Black holes and Abelian instantons
- 1University of Washington
Abstract
A bstract : We argue that the electromagnetic θ -term is a physical parameter of the Standard Model coupled to gravity. Specifically, in the context of 4-dimensional Einstein-Maxwell theory we show that there exist Euclidean field configurations that have finite action, are asymptotically flat, and feature non-zero electromagnetic second Chern number. These “gravitational Abelian instantons” correspond to a dyonic extension of a Euclidean wormhole. We argue that these configurations should be included in the gravitational path integral, and that doing so generates a non-perturbative contribution to the vacuum energy density that is θ -dependent. We provide a Lorentzian interpretation of these instantons as capturing the effect of quantum fluctuations corresponding to pair production and annihilation of charged black holes. When θ is the expectation value of a dynamical axion field, the instantons presented here generate a potential for the axion, thereby breaking the axion shift symmetry. This provides yet another example of how quantum gravity violates global symmetries through the existence of black holes.
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BibTeX
@article{garcia2026black,
title = {{Black holes and Abelian instantons}},
author = {Isabel Garcia Garcia and Elliot Maderazo},
journal = {Journal of High Energy Physics},
year = {2026},
month = oct,
doi = {10.1007/jhep10(2026)029},
url = {https://link.springer.com/10.1007/JHEP10(2026)029},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Black holes and Abelian instantons
AU - Isabel Garcia Garcia
AU - Elliot Maderazo
PY - 2026
DA - 2026/10/02
JO - Journal of High Energy Physics
DO - 10.1007/jhep10(2026)029
UR - https://link.springer.com/10.1007/JHEP10(2026)029
AB - A bstract : We argue that the electromagnetic θ -term is a physical parameter of the Standard Model coupled to gravity. Specifically, in the context of 4-dimensional Einstein-Maxwell theory we show that there exist Euclidean field configurations that have finite action, are asymptotically flat, and feature non-zero electromagnetic second Chern number. These “gravitational Abelian instantons” correspond to a dyonic extension of a Euclidean wormhole. We argue that these configurations should be included in the gravitational path integral, and that doing so generates a non-perturbative contribution to the vacuum energy density that is θ -dependent. We provide a Lorentzian interpretation of these instantons as capturing the effect of quantum fluctuations corresponding to pair production and annihilation of charged black holes. When θ is the expectation value of a dynamical axion field, the instantons presented here generate a potential for the axion, thereby breaking the axion shift symmetry. This provides yet another example of how quantum gravity violates global symmetries through the existence of black holes.
SN - 1029-8479
ER -