The universe is magnetized on all scales probed so far. On the largest scales, galaxies and galaxy clusters host magnetic fields at micro Gauss level coherent up to ten kpc. Recent observational evidence suggests that even intergalactic medium in voids could a weak ∼ 10−16 field, Mpc scales. An intriguing possibility these observed are relic from early universe, albeit one which has been subsequently amplified maintained by dynamo collapsed objects. We review here origin, evolution...

The evolution and viscous damping of cosmic magnetic fields in the early universe is analyzed. Using fact that fluid, electromagnetic, shear energy-momentum tensors are all conformally invariant, transformed from expanding setting into flat spacetime. Particular attention paid to nonlinear Alfv\'en modes. For a small enough field, which satisfies our observational constraints, these wave modes either oscillate negligibly or, when they do oscillate, become overdamped. Hence not suffer Silk on...

We discuss, using simple analytical models and magnetohydrodynamic (MHD) simulations, the origin parameters of turbulence magnetic fields in galaxy clusters. Any pre-existing tangled field must decay a few hundred million years by generating gas motions even if electric conductivity intracluster is high. argue that turbulent can be maintained its dynamo action prevent such amplify random seed net factor typically 104 5 Gyr. Three physically distinct regimes identified evolution First,...

We investigate the interplay of cosmic ray (CR) propagation and advection in galaxy clusters. Propagation form CR diffusion streaming tends to drive radial profiles towards being flat, with equal number density everywhere. Advection by turbulent gas motions produce centrally enhanced profiles. assume that velocity is order sound velocity. This motivated plasma physical arguments. The then usually larger than typical velocities becomes comparable or lower this only for periods trans-...

An inhomogeneous cosmological magnetic field will create Alfv\'en-wave modes that induce a small rotational velocity perturbation on the last scattering surface of microwave background radiation. The mode survives Silk damping much smaller scales than compressional modes. This, in combination with its nature, ensures there be no sharp cutoff anisotropy arc min scales. We estimate which redshifts to present value $3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}\mathrm{G}$ produces...

Helical turbulence may provide the key to generation of large-scale magnetic fields. Turbulence also generically leads rapidly growing small-scale These two processes are usually studied separately. We give here a unified treatment both processes, in case random fields, incorporating simple model nonlinear drift. uncover an interesting plausible saturated state dynamo and novel analogy between quantum mechanical (QM) tunneling A field generated by dynamo, can ``tunnel'' produce correlations,...

We explore the ways in which primordial magnetic fields influence thermal and ionization history of post-recombination Universe. After recombination, Universe becomes mostly neutral, resulting also a sharp drop radiative viscosity. Primordial can then dissipate their energy into intergalactic medium via ambipolar diffusion and, for small enough scales, by generating decaying magnetohydrodynamics turbulence. These processes significantly modify show that dissipation effects fields, redshifts...

We determine the magnetic helicity, along with energy, at high latitudes using data from Ulysses mission. The set spans time period 1993 to 1996. basic assumption of analysis is that solar wind homogeneous. Because speed high, we follow approach first pioneered by Matthaeus et al. (1982, Phys. Rev. Lett. 48, 1256) which, under spatial homogeneity, one can use Fourier transforms field series construct one-dimensional spectra energy and helicity Taylor frozen-in-flow hypothesis valid. That a...

Turbulence is ubiquitous in many astrophysical systems like galaxies, galaxy clusters and possibly even the IGM filaments. We study fluctuation dynamo action turbulent focusing on one observational signature; Faraday rotation measure (RM) from background radio sources seen through magnetic field generated by such a dynamo. simulate (FD) periodic boxes up to resolutions of 512^3, with varying fluid Reynolds numbers, resulting random RMs. show that, though intermittent, it still allows for...

Models of inflationary magnetogenesis with a coupling to the electromagnetic action form ${f}^{2}{F}_{\ensuremath{\mu}\ensuremath{\nu}}{F}^{\ensuremath{\mu}\ensuremath{\nu}}$, are known suffer from several problems. These include strong problem, backreaction problem and also constraints due Schwinger effect. We propose model which resolves all these issues. In our model, function, $f$, grows during inflation transits decaying phase post-inflation. This evolutionary behavior is chosen so as...

We study the generation of helical magnetic fields in a model inflationary magnetogenesis which is free from strong coupling and backreaction problems. To generate fields, we add an ${f}^{2}{\stackrel{\texttildelow{}}{F}}^{\ensuremath{\mu}\ensuremath{\nu}}{F}_{\ensuremath{\mu}\ensuremath{\nu}}$ term to Lagrangian Ratra model. The problems are avoided if take particular behavior function $f$, $f$ increases during inflation decreases postinflation reheating. generated field fully has blue...

During hierarchical clustering, smaller masses generally collapse earlier than larger and so are denser on the average. The core of a small mass halo could be dense enough to resist disruption survive undigested, when it is incorporated into bigger object. We explore possibility that nested sequence undigested cores in center halo, which have survived hierarchical, inhomogeneous form objects, determines structure inner regions. For flat universe with $P(k) \propto k^n$, scaling arguments...

Quasar spectra indicate that the intergalactic medium (IGM) was reionized at some redshift z ≳ 5, probably due to discrete sources of ionizing photons like QSOs and young galaxies. In such a circumstance, ionization fronts will expand away from these until they percolate encompass substantial part IGM. The pressure gradients in front acting on electrons can lead thermally generated electric field. This field have non-vanishing curl hence imply growing magnetic field, provided gradient is not...

Using numerical simulations at moderate magnetic Reynolds numbers up to 220 it is shown that in the kinematic regime, isotropic helical turbulence leads an alpha effect and a turbulent diffusivity whose values are independent of number, $\Rm$, provided $\Rm$ exceeds unity. These coefficients also consistent with expectations from first order smoothing approximation. For small proportional $\Rm$. Over finite time intervals meaningful can be obtained even when there small-scale dynamo action...

We present a simple semi-analytical model of nonlinear, mean-field galactic dynamos and use it to study the effects various magnetic helicity fluxes. The dynamo equations are reduced using `no-$z$' approximation nonlinear system ordinary differential in time; we demonstrate that reproduces accurately earlier results, including those where behaviour is driven by flux. discuss implications interplay two types flux, one produced advection (e.g., due fountain or wind) other, arising from...

Primordial magnetic fields lead to non-Gaussian signals in the cosmic microwave background (CMB) even at lowest order, as stresses and temperature anisotropy they induce depend quadratically on field. In contrast, CMB non-Gaussianity due inflationary scalar perturbations arises only a higher-order effect. We propose novel probe of stochastic primordial that exploits characteristic induce. compute bispectrum (b(l1l2l3)) induced by such large angular scales. find typical value l1(l1 + 1)l3(l3...

We give a pedagogical introduction to two aspects of magnetic fields in the early universe. first focus on how formulate electrodynamics curved space time, defining appropriate and electric writing Maxwell equations terms these fields. then specialize case magnetohydrodynamics expanding emphasize usefulness tetrads this context. review generation during inflationary era, deriving detail predicted spectra for some models. discuss potential problems arising from back reaction effects large...

The origin and maintenance of coherent magnetic fields in the Universe is reviewed with an emphasis on possible challenges that arise their theoretical understanding. We begin interesting possibility originated at some level from early universe. This could be during inflation, electroweak, or quark-hadron phase transitions. These mechanisms can give rise to which strong, but often much smaller coherence scales than galactic scales. Their subsequent turbulent decay decreases strength...

We present the analysis of magnetic field ($B$-field) structure galaxies measured with far-infrared (FIR) and radio (3 6 cm) polarimetric observations. use first data release Survey on extragALactic magnetiSm SOFIA (SALSA) 14 nearby ($<20$ Mpc) resolved (5 arcsec-18 arcsec; $90$ pc--$1$ kpc) imaging observations using HAWC+/SOFIA from $53$ to $214$ \um. compute pitch angle ($\Psi_{B}$) profiles as a function galactrocentric radius. introduce new alignment parameter ($\zeta$) estimate...

ABSTRACT We study the magneto-rotational instability (MRI) dynamo in a geometrically thin disc (H/R ≪ 1) using stratified zero net (vertical) flux shearing box simulations. find that mean fields and electromotive forces (EMFs) oscillate with primary frequency fdyn = 0.017 Ω (approximately nine orbital period), but also have higher harmonics at 3fdyn. Correspondingly, current helicity has two frequencies 2fdyn 4fdyn, which appear to be beat of EMFs, respectively, as expected from magnetic...

Tangled, primordial cosmic magnetic fields create small rotational velocity perturbations on the last scattering surface (LSS) of microwave background radiation (CMBR). Such can contribute significantly to CMBR temperature and polarization anisotropies at large l &gt; 1000 or so, like excess power detected by CBI experiment. The contribution be distinguished from most conventional signals, as they lead dominated odd parity, B-type signal. Experiments DASI WMAP have evidence for l. Many...