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result(s) for
"Chronometers"
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The discovery of longitude
Discusses the history of how longitude came about and how it changed map making forever.
Book
Observational constraints on Barrow holographic dark energy
We use observational data from Supernovae (SNIa) Pantheon sample, as well as from direct measurements of the Hubble parameter from the cosmic chronometers (CC) sample, in order to extract constraints on the scenario of Barrow holographic dark energy. The latter is a holographic dark energy model based on the recently proposed Barrow entropy, which arises from the modification of the black-hole surface due to quantum-gravitational effects. We first consider the case where the new deformation exponent
Δ
is the sole model parameter, and we show that although the standard value
Δ
=
0
, which corresponds to zero deformation, lies within the
1
σ
region, a deviation is favored. In the case where we let both
Δ
and the second model parameter to be free we find that a deviation from standard holographic dark energy is preferred. Additionally, applying the Akaike, Bayesian and Deviance Information Criteria, we conclude that the one-parameter model is statistically compatible with
Λ
CDM
paradigm, and preferred comparing to the two-parameter one. Finally, concerning the present value of the Hubble parameter we find that it is close to the Planck value.
Journal Article
Constraints on barotropic dark energy models by a new phenomenological q(z) parameterization
In this paper, we propose a new phenomenological two parameter parameterization of q(z) to constrain barotropic dark energy models by considering a spatially flat Universe, neglecting the radiation component, and reconstructing the effective equation of state (EoS). This two free-parameter EoS reconstruction shows a non-monotonic behavior, pointing to a more general fitting for the scalar field models, like thawing and freezing models. We constrain the q(z) free parameters using the observational data of the Hubble parameter obtained from cosmic chronometers, the joint-light-analysis Type Ia Supernovae (SNIa) sample, the Pantheon (SNIa) sample, and a joint analysis from these data. We obtain, for the joint analysis with the Pantheon (SNIa) sample a value of q(z) today, \\[q_0=-0.51\\begin{array}{c} +0.09 \\\ -0.10 \\end{array}\\], and a transition redshift, \\[z_t=0.65\\begin{array}{c} +0.19 \\\ -0.17 \\end{array}\\] (when the Universe change from an decelerated phase to an accelerated one). The effective EoS reconstruction and the \\[\\omega '\\]–\\[\\omega \\] plane analysis point towards a transition over the phantom divide, i.e. \\[\\omega =-1\\], which is consistent with a non parametric EoS reconstruction reported by other authors.
Journal Article
BAO signatures in the 2-point angular correlations and the Hubble tension
An observational tension on estimates of the Hubble parameter,
H
0
, using early and late Universe information, is being of intense discussion in the literature. Additionally, it is of great importance to measure
H
0
independently of CMB data and local distance ladder method. In this sense, we analyze 15 measurements of the transversal BAO scale,
θ
BAO
, obtained in a weakly model-dependent approach, in combination with other data sets obtained in a model-independent way, namely, Big Bang Nucleosynthesis (BBN) information, 6 gravitationally lensed quasars with measured time delays by the H0LiCOW team, and measures of cosmic chronometers (CC). We find
H
0
=
74
.
88
-
2.1
+
1.9
km s
-
1
Mpc
-
1
and
H
0
=
72
.
06
-
1.3
+
1.2
km s
-
1
Mpc
-
1
from
θ
BAO
+BBN+H0LiCOW and
θ
BAO
+BBN+CC, respectively, in fully accordance with local measurements. Moreover, we estimate the sound horizon at drag epoch,
r
d
, independent of CMB data, and find
r
d
=
144
.
1
-
5.5
+
5.3
Mpc (from
θ
BAO
+BBN+H0LiCOW) and
r
d
=
150
.
4
-
3.3
+
2.7
Mpc (from
θ
BAO
+BBN+CC). In a second round of analysis, we test how the presence of a possible spatial curvature,
Ω
k
, can influence the main results. We compare our constraints on
H
0
and
r
d
with other reported values. Our results show that it is possible to use a robust compilation of transversal BAO data,
θ
BAO
, jointly with other model-independent measurements, in such a way that the tension on the Hubble parameter can be alleviated.
Journal Article
Measurements of H0 and reconstruction of the dark energy properties from a model-independent joint analysis
Gaussian processes (GP) provide an elegant and model-independent method for extracting cosmological information from the observational data. In this work, we employ GP to perform a joint analysis by using the geometrical cosmological probes such as Supernova Type Ia (SN), Cosmic chronometers (CC), Baryon Acoustic Oscillations (BAO), and the H0LiCOW lenses sample to constrain the Hubble constant H0, and reconstruct some properties of dark energy (DE), viz., the equation of state parameter w, the sound speed of DE perturbations cs2, and the ratio of DE density evolution X=ρde/ρde,0. From the joint analysis SN+CC+BAO+H0LiCOW, we find that H0 is constrained at 1.1% precision with H0=73.78±0.84kms-1Mpc-1, which is in agreement with SH0ES and H0LiCOW estimates, but in ∼6.2σ tension with the current CMB measurements of H0. With regard to the DE parameters, we find cs2<0 at ∼2σ at high z, and the possibility of X to become negative for z>1.5. We compare our results with the ones obtained in the literature, and discuss the consequences of our main results on the DE theoretical framework.
Journal Article
Falsifying cosmological models based on a non-linear electrodynamics
Recently, the nonlinear electrodynamics (NED) has been gaining attention to generate primordial magnetic fields in the Universe and also to resolve singularity problems. Moreover, recent works have shown the crucial role of the NED on the inflation. This paper provides a new approach based on a new model of NED as a source of gravitation to remove the cosmic singularity at the big bang and explain the cosmic acceleration during the inflation era on the background of stochastic magnetic field. Also, we found a realization of a cyclic Universe, free of initial singularity, due to the proposed NED energy density. In addition, we explore whether a NED field without or with matter can be the origin of the late-time acceleration. For this we obtain explicit equations for H(z) and perform a MCMC analysis to constrain the NED parameters by using 31 observational Hubble data (OHD) obtained from cosmic chronometers covering the redshift range 0
Journal Article
A large oxygen-dominated core from the seismic cartography of a pulsating white dwarf
Asteroseismic ‘sounding’ reveals the internal chemical stratification of the white dwarf KIC08626021, which has a central homogeneous core—composed of 86 per cent oxygen—that has a mass of 0.45 solar masses.
The core of a white-dwarf star
White-dwarf stars are the end point of stellar evolution for most stars, and the merger of two of these bodies seems to be responsible for the type Ia supernovae used in cosmology. The interior structure of white-dwarf stars, however, is not well known. Noemi Giammichele and collaborators have used archival data and asteroseismic sounding methods to determine that the hydrogen-deficient white dwarf KIC08626021 contains a central homogeneous core that has a mass of 0.45 solar masses and is 86% oxygen. The core is larger, and the oxygen fraction higher, than predicted by standard models.
White-dwarf stars are the end product of stellar evolution for most stars in the Universe
1
. Their interiors bear the imprint of fundamental mechanisms that occur during stellar evolution
2
,
3
. Moreover, they are important chronometers for dating galactic stellar populations, and their mergers with other white dwarfs now appear to be responsible for producing the type Ia supernovae that are used as standard cosmological candles
4
. However, the internal structure of white-dwarf stars—in particular their oxygen content and the stratification of their cores—is still poorly known, because of remaining uncertainties in the physics involved in stellar modelling codes
5
,
6
. Here we report a measurement of the radial chemical stratification (of oxygen, carbon and helium) in the hydrogen-deficient white-dwarf star KIC08626021 (J192904.6+444708), independently of stellar-evolution calculations. We use archival data
7
,
8
coupled with asteroseismic sounding techniques
9
,
10
to determine the internal constitution of this star. We find that the oxygen content and extent of its core exceed the predictions of existing models of stellar evolution. The central homogeneous core has a mass of 0.45 solar masses, and is composed of about 86 per cent oxygen by mass. These values are respectively 40 per cent and 15 per cent greater than those expected from typical white-dwarf models. These findings challenge present theories of stellar evolution and their constitutive physics, and open up an avenue for calibrating white-dwarf cosmochronology
11
.
Journal Article
A model-independent test of the evolution of gas depletion factor for SPT-SZ and Planck ESZ clusters
The gas mass fraction in galaxy clusters has been widely used to determine cosmological parameters. This method assumes that the ratio of the cluster gas mass fraction to the cosmic baryon fraction (γ(z)) is constant as a function of redshift. In this work, we look for a time evolution of γ(z) at R500 by using both the SPT-SZ and Planck Early SZ (ESZ) cluster data, in a model-independent fashion without any explicit dependence on the underlying cosmology. For this calculation, we use a non-parametric functional form for the Hubble parameter obtained from Gaussian Process regression using cosmic chronometers. We parameterize γ(z) as: γ(z)=γ0(1+γ1z) to constrain the redshift evolution. We find contradictory results between both the samples. For SPT-SZ, γ(z) decreases as a function of redshift (at more than 5σ), whereas a positive trend with redshift is found for Planck ESZ data (at more than 4σ). We however find that the γ1 values for a subset of SPT-SZ and Planck ESZ clusters between the same redshift interval agree to within 1σ. When we allow for a dependence on the halo mass in the evolution of the gas depletion factor, the 4-5σ discrepancy reduces to 2σ.
Journal Article
Model-independent constraints on cosmic curvature: implication from the future space gravitational-wave antenna DECIGO
In order to estimate cosmic curvature from cosmological probes like standard candles, one has to measure the luminosity distance DL(z), its derivative with respect to redshift DL′(z) and the expansion rate H(z) at the same redshift. In this paper, we study how such idea could be implemented with future generation of space-based DECi-hertz Interferometer Gravitational-wave Observatory (DECIGO), in combination with cosmic chronometers providing cosmology-independent H(z) data. Our results show that for the Hubble diagram of simulated DECIGO data acting as a new type of standard siren, it would be able to constrain cosmic curvature with the precision of ΔΩk=0.09 with the currently available sample of 31 measurements of Hubble parameters. In the framework of the third generation ground-based gravitational wave detectors, the spatial curvature is constrained to be ΔΩk=0.13 for Einstein Telescope (ET). More interestingly, compared to other approaches aiming for model-independent estimations of spatial curvature, our analysis also achieve the reconstruction of the evolution of Ωk(z), in the framework of a model-independent method of Gaussian processes (GP) without assuming a specific form. Therefore, one can expect that the newly emerged gravitational wave astronomy can become useful in local measurements of cosmic curvature using distant sources.
Journal Article