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 ($a_0$) and isosinglet ($f_0$) 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 $a_0$ and $f_0$ channels in the ``Asqtad'' improved staggered fermion formulation in a lattice ensemble with lattice spacing $a = 0.12$ 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 $\vert V_{us}\vert$ from kaon semileptonic decays requires the value of the form factor $f_+(q^2=0)$, 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 $f_+(q^2)$ 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 $q^2$ of the form factor is allowed to have an arbitrary value. We give results for the generic situation where the $u$, $d$, and $s$ quark masses are all different, $N_f=1+1+1$, and for the isospin limit, $N_f=2+1$. The expression we obtain for $f_+(q^2)$ 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 $f_+(q^2)$, which has not previously been reported in the literature for the $N_f=1+1+1$ case. Our expressions have already been used in staggered lattice analyses of $f_+(0)$, 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 ${\cal O}(\mu_q^6)$ in the quark chemical potential. We use these series in $\mu_q/T$ to determine lines of constant entropy per baryon number ($S/N_B$) 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 $\mu_q/T$. 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 $S/N_B$ we calculate the energy density and pressure. Within the accuracy of our present analysis we find that the ratio $p/\epsilon$ for $T>T_0$ as well as the softest point of the equation of state, $(p/\epsilon)_{min}\simeq 0.075$, show no significant dependence on $S/N_B$.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 $\Delta(0)/k_B T_c \simeq 1.74$. 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