Exorcising w < -1

Abstract

We show that the combined dimming of Type Ia supernovae induced by both a cosmological constant and the conversion of photons into axions in extra-galactic magnetic fields can impersonate dark energy with an equation of state w < -1. An observer unaware of the presence of photon-axion conversion would interpret the additional dimming as cosmic acceleration faster than that induced by a cosmological constant alone. We find that this mechanism can mimic equations of state as negative as w \simeq - 1.5. Our model does not have any ghosts, phantoms and the like. It is fully consistent with the conventional effective field theory in curved space, and all existing observational constraints on the axions are obeyed.

Figures (4)

• Figure 1: The observed differential distance modulus of high-redshift SNe from Riess relative to an empty universe together with with the the curves for three models: a cosmological constant with $\Omega_m=0.3$ (blue dashed curve), a cosmological constant with $\Omega_m=0.35$ plus photon-axion oscillations with $(L_{dec} H_0)^{-1} =0.25$ (purple solid curve) and a phantom matter with $w=-1.25$ and $\Omega_m=0.35$ (green double-dashed curve). The three curves are practically all indistinguishable, and fit the data equally well.
• Figure 2: The regions allowed by the latest SN observations Riess at 90, 95 and 99 % confidence level in the $w-L_{dec}$ plane. The red curve shows the region allowed by the study of the energy dependence of quasar spectra mogoo. The left panel corresponds to $\Omega_m=0.3$, the middle one to $\Omega_m=0.35$ while the right one to $\Omega_m=0.4$.
• Figure 3: The same as in Fig. \ref{['fig:SNfit']} for $\Omega_m =0.35$, except the region for a larger region of $w$ and $L_{dec}$. This plot illustrates the fact that the original photon-axion mixing proposal ckt would still fit all the SNe observations (and also the WMAP constraints). The only real constraints on the model that disfavor it as an explanation for the majority of the dimming come from the study of the energy dependence of quasar spectra mogoo or from violations of reciprocity baku. The red curve shows the approximate bound from the quasar studies.
• Figure 4: The region allowed by the latest SN observations Riess at the 95 % confidence level in the $\Omega_m -L_{dec}$ plane (blue curves). The equation of state of the dark energy is fixed to be $w=-1$. The red curve again shows the bound from the quasar spectra, while the black contours show the approximate effective values of the equation of state one would obtain by trying to fit the luminosity-distance curves. We can see that values as low as $-1.5$ can be obtained for $w^{fake}$.