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Title: Dark energy equation of state parameter and its evolution at low redshift

Abstract

In this paper, we constrain dark energy models using a compendium of observations at low redshifts. We consider the dark energy as a barotropic fluid, with the equation of state a constant as well the case where dark energy equation of state is a function of time. The observations considered here are Supernova Type Ia data, Baryon Acoustic Oscillation data and Hubble parameter measurements. We compare constraints obtained from these data and also do a combined analysis. The combined observational constraints put strong limits on variation of dark energy density with redshift. For varying dark energy models, the range of parameters preferred by the supernova type Ia data is in tension with the other low redshift distance measurements.

Authors:
; ;  [1]
  1. Indian Institute of Science Education and Research Mohali, SAS Nagar, Mohali 140306, Punjab (India)
Publication Date:
OSTI Identifier:
22676173
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Cosmology and Astroparticle Physics; Journal Volume: 2017; Journal Issue: 06; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; BARYONS; COMPARATIVE EVALUATIONS; DISTANCE; ENERGY DENSITY; ENERGY MODELS; EQUATIONS OF STATE; EVOLUTION; FLUIDS; NONLUMINOUS MATTER; OSCILLATIONS; RED SHIFT; SIMULATION; TIME DEPENDENCE; TYPE I SUPERNOVAE; VARIATIONS

Citation Formats

Tripathi, Ashutosh, Sangwan, Archana, and Jassal, H.K., E-mail: ashutosh_tripathi@fudan.edu.cn, E-mail: archanakumari@iisermohali.ac.in, E-mail: hkjassal@iisermohali.ac.in. Dark energy equation of state parameter and its evolution at low redshift. United States: N. p., 2017. Web. doi:10.1088/1475-7516/2017/06/012.
Tripathi, Ashutosh, Sangwan, Archana, & Jassal, H.K., E-mail: ashutosh_tripathi@fudan.edu.cn, E-mail: archanakumari@iisermohali.ac.in, E-mail: hkjassal@iisermohali.ac.in. Dark energy equation of state parameter and its evolution at low redshift. United States. doi:10.1088/1475-7516/2017/06/012.
Tripathi, Ashutosh, Sangwan, Archana, and Jassal, H.K., E-mail: ashutosh_tripathi@fudan.edu.cn, E-mail: archanakumari@iisermohali.ac.in, E-mail: hkjassal@iisermohali.ac.in. Thu . "Dark energy equation of state parameter and its evolution at low redshift". United States. doi:10.1088/1475-7516/2017/06/012.
@article{osti_22676173,
title = {Dark energy equation of state parameter and its evolution at low redshift},
author = {Tripathi, Ashutosh and Sangwan, Archana and Jassal, H.K., E-mail: ashutosh_tripathi@fudan.edu.cn, E-mail: archanakumari@iisermohali.ac.in, E-mail: hkjassal@iisermohali.ac.in},
abstractNote = {In this paper, we constrain dark energy models using a compendium of observations at low redshifts. We consider the dark energy as a barotropic fluid, with the equation of state a constant as well the case where dark energy equation of state is a function of time. The observations considered here are Supernova Type Ia data, Baryon Acoustic Oscillation data and Hubble parameter measurements. We compare constraints obtained from these data and also do a combined analysis. The combined observational constraints put strong limits on variation of dark energy density with redshift. For varying dark energy models, the range of parameters preferred by the supernova type Ia data is in tension with the other low redshift distance measurements.},
doi = {10.1088/1475-7516/2017/06/012},
journal = {Journal of Cosmology and Astroparticle Physics},
number = 06,
volume = 2017,
place = {United States},
year = {Thu Jun 01 00:00:00 EDT 2017},
month = {Thu Jun 01 00:00:00 EDT 2017}
}
  • The dark energy component of the Universe is often interpreted either in terms of a cosmological constant or as a scalar field. A generic feature of the scalar field models is that the equation of state parameter w{identical_to}P/{rho} for the dark energy need not satisfy w=-1 and, in general, it can be a function of time. Using the Markov chain Monte Carlo method we perform a critical analysis of the cosmological parameter space, allowing for a varying w. We use constraints on w(z) from the observations of high redshift supernovae (SN), the Wilkinson Microwave Anisotropy Probe (WMAP) observations of cosmicmore » microwave background (CMB) anisotropies, and abundance of rich clusters of galaxies. For models with a constant w, the {lambda}CDM(cold dark matter) model is allowed with a probability of about 6% by the SN observations while it is allowed with a probability of 98.9% by WMAP observations. The {lambda}CDM model is allowed even within the context of models with variable w: WMAP observations allow it with a probability of 99.1% whereas SN data allows it with 23% probability. The SN data, on its own, favors phantom-like equation of state (w<-1) and high values for {omega}{sub NR}. It does not distinguish between constant w (with w<-1) models and those with varying w(z) in a statistically significant manner. The SN data allows a very wide range for variation of dark energy density, e.g., a variation by factor ten in the dark energy density between z=0 and z=1 is allowed at 95% confidence level. WMAP observations provide a better constraint and the corresponding allowed variation is less than a factor of 3. Allowing for variation in w has an impact on the values for other cosmological parameters in that the allowed range often becomes larger. There is significant tension between SN and WMAP observations; the best fit model for one is often ruled out by the other at a very high confidence limit. Hence results based on only one of these can lead to unreliable conclusions. Given the divergence in models favored by individual observations, and the fact that the best fit models are ruled out in the combined analysis, there is a distinct possibility of the existence of systematic errors which are not understood.« less
  • The new 182 gold supernova Ia data, the baryon acoustic oscillation measurement and the shift parameter determined from the Sloan Digital Sky Survey, and the three-year Wilkinson Microwave Anisotropy Probe data are combined to reconstruct the dark energy equation of state parameter w(z) and the deceleration parameter q(z). We find that the strongest evidence of acceleration happens around the redshift z{approx}0.2 and the stringent constraints on w(z) lie in the redshift range z{approx}0.2-0.5. At the sweet spot, -1.2<w(z)<-0.6 for the dark energy parametrization w(z)=w{sub 0}+w{sub a}z/(1+z){sup 2} at the 3{sigma} confidence level. The transition redshift z{sub t} when the Universemore » underwent the transition from deceleration to acceleration is derived to be z{sub t}=0.36{sub -0.08}{sup +0.23}. The combined data is also applied to find out the geometry of the Universe, and we find that at the 3{sigma} confidence level, vertical bar {omega}{sub k} vertical bar < or approx. 0.05 for the simple one-parameter dark energy model, and -0.064<{omega}{sub k}<0.028 for the {lambda}CDM model.« less
  • We introduce a simple parametrization of the dark energy equation of state, {omega}, which is motivated from theory and recent experimental data. The theory is related to the tracker solution to alleviate the fine-tuning problem. Recent experimental data indicates that the present value of {omega} is close to -1. We analyze the evolution of {omega} from the separation of CMB peaks and the time variation of the fine structure constant, {alpha}. We find that -1.00{<=}{omega}{sup (0)}{<=}-0.971{sub -0.027}{sup +0.017} and 1.76{sub -0.42}{sup +0.29}x10{sup -4}{<=}(d{omega}/dz){sub z=0}{<=}0.041{sub -0.037}{sup +=} 0{sup .016} at 95% confidence level.
  • We study the dark energy equation of state as a function of redshift in a nonparametric way, without imposing any a priori w(z) (ratio of pressure over energy density) functional form. As a check of the method, we test our scheme through the use of synthetic data sets produced from different input cosmological models that have the same relative errors and redshift distribution as the real data. Using the luminosity-time L{sub X} -T{sub a} correlation for gamma-ray burst (GRB) X-ray afterglows (the Dainotti et al. correlation), we are able to utilize GRB samples from the Swift satellite as probes ofmore » the expansion history of the universe out to z ≈ 10. Within the assumption of a flat Friedmann-Lemaître-Robertson-Walker universe and combining supernovae type Ia (SNeIa) data with baryonic acoustic oscillation constraints, the resulting maximum likelihood solutions are close to a constant w = –1. If one imposes the restriction of a constant w, we obtain w = –0.99 ± 0.06 (consistent with a cosmological constant) with the present-day Hubble constant as H {sub 0} = 70.0 ± 0.6km s{sup –1} Mpc{sup –1} and density parameter as Ω{sub Λ0} = 0.723 ± 0.025, while nonparametric w(z) solutions give us a probability map that is centered at H {sub 0} = 70.04 ± 1km s{sup –1} Mpc{sup –1} and Ω{sub Λ0} = 0.724 ± 0.03. Our chosen GRB data sample with a full correlation matrix allows us to estimate the amount, as well as quality (errors), of data needed to constrain w(z) in the redshift range extending an order of magnitude beyond the farthest SNeIa measured.« less