Gravitational Absorption Lines

Andrea Palessandro, Martin S. Sloth

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Abstract

We consider the gravitational analogue of Lyman-alpha absorption lines in astronomical spectroscopy. If Einstein gravity with minimally coupled matter is valid up to the Planck scale, quantum bound states absorb gravitons of a specific frequency with Planckian cross section, $\sigma_{\text{abs}} \approx l_p^2$. Consequently, one can show that gravitational absorption by bound states is inefficient in ordinary gravity. If observed, gravitational absorption lines would therefore constitute a powerful smoking gun of new exotic astrophysical bound states (near extremal bound states) or new gravitational physics, as well as give direct evidence of the quantized nature of the gravitational field. We provide, as an example of new gravitational physics near the Planck scale, a non-minimal coupling of the matter fields which breaks the equivalence principle on-shell. We lay out a model in which absorption lines in the primordial gravitational wave spectrum are produced as a consequence of this coupling.
Original languageEnglish
Article number043504
JournalPhys. Rev. D.
Volume101
Number of pages33
ISSN2470-0010
DOIs
Publication statusPublished - 4. Feb 2020

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astronomical spectroscopy
gravitation
physics
gravitons
gravitational waves
gravitational fields
equivalence
astrophysics
analogs
cross sections

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Palessandro, Andrea ; Sloth, Martin S. / Gravitational Absorption Lines. In: Phys. Rev. D. 2020 ; Vol. 101.
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Gravitational Absorption Lines. / Palessandro, Andrea; Sloth, Martin S.

In: Phys. Rev. D., Vol. 101, 043504, 04.02.2020.

Research output: Contribution to journalJournal articleResearchpeer-review

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T1 - Gravitational Absorption Lines

AU - Palessandro, Andrea

AU - Sloth, Martin S.

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AB - We consider the gravitational analogue of Lyman-alpha absorption lines in astronomical spectroscopy. If Einstein gravity with minimally coupled matter is valid up to the Planck scale, quantum bound states absorb gravitons of a specific frequency with Planckian cross section, $\sigma_{\text{abs}} \approx l_p^2$. Consequently, one can show that gravitational absorption by bound states is inefficient in ordinary gravity. If observed, gravitational absorption lines would therefore constitute a powerful smoking gun of new exotic astrophysical bound states (near extremal bound states) or new gravitational physics, as well as give direct evidence of the quantized nature of the gravitational field. We provide, as an example of new gravitational physics near the Planck scale, a non-minimal coupling of the matter fields which breaks the equivalence principle on-shell. We lay out a model in which absorption lines in the primordial gravitational wave spectrum are produced as a consequence of this coupling.

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