We present a worldline representation of the one-loop effective action for a Dirac particle coupled to external scalar, pseudoscalar, vector and axialvector fields, which allows one to treat the real and the imaginary parts of the effective action in a unified manner, at the price of having a non-Hermitian Hamiltonian. Unlike other existing worldline representations, our new worldline action...
An $N-$photon dressed propagator in (s)QED at tree level and effective action to one-loop in an arbitrary homogeneous electromagnetic field are examined in a photon low-energy limit. On the line, in a Fock-Schwinger gauge for the $N-$photons, it is discussed how the photons resemble a superposition of homogeneous fields, in addition to the background field. On the loop and on the line, in both...
The worldline formalism is a powerful tool to explore the strong coupling regime of QCD. Together with the AdS/CFT correspondence it leads to powerful results, in particular about meson correlators and meson scattering.
Another application of the worldline formalism that I hope to report is the relation between 2d QCD and the string worldsheet.
If magnetic monopoles exist, they are produced in strong magnetic fields by the electromagnetic dual of the Schwinger pair creation process. This phenomenon can be described non-perturbatively using the worldline instanton approach, and therefore it avoids the problems the strength of the magnetic charge required by the Dirac quantisation condition poses to any perturbative calculations. I...
Affleck et al used worldline instantons to obtain an all-orders-in-$\alpha$ result for Schwinger pair production by a constant electric field.
Dunne and Schubert et al showed how to use instantons to obtain the probability for non-constant fields.
In both cases, and in most subsequent papers, the instantons are closed loops, which give probabilities integrated over particle momenta (and...
In standard uses of the worldline path integral formalism, Dirichlet or periodic boundary conditions are typically employed to calculate relevant quantities. However, when representing wave functions via path integrals, mixed boundary conditions emerge, where one end adheres to a Dirichlet or Neumann condition, while the other satisfies the opposite. Through straightforward examples from...
We will discuss how to use the wordline formalism to compute scattering and bound observables for the classical two-body problem in general relativity, with particular emphasis on the case of Kerr black hole solutions. First, new classical Dirac brackets will be introduced to streamline the calculation of scattering observables for spinning binaries. Then, we will study the geodesic solution...
The Worldline Quantum Field Theory (WQFT) formalism has proven itself a powerful tool for perturbatively calculating the physical observables involved in two-body gravitational scattering events — change in momentum, scattering angles, radiated energy and angular momentum. In this talk I will review the WQFT formalism and summarise this progress. In particular, I will discuss recent work on...
The interaction of quantum fields with classical backgrounds gives rise to several interesting effects. For the study of the non-perturbative ones, the application of suitable resummation techniques is essential.
In this talk we will review recent advances in the development of appropriate resummation techniques, with special emphasis on those related to the first quantised approach. In...
Supergeometric Quantum Field Theories (SG-QFTs) are theories that go beyond the standard supersymmetric framework, since they allow for general scalar-fermion field transformations on the configuration space of a supermanifold, without requiring an equality between bosonic and fermionic degrees of freedom. After revisiting previous considerations, we extend them by calculating the one-loop...
The worldline formalism has been found particularly suitable for calculations in QED in external fields, including effective actions, amplitudes as well as Schwinger pair-creation rates. Here I will give a short summary of what has been achieved in this context, focussing mostly on constant and plane-wave fields.
The rapid advance in gravitational wave detectors has spurred renewed interest in the two-body problem in general relativity. Two perturbative approaches based on quantum field theory have emerged, one based on scattering amplitudes and the other based on worldlines. We argue that the two approaches are equivalent at an intimate level. By systematic algebraic manipulations through the...
In this talk, I will provide a brief review of the reducible contributions
to QED amplitudes in a constant background field from the worldline
perspective. The focus will be on the missing piece in photon-graviton
conversion in a magnetic field. This process is typically studied at tree
level, but one-loop corrections involving scalars and spinors have also been
calculated. Unlike the...
Flying focus beams are exact solutions of the Maxwell equations with spatial focussing, a feature which is absent in plane waves. In the first instance, these flying focus solutions are complex-valued; unfortunately, taking the real part of this field results in background-coupled wave equations for particles interacting with the real background field that are complicated PDEs. In this talk,...
