Tue·Sep 6, 2005Tuesday·September 6, 2005

1. 01*

   Observations on discretization errors in twisted-mass lattice QCD

   Stephen R. Sharpe🇺🇸

   I make a number of observations concerning discretization errors in twisted-mass lattice QCD that can be deduced by applying chiral perturbation theory including lattice artifacts. (1) The line along which the PCAC quark mass vanishes in the twisted mass-twisted mass plane makes an angle to the untwisted mass axis which is a direct measure of O(a) terms in the chiral Lagrangian, and is found numerically to be large; (2) Numerical results for pionic quantities in the mass plane show the qualitative properties predicted by chiral perturbation theory, in particular an asymmetry in slopes between positive and negative untwisted quark masses; (3) By extending the description of the ``Aoki regime'' (where m_q is of size a^2 Lambda_QCD^3) to next-to-leading order in chiral perturbation theory I show how the phase transition lines and lines of maximal twist (using different definitions) extend into this region, and give predictions for the functional form of pionic quantities; (4) I argue that the recent claim that lattice artifacts at maximal twist have apparent infrared singularities in the chiral limit results from expanding about the incorrect vacuum state. Shifting to the correct vacuum (as can be done using chiral perturbation theory) the apparent singularities are summed into non-singular, and furthermore predicted, forms. I further argue that there is no breakdown in the Symanzik expansion in powers of lattice spacing, and no barrier to simulating at maximal twist in the Aoki regime.

   hep-latPRD(2005)·38 citations
2. 02*

   The chiral transition of N_f=2 QCD with fundamental and adjoint fermions

   J. Engels🇩🇪 · S. Holtmann🇩🇪 · T. Schulze (University of Bielefeld, Germany)🇩🇪

   We study QCD with two staggered Dirac fermions both in the fundamental (QCD) and the adjoint representation (aQCD) near the chiral transition. The aim is to find the universality class of the chiral transition and to verify Goldstone effects below the transition. We investigate aQCD, because in that theory the deconfinement and the chiral transitions occur at different temperatures T_d<T_c. Here, we show that the scaling behaviour of the chiral condensate in the vicinity of \beta_c is in full agreeement with that of the 3d O(2) universality class. In the region T_d<T<T_c we confirm the quark mass dependence of the chiral condensate which is expected due to the existence of Goldstone modes like in 3d O(N) spin models. For fundamental QCD we use the p4-action. Here, we find Goldstone effects below T_c like in aQCD and the 3d O(N) spin models, however no O(2)/O(4) scaling near the chiral transition point. The result for QCD may be a consequence of the coincidence of the deconfinement transition with the chiral transition.

   hep-latPoS(2006)·21 citations
3. 03*

   Lattice Gauge Fields Topology Uncovered by Quaternionic sigma-model Embedding

   F.V.Gubarev🇷🇺 · S.M.Morozov (ITEP, Moscow)🇷🇺

   We investigate SU(2) gauge fields topology using new approach, which exploits the well known connection between SU(2) gauge theory and quaternionic projective sigma-models and allows to formulate the topological charge density entirely in terms of sigma-model fields. The method is studied in details and for thermalized vacuum configurations is shown to be compatible with overlap-based definition. We confirm that the topological charge is distributed in localized four dimensional regions which, however, are not compatible with instantons. Topological density bulk distribution is investigated at different lattice spacings and is shown to possess some universal properties.

   hep-lathep-phPRD(2005)·8 citations
4. 04*

   Local Simulation Algorithms for Coulomb Gases with Dynamical Dielectric Effects

   A. Duncan🇺🇸 · R.D. Sedgewick🇺🇸 · R.D. Coalson🇺🇸

   We discuss the application of the local lattice technique of Maggs and Rossetto to problems that involve the motion of objects with different dielectric constants than the background. In these systems the simulation method produces a spurious interaction force which causes the particles to move in an unphysical manner. We show that this term can be removed using a variant of a method known from high-energy physics simulations, the multiboson method, and demonstrate the effectiveness of this corrective method on a system of neutral particles. We then apply our method to a one-component plasma to show the effect of the spurious interaction term on a charged system.

   ↳ cond-mat.softhep-latPRE(2006)·2 citations
5. 05*

   Kertesz line and embedded monopoles in QCD

   M.N. Chernodub🇷🇺

   We propose a new class of defects in QCD which can be viewed as ``embedded'' monopoles made of quark and gluon fields. These objects are explicitly gauge-invariant and they closely resemble the Nambu monopoles in the Standard Electroweak model. We argue that the ``embedded QCD monopoles'' are proliferating in the quark gluon plasma phase while in the low-temperature hadronic phase the spatial proliferation of these objects is suppressed. At realistic quark masses and zero chemical potential the hadronic and quark-gluon phases are generally believed to be connected by a smooth crossover across which all thermodynamic quantities are non-singular. We argue that these QCD phases are separated by a well-defined boundary -- known as the Kertesz line in condensed matter systems -- associated with the onset of the proliferation of the embedded QCD monopoles in the quark gluon plasma phase.

   ↳ hep-phcond-mat.otherhep-lathep-thPRL(2005)·15 citations
6. 06*

   Admissibility Condition and Nontrivial Indices on a Noncommutative Torus

   Keiichi Nagao (Ibaraki U.)🇯🇵

   We study the index of the Ginsparg-Wilson Dirac operator on a noncommutative torus numerically. To do this, we first formulate an admissibility condition which suppresses the fluctuation of gauge fields sufficiently small. Assuming this condition, we generate gauge configurations randomly, and find various configurations with nontrivial indices. We show one example of configurations with index 1 explicitly. This result provides the first evidence that nontrivial indices can be naturally defined on the noncommutative torus by utilizing the Ginsparg-Wilson relation and the admissibility condition.

   ↳ hep-thhep-latPRD(2006)·8 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.