arXiv subjects

Raka Dabhade

Publications and source records attributed to Raka Dabhade.

4 recordsLinked to original sources

arXiv2026

The Dilaton: A Natural Resolution to the Hubble Tension via Spontaneous Scale Symmetry Breaking

The statistical tension between early and late universe measurements of the Hubble constant ($H_0$) suggests that the dark sector is dynamical rather than static. We propose that this dynamics arises from a fundamental symmetry principle: the Spontaneous Breaking of Scale Invariance. We introduce the Dilaton ($\chi$), a Pseudo-Nambu-Goldstone Boson (PNGB) associated with dilatation symmetry breaking. We demonstrate that a simple quadratic mass term in the fundamental theory transforms, via conformal coupling to gravity, into a ''thawing'' exponential potential $V(\phi) \propto e^{-\lambda\phi}$ in the Einstein frame. Using recent Bayesian reconstructions of dark energy dynamics from Planck, Pantheon+, and SH0ES data, we constrain the potential slope to be $\lambda \approx 0.056$. We show that this observational value is not arbitrary but corresponds to a fundamental non-minimal coupling strength of $\xi \approx 7.8 \times 10^{-4}$. The Dilaton mechanism naturally generates the late-time equation of state evolution ($w_0 \approx -0.85$) required to alleviate the Hubble tension while protecting the field mass $m \sim H_0$ through approximate shift symmetry.

astro-ph.CO↗

arXiv2025

Investigating the Correlation between Dark Matter Content, Ages and Mass-to-Light Ratios in Spiral Galaxies

We present an empirical investigation into the relationship between galactic age and dark matter content across a sample of 16 nearby, well-resolved spiral galaxies. Using raw rotation curve data from IOA Tokyo's publicly available repository, we model each galaxy's mass distribution via a three-component decomposition (Hernquist bulge, exponential disk, and a Navarro-Frenk-White (NFW) dark matter halo) fit using Monte Carlo simulations. The onset of dark matter dominance was identified using the NFW scale radius, beyond which we computed the total enclosed mass via Keplerian dynamics. I-band luminosities for these regions were estimated using a calibrated Tully-Fisher relation, yielding precise mass-to-light (M/L) ratios. We further calculated dark matter mass and density using NFW profile equations, and galaxy ages were retrieved through an extensive literature survey of stellar population studies. Our analysis reveals strong positive correlations between galactic age and both dark matter mass (Pearson $r \approx 0.91$; Spearman $\rho \approx 0.93$) and density (Pearson $r \approx 0.91$; Spearman $\rho \approx 0.91$), as well as M/L ratios, suggesting a robust link between evolutionary history and dark matter build-up. These findings are in quantitative agreement with predictions from large-scale cosmological simulations that incorporate assembly bias and smooth accretion-dominated growth, reinforcing the view that older galaxies, having formed earlier in high-density peaks, have accumulated significantly more dark matter over cosmic time. Our results offer observational evidence for time-dependent dark matter assembly and establish galactic age as a meaningful tracer of halo evolution.

astro-ph.GA↗

arXiv2025

A First Order Filter for the Detection of Potentially Habitable Exoplanets

The search for potentially habitable exoplanets is a primary objective in modern astrophysics, yet the vast number of candidates discovered by missions like Kepler and TESS presents a significant challenge for detailed follow-up characterization. An efficient and reliable method for prioritizing the most promising targets is therefore essential. In this paper, we propose a novel first-order filter for identifying potentially habitable worlds based on a simple geometric ratio: the orbital semi-major axis to the stellar diameter ($d/D_s$). Using data from the NASA Exoplanet Archive, we demonstrate that the ideal value for this ratio is not constant, but is dependent on the host star's spectral class. We establish a tiered framework of ideal ratios, beginning with $\approx 108$ for G-type stars (anchored by the Earth-Sun system), and decreasing by a factor of two for K-type ($\approx 54$) and M-type ($\approx 27$) stars, respectively. Our analysis reveals a strong correlation, showing that exoplanets whose $d/D_s$ ratios are close to these empirically derived values consistently exhibit high Earth Similarity Index (ESI) scores. We propose that these tiered ratios represent "Habitability Main Sequences," analogous to the Hertzsprung-Russell diagram for stars, providing a valuable and straightforward tool for the astronomical community to rapidly screen large datasets and efficiently shortlist high-priority candidates for further investigation with next-generation observatories.

astro-ph.EP↗

arXiv2025

A Dynamical Scalar Field Model for Dark Energy: Addressing the Hubble Tension and Cosmic Evolution

We propose a dynamical dark energy model based on a canonical scalar field with a hybrid potential of the form $V(\phi) = V_{0}e^{-\lambda\phi} + V_{1}\phi^{n}$. We constrain the model's 11-dimensional parameter space using a comprehensive combination of cosmological data, including the Planck 2018 Cosmic Microwave Background (CMB) power spectra, Baryon Acoustic Oscillations (BAO), the Pantheon+ supernova sample, SH0ES and the matter power spectrum from SDSS. The model provides an excellent fit to the data, with a reduced chi-squared of $\chi^2_{\text{red}} = 0.989$, while successfully alleviating the Hubble constant tension. Our analysis yields a Hubble constant of $H_0 \approx 72.820$ km/s/Mpc, reducing the discrepancy between early and late-universe measurements. We find that the data favors a 'thawing' quintessence scenario, characterized by a potential slope parameter $\lambda \approx 0.056$. This small but non-zero slope drives a late-time deviation from $\Lambda$CDM ($w(z=0) \approx -0.85$) while preserving the standard expansion history at high redshifts. A model comparison using the Bayesian Information Criterion finds that the standard $\Lambda$CDM model is still slightly preferred ($\Delta\text{BIC} = 2.178$) due to its fewer parameters. Nevertheless, our results demonstrate that this hybrid potential model is a compelling, physically motivated alternative to a cosmological constant.

astro-ph.CO↗