2,592 research outputs found
Staggered Chiral Perturbation Theory
We discuss how to formulate a staggered chiral perturbation theory. This
amounts to a generalization of the Lee-Sharpe Lagrangian to include more than
one flavor (i.e. multiple staggered fields), which turns out to be nontrivial.
One loop corrections to pion and kaon masses and decay constants are computed
as examples in three cases: the quenched, partially quenched, and full
(unquenched) case. The results for the one loop mass and decay constant
corrections have already been presented in Ref. [1].Comment: talk presented by C. Aubin at Lattice2002(spectrum); 3 pages, 1
figur
A Possible Aoki Phase for Staggered Fermions
The phase diagram for staggered fermions is discussed in the context of the
staggered chiral Lagrangian, extending previous work on the subject. When the
discretization errors are significant, there may be an Aoki-like phase for
staggered fermions, where the remnant SO(4) taste symmetry is broken down to
SO(3). We solve explicitly for the mass spectrum in the 3-flavor degenerate
mass case and discuss qualitatively the 2+1-flavor case. From numerical results
we find that current simulations are outside the staggered Aoki phase. As for
near-future simulations with more improved versions of the staggered action, it
seems unlikely that these will be in the Aoki phase for any realistic value of
the quark mass, although the evidence is not conclusive.Comment: 27 pages, 8 figures, uses RevTe
Quasiparticle and Cooper Pair Tunneling in the Vortex State of Bi-2212
From measurements of the c-axis I-V characteristics of intrinsic Josephson
junctions in Bi_2Sr_2CaCu_2O_{8+delta} (Bi-2212) mesas we obtain the field
dependence (H || c) of the quasiparticle (QP) conductivity, sigma_q(H,T), and
of the Josephson critical current density, J_c(H,T). The quasiparticle
conductivity sigma_q(H) increases sharply with H and reaches a plateau at 0.05
T <H< 0.3 T. We explain such behavior by the dual effect of supercurrents
around vortices. First, they enhance the QP DOS, leading to an increase of
sigma_q with H at low H and, second, they enhance the scattering rate for
specular tunneling as pancakes become disordered along the c-axis at higher H,
leading to a plateau at moderate H.Comment: 4 pages, 4 figure
Aubin property and uniqueness of solutions in cone constrained optimization
We discuss conditions for the Aubin property of solutions to perturbed cone constrained programs, by using and refining results given in Klatte and Kummer (Nonsmooth equations in optimization. Kluwer, Dordrecht, 2002). In particular, we show that constraint nondegeneracy and hence uniqueness of the multiplier is necessary for the Aubin property of the critical point map. Moreover, we give conditions under which the critical point map has the Aubin property if and only if it is locally single-valued and Lipschit
Leptonic decay constants f_Ds and f_D in three flavor lattice QCD
We determine the leptonic decay constants in three flavor unquenched lattice
QCD. We use O(a^2)-improved staggered light quarks and O(a)-improved charm
quarks in the Fermilab heavy quark formalism. Our preliminary results, based
upon an analysis at a single lattice spacing, are f_Ds = 263(+5-9)(+/-24) MeV
and f_D = 225(+11-13)(+/-21) MeV. In each case, the first reported error is
statistical while the is the combined systematic uncertainty.Comment: Talk presented at Lattice2004(heavy), Fermilab, June 21-26, 2004. 3
pages, 2 figure
Quantum tunneling in a three dimensional network of exchange coupled single-molecule magnets
A Mn4 single-molecule magnet (SMM) is used to show that quantum tunneling of
magnetization (QTM) is not suppressed by moderate three dimensional exchange
coupling between molecules. Instead, it leads to an exchange bias of the
quantum resonances which allows precise measurements of the effective exchange
coupling that is mainly due to weak intermolecular hydrogen bounds. The
magnetization versus applied field was recorded on single crystals of [Mn4]2
using an array of micro-SQUIDs. The step fine structure was studied via minor
hysteresis loops.Comment: 4 pages, 4 figure
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