arXiv subjects

B. Borasoy

Publications and source records attributed to B. Borasoy.

44 records · Page 3Linked to original sources

arXiv1999

The role of resonances in non-leptonic hyperon decays

We examine the importance of resonances for the non-leptonic hyperon decays in the framework of chiral perturbation theory. Lower lying resonances are included into the effective theory. Integrating out the heavy degrees of freedom in the resonance saturation scheme generates higher order counterterms in the effective Lagrangian, providing an estimate of the pertinent coupling constants. A fit to the eight independent decay amplitudes that are not related by isospin symmetry is performed and reasonable agreement for both s- and p- waves is achieved.

hep-ph↗

arXiv1998

Baryon axial currents

The baryon axial currents are calculated at one-loop order in heavy baryon chiral perturbation theory by employing both a cutoff and dimensional regularization. Data from the semileptonic baryon decays is used to perform a least-squares fit to the two axial couplings D and F of the effective Lagrangian. Predictions for the momentum dependent axial form factors are made and the two different regularization schemes are compared. We also include the spin-3/2 decuplet in the effective theory.

hep-ph↗

arXiv1998

Sigma-terms in heavy baryon chiral perturbation theory revisited

The $σ$-terms are calculated at next-to-leading order in heavy baryon chiral perturbation theory by employing a cutoff regularization. The results do not depend on the cutoff value to the order we are working . The baryon masses and $σ_{πN}(0)$ are used to perform a least-squares fit to the three appearing low-energy constants and predictions for the two $KN$ $σ$-terms and the strange contribution to the nucleon mass are made. The lack of convergence in the chiral expansions of these quantities when regularized dimensionally is overcome in the cutoff scheme. The $σ$-term shifts to the pertinent Cheng-Dashen points are calculated. We also include the spin-3/2 decuplet in the effective theory.

hep-ph↗

arXiv1998

Non-leptonic hyperon decays in chiral perturbation theory

The non-leptonic hyperon decays are analyzed up to one-loop order including all counterterms in the framework of heavy baryon chiral perturbation theory. We use the exchange of the spin-3/2 decuplet resonances as an indication of which low-energy constants contribute significantly to these investigated processes . We choose four independent decay amplitudes that are not related by isospin relations in order to perform a fit for the pertinent low-energy constants and find a satisfactory fit both for s- and p-waves. The chiral corrections to the lowest order forms for the s-waves are moderate whereas there are significant modifications of the p-wave amplitudes.

hep-ph↗

arXiv1997

Working group on $ππ$ and $π$N interactions - Summary

This is the summary of the working group on $ππ$ and $π$N interactions of the Chiral Dynamics Workshop in Mainz, September 1-5, 1997. Each talk is represented by an extended one page abstract. Some additional remarks by the convenors are added

hep-ph↗

arXiv1996

Chiral expansion of baryon masses and $σ$-terms

We analyze the octet baryon masses and the pion/kaon--nucleon $σ$--terms in the framework of heavy baryon chiral perturbation theory. We include {\it all} terms up-to-and-including quadratic order in the light quark masses, $m_q$. We develop a consistent scheme to estimate low--energy constants related to scalar--isoscalar operators in the framework of resonance exchange involving one--loop graphs. The pertinent low--energy constants can only be estimated up to some finite coefficients. Including contributions from loop graphs with intermediate spin--3/2 decuplet and spin--1/2 octet states and from tree graphs including scalar mesons, we use the octet baryon masses and the pion--nucleon $σ$--term to fix all but one of these coefficients. Physical results are insensitive to this remaining parameter. It is also demonstrated that two--loop corrections only modify some of the subleading low--energy constants. We find for the baryon mass in the chiral limit, $m_0 = 770 \pm 110$ MeV. While the corrections of order $m_q^2$ are small for the nucleon, they are still sizeable for the $Λ$, the $Σ$ and the $Ξ$. Therefore a definitive statement about the convergence of three--flavor baryon chiral perturbation can not yet be made. The strangeness content of the nucleon is $y = 0.21 \pm 0.20$. We also estimate the kaon--nucleon $σ$--terms and some two--loops contributions to the nucleon mass.

hep-ph↗

arXiv1995

Chiral Lagrangians for Baryons coupled to massive Spin-1 Fields

We analyze the effective low--energy field theory of Goldstone bosons and baryons chirally coupled to massive spin--1 fields. We use the electromagnetic baryon form factors to demonstrate the formal equivalence between the vector and the tensor field formulation for the spin--1 fields. We also discuss the origin of the so--called Weinberg term in pion--nucleon scattering and the role of $ρ$--meson exchange. Chirally coupled vector mesons do not give rise to this two--pion nucleon seagull interaction but rather to higher order corrections. Some problems of the formal equivalence arising in higher orders and related to loops are touched upon.

hep-ph↗

arXiv1995

Baryon masses and pion-nucleon $σ$-term to second order in the quark masses

We analyze the octet baryon masses and the pion--nucleon $σ$--term in the framework of heavy baryon chiral perturbation theory. In contrast to previous investigations, we include {\it all} terms up-to-and-including quadratic order in the light quark masses. The pertinent low--energy constants are fixed from resonance exchange. This leaves as the only free parameter the baryon mass in the chiral limit, $\krig{m}$. We find $\krig{m} = 749 \pm 125$~MeV together with $σ_{πN} (0) = 48 \pm 10$ ~MeV. We discuss various implications of these results.

hep-ph↗