Gravitational matter creation, multi-fluid cosmology and kinetic theory

Eur. Phys. J. C (2023) 83:244 https://doi.org/10.1140/epjc/s10052-023-11301-8 Regular Article - Theoretical Physics Gravitational matter creation, multi-fluid cosmology and kinetic theory S. R. G. Trevisania , J. A. S. Limab Departamento de Astronomia, Universidade de São Paulo, Rua do Matão, 1226, São Paulo, SP 05508-900, Brazil Received: 19 May 2022 / Accepted: 5 February 2023 © The Author(s) 2023 Abstract A macroscopic and kinetic relativistic description for a decoupled multi-fluid cosmology endowed with gravitationally induced particle production of all components is proposed. The temperature law for each decoupled particle species is also kinetically derived. The present approach points to the possibility of an exact (semi-classical) quantumgravitational kinetic treatment by incorporating back reaction effects for an arbitrary set of dominant decoupled components. As an illustration we show that a cosmology driven by creation of cold dark matter and baryons (without dark energy) evolves like CDM. However, the complete physical emulation is broken when photon creation is added to the mixture thereby pointing to a crucial test in the future. The present analysis also open up a new window to investigate the Supernova-CMB tension on the values of H0 , as well as the S8 tension since creation of all components changes slightly the CMB results and the expansion history both at early and late times. Finally, it is also argued that cross-correlations between CMB temperature maps and the Sunyaev–Zeldovich effect may provide a crucial and accurate test confronting extended CCDM and CDM models. 1 Introduction The late time accelerating stage of the universe is usually explained by assuming the existence of a dominant dark energy (DE) component, in addition to cold dark matter (CDM) and baryons. Its most popular candidate is the cosmological constant () or the rigid energy density of the current false vacuum state (ρV = /8π G). The observational pillars providing convincing evidences for the so-called CDM model include several independent astronomical observations [1,2]. When combined with the primeval inflation for a e-mail: b e-mail: (corresponding author) 0123456789().: V,-vol describing the first stages of the early universe including the resulting scenario (inflation + CDM) is widely known to be considerably simple and quite predictive. Nevertheless, there are two old theoretical cosmological puzzles or mysteries plus at least two recent observational difficulties plaguing the CDM model, namely: (i) the cosmological constant problem [3], (ii) the coincidence problem [4], (iii) the statistical observational discrepancy between measurements of the Hubble constant (H0 ) from Supernovae (SNe) and other distance indicators at low [5] and intermediate redshifts [6–8] as compared with independent estimates at high redshifts based on the CMB angular power spectrum, and (iv) the so-called S8 tension on the (σ8 ,  M ) plane by confronting Planck + CDM estimates with cosmic shear experiments [9], where σ8 measures the current mass fluctuation in a scale of 8h −1 Mpc. Currently (both tensions H0 and S8 are the major observational anomalies plaguing the CDM model (see below). Many attempts to solve or alliviate the theoretical puzzles gave rise to a plethora of dark energy possibilities including different kinds of running vacuum or decaying -models, interactions in the dark sector and other noncanonical scalar fields [10–21]. There are also more fundamental approaches beyond Einstein’s theory, like several extensions of Einstein’s general relativity, among them: F(R), F(R,T) and GaussBonnet type theories [22–27]. In the observational front, Riess and collaborators are now claiming for a statistical discrepancy of 5σ level between the local H0 value and the one predicted by Planck + CDM [28]. This means that CMB-SNe tension remains unsolved regardless of the realistic dark energy model in general relativity. Further, although statistically less significant (2.6σ to 3σ confidence levels) in comparison with the H0 trouble, the S8 estimates based on cosmic shear measurements from weak lensing collaborations, like Kilo-Degree Surveys (KiDS) and the Dark Energy Survey (DES) are providing val- 123 244 Page 2 of 17 √ ues for the parameter S8 = σ8  M /0.3 lower than the earlytime probes [29–31]. Such observations are clearly opening the possibility to cosmic scenarios beyond CDM model. Actually, some authors are claiming that solutions for the H0 and S8 tensions may require changes in the expansion history both at early and late-times (for more details see [32,33]). In this context, the central interest here is to investigate a possible reduction of the dark sector by eliminating within general relativity, all possible species of dark energy, that is, we set  D E ≡ 0 from the very beginning, including the rigid vacuum itself. Therefore, even if early inflation was caused by the dominance of a vacuum state, its energy density was totally spent to create light particles forming the primeval thermal bath, as usually assumed in many spontaneously symmetry breaking models [34,35]. In addition, any subsequent phase transition was also unable to generate a sizable vacuum state potentially capable to accelerate the universe at late times. This means that the alluded discrepancy of the -term and also the coincidence problem would be naturally solved. In scenarios with  D E = 0 new challenges take place. For instance, some mechanism emulating the late time accelerating CDM evolution must to be proposed at the level of the cosmic smooth expansion. Further, any new picture must also be successful in the perturbative approximation. In other words, although only slightly different from CDM evolution, it needs to be as close as possible to the perturbed CDM description. The mechanism adopted here is the gravitationally induced particle creation by the expanding universe, a process already investigated in general relativity and also in alternative theories of gravity. Such investigations were carried out both from microscopic and macroscopic viewpoints. The former is based on methods and techniques from quantum field theory in curved spacetimes [36–42], while the latter rested upon the non-equilibrium irreversible thermodynamic approach [26,43–45]. Here we focus our attention on the irreversible macroscopic and its associated relativistic kinetic counterpart. The basic reasons are briefly outlined below. Some early theoretical attempts [46–51] gave rise a decade ago to a new accelerating cosmology based on the “adiabatic” creation of cold dark matter (CCDM) [52]. In this general relativistic model with ( D E = 0), the cosmic smooth history is fully equivalent to the CDM model. This very compelling aspect is not shared by any previous phenomenological matter creation models. In particular, the transition from a decelerating to the late-time accelerating stage happens at (...truncated)