Inflationary magnetogenesis without the strong coupling problem

Abstract

The simplest gauge invariant models of inflationary magnetogenesis are known to suffer from the problems of either large backreaction or strong coupling, which make it difficult to self-consistently achieve cosmic magnetic fields from inflation with a field strength larger than 10 −32 G today on the Mpc scale. Such a strength is insufficient to act as seed for the galactic dynamo effect, which requires a magnetic field larger than 10 −20 G. In this paper we analyze simple extensions of the minimal model, which avoid both the strong coupling and back reaction problems, in order to generate sufficiently large magnetic fields on the Mpc scale today. First we study the possibility that the coupling function which breaks the conformal invariance of electromagnetism is non-monotonic with sharp features. Subsequently, we consider the effect of lowering the energy scale of inflation jointly with a scenario of prolonged reheating where the universe is dominated by a stiff fluid for a short period after inflation. In the latter case, a systematic study shows upper bounds for the magnetic field strength today on the Mpc scale of 10 −13 G for low scale inflation and 10 −25 G for high scale inflation, thus improving on the previous result by 7-19 orders of magnitude. These results are consistent with the strong coupling and backreaction constraints.

Schwinger effect in 4D de Sitter space and constraints on magnetogenesis in the early universe

“…[21][22][23][24][25][26][27][42][43][44][45][46][47][48][49][50][51][52], in order to explain the origin of the large-scale magnetic fields in our universe. In such inflationary magnetogenesis scenarios, the magnetic fields are generically accompanied by the production of even larger electric fields.…”

“…We stress that, as long as the mass of the charged field is not much larger than the Hubble scale, the constraint is more severe for lower inflation scales. Hence lowering the energy scale of inflation (as was considered in [51,52] to circumvent previous constraints) does not improve the situation.…”

Primordial magnetic fields from the post-inflationary universe

“…k/aH → ∞, the solutions (2.36) are approximated by 37) and its complex conjugate for (aH) −α H (2) α . On the other hand, in the super-horizon limit, i.e.…”

Cosmic magnetization in curved and Lorentz violating space–times

“…Then, as we enter the classic era of radiation we set C ∼ a −x to 'wash out' the QG effects. In a more detailed analysis one may study more complicated profiles for the Cartan parameter C to avoid possible backreaction and similar to strong coupling issues [124,125].…”