Phantom behavior via cosmological creation of particles

Recent determinations of the equation of state of dark energy hint that this may well be of the phantom type, i.e., $w_{de}<-1$. If confirmed by future experiments, this would strongly point to the existence of fields that violate the dominant energy condition, which are known to present serious theoretical difficulties. This paper presents an alternative to this possibility, namely, that the measured equation of state, $w_{de}$, is in reality an effective one, the equation of state of the quantum vacuum, $w_{\mathrm{\Lambda }}=-1$, plus the negative equation of state, $w_c$, associated to the production of particles by the gravitational field acting on the vacuum. To illustrate this, three phenomenological models are proposed and constrained with recent observational data.

Figure 1

Evolution of ratio $\mathrm{\Gamma }/3H$ as a function of the scale factor for the model II (solid, black line) and model III (dashed, red line). In drawing the graphs, we have taken $\beta =0.1$.

Figure 2

Left panel: $1\sigma$ and $2\sigma$ confidence contours for model I obtained from joint analysis $\mathrm{SNIa}+\mathrm{GRB}+\mathrm{BAO}$. Right panel: The same but using the set of data $\mathrm{SNIa}+\mathrm{GRB}+\mathrm{BAO}+H(z)$.

Figure 3

Left panel: $1\sigma$ and $2\sigma$ confidence contours for model II obtained from the joint analysis $\mathrm{SNIa}+\mathrm{GRB}+\mathrm{BAO}$. Right panel: Evolution of the effective EoS in terms of the scale factor; the solid (black) line indicates the best-fit values, and the shaded region indicates the $1\sigma$ uncertainty.

Figure 4

Same as Fig. 3 but using the set of data $\mathrm{SNIa}+\mathrm{GRB}+\mathrm{BAO}+H(z)$.

Figure 5

Left panel: $1\sigma$ and $2\sigma$ confidence contours for model III obtained from joint analysis $\mathrm{SNIa}+\mathrm{GRB}+\mathrm{BAO}$. Right panel: Evolution of the effective EoS in terms of the scale factor; the solid (black) line indicates the best-fit values, and the shaded region indicates the $1\sigma$ uncertainty.

Figure 6

Same as Fig. 5 but using the set of data $\mathrm{SNIa}+\mathrm{GRB}+\mathrm{BAO}+H(z)$.