arXiv subjects

Balakrishna S. Haridasu

Publications and source records attributed to Balakrishna S. Haridasu.

23 records · Page 2Linked to original sources

arXiv2019

Constraints on field flows of quintessence dark energy

The quest for understanding the late-time acceleration is haunted by an immense freedom in the analysis of dynamical models for dark energy in extended parameter spaces. Often-times having no prior knowledge at our disposal, arbitrary choices are implemented to reduce the degeneracies between parameters. We also encounter this issue in the case of quintessence fields, where a scalar degree of freedom drives the late-time acceleration. In this study, we implement a more physical prescription, the \textit{flow} condition, to fine-tune the quintessence evolution for several field potentials. We find that this prescription agrees well with the most recent catalogue of data, namely supernovae type Ia, baryon acoustic oscillations, cosmic clocks and distance to last scattering surface, and it enables us to infer the initial conditions for the field, both potential and cosmological parameters. At $2σ$ we find stricter bounds on the potential parameters $f/m_{pl}>0.26$ and $n<0.15$ for the PNGB and IPL potentials, respectively, while constraints on cosmological parameters remain extremely consistent across all assumed potentials. By implementing information criteria to assess their ability to fit the data, we do not find any evidence against thawing models, which in fact are statistically equivalent to $Λ$CDM, and the freezing ones are moderately disfavoured. Through our analysis we place upper bounds on the slope of quintessence potentials, consequently revealing a strong tension with the recently proposed swampland criterion, finding the 2$σ$ upper bound of $λ\sim 0.31$ for the exponential potential.

astro-ph.CO↗

arXiv2018

An improved model-independent assessment of the late-time cosmic expansion

In the current work, we have implemented an extension of the standard Gaussian Process formalism, namely the Multi-Task Gaussian Process with the ability to perform a joint learning of several cosmological data simultaneously. We have utilised the "low-redshift" expansion rate data from Supernovae Type-Ia (SN), Baryon Acoustic Oscillations (BAO) and Cosmic Chronometers (CC) data in a joint analysis. We have tested several possible models of covariance functions and find very consistent estimates for cosmologically relevant parameters. In the current formalism, we also find provisions for heuristic arguments which allow us to select the best-suited kernel for the reconstruction of expansion rate data. We also utilised our method to account for systematics in CC data and find an estimate of $H_0 = 68.52^{+0.94 + 2.51 (sys)}_{-0.94} $ $\textrm{km/s Mpc}^{-1}$ and a corresponding $r_d = 145.61^{+2.82}_{ - 2.82 - 4.3 (sys)} $ Mpc as our primary result. Subsequently, we find constraints on the present deceleration parameter $q_0 = -0.52 \pm 0.06$ and the transition redshift $z_T = 0.64^{+0.12}_{-0.09}$. All the estimated cosmological parameters are found to be in good agreement with the standard $Λ$CDM scenario. Including the local model-independent $H_0$ estimate to the analysis we find $H_0 = 71.40^{ + 0.30 + 1.65 (sys)}_{- 0.30 } $ $\textrm{km/s Mpc}^{-1}$ and the corresponding $r_d = 141.29^{ + 1.31 }_{-1.31-2.63 (sys)}$ Mpc. Also, the constraints on $r_d H_0$ remain consistent throughout our analysis and also with the model-dependent CMB estimate. Using the $\mathcal{O}m(z)$ diagnostic, we find that the concordance model is very consistent within the redshift range $z \lesssim 2$ and mildly discrepant for $z \gtrsim 2$.

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arXiv2018

Isotropic vs. Anisotropic components of BAO data: a tool for model selection

We conduct a selective analysis of the isotropic ($D_V$) and anisotropic ($AP$) components of the most recent Baryon Acoustic Oscillations (BAO) data. We find that these components provide significantly different constraints and could provide strong diagnostics for model selection, also in view of more precise data to arrive. For instance, in the $Λ$CDM model, we find a mild tension of $\sim 2 σ$ for the $Ω_m$ estimates obtained using $D_V$ and $AP$ separately. Considering both $Ω_k$ and $w$ as free parameters, we find that the concordance model is in tension with the best-fit values provided by the BAO data alone at 2.2$σ$. We complemented the BAO data with the Supernova Ia (SNIa) and Observational \textit{Hubble} datasets to perform a joint analysis on the $Λ$CDM model and its standard extensions. By assuming $Λ$CDM scenario, we find that these data provide $H_0 = 69.4 \pm 1.7$ \text{km/s Mpc$^{-1} $} as the best-fit value for the present expansion rate. In the $kΛ$CDM scenario we find that the evidence for acceleration using the BAO data alone is more than $\sim 5.8σ$, which increases to $8.4 σ$ in our joint analysis.

astro-ph.CO↗

arXiv2018

Cosmological constraints from low-redshift data

In this paper we summarise the constraints that low-redshift data --such as supernovae Ia (SN Ia), baryon acoustic oscillations (BAO) and cosmic chronometers (CC)-- are able to set on the concordance model and its extensions, as well as on inhomogeneous but isotropic models. We provide a broad overlook into these cosmological scenarios and several aspects of data analysis. In particular, we review a number of systematic issues of SN Ia analysis that include magnitude correction techniques, selection bias and their influence on the inferred cosmological constraints. Furthermore, we examine the isotropic and anisotropic components of the BAO data and their individual relevance for cosmological model-fitting. We extend the discussion presented in earlier works regarding the inferred dynamics of cosmic expansion and its present rate from the low-redshift data. Specifically, we discuss the cosmological constraints on the accelerated expansion and related model-selections. In addition, we extensively talk about the Hubble constant problem, then focus on the low-redshift data constraint on $H_0$ that is based on CC. Finally, we present the way in which this result compares the two of high-redshift $H_0$ estimate and local (redshift zero) measurements that are in tension.

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arXiv2017

Strong evidence for an accelerating universe

A recent analysis of the Supernova Ia data claims a 'marginal' ($\sim3σ$) evidence for a cosmic acceleration. This result has been complemented with a non-accelerating $R_{h}=ct$ cosmology, which was presented as a valid alternative to the $Λ$CDM model. In this paper, we use the same analysis to show that a non-marginal evidence for acceleration is actually found. We compare the standard Friedmann models to the $R_{h}=ct$ cosmology by complementing SN Ia data with the Baryon Acoustic Oscillations, Gamma Ray Bursts and Observational Hubble datasets. We also study the power-law model which is a functional generalisation of $R_{h}=ct$. We find that the evidence for late-time acceleration is beyond refutable at a 4.56$σ$ confidence level from SN Ia data alone, and at an even stronger confidence level ($5.38σ$) from our joint analysis. Also, the non-accelerating $R_{h}=ct$ model fails to statistically compare with the $Λ$CDM having a $Δ(\text{AIC})\sim30$.

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