科研之友
微信
新浪微博
Facebook
分享链接
摘要
We find a solution to 4DEinstein-Maxwell theory coupled to a massless dilaton field, for all values of the dilaton coupling, describing a Melvin magnetic field in an expanding universe with `stiff matter%26apos; equation of state parameter omega = +1. As the universe expands, magnetic flux becomes more concentrated around the symmetry axis for dilaton coupling a %26lt; 1/root 3 and more dispersed for a %26gt; 1/root 3. An electric field circulates around the symmetry axis in the direction determined by Lenz%26apos;s law. For a = 0 the magnetic flux through a disc of fixed comoving radius is proportional to the proper area of the disc. This result disagrees with the usual expectation based on a test magnetic field that this flux should be constant, and we show why this difference arises. We also find a Melvin solution in an accelerating universe with w = -7/9 for a dilaton field with a certain exponential potential.
- 出版日期2014-4-7
