2,334 research outputs found
Adaptive multigrid algorithm for the lattice Wilson-Dirac operator
We present an adaptive multigrid solver for application to the non-Hermitian
Wilson-Dirac system of QCD. The key components leading to the success of our
proposed algorithm are the use of an adaptive projection onto coarse grids that
preserves the near null space of the system matrix together with a simplified
form of the correction based on the so-called gamma_5-Hermitian symmetry of the
Dirac operator. We demonstrate that the algorithm nearly eliminates critical
slowing down in the chiral limit and that it has weak dependence on the lattice
volume
A Mammalian Homolog of Drosophila melanogaster Transcriptional Coactivator Intersex Is a Subunit of the Mammalian Mediator Complex
The multiprotein Mediator complex is a coactivator required for transcriptional activation of RNA polymerase II transcribed genes by DNA binding transcription factors. We previously partially purified a Med8-containing Mediator complex from rat liver nuclei (Brower, C. S., Sato, S., Tomomori-Sato, C., Kamura, T., Pause, A., Stearman, R., Klausner, R. D., Malik, S., Lane, W. S., Sorokina, I., Roeder, R. G., Conaway, J. W., and Conaway, R. C. (2002) Proc. Natl. Acad. Sci. U. S. A. 99, 10353–10358). Analysis of proteins present in the most highly enriched Mediator fractions by tandem mass spectrometry led to the identification of several new mammalian Mediator subunits, as well as several potential Mediator subunits. Here we identify one of these proteins, encoded by the previously uncharacterized AK000411 open reading frame, as a new subunit of the mammalian Mediator complex. The AK000411 protein, which we designate hIntersex (human Intersex), shares significant sequence similarity with the Drosophila melanogaster intersex protein, which has functional properties expected of a transcriptional coactivator specific for the Drosophila doublesex transactivator. In addition, we show that hIntersex assembles into a subcomplex with Mediator subunits p28b and TRFP. Taken together, our findings identify a new subunit of the mammalian Mediator and shed new light on the architecture of the mammalian Mediator complex
Instantons and Monopoles in General Abelian Gauges
A relation between the total instanton number and the quantum-numbers of
magnetic monopoles that arise in general Abelian gauges in SU(2) Yang-Mills
theory is established. The instanton number is expressed as the sum of the
`twists' of all monopoles, where the twist is related to a generalized Hopf
invariant. The origin of a stronger relation between instantons and monopoles
in the Polyakov gauge is discussed.Comment: 28 pages, 8 figures; comments added to put work into proper contex
Diffractive Higgs Production by AdS Pomeron Fusion
The double diffractive Higgs production at central rapidity is formulated in
terms of the fusion of two AdS gravitons/Pomerons first introduced by Brower,
Polchinski, Strassler and Tan in elastic scattering. Here we propose a simple
self-consistent holographic framework capable of providing phenomenologically
compelling estimates of diffractive cross sections at the LHC. As in the
traditional weak coupling approach, we anticipate that several phenomenological
parameters must be tested and calibrated through factorization for a
self-consistent description of other diffractive process such as total cross
sections, deep inelastic scattering and heavy quark production in the central
region.Comment: 53 pages, 8 figure
Effective Lagrangian for strongly coupled domain wall fermions
We derive the effective Lagrangian for mesons in lattice gauge theory with
domain-wall fermions in the strong-coupling and large-N_c limits. We use the
formalism of supergroups to deal with the Pauli-Villars fields, needed to
regulate the contributions of the heavy fermions. We calculate the spectrum of
pseudo-Goldstone bosons and show that domain wall fermions are doubled and
massive in this regime. Since we take the extent and lattice spacing of the
fifth dimension to infinity and zero respectively, our conclusions apply also
to overlap fermions.Comment: 26 pp. RevTeX and 3 figures; corrected error in symmetry breaking
scheme and added comments to discussio
Multigrid for Chiral Lattice Fermions: Domain Wall
Critical slowing down for the Krylov Dirac solver presents a major obstacle
to further advances in lattice field theory as it approaches the continuum
solution. We propose a new multi-grid approach for chiral fermions, applicable
to both the 5-d domain wall or 4-d Overlap operator. The central idea is to
directly coarsen the 4-d Wilson kernel, giving an effective domain wall or
overlap operator on each level. We provide here an explicit construction for
the Shamir domain wall formulation with numerical tests for the 2-d Schwinger
prototype, demonstrating near ideal multi-grid scaling. The framework is
designed for a natural extension to 4-d lattice QCD chiral fermions, such as
the M\"obius, Zolotarev or Borici domain wall discretizations or directly to a
rational expansion of the 4-d Overlap operator. For the Shamir operator, the
effective overlap operator is isolated by the use of a Pauli-Villars
preconditioner in the spirit of the K\"ahler-Dirac spectral map used in a
recent staggered MG algorithm [1].Comment: 39 pages, 13 figure
- …