The Inverse Amplitude Method and Adler Zeros

The Inverse Amplitude Method is a powerful unitarization technique to enlarge the energy applicability region of Effective Lagrangians. It has been widely used to describe resonances from Chiral Perturbation Theory as well as for the Strongly Interacting Symmetry Breaking Sector. In this work we show how it can be slightly modified to account also for the sub-threshold region, incorporating correctly the Adler zeros required by chiral symmetry and eliminating spurious poles. These improvements produce negligible effects on the physical region.Comment: 17 pages, 4 figure

Gender-related biases in admission decisions

Journal ArticleThe competitive admission process for educational programs in health sciences usually begins with a screening phase. Raters, who are often the same people who later interview the applicants, screen candidates based on information on their application forms. Only the applicants who survive the screening phase progress to the interview phase

Nature of the f_0(600) from its N_c dependence at two loops in unitarized Chiral Perturbation Theory

By using unitarized two-loop Chiral Perturbation Theory partial waves to describe pion-pion scattering we find that the dominant component of the lightest scalar meson does not follow the q-qbar dependence on the number of colors that, in contrast, is obeyed by the lightest vectors. The method suggests that a subdominant q-qbar component of the f_0(600) possibly originates around 1 GeV.Comment: 4 pages, 1 Figure. To appear in Phys. Rev. Let

Comment on Neutron-Proton Spin-Correlation Parameter A_{ZZ} at 68 Mev

We present two arguments indicating that the large value for the $\epsilon_1$ mixing parameter at 50 MeV, which the Basel group extracted from their recent $A_{zz}$ measurement, may be incorrect. First, there are nucleon-nucleon (NN) potentials which predict the $\epsilon_1$ at 50 MeV substantially below the Basel value and reproduce the Basel $A_{zz}$ data accurately. Second, the large value for $\epsilon_1$ at 50 MeV proposed by the Basel group can only be explained by a model for the NN interaction which is very unrealistic (no $\rho$-meson and essentially a point-like $\pi NN$ vertex) and overpredicts the $\epsilon_1$ in the energy range where it is well determined (150--500 MeV) by a factor of two.Comment: 6 pages text (LaTex) and 2 figures (paper, will be faxed upon request), UI-NTH-930

A Study in Depth of f0(1370)

Claims have been made that f0(1370) does not exist. The five primary sets of data requiring its existence are refitted. Major dispersive effects due to the opening of the 4pi threshold are included for the first time; the sigma -> 4pi amplitude plays a strong role. Crystal Barrel data on pbar-p -> 3pizero at rest require f0(1370) signals of at least 32 and 33 standard deviations in 1S0 and 3P1 annihilation respectively. Furthermore, they agree within 5 MeV for mass and width. Data on pbar-p -> eta-eta-pizero agree and require at least a 19 standard deviation contribution. This alone is sufficient to demonstrate the existence of f0(1370). BES II data for J/Psi -> phi-pi-pi contain a visible f0(1370) signal > 8 standard devations. In all cases, a resonant phase variation is required. The possibility of a second pole in the sigma amplitude due to the opening of the 4pi channel is excluded. Cern-Munich data for pi-pi elastic scattering are fitted well with the inclusion of some mixing between sigma, f0(1370) and f0(1500). The pi-pi widths for f2(1565), rho3(1690), rho3(1990) and f4(2040) are determined.Comment: 25 pages, 22 figures. Typos corrected in Eqs 2 and 7. Introduction rewritten. Conclusions unchange

Flatte-like distributions and the a_0(980)/f_0(980) mesons

We explore the features of Flatte-like parametrizations. In particular, we demonstrate that the large variation in the absolute values of the coupling constants to the pi-eta (or pi-pi) and KKbar channels for the a_0(980) and f_0(980) mesons that one can find in the literature can be explained by a specific scaling behaviour of the Flatte amplitude for energies near the KKbar threshold. We argue that the ratio of the coupling constants can be much better determined from a fit to experimental data.Comment: 12 pages, 12 figure

The nature of σ\sigma, κ\kappa, a0(980)a_0(980) and f0(980)f_0(980)

Masses and widths of the four light scalar mesons $\sigma$, $\kappa$, $a_0$(980) and $f_0$(980) may be reproduced in a model where mesons scatter via a $q\bar{q}$ loop. A transition potential is used to couple mesons to $q\bar{q}$ at a radius of $\sim 0.57$ fm. Inside this radius, there is an infinite bare spectrum of confined $q\bar{q}$ states, for which a harmonic oscillator is chosen here. The coupled-channel system approximately reproduces the features of both light and heavy meson spectroscopy. The generation of $\sigma$, $\kappa$, $a_0(980)$ and $f_0(980)$ is a balance between attraction due to the $q\bar q$ loop and suppression of the amplitudes at the Adler zeros. Phase shifts increase more rapidly as the coupling constant to the mesons increases. This leads to resonant widths which decrease with increasing coupling constant - a characteristically non-perturbative effect.Comment: Plain LaTeX, 10 pages, 3 EPS figures; v2: 11 pages, better-quality figures, extra references, version accepted for publication in Phys. Lett.

CHIRAL SYMMETRY CONSTRAINTS ON THE K+K^+ INTERACTION WITH THE NUCLEAR PION CLOUD

The real part of the $K^{+}$ selfenergy for the interaction of the $K^{+}$ with the pion nuclear cloud is evaluated in lowest order of chiral perturbation theory and is found to be exactly zero in symmetric nuclear matter. This removes uncertainties in that quantity found in former phenomenological analyses and is supported by present experimental data on $K^{+}$ nucleus scattering.Comment: 11 pp, LaTeX file, 4 figures (appended as compressed tar files, uses epsf.sty

On the precision of the theoretical predictions for pi pi scattering

In a recent paper, Pelaez and Yndurain evaluate some of the low energy observables of pi pi scattering and obtain flat disagreement with our earlier results. The authors work with unsubtracted dispersion relations, so that their results are very sensitive to the poorly known high energy behaviour of the scattering amplitude. They claim that the asymptotic representation we used is incorrect and propose an alternative one. We repeat their calculations on the basis of the standard, subtracted fixed-t dispersion relations, using their asymptotics. The outcome fully confirms our earlier findings. Moreover, we show that the Regge parametrization proposed by these authors for the region above 1.4 GeV violates crossing symmetry: Their ansatz is not consistent with the behaviour observed at low energies.Comment: Added more material, mostly in Sects. 7, 8 and 9, in support of the same conclusions. Latex, 28 pages, 3 figure

The two-pion spectra for the reaction \pi^- p -> \pi^0\pi^0 n at 38 GeV/c pion momentum and combined analysis of the GAMS, Crystal Barrel and BNL data

We perform the K-matrix analysis of meson partial waves with IJ^{PC} =00^{++}, 10^{++}, 02^{++}, 12^{++} basing on GAMS data on \pi^-p -> \pi^0\pi^0 n, \eta\eta n, \eta\eta' n together with BNL data on \pi^-p -> K\bar K n and Crystal Barrel data on p\bar p (at rest) -> \pi^0\pi^0\pi^0, \pi^0\eta\eta, \pi^0\pi^0\eta. The positions of the amplitude poles (physical resonances) are determined as well as the positions of the K-matrix poles (bare states) and the values of bare state couplings to two-meson channels. Nonet classification of the determined bare states is discussed.Comment: LaTex, 15 pages and 10 figure