Tue·Sep 17, 2002Tuesday·September 17, 2002

1. 01*

   Unquenched QCD with Light Quarks

   A. Duncan🇺🇸 · E. Eichten🇺🇸 · J. Yoo🇺🇸

   We present recent results in unquenched lattice QCD with two degenerate light sea quarks using the truncated determinant approximation (TDA). In the TDA the infrared modes contributing to the quark determinant are computed exactly up to some cutoff in quark off-shellness (typically 2${\Lambda }_{QCD}$). This approach allows simulations to be performed at much lighter quark masses than possible with conventional hybrid MonteCarlo techniques. Results for the static energy and topological charge distributions are presented using a large ensemble generated on very coarse (6${}^4$) but physically large lattices. Preliminary results are also reported for the static energy and meson spectrum on 10${}^3$x20 lattices (lattice scale $a^{-1}$=1.15 GeV) at quark masses corresponding to pions of mass $\le$ 200 MeV. Using multiboson simulation to compute the ultraviolet part of the quark determinant the TDA approach becomes an exact with essentially no increase in computational effort. Some preliminary results using this fully unquenched algorithm are presented.

   hep-latPRD(2003)·7 citations
2. 02*

   I=2 Pion Scattering Phase Shift with Wilson Fermions

   CP-PACS Collaboration: S. Aoki · M. Fukugita · S. Hashimoto · K-I. Ishikawa · N. Ishizuka · Y. Iwasaki · K. Kanaya · T. Kaneko · Y. Kuramashi · V. Lesk · M. Okawa · Y. Taniguchi · A. Ukawa · T. Yoshié

   We present a lattice QCD calculation of the scattering phase shift for the I=2 $S$-wave two-pion system using the finite size method proposed by Lüscher. We work in the quenched approximation employing the standard plaquette action at $\beta =5.9$ for gluons and the Wilson fermion action for quarks. The phase shift is extracted from the energy eigenvalues of the two-pion system, which are obtained by a diagonalization of the pion 4-point function evaluated for a set of relative spatial momenta. In order to change momentum of the two-pion system, calculations are carried out on $24^3\times 60$, $32^3\times 60$, and $48^3\times 60$ lattices. The phase shift is successfully calculated over the momentum range $0<p^2<0.3{\mathrm{GeV}}^2$.

   hep-latPRD(2003)·60 citations
3. 03*

   Locality and topology with fat link overlap actions

   Tamas G. Kovacs (Pecs U. and NIC/DESY Zeuthen)🇩🇪

   We study the locality and topological properties of fat link clover overlap (FCO) actions. We find that a small amount of fattening (2-4 steps of APE or 1 step of HYP) already results in greatly improved properties compared to the Wilson overlap (WO). We present a detailed study of the localisation of the FCO and its connection to the density of low modes of $A^{†}A$. In contrast to the Wilson overlap, on quenched gauge backgrounds we do not find any dependence of the localization of the FCO on the gauge coupling. This suggests that the FCO remains local in the continuum limit. The FCO also faithfully reproduces the zero mode wave functions of typical lattice instantons, not like the Wilson overlap. After a general discussion of different lattice definitions of the topological charge we also show that the FCO together with the Boulder charge are likely to satisfy the index theorem in the continuum limit. Finally, we present a high statistics computation of the quenched topological susceptibility with the FCO action.

   hep-latPRD(2003)·37 citations
4. 04*

   QCD simulations at small chemical potential

   Ph. de Forcrand🇨🇭 · S. Kim🇰🇷 · T. Takaishi🇯🇵

   Within the reweighting approach, one has the freedom to choose the Monte Carlo action so that it provides a good overlap with the finite-\mu measure but remains simple to simulate. We explore several choices of action in the regime of small \mu. Simulating with a finite isospin chemical potential \mu_I=\mu gives a better overlap than the standard choice \mu=0, with no computational overhead.

   hep-latNucl.Phys.B Proc.Suppl.(2003)·47 citations
5. 05*

   Alternative Numerical Techniques

   G. S. Guralnik🇺🇸 · J. Doll🇺🇸 · R. Easther🇺🇸 · P. Emirdag🇺🇸 · D. D. Ferrante🇺🇸 · S. Hahn🇺🇸 · D. Petrov🇺🇸 · D. Sabo🇺🇸

   Two new approaches to numerical QFT are presented.

   hep-latNucl.Phys.B Proc.Suppl.(2003)·2 citations
6. 06*

   Towards a manifestly gauge invariant and universal calculus for Yang-Mills theory

   Stefano Arnone🇬🇧 · Antonio Gatti🇬🇧 · Tim R. Morris🇬🇧

   A manifestly gauge invariant exact renormalization group for pure SU(N) Yang-Mills theory is proposed, along with the necessary gauge invariant regularisation which implements the effective cutoff. The latter is naturally incorporated by embedding the theory into a spontaneously broken SU(N|N) super-gauge theory, which guarantees finiteness to all orders in perturbation theory. The effective action, from which one extracts the physics, can be computed whilst manifestly preserving gauge invariance at each and every step. As an example, we give an elegant computation of the one-loop SU(N) Yang-Mills beta function, for the first time at finite N without any gauge fixing or ghosts. It is also completely independent of the details put in by hand, e.g. the choice of covariantisation and the cutoff profile, and, therefore, guides us to a procedure for streamlined calculations.

   ↳ hep-thcond-mathep-lathep-phActa Phys.Slov.(2002)·17 citations
7. 07*

   Kosterlitz-Thouless-like deconfinement mechanism in the 2+1 dimensional Abelian Higgs model

   Hagen Kleinert🇩🇪 · Flavio S. Nogueira🇩🇪 · Asle Sudbo🇳🇴

   We point out that the permanent confinement in a compact 2+1-dimensional U(1) Abelian Higgs model is destroyed by matter fields in the fundamental representation. The deconfinement transition is Kosterlitz-Thouless like. The dual theory is shown to describe a three-dimensional gas of point charges with logarithmic interactions which arises from an anomalous dimension of the gauge field caused by critical matter field fluctuations. The theory is equivalent to a sine-Gordon-like theory in 2+1 dimensions with an anomalous gradient energy proportional to $k^3$. The Callan-Symanzik equation is used to demonstrate that this theory has a massless and a massive phase. The renormalization group equations for the fugacity $y(l)$ and stiffness parameter $K(l)$ of the theory show that the renormalization of $K(l)$ induces an anomalous scaling dimension ${\eta }_y$ of $y(l)$. The stiffness parameter of the theory has a universal jump at the transition determined by the dimensionality and ${\eta }_y$. As a byproduct of our analysis, we relate the critical coupling of the sine-Gordon-like theory to an {\it a priori} arbitrary constant that enters into the computation of critical exponents in the Abelian Higgs model at the charged infrared-stable fixed point of the theory, enabling a determination of this parameter. This facilitates the computation of the critical exponent $\nu$ at the charged fixed point in excellent agreement with one-loop renormalization group calculations for the three-dimensional XY-model, thus confirming expectations based on duality transformations.

   ↳ hep-thcond-mathep-latNPB(2003)·35 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.