We study perturbations of a complex scalar field during reheating with no self-interaction in the regime μ ≫ H, when the scalar field has a fast oscillatory behaviour (close to a pressure-less fluid). We focus on the precise determination of the instability scale and find it differs from that associated to a real scalar field. We further look at the probability that unstable fluctuations form Primordial Black Holes (PBHs) obtaining a significant production of tiny PBHs which quickly evaporate and may subsequently leave a population of Planck-mass relics. We finally impose restrictions on the duration and energy scale of the fast oscillations period by considering that such relics constitute, at most, the totality of dark matter in the Universe.
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 ΛCDM, 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/Mpc for the largest interaction strength tested (ξ = 50 b/GeV), improving to 2 h/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/Mpc, being close to 1 h/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.
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