Resonant magnetogenesis from axions

Abstract

We investigate the generation of seed magnetic field through the Chern-Simons coupling between the U(1) gauge field and an axion field that commences to oscillate at various epoch, depending on the mass scale. We address axions which begin oscillation during inflation, reheating, and also the radiation dominated era after the thermalization of the Universe. We study the resonant generation mechanisms and highlight that a small oscillation time scale with respect to that of the cosmic expansion can lead to an efficient generation of (hyper) magnetic field via resonant generation, even for 𝒪(1) coupling. In addition, we demonstrate that the generated field can be helical due to the tachyonic amplification phase prior to the onset of oscillation. Furthermore, it is shown that the parametric resonance during reheating can generate a circularly polarized (hyper) magnetic field in a void region with the present amplitude B0 =3× 10−15Gauss and the coherent length λ0 = 0.3pc without being plagued by the backreaction issue.

The First Three Seconds: a Review of Possible Expansion Histories of the Early Universe

“…Furthermore, a period of nonstandard cosmology may also impact small scale structure formation, potentially enhancing or impeding the formation of dense ultracompact DM microhalos [43,44,45,46,47], axion miniclusters [48,49], and primordial black holes (PBH)s [50,51,52,53,54,55,56]. The survival of nongravitational relics (including, for example and in addition to DM, matterantimatter asymmetry [57,58,59,60,61], primordial magnetic fields [62,63,64,65,66], or effective number of relativistic species [67,68]) will depend on the details of the expansion history and post-inflationary thermalization of radiation. Along with large-scale gravitational effects associated with the expansion history, smaller scale gravitational effects -including horizon-scaled variations of expansion history and associated non-Gaussianities [69,70,71,72,73,74,75,76,77,78], imprints from small-scale clustering of matter [43,79,80], PBHs [81,82,83,84,…”

Nano-Hz Gravitational-Wave Signature from Axion Dark Matter

“…The reported NANOGrav 12.5 year data can also be explained in this scenario if one requires a drastic suppression for the relic axion density. 1 This mechanism is also applicable to generate primordial magnetic field [12,[18][19][20][21], to reduce the abundance of QCD axion [22,23] and provide the correct relic abundance of the dark photon dark matter [24][25][26].…”

The art of simulating the early universe. Part I. Integration techniques and canonical cases

“…Only in this way, we will achieve a certain robustness in the predictions of the potentially observational implications from non-linear high energy phenomena. Furthermore, the techniques developed for studying nonlinear dynamics of classical fields are common to many other non-linear problems in the early universe, like the dynamics of phase transitions [74,75,102,[195][196][197][198][199] and their emission of gravitational waves [200][201][202][203][204][205][206], cosmic defect formation [114,159,[207][208][209][210][211][212][213][214], their later evolution [160-166, 215, 216] and gravitational wave emission [114,167,168,217], axion-like field dynamics [172,175,[218][219][220][221], moduli dynamics [222,223], etc. These techniques can also be used in applications of interest not only to cosmology, but also to other high energy physics areas.…”