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

Ecological Opportunity In Adaptive Radiation Of Galapagos Endemic Land Snails

The classic evolutionary hypothesis of ecological opportunity proposes that both heterogeneity of resources and freedom from enemies promote phenotypic divergence as a response to increased niche availability. Although phenotypic divergence and speciation have often been inferred to be the primary consequences of the release from competition or predation that accompanies a shift to a new adaptive zone, increased phenotypic variation within species is expected to represent the first stage resulting from such a shift. Using measures of intraspecific morphological variation of 30 species of Galapagos endemic land snails in a phylogenetically controlled framework, we show that the number of local congeners and the number of local plant species are associated with lower and higher intraspecific phenotypic variation, respectively. In this clade, ecological opportunity thus explicitly links the role of competition from congeners and the heterogeneity of resources to the extent of intraspecific phenotypic divergence as adaptive radiation proceeds.Integrative Biolog

Tests of non-standard electroweak couplings of right-handed quarks

The standard model can be interpreted as the leading order of a Low-Energy Effective Theory (LEET) invariant under a higher non linearly realized symmetry $S_{nat}\supset SU(2)_W \times U(1)_Y$ equipped with a systematic power counting. Within the minimal version of this ``not quite decoupling'' LEET, the dominant non-standard effect appears at next-to-leading order (NLO) and is a modification of the couplings of fermions to W and Z. In particular, the coupling of right-handed quarks to Z is modified and a direct coupling of right-handed quarks to W emerges. Charged right-handed lepton currents are forbidden by an additional discrete symmetry in the lepton sector originally designed to suppress Dirac neutrino masses. A complete NLO analysis of experimental constraints on these modified couplings is presented. Concerning couplings of light quarks, the interface of the electroweak tests with QCD aspects is discussed in detail.Comment: 56 pages, 14 figures, v2: references added, minor modifications in the text, accepted for publication in JHE

The pion charge radius from charged pion electroproduction

We analyze a low-energy theorem of threshold pion electroproduction which allows one to determine the charge radius of the pion. We show that at the same order where the radius appears, pion loops induce a correction to the momentum dependence of the longitudinal dipole amplitude $L_{0+}^{(-)}$. This model-independent correction amounts to an increase of the pion charge radius squared from the electroproduction data by about 0.26~fm$^2$. It sheds light on the apparent discrepancy between the recent determination of the pion radius from electroproduction data and the one based on pion-electron scattering.Comment: 3 pp, REVTeX, uses eps

Pion-Nucleon Phase Shifts in Heavy Baryon Chiral Perturbation Theory

We calculate the phase shifts in the pion-nucleon scattering using the heavy baryon formalism. We consider phase shifts for the pion energy range of 140 to $200$ MeV. We employ two different methods for calculating the phase shifts - the first using the full third order calculation of the pion-nucleon scattering amplitude and the second by including the resonances $\Delta$ and $N^*$ as explicit degrees of freedom in the Lagrangian. We compare the results of the two methods with phase shifts extracted from fits to the pion-nucleon scattering data. We find good to fair agreement between the calculations and the phase shifts from scattering data.Comment: 14 pages, Latex, 6figures. Revised version to appear in Phys.Rev.

The Internal Proper Motions Of Stars In The Open Cluster M35

Relative proper motions, based on 108 orbits of Hubble Space Telescope Fine Guidance Sensor data extending from 1992 to 2006, are reported for 74 stars in the open cluster M35 (NGC 2168). A subset of 22 of these objects are then used to compute the cluster's internal proper motion dispersions in both right ascension and declination. We find that these dispersions are equal to within their measurement errors. The average one-dimensional dispersion is 0.018 +/- 0.002 arcsec century(-1). When combined with the M35 radial velocity dispersion of 0.65 +/- 0.10 km s(-1) found by Geller et al., this produces a cluster distance of 762 +/- 145 pc. Using isochrone fits to the cluster main sequence, this distance suggests that M35 has an age of about 133 Myr. Although this age is consistent with that typically found for M35, the formal error in the dynamical distance of +/- 19% can accommodate ages between 65 Myr and 201 Myr.McDonald Observator