Scalar induced gravity waves from ultra slow-roll Galileon inflation

We consider the production of secondary gravity waves in Galileon inflation with an ultra-slow roll (USR) phase and show that the spectrum of scalar-induced gravitational waves (SIGWs) in this case is consistent with the recent NANOGrav 15-year data and with sensitivities of other ground and space-based missions, LISA, BBO, DECIGO, CE, ET, HLVK (consists of aLIGO, aVirgo, and KAGRA), and HLV(03). Thanks to the non-renormalization property of Galileon theory, the amplitude of the large fluctuation is controllable at the sharp transitions between SR and USR regions. We show that the behaviour of the GW spectrum, when one-loop effects are included in the scalar power spectrum, is preserved under a shift of the sharp transition scale with peak amplitude $\Omega_{\rm GW}h^2\sim {\cal O}(10^{-6})$, and hence it can cover a wide range of frequencies within ${\cal O}(10^{-9}{\rm Hz} - 10^{7}{\rm Hz})$. An analysis of the allowed mass range for primordial black holes (PBHs) is also performed, where we find that mass values ranging from ${\cal O}(1M_{\odot} - 10^{-18}M_{\odot})$ can be generated over the corresponding allowed range of low and high frequencies.Comment: 25 pages, 2 figures, Comments are welcom

Primordial non-Gaussianity as a saviour for PBH overproduction in SIGWs generated by Pulsar Timing Arrays for Galileon inflation

We investigate the explicit role of negative local non-Gaussianity, $f_{\rm NL}$, in suppressing the abundance of primordial black holes (PBHs) in the single-field model of Galileon inflation. PBH formation requires significantly enhancing the scalar power spectrum, which greatly affects their abundance. The associated frequencies in the nHz regime are also sensitive to the generation of scalar-induced gravitational waves (SIGWs) which may explain the current data from the pulsar timing arrays (PTAs). Our analysis using the threshold statistics on the compaction function demonstrates that Galileon theory not only avoids PBH overproduction using the curvature perturbation enhancements that give $f_{\rm NL} \sim {\cal O}(-6)$, but also generates SIGWs that conform well with the PTA data.Comment: 20 pages (5 pages material+8 pages refs.+7 pages supplementary material), 5 figures (3 figures in material+2 figures in supplementary material), Comments are welcome, Reference list update

Evading no-go for PBH formation and production of SIGWs using Multiple Sharp Transitions in EFT of single field inflation

Deploying \textit{multiple sharp transitions} (MSTs) under a unified framework, we investigate the formation of Primordial Black Holes (PBHs) and the production of Scalar Induced Gravitational Waves (SIGWs) by incorporating one-loop corrected renormalized-resummed scalar power spectrum. With effective sound speed parameter, $1 \leq c_s \leq 1.17$, the direct consequence is the generation of PBH masses spanning $M_{\rm PBH}\sim{\cal O}(10^{-31}M_{\odot}- 10^{4}M_{\odot})$, thus evading well known \textit{No-go theorem} on PBH mass. Our results align coherently with the extensive NANOGrav 15-year data and the sensitivities outlined by other terrestrial and space-based experiments (e.g.: LISA, HLVK, BBO, HLV(O3), etc.).Comment: 14 pages, 3 figures, Comments are welcom

Realisation of the ultra-slow roll phase in Galileon inflation and PBH overproduction

We demonstrate the explicit realisation of the ultra-slow roll phase in the framework of the effective field theory of single-field Galileon inflation. The pulsar timing array (PTA) collaboration hints at the scalar-induced gravity waves (SIGW) from the early universe as an explanation for the origin of the observed signal, which, however, leads to an enhancement in the amplitude of the scalar power spectrum giving rise to the overproduction of primordial black holes (PBHs). In the setup under consideration, we examine the generation of SIGW consistent with PTA (NANOGrav15 and EPTA) data, in addition to which we also consider the impact from QCD crossover at the nHz frequencies and address the PBH overproduction issue assuming linear approximations for the over-density without incorporating non-Gaussian effects from the comoving curvature perturbation. The framework is shown to give rise to SIGWs well consistent with the PTA signal with comfortable PBH abundance, $10^{-3} \lesssim f_{\rm PBH} < 1$, of near solar-mass black holes.62 pages, 23 figures, Comments are welcome, Revised version accepted for publication in JCA

Primordial Black Holes from Effective Field Theory of Stochastic Single Field Inflation at NNNLO

We present a study of the Effective Field Theory (EFT) generalization of stochastic inflation in a model-independent single-field framework and its impact on primordial black hole (PBH) formation. We show how the Langevin equations for the "soft" modes in quasi de Sitter background is described by the Infra-Red (IR) contributions of scalar perturbations, and the subsequent Fokker-Planck equation driving the probability distribution for the stochastic duration ${\cal N}$, significantly modify in the present EFT picture. An explicit perturbative analysis of the distribution function by implementing the stochastic-$\delta N$ formalism is performed up to the next-to-next-to-next-to-leading order (NNNLO) for both the classical-drift and quantum-diffusion dominated regimes. In the drift-dominated limit, we perturbatively analyse the local non-Gaussianity parameters $(f_{\rm NL}, g_{\rm NL}, \tau_{\rm NL})$ with the EFT-induced modifications. In the diffusion-dominated limit, we numerically compute the probability distribution featuring exponential tails at each order of perturbative treatment.Comment: 83 pages, 19 figures, 1 table, Comments are welcome, Reference list updated, New clarifications and discussions added, Updated versio

Primordial black holes from effective field theory of stochastic single field inflation at NNNLO

Abstract We present a study of the Effective Field Theory (EFT) generalization of stochastic inflation in a model-independent single-field framework and its impact on primordial black hole (PBH) formation. We show how the Langevin equations for the “soft” modes in quasi de Sitter background is described by the Infra-Red (IR) contributions of scalar perturbations, and the subsequent Fokker–Planck equation driving the probability distribution for the stochastic duration $$\mathcal {N}$$ N , significantly modify in the present EFT picture. An explicit perturbative analysis of the distribution function by implementing the stochastic- $$\delta N$$ δ N formalism is performed up to the next-to-next-to-next-to-leading order (NNNLO) for both the classical-drift and quantum-diffusion dominated regimes. In the drift-dominated limit, we perturbatively analyse the local non-Gaussianity parameters $$(f_\textrm{NL}, g_\textrm{NL}, \tau _\textrm{NL})$$ ( f NL , g NL , τ NL ) with the EFT-induced modifications. In the diffusion-dominated limit, we numerically compute the probability distribution featuring exponential tails at each order of perturbative treatment

Regularized-renormalized-resummed loop corrected power spectrum of non-singular bounce with Primordial Black Hole formation

Abstract We present a complete and consistent exposition of the regularization, renormalization, and resummation procedures in the setup of having a contraction and then non-singular bounce followed by inflation with a sharp transition from slow-roll (SR) to ultra-slow roll (USR) phase for generating primordial black holes (PBHs). We consider following an effective field theory (EFT) approach and study the quantum loop corrections to the power spectrum from each phase. We demonstrate the complete removal of quadratic UV divergences after renormalization and softened logarithmic IR divergences after resummation and illustrate the scheme-independent nature of our renormalization approach. We further show that the addition of a contracting and bouncing phase allows us to successfully generate PBHs of solar-mass order, $$M_\textrm{PBH}\sim \mathcal{O}(M_{\odot })$$ M PBH ∼ O ( M ⊙ ) , by achieving the minimum e-folds during inflation to be $$\Delta N_{\textrm{Total}}\sim \mathcal{O}(60)$$ Δ N Total ∼ O ( 60 ) and in this process successfully evading the strict no-go theorem. We notice that varying the effective sound speed between $$0.88\leqslant c_{s}\leqslant 1$$ 0.88 ⩽ c s ⩽ 1 , allows the peak spectrum amplitude to lie within $$10^{-3}\leqslant A \leqslant 10^{-2}$$ 10 - 3 ⩽ A ⩽ 10 - 2 , indicating that causality and unitarity remain protected in the theory. We analyse PBHs in the extremely small, $$M_{\textrm{PBH}}\sim \mathcal{O}(10^{-33}-10^{-27})M_{\odot }$$ M PBH ∼ O ( 10 - 33 - 10 - 27 ) M ⊙ , and the large, $$M_{\textrm{PBH}}\sim \mathcal{O}(10^{-6}-10^{-1})M_{\odot }$$ M PBH ∼ O ( 10 - 6 - 10 - 1 ) M ⊙ , mass limits and confront the PBH abundance results with the latest microlensing constraints. We also study the cosmological beta functions across all phases and find their interpretation consistent in the context of bouncing and inflationary scenarios while satisfying the pivot scale normalization requirement. Further, we estimate the spectral distortion effects and shed light on controlling PBH overproduction

An Artificial Intelligence Approach to Transient Stability Assessment

An artificial intelligence approach to online transient stability assessment is briefly discussed, and some crucial requirements for this algorithm are identified. Solutions to these are proposed. Some new attributes are suggested so as to reflect machine dynamics and changes in the network. Also a new representative learning set algorithm has been developed