Jeremy Green

Jeremy Green
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Jeremy Green
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High Energy Physics - Lattice (16)
 
High Energy Physics - Phenomenology (6)
 
Nuclear Theory (4)

Publications Authored By Jeremy Green

We report a calculation of the nucleon axial form factors $G_A^q(Q^2)$ and $G_P^q(Q^2)$ for all three light quark flavors $q\in\{u,d,s\}$ in the range $0\leq Q^2\lesssim 1.2\text{ GeV}^2$ using lattice QCD. This work was done using a single ensemble with pion mass 317 MeV and made use of the hierarchical probing technique to efficiently evaluate the required disconnected loops. Read More

We present high-statistics estimates of the isovector charges of the nucleon from four 2+1-flavor ensembles generated using Wilson-clover fermions with stout smearing and tree-level tadpole improved Symanzik gauge action at lattice spacings $a=0.114$ and $0.080$ fm and with $M_\pi \approx 315$ and 200 MeV. Read More

Results are presented from an ongoing study of the $\rho$ resonance. We use the distillation approach in order to create correlator matrices involving $\rho$ and $\pi\pi$ interpolators. The study is done in a centre-of-mass frame and several moving frames. Read More

We describe a lattice approach for directly computing momentum derivatives of nucleon matrix elements using the Rome method, which we apply to obtain the isovector magnetic moment and Dirac radius. We present preliminary results calculated at the physical pion mass using a 2HEX-smeared Wilson-clover action. For removing the effects of excited-state contamination, the calculations were done at three source-sink separations and the summation method was used. Read More

The anomalous magnetic moment of the muon currently exhibits a discrepancy of about three standard deviations between the experimental value and recent Standard Model predictions. The theoretical uncertainty is dominated by the hadronic vacuum polarization and the hadronic light-by-light (HLbL) scattering contributions, where the latter has so far only been fully evaluated using different models. To pave the way for a lattice calculation of HLbL, we present an expression for the HLbL contribution to $g-2$ that involves a multidimensional integral over a position-space QED kernel function in the continuum and a lattice QCD four-point correlator. Read More

We present a detailed analysis of methods to reduce statistical errors and excited-state contamination in the calculation of matrix elements of quark bilinear operators in nucleon states. All the calculations were done on a 2+1 flavor ensemble with lattices of size $32^3 \times 64$ generated using the rational hybrid Monte Carlo algorithm at $a=0.081$~fm and with $M_\pi=312$ MeV. Read More

We present preliminary results from a lattice QCD calculation of the H-dibaryon using two flavors of $\mathcal{O}(a)$ improved Wilson fermions. We employ local six-quark interpolating operators at the source with a combination of local six-quark and two-baryon operators at the sink with the appropriate quantum numbers of the H-dibaryon and its coupling to the two-baryon channels. We find that the two-baryon operators provide an improved overlap onto the ground state in comparison to the local six-quark operators. Read More

We report calculations of hadronic light-by-light scattering amplitudes via lattice QCD evaluation of Euclidean four-point functions of vector currents. These initial results include only the fully quark-connected contribution. Particular attention is given to the case of forward scattering, which can be related via dispersion relations to the $\gamma^* \gamma^* \to$ hadrons cross section, and thus allows lattice data to be compared with phenomenology. Read More

We perform a lattice QCD calculation of the hadronic light-by-light scattering amplitude in a broad kinematical range. At forward kinematics, the results are compared to a phenomenological analysis based on dispersive sum rules for light-by-light scattering. The size of the pion pole contribution is investigated for momenta of typical hadronic size. Read More

We report a direct lattice QCD calculation of the strange nucleon electromagnetic form factors $G_E^s$ and $G_M^s$ in the kinematic range $0 \leq Q^2 \lesssim 1.2\: {\rm GeV}^2$. For the first time, both $G_E^s$ and $G_M^s$ are shown to be nonzero with high significance. Read More

Recent progress in lattice QCD calculations of nucleon structure will be presented. Calculations of nucleon matrix elements and form factors have long been difficult to reconcile with experiment, but with advances in both methodology and computing resources, this situation is improving. Some calculations have produced agreement with experiment for key observables such as the axial charge and electromagnetic form factors, and the improved understanding of systematic errors will help to increase confidence in predictions of unmeasured quantities. Read More

We present early results from a lattice QCD study seeking a bound $H$-dibaryon using $N_f=2$ flavors of $O(a)$ improved Wilson fermions and a quenched strange quark. We compute a matrix of two-point functions using operators consisting of the two independent local products of six positive-parity-projected quarks with the appropriate quantum numbers, which belong to the singlet and 27-plet irreducible representations of flavor SU(3). To expand this basis, we also independently vary the quark-field smearing, and apply a new scheme to reduce the noise caused by smearing. Read More

We present nucleon observables - primarily isovector vector form factors - from calculations using 2+1 flavors of Wilson quarks. One ensemble is used for a dedicated high-precision study of excited-state effects using five source-sink separations between 0.7 and 1. Read More

We present isovector nucleon observables: the axial, tensor, and scalar charges and the Dirac radius. Using the BMW clover-improved Wilson action and pion masses as low as 149 MeV, we achieve good control over chiral extrapolation to the physical point. Our analysis is done using three different source-sink separations in order to identify excited-state effects, and we make use of the summation method to reduce their size. Read More

Among the sources of systematic error in nucleon structure calculations is contamination from unwanted excited states. In order to measure this systematic error, we vary the operator insertion time and source-sink separation independently. We compute observables for three source-sink separations between 0. Read More

Using lattice QCD, a diquark can be studied in a gauge-invariant manner by binding it to a static quark in a heavy-light-light hadron. We compute the simultaneous two-quark density of a diquark, including corrections for periodic boundary conditions. We define a correlation function to isolate the intrinsic correlations of the diquark and reduce the effects caused by the presence of the static quark. Read More