17,324 research outputs found
Low-Energy Behavior of Gluons and Gravitons from Gauge Invariance
We show that at tree level, on-shell gauge invariance can be used to fully
determine the first subleading soft-gluon behavior and the first two subleading
soft-graviton behaviors. Our proofs of the behaviors for n-gluon and n-graviton
tree amplitudes are valid in D dimensions and are similar to Low's proof of
universality of the first subleading behavior of photons. In contrast to
photons coupling to massive particles, in four dimensions the soft behaviors of
gluons and gravitons are corrected by loop effects. We comment on how such
corrections arise from this perspective. We also show that loop corrections in
graviton amplitudes arising from scalar loops appear only at the second soft
subleading order. This case is particularly transparent because it is not
entangled with graviton infrared singularities. Our result suggests that if we
set aside the issue of infrared singularities, soft-graviton Ward identities of
extended BMS symmetry are not anomalous through the first subleading order.Comment: RevTeX, 5 figures, 28 pages; v3 minor corrections and clarification
A precise determination of the Bc mass from dynamical lattice QCD
We perform a precise calculation of the mass of the B_c meson using
unquenched configurations from the MILC collaboration including 2+1 flavours of
improved staggered quarks. Lattice NRQCD and the Fermilab formalism are used to
describe the b and c quarks respectively. We find the mass of the B_c meson to
be 6.304(16) GeVComment: Talk presented at Lattice2004(heavy), Fermilab, June 21-26. 3 pages,
2 figure
The new definition of lattice gauge fields and the Landau gauge
The Landau gauge fixing algorithm in the new definition of gauge fields is
presented. In this algorithm a new solver of the Poisson equations based on the
Green's function method is used. Its numerical performance of the gauge fixing
algorithm is presented. Performance of the smeared gauge fixing in SU(3) is
also investigated.Comment: LATTICE98(Algorithms) 3 pages 3, 3 eps figure
Frustration in Finite Density QCD
We present a detailed analysis of the QCD partition function in the Grand
Canonical formalism. Using the fugacity expansion we find evidence for
numerical instabilities in the standard evaluation of its coefficients. We
discuss the origin of this problem and propose an issue to it. The correct
analysis shows no evidence for a discontinuity in the baryonic density in the
strong coupling limit. The moderate optimism that was inspired by the Grand
Canonical Partition Function calculations in the last years has to be
considered ill-founded.Comment: 9 pages, 6 Postscript figures; some comments adde
The Arecibo Galaxy Environment Survey V : The Virgo Cluster (I)
We present 21 cm observations of a 10 2 degree region in the Virgo
cluster, obtained as part of the Arecibo Galaxy Environment Survey. 289 sources
are detected over the full redshift range (-2,000 + 20,000
km/s) with 95 belonging to the cluster ( 3,000 km/s). We combine
our observations with data from the optically selected Virgo Cluster Catalogue
(VCC) and the Sloan Digital Sky Survey (SDSS). Most of our detections can be
clearly associated with a unique optical counterpart, and 30% of the cluster
detections are new objects fainter than the VCC optical completeness limit. 7
detections may have no optical counterpart and we discuss the possible origins
of these objects. 7 detections appear associated with early-type galaxies. We
perform HI stacking on the HI-undetected galaxies listed in the VCC in this
region and show that they must have significantly less gas than those actually
detected in HI. Galaxies undetected in HI in the cluster appear to be really
devoid of gas, in contrast to a sample of field galaxies from ALFALFA.Comment: 23 pages, 22 figures, 4 table
Phase transition(s) in finite density QCD
The Grand Canonical formalism is generally used in numerical simulations of
finite density QCD since it allows free mobility in the chemical potential
. We show that special care has to be used in extracting numerical results
to avoid dramatic rounding effects and spurious transition signals. If we
analyze data correctly, with reasonable statistics, no signal of first order
phase transition is present and results using the Glasgow prescription are
practically coincident with the ones obtained using the modulus of the
fermionic determinant.Comment: 6 pages, 5 ps figs. To appear in Proceedings of "QCD at Finite Baryon
Density" workshop, Bielefeld, 27-30 April 199
Properties of charmonium in lattice QCD with 2+1 flavors of improved staggered sea quarks
We use the dynamical gluon configurations provided by the MILC collaboration
in a study of the charmonium spectrum and psi leptonic width. We examine sea
quark effects on mass splitting and on the leptonic decay matrix element for
light masses as low as m_s/5, while keeping the strange quark mass fixed and
the lattice spacing nearly constant.Comment: Lattice2003(heavy
Large Wilson loops with overlap and clover fermions: Two-loop evaluation of the b-quark mass shift and the quark-antiquark potential
We compute, to two loops in pertubation theory, the fermionic contribution to
rectangular RxT Wilson loops, for different values of R and T.
We use the overlap fermionic action. We also employ the clover action, for
comparison with existing results in the literature.
In the limit R, T -> Infinity our results lead to the shift in the b-quark
mass. We also evaluate the perturbative static potential as T -> Infinity.Comment: 24 pages, 14 figures, 14 table
- âŠ