Cosmic Magnetic Fields Exert Negative Pressure and Act as a Cosmological Constant

Recently there has been mounting evidence for the existence of a cosmological constant (CC). Here we show that cosmic magnetic fields act as a CC, having negative pressure and tending to cause cosmological acceleration. However, if present-day estimates of the intensity of these fields are correct, they would be too weak to be the cause of the acceleration. It is pointed out that large-scale coherent Yang-Mills field structures can also act as a CC