In the scalar field dark matter model virialized halos present condensed central cores called boson stars. Considering the equivalent process during reheating, we look at the formation of primordial black holes (PBHs) through the gravitational collapse of structures virialized in this era. We present the criteria necessary for collapse of either the whole structure, or that of the central core, in terms of the threshold amplitude for the primordial density contrast. This is computed for both the free and the self-interacting scalar fields. We discuss the relevance of our results for the abundance of PBHs.

We present a sample of 74 gamma-ray bursts (GRBs) from the Fermi-GBM catalogue for which we compute the distance moduli and use them to constrain effective dark energy models. To overcome the circularity problem affecting GRBs as distance indicators, we calibrate the Amati relation of our sample with a cosmology-independent technique. Specifically, we use the latest observational Hubble parameter data, including associated systematics, to approximate the cosmic expansion through a Bezier parametric curve. We subsequently obtain the distance moduli of the GRBs and include the data in a suite of recent cosmological observations of the expansion history (Planck Compressed 2018, 2012 BOSS release of BAO data, and Pantheon SN Ia), to compute Bayesian posterior constraints for the standard cosmological model Lambda cold dark matter (ΛCDM), as well as ωCDM, and the CPL parametrization. Throughout the analysis, we strive to keep under control the error propagation and limit our GRB sample to avoid observational bias. As a result, we find no evidence in favour of the alternatives to ΛCDM model. The latter agrees very well with our calibrated sample of GRBs and presently available luminosity distance probes.

At times prior to big bang nucleosynthesis, the Universe could show a primordial structure formation period if dominated by a fast oscillating inflaton field during reheating. In this context, we have postulated a new mechanism of primordial black hole formation [Padilla et al., Phys. Rev. D, 106, 023519 (2022)], that draws on the analogy between an extended reheating era and the scalar field dark matter model, contemplating the gravitational collapse of inflaton halos and inflaton stars. In this paper we look at the requirements for the realization of this new mechanism. We show that a generic primordial power spectrum with a peak at small scales is most suitable for the production of a considerable number of primordial black holes (PBHs). When such a requirement is met, and if reheating lasts long enough, large populations of PBHs with $M_{\mathrm{PBH}}\sim 1\mathrm{gram}$ may be produced. We find, in particular, that the mass fraction of PBHs is orders of magnitude larger than that obtained when PBHs form via direct collapse in a Universe dominated by radiation or pressureless dust. Looking at observable implications of our findings, we explore the possibility that Planck mass relic remnants of the evaporation of the PBHs could contribute to be the totality of the dark matter in the Universe.

The study of reheating in inflationary models is crucial to understand the early universe and obtain information about the dynamics and parameters of inflation. The reheating temperature $$T_{re}$$Tre and the duration of the reheating phase, quantified by the number ofe-folds $$N_{re}$$Nre , have significant implications for particle production, thermalisation, and the primordial power spectrum. The duration of reheating affects the abundance of particles, including dark matter, and shapes the primordial power spectrum and the anisotropies of the cosmic microwave background. By combining cosmological observations and theoretical considerations, we can constrain both $$T_{re}$$Tre and $$N_{re}$$Nre , which in turn restrict the spectral index $$n_s$$ns , the tensor-to-scalar ratior, and the parameters of the inflationary model. The use of consistency relations between observables, such as $$n_s$$ns andr, provides additional constraints on inflationary models and determines limits for other observables, such as the running of the scalar spectral index. These limits are valuable for assessing the viability of models and can serve to specify priors in Bayesian analyses of specific models. As an example of how to proceed, we study in detail a particular case of a generalized $$\alpha $$α -attractor model that accurately reproduces the observed quantities. We present equations for the conditions of instantaneous reheating, establish consistency relations, and explore the generalized $$\alpha $$α -attractor model using cosmological data. We study the model defined by its potential as a given formula and, furthermore, considering its possible origin in supergravity theories, we impose constraints on the reheating temperature to avoid the overproduction of gravitinos.

If, after primordial inflation, the Universe undergoes a relatively long reheating period, it could present a phase of matter domination supported by the oscillating inflaton field. During this epoch, small perturbations from the inflaton that reenter the cosmological horizon could virialize to form inflaton structures. If the primordial overdensities are large enough, their associated inflaton structures could collapse to form primordial black holes (PBHs) [L. E. Padilla et al., New mechanism for primordial black hole formation during reheating, Phys. Rev. D 106, 023519 (2022); hereinafter P1.]. For this to happen at a considerable rate, the primordial power spectrum should be enhanced at small scales, a feature typically induced in single-field inflation through an ultraslow roll phase (produced by a nearly inflection point in the inflationary potential). In this paper we consider two specific inflationary potentials that present this nearly inflection point, and we look at the PBH formation rate through the mechanism proposed in P1. We report on constraints to these two specific models from the bounds to PBH abundances. This serves as an illustration of the usefulness of the PBH formation mechanism proposed in P1.