Lemon: an MPI parallel I/O library for data encapsulation using LIME

We introduce Lemon, an MPI parallel I/O library that is intended to allow for efficient parallel I/O of both binary and metadata on massively parallel architectures. Motivated by the demands of the Lattice Quantum Chromodynamics community, the data is stored in the SciDAC Lattice QCD Interchange Message Encapsulation format. This format allows for storing large blocks of binary data and corresponding metadata in the same file. Even if designed for LQCD needs, this format might be useful for any application with this type of data profile. The design, implementation and application of Lemon are described. We conclude with presenting the excellent scaling properties of Lemon on state of the art high performance computers

Topology, Random Matrix Theory and the spectrum of the Wilson Dirac operator

We study the spectrum of the hermitian Wilson Dirac operator in the epsilon-regime of QCD in the quenched approximation and compare it to predictions from Wilson Random Matrix Theory. Using the distributions of single eigenvalues in the microscopic limit and for specific topological charge sectors, we examine the possibility of extracting estimates of the low energy constants which parametrise the lattice artefacts in Wilson chiral perturbation theory. The topological charge of the field configurations is obtained from a field theoretical definition as well as from the flow of eigenvalues of the hermitian Wilson Dirac operator, and we determine the extent to which the two are correlated.Comment: 7 pages, 5 figures, proceedings of the XXIX International Symposium on Lattice Field Theory - Lattice 2011, July 10-16, 2011, Squaw Valley, Lake Tahoe, Californi

Bulk transitions of twelve flavor QCD and UA(1)U_A(1) symmetry

We present an update on our ongoing study on the nature of the bulk transition observed at strong coupling in the SU(3) gauge theory with N_f = 12 flavors in the fundamental representation. We show evidence that there is a first order chiral symmetry breaking bulk transition separating a region at weak coupling where chiral symmetry is restored from a region at strong coupling where chiral symmetry is broken. We also discuss hints of a separate partial restoration of U_A(1) at weaker coupling. The results are in agreement with restoration of conformality in non abelian gauge theories as the number of flavors is increased.Comment: 7 pages, 10 figures, XXIX International Symposium on Lattice Field Theor

The bulk transition of many-flavour QCD and the search for a UVFP at strong coupling

We explore the nature of the bulk transition observed at strong coupling in the SU(3) gauge theory with Nf=12 fermions in the fundamental representation. The transition separates a weak coupling chirally symmetric phase from a strong coupling chirally broken phase and is compatible with the scenario where conformality is restored by increasing the flavour content of a non abelian gauge theory. We explore the intriguing possibility that the observed bulk transition is associated with the occurrence of an ultraviolet fixed point (UVFP) at strong coupling, where a new theory emerges in the continuum

Spectral properties of the Wilson Dirac operator in the ϵ\epsilon-regime

We investigate the spectral properties of the Wilson Dirac operator in quenched QCD in the microscopic regime. We distinguish the topological sectors using the index as determined by the Wilson flow method. Consequently, the distributions of the low-lying eigenvalues of the Wilson Dirac operator can be compared in each of the topological sectors to predictions from random matrix theory applied to the $\epsilon$-regime of chiral perturbation theory. We find rather good agreement for volumes as small as $(1.5 \, \text{fm})^4$ and lattice spacings as coarse as $0.1\, \text{fm}$, and demonstrate that it is indeed possible to extract low-energy constants for Wilson fermions from the spectral properties of the Wilson Dirac operator.Comment: Changed normalizations for some of the results, cosmetic updates to several plots. Conclusions not affected. Version accepted for publication by JHEP. 22 pages, 12 figure