14652665
What can Lattice QCD theorists learn from NMR spectroscopists
The Lattice QCD (LQCD) community has occasionally gone through periods of self-examination of its data analysis methods and compared them with methods used in other disciplines [22, 16, 18]. This process has shown that the techniques widely used elsewhere may also be useful in analyzing LQCD data. It seems that we are in such a period now with many groups trying what are generally called Bayesian methods such as Maximal Entropy (MEM) or constrained fitting [19, 15, 1, 7, 5, and many others]. In these proceedings we will attempt to apply this process to a comparison of data modeling techniques used in LQCD and NMR Spectroscopy to see if there are methods which may also be useful when applied to LQCD data.
117040988
Lattice QCD determination of states with spin 5/2 or higher in the spectrum of nucleons
Energies for excited isospin 1/2 states that include the nucleon are computed using quenched, anisotropic lattices. Baryon interpolating field operators that are used include nonlocal operators that provide G{sub 2} irreducible representations of the octahedral group. States with spin 5/2 or higher are identified as degenerate energies that occur in irreducible representations of the octahedral group corresponding to the subduction of the continuum spin.
8077181
The Conformal Window in SU(3) Yang-Mills
Yang-Mills theory is known to exhibit very different behavior as the number of light fermion flavors N f is varied. In particular, for sufficiently large N f the theory changes fro confining to conformal behavior in the infrared. We have obtained results for SU(3) Yang-Mills, based on the study of the running coupling through the Schrodinger Functional approach, that the transition between these two phases occurs between 8 and 12 flavors. I will present the details of our staggered fermion simulations at N f = 8 and 12.
6851820
The Effect of Reduced Spatial Symmetries on Lattice States: Results for Non-zero Linear Momentum
The irreducible representations of the cubic space group are described and used to determine the mapping of continuum states to lattice states with non-zero linear momentum. The Clebsch-Gordan decomposition is calculated from the character table for the cubic space group. These results are used to identify multiparticle states which appear in the hadron spectrum on the lattice.
94025058
Lattice QCD and nucleon resonances
Abstract Lattice calculations provide an ab initio means for the study of QCD. Recent progress at understanding the spectrum and structure of nucleons from lattice QCD studies is reviewed. Measurements of the masses of the lightest particles for the lowest spin values are described and related to predictions of the quark model. Measurements of the mass of the first radial excitation of the nucleon, the so-called Roper resonance, obtained using Bayesian statistical analyses, are detailed. The need to perform calculations at realistically light values of the pion mass is emphasised, and the exciting progress at attaining such masses is outlined. The talk concludes with future prospects, emphasising the importance of constructing a basis of interpolating operators that is sensitive to three-quark states, to multi-quark states, and to excited glue.
14915954
Dynamical lattice QCD thermodynamics with domain wall fermions
We present results from simulations of two flavor QCD thermodynamics at N_t=4 with domain wall fermions. In contrast to other lattice fermion formulations, domain wall fermions preserve the full chiral symmetry of the continuum at finite lattice spacing (up to terms exponentially small in an extra parameter). Just above the phase transition, we find that the axial U(1) symmetry is broken only by a small amount. We discuss an ongoing calculation to determine the order and properties of the phase transition using domain wall fermions, since the global symmetries of the theory are expected to be important here.
13865546
Evidence for wavelike energy transfer through quantum coherence in photosynthetic systems
Photosynthetic complexes are exquisitely tuned to capture solar light efficiently, and then transmit the excitation energy to reaction centres, where long term energy storage is initiated. The energy transfer mechanism is often described by semiclassical models that invoke ‘hopping’ of excited-state populations along discrete energy levels. Two-dimensional Fourier transform electronic spectroscopy has mapped these energy levels and their coupling in the Fenna–Matthews–Olson (FMO) bacteriochlorophyll complex, which is found in green sulphur bacteria and acts as an energy ‘wire’ connecting a large peripheral light-harvesting antenna, the chlorosome, to the reaction centre. The spectroscopic data clearly document the dependence of the dominant energy transport pathways on the spatial properties of the excited-state wavefunctions of the whole bacteriochlorophyll complex. But the intricate dynamics of quantum coherence, which has no classical analogue, was largely neglected in the analyses—even though electronic energy transfer involving oscillatory populations of donors and acceptors was first discussed more than 70 years ago, and electronic quantum beats arising from quantum coherence in photosynthetic complexes have been predicted and indirectly observed. Here we extend previous two-dimensional electronic spectroscopy investigations of the FMO bacteriochlorophyll complex, and obtain direct evidence for remarkably long-lived electronic quantum coherence playing an important part in energy transfer processes within this system. The quantum coherence manifests itself in characteristic, directly observable quantum beating signals among the excitons within the Chlorobium tepidum FMO complex at 77 K. This wavelike characteristic of the energy transfer within the photosynthetic complex can explain its extreme efficiency, in that it allows the complexes to sample vast areas of phase space to find the most efficient path.
123387338
Design Studies for a High-Repetition-Rate FEL Facility at LBNL
Lawrence Berkeley National Laboratory (LBNL) is working to address the needs of the primary scientific Grand Challenges now being considered by the U.S. Department of Energy, Office of Basic Energy Sciences: we are exploring scientific discovery opportunities, and new areas of science, to be unlocked with the use of advanced photon sources. A partnership of several divisions at LBNL is working to define the science and instruments needed in the future. To meet these needs, we propose a seeded, high-repetition-rate, free-electron laser (FEL) facility. Temporally and spatially coherent photon pulses, of controlled duration ranging from picosecond to sub-femtosecond, are within reach in the vacuum ultraviolet (VUV) to soft X-ray regime, and LBNL is developing critical accelerator physics and technologies toward this goal. We envision a facility with an array of FELs, each independently configurable and tunable, providing a range of photon-beam properties with high average and peak flux and brightness.