this category including those with an inflection point in the potential [7,. Other examples of feature are a tiny bump or dip [61][62][63][64][65][66], an upward or downward step [67][68][69][70][71][72], polynomial shape [73][74][75][76] and Coleman-Weinberg potential [39,77,78]. In these examples, modification of potential makes a sharp η transition on the inflaton dynamics.…”

Primordial black holes ensued from exponential potential and coupling parameter in nonminimal derivative inflation model

“…Using the scalar (12) and tensor (16) power spectra in non-canonical model, the tensor-toscalar ratio r could easily be computed as…”

“…indicates a minute peaked function of φ in charge of modifying the basic potential on small scales in order to make the inflaton slow down and amplify the scalar power spectrum without disturbing effect on CMB scales. Pursuant to [16,32] the bump function is taken as the consistency of the model with CMB observation on large scales is guaranteed but also the amplification of P R on smaller scales could be occurred.…”

“…PBHs with mass O(10 −5 )M ⊙ and abundance O(10 −2 ), can be located in the permitted span of OGEL data [26] and they can be suitable to expound the ultrashorttimescale microlensing events in this zone. Due to the fact that, There is no constraint on PBHs abundance in the mass scope of O(10 −16 − 10 −11 )M ⊙ , the located PBHs in this zone could be contemplated as an appropriate candidate for the DM content in its totality [13][14][15][16][17][18][19][20][21].…”

“…In the SM of inflation, the USR span to produce PBHs could be attained either by dint of an inflection point in the inflationary potential [28][29][30][31], or adding a correction term like a bump/dip to the base potential to reduce the velocity of the inflaton [16,32].…”