1 research outputs found
Magnetogenesis from Cosmic String Loops
Large-scale coherent magnetic fields are observed in galaxies and clusters,
but their ultimate origin remains a mystery. We reconsider the prospects for
primordial magnetogenesis by a cosmic string network. We show that the magnetic
flux produced by long strings has been overestimated in the past, and give
improved estimates. We also compute the fields created by the loop population,
and find that it gives the dominant contribution to the total magnetic field
strength on present-day galactic scales. We present numerical results obtained
by evolving semi-analytic models of string networks (including both one-scale
and velocity-dependent one-scale models) in a Lambda-CDM cosmology, including
the forces and torques on loops from Hubble redshifting, dynamical friction,
and gravitational wave emission. Our predictions include the magnetic field
strength as a function of correlation length, as well as the volume covered by
magnetic fields. We conclude that string networks could account for magnetic
fields on galactic scales, but only if coupled with an efficient dynamo
amplification mechanism.Comment: 10 figures; v3: small typos corrected to match published version.
MagnetiCS, the code described in paper, is available at
http://markcwyman.com/ and
http://www.damtp.cam.ac.uk/user/dhw22/code/index.htm