5,650 research outputs found
Heavy Dynamical Fermions in Lattice QCD
It is expected that the only effect of heavy dynamical fermions in QCD is to
renormalize the gauge coupling. We derive a simple expression for the shift in
the gauge coupling induced by flavors of heavy fermions. We compare this
formula to the shift in the gauge coupling at which the
confinement-deconfinement phase transition occurs (at fixed lattice size) from
numerical simulations as a function of quark mass and . We find remarkable
agreement with our expression down to a fairly light quark mass. However,
simulations with eight heavy flavors and two light flavors show that the eight
flavors do more than just shift the gauge coupling. We observe
confinement-deconfinement transitions at induced by a large number of
heavy quarks. We comment on the relevance of our results to contemporary
simulations of QCD which include dynamical fermions.Comment: COLO-HEP-311, 26 pages and 6 postscript figures; file is a shar file
and all macros are (hopefully) include
An adaptive pseudo-spectral method for reaction diffusion problems
The spectral interpolation error was considered for both the Chebyshev pseudo-spectral and Galerkin approximations. A family of functionals I sub r (u), with the property that the maximum norm of the error is bounded by I sub r (u)/J sub r, where r is an integer and J is the degree of the polynomial approximation, was developed. These functionals are used in the adaptive procedure whereby the problem is dynamically transformed to minimize I sub r (u). The number of collocation points is then chosen to maintain a prescribed error bound. The method is illustrated by various examples from combustion problems in one and two dimensions
The Traveling Salesman Problem: Low-Dimensionality Implies a Polynomial Time Approximation Scheme
The Traveling Salesman Problem (TSP) is among the most famous NP-hard
optimization problems. We design for this problem a randomized polynomial-time
algorithm that computes a (1+eps)-approximation to the optimal tour, for any
fixed eps>0, in TSP instances that form an arbitrary metric space with bounded
intrinsic dimension.
The celebrated results of Arora (A-98) and Mitchell (M-99) prove that the
above result holds in the special case of TSP in a fixed-dimensional Euclidean
space. Thus, our algorithm demonstrates that the algorithmic tractability of
metric TSP depends on the dimensionality of the space and not on its specific
geometry. This result resolves a problem that has been open since the
quasi-polynomial time algorithm of Talwar (T-04)
Role of golimumab, a TNF-alpha inhibitor, in the treatment of the psoriatic arthritis
Psoriatic arthritis (PsA) is an inflammatory arthritis that affects many psoriasis patients and can often have a debilitating disease progression. Golimumab is a new tumor necrosis factor (TNF) antagonist recently approved by the FDA for controlling signs and symptoms of psoriatic arthritis. In a Phase III clinical trial in patients with PsA, patients receiving golimumab showed significant improvement in the signs and symptoms of disease. It was usually well tolerated, but adverse events generally occurred more in patients receiving golimumab compared to placebo. Golimumab has also recently shown efficacy in slowing structural damage in PsA. This new biologic therapy provides physicians with another option in the treatment of this inflammatory arthritis while offering patients certain advantages over other TNF antagonists
Topological susceptibility in full QCD at zero and finite temperature
We present a study of the topological susceptibility on the lattice
for full QCD with 2 and 4 flavours of staggered fermions at zero and finite
temperature T. We find that presents a sharp drop across the
deconfinement transition. We also study the dependence of on the quark
mass at T=0: we have no conclusive evidence for the expected chiral behaviour.Comment: latex source, 8 pages, 4 figure
Canted antiferromagnetism in phase-pure CuMnSb
We report the low-temperature properties of phase-pure single crystals of the
half-Heusler compound CuMnSb grown by means of optical float-zoning. The
magnetization, specific heat, electrical resistivity, and Hall effect of our
single crystals exhibit an antiferromagnetic transition at and a second anomaly at a temperature . Powder and single-crystal neutron diffraction establish an
ordered magnetic moment of ,
consistent with the effective moment inferred from the Curie-Weiss dependence
of the susceptibility. Below , the Mn sublattice displays
commensurate type-II antiferromagnetic order with propagation vectors and
magnetic moments along (magnetic space group ).
Surprisingly, below , the moments tilt away from by
a finite angle , forming a canted antiferromagnetic
structure without uniform magnetization consistent with magnetic space group
. Our results establish that type-II antiferromagnetism is not the
zero-temperature magnetic ground state of CuMnSb as may be expected of the
face-centered cubic Mn sublattice.Comment: 14 pages, 15 figure
Detection of HC11N in the Cold Dust Cloud TMC-1
Two consecutive rotational transitions of the long cyanopolyyne HC11N,
J=39-38, and J=38-37, have been detected in the cold dust cloud TMC-1 at the
frequencies expected from recent laboratory measurements by Travers et al.
(1996), and at about the expected intensities. The astronomical lines have a
mean radial velocity of 5.8(1) km/s, in good agreement with the shorter
cyanopolyynes HC7N and HC9N observed in this very sharp-lined source [5.82(5)
and 5.83(5) km/s, respectively]. The column density of HC11N is calculated to
be 2.8x10^(11) cm^(-2). The abundance of the cyanopolyynes decreases smoothly
with length to HC11N, the decrement from one to the next being about 6 for the
longer carbon chains.Comment: plain tex 10 pages plus 3 ps fig file
Quarkonium mass splittings in three-flavor lattice QCD
We report on calculations of the charmonium and bottomonium spectrum in
lattice QCD. We use ensembles of gauge fields with three flavors of sea quarks,
simulated with the asqtad improved action for staggered fermions. For the heavy
quarks we employ the Fermilab interpretation of the clover action for Wilson
fermions. These calculations provide a test of lattice QCD, including the
theory of discretization errors for heavy quarks. We provide, therefore, a
careful discussion of the results in light of the heavy-quark effective
Lagrangian. By and large, we find that the computed results are in agreement
with experiment, once parametric and discretization errors are taken into
account.Comment: 21 pages, 17 figure
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