Degeneracy between primordial non-Gaussianity and interaction in the dark sector

If dark energy and dark matter interact via exchange of energy and momentum, then this may affect the galaxy power spectrum on large scales. When this happens, it may be degenerate with the signal from primordial non-Gaussianity via a scale-dependent bias. We consider a class of interacting dark energy models and show that the matter overdensity is scale dependent on large scales. We estimate the effective non-Gaussianity arising from the large-scale effects of interaction in the dark sector. The signal of dark sector interaction can be disentangled from a primordial non-Gaussian signal by measuring the power at two redshifts.

Figure 1

Left: Evolution of the effective dark energy equation of state, $w_x^{\mathrm{eff}}$, with $w_x=-0.9$ and for different $\mathrm{\Gamma }>0$, in the IDE model (26). The $\mathrm{\Gamma }=0$ limit is $w_x^{\mathrm{eff}}=w_x=-0.9$. Right: The $\mathrm{\Gamma }<0$ case, with $w_x=-1.1$.

Figure 2

Left: Relative galaxy overdensity [see (48)] at $a=1$ with dark sector interactions, for different $\mathrm{\Gamma }>0$ and with $w_x=-0.9$. The vertical dashed line is the Hubble scale, $k=H_0$. The $\mathrm{\Gamma }=0$ limit is the horizontal line through 0. We used $b(1)=2$. Right: The $\mathrm{\Gamma }<0$ case, with $w_x=-1.1$.

Figure 3

The relative galaxy overdensity as in Fig. 2 but for the case of PNG, with $f_{\mathrm{NL}}<0$ (left) and $f_{\mathrm{NL}}>0$ (right).

Figure 4

Left: Galaxy power spectrum $P_g$ at $a=1$ for an IDE model with $\mathrm{\Gamma }=0.03H_0$ and for a PNG model with $f_{\mathrm{NL}}=-7.69$. The black (solid) line is the fiducial $w\mathrm{CDM}$ model without interaction or PNG. We set $b(1)=2$ and $w_x=-0.9$. Right: For $\mathrm{\Gamma }=-0.03H_0$ and $f_{\mathrm{NL}}=4.81$, with $w_x=-1.1$.

Figure 5

Left: Effective PNG parameter $f_{\mathrm{NL}}^{\mathrm{eff}}$ corresponding to interaction rate $\mathrm{\Gamma }>0$ at different redshift values. We take $w_x=-0.9$. Right: For $\mathrm{\Gamma }<0$ and $w_x=-1.1$.