On the road to percent accuracy VI: the nonlinear power spectrum for
  interacting dark energy with baryonic feedback and massive neutrinos
  Understanding nonlinear structure formation is crucial for fully exploring
the data generated by stage IV surveys, requiring accurate modelling of the
power spectrum. This is challenging for deviations from $\Lambda$CDM, but we
must ensure that alternatives are well tested, to avoid false detections. We
present an extension of the halo model reaction framework for interacting dark
energy. We modify the halo model including the additional force present in the
Dark Scattering model and implement it into ReACT. The reaction is combined
with a pseudo spectrum from EuclidEmulator2 and compared to N-body simulations.
Using standard mass function and concentration-mass relation, we find
predictions to be 1 % accurate at $z=0$ up to $k=0.8~h/{\rm Mpc}$ for the
largest interaction strength tested ($\xi=50$ b/GeV), improving to $2~h/{\rm
Mpc}$ at $z=1$. For smaller interaction strength ($10$ b/GeV), we find 1 %
agreement at $z=1$ up to scales above $3.5~h/{\rm Mpc}$, being close to
$1~h/{\rm Mpc}$ at $z=0$. Finally, we improve our predictions with the
inclusion of baryonic feedback and massive neutrinos and study degeneracies
between the effects of these contributions and those of the interaction.
Limiting the scales to where our modelling is 1 % accurate, we find a
degeneracy between the interaction and feedback, but not with massive
neutrinos. We expect the degeneracy with feedback to be resolvable by including
smaller scales. This work represents the first analytical tool for calculating
the nonlinear spectrum for interacting dark energy models.
