In pure axion inflation, detectable gravitational wave signals arise only in parameter regions with strong backreaction that violate the upper bound on ΔN_eff.
Consistent generation of magnetic fields in axion inflation models
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abstract
There has been a growing evidence for the existence of magnetic fields in the extra-galactic regions, while the attempt to associate their origin with the inflationary epoch alone has been found extremely challenging. We therefore take into account the consistent post-inflationary evolution of the magnetic fields that are originated from vacuum fluctuations during inflation. In the model of our interest, the electromagnetic (EM) field is coupled to a pseudo-scalar inflaton $\phi$ through the characteristic term $\phi F\tilde F$, breaking the conformal invariance. This interaction dynamically breaks the parity and enables a continuous production of only one of the polarization states of the EM field through tachyonic instability. The produced magnetic fields are thus helical. We find that the dominant contribution to the observed magnetic fields in this model comes from the modes that leave the horizon near the end of inflation, further enhanced by the tachyonic instability right after the end of inflation. The EM field is subsequently amplified by parametric resonance during the period of inflaton oscillation. Once the thermal plasma is formed (reheating), the produced helical magnetic fields undergo a turbulent process called inverse cascade, which shifts their peak correlation scales from smaller to larger scales. We consistently take all these effects into account within the regime where the perturbation of $\phi$ is negligible and obtain $B_{\rm eff} \sim 10^{-19}$G, indicating the necessity of additional mechanisms to accommodate the observations.
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Lattice simulations show that Schwinger currents saturate gauge-field production in axion inflation, yielding universal conductivity and magnetic-field values at the onset of strong backreaction.
Axion-like particles in the trapped misalignment mechanism produce observable gravitational waves while generating intergalactic magnetic fields that exceed blazar lower bounds in the parameter space promising for gravitational wave detection.
Finite conductivity of the plasma suppresses parametric resonance amplification of electromagnetic fields from ultralight pseudoscalar dark matter, making it impossible to generate magnetic fields of sufficient strength in cosmic voids for observationally viable couplings.
citing papers explorer
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Gravitational waves from axion inflation in the gradient expansion formalism. Part I. Pure axion inflation
In pure axion inflation, detectable gravitational wave signals arise only in parameter regions with strong backreaction that violate the upper bound on ΔN_eff.
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Schwinger effect in axion inflation on a lattice
Lattice simulations show that Schwinger currents saturate gauge-field production in axion inflation, yielding universal conductivity and magnetic-field values at the onset of strong backreaction.
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Audible Axion Magnetogenesis: Linking Intergalactic Magnetic Fields and Gravitational Waves
Axion-like particles in the trapped misalignment mechanism produce observable gravitational waves while generating intergalactic magnetic fields that exceed blazar lower bounds in the parameter space promising for gravitational wave detection.
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Suppressed Magnetogenesis from Ultralight Dark Matter due to Finite Conductivity
Finite conductivity of the plasma suppresses parametric resonance amplification of electromagnetic fields from ultralight pseudoscalar dark matter, making it impossible to generate magnetic fields of sufficient strength in cosmic voids for observationally viable couplings.