David Wilson
Simons Postdoctoral Fellow
Lloyd Building B2.19,
School of Mathematics,
Trinity College Dublin,
College Green,
Dublin
email: djwilson@maths.tcd.ie
phone: +353 1896 8491
dept fax: +353 1896 2282
Teaching
Research interests
I work in the field of hadron spectroscopy which can be understood using Quantum Chromodynamics (QCD), part of the Standard Model of Particle Physics. QCD is a stronglycoupled field theory at the energies where hadrons arise, meaning that perturbation does not apply, posing a significant calculational challenge. One method which has shown great promise in recent years is Lattice QCD, where the quantum fluctuations in a finite volume are sampled numerically using MonteCarlo methods, to extract finite volume spectra. Using a mapping originally derived by Lüscher and extended by many others, these finite volume energy levels can be used to constrain infinite volume hadron scattering amplitudes. My current research is on numerical extractions of coupledchannel scattering amplitudes, which are in turn used to understand hadron resonances as poles in the complex energy plane.
Career
2016present  Postdoc, School of Mathematics, Trinity College Dublin, Ireland 
20152016  Postdoc, DAMTP, University of Cambridge, UK 
20122015  Postdoc, Old Dominion University and Jefferson Lab, Virginia, USA 
20102012  Postdoc, Argonne National Laboratory, Illinois, USA 
20062010  PhD student, IPPP, University of Durham, UK 
Recent Research Highlights

Raúl A. Briceño, Jozef J. Dudek, Robert G. Edwards and David J. Wilson (for the Hadron Spectrum Collaboration).
Published in Phys.Rev.Lett. 118 (2017) no.2, 022002
A recent article with members of the Hadron Spectrum Collaboration was featured on the cover of Physical Review Letters.
In this article, we present for the first time a determination of the energy dependence of the isoscalar $\pi\pi$ elastic scattering phase shift within a firstprinciples numerical lattice approach to QCD. Hadronic correlation functions are computed including all required quark propagation diagrams, and from these the discrete spectrum of states in the finite volume defined by the lattice boundary is extracted. From the volume dependence of the spectrum, we obtain the
Swave phase shift up to the $K\bar{K}$ threshold. Calculations are performed at two values of the u,d quark mass corresponding to
$m_\pi=236,391$ MeV, and the resulting amplitudes are described in terms of a $\sigma$ meson which evolves from a bound state below the
$\pi\pi$ threshold at the heavier quark mass to a broad resonance at the lighter quark mass.


Graham Moir, Michael Peardon, Sinéad M. Ryan, Christopher E. Thomas and David J. Wilson (for the Hadron Spectrum Collaboration).
Published in JHEP 1610 (2016) 011
In this study, we present the first lattice QCD study of coupledchannel $D\pi$, $D\eta$ and $D_{s}\bar{K}$ scattering in isospin1/2 in three partial waves. Using distillation, we compute matrices of correlation functions with bases of operators capable of resolving both meson and mesonmeson contributions to the spectrum. These correlation matrices are analysed using a variational approach to extract the finitevolume energy eigenstates. Utilising Lüscher's method and its extensions, we constrain scattering amplitudes in $S$, $P$ and $D$wave as a function of energy. By analytically continuing the scattering amplitudes to complex energies, we investigate the $S$matrix singularities. Working at $m_\pi \approx 391$ MeV, we find a pole corresponding to a $J^{P} = 0^{+}$ nearthreshold bound state with a large coupling to $D\pi$. We also find a deeply bound $J^{P} = 1^{}$ state, and evidence for a $J^{P} = 2^{+}$ narrow resonance coupled predominantly to $D\pi$.


Raúl A. Briceño, Jozef J. Dudek, Robert G. Edwards, Christian J. Shultz, Christopher E. Thomas and David J. Wilson (for the Hadron Spectrum Collaboration).
Published in Phys.Rev. D93 (2016) no.11, 114508
In this paper, we present a determination of the $P$wave $\pi\pi\to\pi\gamma^\star$ transition amplitude from lattice quantum chromodynamics. Matrix elements of the vector current in a finitevolume are extracted from threepoint correlation functions, and from these we determine the infinitevolume amplitude using a generalization of the LellouchLüscher formalism. We determine the amplitude for a range of discrete values of the $\pi\pi$ energy and virtuality of the photon, and observe the expected dynamical enhancement due to the $\rho$ resonance. Describing the energy dependence of the amplitude, we are able to analytically continue into the complex energy plane and from the residue at the $\rho$ pole extract the $\rho\to \pi \gamma^\star$ transition form factor. This calculation, at $m_\pi\approx 400$ MeV, is the first to determine the form factor of an unstable hadron within a first principles approach to QCD.


Jozef J. Dudek, Robert G. Edwards and David J. Wilson (for the Hadron Spectrum Collaboration)
Published in Phys.Rev. D93 (2016) no.9, 094506
In this article, we present the first calculation of coupledchannel mesonmeson scattering in the isospin $=1$, $G$parity negative sector, with channels $\pi\eta$, $K\bar K$ and $\pi\eta^\prime$, in a firstprinciples approach to QCD. From the discrete spectrum of eigenstates in three volumes extracted from lattice QCD correlation functions we determine the energy dependence of the $S$matrix, and find that the $S$wave features a prominent cusplike structure in $\pi\eta \to \pi\eta$ close to $K\bar{K}$ threshold coupled with a rapid turn on of amplitudes leading to the $K\bar K$ finalstate. This behavior is traced to an $a_0(980)$like resonance, strongly coupled to both $\pi\eta$ and $K\bar K$, which is identified with a pole in the complex energy plane, appearing on only a single unphysical Riemann sheet. Consideration of $D$wave scattering suggests a narrow tensor resonance at higher energy.

Further published work and preprints can be found at
inspire and
arXiv.org.