# Gravitational Absorption Lines

Andrea Palessandro, Martin S. Sloth

Research output: Contribution to journalJournal articleResearchpeer-review

### 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 language English 043504 Phys. Rev. D. 101 33 2470-0010 https://doi.org/10.1103/PhysRevD.101.043504 Published - 4. Feb 2020

### Fingerprint

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

### Cite this

Palessandro, Andrea ; Sloth, Martin S. / Gravitational Absorption Lines. In: Phys. Rev. D. 2020 ; Vol. 101.
@article{c8874b5a7b604738b079bb971d3a59b7,
title = "Gravitational Absorption Lines",
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.",
keywords = "hep-th, astro-ph.CO, gr-qc",
author = "Andrea Palessandro and Sloth, {Martin S.}",
year = "2020",
month = "2",
day = "4",
doi = "10.1103/PhysRevD.101.043504",
language = "English",
volume = "101",
journal = "Physical Review D",
issn = "2470-0010",
publisher = "American Physical Society",

}

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

TY - JOUR

T1 - Gravitational Absorption Lines

AU - Palessandro, Andrea

AU - Sloth, Martin S.

PY - 2020/2/4

Y1 - 2020/2/4

N2 - 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.

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.

KW - hep-th

KW - astro-ph.CO

KW - gr-qc

U2 - 10.1103/PhysRevD.101.043504

DO - 10.1103/PhysRevD.101.043504

M3 - Journal article

VL - 101

JO - Physical Review D

JF - Physical Review D

SN - 2470-0010

M1 - 043504

ER -