27,411 research outputs found
A New Genus and Species of Isotomidae (Collembola), and a Redescription of \u3ci\u3eCryptopygus Exilus\u3c/i\u3e (Gisin) N. Comb
A new genus and species of Collembola in the family lsotomidae are described from Michigan: Micranurophorus musci n. g., n. sp. A redescription of Cryptopygus exilis (Gisin) (= Isotomina exilis Gisin) is also given, based on specimens from Michigan. The new genus is characterized by the lack of a furcula and by abdominal chaetotaxy similar to Isotomodes. It is related to Pseudanurophorus
Scalar Meson Spectroscopy with Lattice Staggered Fermions
With sufficiently light up and down quarks the isovector () and
isosinglet () scalar meson propagators are dominated at large distance by
two-meson states. In the staggered fermion formulation of lattice quantum
chromodynamics, taste-symmetry breaking causes a proliferation of two-meson
states that further complicates the analysis of these channels. Many of them
are unphysical artifacts of the lattice approximation. They are expected to
disappear in the continuum limit. The staggered-fermion fourth-root procedure
has its purported counterpart in rooted staggered chiral perturbation theory
(rSXPT). Fortunately, the rooted theory provides a strict framework that
permits the analysis of scalar meson correlators in terms of only a small
number of low energy couplings. Thus the analysis of the point-to-point scalar
meson correlators in this context gives a useful consistency check of the
fourth-root procedure and its proposed chiral realization. Through numerical
simulation we have measured correlators for both the and channels
in the ``Asqtad'' improved staggered fermion formulation in a lattice ensemble
with lattice spacing fm. We analyze those correlators in the context
of rSXPT and obtain values of the low energy chiral couplings that are
reasonably consistent with previous determinations.Comment: 23 pp., 3 figs., submitted to Phys. Rev.
Semileptonic Kaon Decay in Staggered Chiral Perturbation Theory
The determination of from kaon semileptonic decays
requires the value of the form factor , which can be calculated
precisely on the lattice. We provide the one-loop partially quenched staggered
chiral perturbation theory expressions that may be employed to analyze
staggered simulations of with three light flavors. We consider both
the case of a mixed action, where the valence and sea sectors have different
staggered actions, and the standard case where these actions are the same. The
momentum transfer of the form factor is allowed to have an arbitrary
value. We give results for the generic situation where the , , and
quark masses are all different, , and for the isospin limit,
. The expression we obtain for is independent of the mass
of the (valence) spectator quark. In the limit of vanishing lattice spacing,
our results reduce to the one-loop continuum partially quenched expression for
, which has not previously been reported in the literature for the
case. Our expressions have already been used in staggered lattice
analyses of , and should prove useful in future calculations as well.Comment: 33 pages, 5 figures; v2: some referencing change
\u3ci\u3eCryptopygus Bipunctatus\u3c/i\u3e (Collembola: Isotomidae) in North America, and \u3ci\u3eC. Posteroculatus\u3c/i\u3e N. Comb.
Specimens of Cryptopygus bipunctatus are reported and described from North America (Michigan) for the first time. The species is easily recognized by its lack of color, one pair of ocelli on black eyespots, and one flair of ventral manubrial setae. Michigan and European specimens are very· similar. A very similar Polish species, Isotomina posteroculata, is transferred to Cryptopygus
Staggered Chiral Perturbation Theory and the Fourth-Root Trick
Staggered chiral perturbation theory (schpt) takes into account the
"fourth-root trick" for reducing unwanted (taste) degrees of freedom with
staggered quarks by multiplying the contribution of each sea quark loop by a
factor of 1/4. In the special case of four staggered fields (four flavors,
nF=4), I show here that certain assumptions about analyticity and phase
structure imply the validity of this procedure for representing the rooting
trick in the chiral sector. I start from the observation that, when the four
flavors are degenerate, the fourth root simply reduces nF=4 to nF=1. One can
then treat nondegenerate quark masses by expanding around the degenerate limit.
With additional assumptions on decoupling, the result can be extended to the
more interesting cases of nF=3, 2, or 1. A apparent paradox associated with the
one-flavor case is resolved. Coupled with some expected features of unrooted
staggered quarks in the continuum limit, in particular the restoration of taste
symmetry, schpt then implies that the fourth-root trick induces no problems
(for example, a violation of unitarity that persists in the continuum limit) in
the lowest energy sector of staggered lattice QCD. It also says that the theory
with staggered valence quarks and rooted staggered sea quarks behaves like a
simple, partially-quenched theory, not like a "mixed" theory in which sea and
valence quarks have different lattice actions. In most cases, the assumptions
made in this paper are not only sufficient but also necessary for the validity
of schpt, so that a variety of possible new routes for testing this validity
are opened.Comment: 39 pages, 3 figures. v3: minor changes: improved explanations and
less tentative discussion in several places; corresponds to published versio
The isentropic equation of state of 2-flavor QCD
Using Taylor expansions of the pressure obtained previously in studies of
2-flavor QCD at non-zero chemical potential we calculate expansion coefficients
for the energy and entropy densities up to in the quark
chemical potential. We use these series in to determine lines of
constant entropy per baryon number () that characterize the expansion of
dense matter created in heavy ion collisions. In the high temperature regime
these lines are found to be well approximated by lines of constant .
In the low temperature phase, however, the quark chemical potential is found to
increase with decreasing temperature. This is in accordance with resonance gas
model calculations. Along the lines of constant we calculate the energy
density and pressure. Within the accuracy of our present analysis we find that
the ratio for as well as the softest point of the equation
of state, , show no significant dependence on
.Comment: 7 pages, 10 figure
A Lattice Study of the Gluon Propagator in Momentum Space
We consider pure glue QCD at beta=5.7, beta=6.0 and beta=6.3. We evaluate the
gluon propagator both in time at zero 3-momentum and in momentum space. From
the former quantity we obtain evidence for a dynamically generated effective
mass, which at beta=6.0 and beta=6.3 increases with the time separation of the
sources, in agreement with earlier results. The momentum space propagator G(k)
provides further evidence for mass generation. In particular, at beta=6.0, for
k less than 1 GeV, the propagator G(k) can be fit to a continuum formula
proposed by Gribov and others, which contains a mass scale b, presumably
related to the hadronization mass scale. For higher momenta Gribov's model no
longer provides a good fit, as G(k) tends rather to follow an inverse power
law. The results at beta=6.3 are consistent with those at beta=6.0, but only
the high momentum region is accessible on this lattice. We find b in the range
of three to four hundred MeV and the exponent of the inverse power law about
2.7. On the other hand, at beta=5.7 (where we can only study momenta up to 1
GeV) G(k) is best fit to a simple massive boson propagator with mass m. We
argue that such a discrepancy may be related to a lack of scaling for low
momenta at beta=5.7. {}From our results, the study of correlation functions in
momentum space looks promising, especially because the data points in Fourier
space turn out to be much less correlated than in real space.Comment: 19 pages + 12 uuencoded PostScript picture
Renormalization of the Lattice Heavy Quark Classical Velocity
In the lattice formulation of the Heavy Quark Effective Theory (LHQET), the
classical velocity is renormalized. The origin of this renormalization is the
reduction of Lorentz (or O(4)) invariance to (hyper)cubic invariance. The
renormalization is finite and depends on the form of the decretization of the
reduced heavy quark Dirac equation. For the Forward Time - Centered Space
discretization, the renormalization is computed both perturbatively, to one
loop, and non-perturbatively using an ensemble of lattices provided by the
Fermilab lattice collaboration. The estimates of the leading (linear) shift
agree, and indicate that for small classical velocities, the renormalized
velocity is reduced by about 25-30% relative to its bare (input) value.Comment: 4 pages in uuencoded compressed postscript (using uufiles); Talk
given at Lattice '95 (Melbourne
String breaking in Lattice QCD
The separation of a heavy quark and antiquark pair leads to the formation of
a tube of flux, or string, which should break in the presence of light
quark-antiquark pairs. This expected zero temperature phenomenon has proven
elusive in simulations of lattice QCD. We present simulation results that show
that the string does break in the confining phase at nonzero temperature.Comment: LATTICE98(hightemp), 3 pages, 4 figures, LaTe
Tunneling Spectroscopy and Vortex Imaging in Boron-Doped Diamond
We present the first scanning tunneling spectroscopy study of
single-crystalline boron doped diamond. The measurements were performed below
100 mK with a low temperature scanning tunneling microscope. The tunneling
density of states displays a clear superconducting gap. The temperature
evolution of the order parameter follows the weak coupling BCS law with
. Vortex imaging at low magnetic field also
reveals localized states inside the vortex core that are unexpected for such a
dirty superconductor.Comment: 4 pages, 4 figures, replaced with revised versio
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