Results for "S. A. R. Horsley"

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Transformation optics, isotropic chiral media, and non-Riemannian geometryJan 10 2011Jan 14 2011The geometrical interpretation of electromagnetism in transparent media (transformation optics) is extended to include media with isotropic, inhomogeneous, chirality. It is found that such media may be described through introducing the non-Riemannian ... More
The KdV hierarchy in opticsMar 10 2016There is a well explored relationship between quantum mechanical scattering from a potential and the Korteweg-de Vries (KdV) equation of fluid dynamics: if the potential is 'evolved' according to the KdV equation then it will have the same reflectivity ... More
Motion of macroscopic bodies in the electromagnetic fieldJan 17 2013A theory is presented for calculating the effect of the electromagnetic field on the centre of mass of a macroscopic dielectric body that is valid in both quantum and classical regimes. We apply the theory to find the classical equation of motion for ... More
Canonical quantization of the electromagnetic field interacting with a moving dielectricMay 02 2012Jul 24 2012The electromagnetic field is canonically quantized in the presence of a linear, dispersive and dissipative medium that is in uniform motion. Specifically we calculate the change in the normal modes of the coupled matter-field system and find a Hamiltonian ... More
Consistency of certain constitutive relations with quantum electromagnetismJun 10 2011Sep 19 2012Recent work by Philbin [1] has provided a Lagrangian theory that establishes a general method for the canonical quantization of the electromagnetic field in any dispersive, lossy, linear dielectric. Working from this theory, we extend the Lagrangian description ... More
Indifferent electromagnetic modes: bound states and topologyApr 12 2019At zero energy the Dirac equation has interesting behaviour. The asymmetry in the number of spin up and spin down modes is determined by the topology of both space and the gauge field in which the system sits. An analogous phenomenon also occurs in electromagnetism. ... More
Polariton excitation rates from time dependent dielectricsApr 11 2016In recent years, a rigorous quantum mechanical model for the interaction between light and macroscopic dispersive, lossy dielectrics has emerged -macroscopic QED- allowing the application of the usual methods of quantum field theory. Here, we apply time ... More
Negative frequencies in wave propagation: a microscopic modelJan 21 2016A change in the sign of the frequency of a wave between two inertial reference frames corresponds to a reversal of the phase velocity. Yet from the point of view of the relation $E=\hbar\omega$, a positive quantum of energy apparently becomes a negative ... More
Canonical quantization of electromagnetism in spatially dispersive mediaSep 02 2013Jan 27 2014We find the action that describes the electromagnetic field in a spatially dispersive, homogeneous medium. This theory is quantized and the Hamiltonian is diagonalized in terms of a continuum of normal modes. It is found that the introduction of nonlocal ... More
Damping the zero-point energy of a harmonic oscillatorApr 03 2013Jul 31 2013The physics of quantum electromagnetism in an absorbing medium is that of a field of damped harmonic oscillators. Yet until recently the damped harmonic oscillator was not treated with the same kind of formalism used to describe quantum electrodynamics ... More
The cutoff-dependence of the Casimir force within an inhomogeneous mediumFeb 21 2013We consider the ground state energy of the electromagnetic field in a piston geometry. In the idealised case, where the piston and the walls of the chamber are taken as perfect mirrors, the Casimir pressure on the piston is finite and independent of the ... More
Wave propagation in complex coordinatesJul 17 2015We investigate the analytic continuation of wave equations into the complex position plane. For the particular case of electromagnetic waves we provide a physical meaning for such an analytic continuation in terms of a family of closely related inhomogeneous ... More
Radiation pressure on a moving body: beyond the Doppler effectNov 18 2011The dependence of macroscopic radiation pressure on the velocity of the object being pushed is commonly attributed to the Doppler effect. This need not be the case, and here we highlight velocity dependent radiation pressure terms that have their origins ... More
Radiation 'damping' in atomic photonic crystalsJul 12 2010The force exerted on a material by an incident beam of light is dependent upon the material's velocity in the laboratory frame of reference. This velocity dependence is known to be diffcult to measure, as it is proportional to the incident optical power ... More
Non-reflecting permittivity profiles and the spatial Kramers-Kronig relationsFeb 28 2015We show that if the permittivity profile of a planar dielectric medium is an analytic function in the upper (lower) half complex position plane then it won't reflect radiation from the left (right), whatever the angle of incidence. Consequently, using ... More
Radiation pressure, moving media, and multilayer systemsAug 06 2012Aug 16 2012A general theory of optical forces on moving bodies is here developed in terms of generalized/4x4 transfer and scattering matrices. Results are presented for a planar dielectric multilayer of arbitrary refractive index placed in an otherwise empty space ... More
Asymptotic quantum degeneracy at a 2D cornerJul 19 2010Nov 21 2011In quantum mechanics, asymptotic degeneracy is often considered in the context of a particle in a symmetric double-well potential, and is the phenomenon whereby pairs of energy levels come together to form doubly degenerate levels in response to an increase ... More
Active absorption of electromagnetic pulses in a cavityDec 09 2014We show that a pulse of electromagnetic radiation launched into a cavity can be completely absorbed into an infinitesimal region of space, provided one has a high degree of control over the current flowing through this region. We work out explicit examples ... More
Renormalization of four-fermion operators for higher twist calculationsSep 28 1998The evaluation of the higher twist contributions to Deep Inelastic Scattering amplitudes involves a non trivial choice of operator bases for the higher orders of the OPE expansion of the two hadronic currents. In this talk we discuss the perturbative ... More
Renormalisation and off-shell improvement in lattice perturbation theoryJul 05 2000We discuss the improvement of flavour non-singlet point and one-link lattice quark operators, which describe the quark currents and the first moment of the DIS structure functions respectively. Suitable bases of improved operators are given, and the corresponding ... More
A lattice study of the spin structure of the Lambda hyperonAug 13 2002The internal spin structure of the Lambda is of special importance for the understanding of the spin structure of hadrons in general. The comparison between the nucleon and Lambda allows for a test of the relevant flavour-symmetry breaking effects. Using ... More
Direct manipulation of wave amplitude and phase through inverse design of isotropic mediaJan 21 2017Aug 03 2017In this article we propose a new design methodology allowing us to control both ampli- tude and phase of electromagnetic waves from a cylindrical incident wave. This results in isotropic materials and does not resort to transformation optics or its quasi-conformal ... More
Local bilinear operators on the lattice and their perturbative renormalisation including O(a) effectsNov 05 1997Some basic concepts are discussed to derive renormalisation factors of local lattice operators relevant to deep inelastic structure functions and to other measurable quantities. These $Z$ factors can be used to relate matrix elements measured by lattice ... More
The spin structure of the Lambda hyperon in quenched lattice QCDOct 12 2001It has been suggested to use the production of Lambda hyperons for investigating the nucleon spin structure. The viability of this idea depends crucially on the spin structure of the Lambda. Using nonperturbatively O(a) improved Wilson fermions in the ... More
Optical non-reciprocity of cold atom Bragg mirrors in motionMay 08 2013Reciprocity is fundamental to light transport and is a concept that holds also in rather complex systems. Yet, reciprocity can be switched off even in linear, isotropic and passive media by setting the material structure into motion. In highly dispersive ... More
Higher-twist contributions to the Structure Functions coming from 4-fermion operatorsAug 24 1999We evaluate the contribution of a class of higher-twist operators to the lowest moment of the Structure Functions, by computing appropriate matrix elements of six four-fermion operators in the quenched approximation. Their perturbative renormalization ... More
Perturbative Renormalization of Improved Lattice OperatorsSep 16 1997Nov 10 1997We derive bases of improved operators for all bilinear quark currents up to spin two (including the operators measuring the first moment of DIS Structure Functions), and compute their one-loop renormalization constants for arbitrary coefficients of the ... More
Revisiting the Bragg reflector to illustrate some modern developments in opticsJan 20 2013Apr 05 2013A series of thin layers of alternating refractive index is known to make a good optical mirror over certain bands of frequency. Such a device - often termed the Bragg reflector - is usually introduced to students within the first years of an undergraduate ... More
The Deep-Inelastic Structure Functions of $π$ and $ρ$ MesonsOct 09 1997We compute the lower moments of the structure functions of $\pi$ and $\rho$. Of particular interest are the spin-dependent structure functions of the $\rho$ as they give new information about quark binding effects.
A lattice evaluation of four-quark operators in the nucleonMar 30 2001Nucleon matrix elements of various four-quark operators are evaluated in quenched lattice QCD using Wilson fermions. Some of these operators give rise to twist-four contributions to nucleon structure functions. Furthermore, they bear valuable information ... More
Applied lattice gauge calculations: diquark content of the nucleonAug 05 2002As an example of an application of lattice QCD we describe a computation of four-quark operators in the nucleon. The results are interpreted in a diquark language.
Higher-Twist Contribution to Pion Structure Function: 4-Fermi OperatorsAug 12 1999Dec 30 1999We present quenched lattice QCD results for the contribution of higher-twist operators to the lowest non-trivial moment of the pion structure function. To be specific, we consider the combination $F_2^{\pi^+} + F_2^{\pi^-} - 2 F_2^{\pi^0}$ which has $I ... More
Calculating coherent light-wave propagation in large heterogeneous mediaDec 26 2018Understanding the interaction of light with a highly scattering material is essential for optical microscopy of optically thick and heterogeneous biological tissues. Ensemble-averaged analytic solutions cannot provide more than general predictions for ... More
Localized exciton-polariton modes in dye-doped nanospheres: a quantum approachJun 03 2015Sep 16 2015We model a dye-doped polymeric nanosphere as an ensemble of quantum emitters and use it to investigate the localized exciton-polaritons supported by such a nanosphere. By determining the time evolution of the density matrix of the collective system, we ... More
A lattice study of the strangeness content of the nucleonNov 30 2011We determine the quark contributions to the nucleon spin Delta s, Delta u and Delta d as well as their contributions to the nucleon mass, the sigma-terms. This is done by computing both, the quark line connected and disconnected contributions to the respective ... More
Four-quark operators in hadronsOct 26 2000We present calculations of matrix elements of 4-quark operators in the pion and in the nucleon extracted from quenched Monte Carlo simulations at beta = 6.0 using Wilson fermions. These operators are relevant for higher-twist effects. We are particularly ... More
Pion and Rho Structure Functions from Lattice QCDMar 21 1997We calculate the lower moments of the deep-inelastic structure functions of the pion and the rho meson on the lattice. Of particular interest to us are the spin-dependent structure functions of the rho. The calculations are done with Wilson fermions and ... More
Hadron Structure Functions from Lattice QCD -- 1997Jun 25 1997Jul 14 1997We review the status of lattice calculations of the deep-inelastic structure functions of the nucleon. In addition, we present some results on the pion and rho structure functions.
The strong coupling constant from lattice QCD with N_f=2 dynamical quarksNov 05 2001Nov 16 2001We compute $\Lambda_{\bar{MS}}$ for two flavors of light dynamical quarks using non-perturbatively $O(a)$ improved Wilson fermions. We improve on a recent calculation by employing Pad\'e-improved two-loop and three-loop perturbation theory to convert ... More
Determination of $Λ_{\overline{MS}}$ from quenched and $N_f = 2$ dynamical QCDMar 21 2001Sep 12 2001The scale parameter $\Lambda_{\overline{MS}}$ is computed on the lattice in the quenched approximation and for $N_f = 2$ flavors of light dynamical quarks. The dynamical calculation is done with non-perturbatively $O(a)$ improved Wilson fermions. In the ... More
$O(a)$ Improvement for Quenched Wilson FermionsJan 24 1998We briefly describe some of our recent results for the mass spectrum and matrix elements using $O(a)$ improved fermions for quenched QCD. Where possible a comparison is made between improved and Wilson fermions.
Towards a lattice calculation of $Δq$ and $δq$May 31 1999Within the framework of lattice QCD a high statistics computation of the nucleon axial and tensor charges is given. Particular attention is paid to the chiral and continuum extrapolations.
Improved Quenched QCD on Large Lattices - First ResultsSep 09 1997Continuing our investigations of quenched QCD with improved fermions we have started simulations for lattice size 32^3 x 64 at beta=6.2. We present first results for light hadron masses at kappa=0.13520, 0.13540, and 0.13555. Moreover we compare our initial ... More
Non-perturbative improvement and renormalization of lattice operatorsOct 08 1997The Alpha Collaboration has proposed an optimal value for c_SW in the Sheikholeslami-Wohlert action, chosen to remove O(a) effects. To measure hadronic matrix elements to the same accuracy we need a method of finding O(a) improved operators, and their ... More
Nucleon form factors and O(a) ImprovementSep 24 1998Nucleon form factors have been extensively studied both experimentally and theoretically for many years. We report here on new results of a high statistics quenched lattice QCD calculation of vector and axial-vector nucleon form factors at low momentum ... More
$O(a)$ Improvement of Nucleon Matrix ElementsSep 13 1997Sep 25 1997We report on preliminary results of a high statistics quenched lattice QCD calculation of nucleon matrix elements within the Symanzik improvement programme. Using the recently determined renormalisation constants from the Alpha Collaboration we present ... More
On balanced incomplete block designs with specified weak chromatic numberSep 27 2012Sep 03 2013A weak $c$-colouring of a balanced incomplete block design (BIBD) is a colouring of the points of the design with $c$ colours in such a way that no block of the design has all of its vertices receive the same colour. A BIBD is said to be weakly $c$-chromatic ... More
Perturbative Renormalisation of the Second Moment of Generalised Parton DistributionsOct 06 2004We calculate the non-forward quark matrix elements of operators with two covariant derivatives needed for the renormalisation of the second moment of generalised parton distributions in one-loop lattice perturbation theory using Wilson fermions. For some ... More
Doyen-Wilson results for odd length cycle systemsNov 14 2014Jun 12 2015For each odd $m \geq 3$ we completely solve the problem of when an $m$-cycle system of order $u$ can be embedded in an $m$-cycle system of order $v$, barring a finite number of possible exceptions. In cases where $u$ is large compared to $m$, where $m$ ... More
Towards a Non-Perturbative Calculation of DIS Wilson CoefficientsSep 24 1998We verify the operator product expansion (OPE) of deep inelastic scattering (DIS) on the lattice and present first results of a non-perturbative calculation of the Wilson coefficients.
Nanoscale design of the local density of optical statesSep 14 2018Sep 21 2018We propose a design concept for tailoring the local density of optical states (LDOS) in dielectric nanostructures, based on the phase distribution of the scattered optical fields induced by point-like emitters. First we demonstrate that the LDOS can be ... More
Operator improvement for Ginsparg-Wilson fermionsAug 20 1999The improvement of fermionic operators for Ginsparg-Wilson fermions is investigated. We present explicit formulae for improved Green's functions, which apply both on-shell and off-shell.
Perturbative Renormalisation for Low Moments of Generalised Parton Distributions with Clover FermionsNov 19 2005We present the non-forward quark matrix elements of operators with one and two covariant derivatives needed for the renormalisation of the first and second moments of generalised parton distributions in one-loop lattice perturbation theory using clover ... More
Nanoscale design of the local density of optical statesSep 14 2018Mar 08 2019We propose a design concept for tailoring the local density of optical states (LDOS) in dielectric nanostructures, based on the phase distribution of the scattered optical fields induced by point-like emitters. First we demonstrate that the LDOS can be ... More
Perturbative determination of $c_{SW}$ for plaquette and Symanzik gauge action and stout link clover fermionsJul 02 2008Using plaquette and Symanzik improved gauge action and stout link clover fermions we determine the improvement coefficient $c_{SW}$ in one-loop lattice perturbation theory from the off-shell quark-quark-gluon three-point function. In addition, we compute ... More
Perturbative determination of $c_{SW}$ with Symanzik improved gauge action and stout smearingOct 04 2007We determine the improvement factor $c_{SW}$ in one-loop lattice perturbation theory for the plaquette and Symanzik improved gauge actions. The fermionic action is ${\mathcal{O}(a)}$ clover improved with one-time stout smearing. $c_{SW}$ is derived from ... More
One-loop Renormalisation of Lattice QCD Operators for Non-forward Matrix Elements: From Clover to Overlap FermionsOct 09 2006We consider the renormalisation of composite quark-antiquark operators with one and two lattice covariant derivatives related to the lowest moments of generalised parton distributions (GPDs) and meson distribution amplitudes (DAs). Their matrix elements ... More
New results for non-perturbative order(a) improvement in light hadronsOct 07 1997Oct 08 1997We have results from light hadron simulations in quenched QCD at beta=6.0 and 6.2 using non-perturbatively improved Sheikholeslami-Wohlert fermions in an effort to remove all order(a) effects. From looking at hadron masses and splittings and the RG-invariant ... More
The Light Hadron Mass Spectrum with Non-Perturbatively O(a) Improved Wilson FermionsSep 02 1996Sep 03 1996We compute the light hadron mass spectrum in quenched lattice QCD at $\beta = 6.0$ using the Sheikholeslami-Wohlert fermionic action. The calculation is done for several choices of the coefficient $c_{SW}$, including $c_{SW} = 0$ and the recently proposed ... More
A class of invisible inhomogeneous media and the control of electromagnetic wavesAug 19 2016Nov 27 2016We propose a general method to arbitrarily manipulate an electromagnetic wave propagating in a two-dimensional medium, without introducing any scattering. This leads to a whole class of isotropic spatially varying permittivity and permeability profiles ... More
Decompositions of complete multigraphs into stars of varying sizesJul 27 2018Sep 09 2018In 1979 Tarsi showed that an edge decomposition of a complete multigraph into stars of size $m$ exists whenever the obvious necessary conditions hold. In 1996 Lin and Shyu gave necessary and sufficient conditions for the existence of an edge decomposition ... More
Decomposing $K_{u+w}-K_u$ into cycles of various lengthsMar 12 2016We prove that the complete graph with a hole $K_{u+w}-K_u$ can be decomposed into cycles of arbitrary specified lengths provided that the obvious necessary conditions are satisfied, each cycle has length at most $\min(u,w)$, and the longest cycle is at ... More
On-shell and off-shell improvement for Ginsparg-Wilson fermionsSep 29 1999We discuss the improvement of bilinear fermionic operators for Ginsparg-Wilson fermions. We present explicit formulae for improved Green's functions, which apply both on-shell and off-shell.
Higher-twist corrections to nucleon structure functions from lattice QCDJun 10 1999A genuinely non-perturbative evaluation of higher-twist contributions to the structure functions of the nucleon, with all mixing effects and renormalon ambiguities taken care of, is presented. Higher-twist corrections turn out to be significant at moderate ... More
One-loop renormalisation for the second moment of GPDs with Wilson fermionsSep 08 2004We calculate the non-forward quark matrix elements for operators with two covariant derivatives in one-loop lattice perturbation theory using Wilson fermions. These matrix elements are needed in the renormalisation of the second moment of generalised ... More
Renormalisation of Composite Operators in Lattice Perturbation Theory with Clover Fermions: Non-forward Matrix ElementsMay 04 2006May 06 2008We consider the renormalisation of lattice QCD operators with one and two covariant derivatives related to the first and second moments of generalised parton distributions and meson distribution amplitudes. Employing the clover fermion action we calculate ... More
Operator product expansion on the lattice: analytic Wilson coefficientsOct 10 2006We present first results for Wilson coefficients of operators up to first order in the covariant derivatives for the case of Wilson fermions. They are derived from the off-shell Compton scattering amplitude $\mathcal{W}_{\mu\nu}(a,p,q)$ of massless quarks ... More
The Nambu-Jona-Lasinio model with staggered fermionsJan 06 1994We investigate the neighbourhood of the chiral phase transition in a lattice Nambu--Jona-Lasinio model, using both Monte Carlo methods and lattice Schwinger-Dyson equations.
Lattice Renormalization of Quark OperatorsOct 13 1997We have technically improved the non-perturbative renormalization method, proposed by Martinelli et al., by using quark momentum sources and sinks. Composite two-fermion operators up to three derivatives have been measured for Wilson fermions and Sheikholeslami-Wohlert ... More
Perturbative renormalisation of quark bilinear operators for overlap fermions with and without stout links and improved gauge actionSep 21 2005Sep 27 2005We calculate lattice renormalisation constants of local and one-link quark operators for overlap fermions and improved gauge actions in one-loop perturbation theory. For the local operators we stout smear the SU(3) links in the fermionic action. Using ... More
Renormalisation of one-link quark operators for overlap fermions with Lüscher-Weisz gauge actionMay 14 2005We compute lattice renormalisation constants of one-link quark operators ({\it i.e.} operators with one covariant derivative) for overlap fermions and L\"uscher-Weisz gauge action in one-loop perturbation theory. Among others, such operators enter the ... More
The SU(3) Beta Function from Numerical Stochastic Perturbation TheorySep 17 2013Nov 06 2013The SU(3) beta function is computed from Wilson loops to 20th order numerical stochastic perturbation theory. An attempt is made to include massless fermions, whose contribution is known analytically to 4th order. The question whether the theory admits ... More
One-loop renormalisation of quark bilinears for overlap fermions with improved gauge actionsApr 07 2004Jan 21 2005We compute lattice renormalisation constants of local bilinear quark operators for overlap fermions and improved gauge actions. Among the actions we consider are the Symanzik, L\"uscher-Weisz, Iwasaki and DBW2 gauge actions. The results are given for ... More
Spin Structure Functions from Lattice QCDNov 05 1997We report on new results of the spin dependent structure functions $g_1$ and $h_1$ of the nucleon. An attempt is made to convert the moments, which is what one computes on the lattice, to quark distribution functions.
Scaling of Non-Perturbatively O(a) Improved Wilson Fermions: Hadron Spectrum, Quark Masses and Decay ConstantsJul 17 1997We compute the hadron mass spectrum, the quark masses and the meson decay constants in quenched lattice QCD with non-perturbatively $O(a)$ improved Wilson fermions. The calculations are done for two values of the coupling constant, $\beta = 6.0$ and 6.2, ... More
Spectroscopy and Renormalisation Group Flow of a Lattice Nambu-Jona-Lasinio ModelJan 13 1994We investigate a lattice Nambu--Jona-Lasinio model both by the Monte Carlo method and Schwinger-Dyson equations. A comparison allows the discussion of finite size effects and the extrapolation to infinite volume. We pay special attention to the identification ... More
Progress towards a lattice determination of (moments of) nucleon structure functionsNov 08 2001Using unimproved and non-perturbatively O(a) improved Wilson fermions, results are given for the three lowest moments of unpolarised nucleon structure functions. Renormalisation, chiral extrapolation and the continuum limit of the matrix elements are ... More
A class of amplitude modulating and invisible inhomogeneous mediaAug 19 2016We propose a general method to arbitrarily manipulate the amplitude of an electromagnetic wave propagating in a two-dimensional medium, without introducing any scattering. This leads to a whole class of isotropic spatially varying permittivity and permeability ... More
Polarized and Unpolarized Nucleon Structure Functions from Lattice QCDAug 03 1995Sep 11 1995We report on a high statistics quenched lattice QCD calculation of the deep-inelastic structure functions $F_1$, $F_2$, $g_1$ and $g_2$ of the proton and neutron. The theoretical basis for the calculation is the operator product expansion. We consider ... More
Perturbative Renormalization of Lattice Bilinear Quark OperatorsMar 10 1996Our aim is to compute the lower moments of the unpolarized and polarized deep-inelastic structure functions of the nucleon on the lattice. The theoretical basis of the calculation is the operator product expansion. To construct operators with the appropriate ... More
Lattice Operators for Moments of the Structure Functions and their Transformation under the Hypercubic GroupFeb 28 1996For lattice operators that are relevant to the calculation of moments of nucleon structure functions we investigate the transformation properties under the hypercubic group. We give explicit bases of irreducible subspaces for tensors of rank up to 4.
Towards a Lattice Calculation of the Nucleon Structure FunctionsDec 10 1994Dec 13 1994We have initiated a programme to compute the lower moments of the unpolarised and polarised deep inelastic structure functions of the nucleon in the quenched approximation. We review our progress to date.
Polarized Nucleon Structure Functions from Lattice QCDNov 27 1995We describe a high statistics quenched QCD calculation of the moments of the polarized deep-inelastic structure functions g_1 and g_2 of the proton and neutron.
An Update on Distribution Amplitudes of the Nucleon and its Parity PartnerDec 02 2011The calculation of baryon wave functions at small inter-quark separations is an ongoing effort within the QCDSF collaboration. In this update on normalization constants and distribution amplitudes of the nucleon and its negative parity partner, N* (1535), ... More
A lattice determination of the second moment of the polarised valence quark distributionAug 07 1997We perform a Monte Carlo calculation of the second moment of the polarised valence quark distributions in the nucleon, using quenched Wilson fermions. The special feature of this moment is that it is directly accessible experimentally. At a scale of $\mu ... More
Generalized Parton Distributions from Lattice QCDApr 26 2003Dec 29 2003We perform a quenched lattice calculation of the first moment of twist-two generalized parton distribution functions of the proton, and assess the total quark (spin and orbital angular momentum) contribution to the spin of the proton.
Calculation of Moments of Structure FunctionsSep 26 2002The progress on the lattice computation of low moments of both the unpolarised and polarised nucleon structure functions is reviewed with particular emphasis on continuum and chiral extrapolations and comparison between quenched and unquenched fermions. ... More
Clover improvement for stout-smeared 2+1 flavour SLiNC fermions: perturbative resultsSep 29 2008For the Stout Link Non-perturbative Clover (SLiNC) action we determine in one-loop lattice perturbation theory the critical hopping parameter $\kappa_c$ and the clover parameter $c_{SW}$ which is needed for $\mathcal{O}(a)$ improvement. Performing this ... More
Nucleon axial charge and pion decay constant from two-flavor lattice QCDFeb 09 2013Mar 01 2014The axial charge of the nucleon $g_A$ and the pion decay constant $f_\pi$ are computed in two-flavor lattice QCD. The simulations are carried out on lattices of various volumes and lattice spacings. Results are reported for pion masses as low as $m_\pi=130\,\mbox{MeV}$. ... More
Resolving Exceptional Configurations in Quenched Lattice QCDSep 23 1998Quenched lattice QCD calculations with Wilson-type fermions at small quark masses are impeded by exceptional configurations. We show how this problem can be resolved in a practicable way without changing the physics in the chiral limit.
Nucleon form factors and structure functionsJan 12 2011We give an update on our ongoing efforts to compute the nucleon's form factors and moments of structure functions using Nf=2 flavours of non-perturbatively improved Clover fermions. We focus on new results obtained on gauge configurations where the pseudo-scalar ... More
Disconnected contributions to D-meson semi-leptonic decay form factorsNov 17 2011We calculate the disconnected contribution to the form factor for the semileptonic decay of a D-meson into a final state, containing a flavor singlet eta meson. We use QCDSF n_f=2+1 configurations at the flavor symmetric point m_u=m_d=m_s and the partially ... More
Dirac and Pauli form factors from lattice QCDJun 17 2011We present a comprehensive analysis of the electromagnetic form factors of the nucleon from a lattice simulation with two flavors of dynamical O(a)-improved Wilson fermions. A key feature of our calculation is that we make use of an extensive ensemble ... More
Nucleon and $N^* (1535)$ Distribution AmplitudesNov 04 2010The QCDSF collaboration has investigated the distribution amplitudes and wavefunction normalization constants of the nucleon and its parity partner, the $N^* (1535)$. We report on recent progress in the calculation of these quantities on configurations ... More
Nucleon electromagnetic form factors on the lattice and in chiral effective field theoryMar 25 2003Mar 04 2005We compute the electromagnetic form factors of the nucleon in quenched lattice QCD, using non-perturbatively improved Wilson fermions, and compare the results with phenomenology and chiral effective field theory.
Composite operators in lattice QCD: nonperturbative renormalizationSep 01 1998We investigate the nonperturbative renormalization of composite operators in lattice QCD restricting ourselves to operators that are bilinear in the quark fields. These include operators which are relevant to the calculation of moments of hadronic structure ... More
Finite Size Effects in Nucleon Masses in Dynamical QCDSep 12 2002For lattice calculations with light dynamical quarks, finite size effects have become an important aspect. We study finite size effects in nucleon masses on N_f=2 dynamical lattices of 1-2 fm. Predictions for the finite size effects are obtained in one-loop ... More
Structure of the NucleonDec 08 2003Generalized parton distributions provide information on the longitudinal and transverse distribution of partons in the fast moving nucleon. Furthermore, they contain information on the spin structure of the nucleon. First results of a lattice study of ... More
A novel approach to nonperturbative renormalization of singlet and nonsinglet lattice operatorsOct 12 2014A novel method for nonperturbative renormalization of lattice operators is introduced, which lends itself to the calculation of renormalization factors for nonsinglet as well as singlet operators. The method is based on the Feynman-Hellmann relation, ... More