We analyze the magnitude-redshift data of type Ia supernovae included in the Union and Union2 compilations in the framework of an anisotropic Bianchi type I cosmological model and in the presence of a dark-energy fluid with anisotropic equation of state. We find that the amount of deviation from isotropy of the equation of state of dark energy, the skewness $\delta${}, and the present level of anisotropy of the large-scale geometry of the Universe, the actual shear $\Sigma${}0, are constrained in the ranges -0.16$\lesssim${}$\delta${}$\lesssim${}0.12 and -0.012$\lesssim${}$\Sigma${}0$\lesssim${}0.012 (1$\sigma${} C.L.) by Union2 data. Supernova data are then compatible with a standard isotropic universe ($\delta${}=$\Sigma${}0=0), but a large level of anisotropy, both in the geometry of the Universe and in the equation of state of dark energy, is allowed.

We reanalyze the production of seed magnetic fields during inflation in $(R/m^2{)}^n{F}_{\mu \nu }{F}^{\mu \nu }$ and $I{F}_{\mu \nu }{F}^{\mu \nu }$ models, where $n$ is a positive integer, $R$ the Ricci scalar, $m$ a mass parameter, and $I\propto {\eta }^{\alpha }$ a power-law function of the conformal time $\eta$, with $\alpha$ a positive real number. If $m$ is the electron mass, the produced fields are uninterestingly small for all $n$. Taking $m$ as a free parameter, we find that, for $n\ge 2$, the produced magnetic fields can be sufficiently strong in order to seed the dynamo mechanism and then to explain galactic magnetism. For $\alpha \gtrsim 2$, there is always a window in the parameters defining inflation such that the generated magnetic fields are astrophysically interesting. Moreover, if inflation is (almost) de Sitter and the produced fields almost scale invariant ($\alpha \simeq 4$), their intensity can be strong enough to directly explain the presence of microgauss galactic magnetic fields.

We study the evolution of an inflation-generated magnetic field, due to its coupling to fluid motions, during cosmological phase transitions. We find that the magnetic field stays almost unchanged on large scales, while on small scales, the spectrum is modified in such a way that power at small scales becomes progressively suppressed. We also show that the magnetic field generates turbulent motions in the initially turbulence-free plasma. On large scales, the slope of the resulting kinetic energy spectrum is consistent with that of white noise.

The presence of a nonconformally invariant term in the photon sector of the Lorentz-violating extension of the standard model of particle physics, the “Kostelecký term” ${\mathcal{L}}_K\propto (k_F{)}_{\alpha \beta \mu \nu }{F}^{\alpha \beta }{F}^{\mu \nu }$, enables a superadiabatic amplification of magnetic vacuum fluctuations during de Sitter inflation. For a particular form of the external tensor $k_F$ that parametrizes Lorentz violation, the generated field possesses a planar symmetry at large cosmological scales and can have today an intensity of order of nanogauss for a wide range of values of parameters defining inflation. This peculiar magnetic field could account for the presently observed galactic magnetic fields and induces a small anisotropization of the Universe at cosmological scales. The resulting Bianchi I model could explain the presumedly low quadrupole power in the cosmic microwave background radiation.

We study the generation of primeval magnetic fields during inflation era in nonlinear theories of electrodynamics. Although the intensity of the produced fields strongly depends on characteristics of inflation and on the form of electromagnetic Lagrangian, our results do not exclude the possibility that these fields could be astrophysically interesting.

We calculate, in the free Maxwell theory, the renormalized quantum vacuum expectation value of the two-point magnetic correlation function in de Sitter inflation. We find that quantum magnetic fluctuations remain constant during inflation instead of being washed out adiabatically, as usually assumed in the literature. The quantum-to-classical transition of super-Hubble magnetic modes during inflation allow us to treat the magnetic field classically after reheating, when it is coupled to the primeval plasma. The actual magnetic field is scale independent and has an intensity of $\mathrm{\text{few}}\ifmmode\times\else\texttimes\fi{}{10}^{-12}\text{ }\text{ }\mathrm{G}$ if the energy scale of inflation is $\mathrm{\text{few}}\ifmmode\times\else\texttimes\fi{}{10}^{16}\text{ }\text{ }\mathrm{GeV}$. Such a field accounts for galactic and galaxy cluster magnetic fields.