Scalar Čerenkov radiation from high-energy cosmic rays
Entity
UAM. Departamento de Física TeóricaPublisher
American Physical SocietyDate
2022-05-26Citation
10.1103/PhysRevD.105.104058
Physical Review D 105.10 (2022): 104058
ISSN
2470-0010 (print); 2470-0029 (online)DOI
10.1103/PhysRevD.105.104058Editor's Version
https://doi.org/10.1103/PhysRevD.105.104058Subjects
Gravitation; Dark Energy; Bimetric Theories; FísicaRights
© 2022 American Physical SocietyAbstract
As first noted by Robert Wagoner in the 1970s, if a scalar field is nonminimally coupled to the Ricci scalar and propagates at subluminal speeds, then there exists the possibility of scalar Cerenkov radiation from a moving particle. The mere observation of high-energy cosmic rays could in principle rule out the existence of such scalar fields since any particle moving faster than scalar perturbations would lose energy in the form of scalar waves until it moves slower than those. We compute in detail the energy loss to scalar waves and find that it scales with the square of the ultraviolet (UV) cutoff frequency of the effective field theory (EFT) of gravity. For dark-energy-motivated EFTs, the UV cutoff can be low, in which case that energy loss could always be negligible. In contrast, if viewed as a covariant theory valid at all scales or as an EFT valid at higher energies, perhaps even all the way up to the Planck scale, as may be the case if motivated by quantum-gravity perspectives, then the energy loss to scalar waves may diverge or become dramatically large. In this case, high-energy cosmic rays of extragalactic origin stringently constrain any conformally coupled scalar fields with noncanonical kinetic terms, although a minimum scalar phase velocity is required to trust the EFT
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Google Scholar:Dalang, Charles
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Fleury, Pierre Baptiste
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Lombriser, Lucas
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