11,603 research outputs found
Glauber dynamics for the quantum Ising model in a transverse field on a regular tree
Motivated by a recent use of Glauber dynamics for Monte-Carlo simulations of
path integral representation of quantum spin models [Krzakala, Rosso,
Semerjian, and Zamponi, Phys. Rev. B (2008)], we analyse a natural Glauber
dynamics for the quantum Ising model with a transverse field on a finite graph
. We establish strict monotonicity properties of the equilibrium
distribution and we extend (and improve) the censoring inequality of Peres and
Winkler to the quantum setting. Then we consider the case when is a regular
-ary tree and prove the same fast mixing results established in [Martinelli,
Sinclair, and Weitz, Comm. Math. Phys. (2004)] for the classical Ising model.
Our main tool is an inductive relation between conditional marginals (known as
the "cavity equation") together with sharp bounds on the operator norm of the
derivative at the stable fixed point. It is here that the main difference
between the quantum and the classical case appear, as the cavity equation is
formulated here in an infinite dimensional vector space, whereas in the
classical case marginals belong to a one-dimensional space
Multigrid solution of compressible turbulent flow on unstructured meshes using a two-equation model
The system of equations consisting of the full Navier-Stokes equations and two turbulence equations was solved for in the steady state using a multigrid strategy on unstructured meshes. The flow equations and turbulence equations are solved in a loosely coupled manner. The flow equations are advanced in time using a multistage Runge-Kutta time stepping scheme with a stability bound local time step, while the turbulence equations are advanced in a point-implicit scheme with a time step which guarantees stability and positively. Low Reynolds number modifications to the original two equation model are incorporated in a manner which results in well behaved equations for arbitrarily small wall distances. A variety of aerodynamic flows are solved for, initializing all quantities with uniform freestream values, and resulting in rapid and uniform convergence rates for the flow and turbulence equations
Quark Masses and Renormalization Constants from Quark Propagator and 3-point Functions
We have computed the light and strange quark masses and the renormalization
constants of the quark bilinear operators, by studying the large-p^2 behaviour
of the lattice quark propagator and 3-point functions. The calculation is
non-perturbatively improved, at O(a), in the chiral limit. The method used to
compute the quark masses has never been applied so far, and it does not require
an explicit determination of the quark mass renormalization constant.Comment: LATTICE99 (Improvement and Renormalization) - 3 pages, 2 figure
A Theoretical Prediction of the Bs-Meson Lifetime Difference
We present the results of a quenched lattice calculation of the operator
matrix elements relevant for predicting the Bs width difference. Our main
result is (\Delta\Gamma_Bs/\Gamma_Bs)= (4.7 +/- 1.5 +/- 1.6) 10^(-2), obtained
from the ratio of matrix elements, R(m_b)=/<\bar
B_s^0|Q_L|B_s^0>=-0.93(3)^(+0.00)_(-0.01). R(m_b) was evaluated from the two
relevant B-parameters, B_S^{MSbar}(m_b)=0.86(2)^(+0.02)_(-0.03) and
B_Bs^{MSbar}(m_b) = 0.91(3)^(+0.00)_(-0.06), which we computed in our
simulation.Comment: 21 pages, 7 PostScript figure
Non-perturbatively Renormalized Light-Quark Masses with the Alpha Action
We have computed the light quark masses using the O(a^2) improved Alpha
action, in the quenched approximation. The renormalized masses have been
obtained non-perturbatively. By eliminating the systematic error coming from
the truncation of the perturbative series, our procedure removes the
discrepancies, observed in previous calculations, between the results obtained
using the vector and the axial-vector Ward identities. It also gives values of
the quark masses larger than those obtained by computing the renormalization
constants using (boosted) perturbation theory. Our main results, in the RI
(MOM) scheme and at a renormalization scale \mu=2 GeV, are m^{RI}_s= 138(15)
MeV and m^{RI}_l= 5.6(5) MeV, where m^{RI}_s is the mass of the strange quark
and m^{RI}_l=(m^{RI}_u+m^{RI}_d)/2 the average mass of the up-down quarks. From
these results, which have been obtained non-perturbatively, by using continuum
perturbation theory we derive the \bar{MS} masses, at the same scale, and the
renormalization group invariant (m^{RGI}) masses. We find m^{NLO \bar{MS}}_s=
121(13)$ MeV and m^{NLO\bar{MS}}_l= 4.9(4) MeV at the next-to-leading order;
m^{N^2LO \bar{MS}}_s= 111(12) MeV, m^{N^2LO \bar{MS}}_l= 4.5(4) MeV, m_s^{RGI}=
177(19) MeV and m^{RGI}_l= 7.2(6) MeV at the next-to-next-to-leading order.Comment: 13 pages, 1 figur
Combined Relativistic and static analysis for all Delta B=2 operators
We analyse matrix elements of Delta B=2 operators by combining QCD results
with the ones obtained in the static limit of HQET. The matching of all the QCD
operators to HQET is made at NLO order. To do that we have to include the
anomalous dimension matrix up to two loops, both in QCD and HQET, and the one
loop matching for all the Delta B=2 operators. The matrix elements of these
operators are relevant for the prediction of the B-\bar B mixing, B_s meson
width difference and supersymmetric effects in Delta B=2 transitions.Comment: 3 pages, 1 figure. Lattice2001(heavyquark
Electromagnetic and strong isospin-breaking corrections to the muon from Lattice QCD+QED
We present a lattice calculation of the leading-order electromagnetic and
strong isospin-breaking corrections to the hadronic vacuum polarization (HVP)
contribution to the anomalous magnetic moment of the muon. We employ the gauge
configurations generated by the European Twisted Mass Collaboration (ETMC) with
dynamical quarks at three values of the lattice spacing ( fm) with pion masses between and
MeV. The results are obtained adopting the RM123 approach in the
quenched-QED approximation, which neglects the charges of the sea quarks. Quark
disconnected diagrams are not included. After the extrapolations to the
physical pion mass and to the continuum and infinite-volume limits the
contributions of the light, strange and charm quarks are respectively equal to
, and . At leading order in and we obtain , which is currently the most accurate determination of the
isospin-breaking corrections to .Comment: 23 pages, 7 figures, 5 tables. Version to appear in PRD. A bug in the
update of the strange and charm contributions is removed and an extended
discussion on the identification of the ground-state is included. arXiv admin
note: text overlap with arXiv:1808.00887, arXiv:1707.0301
Decays with Domain Wall Fermions: Towards Physical Results
We are using domain wall fermions to study matrix elements by
measuring and matrix elements on the lattice and
employing chiral perturbation theory to relate these to the desired physical
result. The residual chiral symmetry breaking of domain wall fermions with a
finite extent in the fifth dimension impacts these measurements. Using the
Ward-Takahashi identities, we investigate residual chiral symmetry breaking
effects for divergent quantities and study pathologies of the quenched
approximation for small quark mass. We then discuss the operator
, where chiral symmetry is vital for the subtraction of unphysical
effects.Comment: 4 pages, 3 figures, Lattice 2000 (Hadronic Matrix Elements), RBC
Collaboration, corrected equations 2 and
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