Parameter dependence of magnetized CMB observables

Abstract

Pre-decoupling magnetic fields affect the scalar modes of the geometry and produce observable effects which can be constrained also through the use of current (as opposed to forthcoming) data stemming from the Cosmic Microwave Background observations. The dependence of the temperature and polarization angular power spectra upon the parameters of an ambient magnetic field is encoded in the scaling properties of a set of basic integrals whose derivation is simplified in the limit of small angular scales. The magnetically-induced distortions patterns of the relevant observables can be computed analytically by employing scaling considerations which are corroborated by numerical results. The parameter space of the magnetized Cosmic Microwave background anisotropies is also discussed in the light of the obtained analytical results.

Spectator stresses and CMB observables

“…[7,8] differ from the ones employed here (and match with the ones of [5] and references therein). The differences result, in a nutshell, from a different signature of the metric, from a different naming of the perturbed degrees of freedom and from a slightly different convention in the Rayleigh expansion of the brightness perturbations.…”

“…2). Spectator stresses can be treated and discussed in conjunction with a dominant adiabatic mode; absent the adiabatic mode the shapes of the TT correlations have intermediate features between the isocurvature humps of the CDM-radiation mode [9]; the situation is also different from the case of the magnetized CMB observables when the adiabatic mode is absent [5] (see also [13]). There has been recently some confusing statement in the literature.…”

“…The first regime of evolution dictated by the equations derived here avoids a potentially stiff problem if α is initially very small. The Boltzmann solvers is a modified version of [5,13] which, in turn, based on [7,8]. From Fig.…”

“…There exist however physical situations in which the anisotropic stress does not belong to species which are dominant today. Examples in this direction are numerous and include, for instance, spectator scalar fields evolving (without being dominant) during the various stages of the life of the Universe or even large-scale magnetic fields (see, for instance, [5] and references therein). There is an important caveat to the latter statement: unlike large-scale magnetic fields, gravitating anisotropic stresses do not couple to the charged species of the plasma.…”

Gradient expansion, curvature perturbations, and magnetized plasmas

“…Since we do see magnetic fields today over large distance scales, it seems natural to scrutinize their impact on the CMB observables. This is the motivation of a program aimed at bringing the unconventional study of magnetized CMB anisotropies to the same standard of the more conventional adiabatic 1 paradigm (see [7][8][9][10] and references therein). While different approaches to the problem are certainly available [11][12][13][14][15] (see [16] for a more complete list of earlier references), the path followed in [7,8] led to the calculation of the temperature and polarization anisotropies induced by the magnetized (adiabatic and entropic) initial conditions.…”