80 research outputs found
Comparing the R algorithm and RHMC for staggered fermions
The R algorithm is widely used for simulating two flavours of dynamical
staggered fermions. We give a simple proof that the algorithm converges to the
desired probability distribution to within O(dt^2) errors, but show that the
relevant expansion parameter is (dt/m)^2, m being the quark mass. The Rational
Hybrid Monte Carlo (RHMC) algorithm provides an exact (i.e., has no step size
errors) alternative for simulating the square root of the staggered Dirac
operator. We propose using it to test the validity of the R algorithm for
simulations carried out with dt m.Comment: 3 pages, proceedings from Lattice 2002 poster presentatio
The RHMC Algorithm for 2 Flavours of Dynamical Staggered Fermions
We describe an implementation of the Rational Hybrid Monte Carlo (RHMC)
algorithm for dynamical computations with two flavours of staggered quarks. We
discuss several variants of the method, the performance and possible sources of
error for each of them, and we compare the performance and results to the
inexact R algorithm.Comment: Lattice2003(machine) 3 pages, 1 figure. Added referenc
On the Dynamics of Light Quarks in QCD
We describe recent results concerning the behavior of lattice QCD with light
dynamical Wilson and Staggered quarks. We show that it is possible to reach
regions of parameter space with light pions using Wilson
fermions. If the Hybrid Molecular Dynamics (HMD) algorithm is used with the
same parameters it gives incorrect results. We also present preliminary results
using a higher-order integration scheme.Comment: 4 pages (all in postscript), proceedings of LAT'9
Continuous-time quantum walk on integer lattices and homogeneous trees
This paper is concerned with the continuous-time quantum walk on Z, Z^d, and
infinite homogeneous trees. By using the generating function method, we compute
the limit of the average probability distribution for the general isotropic
walk on Z, and for nearest-neighbor walks on Z^d and infinite homogeneous
trees. In addition, we compute the asymptotic approximation for the probability
of the return to zero at time t in all these cases.Comment: The journal version (save for formatting); 19 page
Algorithms for Lattice QCD with Dynamical Fermions
We consider recent progress in algorithms for generating gauge field
configurations that include the dynamical effects of light fermions. We survey
what has been achieved in recent state-of-the-art computations, and examine the
trade-offs between performance and control of systematic errors. We briefly
review the use of polynomial and rational approximations in Hybrid Monte Carlo
algorithms, and some of the theory of on-shell chiral fermions on the lattice.
This provides a theoretical framework within which we compare algorithmic
alternatives for their implementation; and again we examine the trade-offs
between speed and error control.Comment: Review presented at Lattice2004(plenary), Fermilab, June 21-26, 2004.
14 pages, 8 figure
Resummations of free energy at high temperature
We discuss resummation strategies for free energy in quantum field theories
at nonzero temperatures T. We point out that resummations should be performed
for the short- and long-distance parts separately in order to avoid spurious
interference effects and double-counting. We then discuss and perform Pade
resummations of these two parts for QCD at high T. The resummed results are
almost invariant under variation of the renormalization and factorization
scales. We perform the analysis also in the case of the massless scalar
theory.Comment: 16 pages, revtex4, 15 eps-figures; minor typographic errors
corrected; the version as it appears in Phys.Rev.
Quenched Lattice QCD with Domain Wall Fermions and the Chiral Limit
Quenched QCD simulations on three volumes, , and
and three couplings, , 5.85 and 6.0 using domain
wall fermions provide a consistent picture of quenched QCD. We demonstrate that
the small induced effects of chiral symmetry breaking inherent in this
formulation can be described by a residual mass (\mres) whose size decreases
as the separation between the domain walls () is increased. However, at
stronger couplings much larger values of are required to achieve a given
physical value of \mres. For and , we find
\mres/m_s=0.033(3), while for , and ,
\mres/m_s=0.074(5), where is the strange quark mass. These values are
significantly smaller than those obtained from a more naive determination in
our earlier studies. Important effects of topological near zero modes which
should afflict an accurate quenched calculation are easily visible in both the
chiral condensate and the pion propagator. These effects can be controlled by
working at an appropriately large volume. A non-linear behavior of in
the limit of small quark mass suggests the presence of additional infrared
subtlety in the quenched approximation. Good scaling is seen both in masses and
in over our entire range, with inverse lattice spacing varying between
1 and 2 GeV.Comment: 91 pages, 34 figure
Setting and analysis of the multi-configuration time-dependent Hartree-Fock equations
In this paper we motivate, formulate and analyze the Multi-Configuration
Time-Dependent Hartree-Fock (MCTDHF) equations for molecular systems under
Coulomb interaction. They consist in approximating the N-particle Schrodinger
wavefunction by a (time-dependent) linear combination of (time-dependent)
Slater determinants. The equations of motion express as a system of ordinary
differential equations for the expansion coefficients coupled to nonlinear
Schrodinger-type equations for mono-electronic wavefunctions. The invertibility
of the one-body density matrix (full-rank hypothesis) plays a crucial role in
the analysis. Under the full-rank assumption a fiber bundle structure shows up
and produces unitary equivalence between convenient representations of the
equations. We discuss and establish existence and uniqueness of maximal
solutions to the Cauchy problem in the energy space as long as the density
matrix is not singular. A sufficient condition in terms of the energy of the
initial data ensuring the global-in-time invertibility is provided (first
result in this direction). Regularizing the density matrix breaks down energy
conservation, however a global well-posedness for this system in L^2 is
obtained with Strichartz estimates. Eventually solutions to this regularized
system are shown to converge to the original one on the time interval when the
density matrix is invertible.Comment: 48 pages, 1 figur
Quantum walks: a comprehensive review
Quantum walks, the quantum mechanical counterpart of classical random walks,
is an advanced tool for building quantum algorithms that has been recently
shown to constitute a universal model of quantum computation. Quantum walks is
now a solid field of research of quantum computation full of exciting open
problems for physicists, computer scientists, mathematicians and engineers.
In this paper we review theoretical advances on the foundations of both
discrete- and continuous-time quantum walks, together with the role that
randomness plays in quantum walks, the connections between the mathematical
models of coined discrete quantum walks and continuous quantum walks, the
quantumness of quantum walks, a summary of papers published on discrete quantum
walks and entanglement as well as a succinct review of experimental proposals
and realizations of discrete-time quantum walks. Furthermore, we have reviewed
several algorithms based on both discrete- and continuous-time quantum walks as
well as a most important result: the computational universality of both
continuous- and discrete- time quantum walks.Comment: Paper accepted for publication in Quantum Information Processing
Journa
Linkage in mice of genes controlling an immunoglobulin kappa-chain marker and the surface alloantigen Ly-3 on T lymphocytes
Evidence obtained using recombinant inbred and congenic mouse strains has shown that the PC8 locus responsible for determining a marker on a single k chain in inbred mice is linked to the Ly - 2,3 locus on chromosome 6. The upper limit of the map distance between these loci is approximately three centimorgans. This finding is discussed in relation to other known light-chain variants that are associated with the Ly - 2,3 locus.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46753/1/251_2005_Article_BF01563929.pd
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