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Assisting pre-big bang phenomenology through short-lived axions

V. Bozza, M. Gasperini, M. Giovannini, G. Veneziano

Abstract

We present the results of a detailed study of how isocurvature axion fluctuations are converted into adiabatic metric perturbations through axion decay, and discuss the constraints on the parameters of pre-big bang cosmology needed for consistency with present CMB-anisotropy data. The large-scale normalization of temperature fluctuations has a non-trivial dependence both on the mass and on the initial value of the axion. In the simplest, minimal models of pre-big bang inflation, consistency with the COBE normalization requires a slightly tilted (blue) spectrum, while a strictly scale-invariant spectrum requires mild modifications of the minimal backgrounds at large curvature and/or string coupling.

Assisting pre-big bang phenomenology through short-lived axions

Abstract

We present the results of a detailed study of how isocurvature axion fluctuations are converted into adiabatic metric perturbations through axion decay, and discuss the constraints on the parameters of pre-big bang cosmology needed for consistency with present CMB-anisotropy data. The large-scale normalization of temperature fluctuations has a non-trivial dependence both on the mass and on the initial value of the axion. In the simplest, minimal models of pre-big bang inflation, consistency with the COBE normalization requires a slightly tilted (blue) spectrum, while a strictly scale-invariant spectrum requires mild modifications of the minimal backgrounds at large curvature and/or string coupling.

Paper Structure

This paper contains 29 equations, 1 figure.

Figures (1)

  • Figure 1: Plot of the COBE normalization condition for $\sigma_i=1$, $f(1)=0.33$, $m=10^{10}$ GeV, $k_1/k_s=k_1/k_{\rm eq}\simeq 10^{27} (H_1/M_{\rm P})^{1/2}(m/M_{\rm P})^{1/3}$, and for various values of the inflation scale $H_1$. The four curves correspond, from left to right respectively, to $\log (H_1/M_{\rm P})=-4,-3,-2,-1$.