The hand-made tail: non-perturbative tails from multifield inflation

Achúcarro, Ana; Céspedes, Sebastián; Davis, Anne-Christine; Palma, Gonzalo A.

doi:10.1007/jhep05(2022)052

Cited by 20 publications

(19 citation statements)

References 77 publications

(117 reference statements)

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“…In regimes with very flat inflationary potential, when the gradient-induced velocity cannot proceed the inflation, quantum diffusion plays role in determining the PBH abundance. Since PBHs form in regimes with large curvature perturbations, beyond a threshold, this has been an early motivation for studying the inflection points, flat potentials and analyzing the PDF tail [74,75,[78][79][80][81][82][83][84][85][86][87][88]. In this paper we study the effect of the transition-induced form of noise amplitudes on the tail, compute the decay exponent of the PDF in our model and calculate its dependence on the diffusion strength.…”

Section: Introductionmentioning

confidence: 99%

Quantum diffusion in sharp transition to non-slow-roll phase

Ahmadi

Noorbala

Feyzabadi

et al. 2022

J. Cosmol. Astropart. Phys.

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Transitions between different inflationary slow-roll scenarios are known to provide short non-slow-roll periods with non-trivial consequences. We consider the effect of quantum diffusion on the inflationary dynamics in a transition process. Using the stochastic δ𝒩 formalism, we follow the detailed evolution of noises through a sharp transition modeled by the Starobinsky potential, although some of our results apply to any sharp transition. We find how the stochastic noise induced by the transition affects the coarse-grained fields. We then consider the special case that the potential is flat after the transition. It is found that, during a particular phase of evolution, the noise we obtain cannot drive the inflaton past the classically unreachable field values; so the boundary crossing is delayed. By deriving the characteristic function, we also study the tail behavior for the distribution of curvature perturbations ζ, which we find to decay faster than exp(-3ζ).

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Section: Introductionmentioning

confidence: 99%

Quantum diffusion in sharp transition to non-slow-roll phase

Ahmadi

Noorbala

Feyzabadi

et al. 2022

J. Cosmol. Astropart. Phys.

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“…As demonstrated in our study, the fully nonlinear mapping between R and δφ plays a key role for the tail of the PDF. Meanwhile, the stochastic effects during inflation may also lead to nontrivial non-Gaussian tails [13][14][15][16][17]. Thus it is encouraging to extend our current analysis to incorporate more general considerations.…”

Section: Discussionmentioning

confidence: 87%

“…Except for the n-point correlators, there in principle exist significant phenomenological implications in the probability distribution of curvature perturbations that are not captured by perturbative approaches (see [7][8][9][10][11][12][13][14][15][16][17] for recent discussions). In particular, the perturbation theory breaks down at the tail of the distribution where fluctuations are large and rare.…”

Section: Introductionmentioning

confidence: 99%

Highly non-Gaussian tails and primordial black holes from single-field inflation

Cai

Sasaki

et al. 2022

J. Cosmol. Astropart. Phys.

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For primordial perturbations, deviations from Gaussian statistics on the tail of the probability distribution can be associated with non-perturbative effects of inflation. In this paper, we present some particular examples in which the tail of the distribution becomes highly non-Gaussian although the statistics remains almost Gaussian in the perturbative regime. We begin with an extension of the ultra-slow-roll inflation that incorporates a transition process, where the inflaton climbs up a tiny potential step at the end of the non-attractor stage before it converges to the slow-roll attractor. Through this example, we identify the key role of the off-attractor behaviour for the upward-step transition, and then extend the analysis to another type of the transition with two slow-roll stages connected by a tiny step. We perform both the perturbative and non-perturbative analyses of primordial fluctuations generated around the step in detail, and show that the tiny but nontrivial transition may affect large perturbations in the tail of the distribution, while the perturbative non-Gaussianity remains small. Our result indicates that the non-Gaussian tails can have rich phenomenology which has been overlooked in conventional analyses. We also study the implications of this non-Gaussian tail for the formation of primordial black holes, and find that their mass fraction can be parametrically amplified by several orders of magnitudes in comparison with the case of the Gaussian distribution. Additionally, we also discuss a mechanism of primordial black holes formation for this upward step inflation model by trapping the inflaton in the bottom of the step.

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“…This indicates that the backreaction of quantum fluctuations onto the background dynamics plays an important role in this model, and the goal of this paper is to carefully study this effect. If large fluctuations are produced, such a backreaction effect is known to be crucial in shaping their statistical properties [25,[37][38][39][40][41][42][43][44] so this is also why it must be properly accounted for. We do so by using the stochastic-δN formalism [7,[45][46][47], in which small-scales quantum fluctuations shift the background dynamics when they are stretched to large distances, and effectively act as a random noise.…”

Section: Introductionmentioning

confidence: 99%

Uphill inflation

Briaud¹,

Vennin²

2023

Preprint

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Primordial black holes (PBH) may form from large cosmological perturbations, produced during inflation when the inflaton's velocity is sufficiently slowed down. This usually requires very flat regions in the inflationary potential. In this paper we investigate another possibility, namely that the inflaton climbs up its potential. When it turns back, its velocity crosses zero, which triggers a short phase of "uphill inflation" during which cosmological perturbations grow at a very fast rate. This naturally occurs in double-well potentials if the width of the well is close to the Planck scale. We include the effect of quantum diffusion in this scenario, which plays a crucial role, by means of the stochastic-δN formalism. We find that ultra-light black holes are produced with very high abundances, which do not depend on the energy scale at which uphill inflation occurs, and which suffer from substantially less fine tuning than in alternative PBH-production models. They are such that PBHs later drive a phase of PBH domination.

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The hand-made tail: non-perturbative tails from multifield inflation

Cited by 20 publications

References 77 publications

Quantum diffusion in sharp transition to non-slow-roll phase

Quantum diffusion in sharp transition to non-slow-roll phase

Highly non-Gaussian tails and primordial black holes from single-field inflation

Uphill inflation

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