Conservative Scattering of Reissner-Nordstr\"om Black Holes at Third Post-Minkowskian Order

Using a recently developed effective field theory formalism for extreme mass ratios [2308.14832], we present a calculation of charged black hole scattering at third post-Minkowskian order. The charges and masses are kept arbitrary, and the result interpolates from the scattering of Schwarzschild to extremal charged black holes, and beyond to charged particles in electrodynamics -- agreeing with previously reported results in all such limits. The computation of the radial action is neatly organized in powers of the mass ratio. The probe (0SF) contributions are readily computed by direct integration of the radial momentum, and we use the effective field theory to compute the subleading (1SF) contributions via background-field Feynman rules supplemented by an operator encoding recoil of the background. Together these contributions completely determine the conservative physics at order~$\mathcal{O}(G^{3})$.Comment: 36 pages, 3 figure

Gauge Invariant Propagators and States in Quantum Electrodynamics

We study gauge invariant states in QED, where states are understood in terms of data living on the boundary of gauge invariant path-integrals. This is done for both scalar and spinor QED, and for boundaries that are either time slices, or the boundaries of a 'causal diamond'. We discuss both the case where the gauge field falls off to zero at the boundaries, and the case of 'large gauge transformations', where it remains finite at the boundaries. The dynamics are discussed using the gauge-invariant propagator, describing motion of both the particles and the field between the boundaries. We demonstrate how the path-integral naturally generates a 'Coulomb-field' dressing factor for states living on time-slices, and how this is done without fixing any gauge. We show that the form of the dressing depends only on the nature of the boundaries. We also derive the analogous dressing for states defined on null infinity, showing both its Coulombic parts as well as soft-photon parts.Comment: 24 pages, 3 figure

Effective Field Theory for Extreme Mass Ratios

We derive an effective field theory describing a pair of gravitationally interacting point particles in an expansion in their mass ratio, also known as the self-force (SF) expansion. The 0SF dynamics are trivially obtained to all orders in Newton's constant by the geodesic motion of the light body in a Schwarzschild background encoding the gravitational field of the heavy body. The corrections at 1SF and higher are generated by perturbations about this configuration -- that is, the geodesic deviation of the light body and the fluctuation graviton -- but crucially supplemented by an operator describing the recoil of the heavy body as it interacts with the smaller companion. Using this formalism we compute new results at third post-Minkowskian order for the conservative dynamics of a system of gravitationally interacting massive particles coupled to a set of additional scalar and vector fields.Comment: 9 pages, 1 figur

Self-care support for children and adolescents with long-term conditions : the REfOCUS evidence synthesis

Background: Self-care support (e.g. education, training, peer/professional support) is intended to enhance the self-care capacities of children and young people, while simultaneously reducing the financial burden facing health-care systems. Objectives: To determine which models of self-care support for long-term conditions (LTCs) are associated with significant reductions in health utilisation and costs without compromising outcomes for children and young people. Design: Systematic review with meta-analysis. Population: Children and young people aged 0–18 years with a long-term physical or mental health condition (e.g. asthma, depression). Intervention: Self-care support in health, social care, educational or community settings. Comparator: Usual care. Outcomes: Generic/health-related quality of life (QoL)/subjective health symptoms and health service utilisation/costs. Design: Randomised/non-randomised trials, controlled before-and-after studies, and interrupted time series designs. Data sources: MEDLINE, EMBASE, PsycINFO, Cumulative Index to Nursing and Allied Health Literature, ISI Web of Science, NHS Economic Evaluation Database, The Cochrane Library, Health Technology Assessment database, Paediatric Economic Database Evaluation, IDEAS, reference scanning, targeted author searches and forward citation searching. All databases were searched from inception to March 2015. Methods: We conducted meta-analyses, simultaneously plotting QoL and health utilisation effects. We conducted subgroup analyses for evidence quality, age, LTC and intervention (setting, target, delivery format, intensity). Results: Ninety-seven studies reporting 114 interventions were included. Thirty-seven studies reported adequate allocation concealment. Fourteen were UK studies. The vast majority of included studies recruited children and young people with asthma (n = 66, 68%). Four per cent of studies evaluated ‘pure’ self-care support (delivered through health technology without additional contact), 23% evaluated facilitated self-care support (≤ 2 hours’/four sessions’ contact), 65% were intensively facilitated (≥ 2 hours’/four sessions’ contact) and 8% were case management (≥ 2 hours’ support with multidisciplinary input). Self-care support was associated with statistically significant, minimal benefits for QoL [effect size (ES) –0.17, 95% confidence interval (CI) –0.23 to –0.11], but lacked clear benefit for hospital admissions (ES –0.05, 95% CI –0.12 to 0.03). This finding endured across intervention intensities and LTCs. Statistically significant, minimal reductions in emergency use were observed (ES –0.11, 95% CI –0.17 to –0.04). The total cost analysis was limited by the small number of data. Subgroup analyses revealed statistically significant, minimal reductions in emergency use for children aged ≤ 13 years (ES –0.10, 95% CI –0.17 to –0.04), children and young people with asthma (ES –0.12, 95% CI –0.18 to –0.06) and children and young people receiving ≥ 2 hours per four sessions of support (ES –0.10, 95% CI –0.17 to –0.03). Preliminary evidence suggested that interventions that include the child or young person, and deliver some content individually, may optimise QoL effects. Face-to-face delivery may help to maximise emergency department effects. Caution is required in interpreting these findings. Limitations: Identification of optimal models of self-care support is challenged by the size and nature of evidence available. The emphasis on meta-analysis meant that a minority of studies with incomplete but potentially relevant data were excluded. Conclusions: Self-care support is associated with positive but minimal effects on children and young people’s QoL, and minimal, but potentially important, reductions in emergency use. On current evidence, we cannot reliably conclude that self-care support significantly reduces health-care costs. Future work: Research is needed to explore the short- and longer-term effects of self-care support across a wider range of LTCs. Study registration: This study is registered as PROSPERO CRD42014015452. Funding: The National Institute for Health Research Health Services and Delivery Research programme

A study of the quantum-to-classical transition in gravity, and a study of the consequences of constraints in gauge theory path-integrals

In this thesis we discuss various aspects of low energy quantum gravity from a number of different angles. The ultimate goal we have in mind is to prepare ourselves for the upcoming wave of low-energy experiments which may test quantum gravity. In the first part of this thesis we remain within "conventional'' quantum theory. We start with a study of quantum decoherence via the emission of low energy gravitational radiation. We find that after sufficiently long times this radiation can completely decohere a matter system. In studying decoherence we needed a better understanding of gauge invariance and physical states in path-integrals with prescribed boundary data. We generalize the standard Faddeev-Popov procedure to fit this purpose, and in doing so we better understand the nature of electric fields around quantum charges. The analogous work is also done in linearized quantum gravity. This language is useful for analyzing the debate around a recently proposed gravitational-entanglement experiment. We do such an analysis, and ultimately agree that these experiments indeed test conventional quantum gravity. As a tangential project we study the interactions of quarks in a background gluon condensate, and show how this can cause confinement. In the second part of the thesis we study an "alternative'' quantum gravity theory, the Correlated WorldLine (CWL) theory. We study the theory perturbatively, and also make use of a large-N expansion to study it non-perturbatively. We apply our results to physical systems: verifying that two-path systems experience "path-bunching'' which suppresses superpositions of massive objects. We also predict a frequency band in the microhertz range where tests of CWL involving massive objects are expected to see a signature.Science, Faculty ofPhysics and Astronomy, Department ofGraduat

Manifestly gauge invariant transition amplitudes and thermal influence functionals in QED and linearized gravity

Einstein’s theory of General Relativity tells us that gravity is not a force but rather it is the curvature of spacetime itself. Spacetime is a dynamical object evolving and interacting similar to any other system in nature. The equivalence principle requires everything to couple to gravity in the same way. Consequently, as a matter of principle it is impossible to truly isolate a system|it will always be interacting with the dynamical spacetime in which it resides. This may be detrimental for large mass quantum systems since interaction with an environment can decohere a quantum system, rendering it effectively classical. To understand the effect of a ‘spacetime environment’, we compute the Feynman-Vernon influence functional (IF), a useful tool for studying decoherence. We compute the IF for both the electromagnetic and linearized gravitational fields at finite temperature in a manifestly gauge invariant way. Gauge invariance is maintained by using a modification of the Faddeev-Popov technique which results in the integration over all gauge equivalent configurations of the system. As an intermediate step we evaluate the gauge invariant transition amplitude for the gauge fields in the presence of sources. When used as an evolution kernel the transition amplitude projects initial data onto a physical (gauge-invariant) subspace of the Hilbert space and time-evolves the states within that physical subspace. The states in this physical subspace satisfy precisely the same constraint equations which one implements in the constrained quantization method of Dirac. Thus we find that our approach is the path-integral equivalent of Dirac’s. In the gauge invariant computation it is clear that for gauge theories the appropriate separation between system and environment is not a) matter and gauge field, but rather b) matter (dressed with a coherent field) and radiation field. This implies that only the state of the radiation field can be traced out to obtain a reduced description of the matter. We stress the importance of gauge invariance and the implementation of constraints because it resolves the disagreement between results in reported recent literature in which influence functionals were computed in different gauges without consideration of constraints.Science, Faculty ofPhysics and Astronomy, Department ofGraduat

QCD Meets Gravity 2023

The standard approximations to the two-body problem in General Relativity include weak-field perturbation theory (“PN’’ and “PM’’) and a strong-field scheme which expands in powers of the mass ratio but retains all orders in G-Newton, ie. “self-force’’. I’ll discuss recent work which used inspiration from self-force to simplify perturbative computations. We introduce an effective field theory describing a pair of gravitationally interacting point particles in an expansion in their mass ratio. The leading (0SF) dynamics are trivially described by geodesic motion in curved spacetime and at higher SF orders the perturbations of the 0SF exact solution are accounted for by a small number of operators, eg. a recoil operator encoding backreaction onto the heavy body. Rather than building-up curved spacetime perturbatively, this approach leverages known non-perturbative solutions and unpacks them into very simple perturbative building blocks—suggesting a path towards simplified multi-loop integrands for higher PM orders. We’ll mention a variety of old and new two-loop results computed using this EFT