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Jeff Forshaw

Publications and source records attributed to Jeff Forshaw.

16 recordsLinked to original sources
arXiv2025

Towards a Manifestly Causal Approach to Particle Scattering

We introduce a new, probability-level approach to calculations in scalar field particle scattering. The approach involves the implicit summation over final states, which makes causality manifest since retarded propagators emerge naturally. Novel diagrams represent algebraic terms at the probability level, akin to Feynman diagrams at the amplitude level. We conjecture a list of rules that generate all probability-level diagrams for particle scattering processes in which one is fully inclusive over final states that contain no initial-state particles. These rules are confirmed using some fixed-order examples. The inclusivity and causal structure of this formalism may offer insights into the cancellation of infrared divergences if applied to gauge theory calculations.

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arXiv2025

A holographic analysis of the pion

Being simultaneously a bound state and a pseudo-Goldstone boson of chiral symmetry breaking, the pion is an ideal probe of the intertwined phenomena of confinement and chiral symmetry breaking in QCD. Here, we compute the low energy pion observables with light-front holography, taking into account longitudinal dynamics using an ansatz that explores the strong degeneracy of the `t Hooft and Li-Vary models as well as their underlying connection in $\mathrm{AdS}_3$ as recently noted by Vegh.

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arXiv2025

A new study of the Unruh effect

We revisit the Unruh effect within a general framework based on direct, probability-level calculations. We rederive the transition rate of a uniformly accelerating Unruh-DeWitt monopole detector coupled to a massive scalar field, from both the perspective of an inertial (Minkowski) observer and an accelerating (Rindler) observer. We show that, for a measurement at a finite time after the initial state is prepared, the two perspectives give the same transition rate. We confirm that an inertial detector in a thermal bath of Minkowski particles responds differently to the accelerated detector (which perceives a thermal bath of Rindler particles), except in the case of a massless field where there is agreement at all times. Finally, new numerical results for the transition rate are presented and explained, highlighting the transient effects caused by forcing the field to initially be in the Minkowski vacuum state.

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arXiv2024

A holographic analysis of the pion

Inspired by light-front holography, we compute the pion mass, charge radius, decay constant, electromagnetic form factor and electromagnetic transition form factor. To do so, we model the longitudinal quark dynamics using potentials due to 't Hooft and to Li & Vary. We find a longitudinal wavefunction that is rather more peaked about $x \sim 1/2$ than in previous studies. We also explore the strong degeneracy between these two potentials and conclude by noting that one scenario that accords well with the data also maps onto an equation previously noted by Vegh that describes the dynamics of a four-segmented string in $\mathrm{AdS}_3$.

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arXiv2017

Fock-space projection operators for semi-inclusive final states

We present explicit expressions for Fock-space projection operators that correspond to realistic final states in scattering experiments. Our operators automatically sum over unobserved quanta and account for non-emission into sub-regions of momentum space.

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arXiv2017

Working directly with probabilities in quantum field theory

We present a novel approach to computing transition probabilities in quantum field theory, which allows them to be written directly in terms of expectation values of nested commutators and anti-commutators of field operators, rather than squared matrix elements. We show that this leads to a diagrammatic expansion in which the retarded propagator plays a dominant role. As a result, one is able to see clearly how faster-than-light signalling is prevented between sources and detectors. Finally, we comment on potential implications of this approach for dealing with infra-red divergences.

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arXiv2016

Probabilities and signalling in quantum field theory

We present an approach to computing probabilities in quantum field theory for a wide class of source-detector models. The approach works directly with probabilities and not with squared matrix elements, and the resulting probabilities can be written in terms of expectation values of nested commutators and anti-commutators. We present results that help in the evaluation of these, including an expression for the vacuum expectation values of general nestings of commutators and anti-commutators in scalar field theory. This approach allows one to see clearly how faster-than-light signalling is prevented, because it leads to a diagrammatic expansion in which the retarded propagator plays a prominent role. We illustrate the formalism using the simple case of the much-studied Fermi two-atom problem.

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arXiv2015

Negative-frequency modes in quantum field theory

We consider a departure from standard quantum field theory, constructed so as to permit momentum eigenstates of both positive and negative energy. The resulting theory is intriguing because it brings about the cancellation of leading ultra-violet divergences and the absence of a zero-point energy. The theory gives rise to tree-level source-to-source transition amplitudes that are manifestly causal and consistent with standard S-matrix elements. It also leads to the usual result for the oblique corrections to the standard electroweak theory. Remarkably, the latter agreement relies on the breakdown of naive perturbation theory due to resonance effects. It remains to be shown that there are no problems with perturbative unitarity.

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arXiv2014

Manifest causality in quantum field theory with sources and detectors

We introduce a way to compute scattering amplitudes in quantum field theory including the effects of particle production and detection. Our amplitudes are manifestly causal, by which we mean that the source and detector are always linked by a connected chain of retarded propagators. We show how these amplitudes can be derived from a path integral, using the Schwinger-Keldysh "in-in" formalism. Focussing on phi-cubed theory, we confirm that our approach agrees with the standard S-matrix approach in the case of positive energy plane-wave scattering.

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arXiv2011

Extracting Higgs boson couplings using a jet veto

We show that the Higgs boson's effective couplings to gluons and to weak vector bosons can be extracted simultaneously from an analysis of Higgs plus dijet events by studying the dependence of the observed cross-section upon a third-jet veto.

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arXiv2007

Soft gluons in Higgs plus two jet production

We investigate the effects of an all order QCD resummation of soft gluon emissions for Higgs boson production in association with two hard jets. We consider both the gluon-gluon fusion and weak boson fusion processes and show how to resum a large part of the leading logarithms in the jet veto scale. Our resummation improves on previous analyses which also aim to include the effects of multiple soft gluon radiation. In addition we calculate the interference between weak boson fusion and gluon-gluon fusion and find that it is small.

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arXiv2004

Summary of the Activities of the Working Group I on High Energy and Collider Physics

This is a summary of the projects undertaken by the Working Group I on High Energy Collider Physics at the Eighth Workshop on High Energy Physics Phenomenology (WHEPP8) held at the Indian Institute of Technology, Mumbai, January 5-16, 2004. The topics covered are (i) Higgs searches (ii) supersymmetry searches (iii) extra dimensions and (iv) linear collider.

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arXiv2001

Double Diffractive Higgs and Di-photon Production at the Tevatron and LHC

We use the POMWIG Monte Carlo generator to predict the cross-sections for double diffractive higgs and di-photon production at the Tevatron and LHC. We find that the higgs production cross-section is too small to be observable at Tevatron energies, and even at the LHC observation would be difficult. Double diffractive di-photon production, however, should be observable within one year of Tevatron Run II.

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arXiv1999

Hard Colour Singlet Exchange at the Tevatron

We have performed a detailed phenomenological investigation of the hard colour singlet exchange process which is observed at the Tevatron in events which have a large rapidity gap between outgoing jets. We include the effects of multiple interactions to obtain a prediction for the gap survival factor. Comparing the data on the fraction of gap events with the prediction from BFKL pomeron exchange we find agreement provided that a constant value of alpha_s is used in the BFKL calculation. Moreover, the value of alpha_s is in line with that extracted from measurements made at HERA.

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