Computational Applied Mathematics Seminar

Visualisation Room (201)

Lloyd Building
Trinity College Dublin

Tuesdays at 2:00 pm

Date Speaker Institute Title
WEDS 19 Sept 2012 AT 11AM Liuming Liu TCD Interactions of Charmed Mesons with Light Pseudoscalar Mesons from Lattice QCD and Implications on the Nature of the Ds0*(2317)
View abstract We study the scattering of light pseudoscalar mesons (π, K) off charmed mesons (D, Ds) in full lattice QCD. The S-wave scattering lengths are calculated using Lüscher's finite volume technique. We use a relativistic formulation for the charm quark. For the light quark, we use domain-wall fermions in the valence sector and improved Kogut-Susskind sea quarks. We calculate the scattering lengths of isospin-3/2 D π, Ds π, Ds K, isospin-0 D Kbar and isospin-1 D Kbar channels on the lattice. For the chiral extrapolation, we use a chiral unitary approach to next-to-leading order, which at the same time allows us to give predictions for other channels. It turns out that the interpretation of the Ds0*(2317) as a DK molecule is consistent with the results. At the same time, we also update a prediction for the isospin breaking hadronic decay width Gamma(Ds0*(2317) -> Ds π) to (89 +/- 27) keV.
2 Oct 2012 John Bulava CERN Lattice Higgs-Yukawa simulations and BSM phenomenology
View abstract The discovery of a 125GeV Higgs at the LHC has put severe constraints on BSM phenomena. Vacuum stability bounds calculated from lattice simulations of a chiral Higgs-Yukawa model indicate that a 125GeV Standard Model Higgs boson is incompatible with a naive fourth generation of quarks with mass greater than ~300GeV. In addition to Higgs boson mass bounds, we present results on the electroweak phase transition in such a model as well as investigations of a novel bulk phase transition at very large Yukawa coupling.
23 Oct 2012 Michael Döring HISKP, Bonn Finite volume methods to extract resonances
View abstract Lattice gauge simulations allow for the ab-initio approach to hadronic resonances. To connect lattice results to the physical limit, chiral effective field theory serves to take account of finite volume effects as will be discussed in this talk. Varying the volume, applying hybrid boundary conditions, or working in moving frames promises to extract a maximum of information from lattice data. Such approaches are applied to coupled-channel pion-kaon and pion-pion scattering for which the required precision on lattice data are determined to access the broad scalar resonances. Also, coupled-channel meson-baryon scattering will be discussed including an outlook to three-body dynamics.
6 Nov 2012 AT 2:30PM Szabolcs Borsányi Wuppertal An easy scale setting in lattice QCD
View abstract Every lattice group has a favourite method to determine the lattice spacing. The Budapest-Marseille-Wuppertal group has recently introduced the w0 scale. I'll tell you why we like it so much. [arXiv:1203.4469]
13 Nov 2012 Alberto Ramos NIC at DESY, Zeuthen Nucleon sigma terms and dark matter searches
View abstract Direct dark matter detection is one of the challenges of the decade and can be a window to physics beyond the standard model. To interpret the results on dark matter searches it is crucial to understand the probability to detect these particles in actual experiments. I will try to review how lattice QCD can actually help us in this task. I will review the different strategies used to compute these sigma terms on the lattice focusing in some recent computations.
4 Dec 2012 Marina Marinkovic Southampton Fundamental parameters of QCD from non-perturbative methods
View abstract One of the long term project of the ALPHA collaboration is the computation of the input parameters of perturbative QCD in terms of low energy hadronic observables. We use the Schroedinger functional strategy to overcome the multi-scale problem in QCD and keep full control over the systematic errors. In this talk, I will present the scale setting for dimensionful quantities in CLS/ALPHA two flavor simulations. To control its dependence on the light quark mass, two different strategies for the chiral extrapolation are applied. This has enabled us to complete the non-perturbative calculations of the strange quark mass and the Lambda parameter in two flavor QCD. Finally, I will show an improved computation of the running of the Scroedinger functional coupling in four flavor QCD. This was the first step towards the computation of the Lambda parameter in the four flavor theory in physical units.
29 Jan 2013 Silas Beane New Hampshire/Bonn Nuclear physics from lattice QCD: a status report
View abstract I will discuss recent progress in calculating nuclear physics interactions and properties using lattice QCD. I will first focus on an area in which lattice QCD will soon be competitive with experiment; specifically, I will consider simple hypernuclear processes which are essential input into the nuclear equation of state relevant for a description of dense astrophysical objects. I will also discuss recent calculations of the spectrum of light nuclei and hypernuclei at the flavor SU(3) symmetric point. Finally, I will discuss very recent work which determines the nucleon-nucleon s-wave phase shifts at the SU(3) point.
WEDS 6 Feb 2013 AT 1:30PM Constantia Alexandrou Cyprus Results and open issues in hadron structure
19 Feb 2013 Thomas Rae Mainz Nucleon electromagnetic form factors from the lattice
View abstract We present recent results for the nucleon electromagnetic form factors, as well as the nucleon axial charge using lattice QCD. This includes the determination of the corresponding charge radii. The standard approach is to extract the form factors via a plateau fit to the lattice data using a 'large-enough' time separation between the operators at the source and sink. To check that this removes excited state contaminations to an acceptable level, we employ two further extraction methods: a fit that explicitly accounts for the contamination; and the use of a summed operator insertion, which suppresses the contamination. A comparison of the methods allows for the study of systematic effects related to excited state contributions entering in the q^2 dependence of the form factors. For this study we use the CLS ensembles using non-perturbatively O(a) improved Wilson fermions in Nf=2 QCD.
FRIDAY 1 Mar 2013, New Seminar Room, School of Maths Leonard Fister NUI Maynooth Confinement from Correlation Functions
View abstract We study confinement of static quarks via the Polyakov loop potential, which can be computed in functional continuum methods from low-order correlation functions. This links confinement of quarks to thermal n-point functions of pure gauge theory. The temperature-dependent two-point functions are studied in detail. This also allows for computations of thermodynamic quantities, i.e. the pressure.
5 Mar 2013 Vincent Drach NIC at DESY, Zeuthen Sigma terms of the nucleon from lattice QCD and Dark Matter searches
View abstract Detection of Dark Matter would certainly be a major breakthrough in particle physics. After reviewing why interpreting results obtained by direct detection experiments suffer from a large systematic uncertainty related to the so-called sigma terms of the Nucleon. I will present our strategy to compute directly the corresponding matrix elements using lattice QCD. I will discuss the lattice techniques and our analysis of systematic uncertainties. Finally I will present some preliminary results and compare them to other recent computations.
30 Apr 2013 AT 11:00AM,
New Seminar Room, School of Maths
Agostino Patella Plymouth Anomalous dimension of the chiral condensate from the Dirac-operator spectrum
View abstract A strategy for computing the anomalous dimension of the chiral condensate at the fixed point in infrared-conformal gauge theories from lattice simulations is discussed. The method is based on the scaling of the spectral density of the Dirac operator or rather its integral, the mode number. It is relatively cheap, mainly for two reasons: (a) the mode number can be determined with quite high accuracy, and (b) the anomalous dimension of the chiral condensate is extracted from a fit of several observables on the same set of configurations (no scaling in the Lagrangian parameters is needed).

As an example the anomalous dimension of the chiral condensate has been computed in the SU(2) theory with 2 Dirac fermions in the adjoint representation of the gauge group. In this particular case, the proposed strategy has proved to be very robust and effective. Old and new preliminary results will be presented.

Changed by Christopher Thomas (thomasc(at) 19 Apr 2013