53 research outputs found
Relaxing the σ8-tension through running vacuum in the Universe
It has recently been shown that the class of running vacuum models (RVMs) has the capacity to fit the overall cosmological observations better than the concordance ΛCDM model, therefore supporting the possibility of dynamical dark energy (DE). Apart from the cosmic microwave background (CMB) anisotropies, the most crucial datasets involved are: i) baryonic acoustic oscillations (BAO), and ii) direct large scale structure (LSS) formation data. Analyses mainly focusing on CMB and with insufficient BAO+LSS input generally fail to capture the dynamical DE signature, whereas the few existing studies accounting for the wealth of known CMB+BAO+LSS data (see in particular Sol\`a, G\'omez-Valent \& de Cruz P\'erez 2015, 2017; and Zhao et al. 2017) do converge to the remarkable conclusion that dynamical DE might well be encoded in the current cosmological observations at a 3−4σ c.l. A decisive factor is the persistent σ8-tension between the ΛCDM and the data. Because the issue is obviously pressing, we devote this work to explain how and why running vacuum in the expanding universe successfully relaxes the existing σ8-tension and describes the LSS formation data significantly better than the ΛCDM
Cosmic chronometers to calibrate the ladders and measure the curvature of the Universe. A model-independent study
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, , and the robustness of the cosmological
principle (CP) at with a model-agnostic approach. We do so by
reconstructing and the curvature parameter using
Gaussian Processes. Moreover, we use CCH in combination with radial and angular
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, , from each BAO data point and check their consistency. Given the
precision allowed by the CCH data, we find that , and
are fully compatible (at 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 mag,
Mpc and ( C.L.).
These values have been obtained without using any information from the main
data sets involved in the 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 mag, Mpc
and .Comment: 17 pages, 10 figures, 5 table
Stringy Running Vacuum Model and current Tensions in Cosmology
We discuss the potential alleviation of both the Hubble and the growth of
galactic structure data tensions observed in the current epoch of Cosmology in
the context of the so-called Stringy Running Vacuum Model (RVM) of Cosmology.
This is a gravitational field theory coupled to matter, which, at early eras,
contains gravitational (Chern-Simons (CS) type) anomalies and torsion, arising
from the fundamental degrees of freedom of the massless gravitational multiplet
of an underlying microscopic string theory. The model leads to RVM type
inflation without external inflatons, arising from the quartic powers of the
Hubble parameter that characterise the vacuum energy density due to
primordial-gravitational-wave-induced anomaly CS condensates, and dominate the
inflationary era. In modern eras, of relevance to this work, the gravitational
anomalies are cancelled by chiral matter, generated at the end of the RVM
inflationary era, but cosmic radiation and other matter fields are still
responsible for a RVM energy density with terms exhibiting a
quadratic-power-of-Hubble-parameter dependence, but also products of the latter
with logarithmic -dependencies, arising from potential quantum-gravity and
quantum-matter loop effects. In this work, such terms are examined
phenomenologically from the point of view of the potential alleviation of the
aforementioned current tensions in Cosmology. Using standard information
criteria, we find that these tensions can be substantially alleviated in a way
consistent not only with the data, but also with the underlying microscopic
theory predictions, associated with the primordial dynamical breaking of
supergravity that characterise a pre-RVM-inflationary phase of the model.Comment: 38 pages, 6 figures, 7 tables. Version accepted for publication in
Classical and Quantum Gravity. Extended discussion (new section VII),
improved Figure 6, corrected typos and references adde
String-inspired running-vacuum cosmology, quantum corrections and the current cosmological tensions
In the context of a string-inspired running vacuum model (RVM) of cosmology
with anomalies and torsion-induced axion-like fields, we discuss quantum
corrections to the corresponding energy density, in approximately de Sitter
eras, during which the Hubble parameter varies very slowly with the
cosmic time . Such corrections arise either from graviton loops in the
corresponding gravitational theory, or from path integration of massive quantum
matter fields. They depend logarithmically on , in the form , . In the modern eras, for which the terns are
dominant, such corrections may contribute to an alleviation of the currently
observed cosmological and structure-growth tensions. In particular, we
argue that such an effect is accomplished for a (dynamically-broken)
supergravity-based RVM cosmological model. In the current de-Sitter era, for
this case, rather surprisingly, the quantum graviton corrections dominate those
due to matter fields, provided the scale of the primordial (pre-RVM inflation)
dynamical breaking of local supersymmetry lies near the reduced Planck scale,
which is a natural assumption in the context of the model.Comment: 12 pages, latex (uses special (Springer Proceedings) macros), one pdf
figure incorporated; Invited plenary talk (NEM) at 40th Conference on Recent
Developments in High Energy Physics and Cosmology of the Hellenic High Energy
Physics Society (HEP2023, 5-7 April 2023, U. of Ioannina (Greece)), based
partly on e-Print:2305.15774 [gr-qc]. arXiv admin note: text overlap with
arXiv:2306.0806
Late-time phenomenology required to solve the tension in view of the cosmic ladders and the anisotropic and angular BAO data sets
The mismatch between the value of the Hubble parameter
measured by SH0ES and the one inferred from the inverse distance ladder (IDL)
constitutes the biggest tension afflicting the standard model of cosmology,
which could be pointing to the need of physics beyond CDM. In this
paper we study the background history required to solve the tension if we
consider standard prerecombination physics, paying special attention to the
role played by the data on baryon acoustic oscillations (BAO) employed to build
the IDL. We show that the anisotropic BAO data favor an ultra-late-time
(phantom-like) enhancement of at to solve the tension,
accompanied by a transition in the absolute magnitude of supernovae of Type Ia
in the same redshift range. The effective dark energy (DE) density must
be smaller than in the standard model at higher redshifts. Instead, when
angular BAO data (claimed to be less subject to model dependencies) is employed
in the analysis, we find that the increase of starts at much higher
redshifts, typically in the range . In this case, could
experience also a transition (although much smoother) and the effective DE
density becomes negative at . Both scenarios require a violation of
the weak energy condition (WEC), but leave an imprint on completely different
redshift ranges and might also have a different impact on the perturbed
observables. They allow for the effective crossing of the phantom divide.
Finally, we employ two alternative methods to show that current data from
cosmic chronometers do not exclude the violation of the WEC, but do not add any
strong evidence in its favor neither. Our work puts the accent on the utmost
importance of the choice of the BAO data set in the study of the possible
solutions to the tension.Comment: 20 pages, 13 figures, 3 table
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