Multichannel parametrization of \pi N scattering amplitudes and extraction of resonance parameters

We present results of a new multichannel partial-wave analysis for \pi N scattering in the c.m. energy range 1080 to 2100 MeV. This work explicitly includes \eta N and K \Lambda channels and the single pion photoproduction channel. Resonance parameters were extracted by fitting partial-wave amplitudes from all considered channels using a multichannel parametrization that is consistent with S-matrix unitarity. The resonance parameters so obtained are compared to predictions of quark models

A UV completion of scalar electrodynamics

In previous works, we constructed UV-finite and unitary scalar field theories with an infinite spectrum of propagating modes for arbitrary polynomial interactions. In this paper, we introduce infinitely many massive vector fields into a U(1) gauge theory to construct a theory with UV-finiteness and unitarity.Comment: 25 page

Parameterization dependence of T matrix poles and eigenphases from a fit to piN elastic scattering data

We compare fits to piN elastic scattering data, based on a Chew-Mandelstam K-matrix formalism. Resonances, characterized by T-matrix poles, are compared in fits generated with and without explicit Chew-Mandelstam K-matrix poles. Diagonalization of the S matrix yields the eigenphase representation. While the eigenphases can vary significantly for the different parameterizations, the locations of most T-matrix poles are relatively stable.Comment: 6 pages, 3 figures, 1 tabl

Gauge equivalence in QCD: the Weyl and Coulomb gauges

The Weyl-gauge ($A_0^a=0)$ QCD Hamiltonian is unitarily transformed to a representation in which it is expressed entirely in terms of gauge-invariant quark and gluon fields. In a subspace of gauge-invariant states we have constructed that implement the non-Abelian Gauss's law, this unitarily transformed Weyl-gauge Hamiltonian can be further transformed and, under appropriate circumstances, can be identified with the QCD Hamiltonian in the Coulomb gauge. We demonstrate an isomorphism that materially facilitates the application of this Hamiltonian to a variety of physical processes, including the evaluation of $S$-matrix elements. This isomorphism relates the gauge-invariant representation of the Hamiltonian and the required set of gauge-invariant states to a Hamiltonian of the same functional form but dependent on ordinary unconstrained Weyl-gauge fields operating within a space of ``standard'' perturbative states. The fact that the gauge-invariant chromoelectric field is not hermitian has important implications for the functional form of the Hamiltonian finally obtained. When this nonhermiticity is taken into account, the ``extra'' vertices in Christ and Lee's Coulomb-gauge Hamiltonian are natural outgrowths of the formalism. When this nonhermiticity is neglected, the Hamiltonian used in the earlier work of Gribov and others results.Comment: 25 page

Present status of the nonstrange and other flavor partners of the exotic Theta+ baryon

Given the existing empirical information about the exotic Theta+ baryon, we analyze possible properties of its SU(3)F-partners, paying special attention to the nonstrange member of the antidecuplet N*. The modified piN partial-wave analysis presents two candidate masses, 1680 MeV and 1730 MeV. In both cases, the N* should be rather narrow and highly inelastic. Our results suggest several directions for experimental studies that may clarify properties of the antidecuplet baryons, and structure of their mixing with other baryons. Recent experimental evidence from the GRAAL and STAR Collaborations could be interpreted as observations of a candidate for the Theta+ nonstrange partner.Comment: 4 pages, 1 figure, talk given at the Topical Group on Hadron Physics (Fermilab, Oct. 24-26, 2004

A New Renormalization Scheme of Fermion Fields in Electroweak Standard Model

This paper has been withdrawn by the author,due a immature idea.Comment: 6 page

Non-perturbative Landau gauge and infrared critical exponents in QCD

We discuss Faddeev-Popov quantization at the non-perturbative level and show that Gribov's prescription of cutting off the functional integral at the Gribov horizon does not change the Schwinger-Dyson equations, but rather resolves an ambiguity in the solution of these equations. We note that Gribov's prescription is not exact, and we therefore turn to the method of stochastic quantization in its time-independent formulation, and recall the proof that it is correct at the non-perturbative level. The non-perturbative Landau gauge is derived as a limiting case, and it is found that it yields the Faddeev-Popov method in Landau gauge with a cut-off at the Gribov horizon, plus a novel term that corrects for over-counting of Gribov copies inside the Gribov horizon. Non-perturbative but truncated coupled Schwinger-Dyson equations for the gluon and ghost propagators $D(k)$ and $G(k)$ in Landau gauge are solved asymptotically in the infrared region. The infrared critical exponents or anomalous dimensions, defined by $D(k) \sim 1/(k^2)^{1 + a_D}$ and $G(k) \sim 1/(k^2)^{1 + a_G}$ are obtained in space-time dimensions $d = 2, 3, 4$. Two possible solutions are obtained with the values, in $d = 4$ dimensions, $a_G = 1, a_D = -2$, or $a_G = [93 - (1201)^{1/2}]/98 \approx 0.595353, a_D = - 2a_G$.Comment: 26 pages. Modified 2.25.02 to update references and to clarify Introduction and Conclusio

Scaling hard vertical surfaces with compliant microspine arrays

A new approach for climbing hard vertical surfaces has been developed that allows a robot to scale concrete, stucco, brick and masonry walls without using suction or adhesives. The approach is inspired by the mechanisms observed in some climbing insects and spiders and involves arrays of microspines that catch on surface asperities. The arrays are located on the toes of the robot and consist of a tuned, multi-link compliant suspension. In this paper we discuss the fundamental issues of spine allometric scaling versus surface roughness and the suspension needed to maximize the probability that each spine will find a useable surface irregularity and to distribute climbing tensile and shear loads among many spines. The principles are demonstrated with a new climbing robot that can scale a wide range of exterior walls

The energies and residues of the nucleon resonances N(1535) and N(1650)

We extract pole positions for the N(1535) and N(1650) resonances using two different models. The positions are determined from fits to different subsets of the existing $\pi N\to\pi N$, $\pi N\to\eta N$ and $\gamma p\to\eta p$ data and found to be 1515(10)--i85(15)MeV and 1660(10)--i65(10)MeV, when the data is described in terms of two poles. Sensitivity to the choice of fitted data is explored. The corresponding $\pi \pi$ and $\eta \eta$ residues of these poles are also extracted.Comment: 9 page