It is assumed in standard cosmology that the Universe underwent a period of inflation in its earliest phase, providing the seeds for structure formation through vacuum fluctuations of the inflaton scalar field. These fluctuations get stretched by the quasiexponential expansion of the Universe and become squeezed. The aim of this paper is to deepen the understanding of the squeezing process, considering the effect of self -interactions. Axion-like particles can provide a useful setup to study this effect. Specifically we focus on the consequences that a non -trivial evolution of the background axion field has on the squeezing of the perturbations. We follow the evolution of the axion's fluctuation modes from the horizon exit during inflation to the radiation-dominated epoch. We compute Bogoliubov coefficients and squeezing parameters, which are linked to the axion particle number and isocurvature perturbation. We find that the quantum mechanical particle production and the squeezing of the perturbations are enhanced, if one accounts for anharmonic effects, i.e., the effect of higher order terms in the potential. This effect becomes particularly strong towards the hilltop of the potential.

Anharmonic effects on the squeezing of axion perturbations / Danieli, Valentina; Kobayashi, Takeshi; Bartolo, Nicola; Matarrese, Sabino; Viel, Matteo. - In: JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS. - ISSN 1475-7516. - 2024:04(2024), pp. 1-31. [10.1088/1475-7516/2024/04/058]

Anharmonic effects on the squeezing of axion perturbations

Danieli, Valentina;Kobayashi, Takeshi;Bartolo, Nicola;Matarrese, Sabino;Viel, Matteo
2024-01-01

Abstract

It is assumed in standard cosmology that the Universe underwent a period of inflation in its earliest phase, providing the seeds for structure formation through vacuum fluctuations of the inflaton scalar field. These fluctuations get stretched by the quasiexponential expansion of the Universe and become squeezed. The aim of this paper is to deepen the understanding of the squeezing process, considering the effect of self -interactions. Axion-like particles can provide a useful setup to study this effect. Specifically we focus on the consequences that a non -trivial evolution of the background axion field has on the squeezing of the perturbations. We follow the evolution of the axion's fluctuation modes from the horizon exit during inflation to the radiation-dominated epoch. We compute Bogoliubov coefficients and squeezing parameters, which are linked to the axion particle number and isocurvature perturbation. We find that the quantum mechanical particle production and the squeezing of the perturbations are enhanced, if one accounts for anharmonic effects, i.e., the effect of higher order terms in the potential. This effect becomes particularly strong towards the hilltop of the potential.
2024
2024
04
1
31
058
10.1088/1475-7516/2024/04/058
https://arxiv.org/abs/2309.13112
Danieli, Valentina; Kobayashi, Takeshi; Bartolo, Nicola; Matarrese, Sabino; Viel, Matteo
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/20.500.11767/139731
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