Effects of the intergalactic plasma on supernova dimming via photonaxion oscillations
Abstract
We have recently proposed a mechanism of photonaxion oscillations as a way of rendering supernovae dimmer without cosmic acceleration. Subsequently, it has been argued that the intergalactic plasma may interfere adversely with this mechanism by rendering the oscillations energy dependent. Here we show that this energy dependence is extremely sensitive to the precise value of the free electron density in the Universe. Decreasing the electron density by only a factor of 4 is already sufficient to bring the energy dependence within the experimental bounds. Models of the intergalactic medium show that for redshifts /z<1 about 97% of the total volume of space is filled with regions of density significantly lower than the average density. From these models we estimate that the average electron density in most of space is lower by at least a factor of 15 compared to the estimate based on one half of all baryons being uniformly distributed and ionized. Therefore the energy dependence of the photonaxion oscillations is consistent with experiment, and the oscillation model remains a viable alternative to the accelerating Universe for explaining the supernova observations. Furthermore, the electron density does give rise to a sufficiently large plasma frequency which cuts off the photonaxion mixing above microwave frequencies, shielding the cosmic microwave photons from axion conversions and significantly relaxing the lower bounds on the axion mass implied by the oscillation model.
 Publication:

Physics Letters B
 Pub Date:
 May 2002
 DOI:
 10.1016/S03702693(02)017653
 arXiv:
 arXiv:hepph/0112212
 Bibcode:
 2002PhLB..535...33C
 Keywords:

 High Energy Physics  Phenomenology;
 Astrophysics;
 General Relativity and Quantum Cosmology;
 High Energy Physics  Theory
 EPrint:
 5 pages, LaTeX, 2 figures included