# A solution to the anisotropy problem in bouncing cosmologies

Research output: Contribution to journal › Article › peer-review

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**A solution to the anisotropy problem in bouncing cosmologies.** / Bozza, V.; Bruni, Marco.

Research output: Contribution to journal › Article › peer-review

### Harvard

*Journal of Cosmology and Astroparticle Physics*, vol. 2009, no. 10, pp. 014-014. https://doi.org/10.1088/1475-7516/2009/10/014

### APA

*Journal of Cosmology and Astroparticle Physics*,

*2009*(10), 014-014. https://doi.org/10.1088/1475-7516/2009/10/014

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### Bibtex

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### RIS

TY - JOUR

T1 - A solution to the anisotropy problem in bouncing cosmologies

AU - Bozza, V.

AU - Bruni, Marco

PY - 2009

Y1 - 2009

N2 - Bouncing cosmologies are often proposed as alternatives to standard inflation for the explanation of the homogeneity and flatness of the universe. In such scenarios, the present cosmological expansion is preceded by a contraction phase. However, during the contraction, in general the anisotropy of the universe grows and eventually leads to a chaotic mixmaster behavior. This would either be hard to reconcile with observations or even lead to a singularity instead of the bounce. In order to preserve a smooth and isotropic bounce, the source for the contraction must have a super-stiff equation of state with P/ρ = w > 1. In this letter we propose a new mechanism to solve the anisotropy problem for any low-energy value of w by arguing that high energy physics leads to a modification of the equation of state, with the introduction of non-linear terms. In such a scenario, the anisotropy is strongly suppressed during the high energy phase, allowing for a graceful isotropic bounce, even when the low-energy value of w is smaller than unity.

AB - Bouncing cosmologies are often proposed as alternatives to standard inflation for the explanation of the homogeneity and flatness of the universe. In such scenarios, the present cosmological expansion is preceded by a contraction phase. However, during the contraction, in general the anisotropy of the universe grows and eventually leads to a chaotic mixmaster behavior. This would either be hard to reconcile with observations or even lead to a singularity instead of the bounce. In order to preserve a smooth and isotropic bounce, the source for the contraction must have a super-stiff equation of state with P/ρ = w > 1. In this letter we propose a new mechanism to solve the anisotropy problem for any low-energy value of w by arguing that high energy physics leads to a modification of the equation of state, with the introduction of non-linear terms. In such a scenario, the anisotropy is strongly suppressed during the high energy phase, allowing for a graceful isotropic bounce, even when the low-energy value of w is smaller than unity.

U2 - 10.1088/1475-7516/2009/10/014

DO - 10.1088/1475-7516/2009/10/014

M3 - Article

VL - 2009

SP - 14

EP - 14

JO - Journal of Cosmology and Astroparticle Physics

JF - Journal of Cosmology and Astroparticle Physics

SN - 1475-7516

IS - 10

ER -

ID: 68219