Browsing by Autor "Arjun Dey"

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    Galaxy-multiplet clustering from DESI DR2
    (Oxford University Press, 2025) Hanyue Wang; Daniel J. Eisenstein; J. Aguilar; S. P. Ahlen; D. Bianchi; David H. Brooks; T. Claybaugh; Axel de la Macorra; Arjun Dey; Biprateep Dey
    ABSTRACT We present an efficient estimator for higher order galaxy clustering using small groups of nearby galaxies, or multiplets. Using the Luminous Red Galaxy sample from the Dark Energy Spectroscopic Instrument (DESI) Data Release 2, we identify galaxy multiplets as discrete objects and measure their cross-correlations with the general galaxy field. Our results show that the multiplets exhibit stronger clustering bias as they trace more massive dark matter haloes than individual galaxies. When comparing the observed clustering statistics with the mock catalogues generated from the N-body simulation AbacusSummit, we find that the mocks underpredict multiplet clustering despite reproducing the galaxy two-point autocorrelation reasonably well. This discrepancy indicates that the standard Halo Occupation Distribution (HOD) model is insufficient to describe the properties of galaxy multiplets, revealing the greater constraining power of this higher order statistic on galaxy–halo connection and the possibility that multiplets are specific to additional assembly bias. We demonstrate that incorporating secondary biases into the HOD model improves agreement with the observed multiplet statistics, specifically by allowing galaxies to preferentially occupy haloes in denser environments. Our results highlight the potential of utilizing multiplet clustering, beyond traditional two-point correlation measurements, to break degeneracies in models describing the galaxy–dark matter connection.
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    Updated cosmological constraints on axion dark energy with DESI
    (American Physical Society, 2025) L. Arturo Ureña–López; F. Lozano-Rodríguez; J. O. Román-Herrera; José Edgar Madriz Aguilar; S. P. Ahlen; D. Bianchi; David J. Brooks; T. Claybaugh; Axel de la Macorra; Arjun Dey
    We present updated constraints on the parameters of an axion dark energy model, for which we took into account the properties of its characteristic potential and its full cosmological evolution. We show that the values of the axion parameters appear sufficiently constrained by the data, including the latest DESI DR1, and are consistent with the theoretical expectations of a field mass ${m}_{a}$ in the ultralight regime $\mathrm{log}({m}_{a}{c}^{2}/\mathrm{eV})\ensuremath{\simeq}\ensuremath{-}32.60\ifmmode\pm\else\textpm\fi{}0.12$, and an effective energy scale ${f}_{a}$ close to the reduced Planck energy $\mathrm{log}({f}_{a}/{M}_{\mathrm{Pl}})\ensuremath{\simeq}\ensuremath{-}0.28\ifmmode\pm\else\textpm\fi{}0.19$. Our results also support the idea of dynamical dark energy, although Bayesian evidence still favors the phenomenological dark energy model ${w}_{0}{w}_{a}$ over the axion dark energy, with the Bayes factor indicating moderate and weak strength of the evidence, respectively, when the models are compared to the cosmological constant $\mathrm{\ensuremath{\Lambda}}$. However, the results suggest that axion dark energy remains a well-motivated model and its parameters may be better constrained if the upcoming DESI data show further evidence for dynamical dark energy.