13 research outputs found
Spatial energy spectrum of primordial magnetic fields
Here, we analyze the primordial magnetic field transition between a radiative
and a matter-dominated universe. The gravitational structure formation affects
its evolution and energy spectrum. The structure excitation can trigger
magnetic field amplification and the steepening of its energy density spectrum.Comment: 8 pages, 2 figures, accepted for A&
A study of diffusive shock acceleration as a process explaining observations of 1 E0657-56 galaxy cluster
Chandra X-ray observations of the 1 E0657-56 galaxy cluster diffuse emission
reveal the existence of large scale cluster merger shock. We study the observed
radio and X-ray data of this cluster as a possible result of the diffusive
shock acceleration. This model can explain the observations within reasonable
ranges of physical parameters for the shock and the intracluster medium. The
expected nonthermal soft and hard X-ray fluxes are predicted.Comment: 9 pages, accepted for Acta Phys. Polon.
Acoustic instabilities at the transition from the radiation-dominated to the matter-dominated universe
The transition from acoustic noise in the radiation-dominated universe to the
density structures in the matter dominated epoch is considered. The initial
state is a stochastic field of sound waves moving in different directions. The
construction of the initial state is compatible with the hyperbolic type of
propagation equation for density perturbations, and parallel to the theory of
stochastic background of gravitational waves. Instantaneous transition between
the cosmological epochs is assumed, and Darmois-Israel joining conditions are
applied to match solutions for sound waves with growing or decaying modes at
the decoupling. As a result a substantial amplification of the low scale
structures is obtained.Comment: 11 pages, 6 figures, accepted to A&
Cosmology with inhomogeneous magnetic fields
We review spacetime dynamics in the presence of large-scale electromagnetic
fields and then consider the effects of the magnetic component on perturbations
to a spatially homogeneous and isotropic universe. Using covariant techniques,
we refine and extend earlier work and provide the magnetohydrodynamic equations
that describe inhomogeneous magnetic cosmologies in full general relativity.
Specialising this system to perturbed Friedmann-Robertson-Walker models, we
examine the effects of the field on the expansion dynamics and on the growth of
density inhomogeneities, including non-adiabatic modes. We look at scalar
perturbations and obtain analytic solutions for their linear evolution in the
radiation, dust and inflationary eras. In the dust case we also calculate the
magnetic analogue of the Jeans length. We then consider the evolution of vector
perturbations and find that the magnetic presence generally reduces the decay
rate of these distortions. Finally, we examine the implications of magnetic
fields for the evolution of cosmological gravitational waves.Comment: Typos corrected. Version to appear in Physics Report