2,539 research outputs found
Twisted-mass reweighting for O(a) improved Wilson fermions
We test the reweighting of the quark determinant of O(a) improved Wilson
fermions in the domain-decomposed hybrid Monte-Carlo algorithm. Specifically,
we implement a reweighting in a twisted-mass parameter proposed by Palombi and
L\"uscher in QCD. We find that at equal acceptance rate, the
algorithm is significantly more stable on a lattice upon
switching on the reweighting parameter. At the same time, the reweighting
factor does not fluctuate strongly and hence is under control. At equal
statistics, the uncertainty on the pion correlator is comparable to the case of
the standard, unreweighted algorithm.Comment: 7 pages, 5 figures, XXIX International Symposium On Lattice Field
Theor
Calculation of the pion electromagnetic form factor from lattice QCD
We present a lattice calculation of the vector form factor of the pion for
two flavours of non-perturbatively O(a) improved Wilson fermions. For the
measurements we utilise the CLS ensembles which include various lattice
spacings and pion masses down to about 250 MeV. To obtain a fine momentum
resolution near zero momentum transfer (q^2) partially twisted boundary
conditions are employed using several twist angles. Due to the fine resolution
around q^2=0 we are able to determine the slope of the form factor and, in
turn, extract the charge radius of the pion without any model dependence. The
results for the form factor and the charge radius are then compared to chiral
perturbation theory and phenomenological models which are used to extrapolate
the results to the physical point.Comment: 4 pages, 4 figures, talk presented at Hadron 2011: 14th International
Conference on Hadron Spectroscopy, Munich, German
Pressure-Induced Superconductivity in Sc to 74 GPa
Using a diamond anvil cell with nearly hydrostatic helium pressure medium we
have significantly extended the superconducting phase diagram Tc(P) of Sc, the
lightest of all transition metals. We find that superconductivity is induced in
Sc under pressure, Tc increasing monotonically to 8.2 K at 74.2 GPa. The Tc(P)
dependences of the trivalent d-electron metals Sc, Y, La, and Lu are compared
and discussed within a simple s-d charge transfer framework.Comment: to be published in Phys. Rev. B (Brief Reports
Towards the Nf = 2 deconfinement transition temperature with O(a) improved Wilson fermions
A lot of effort in lattice simulations over the last years has been devoted to studies of the QCD deconfinement transition. Most state-of-the-art simulations use rooted staggered fermions, while Wilson fermions are affected by large systematic uncertainties, such as coarse lattices or heavy sea quarks. Here we report on an ongoing study of the transition, using two degenerate flavours of nonperturbatively O(a) improved Wilson fermions. We start with Nt = 12 and 16 lattices and pion masses of 600 to 450 MeV, aiming at chiral and continuum limits with light quarks
Towards the N_f=2 deconfinement transition temperature with O(a) improved Wilson fermions: An update
We give an update on our current project to determine the transition
temperature and the order of the deconfinement transition in the chiral limit
of two flavour QCD. We use nonperturbatively O(a) improved Wilson fermions of
the Sheikholeslami-Wohlert type, employing the efficient deflation accelerated
DDHMC algorithm. We start at lattices with N_t>=12 and pion masses below 600
MeV, aiming at chiral and continuum limits with light quarks.Comment: 3 pages, 4 figures, talk given at "Quark Confinement and the Hadron
Spectrum IX", Madrid, Spain, Aug. 30-Sep. 3, 2010, submitted to AIP
Conference Proceeding
QCD thermodynamics with O(a) improved Wilson fermions at Nf=2
We present an update of our study of the phase diagram of two-flavour QCD at
zero baryon density with dynamical improved Wilson quarks. All
simulations are done on lattices with a temporal extent of and spatial
extent and 64, ensuring that discretisation effects are small and
finite size effects can be controlled. In the approach to the chiral limit we
currently have three scans with pion masses between 540 and 200 MeV. In this
proceedings article the focus is on the new scan at MeV and the
measurement of screening masses. We also present first results concerning a
test of scaling in the approach to the chiral limit and the chiral
extrapolation of the difference of screening masses in scalar and pseudoscalar
channels, which provides a measure for the strength of the anomalous breaking
of the symmetry.Comment: 7 pages, 5 figures, talk presented at the 31st International
Symposium on Lattice Field Theory (Lattice 2013), 29 July - 3 August 2013,
Mainz, German
A new representation of the Adler function for lattice QCD
We address several aspects of lattice QCD calculations of the hadronic vacuum
polarization and the associated Adler function. We implement a representation
derived previously which allows one to access these phenomenologically
important functions for a continuous set of virtualities, irrespective of the
flavor structure of the current. Secondly we present a theoretical analysis of
the finite-size effects on our particular representation of the Adler function,
based on the operator product expansion at large momenta and on the spectral
representation of the Euclidean correlator at small momenta. Finally, an
analysis of the flavor structure of the electromagnetic current correlator is
performed, where a recent theoretical estimate of the Wick-disconnected diagram
contributions is rederived independently and confirmed.Comment: 9 pages, 5 figure
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