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Gunnar S. Bali

Publications and source records attributed to Gunnar S. Bali.

At least 73 records · Page 4Linked to original sources

Fluctuations of the baryonic flux-tube junction from effective string theory

In quenched QCD, where the dynamic creation of quark-antiquark pairs out of the vacuum is neglected, a confined baryonic system composed of three static quarks exhibits string-like behaviour at large interquark separation, with the formation of flux tubes characterized by the geometry of the so-called Y ansatz. We study the fluctuations of the junction of the three flux tubes, assuming the dynamics to be governed by an effective bosonic string model. We show that the asymptotic behaviour of the effective width of the junction grows logarithmically with the distance between the sources, with the coefficient depending on the number of joining strings, on the dimension of spacetime and on the string tension.

hep-th↗

Charmonia from Lattice QCD

Recent lattice QCD results on charmonium properties are reviewed. I comment on molecules and hybrid states as well as on future studies of states near strong decay thresholds.

hep-lat↗

Observation of String Breaking in QCD

We numerically investigate the transition of the static quark-antiquark string into a static-light meson-antimeson system. Improving noise reduction techniques, we are able to resolve the signature of string breaking dynamics for n_f=2 lattice QCD at zero temperature. This result can be related to properties of quarkonium systems. We also study short-distance interactions between two static-light mesons.

hep-lat↗

QCD Phenomenology of Static Sources

We discuss the spectrum of open string and point particle excitations in QCD with various source representations. Some general relations are introduced and lattice results presented. In particular we discuss the short-distance behaviour, relate this to perturbation theory expectations and comment on the matching between low energy matrix elements and high energy Wilson coefficients, within the framework of effective field theories.

hep-ph↗

Recent Developments in Lattice QCD

Recent trends in lattice QCD calculations and latest results are reviewed, with particular emphasis on multiquark-states and the nucleon structure.

nucl-th↗

QCD phenomenology of static sources and gluonic excitations at short distances

New lattice data for the Pi_u and Sigma_u^- potentials at short distances are presented. We compare perturbation theory to the lower static hybrid potentials and find good agreement at short distances, once the renormalon ambiguities are accounted for. We use the non-perturbatively determined continuum-limit static hybrid and ground state potentials at short distances to determine the gluelump energies. The result is consistent with an estimate obtained from the gluelump data at finite lattice spacings. For the lightest gluelump, we obtain Lambda_B^{RS}(nu_f=2.5/r_0)=[2.25\pm 0.10(latt.)\pm 0.21 (th.)\pm 0.08 (Lambda_{MS})]/r_0 in the quenched approximation with r_0^{-1} approx 400 MeV. We show that, to quote sensible numbers for the absolute values of the gluelump energies, it is necessary to handle the singularities of the singlet and octet potentials in the Borel plane. We propose to subtract the renormalons of the short-distance matching coefficients, the potentials in this case. For the singlet potential the leading renormalon is already known and related to that of the pole mass, for the octet potential a new renormalon appears, which we approximately evaluate. We also apply our methods to heavy light mesons in the static limit and from the lattice simulations available in the literature we obtain the quenched result \bar{Lambda}^{RS}(nu_f=2.5/r_0)=[1.17\pm 0.08(latt.)\pm 0.13 (th.) \pm 0.09 (Lambda_{MS})]/r_0. We calculate m_{b,MS}(m_{b,MS}) and apply our methods to gluinonia whose dynamics are governed by the singlet potential between adjoint sources. We can exclude non-standard linear short-distance contributions to the static potentials, with good accuracy.

hep-ph↗

Lattice calculations of hadron properties

Recent lattice studies of hadron properties, in particular of exotic states and charmonia are reviewed. Sea quark and quark mass effects are discussed as well as decays and mixing.

hep-lat↗

Baryons from the lattice: past, present and future

I review recent lattice results on the spectrum and structure of baryons. Limitations due to the quenched approximation and un-physically heavy up and down quarks are discussed, and interfaces between first principles studies of QCD (or approximations to it) and ``model building'' are highlighted.

nucl-th↗

Perturbative Wilson loops with massive sea quarks on the lattice

We present O(g^4) calculations of both planar and non-planar Wilson loops for various actions in the presence of sea quarks. In particular, the plaquette, the static potential and the static self energy are calculated to this order for massive Wilson, Sheikholeslami-Wohlert and Kogut-Susskind fermions, including the mass and n_f dependence. The results can be used to obtain alpha_{MS} and m_b(m_b) from lattice simulations. We compare our perturbative calculations to simulation data of the static potential and report excellent qualitative agreement with boosted perturbation theory predictions for distances r<1/GeV. We are also able to resolve differences in the running of the coupling between n_f=2 and n_f=0 static potentials. We compute perturbative estimates of the ``beta-shifts'' of QCD with sea quarks, relative to the quenched theory, which we find to agree within 10 % with non-perturbative simulations. This is done by matching the respective static potentials at large distances. The prospects of determining the QCD running coupling from low energy hadron phenomenology in the near future are assessed. We obtain the result $Λ^{(2)}_{\bar{MS}}r_0=0.69(15)$ for the two flavour QCD Lambda-parameter from presently available lattice data where $r_0^{-1}\approx 400$ MeV and estimate $α_{\bar{MS}}^{(5)}(m_Z)=0.1133(59)$.

hep-lat↗

Quark mass effects on the topological susceptibility in QCD

We investigate topology in lattice simulations of QCD with two flavours of dynamical Wilson fermions. At various sea quark masses we find reasonable agreement between results for the topological charge from fermionic and gluonic definitions, the latter with cooling. We study correlations of the topological charge with light hadronic observables and find effects in the flavour singlet pseudoscalar channel. The quark mass dependence of the topological susceptibility, $χ$, is in agreement with the leading order small m_pi expectation, chi=(f_pi m_pi)^2/4.

hep-lat↗

QCD Potentiology

We review the connection between QCD and potential models of quarkonia in the framework of effective field theories, with an emphasis on non-perturbative methods such as lattice simulations. The static and heavy quark potentials are introduced and the applicability of the non-relativistic and adiabatic approximations are discussed. The roles of so-called hybrid potentials are explored and we comment on the QCD analogue of the QED Lamb shift.

hep-ph↗

Casimir scaling of SU(3) static potentials

Potentials between static colour sources in eight different representations are computed in four dimensional SU(3) gauge theory. The simulations have been performed with the Wilson action on anisotropic lattices where the renormalised anisotropies have been determined non-perturbatively. After an extrapolation to the continuum limit we are able to exclude any violations of the Casimir scaling hypothesis that exceed 5% for source separations of up to 1 fm.

hep-lat↗

QCD forces and heavy quark bound states

The present knowledge of QCD confining forces between static test charges is summarised, with an emphasis on lattice results. Recent developments in relating QCD potentials to quarkonium properties by use of effective field theory methods are presented. The validity of non-relativistic QCD and the adiabatic approximation with respect to heavy quark bound states is explored. Besides the static potential and relativistic correction terms, the spectra of glueballs and gluinoballs, hybrid excitations of the QCD flux tube between fundamental colour sources, potentials between charges in various representations of the SU(3) gauge group, and multi-particle interactions are discussed. Some implications for quarkonia systems and quark-gluon hybrid mesons are drawn.

hep-ph↗

Static potentials and glueball masses from QCD simulations with Wilson sea quarks

We calculate glueball and torelon masses as well as the lowest lying hybrid potential in addition to the static ground state potential in lattice simulations of QCD with two flavours of dynamical Wilson fermions. The results are obtained on lattices with $16^3\times 32$ and $24^3\times 40$ sites at $β=5.6$, corresponding to a lattice spacing, $a^{-1}=2.65^{+5}_{-8}$ GeV, as determined from the Sommer force radius, at physical sea quark mass. The range spanned in the present study of five different quark masses is reflected in the ratios, $0.83\geq m_π/m_ρ\geq 0.57$.

hep-lat↗

Casimir scaling or flux counting?

Potentials between two static sources in various representations of the SU(3) gauge group are determined on anisotropic 3+1 dimensional lattices. Strong evidence in favour of "Casimir scaling" is found.

hep-lat↗

Overview from lattice QCD

I review recent Lattice results. In particular, the confinement mechanism and string breaking, glueballs and hybrid mesons as well as light hadron spectroscopy are discussed.

hep-lat↗

Are there short distance non-perturbative contributions to the QCD static potential?

We find that perturbation theory fails to describe the short range static potential as obtained from quenched lattice simulations, at least for source separations r > 1/(6 GeV). The difference between the non-perturbatively determined potential and perturbation theory at short distance is well parameterised by a linear term with a slope of approximately 1.2 GeV^2 that is significantly bigger than the string tension, sigma = 0.21 GeV^2

hep-ph↗