arXiv subjects

P. Millington

Publications and source records attributed to P. Millington.

4 recordsLinked to original sources

arXiv2025

Vortex stability in pseudo-Hermitian theories

Pseudo-Hermitian (including $\mathcal{PT}$-symmetric) field theories support phenomenology that cannot be replicated in standard Hermitian theories. We describe a concrete example in which the vortex solutions that are realised in a prototypical pseudo-Hermitian field theory exhibit a novel metastability, despite the model parameters residing within the naively stable regime of exact antilinear symmetry of the vacuum theory. This instability is identified analytically and confirmed through numerical simulations, and it arises from the small breaking of the underlying antilinear symmetry of the pseudo-Hermitian theory due to the presence of the topological defect. This leads to spacetime-dependent parameters in the equations of motion governing fluctuations around the vortex, inducing non-trivial exceptional-point structures and complex frequencies within their spectrum. Aside from offering intriguing possibilities for cosmology, this result serves to illustrate the ability to produce long-lived metastable configurations in pseudo-Hermitian field theories of relevance beyond cosmology and high energy physics.

hep-th↗

arXiv2024

Axion-Photon Mixing in 3D: Classical Equations and Geometric Optics

Light particle-photon mixing in magnetised plasmas plays a vital role in constraining the existence of new physics, especially axions, dark photons, and ultra-high-frequency gravitational waves. Recently, we derived an expression for the resonant conversion of axions to photons in inhomogeneous media using kinetic theory to derive photon transport equations. In this work, we show how the same expression for the conversion probability can be obtained from the classical wave equations of axion-electrodynamics by deriving an equivalent transport equation along the photon worldline. This result provides further corroboration of this expression for the resonant production of photons from light particles, which has also recently been supported by independent numerical simulations of full axion-electrodynamics. In addition, this new approach provides a more general expression that accounts for mixing away from resonance, which is integrated along the whole worldline of the photon in a way that naturally incorporates a curved photon trajectory relevant to refractive media where the photon and light-particle worldlines differ.

hep-ph↗

arXiv2023

Axion-Photon Conversion in 3D Media and Astrophysical Plasmas

With axions now a primary candidate for dark matter, understanding their indirect astrophysical signatures is of paramount importance. Key to this is the production of photons from axions in magnetised astrophysical plasmas. While simple formulae for axion-photon mixing in 1D have been sketched several decades ago, there has recently been renewed interest in robust calculations for this process in arbitrary 3D plasmas. These calculations are vital for understanding, amongst other things, the radio production from axion dark matter conversion in neutron stars, which may lead to indirect axion dark matter detection with current telescopes or future searches, e.g., by the SKA. In this paper, we derive the relevant transport equations in magnetised plasmas. These equations describe both the production and propagation of photons in an arbitrary 3D medium due to the resonant conversion of axions into photons. They also fully incorporate the refraction of photons, and we find no evidence for a conjectured phenomenon of dephasing. Our result is free of divergences that plagued previous calculations, and our kinetic theory description provides a direct link between ray tracing and the production mechanism. These results mark an important step toward solving one of the major open questions concerning indirect searches of axions in recent years, namely how to compute the photon production rate from axions in arbitrary 3D plasmas.

hep-ph↗

arXiv2021

EuCAPT White Paper: Opportunities and Challenges for Theoretical Astroparticle Physics in the Next Decade

Astroparticle physics is undergoing a profound transformation, due to a series of extraordinary new results, such as the discovery of high-energy cosmic neutrinos with IceCube, the direct detection of gravitational waves with LIGO and Virgo, and many others. This white paper is the result of a collaborative effort that involved hundreds of theoretical astroparticle physicists and cosmologists, under the coordination of the European Consortium for Astroparticle Theory (EuCAPT). Addressed to the whole astroparticle physics community, it explores upcoming theoretical opportunities and challenges for our field of research, with particular emphasis on the possible synergies among different subfields, and the prospects for solving the most fundamental open questions with multi-messenger observations.

astro-ph.HE↗