Minimal Magnetogenesis: The Role of Inflationary Perturbations and ALPs, and Its Gravitational Wave Signatures

Abstract

Any attempt to understand the ubiquitous nature of the magnetic field in the present universe seems to lead us towards its primordial origin. For large-scale magnetic fields, however, their strength and length scale may not necessarily originate from a singular primordial mechanism, namely inflationary magnetogenesis, which has been a popular consideration in the literature. In this paper, we propose a minimal scenario wherein a large-scale magnetic field is generated from the inflationary perturbation without any non-conformal coupling. Due to their origin in the inflationary scalar spectrum, these primordial fields are inherently weak, with their strength suppressed by the small amplitude of scalar fluctuations. We then consider the coupling between this large-scale weak primordial magnetic field and a light axion of mass $<10^{-28}$ eV, which is assumed to be frozen in a misaligned state until the photon decoupling. After the decoupling, when the universe enters into a dark age, the light axion coherently oscillates. By appropriately tuning the axion-photon coupling parameter $\alpha$, we demonstrate that a large-scale magnetic field of sufficient strength can indeed be generated through tachyonic resonance. We further show that the produced magnetic field induces a unique spectrum with multiple peaks of secondary gravitational waves, which the upcoming CMB-S4 can probe through B-mode polarization. The strength can be sufficient enough to violate the PLANCK bound on tensor-to-scalar ratio $r\lesssim 0.036$. Such a violation leads to a constraint on $\alpha \lesssim 80$. With this limiting value of the coupling, we find that present-day magnetic field strength could be as high as $10^{-10}$ Gauss at Mpc scale, consistent with observation.

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References in corpus (28)

• Primordial Black Holes and Slow-Roll Violation
• Lower limit on the strength and filling factor of extragalactic magnetic fields
• Generation of Large-Scale Magnetic Fields in Single-Field Inflation
• Reheating constraints to inflationary models
• CMB-S4: Forecasting Constraints on Primordial Gravitational Waves
• PBHs and secondary GWs from ultra slow roll and punctuated inflation
• Induced gravitational waves as a probe of thermal history of the universe
• Ultra slow-roll inflation demystified
• Adding helicity to inflationary magnetogenesis
• Evolution of Primordial Magnetic Fields from Phase Transitions
• Scalar induced gravitational waves in inflation with gravitationally enhanced friction
• A lower bound on intergalactic magnetic fields from time variability of 1ES 0229+200 from MAGIC and Fermi/LAT observations
• Implications of stochastic effects for primordial black hole production in ultra-slow-roll inflation
• Constraints on Primordial Magnetic Fields from Planck combined with the South Pole Telescope CMB B-mode polarization measurements
• Galactic Dynamos
• A new upper limit on the axion-photon coupling with an extended CAST run with a Xe-based Micromegas detector
• Primordial black holes and induced gravitational waves in $k$-inflation
• Small scale induced gravitational waves from primordial black holes, a stringent lower mass bound, and the imprints of an early matter to radiation transition
• Chiral Gravitational Waves Produced in a Helical Magnetogenesis Model
• Could PBHs and secondary GWs have originated from squeezed initial states?
• Constraints on Primordial Magnetic Fields from their impact on the ionization history with Planck 2018
• On the challenges in the choice of the non-conformal coupling function in inflationary magnetogenesis
• Primordial magnetic helicity evolution with a homogeneous magnetic field from inflation
• Gravitational wave generation in a viable scenario of inflationary magnetogenesis
• Probing the reheating phase through primordial magnetic field and CMB
• The Big Bang could be anisotropic. The case of Bianchi I model
• Inflationary magnetogenesis with a self-consistent coupling function
• Magnetogenesis from isocurvature initial conditions