Abstract
Massless chiral excitations can arise from the interactions between a fermion and an axion string, propagating along the string and allowing it to superconduct. The properties of these excitations, or zero modes, dictate how the string interacts with light and can thus have important phenomenological consequences. In this paper, we add a nowhere-vanishing Dirac mass for the fermion in the usual model of axion electrodynamics. We find that the zero modes exhibit an interesting phase structure in which they delocalize from the string’s core as the mass increases, up until a critical value past which they disappear. We study this structure from an analytic perspective, with explicit numerical solutions, and via anomaly inflow arguments. Finally, we derive the two-dimensional effective theory of the zero mode and its interactions with the four-dimensional gauge field and show how this effective theory breaks down as the zero modes delocalize.
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Acknowledgments
We are grateful to Clay Cordova, Nicolas Fernandez, Junwu Huang, Austin Joyce, Seth Koren, Ho Tat Lam, Cody Long, Rashmish Mishra, Matthew Reece, Shu-Heng Shao and Tanmay Vachaspati for useful conversations. We are also especially grateful to Matthew Reece for comments on the manuscript. HB, KF, SH and JS are supported in part by the DOE grant DE-SC0013607. KF and SH are also supported in part by the Alfred P. Sloan Foundation Grant No. G-2019-12504. HB, KF and JS are also supported in part by NASA Grant 80NSSC20K0506.
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Bagherian, H., Fraser, K., Homiller, S. et al. Zero modes of massive fermions delocalize from axion strings. J. High Energ. Phys. 2024, 79 (2024). https://doi.org/10.1007/JHEP05(2024)079
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DOI: https://doi.org/10.1007/JHEP05(2024)079