First Search for Kaluza-Klein Gravitons and Radion Using Planck Data

Alexander P. Cassem; Soubhik Kumar

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arXiv · 2607.02651

First Search for Kaluza-Klein Gravitons and Radion Using Planck Data

Alexander P. Cassem·Soubhik Kumar

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Abstract

Heavy moduli and Kaluza-Klein (KK) gravitons from extra dimensions may evade terrestrial probes but can be produced during inflation, generating primordial non-Gaussianity (NG) through unavoidable couplings to density perturbations. In a warped five-dimensional (5D) model, we compute the full radion- and KK-graviton-mediated bispectra and perform the first search for these signals using Planck 2018 temperature and polarization data. We find no significant evidence for NG, with the maximum significance being $1.8\sigma$ for $m_{\rm KK}\approx 1.6H$. We also identify a 5D setup which naturally generates NG with $f_{\rm NL}\sim 1-50$, within the reach of future surveys.

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Alexander P. Cassem, Soubhik Kumar. 2026-07-02. First Search for Kaluza-Klein Gravitons and Radion Using Planck Data. https://arxiv.org/abs/2607.02651

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