All Outputs (72)

Black holes in self-tuning cubic Horndeski cosmology (2020)
Journal Article
Emond, W. T., Lehébel, A., & Saffin, P. M. (2020). Black holes in self-tuning cubic Horndeski cosmology. Physical Review D, 101(8), Article 084008. https://doi.org/10.1103/physrevd.101.084008

Observations of neutron star mergers in the late Universe have given significant restrictions to the class of viable scalar-tensor theories. In this paper we construct black holes within the “self-tuning” class of this restricted set, whereby the bar... Read More about Black holes in self-tuning cubic Horndeski cosmology.

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.

Quantum tunnelling, real-time dynamics and Picard-Lefschetz thimbles (2019)
Journal Article
Mou, Z.-G., Saffin, P. M., & Tranberg, A. (2019). Quantum tunnelling, real-time dynamics and Picard-Lefschetz thimbles. Journal of High Energy Physics, 2019(11), Article 135. https://doi.org/10.1007/jhep11%282019%29135

We follow up the work, where in light of the Picard-Lefschetz thimble approach, we split up the real-time path integral into two parts: the initial density matrix part which can be represented via an ensemble of initial conditions, and the dynamic pa... Read More about Quantum tunnelling, real-time dynamics and Picard-Lefschetz thimbles.

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.

Real-time quantum dynamics, path integrals and the method of thimbles (2019)
Journal Article
Mou, Z.-G., Saffin, P. M., Tranberg, A., & Woodward, S. (2019). Real-time quantum dynamics, path integrals and the method of thimbles. Journal of High Energy Physics, 2019(6), Article 94. https://doi.org/10.1007/jhep06%282019%29094

Direct numerical evaluation of the real-time path integral has a well-known sign problem that makes convergence exponentially slow. One promising remedy is to use Picard-Lefschetz theory to flow the domain of the field variables into the complex plan... Read More about Real-time quantum dynamics, path integrals and the method of thimbles.

Well-tempered cosmology (2019)
Journal Article
Emond, W. T., Li, C., Saffin, P. M., & Zhou, S.-Y. (2019). Well-tempered cosmology. Journal of Cosmology and Astroparticle Physics, 2019(05), Article 038. https://doi.org/10.1088/1475-7516/2019/05/038

We examine an approach to cosmology, known as Well-Tempering, that allows for a de Sitter phase whose expansion is independent of the cosmological constant. Starting from a generic scalar-tensor theory compatible with the recent gravitational wave ob... Read More about Well-tempered cosmology.

Dark Energy after GW170817 Revisited (2019)
Journal Article
Copeland, E. J., Kopp, M., Padilla, A., Saffin, P. M., & Skordis, C. (2019). Dark Energy after GW170817 Revisited. Physical Review Letters, 122(6), Article 061301. https://doi.org/10.1103/physrevlett.122.061301

We revisit the status of scalar-tensor theories with applications to dark energy in the aftermath of the gravitational wave signal GW170817 and its optical counterpart GRB170817A. At the level of the cosmological background, we identify a class of th... Read More about Dark Energy after GW170817 Revisited.

Higher order clockwork gravity (2018)
Journal Article
Niedermann, F., Padilla, A., & Saffin, P. M. (2018). Higher order clockwork gravity. Physical Review D, 98(10), Article 104014. https://doi.org/10.1103/physrevd.98.104014

We present a higher order generalisation of the clockwork mechanism starting from an underlying non-linear multigravity theory with a single scale and nearest neighbour ghost-free interactions. Without introducing any hierarchies in the underlying po... Read More about Higher order clockwork gravity.

Boltzmann equations for preheating (2018)
Journal Article
Emond, W. T., Millington, P., & Saffin, P. M. (2018). Boltzmann equations for preheating. Journal of Cosmology and Astroparticle Physics, 2018(09), Article 041. https://doi.org/10.1088/1475-7516/2018/09/041

We derive quantum Boltzmann equations for preheating by means of the density matrix formalism, which account for both the non-adiabatic particle production and the leading collisional processes between the produced particles. In so doing, we illustra... Read More about Boltzmann equations for preheating.

Rotating kinky braneworlds (2018)
Journal Article
Niedermann, F., & Saffin, P. M. (2018). Rotating kinky braneworlds. Journal of High Energy Physics, 2018(7), Article 183. https://doi.org/10.1007/jhep07%282018%29183

Cylindrical braneworlds have been used in the literature as a convenient way to resolve co-dimension-two branes. They are prevented from collapsing by a massless worldvolume field with non-trivial winding, but here we discuss another way of preventin... Read More about Rotating kinky braneworlds.

Simulations of cold electroweak baryogenesis: dependence on the source of CP-violation (2018)
Journal Article
Mou, Z.-G., Saffin, P. M., & Tranberg, A. (2018). Simulations of cold electroweak baryogenesis: dependence on the source of CP-violation. Journal of High Energy Physics, 2018(5), Article 197. https://doi.org/10.1007/JHEP05%282018%29197

We compute the baryon asymmetry created in a tachyonic electroweak symmetry breaking transition, focusing on the dependence on the source of effective CP-violation. Earlier simulations of Cold Electroweak Baryogenesis have almost exclusively consider... Read More about Simulations of cold electroweak baryogenesis: dependence on the source of CP-violation.

Simulations of Cold Electroweak Baryogenesis: quench from portal coupling to new singlet field (2018)
Journal Article
Mou, Z.-G., Saffin, P. M., & Tranberg, A. (2018). Simulations of Cold Electroweak Baryogenesis: quench from portal coupling to new singlet field. Journal of High Energy Physics, 2018(1), Article 103. https://doi.org/10.1007/JHEP01%282018%29103

We compute the baryon asymmetry generated from Cold Electroweak Baryogenesis, when a dynamical Beyond-the-Standard-Model scalar singlet field triggers the spinodal transition. Using a simple potential for this additional field, we match the speed of... Read More about Simulations of Cold Electroweak Baryogenesis: quench from portal coupling to new singlet field.

Recrudescence of massive fermion production by oscillons (2017)
Journal Article
Saffin, P. M. (in press). Recrudescence of massive fermion production by oscillons. Journal of High Energy Physics, 2017(7), Article 126. https://doi.org/10.1007/JHEP07%282017%29126

We bring together the physics of preheating, following a period of inflation, and the dynamics of non-topological solitons, namely oscillons. We show that the oscillating condensate that makes up an oscillon can be an efficient engine for producing h... Read More about Recrudescence of massive fermion production by oscillons.

Simulations of “tunnelling of the 3rd kind” (2017)
Journal Article
Mou, Z.-G., Saffin, P. M., Tognarelli, P., & Tranberg, A. (2017). Simulations of “tunnelling of the 3rd kind”. Journal of High Energy Physics, 2017(7), https://doi.org/10.1007/JHEP07%282017%29015

We consider the phenomenon of ``tunnelling of the 3rd kind" \cite{third}, whereby a magnetic field may traverse a classically impenetrable barrier by pair creation of unimpeded quantum fermions. These propagate through the barrier and generate a magn... Read More about Simulations of “tunnelling of the 3rd kind”.

Simulations of Cold Electroweak Baryogenesis: finding the optimal quench time (2017)
Journal Article
Mou, Z.-G., Saffin, P. M., & Tranberg, A. (2017). Simulations of Cold Electroweak Baryogenesis: finding the optimal quench time. Journal of High Energy Physics, 2017(7), https://doi.org/10.1007/JHEP07%282017%29010

We revisit the numerical computation of the baryon asymmetry from Cold
Electroweak Baryogenesis given the physical Higgs mass. We investigate the dependence of the asymmetry on the speed at which electroweak symmetry breaking takes place. The maximu... Read More about Simulations of Cold Electroweak Baryogenesis: finding the optimal quench time.

Simulations of Cold Electroweak Baryogenesis: hypercharge U(1) and the creation of helical magnetic fields (2017)
Journal Article
Mou, Z.-G., Saffin, P. M., & Tranberg, A. (2017). Simulations of Cold Electroweak Baryogenesis: hypercharge U(1) and the creation of helical magnetic fields. Journal of High Energy Physics, 2017(6), https://doi.org/10.1007/JHEP06%282017%29075

We perform numerical simulations of Cold Electroweak Baryogenesis, including for the first time in the Bosonic sector the full electroweak gauge group SU(2)×U(1) and CP-violation. We find that the maximum generated baryon asymmetry is reduced by a fa... Read More about Simulations of Cold Electroweak Baryogenesis: hypercharge U(1) and the creation of helical magnetic fields.

Highly excited strings I: Generating function (2017)
Journal Article
Skliros, D. P., Copeland, E. J., & Saffin, P. M. (in press). Highly excited strings I: Generating function. Nuclear Physics B, https://doi.org/10.1016/j.nuclphysb.2016.12.022

This is the first of a series of detailed papers on string amplitudes with highly excited strings (HES). In the present paper we construct a generating function for string amplitudes with generic HES vertex operators using a fixed-loop momentum forma... Read More about Highly excited strings I: Generating function.

Disformally self-tuning gravity (2016)
Journal Article
Emond, W. T., & Saffin, P. M. (in press). Disformally self-tuning gravity. Journal of High Energy Physics, 2016(3), https://doi.org/10.1007/JHEP03%282016%29161

We extend a previous self-tuning analysis of the most general scalar-tensor theory of gravity in four dimensions with second order field equations by considering a generalized coupling to the matter sector. Through allowing a disformal coupling to ma... Read More about Disformally self-tuning gravity.

The Parametrized Post-Newtonian-Vainshteinian formalism (2015)
Journal Article
Avilez-Lopez, A., Padilla, A., Saffin, P. M., & Skordis, C. (2015). The Parametrized Post-Newtonian-Vainshteinian formalism. Journal of Cosmology and Astroparticle Physics, 2015(6), Article 044. https://doi.org/10.1088/1475-7516/2015/06/044

Light degrees of freedom that modify gravity on cosmological scales must be "screened" on solar system scales in order to be compatible with data. The Vainshtein mechanism achieves this through a breakdown of classical perturbation theory, as large i... Read More about The Parametrized Post-Newtonian-Vainshteinian formalism.

Cold Baryogenesis from first principles in the two-Higgs doublet model with fermions (2015)
Journal Article
Mou, Z.-G., Saffin, P. M., & Tranberg, A. (2015). Cold Baryogenesis from first principles in the two-Higgs doublet model with fermions. Journal of High Energy Physics, 2015, https://doi.org/10.1007/JHEP06%282015%29163

We present a first-principles numerical computation of the baryon asymmetry in electroweak-scale baryogenesis. For the scenario of Cold Baryogenesis, we consider a one fermion-family reduced CP-violating two Higgs-doublet model, including a classical... Read More about Cold Baryogenesis from first principles in the two-Higgs doublet model with fermions.