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IR/UV mixing from local similarity maps of scalar non-Hermitian field theories (2022)
Journal Article
Chernodub, M. N., & Millington, P. (2022). IR/UV mixing from local similarity maps of scalar non-Hermitian field theories. Physical Review D, 105(7), Article 076020. https://doi.org/10.1103/physrevd.105.076020

We propose to "gauge"the group of similarity transformations that acts on a space of non-Hermitian scalar theories. We introduce the "similarity gauge field,"which acts as a gauge connection on the space of non-Hermitian theories characterized by (an... Read More about IR/UV mixing from local similarity maps of scalar non-Hermitian field theories.

Non-Hermiticity: a new paradigm for model building in particle physics (2022)
Journal Article
Millington, P. (2022). Non-Hermiticity: a new paradigm for model building in particle physics. Proceedings of Science, 398, Article 735. https://doi.org/10.22323/1.398.0735

Non-Hermitian quantum theories have been applied in many other areas of physics. In this note, I will briefly review recent developments in the formulation of non-Hermitian quantum field theories, highlighting features that are unique compared to Her... Read More about Non-Hermiticity: a new paradigm for model building in particle physics.

Fifth forces and broken scale symmetries in the Jordan frame (2022)
Journal Article
Copeland, E. J., Millington, P., & Sevillano Muñoz, S. (2022). Fifth forces and broken scale symmetries in the Jordan frame. Journal of Cosmology and Astroparticle Physics, 2022(02), Article 016. https://doi.org/10.1088/1475-7516/2022/02/016

We study the origin of fifth forces in scalar-tensor theories of gravity in the so-called Jordan frame, where the modifications to the gravitational sector are manifest. We focus on theories of Brans-Dicke type in which an additional scalar field is... Read More about Fifth forces and broken scale symmetries in the Jordan frame.

Benchmarking regulator-sourced 2PI and average 1PI flow equations in zero dimensions (2021)
Journal Article
Millington, P., & Saffin, P. M. (2021). Benchmarking regulator-sourced 2PI and average 1PI flow equations in zero dimensions. Journal of Physics A: Mathematical and Theoretical, 54(46), Article 465401. https://doi.org/10.1088/1751-8121/ac2d00

We elucidate the regulator-sourced 2PI and average 1PI approaches for deriving exact flow equations in the case of a zero dimensional quantum field theory, wherein the scale dependence of the usual renormalisation group evolution is replaced by a sim... Read More about Benchmarking regulator-sourced 2PI and average 1PI flow equations in zero dimensions.

Erratum: Alternative flow equation for the functional renormalization group [Phys. Rev. D 100, 101702(R) (2019)] (2021)
Journal Article
Alexander, E., Millington, P., Nursey, J., & Saffin, P. M. (2021). Erratum: Alternative flow equation for the functional renormalization group [Phys. Rev. D 100, 101702(R) (2019)]. Physical Review D, 104(6), Article 069906. https://doi.org/10.1103/physrevd.104.069906

We correct the functional identity reported in our paper for the inverse two-point function, as obtained from the 2PI effective action. The original conclusions are otherwise unaffected. The 2PI effective action is convex with respect to the variable... Read More about Erratum: Alternative flow equation for the functional renormalization group [Phys. Rev. D 100, 101702(R) (2019)].

Fifth-force screening around extremely compact sources (2021)
Journal Article
Burrage, C., Elder, B., Millington, P., Saadeh, D., & Thrussell, B. (2021). Fifth-force screening around extremely compact sources. Journal of Cosmology and Astroparticle Physics, 2021(August 2021), Article JCAP08(2021)052. https://doi.org/10.1088/1475-7516/2021/08/052

Many non-linear scalar field theories possess a screening mechanism that can suppress any associated fifth force in dense environments. As a result, these theories can evade local experimental tests of new forces. Chameleon-like screening, which occu... Read More about Fifth-force screening around extremely compact sources.

Statistics on Lefschetz thimbles: Bell/Leggett-Garg inequalities and the classical-statistical approximation (2021)
Journal Article
Millington, P., Mou, Z., Saffin, P. M., & Tranberg, A. (2021). Statistics on Lefschetz thimbles: Bell/Leggett-Garg inequalities and the classical-statistical approximation. Journal of High Energy Physics, 2021(3), Article 77. https://doi.org/10.1007/jhep03%282021%29077

Inspired by Lefschetz thimble theory, we treat Quantum Field Theory as a statistical theory with a complex Probability Distribution Function (PDF). Such complex-valued PDFs permit the violation of Bell-type inequalities, which cannot be violated by a... Read More about Statistics on Lefschetz thimbles: Bell/Leggett-Garg inequalities and the classical-statistical approximation.

Discrete spacetime symmetries and particle mixing in non-Hermitian scalar quantum field theories (2020)
Journal Article
Alexandre, J., Ellis, J., & Millington, P. (2020). Discrete spacetime symmetries and particle mixing in non-Hermitian scalar quantum field theories. Physical Review D, 102(12), https://doi.org/10.1103/PhysRevD.102.125030

We discuss second quantization, discrete symmetry transformations, and inner products in free non-Hermitian scalar quantum field theories with PT symmetry, focusing on a prototype model of two complex scalar fields with anti-Hermitian mass mixing. Wh... Read More about Discrete spacetime symmetries and particle mixing in non-Hermitian scalar quantum field theories.

Fifth forces and discrete symmetry breaking (2020)
Journal Article
Millington, P. (2020). Fifth forces and discrete symmetry breaking. Journal of Physics: Conference Series, 1586, Article 012024. https://doi.org/10.1088/1742-6596/1586/1/012024

Modifications of general relativity often involve coupling additional scalar fields to the Ricci scalar, leading to scalar-tensor theories of Brans-Dicke type. If the additional scalar fields are light, they can give rise to long-range fifth forces,... Read More about Fifth forces and discrete symmetry breaking.

Symmetry properties of non-Hermitian PT-symmetric quantum field theories (2020)
Journal Article
Millington, P. (2020). Symmetry properties of non-Hermitian PT-symmetric quantum field theories. Journal of Physics: Conference Series, 1586, Article 012001. https://doi.org/10.1088/1742-6596/1586/1/012001

We describe recent progress in understanding the continuous symmetry properties of non-Hermitian, ${\mathscr{PT}}$-symmetric quantum field theories. Focussing on a simple non-Hermitian theory composed of one complex scalar and one complex pseudoscala... Read More about Symmetry properties of non-Hermitian PT-symmetric quantum field theories.

PT-symmetric non-Hermitian quantum field theories with supersymmetry (2020)
Journal Article
Millington, P., Alexandre, J., & Ellis, J. (2020). PT-symmetric non-Hermitian quantum field theories with supersymmetry. Physical Review D, 101(8), https://doi.org/10.1103/physrevd.101.085015

We formulate supersymmetric non-Hermitian quantum field theories with PT symmetry, starting with free chiral boson/fermion models and then including trilinear superpotential interactions. We consider models with both Dirac and Majorana fermions, anal... Read More about PT-symmetric non-Hermitian quantum field theories with supersymmetry.

Alternative flow equation for the functional renormalization group (2019)
Journal Article
Alexander, E., Millington, P., Nursey, J., & Saffin, P. M. (2019). Alternative flow equation for the functional renormalization group. Physical Review D, 100(10), Article 101702(R). https://doi.org/10.1103/physrevd.100.101702

We derive an alternative to the Wetterich-Morris-Ellwanger equation by means of the two-particle irreducible (2PI) effective action, exploiting the method of external sources due to Garbrecht and Millington. The latter allows the two-point source of... Read More about Alternative flow equation for the functional renormalization group.

Open quantum dynamics induced by light scalar fields (2019)
Journal Article
Burrage, C., Käding, C., Millington, P., & Minár, J. (2019). Open quantum dynamics induced by light scalar fields. Physical Review D, 100(7), Article 076003. https://doi.org/10.1103/PhysRevD.100.076003

We consider the impact of a weakly coupled environment comprising a light scalar field on the open dynamics of a quantum test mass, resulting in a master equation for the test mass that features corrections to the coherent dynamics, as well as decohe... Read More about Open quantum dynamics induced by light scalar fields.

Influence functionals, decoherence and conformally coupled scalars (2019)
Journal Article
Burrage, C., Käding, C., Millington, P., & Minář, J. (2019). Influence functionals, decoherence and conformally coupled scalars. Journal of Physics: Conference Series, 1275(1), Article 012041. https://doi.org/10.1088/1742-6596/1275/1/012041

Some of the simplest modifications to general relativity involve the coupling of additional scalar fields to the scalar curvature. By making a Weyl rescaling of the metric, these theories can be mapped to Einstein gravity with the additional scalar f... Read More about Influence functionals, decoherence and conformally coupled scalars.

Visualising quantum effective action calculations in zero dimensions (2019)
Journal Article
Millington, P., & Saffin, P. M. (2019). Visualising quantum effective action calculations in zero dimensions. Journal of Physics A: Mathematical and Theoretical, 52(40), Article 405401. https://doi.org/10.1088/1751-8121/ab37e6

© 2019 IOP Publishing Ltd. We present an explicit treatment of the two-particle-irreducible (2PI) effective action for a zero-dimensional quantum field theory. The advantage of this simple playground is that we are required to deal only with function... Read More about Visualising quantum effective action calculations in zero dimensions.

Corrigendum: Quasi-normal modes and fermionic vacuum decay around a Kerr black hole (2019 Class. Quantum Grav. 36 035005) (2019)
Journal Article
Coutant, A., & Millington, P. (2019). Corrigendum: Quasi-normal modes and fermionic vacuum decay around a Kerr black hole (2019 Class. Quantum Grav. 36 035005). Classical and Quantum Gravity, 36(19), 1-2. https://doi.org/10.1088/1361-6382/ab3a23

© 2019 IOP Publishing Ltd Printed in the UK. Due to a mismatch of conventions, some errors arose in the discussion of the electric toy model and the corresponding figure, which we correct herein. We also correct two other minor oversights and provide... Read More about Corrigendum: Quasi-normal modes and fermionic vacuum decay around a Kerr black hole (2019 Class. Quantum Grav. 36 035005).

Gauge invariance and the Englert-Brout-Higgs mechanism in non-Hermitian field theories (2019)
Journal Article
Alexandre, J., Ellis, J., Millington, P., & Seynaeve, D. (2019). Gauge invariance and the Englert-Brout-Higgs mechanism in non-Hermitian field theories. Physical Review D, 99(7), 1-9. https://doi.org/10.1103/physrevd.99.075024

We discuss PT-symmetric Abelian gauge field theories as well as their extension to the Englert-Brout-Higgs mechanism for generating a mass for a vector boson. Gauge invariance is not straightforward, and we discuss the different related problems as w... Read More about Gauge invariance and the Englert-Brout-Higgs mechanism in non-Hermitian field theories.

Symmetron scalar fields: modified gravity, dark matter, or both? (2019)
Journal Article
Burrage, C., Copeland, E. J., Käding, C., & Millington, P. (2019). Symmetron scalar fields: modified gravity, dark matter, or both?. Physical Review D, 99(4), Article 043539. https://doi.org/10.1103/physrevd.99.043539

Scalar fields coupled to gravity through the Ricci scalar have been considered both as dark matter candidates and as a possible modified gravity explanation for galactic dynamics. It has recently been demonstrated that the dynamics of baryonic matter... Read More about Symmetron scalar fields: modified gravity, dark matter, or both?.

Particle level screening of scalar forces in 1+1 dimensions (2019)
Journal Article
Burrage, C., Elder, B., & Millington, P. (2019). Particle level screening of scalar forces in 1+1 dimensions. Physical Review D, 99(2), Article 024045. https://doi.org/10.1103/physrevd.99.024045

We investigate how nonlinear scalar field theories respond to point sources. Taking the symmetron as a specific example of such a theory, we solve the nonlinear equation of motion in one spatial dimension for (i) an isolated point source and (ii) two... Read More about Particle level screening of scalar forces in 1+1 dimensions.