Despite the fact that a rigid -term is a fundamental building block of the concordance ΛCDM model, we show that a large class of cosmological scenarios with dynamical vacuum energy density together ...with a dynamical gravitational coupling G or a possible non-conservation of matter, are capable of seriously challenging the traditional phenomenological success of the ΛCDM. In this paper, we discuss these "running vacuum models" (RVMs), in which consists of a nonvanishing constant term and a series of powers of the Hubble rate. Such generic structure is potentially linked to the quantum field theoretical description of the expanding universe. By performing an overall fit to the cosmological observables SN Ia+BAO+H(z)+LSS+BBN+CMB (in which the WMAP9, Planck 2013, and Planck 2015 data are taken into account), we find that the class of RVMs appears significantly more favored than the ΛCDM, namely, at an unprecedented level of . Furthermore, the Akaike and Bayesian information criteria confirm that the dynamical RVMs are strongly preferred compared to the conventional rigid -picture of the cosmic evolution.
In this work, we provide updated constraints on coupled dark energy (CDE) cosmology with Peebles-Ratra (PR) potential and constant coupling strength β. This modified gravity scenario introduces a ...fifth force between dark matter particles, mediated by a scalar field that plays the role of dark energy. The mass of the dark matter particles does not remain constant, but changes with time as a function of the scalar field. Here we focus on the phenomenological behavior of the model, and assess its ability to describe updated cosmological datasets that include the Planck 2018 cosmic microwave background (CMB) temperature, polarization and lensing, baryon acoustic oscillations, the Pantheon compilation of supernovae of Type Ia, data on H(z) from cosmic chronometers, and redshift-space distortions. We also study the impact of the local measurement of H0 from SH0ES and the strong-lensing time delay data from the H0LICOW Collaboration on the parameter that controls the strength of the interaction in the dark sector. We find a peak corresponding to a coupling β>0 and to a potential parameter α>0, more or less evident depending on the dataset combination. We show separately the impact of each dataset and remark that CMB lensing is especially the one dataset that shifts the peak the most towards ΛCDM. When a model selection criterion based on the full Bayesian evidence is applied, however, ΛCDM is still preferred in all cases, due to the additional parameters introduced in the CDE model.
Possible signals of vacuum dynamics in the Universe Solà Peracaula, Joan; de Cruz Pérez, Javier; Gómez-Valent, Adrià
Monthly notices of the Royal Astronomical Society,
08/2018, Volume:
478, Issue:
4
Journal Article
Peer reviewed
Open access
ABSTRACT
We study a generic class of time-evolving vacuum models which can provide a better phenomenological account of the overall cosmological observations as compared to the Λ cold dark matter ...(ΛCDM). Among these models, the running vacuum model (RVM) appears to be the most motivated and favoured one, at a confidence level of ∼3σ. We further support these results by computing the Akaike and Bayesian information criteria. Our analysis also shows that we can extract fair signals of dynamical dark energy (DDE) by confronting the same set of data to the generic XCDM and CPL parametrizations. In all cases we confirm that the combined triad of modern observations on baryonic acoustic oscillations, large-scale structure formation, and the cosmic microwave background, provide the bulk of the signal sustaining a possible vacuum dynamics. In the absence of any of these three crucial data sources, the DDE signal cannot be perceived at a significant confidence level. Its possible existence could be a cure for some of the tensions existing in the ΛCDM when confronted to observations.
ABSTRACT
We use the state-of-the-art data on cosmic chronometers (CCH) and the Pantheon+compilation of supernovae of Type Ia (SNIa) to test the constancy of the SNIa absolute magnitude, M, and the ...robustness of the cosmological principle (CP) at z ≲ 2 with a model-agnostic approach. We do so by reconstructing M(z) and the curvature parameter Ωk(z) using Gaussian Processes. Moreover, we use CCH in combination with data on baryon acoustic oscillations (BAO) from various galaxy surveys (6dFGS, BOSS, eBOSS, WiggleZ, DES Y3) to measure the sound horizon at the baryon-drag epoch, rd, from each BAO data point and check their consistency. Given the precision allowed by the CCH, we find that M(z), Ωk(z), and rd(z) are fully compatible (at $\lt 68$ per cent C.L.) with constant values. This justifies our final analyses, in which we put constraints on these constant parameters under the validity of the CP, the metric description of gravity and standard physics in the vicinity of the stellar objects, but otherwise in a model-independent way. If we exclude the SNIa contained in the host galaxies employed by SH0ES, our results read $M=(-19.314^{+0.086}_{-0.108})$ mag, rd = (142.3 ± 5.3) Mpc, and $\Omega _k=-0.07^{+0.12}_{-0.15}$, with H0 = (71.5 ± 3.1) km s−1 Mpc−1 (68 per cent C.L.). These values are independent of the main data sets involved in the H0 tension, namely, the cosmic microwave background and the first two rungs of the cosmic distance ladder. If, instead, we also consider the SNIa in the host galaxies, calibrated with Cepheids, we measure $M=(-19.252^{+0.024}_{-0.036})$ mag, $r_\mathrm{ d}=(141.9^{+5.6}_{-4.9})$ Mpc, $\Omega _\mathrm{ k}=-0.10^{+0.12}_{-0.15}$, and $H_0=(74.0^{+0.9}_{-1.0})$ km s−1 Mpc−1.
Dark energy could play a role at redshifts z ≫ O (1). Many quintessence models possess scaling or attractor solutions where the fraction of dark energy follows the dominant component in previous ...epochs of the Universe's expansion, or phase transitions may happen close to the time of matter-radiation equality. A non-negligible early dark energy (EDE) fraction around matter-radiation equality could contribute to alleviate the well-known H0 tension. In this work, we constrain the fraction of EDE using two approaches: first, we use a fluid parametrization that mimics the plateaux of the dominant components in the past. An alternative tomographic approach constrains the EDE density in binned redshift intervals. The latter allows us to reconstruct the evolution of Ωde(z) before and after the decoupling of the cosmic microwave background (CMB) photons. We have employed Planck data 2018, the Pantheon compilation of supernovae of Type Ia (SNIa), data on galaxy clustering, the prior on the absolute magnitude of SNIa by SH0ES, and weak lensing data from KiDS + VIKING − 450 and DES-Y1. When we use a minimal parametrization mimicking the background plateaux, EDE has only a small impact on current cosmological tensions. We show how the constraints on the EDE fraction weaken considerably when its sound speed is allowed to vary. By means of our binned analysis we put very tight constraints on the EDE fraction around the CMB decoupling time, ≲ 0.4 % at 2σ c.l. We confirm previous results that a significant EDE fraction in the radiation-dominated epoch loosens the H0 tension, but tends to worsen the tension for σ8. A subsequent presence of EDE in the matter-dominated era helps to alleviate this issue. When both the SH0ES prior and weak lensing data are considered in the fitting analysis in combination with data from CMB, SNIa and baryon acoustic oscillations, the EDE fractions are constrained to be ≲ 2.6 % in the radiation-dominated epoch and ≲ 1.5 % in the redshift range z ∈ (100, 1000 ) at 2σ c.l. The two tensions remain with a statistical significance of ~ 2–3σ c.l.
We focus on the class of cosmological models with a time-evolving vacuum energy density of the form
$\rho _\Lambda (H)=C_0+C_1 H+C_2 H^2$
, where H is the Hubble rate. Higher powers of H could be ...important for the early inflationary epoch, but are irrelevant afterwards. We study these models at the background level and at the perturbations level, both at the linear and at the non-linear regime. We find that those with C
0 = 0 are seriously hampered, as they are unable to fit simultaneously the current observational data on Hubble expansion and the linear growth rate of clustering. This is in contrast to the C
0 ≠ 0 models, including the concordance Λ cold dark matter (ΛCDM) model. We also compute the redshift distribution of clusters predicted by all these models, in which the analysis of the non-linear perturbations becomes crucial. The outcome is that the models with C
0 = 0 predict a number of counts with respect to the concordance model which is much larger, or much smaller, than the ΛCDM and the dynamical models with C
0 ≠ 0. The particular case
$\rho _\Lambda (H)\propto H$
(the pure lineal model), which in the past was repeatedly motivated by several authors from QCD arguments applied to cosmology, is also addressed and we assess in detail its phenomenological status. We conclude that the most favoured models are those with C
0 ≠ 0, and we show how to discriminate them from the ΛCDM.
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