Mixing-Matrix Renormalization Revisited

We study the renormalization of normal mixing matrices, which includes hermitian and unitary matrices as particular cases. We give a minimal, multiplicative parametrization of counterterms, and compute the renormalized Lagrangian to one-loop order in several models with N species of fermions, both in on-shell and MS schemes. In on-shell scheme the mass-degenerate case is considered separately.Comment: 23+1 LaTeX pages, no figures, uses amslatex, amsfont

Three and Two-Point One-Loop Integrals in Heavy Particle Effective Theories

We give a complete analytical computation of three and two-point loop integrals occurring in heavy-particle theories, involving a velocity change, for arbitrary real values of the external masses and residual momenta.Comment: 16 pages, Latex2e, no figure

Polarized pK−pK^- scattering in Unitary Baryon Chiral Perturbation Theory

We study $pK^-$ scattering in the energy range from threshold through the $\Lambda(1520)$ peak in UBChPT, taking into account $\mathcal{O}(q)$ vertices from meson-baryon contact interactions and $s$- and $u$-channel ground-state baryon exchange, $s$- and $u$-channel decuplet- and nonet-baryon exchange and $t$-channel vector-meson exchange, as well as $\mathcal{O}(q^2)$ flavor-breaking vertices. Detailed fits to data are presented, including a substantial body of differential cross-section data with meson momentum $q_\mathrm{lab} > 300$ MeV not considered in previous treatments.Comment: v2: Two references added

Vertex integrals in heavy-particle theories

We give the results of complete analytical computations of two- and three-point loop integrals ocurring in heavy particle theories, with and without velocity change, for arbitrary values of external momenta and masses.Comment: 4 pages, Latex2e + aipproc, contributed talk at the VIII Mexican Workshop on Particles and Fields, Nov. 14-20, 2001, Zacatecas, Mexico, to appear in the AIP Proceedings. One reference correcte

Rotating frames and gauge invariance in two-dimensional many-body quantum systems

We study the quantization of many-body systems in two dimensions in rotating coordinate frames using a gauge invariant formulation of the dynamics. We consider reference frames defined by linear and quadratic gauge conditions. In both cases we discuss their Gribov ambiguities and commutator algebra. We construct the momentum operators, inner-product and Hamiltonian in both types of gauges, for systems with and without translation invariance. The analogy with the quantization of QED in non-covariant gauges is emphasized. Our results are applied to quasi-rigid systems in the Eckart frame.Comment: 18 pages, LaTeX2e, AmsLaTe

Perturbative thresholds in the physical region

We consider unstable-particle scattering in the context of 3-body processes. We show that all partial-wave cross-sections are finite and positive, and the total cross-section is proportional to the transverse size of space in the region of on-shell particle exchange. We comment on the role of loop corrections.Comment: 13 + 1 pages, plain LaTeX 2e + PostScript, to appear in Z. Phys.