Cosmic magnetism, curvature, and the expansion dynamics - art. no. 103519

We discuss how a cosmological magnetic field could affect the expansion of the universe through its interaction with the spacetime geometry. The tensi on of the field lines means that the magneto-curvature coupling tends to ac celerate positively curved regions and decelerate those with negative curva ture. Depending on the equation of state of the matter, the effect varies f rom mimicking that of a cosmological constant to resembling a time-decaying quintessence. Most interestingly, the coupling between magnetism and geome try implies that even weak fields have a significant impact if the curvatur e contribution is strong. This leads to kinematical complications that can inhibit the onset of the accelerated phase in spatially open inflationary m odels. We employ a simple cosmological model to illustrate these effects an d examine the conditions necessary for them to have an appreciable impact.