Visualisation Room (201)
Lloyd Building
Trinity College Dublin
Time: 2:00 pm
| Date | Speaker | Institute | Title |
| 07 Oct 2009 | Dhagash Mehta | National University Of Ireland, Maynooth | Algebraic Geometry and Landau Gauge Fixing on the Lattice
View abstract On the lattice, the standard way to fix Landau gauge is to minimizing the so-called lattice Landau gauge (LLG)-fixing functional numerically. Minimizing a multivariate function efficiently is one of the fundamental problems in many branches of theoretical physics. The conventional numerical minimization methods such as Simulated Annealing and Over-relaxation are known to fail in obtaining the global minimum. We observe that the extremizing equations for the LLG-fixing functional and, in general, for multivariate functions arising in many physical phenomena have 'polynomial-like' non-linearity. After explaining how one can transform the extremizing equations for the LLG, for the compact U(1) case as an example, to a system of multivariate polynomial equations, we propose a few methods to solve these equations and obtain all the extrema of the LLG-fixing functional. I will demonstrate our preliminary results from both these methods. If time permits, I will also present the results for the modified lattice Landau gauge which was proposed recently, in order to establish the BRST symmetry on the lattice. |
| 28 Oct 2009 | John Bulava | Von Neumann Institute for Computing(NIC) at DESY, Zeuthen | The use of All-to-all propagators in Lattice QCD determinations of excited hadron spectra View abstract All-to-all propagators are needed to reliably extract the masses of excited hadron states from Lattice QCD simulations. I will report on preliminary results obtained using a recently proposed exact all-to-all algorithm. These results include excited baryon and meson spectra as well as moving hadrons. I will then introduce the Variance-Reduced Stochastic LapH (VRSL) all-to-all method which may be required to analyze large-volume lattice ensembles. The efficacy of the VRSL method is also discussed. |
| 11 Nov 2009 | Patrick Fritzsch | University of Southampton | Non-perturbative tests of HQET in small-volume two-flavour QCD View abstract I quantitatively investigate the quark mass dependence of current matrix elements and energies, calculated over a wide range of quark masses in the continuum limit of small-volume two-flavour lattice QCD. By a precise comparison of these observables as functions of the heavy quark mass with the predictions of HQET we are able to verify that their large quark mass behaviour is described by the effective theory. I furthermore report about the status of ongoing simulations carried out by the ALPHA collaboration with the goal of a fully non-perturbative matching of HQET and QCD. |
| 25 Nov 2009 | Carlos Pena | Universidad Autonma de Madrid | Exploring the low-energy regime of QCD with very light quarks View abstract In recent years Lattice QCD computations near the chiral limit have become possible, allowing for detailed studies of the dynamics of light mesons. In this context, the effective description of strong interactions at low energies via Chiral Perturbation Theory has a dual role: while still needed as a tool to further our understanding of the dynamics, the quantitative reach of ChiPT is being simultaneously tested by direct comparison with QCD. One particularly interesting development is the use of finite-volume chiral regimes to control systematic uncertainties in the determination of low-energy couplings. I will discuss the main ideas underlying the technique, as well as recent results for both strong and weak LECs. |
| 19 Jan 2010 | Niall Moran | NUI Maynooth (DAQIST) | Supersymmetric Lattice models View abstract I introduce a family of supersymmetric models on one and two dimensional lattices. These models exhibit many interesting properties including extensive ground state degeneracy, superfrustration and supertopological phases. I show how the Witten index and cohomology considerations can be used to calculate the ground state degeneracy on different lattices and provide insights about the possible structure of the ground state. Numerical approaches are discussed and details of our own large scale exact diagonalisation code will be presented. |
| 9 Mar 2010 | Olaf Kaczmarek | Bielefeld | Hadronic Correlation and Spectral Functions at Finite Temperature View abstract Hadronic correlation functions are important tools to analyze thermal modifications of the QCD medium at high temperatures and allow to extract important quantities that are relevant for the understanding of the states of matter produced in heavy ion experiments. Using non-perturbatively improved Wilson fermions we have calculated hadronic correlation functions in the light and charm quark sector on large quenched lattices close to the continuum limit. Thermal effects are analyzed on the basis of the correlation functions and spectral functions. On the basis of the vector spectral function we calculate dilepton rates from the quark gluon plasma and discuss the possibility of extracting transport coefficients, like diffusion constants and electrical conductivity, from the small frequency limit of the spectral functions. |
| 23 Mar 2010 | Jack Laiho | Glasgow | The neutral kaon mixing parameter from lattice QCD. View abstract A calculation of the kaon mixing parameter B_K using unquenched lattice QCD is presented along with a complete systematic error budget. The calculation was performed at two lattice spacings and uses non-perturbative matching. |
| 30 Mar 2010 | Enno E. Scholz | Regensburg | Physical Results from 2+1 Flavor Lattice-QCD with Domain Wall Fermions and Chiral Perturbation Theory View abstract I will report on the ongoing programme of the RBC and UKQCD Collaborations to simulate Quantum Chromodynamics (QCD) with 2+1 flavors on the lattice using the Domain Wall fermion formulation. In particular, I will present the results for the masses of the light mesons and their decay constants and will discuss the applicability of chiral perturbation theory in the pion and kaon sectors to extract "physical results", meaning results extrapolated to light quark masses as realized in Nature. The Domain Wall fermion formulation and its improved chiral properties are in particular advantageous in the extraction of B_K, the kaon bag parameter, which is needed to describe the mixing of the neutral kaons. Physical results for B_K using dynamical 2+1 flavor Domain Wall fermions will be presented as well. |