Professor PAUL SAFFIN's Outputs (76)

Computing real-time quantum path integrals on Sewed, almost-Lefschetz thimbles (2025)
Journal Article
Mou, Z.-G., Saffin, P. M., & Tranberg, A. (2025). Computing real-time quantum path integrals on Sewed, almost-Lefschetz thimbles. Journal of High Energy Physics, 2025(3), Article 58. https://doi.org/10.1007/jhep03%282025%29058

We present a method to compute real-time path integrals numerically, by Monte-Carlo sampling on near-Lefschetz thimbles. We present a collection of tools based on the Lefschetz thimble methods, which together provide an alternative to existing method... Read More about Computing real-time quantum path integrals on Sewed, almost-Lefschetz thimbles.

Perturbative gravitational wave predictions for the real-scalar extended Standard Model (2025)
Journal Article
Gould, O., & Saffin, P. M. (2025). Perturbative gravitational wave predictions for the real-scalar extended Standard Model. Journal of High Energy Physics, 2025(3), Article 105. https://doi.org/10.1007/jhep03%282025%29105

We perform a state-of-the-art study of the cosmological phase transitions of the real-scalar extended Standard Model. We carry out a broad scan of the parameter space of this model at next-to-next-to-leading order in powers of couplings. We use effec... Read More about Perturbative gravitational wave predictions for the real-scalar extended Standard Model.

Black holes in multimetric gravity. II. Hairy solutions and linear stability of the non- and partially proportional branches (2025)
Journal Article
Wood, K., Saffin, P. M., & Avgoustidis, A. (2025). Black holes in multimetric gravity. II. Hairy solutions and linear stability of the non- and partially proportional branches. Physical Review D, 111(2), Article 024057. https://doi.org/10.1103/PhysRevD.111.024057

Owing to our work in part I of this series of papers, it is understood that the analytically known black hole solutions in the theory of ghost-free multimetric gravity can be split into three distinct classes and that one of these classes—the proport... Read More about Black holes in multimetric gravity. II. Hairy solutions and linear stability of the non- and partially proportional branches.

Perturbative gravitational wave predictions for the real scalar extended Standard Model, dataset (2024)
Data
(2024). Perturbative gravitational wave predictions for the real scalar extended Standard Model, dataset. [Data]. https://doi.org/10.5281/zenodo.14031506

This deposit contains data from a perturbative study of cosmological phase transitions in the real singlet scalar extension of the Standard Model (xSM). The data relates to the paper "Perturbative gravitational wave predictions for the real scalar ex... Read More about Perturbative gravitational wave predictions for the real scalar extended Standard Model, dataset.

de Sitter vacua in O(d,d) invariant cosmology (2024)
Journal Article
Liu, Y., Padilla, A., Saffin, P. M., & Smith, R. G. C. (2024). de Sitter vacua in O(d,d) invariant cosmology. Physical Review D, 110(6), Article 063522. https://doi.org/10.1103/physrevd.110.063522

We perform a thorough analysis of de Sitter solutions in O⁡(𝑑,𝑑) invariant cosmologies. Starting with a homogeneous and isotropic framework we examine conditions for the existence of such solutions to the vacuum field equations, nonperturbative in 𝛼′... Read More about de Sitter vacua in O(d,d) invariant cosmology.

Black holes in multimetric gravity (2024)
Journal Article
Wood, K., Saffin, P. M., & Avgoustidis, A. (2024). Black holes in multimetric gravity. Physical Review D, 109(12), Article 124006. https://doi.org/10.1103/physrevd.109.124006

We construct a wide class of black hole solutions to the general theory of ghost-free multimetric gravity in arbitrary spacetime dimension, extending and generalizing the known results in four-dimensional dRGT massive gravity and bigravity. The solut... Read More about Black holes in multimetric gravity.

Boson star superradiance (2024)
Journal Article
Gao, H.-Y., Saffin, P. M., Wang, Y.-J., Xie, Q.-X., & Zhou, S.-Y. (2024). Boson star superradiance. Science China Physics, Mechanics and Astronomy, 67(6), Article 260413. https://doi.org/10.1007/s11433-023-2357-4

Recently, it has been realized that in some systems internal space rotation can induce energy amplification for scattered waves, similar to rotation in real space. In particularly, it has been shown that energy extraction is possible for a Q-ball, a... Read More about Boson star superradiance.

Ringdowns for black holes with scalar hair: The large mass case (2024)
Journal Article
D’Addario, G., Padilla, A., Saffin, P. M., Sotiriou, T. P., & Spiers, A. (2024). Ringdowns for black holes with scalar hair: The large mass case. Physical Review D, 109(8), Article 084046. https://doi.org/10.1103/physrevd.109.084046

Deviations from general relativity can alter the quasinormal mode (QNM) ringdown of perturbed black holes. It is known that a shift-symmetric (hence massless) scalar can only introduce black hole hair if it couples to the Gauss-Bonnet invariant, in w... Read More about Ringdowns for black holes with scalar hair: The large mass case.

Quantum corrected Q-ball dynamics (2024)
Journal Article
Xie, Q.-X., Saffin, P. M., Tranberg, A., & Zhou, S.-Y. (2024). Quantum corrected Q-ball dynamics. Journal of High Energy Physics, 2024(1), Article 165. https://doi.org/10.1007/jhep01%282024%29165

The physics of individual Q-balls and interactions between multiple Q-balls are well-studied in classical numerical simulations. Interesting properties and phenomena have been discovered, involving stability, forces, collisions and swapping of charge... Read More about Quantum corrected Q-ball dynamics.

Q-Ball Superradiance (2023)
Journal Article
Saffin, P. M., Xie, Q.-X., & Zhou, S.-Y. (2023). Q-Ball Superradiance. Physical Review Letters, 131(11), Article 111601. https://doi.org/10.1103/physrevlett.131.111601

Q-balls are nontopological solitons that coherently rotate in field space. We show that these coherent rotations can induce superradiance for scattering waves, thanks to the fact that the scattering involves two coupled modes. Despite the conservatio... Read More about Q-Ball Superradiance.

Clockwork cosmology (2023)
Journal Article
Wood, K., Saffin, P. M., & Avgoustidis, A. (2023). Clockwork cosmology. Journal of Cosmology and Astroparticle Physics, 2023(07), Article 062. https://doi.org/10.1088/1475-7516/2023/07/062

The higher order generalisation of the clockwork mechanism to gravitational interactions provides a means to generate an exponentially suppressed coupling to matter from a fundamental theory of multiple interacting gravitons, without introducing larg... Read More about Clockwork cosmology.

Vertex functions and their flow equations from the 2PI effective action (2022)
Journal Article
Millington, P., & Saffin, P. M. (2022). Vertex functions and their flow equations from the 2PI effective action. Journal of Physics A: Mathematical and Theoretical, 55(43), Article 435402. https://doi.org/10.1088/1751-8121/ac99ae

By exploiting the convexity of the two-particle-irreducible effective action, we describe a procedure for extracting n-point vertex functions. This procedure is developed within the context of a zero-dimensional ‘quantum field theory’ and subsequentl... Read More about Vertex functions and their flow equations from the 2PI effective action.

Optimisation of Thimble simulations and quantum dynamics of multiple fields in real time (2022)
Journal Article
Woodward, S., Saffin, P. M., Mou, Z. G., & Tranberg, A. (2022). Optimisation of Thimble simulations and quantum dynamics of multiple fields in real time. Journal of High Energy Physics, 2022(10), Article 82. https://doi.org/10.1007/JHEP10%282022%29082

We apply the Generalised Thimble approach to the computation of exact path integrals and correlators in real-time quantum field theory. We first investigate the details of the numerical implementation and ways of optimizing the algorithm. We subseque... Read More about Optimisation of Thimble simulations and quantum dynamics of multiple fields in real time.

Charge-swapping Q-balls in a logarithmic potential and Affleck-Dine condensate fragmentation (2022)
Journal Article
Hou, S. Y., Saffin, P. M., Xie, Q. X., & Zhou, S. Y. (2022). Charge-swapping Q-balls in a logarithmic potential and Affleck-Dine condensate fragmentation. Journal of High Energy Physics, 2022(7), Article 60. https://doi.org/10.1007/JHEP07%282022%29060

We study charge-swapping Q-balls, a kind of composite Q-ball where positive and negative charges co-exist and swap with time, in models with a logarithmic potential that arises naturally in supersymmetric extensions of the Standard Model. We show tha... Read More about Charge-swapping Q-balls in a logarithmic potential and Affleck-Dine condensate fragmentation.

Gravitational collapse of quantum fields and Choptuik scaling (2022)
Journal Article
Berczi, B., Saffin, P. M., & Zhou, S.-Y. (2022). Gravitational collapse of quantum fields and Choptuik scaling. Journal of High Energy Physics, 2022(2), Article 183. https://doi.org/10.1007/jhep02%282022%29183

Gravitational collapse into a black hole has been extensively studied with classical sources. We develop a new formalism to simulate quantum fields forming a black hole. By choosing a convenient coherent state, this formalism taps into well-establish... Read More about Gravitational collapse of quantum fields and Choptuik scaling.

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)].

Gravitational collapse with quantum fields (2021)
Journal Article
Berczi, B., Saffin, P. M., & Zhou, S.-Y. (2021). Gravitational collapse with quantum fields. Physical Review D, 104(4), Article L041703. https://doi.org/10.1103/PhysRevD.104.L041703

Gravitational collapse into a black hole has been extensively studied with classical sources. We develop a new formalism to simulate quantum fields forming a black hole. This formalism utilizes well-established techniques used for classical collapse... Read More about Gravitational collapse with quantum fields.

Charge-Swapping Q-balls and Their Lifetimes (2021)
Journal Article
Xie, Q.-X., Saffin, P. M., & Zhou, S.-Y. (2021). Charge-Swapping Q-balls and Their Lifetimes. Journal of High Energy Physics, 2021(7), Article 62. https://doi.org/10.1007/jhep07%282021%29062

For scalar theories accommodating spherically symmetric Q-balls, there are also towers of quasi-stable composite Q-balls, called charge swapping Q-balls (CSQs). We investigate the properties, particularly the lifetimes, of these long-lived CSQs in 2+... Read More about Charge-Swapping Q-balls and Their Lifetimes.

Dipole radiation and beyond from axion stars in electromagnetic fields (2021)
Journal Article
Amin, M. A., Long, A. J., Mou, Z.-G., & Saffin, P. M. (2021). Dipole radiation and beyond from axion stars in electromagnetic fields. Journal of High Energy Physics, 2021(6), Article 182. https://doi.org/10.1007/jhep06%282021%29182

We investigate the production of photons from coherently oscillating, spatially localized clumps of axionic fields (oscillons and axion stars) in the presence of external electromagnetic fields. We delineate different qualitative behaviour of the pho... Read More about Dipole radiation and beyond from axion stars in electromagnetic fields.