Cosmological magnetic fields

Magnetic fields are observed not only in stars, but in galaxies, clusters, and even high redshift Lyman-alpha systems. In principle, these fields coul d play an important role in structure formation and also affect the anisotr opies in the cosmic microwave background radiation (CMB). The study of cosm ological magnetic fields aims not only to quantify these effects on large-s cale structure and the CMB, but also to answer one of the outstanding puzzl es of modem cosmology: when and how do magnetic fields originate? They are either primordial, i.e. created before the onset of structure formation, or they are generated during the process of structure formation itself.