HEP Lattice·hep-lat
14 papers—14 primary·0 cross-listed·reconstructed*
Stefano Lottini🇮🇹 · Ferdinando Gliozzi🇮🇹
We present a high-precision numerical study of 3D random percolation viewed as a confining gauge theory. Using large correlation matrices among multiform Wilson loops we determine the low-lying masses in various spin channels.
Chulwoo Jung (for the RBC-Bielefeld Collaboration)🇺🇸
We present an exploratory study of the thermodynamics of QCD with an improved staggered fermions using the QCDOC supercomputer. We use a p4 action with MILC-style smeared links (Fat 7). Some details of the implementation of the p4 action on QCDOC are discussed and performance benchmarks are given. We show preliminary results for the quark mass dependence of the pseudo-critical temperature from several lattice volumes . We also make a comparison between p4fat7 and the old p4 action.
Keh-Fei Liu🇺🇸 · Nilmani Mathur🇺🇸
We review lattice calculations of pentaquarks and discuss issues pertaining to interpolation fields, distinguishing the signal of pentaquarks from those of the KN scattering states, chiral symmetry, and ghost state contaminations.
Tetsuya Onogi🇯🇵 · Tomohisa Takimi🇯🇵
We study the lattice model for the supersymmetric Yang-Mills theory in two dimensions proposed by Cohen, Kaplan, Katz, and Unsal. We re-examine the formal proof for the absence of susy breaking counter terms as well as the stability of the vacuum by an explicit perturbative calculation for the case of U(2) gauge group. Introducing fermion masses and treating the bosonic zero momentum mode nonperturbatively, we avoid the infra-red divergences in the perturbative calculation. As a result, we find that there appear mass counter terms for finite volume which vanish in the infinite volume limit so that the theory needs no fine-tuning.
Seikou Kato🇯🇵 · Kei-Ichi Kondo🇯🇵
We give a short review of the recently obtained result that the magnetic monopole promoted to the dyon due to the vacuum angle resolves the U(1) problem in the sense that the dyon obtained in this way gives a dominant contribution to the topological susceptibility
A. Nakamura🇯🇵 · S. Sakai🇯🇵
We present transport coefficients (shear viscosity, , and bulk viscosity, ) for the gluon system obtained by the lattice QCD. This is an indispensable calculation towards the understanding of ``New State of Matter'' observed in RHIC. We study the temperature regions of RHIC () and much higher ones up to . In RHIC regions, the ratio of shear viscosity to entropy density, , is around , and satisfies the KSS bound. At high temperature, becomes two or three oder of magnitude larger. Our calculation has two limitations: (i) the use of the quench approximation, i.e., without quark pair creation-annihilation effects on vacuum, and (ii) the use of an ansatz for the spectral function. The first point has been well studied in calculations of the spectroscopy and the phase-transition behavior. To investigate the second point, we compare our results with perturbative calculations in high -regions, and also check the effects of the modification of the spectral function on the viscosity.
Matthias Nyfeler🇨🇭 · Michele Pepe🇨🇭 · Uwe-Jens Wiese (University of Bern)🇨🇭
Using D-theory we construct a new efficient cluster algorithm for the Ising model. The construction is very different from the standard Swendsen-Wang algorithm and related to worm algorithms. With the new algorithm we have measured the correlation function with high precision over a surprisingly large number of orders of magnitude.
B. B. Beard (Christian Brothers U.)🇺🇸 · M. Pepe🇨🇭 · S. Riederer🇨🇭 · U.-J. Wiese (Bern U.)🇨🇭
We construct an efficient cluster algorithm for ferromagnetic SU(N)-symmetric quantum spin systems. Such systems provide a new regularization for CP(N-1) models in the framework of D-theory, which is an alternative non-perturbative approach to quantum field theory formulated in terms of discrete quantum variables instead of classical fields. Despite several attempts, no efficient cluster algorithm has been constructed for CP(N-1) models in the standard formulation of lattice field theory. In fact, there is even a no-go theorem that prevents the construction of an efficient Wolff-type embedding algorithm. We present various simulations for different correlation lengths, couplings and lattice sizes. We have simulated correlation lengths up to 250 lattice spacings on lattices as large as 640x640 and we detect no evidence for critical slowing down.
Uwe-Jens Wiese (Bern University)🇨🇭
Field theories are usually quantized by performing a path integral over configurations of classical fields. This is the case both in perturbation theory and in Wilson's nonperturbative lattice field theory. D-theory is an alternative nonperturbative formulation of field theory in which classical fields emerge from the low-energy collective dynamics of discrete quantum variables (quantum spins and their gauge analogs -- quantum links) which undergo dimensional reduction. D-theory was developed some time ago as a discrete approach to U(1) and SU(2) pure gauge theories, extended to SU(N) gauge theories and full QCD, and also applied to a variety of other models. On the practical side, D-theory provides a framework for the development of efficient numerical methods, such as cluster algorithms. For example, in the D-theory formulation of CP(N-1) models one can simulate efficiently at non-zero chemical potential or at non-zero vacuum angle theta. On the conceptual side, D-theory offers a natural solution for the nonperturbative hierarchy problem of chiral symmetry in QCD. We also take a broader nonperturbative view on fundamental physics and speculate that D-theory variables -- i.e. quantum spins and quantum links -- may be promising candidates for the physical degrees of freedom that Nature has chosen to regularize the standard model physics at ultra-short distances.
E. G. Floratos🇬🇷 · S. Nicolis🇫🇷
We construct unitary evolution operators on a phase space with power of two discretization. These operators realize the metaplectic representation of the modular group SL(2,Z_{2^n}). It acts in a natural way on the coordinates of the non-commutative 2-torus, T_{2^n}^2$ and thus is relevant for non-commutative field theories as well as theories of quantum space-time. The class of operators may also be useful for the efficient realization of new quantum algorithms.
R. V. Gavai🇮🇳 · Sourendu Gupta🇮🇳
We report measurements of diagonal susceptibilities for the baryon number, chi_B, electrical charge, chi_Q, third component of isospin, chi_I, strangeness, chi_S, and hypercharge, chi_Y, as well as the off-diagonal chi_BQ, chi_BY, chi_BS, etc. We show that the ratios of susceptibilities in the high temperature phase are robust variables, independent of lattice spacing, and therefore give predictions for experiments. We also investigate strangeness production and flavour symmetry breaking matrix elements at finite temperature. Finally, we present evidence that in the high temperature phase of QCD the different flavour quantum numbers are excited in linkages which are exactly the same as one expects from quarks. We present some investigations of these quark-like quasi particles.
M. Gürtler🇩🇪 · R. Horsley🇬🇧 · P. E. L. Rakow🇬🇧 · C. J. Roberts🇬🇧 · G. Schierholz🇩🇪 · T. Streuer (QCDSF collaboration)🇩🇪
Using non-perturbative techniques we have found the renormalisation factor, Z, in the RI-MOM scheme for quark bilinear operators in quenched QCD. We worked with overlap fermions using the Luescher-Weisz gauge action. Our calculation was performed at beta=8.45 at a lattice spacing of 1/a=2.1 GeV using a value of rho=1.4. Our results show good agreement between the vector and the axial vector in the zero mass limit. This shows that overlap fermions have good chiral properties. To attempt to improve the discretisation errors in our results we subtracted the O(a^2) terms in one-loop lattice perturbation theory from the Monte Carlo Green functions. In particular we paid attention to the operators for the observable <x>. We found a value for the renormalisation constants Z^msbar_(v_2b) and Z^msbar_(v_2a) just less than 1.9 at mu=1/a=2.1 GeV.
On the lattice searching for the gluon condensate is difficult because a large perturbative contribution to the expectation value of the action has to be subtracted before looking for a small contribution from a possible gluon condensate. The perturbative calculation therefore has to be very precise. We use a modified version of stochastic perturbation theory to calculate a perturbative series in a boosted coupling, which converges more rapidly than the series with the usual lattice coupling, reducing the uncertainties in our results. We do not see any condensate of dimension two, as suggested by some earlier lattice studies, but we do find a contribution from a dimension four condensate. The value of this condensate is approximately 0.04(1) GeV^4, but with large uncertainties.
N. Christian🇩🇪 · K. Jansen🇩🇪 · K. Nagai🇩🇪 · B. Pollakowski🇩🇪
We discuss the scaling behaviour of different fermion actions in dynamical simulations of the 2-dimensional massive Schwinger model. We have chosen Wilson, hypercube, twisted mass and overlap fermion actions. As physical observables, the pion mass and the scalar condensate are computed for the above mentioned actions at a number of coupling values and fermion masses. We also discuss possibilities to simulate overlap fermions dynamically avoiding problems with low-lying eigenvalues of the overlap kernel.
* 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.