Looking out for the Galileon in the nanohertz gravitational wave sky

Abstract

We study the polarizations induced by the Galileon as a stochastic gravitational wave background in the cross correlated power in a pulsar timing array. Working within Galileon gravity, we first show that the scalar gravitational wave signature of the Galileon is encoded solely in its effective mass, which is controlled by the bare mass, conformal coupling, and a tadpole. Then, we study the phenomenology of the Galileon induced scalar polarizations and place observational constraints on these using the present NANOGrav data set. Our results feature longitudinal spatial correlation, indicative of a $10^{-22}$ eV {subluminal} Galileon, and show the Galileon polarizations as a statistically compelling source of the observed spatial correlation across millisecond pulsars, if there is any.

arXiv comment6 pages + refs + supp, 4 figures, 1 table, v3: to appear in PLB, our codes in https://github.com/reggiebernardo/galileon_pta

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• Constraining gravitational wave propagation using pulsar timing array correlations
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• Search for Non-Tensorial Gravitational-Wave Backgrounds in the NANOGrav 15-Year Data Set
• Testing gravity with cosmic variance-limited pulsar timing array correlations
• Beyond the Hellings-Downs curve: Non-Einsteinian gravitational waves in pulsar timing array correlations
• Charting the Nanohertz Gravitational Wave Sky with Pulsar Timing Arrays
• Correlations for an anisotropic polarized stochastic gravitational wave background in pulsar timing arrays
• Toward a test of Gaussianity of a gravitational wave background
• Tadpole Cosmology: Milne Solution as a Cosmological Constant Hideout