Kerstin E. Kunze

Perturbations in stochastic inflation

The perturbative approach to stochastic inflation is used to determine the spectrum of density fluctuations and gravitational waves due to the coarse grained field. The amplitude of the curvature fluctuation spectrum, the spectral index and the running of the spectral index are in general found to be smaller than in the standard approach to inflation. Furthermore, the amount of non-Gaussianity due to the second-order perturbation is estimated.

Primordial magnetic fields and nonlinear electrodynamics

The creation of large scale magnetic fields is studied in an inflationary universe where electrodynamics is assumed to be nonlinear. After inflation ends electrodynamics becomes linear and thus the description of reheating and the subsequent radiation dominated stage are unaltered. The nonlinear regime of electrodynamics is described by Lagrangians having a power-law dependence on one of the invariants of the electromagnetic field. It is found that there is a range of parameters for which primordial magnetic fields of cosmologically interesting strengths can be created.

Large scale magnetic fields from gravitationally coupled electrodynamics

The generation of primordial magnetic seed fields during inflation is studied in a theory derived from the one-loop vacuum polarization effective action of the photon in a curved background. This includes terms which couple the curvature to the Maxwell tensor. The resulting magnetic field strength is estimated in a model where the inflationary phase is directly matched to the standard radiation dominated era. The allowed parameter region is analyzed and compared with the bounds necessary to seed the galactic magnetic field. It is found that magnetic fields of cosmologically interesting field strengths can be generated.

Faraday rotation, stochastic magnetic fields and CMB maps

The high- and low-frequency descriptions of the predecoupling plasma are deduced from the Vlasov-Landau treatment generalized to curved space-times and in the presence of the relativistic fluctuations of the geometry. It is demonstrated that the interplay between one-fluid and two-fluid treatments is mandatory for a complete and reliable calculation of the polarization observables. The Einstein-Boltzmann hierarchy is generalized to handle the dispersive propagation of the electromagnetic disturbances in the predecoupling plasma. Given the improved physical and numerical framework, the polarization observables are computed within the magnetized {lambda}CDM paradigm (m{lambda}CDM). In particular, the Faraday-induced B-mode is consistently estimated by taking into account the effects of the magnetic fields on the initial conditions of the Boltzmann hierarchy, on the dynamical equations, and on the dispersion relations. The complete calculations of the angular power spectra constitute the first step for the derivation of magnetized maps of the CMB temperature and polarization which are here obtained for the first time and within the minimal m{lambda}CDM model. The obtained results set the ground for direct experimental scrutiny of large-scale magnetism via the low- and high-frequency instruments of the Planck explorer satellite.

Curved dilatonic brane worlds

We construct a broad family of exact solutions to the five-dimensional Einstein equations coupled to a scalar field with an exponential potential. Embedding a three-brane in these bulk space-times in a particular way we obtain a class of self-tuned curved brane worlds in which the vacuum energy on the brane is gravitationally idle, the four-dimensional geometry being insensitive to the value of the brane tension. This self-tuning arises from cancellations, enforced by the junction conditions, between the scalar field potential, the brane vacuum energy and the matter on the brane. Finally, we study some physically relevant examples and their dynamics.

Generalized CMB initial conditions with pre-equality magnetic fields

The most general initial conditions of cosmic microwave background anisotropies, compatible with the presence of pre-equality magnetic fields, are derived. When the plasma is composed of photons, baryons, electrons, cold dark matter particles and neutrinos, the initial data of the truncated Einstein-Boltzmann hierarchy contemplate one magnetized adiabatic mode and four (magnetized) nonadiabatic modes. After obtaining the analytical form of the various solutions, the Einstein-Boltzmann hierarchy is numerically integrated for the corresponding sets of initial data. The TT, TE and EE angular power spectra are illustrated and discussed for the magnetized generalization of the cold dark matter-radiation mode, of the baryon-radiation mode and of the nonadiabatic mode of the neutrino sector. Mixtures of initial conditions are examined by requiring that the magnetized adiabatic mode dominates over the remaining nonadiabatic contributions. In the latter case, possible degeneracies between complementary sets of initial data might be avoided through the combined analysis of the TT, TE and EE angular power spectra at high multipoles (i.e. l>1000)

Primordial magnetic seed fields from extra dimensions

Dynamical extra dimensions break the conformal invariance of Maxwells equations in four dimensions. A higher-dimensional background with n contracting extra dimensions and four expanding dimensions is matched to an effectively four-dimensional standard radiation dominated universe. The resulting spectrum for the magnetic field is calculated taking into account also the momenta along the extra dimensions. Imposing constraints from observations an upper limit on the strength of magnetic seed fields is found. Depending on the number of extra dimensions, cosmologically interesting magnetic fields can be created.

CMB anisotropies in the presence of a stochastic magnetic field

Primordial magnetic fields present since before the epoch of matter-radiation equality have an effect on the anisotropies of the cosmic microwave background (CMB). The CMB anisotropies due to scalar perturbations are calculated in the gauge-invariant formalism for magnetized adiabatic initial conditions. Furthermore, the linear matter power spectrum is calculated. Numerical solutions are complemented by a qualitative analysis.

Cosmological magnetic fields

Magnetic fields are observed on nearly all scales in the Universe, from stars and galaxies up to galaxy clusters and even beyond. The origin of cosmic magnetic fields is still an open question, however a large class of models puts its origin in the very early Universe. A magnetic dynamo amplifying an initial seed magnetic field could explain the present day strength of the galactic magnetic field. However, it is still an open problem how and when this initial magnetic field was created.Observations of the cosmic microwave background (CMB) provide a window to the early Universe and might therefore be able to tell us whether cosmic magnetic fields are of a primordial cosmological origin and at the same time constrain its parameters.We will give an overview of the observational evidence of large-scale magnetic fields, describe generation mechanisms of primordial magnetic fields and possible imprints in the CMB.

Effects of helical magnetic fields on the cosmic microwave background

A complete numerical calculation of the temperature anisotropies and polarization of the cosmic microwave background in the presence of a stochastic helical magnetic field is presented which includes the contributions due to scalar, vector and tensor modes. The correlation functions of the magnetic field contributions are calculated numerically including a Gaussian window function to effectively cut off the magnetic field spectrum due to damping. Apart from parity-even correlations the helical nature of the magnetic field induces parity-odd correlations between the