scholarly journals Revisiting a Negative Cosmological Constant from Low-Redshift Data

Symmetry ◽  
2019 ◽  
Vol 11 (8) ◽  
pp. 1035 ◽  
Author(s):  
Luca Visinelli ◽  
Sunny Vagnozzi ◽  
Ulf Danielsson
Keyword(s):  
Dark Energy ◽  
Cosmological Constant ◽  
Model Comparison ◽  
High Redshift ◽  
Acoustic Oscillation ◽  
Energy Sector ◽  
Energy Component ◽  
Distance Measurements ◽  
Negative Cosmological Constant ◽  
Dark Energy Component

Persisting tensions between high-redshift and low-redshift cosmological observations suggest the dark energy sector of the Universe might be more complex than the positive cosmological constant of the Λ CDM model. Motivated by string theory, wherein symmetry considerations make consistent AdS backgrounds (i.e., maximally-symmetric spacetimes with a negative cosmological constant) ubiquitous, we explore a scenario where the dark energy sector consists of two components: a negative cosmological constant, with a dark energy component with equation of state w ϕ on top. We test the consistency of the model against low-redshift baryon acoustic oscillation and Type Ia supernovae distance measurements, assessing two alternative choices of distance anchors: the sound horizon at baryon drag determined by the Planck collaboration and the Hubble constant determined by the SH0ES program. We find no evidence for a negative cosmological constant and mild indications for an effective phantom dark energy component on top. A model comparison analysis reveals that the Λ CDM model is favoured over our negative cosmological constant model. While our results are inconclusive, should low-redshift tensions persist with future data, it would be worth reconsidering and further refining our toy negative cosmological constant model by considering realistic string constructions.

GRAVITATIONAL LENSING CONSTRAINT ON THE COSMIC EQUATION OF STATE

2003 ◽  
Vol 12 (05) ◽  
pp. 953-962 ◽  
Author(s):  
DEEPAK JAIN ◽  
ABHA DEV ◽  
N. PANCHAPAKESAN ◽  
S. MAHAJAN ◽  
V. B. BHATIA
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Gravitational Lensing ◽  
Energy Component ◽  
Distance Measurements ◽  
Dark Energy Component ◽  
Highly Sensitive ◽  
Type Ia ◽  
Image Separation ◽  
Ia Supernovae

Recent redshift-distance measurements of Type Ia supernovae (SNe Ia) at cosmological distances suggest that two-third of the energy density of the universe is dominated by dark energy component with an effective negative pressure. This dark energy component is described by the equation of state px= wρx(w ≥ - 1). We use gravitational lensing statistics to constrain the equation of state of this dark energy. We use n(Δθ), the image separation distribution function of lensed quasars, as a tool to probe w. We find that for the observed range of Ωm~ 0.2–0.4, w should lie between -0.8 ≤ w ≤ -0.4 in order to have five lensed quasars in a sample of 867 optical quasars. This limit is highly sensitive to lens and Schechter parameters and the evolution of galaxies.

scholarly journals QUANTUM EFFECTS AND SUPERQUINTESSENCE IN THE NEW AGE OF PRECISION COSMOLOGY

2004 ◽  
Vol 13 (10) ◽  
pp. 2255-2259 ◽  
Author(s):  
E. GUNZIG ◽  
ALBERTO SAA
Keyword(s):  
Experimental Data ◽  
Dark Energy ◽  
Energy Density ◽  
Cosmological Constant ◽  
Classical Approach ◽  
Constant Ratio ◽  
Energy Component ◽  
Dark Energy Component ◽  
Type Ia ◽  
The Universe

Recent observations of Type Ia supernova at high redshifts establish that the dark energy component of the universe has (a probably constant) ratio between pressure and energy density [Formula: see text]. The conventional quintessence models for dark energy are restricted to the range -1≤w<0, with the cosmological constant corresponding to w=-1. Conformally coupled quintessence models are the simplest ones compatible with the marginally allowed superaccelerated regime (w<-1). However, they are known to be plagued with anisotropic singularities. We argue here that the extension of the classical approach to the semiclassical one, with the inclusion of quantum counterterms necessary to ensure the renormalization, can eliminate the anisotropic singularities preserving the isotropic behavior of conformally coupled superquintessence models. Hence, besides of having other interesting properties, they are consistent candidates to describe the superaccelerated phases of the universe compatible with the present experimental data.

scholarly journals Cosmological dynamics and dark energy from nonlocal infrared modifications of gravity

2014 ◽  
Vol 29 (22) ◽  
pp. 1450116 ◽  
Author(s):  
Stefano Foffa ◽  
Michele Maggiore ◽  
Ermis Mitsou
Keyword(s):  
Dark Energy ◽  
Cosmological Constant ◽  
Mass Parameter ◽  
Einstein Equations ◽  
Nonlocal Term ◽  
Extended Model ◽  
Energy Component ◽  
Eos Parameter ◽  
Dark Energy Component ◽  
Dynamical Dark Energy

We study the cosmological dynamics of a recently proposed infrared modification of the Einstein equations, based on the introduction of a nonlocal term constructed with m2gμν□-1R, where m is a mass parameter. The theory generates automatically a dynamical dark energy component, that can reproduce the observed value of the dark energy density without introducing a cosmological constant. Fixing m so to reproduce the observed value Ω DE ≃0.68, and writing w DE (a) = w0+(1-a)wa, the model provides a neat prediction for the equation of state parameters of dark energy, w0≃-1.042 and wa≃-0.020, and more generally provides a pure prediction for w DE as a function of redshift. We show that, because of some freedom in the definition of □-1, one can extend the construction so to define a more general family of nonlocal models. However, in a first approximation this turns out to be equivalent to adding an explicit cosmological constant term on top of the dynamical dark energy component. This leads to an extended model with two parameters, ΩΛ and m. Even in this extension the EOS parameter w0 is always on the phantom side, in the range -1.33 ≲w0≤-1, and there is a prediction for the relation between w0 and wa.

scholarly journals OBSERVATIONAL CONSTRAINTS ON THE GENERALIZED CHAPLYGIN GAS

2009 ◽  
Vol 18 (13) ◽  
pp. 2007-2022 ◽  
Author(s):  
SERGIO DEL CAMPO ◽  
J. R. VILLANUEVA
Keyword(s):  
Dark Energy ◽  
Cosmological Model ◽  
Chaplygin Gas ◽  
Observational Constraints ◽  
Energy Component ◽  
Generalized Chaplygin Gas ◽  
Astronomical Data ◽  
Astronomical Observations ◽  
Dark Energy Component ◽  
Two Parameters

In this paper we study a quintessence cosmological model in which the dark energy component is considered to be the generalized Chaplygin gas and the curvature of the three-geometry is taken into account. Two parameters characterize this sort of fluid: ν and α. We use different astronomical data for restricting these parameters. It is shown that the constraint ν ≲ α agrees well enough with the astronomical observations.

MASS INHOMOGENEITIES AND THE ANGULAR SIZE-REDSHIFT RELATION

2004 ◽  
Vol 13 (07) ◽  
pp. 1309-1313 ◽  
Author(s):  
JAILSON S. ALCANIZ ◽  
JOSÉ A. S. LIMA ◽  
RAIMUNDO SILVA
Keyword(s):  
Dark Energy ◽  
Angular Size ◽  
Matter Density ◽  
Radio Sources ◽  
Density Parameter ◽  
Energy Component ◽  
Dark Energy Component ◽  
Smoothness Parameter ◽  
Best Fit ◽  
Size Data

We investigate the influence of mass inhomogeneities on the angular size-redshift test through a statistical analysis of angular size data for a large sample of milliarcsecond radio sources. The results are based on flat models driven by nonrelativistic matter plus a dark energy component in the form of a relic cosmological constant. To model the mass inhomogeneities we use the Zeldovich–Kantowski distance formula (also known as Dyer–Roeder distance redshift relation) which is characterized by the smoothness parameter α. Marginalizing over the characteristic angular size l and assuming a Gaussian prior on the matter density parameter, i.e., Ωm=0.35±0.07, the best fit model occurs at Ωm=0.35 and α=0.8. For an analysis without priors and minimizing χ2 for the parameters l, Ωm and α we find that a conventional homogeneous scenario (α=1) with Ωm=0.2 and D=22.6h-1 pc constitutes the best fit model for the present angular size data.

scholarly journals Novel null-test for the Λ cold dark matter model with growth-rate data

2015 ◽  
Vol 24 (06) ◽  
pp. 1550045 ◽  
Author(s):  
Savvas Nesseris ◽  
Domenico Sapone
Keyword(s):  
Dark Energy ◽  
Cold Dark Matter ◽  
Statistical Tests ◽  
Cosmological Parameters ◽  
Accelerated Expansion ◽  
Late Time ◽  
Energy Component ◽  
Dark Energy Component ◽  
Standard Cosmological Model ◽  
Flrw Universe

Current and upcoming surveys will measure the cosmological parameters with an extremely high accuracy. The primary goal of these observations is to eliminate some of the currently viable cosmological models created to explain the late-time accelerated expansion (either real or only inferred). However, most of the statistical tests used in cosmology have a strong requirement: the use of a model to fit the data. Recently there has been an increased interest on finding tests that are model independent, i.e. to have a function that depends entirely on observed quantities and not on the model, see for instance [C. Clarkson, B. Bassett and T. H. C. Lu, Phys. Rev. Lett.101 (2008) 011301, arXiv:0712.3457 [astro-ph]]. In this paper, we present an alternative consistency check at the perturbative level for a homogeneous and isotropic Universe filled with a dark energy component. This test makes use of the growth of matter perturbations data and it is able to detect a deviation from the standard cosmological model, which could later be attributed to a clustering dark energy component, a tension in the data or a modification of gravity, within the framework of a Friedmann–Lemaître–Robertson–Walker (FLRW) universe.

scholarly journals Cosmological Constraints on the Coupling Model from Observational Hubble Parameter and Baryon Acoustic Oscillation Measurements

Universe ◽  
2021 ◽  
Vol 7 (3) ◽  
pp. 57
Author(s):  
Shulei Cao ◽  
Tong-Jie Zhang ◽  
Xinya Wang ◽  
Tingting Zhang
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Hubble Parameter ◽  
Cold Dark Matter ◽  
High Redshift ◽  
Coupling Model ◽  
Acoustic Oscillation ◽  
Baryon Acoustic Oscillation ◽  
Best Fitting ◽  
Age Of The Universe

In the paper, we consider two models in which dark energy is coupled with either dust matter or dark matter, and discuss the conditions that allow more time for structure formation to take place at high redshifts. These models are expected to have a larger age of the universe than that of ΛCDM [universe consists of cold dark matter (CDM) and dark energy (a cosmological constant, Λ)], so it can explain the formation of high redshift gravitationally bound systems which the ΛCDM model cannot interpret. We use the observational Hubble parameter data (OHD) and Hubble parameter obtained from cosmic chronometers method (H(z)) in combination with baryon acoustic oscillation (BAO) data to constrain these models. With the best-fitting parameters, we discuss how the age, the deceleration parameter, and the energy density parameters evolve in the new universes, and compare them with that of ΛCDM.

scholarly journals THERMODYNAMIC OF THE GHOST DARK ENERGY UNIVERSE

2012 ◽  
Vol 27 (31) ◽  
pp. 1250182 ◽  
Author(s):  
CHAO-JUN FENG ◽  
XIN-ZHOU LI ◽  
XIAN-YONG SHEN
Keyword(s):  
Dark Energy ◽  
Vacuum Energy ◽  
Hawking Temperature ◽  
Frw Universe ◽  
Energy Component ◽  
Ghost Dark Energy ◽  
Dark Energy Component ◽  
Acceleration Of The Universe ◽  
The Universe ◽  
Friedmann Robertson Walker

Recently, the vacuum energy of the QCD ghost in a time-dependent background is proposed as a kind of dark energy candidate to explain the acceleration of the Universe. In this model, the energy density of the dark energy is proportional to the Hubble parameter H, which is the Hawking temperature on the Hubble horizon of the Friedmann–Robertson–Walker (FRW) Universe. In this paper, we generalized this model and chose the Hawking temperature on the so-called trapping horizon, which will coincide with the Hubble temperature in the context of flat FRW Universe dominated by the dark energy component. We study the thermodynamics of Universe with this kind of dark energy and find that the entropy-area relation is modified, namely, there is another new term besides the area term.

scholarly journals AN INVERSE f(R) GRAVITATION FOR COSMIC SPEED UP, AND DARK ENERGY EQUIVALENT

2008 ◽  
Vol 23 (23) ◽  
pp. 1929-1937 ◽  
Author(s):  
SOHRAB RAHVAR ◽  
YOUSEF SOBOUTI
Keyword(s):  
Dark Energy ◽  
Modified Gravity ◽  
Scale Factor ◽  
The State ◽  
Frw Universe ◽  
Energy Component ◽  
Energy Equivalent ◽  
Dark Energy Component ◽  
Speed Up ◽  
Frw Metric

To explain the cosmic speed up, brought to light by the recent SNIa and CMB observations, we propose the following: (a) In a spacetime endowed with a FRW metric, we choose an empirical scale factor that best explains the observations. (b) We assume a modified gravity, generated by an unspecified field Lagrangian, f(R). (c) We use the adopted empirical scale factor to work back retroactively to obtain f(R), hence the term "Inverse f(R)". (d) Next we consider the classic GR and a conventional FRW universe that, in addition to its known baryonic content, possesses a hypothetical "Dark Energy" component. We compare the two scenarios and find the density, the pressure, and the equation of the state of the Dark Energy required to make up for the differences between the conventional and the modified GR models.

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