arXiv subjects

Shubham Barua

Publications and source records attributed to Shubham Barua.

8 recordsLinked to original sources

arXiv2026

Impact of CMB low-$\ell$ EE polarization data on dark energy parameterizations

Measurement of the optical depth to reionization ($\tau_\mathrm{reio}$) is largely driven by the large-scale EE polarization data of CMB ($\ell<30$). Removing the low-$\ell$ EE data potentially alleviates various cosmological tensions. In this work, we study the effect of the low-$\ell$ EE polarization measurements on the CPL, JBP and BA dark energy parameterizations using CMB data from Planck and ACT DR6, combined with DESI BAO and PantheonPlus compilation of Type Ia supernovae. We find that excluding low-$\ell$ EE data shifts $\tau_\mathrm{reio}$ and $A_s$ to higher values through the unbroken $A_s-\tau_\mathrm{reio}$ degeneracy with a $\sim(1.4-1.8)\sigma$ shift in $A_s$ for $\Lambda$CDM and JBP, and a milder $\sim 1\sigma$ shift for CPL and BA. The equation of state (EOS) for all three parameterizations moves towards the quintessence regime ($w(z) > -1$) upon exclusion of low-$\ell$ EE data, driven primarily by the strengthening of the $w_a-A_s$ and the $w_a-\tau_\mathrm{reio}$ correlations, with a small effect from the correlations of $w_0$ with $A_s$ and $\tau_\mathrm{reio}$. The most prominent effect occurs in JBP, where the EOS lies entirely within the quintessence regime at $1\sigma$ when excluding low-$\ell$ EE data. Model comparison through AIC shows positive evidence in favor of CPL and BA and weak evidence in favor of JBP, robust to the inclusion of low-$\ell$ EE data and CMB data used. DIC model comparison shows strong evidence in favor of CPL and BA when low-$\ell$ EE data is included, and positive evidence when it is excluded. For JBP, we get positive (weak) evidence when including (excluding) low-$\ell$ EE data over $\Lambda$CDM.

astro-ph.CO↗

arXiv2026

Probing cosmic anisotropy with galaxy clusters and supernovae

Using $\Lambda$CDM and Pad\'e-(2,1) cosmography, we study directional variations in the Hubble constant, $H_0$, using galaxy cluster and Type Ia Supernovae (from Pantheon Plus) by the hemisphere decomposition method. Since there is a degeneracy between $H_0$ and absolute magnitude $M_B$ for Supernovae, Cepheid host calibration is usually required to constrain $H_0$. Hence, in this work in order to complement the Cepheid host calibration in Supernovae, we also use calibrations based on galaxy cluster scaling relations. We find that there is a $\lesssim 1\sigma$ difference in $H_0$ variations when using galaxy clusters as calibrators compared to Cepheids highlighting that the variations in $H_0$ are robust across different calibration methods. Across all combinations of models and data sets used, we obtain a consistent deviation $\sim 2\sigma$ from isotropy. In nearly all cases, we notice that the maximum $\Delta H_0$ aligns with the CMB dipole direction.

astro-ph.CO↗

arXiv2025

Testing the cosmic distance duality relation using model-independent approach

In this work, we test the cosmic distance duality relation (CDDR) using the arbitrary redshift pivot Pad\'e-(2,1) expansion methodology developed in arXiv:2509.16196. This approach allows us to constrain cosmography parameters and test CDDR at any redshift. Further, it does not rely on data reconstructions or extrapolations of the cosmography parameters to higher redshifts. We employ observational data from the Dark Energy Spectroscopic Instrument (DESI) Baryon Acoustic Oscillation dataset, cosmic chronometers (CC), and Type Ia supernovae from the Pantheon Plus (PP) and Dark Energy Survey Year 5 (DESY5) compilations. We find no significant deviations from the standard CDDR relation in the range $0\lesssim z \lesssim 1$ when considering DESI$+r_d$ dataset in combination with PP$+$CC and DESY5$+$CC datasets. However, on imposing a Gaussian prior on $M_B \in \mathcal{N}(-19.253, 0.027)$ (instead of treating it as a free parameter) in the dataset combination PP$+$CC, we find CDDR violation at a level of $(3-5)\sigma.$

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arXiv2025

Cosmological Constraints on Neutrino Masses in a Second-Order CPL Dark Energy Model

Recent DESI results indicate a strong preference for dynamical dark energy (DE) when baryon acoustic oscillation (BAO) measurements are combined with supernovae (SNe) and cosmic microwave background (CMB) data using the Chevallier-Polarski-Linder (CPL) parameterization. We analyze the exponential (EXP) parameterization, which introduces a second-order correction to CPL. We determine and compare the 95% upper bounds on the sum of neutrino masses for three dark energy (DE) models -- $\Lambda$CDM, CPL, and EXP -- across four neutrino mass hierarchies (1 massive/2 massless, degenerate, normal, inverted) and multiple dataset combinations (CMB$+$BAO, CMB$+$BAO$+$PantheonPlus, CMB$+$BAO$+$DESY5), employing both Bayesian and frequentist frameworks with physical lower limits from oscillation experiments (0.059 eV and 0.11 eV). Our results show that CPL yields tighter ($\lesssim10$%) bounds compared to EXP. We further confirm earlier findings that neutrino mass constraints are only mildly sensitive to the assumed hierarchy and that the frequentist bounds are tighter than Bayesian ones. Furthermore, the imposed oscillation lower limits, the datasets used and the DE parameterizations play a crucial role in the inferred cosmological neutrino mass bounds. For the datasets, hierarchies, and DE parameterizations considered, we find no statistically significant evidence for nonzero neutrino mass consistent with oscillation lower limits.

astro-ph.CO↗

arXiv2025

On frequentist confidence intervals in a non-Gaussian regime

We study frequentist confidence intervals based on graphical profile likelihoods (Wilks' theorem, likelihood integration), and the Feldman-Cousins (FC) prescription, a generalisation of the Neyman belt construction, in a setting with non-Gaussian Markov chain Monte Carlo (MCMC) posteriors. Our simplified setting allows us to recycle the MCMC chain as an input in all methods, including mock simulations underlying the FC approach. We find all methods agree to within $10 \%$ in the close to Gaussian regime, but extending methods beyond their regime of validity leads to greater discrepancies. Importantly, we recover a $\sim 2 \sigma$ shift in cosmological parameters between low and high redshift cosmic chronometer data with the FC method, but only when one fits all parameters back to the mocks. We observe that fixing parameters, a common approach in the literature, risks underestimating confidence intervals.

astro-ph.CO↗

arXiv2025

Constraints on Dark Energy Models Using Late Universe Probes

We use late Universe probes - Type Ia Supernovae from the PantheonPlus compilation, Quasars, and Dark Energy Spectroscopic Instrument (DESI) Data Release 1 (DR1) BAO data - along with Cosmic Chronometers or Megamasers to constrain various dark energy parameterizations. These include the standard $\Lambda$CDM model ($w_0=-1,w_a=0$), as well as the Chevallier-Polarski-Linder (CPL), Barboza-Alcaniz (BA), Jassal-Bagla-Padmanabhan (JBP), Exponential (EXP), and Transitional Dark Energy (TDE) parameterizations. We find that across all parameterizations, the constrained values of $w_0$ and $w_a$ remain within $(1-2)\sigma$ of the standard $\Lambda$CDM model, irrespective of spatial curvature, dataset combinations, or prior choices. We find from Bayesian model comparison that $\Lambda$CDM remains the most favored model for both flat and non-flat cases, with results remaining robust under different priors. Across all dataset combinations, we reaffirm the fact that LRG1 and LRG2 data points from the DESI BAO dataset are responsible for driving the preference for dynamical dark energy.

astro-ph.CO↗

arXiv2025

Determination of Hubble constant from Megamaser Cosmology Project using Profile Likelihood

The Megamaser Cosmology Project inferred a value for the Hubble constant given by $H_0=73.9 \pm 3.0 $ km/sec/Mpc. This value was obtained using Bayesian inference by marginalizing over six nuisance parameters, corresponding to the velocities of the megamaser galaxy systems. We obtain an independent estimate of the Hubble constant with the same data using frequentist inference. For this purpose, we use profile likelihood to dispense with the aforementioned nuisance parameters. The frequentist estimate of the Hubble constant is given by $H_0=73.5^{+3.0}_{-2.9}$ km/sec/Mpc and agrees with the Bayesian estimate to within $0.2\sigma$, and both approaches also produce consistent confidence/credible intervals. Therefore, this analysis provides a proof-of-principle application of profile likelihood in dealing with nuisance parameters in cosmology, which is complementary to Bayesian analysis.

astro-ph.IM↗

arXiv2024

Effect of Peak Absolute Magnitude of Type Ia Supernovae and Sound Horizon Values on Hubble Tension using DESI results

We apply data-motivated priors on the peak absolute magnitude of Type Ia supernovae ($M$) and the sound horizon at the drag epoch ($r_d$), to study how the $M-r_d$ degeneracy affects low redshift measurements of the Hubble constant, and then compare these estimates to the Planck estimated value of the Hubble constant. We use the data from Pantheon$+$, Cosmic Chronometers, and the Dark Energy Spectroscopic Instrument Data Release 1 (DESI DR1) Baryon Acoustic Oscillations (BAO) results for this purpose. We reaffirm the fact that there is a degeneracy between $M$ and $r_d$, and modifying the $r_d$ values to reconcile the discrepancy in Hubble constant values also requires a change in the peak absolute magnitude $M$. For certain $M$ and $r_d$ priors, the discrepancy is found to reduce to be as low as (1.2-2) $\sigma$ when considering the spatially flat $\Lambda$CDM model. We also notice that for our datasets considered, the Gaussian prior combination of $M \in \mathcal{N} (-19.253,0.027)$ (obtained from SH0ES) and $r_d \in \mathcal{N} (147.05,0.3)$ Mpc (determined from Planck CMB measurements) is least favored as compared to other prior combinations for the $\Lambda$CDM model.

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