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M. Napsuciale

Publications and source records attributed to M. Napsuciale.

46 records · Page 3Linked to original sources
arXiv2000

Chiral loops and a_0(980) exchange in ϕ->π^0ηγ

The radiative $ϕ\toπ^0ηγ$ decay is discussed emphasizing the effects of the $a_0$(980) scalar resonance which dominates the high values of the $π^0η$ invariant mass spectrum. In its lowest part, the proposed amplitude coincides with the reliable and ChPT-inspired contribution coming from chiral loops. The $a_0$(980) resonance is then incorporated exploiting the complementarity between ChPT and the linear sigma model for this channel. The recently reported experimental invariant mass distribution and branching ratio can be satisfactorily accommodated in our framework. For the latter, a value of $B(ϕ\toπ^0ηγ)$ in the range $(0.75$--$0.95)\times 10^{-4}$ is predicted.

hep-ph↗
arXiv1999

$γγ\to π^0 π^0$ as a test for the existence of a light $σ$ meson

We work out predictions of the Linear Sigma Model for the $γγ\toπ^0 π^0$ cross section. We consider the sigma width, which is introduced in a consistent way with chiral Ward identities. The results of Chiral Perturbation Theory are recovered in the $m_σ\to \infty$ limit. A fit to existing experimental results is consistent with a light and broad $σ$ meson.

hep-ph↗
arXiv1999

Pion Scattering Revisited

Chiral Ward identities lead to consistent accounting for the sigma's width in the linear sigma model's Feynman rules. Reanalysis of pion scattering data at threshold imply a mass for the sigma of 600+ 200 - 100 MeV.

hep-ph↗
arXiv1999

The Linear Sigma Model at Work: Succesful Postdictions for Pion Scattering

We enforce chiral Ward identities on the vertices of the linear sigma model to take into account the width of the scalar sigma, considered as a true physical resonance. We consider pion scattering at very low energies and, from a fit to the measured phase shifts in the various angular momentum and isospin channels, conclude a mass for the sigma of 600+200-100 MeV. Its width turns out to be of the same size.

hep-ph↗
arXiv1999

The omega to rho pi transition and omega to rho 3 pi decay

We evaluate the omega to rho pi transition and the omega to 3 pi decay using a Quark Level Linear Sigma Model ($QLσM$). We obtain $g^{QLσM}_{ωρπ}= (10.33 - 14.75) GeV^{-1}$ to be compared with other model dependent estimates averaging to $g_{ωρπ} = 16 GeV^{-1}$. We show that in the $QLσM$ a contact term is generated for the $ω\to 3 π$ decay. Although the contact contribution by itself is small, the interference effects turn out to be important.

hep-ph↗
arXiv1998

Scalar meson masses and mixing angle in a U(3)XU(3) Linear Sigma Model

Meson properties are considered within a U(3)\times U(3) Linear Sigma Model(LSM). The importance of the U_A(1)-breaking term and the OZI rule violating term in the generation of meson masses and mixing angles is stressed. The LSM parameters are fitted to the pseudoscalar meson spectrum thus giving predictions for scalar meson properties. The model predicts a scalar meson nonet whose members are: {σ(\approx 400), f_0(980), κ(\approx 900) and a_0(980)} resonances. Scalar meson mixing angle (in the {|ns>, |s>} basis) is predicted to be ϕ_S\approx -14^\circ. Therefore the f_0(980) is predominantly strange while the σ(\approx 400) is mostly non-strange. The model also gives a pseudoscalar mixing angle ϕ_P\approx 35^\circ which corresponds to θ_P \approx -19^\circ in the singlet-octet basis. Comparison with chiral perturbation theory shows that L_8 is saturated by scalar mesons exchange. However, LSM predicts that L_5 is not saturated by scalar mesons exchange as assumed in the literature.

hep-ph↗
arXiv1998

Inclusive J/psi production in Upsilon decay via color-octet mechanisms

Calculations for inclusive J/psi production in Upsilon decay through the color-octet mechanisms b\bar b[^3S_1, 1] -> c \bar c[^{2s+1}L_J, 8] + g are presented. It is shown that these O(alpha^5_sv^4_c) contributions compete with other color-octet mechanisms considered in the literature. A critical numerical analysis of the color-octet contributions to Upsilon -> J/psi + X shows that further work in this channel, both theoretical and experimental, is necessary in order to clearly understand the significance of the color-octet component of the c \bar c component inside the J/psi system.

hep-ph↗
arXiv1996

Heavy Baryon Spin 3/2 Theory and Radiative Decays of the Decuplet

We study the radiative decays of the decuplet $(3/2 \to 1/2 γ)$ using Heavy Baryon Chiral Perturbation Theory (HBChPT). We emphasize the problems faced by the interacting spin 3/2 field theory. We argue that, to lowest order in the $1/m$ expansion, HBChPT provides a framework where R-invariance and the appropiated constraints for the interacting spin 3/2 fields are consistently incorporated. We perform a gauge invariant calculation of the decay amplitudes, to lowest order in $1/m$ and to order $w^2/Λ^2_χ$ in the chiral expansion and report analytical results for the one-loop contributions to the two form factors involved in the $3/2 \to 1/2 γ$ transitions. Parameters independent predictions for the SU(3) forbidden decays are presented.

hep-ph↗