Thesis
The QCD axion, generally
- Abstract:
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The parameter space to be probed in searches for the axion particle is vast and appears impractical unless more theoretical guidance is provided. This thesis explores the uses of generalised symmetries in identifying promising regions of parameter space for existing and novel experimental axion searches.
We consider the general form of the axion-photon coupling to all orders in the axion. We demonstrate that there exists a model-independent relationship between the axion-photon coupling and the axion mass through a non-invertible generalised symmetry of the axion, thus providing a correlation between the two quantities crucial to current axion searches.
We proceed by exploring the confinement of instantons. Motivated by the absence of global symmetries in quantum gravity, we demonstrate that the vacuum acts as a superconductor when a higher-form generalised symmetry of the particle dual to the axion is absent. In this superconducting phase, instantons are confined by the worldline action of a particle-like soliton travelling between the instantons. We calculate the cost of this additional worldline suppression, comment on the required particle spectrum, and relevance for the strong CP problem.
Finally, we study the minimal requirements to obtain axions of exponentially high quality while also being compatible with a post-inflationary scenario, thereby motivating axion searches in higher-mass regions. These ingredients occur in theories where an axion protected by a higher-form generalised symmetry mixes with the phase of a complex scalar field. We explore how these scenarios arise in extra-dimensional models, including heterotic string theory.
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- Files:
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(Preview, Dissemination version, pdf, 1.1MB, Terms of use)
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Authors
Contributors
+ Agarwal, P
- Institution:
- University of Oxford
- Division:
- MPLS
- Department:
- Physics
- Role:
- Supervisor
+ Prins Bernhard Cultuurfonds
More from this funder
- Funder identifier:
- https://ror.org/05j159997
- Grant:
- 40038041
- Programme:
- Cultuurfondsbeurs
+ Science and Technology Facilities Council
More from this funder
- Funder identifier:
- https://ror.org/057g20z61
- Grant:
- 2397217
- Programme:
- STFC Studenship
- DOI:
- Type of award:
- DPhil
- Level of award:
- Doctoral
- Awarding institution:
- University of Oxford
- Language:
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English
- Keywords:
- Subjects:
- Deposit date:
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2026-01-29
- ARK identifier:
Terms of use
- Copyright holder:
- Arthur Platschorre
- Copyright date:
- 2025
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