N-flationary Magnetic Fields

Abstract

There is increasing interest in the role played by pseudo Nambu-Goldstone bosons (pNGBs) in the construction of string-inspired models of inflation. In these models the inflaton is expected to be coupled to gauge fields, and will lead to the generation of magnetic fields that can be of cosmological interest. We study the production of such fields mainly focusing on the model of N-flation, where the collective effect of several pNGBs drives inflation. Because the produced fields are maximally helical, inverse cascade processes in the primordial plasma increase significantly their coherence length. We discuss under what conditions inflation driven by pNGBs can account for the observed cosmological magnetic fields. A constraint on the parameters of this class of inflationary scenarios is also derived by requiring that the magnetic field does not backreact on the inflating background.

A review of axion inflation in the era of Planck

“…Coupling to an Abelian gauge field Starting from ref. [43], it has been recently understood that the inflaton coupling to a gauge field through the shift-symmetric operator α 4f φFF (where α is a dimensionless coefficient) can play a nontrivial role already during inflation. In fact, due to this coupling, one helicity of the gauge field experiences a tachyonic growth.…”

“…Therefore, all the signatures associated to this production are very sensitive to small variations of ξ in the relevant ξ > ∼ 1 region. The original work [43] studied under which conditions this production can result in sufficiently large magnetic fields, under the assumption that the gauge field coupled to the axion is the photon. This issue was further studied in [45], which reaches more pessimistic conclusions than [43], based on different assumptions on the inverse cascade post-inflationary evolution of the magnetic field.…”

“…(11), with ξ constant, is solved by Coulomb functions. The solution with initial conditions in the adiabatic vacuum is well approximated by [43] …”

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.…”

Quasinormal modes of black holes localized on the Randall-Sundrum 2-brane

“…Although no exact solutions describing localized black holes have been known so far in the original five-dimensional Randall-Sundrum setup, exact fourdimensional (4D) black holes localized on 2-branes in AdS have been constructed by Emparan, Horowitz, and Myers [16,17] (see also [18]). Their black hole solution serves as an interesting toy model of the lower dimensional Randall-Sundrum braneworld, and helps us to understand aspects of small and large localized black holes.…”