Fluctuations of inflationary magnetogenesis

Abstract

This analysis aims at exploring what can be said about the growth rate of magnetized inhomogeneities under two concurrent hypotheses: a phase of quasi-de Sitter dynamics driven by a single inflaton field and the simultaneous presence of a spectator field coupled to gravity and to the gauge sector. Instead of invoking ad hoc correlations between the various components, the system of scalar inhomogeneities is diagonalized in terms of two gauge-invariant quasi-normal modes whose weighted sum gives the curvature perturbations on comoving orthogonal hypersurfaces. The predominance of the conventional adiabatic scalar mode implies that the growth rate of magnetized inhomogeneities must not exceed 2.2 in Hubble units if the conventional inflationary phase is to last about 70 efolds and for a range of slow roll parameters between 0.1 and 0.001. Longer and shorter durations of the quasi-de Sitter stage lead, respectively, either to tighter or to looser bounds which are anyway more constraining than the standard backreaction demands imposed on the gauge sector. Since a critical growth rate of order 2 leads to a quasi-flat magnetic energy spectrum, the upper bounds on the growth rate imply a lower bound on the magnetic spectral index. The advantages of the uniform curvature gauge are emphasized and specifically exploited throughout the treatment of the multicomponent system characterizing this class of problems.

37 pages, 4 figures

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• Scale-invariant Helical Magnetic Fields from Inflation
• Critical constraint on inflationary magnetogenesis
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• Constraints on Primordial Magnetic Fields from Inflation
• Magneto-reheating constraints from curvature perturbations
• Revisiting Magnetogenesis during Inflation
• Scalar perturbations from inflation in the presence of gauge fields
• Probing large-scale magnetism with the Cosmic Microwave Background
• Inflationary susceptibilities, duality and large-scale magnetic fields generation
• Primordial perturbations from dilaton-induced gauge fields
• Narrowing the window of inflationary magnetogenesis
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• Spurious gauge-invariance of higher-order contributions to the spectral energy density of the relic gravitons
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• Bootstrapping from inflationary magnetogenesis to CMB initial conditions
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• Super-horizon resonant magnetogenesis during inflation
• Effective anisotropic stresses of the relic gravitons
• Spectator Higgs, large-scale gauge fields and the non-minimal coupling to gravity
• Tensor to scalar ratio from single field magnetogenesis
• The Impact of Inhomogeneous Perturbations of the Inflaton on the Cosmological Primordial Magnetic Field