arXiv subjects

Roshna K

Publications and source records attributed to Roshna K.

4 recordsLinked to original sources

arXiv2026

Constraining dark energy models using Jackknife and Bootstrap resampling

Analyses of type Ia supernovae have helped us shed light on the existence and nature of dark energy. Most of these analyses have relied on Bayesian techniques. In this work, we employ resampling techniques, namely Jackknife and Bootstrap, together with generalised least squares, to analyse supernova data. We first calibrate these techniques using near-ideal mock data and versions of the PantheonPlus data, and compare their performance with Bayesian methods. We find that with near-ideal mock data, Jackknife can yield better constraints. We then apply these methods to constrain parameters of flat $\Lambda$CDM, $\Lambda$CDM, flat $w$CDM, $w$CDM, and flat $w_0\,w_a$CDM models from the PantheonPlus and SH0ES (PPS) data. We observe that constraints obtained with different techniques for three- and four-parameter models are largely consistent. We also find that the Hubble tension is less significant with constraints from the Jackknife. For instance, we find that Jackknife estimates $h\,=\,0.743\,\pm\,0.029$ from PPS data, making the Planck value well within $3\sigma$. Moreover, we estimate $h\,=\,0.678\,\pm\,0.052$ from PantheonPlus data when we only consider sources with $z > 0.01$, in which case there is no tension with the Planck estimate. These results highlight the importance of using multiple techniques while analysing data and warrant further investigation.

astro-ph.CO↗

arXiv2025

Power Suppression and Lensing Anomaly -- A phenomenological investigation

Primordial power spectra with low power at long wavelengths can alleviate lensing anomaly. However the extent to which data favours such a primordial spectra is not clear. In this work, we investigate power suppression and related mitigation of lensing anomaly with the help of phenomenological models which are valid over scales of interest. We consider simple extensions to nearly scale invariant power spectra such as those which includes running and running of running of spectral index. We perform Bayesian analysis of these models, which are agnostic about power suppression, with Planck legacy data and show that data tend to choose parameters which leads to power suppression at low multipoles. We then investigate the connection between power suppression and alleviation of lensing anomaly and show that lensing anomaly is mitigated the most in models with maximum suppression of power at low multipoles. We also analyse the significance of these findings using information criteria. These results are further analyzed in the light of Planck Release 4 data using CamSpec, HiLLiPoP and LoLLiPoP likelihoods in which departure of lensing parameter from one is significantly reduced. Furthermore, we investigate the ability of near-ultimate future CMB missions such as ECHO to put tighter constraints on these models and to settle the issue. We conclude that we can make stronger conclusions about the presence of power suppression in the future by studying such simple phenomenological models.

astro-ph.CO↗

arXiv2024

Viability of loop quantum cosmology at the level of bispectrum

Observations by Planck indicate that CMB anisotropies are consistent with predictions of nearly Gaussian primordial perturbations as the one generated in slow-roll inflation. On the other hand, loop quantum cosmology (LQC) generates a non-Gaussian bispectrum. In particular, calculations of primordial bispectrum generated in LQC shows that the non-Gaussianity function $f_{_{\rm NL}}(k_1,\, k_2,\, k_3)$ is highly scale-dependent and oscillatory at long wavelengths and is nearly scale-invariant as in slow-roll at small scales. We discuss the viability of such a non-Gaussian bispectrum in the light of observations by Planck. More specifically, we model the bispectrum generated in LQC and compute its imprints on the CMB bispectrum. We then show that the CMB bispectrum generated in LQC though non-Gaussian, due to its highly oscillatory nature, is similar to that generated in slow-roll inflation and hence consistent with the observations by Planck.

astro-ph.CO↗

arXiv2023

Estimation of imprints of the bounce in loop quantum cosmology on the bispectra of cosmic microwave background

Primordial non-Gaussianity has set strong constraints on models of the early universe. Studies have shown that Loop Quantum Cosmology (LQC), which is an attempt to extend inflationary scenario to planck scales, leads to a strongly scale dependent and oscillatory non-Gaussianity. In particular, the non-Gaussianity function $f_{_{\rm NL}} (k_1,\, k_2,\, k_3)$ generated in LQC, though similar to that generated during slow roll inflation at small scales, is highly scale dependent and oscillatory at long wavelengths. In this work, we investigate the imprints of such a primordial bispectrum in the bispectrum of Cosmic Microwave Background (CMB). Inspired by earlier works, we propose an analytical template for the primordial bispectrum in LQC. We write the template as a sum of strongly scale dependent and oscillatory part, which captures the contribution due to the bounce, and a part which captures the scale invariant behaviour similar to that of slow roll. We then compute the reduced bispectra of temperature and electric polarisation and their three-point cross-correlations corresponding to these two parts. We show that the contribution from the bounce to the reduced bispectrum is negligible compared to that from the scale-independent part. Thus, we conclude that the CMB bispectra generated in LQC will be similar to that generated in slow roll inflation. We conclude with a discussion of our results and its implications to LQC.

astro-ph.CO↗