On the absence of fifth-order contributions to the nucleon mass in heavy-baryon chiral perturbation theory

(New version with some expanded discussion; figures and minor typos corrected.) We have calculated the contribution proportional to the fifth power of the pion mass in the chiral expansion of the nucleon mass in two flavour HBCPT. Only one irreducible two-loop integral enters, and this vanishes. All other corrections in the heavy-baryon limit can be absorbed in the physical pion-nucleon coupling constant which enters in the third order term, and so there are no contributions at fifth order. Including finite nucleon mass corrections, the only contribution agrees with the expansion of the relativistic one-loop graph in powers of the ration of the pion and nucleon masses, and is only 0.3% of the third order term. This is an encouraging result for the convergence of two-flavour heavy-baryon chiral perturbation theory.Comment: 4 pages RevTex, 4 eps figure

Baryon Electromagnetic Properties in Partially Quenched Heavy Hadron Chiral Perturbation Theory

The electromagnetic properties of baryons containing a heavy quark are calculated at next-to-leading order in partially quenched heavy hadron chiral perturbation theory. Calculations are performed for three light flavors in the isospin limit and additionally for two light non-degenerate flavors. We use partially-quenched charge matrices that are easy to implement on the lattice. The results presented are necessary for the light quark mass extrapolation and zero-momentum extrapolation of lattice QCD and partially quenched lattice QCD calculations of heavy hadron electromagnetic properties. Additionally relations between the sextet electromagnetic form factors and transition form factors are derived.Comment: 29 pages, 3 figures, RevTex

Integrating out the heaviest quark in N--flavour ChPT

We extend a known method to integrate out the strange quark in three flavour chiral perturbation theory to the context of an arbitrary number of flavours. As an application, we present the explicit formulae to one--loop accuracy for the heavy quark mass dependency of the low energy constants after decreasing the number of flavours by one while integrating out the heaviest quark in N--flavour chiral perturbation theory.Comment: 18 pages, 1 figure. Text and references added. To appear in EPJ

Strangeness in the Scalar Form Factor of the Nucleon

The scalar form factor of the nucleon and related physical quantities are investigated in the framework of the semibosonized SU(3) Nambu-Jona-Lasinio soliton model. We take into account the rotational $1/N_c$ corrections and linear $m_s$ corrections. The strangeness content of the nucleon in the scalar form factor is discussed in detail. In particular, it is found that the $m_s$ corrections play an essential role of reducing the $\langle N | \bar{s} s | N \rangle$ arising from the leading order and rotational $1/N_c$ contributions. We obtain the \sigma_{\pi N} (0)=40.80\;\mbox{MeV}, \Delta \sigma = \sigma_{\pi N} (2m^{2}_{\pi})-\sigma_{\pi N} (0) = 18.18\;\mbox{MeV} and \langle r^2\rangle^{S}_{N} = 1.50\;\mbox{fm}^2. The results are in a remarkable agreement with empirical data analyzed by Gasser, Leutwyler, and Sainio~\cite{gls}.Comment: 13 pages, RevTex is used. 3 figures as uufiles are include

Chiral perturbation theory with Wilson-type fermions including a2a^2 effects: Nf=2N_f=2 degenerate case

We have derived the quark mass dependence of $m_{\pi}^2$, $m_{\rm AWI}$ and $f_{\pi}$, using the chiral perturbation theory which includes the $a^2$ effect associated with the explicit chiral symmetry breaking of the Wilson-type fermions, in the case of the $N_f=2$ degenerate quarks. Distinct features of the results are (1) the additive renormalization for the mass parameter $m_q$ in the Lagrangian, (2) $O(a)$ corrections to the chiral log ($m_q\log m_q$) term, (3) the existence of more singular term, $\log m_q$, generated by $a^2$ contributions, and (4) the existence of both $m_q\log m_q$ and $\log m_q$ terms in the quark mass from the axial Ward-Takahashi identity, $m_{\rm AWI}$. By fitting the mass dependence of $m_\pi^2$ and $m_{\rm AWI}$, obtained by the CP-PACS collaboration for $N_f=2$ full QCD simulations, we have found that the data are consistently described by the derived formulae. Resumming the most singular terms $\log m_q$, we have also derived the modified formulae, which show a better control over the next-to-leading order correction.Comment: 21 pages, 4 figures (10 eps files), Revtex4, some discussions and references added, the final version to appear in PR

Chiral Corrections to Lattice Calculations of Charge Radii

Logarithmic divergences in pion and proton charge radii associated with chiral loops are investigated to assess systematic uncertainties in current lattice determinations of charge radii. The chiral corrections offer a possible solution to the long standing problem of why present lattice calculations yield proton and pion radii which are similar in size.Comment: PostScript file only. Ten pages. Figures included. U. of MD Preprint #92-19

Thermal Pions at Finite Isospin Chemical Potential

The density corrections, in terms of the isospin chemical potential $\mu_I$, to the mass of the pions are studied in the framework of the SU(2) low energy effective chiral lagrangian. The pion decay constant $f_{\pi}(T, \mu_{I})$ is also analized. As a function of temperature for $\mu_I =0$, the mass remains quite stable, starting to grow for very high values of $T$, confirming previous results. However, there are interesting corrections to the mass when both effects (temperature and chemical potential) are simultaneously present. At zero temperature the $\pi ^{\pm}$ should condensate when $\mu_{I} = \mp m_{\pi}$. This is not longer valid anymore at finite $T$. The mass of the $\pi_0$ acquires also a non trivial dependence on $\mu_I$ due to the finite temperature.Comment: 13 pages, 5 figure

A global fit of ππ\pi\pi and πK\pi K elastic scattering in ChPT with dispersion relations

We apply the one-loop results of the $SU(3)_L\times SU(3)_R$ ChPT suplemented with the inverse amplitude method to fit the available experimental data on $\pi\pi$ and $\pi K$ scattering. With esentially only three parameters we describe accurately data corresponding to six different channels, namely $(I,J)=(0,0), (2,0), (1,1), (1/2,0), (3/2,0)$ and $(1/2,1)$. In addition we reproduce the first resonances of the $(1,1)$ and $(1/2,1)$ channel with the right mass corresponding to the $\rho$ and the $K^*(892)$ particles.Comment: 19 pages, 5 figures available on request, FT/UCM/10/9

Pion propagation in real time field theory at finite temperature

We describe how the thermal counterpart of a vacuum two-point function may be obtained in the real time formalism in a simple way by using directly the $2\times 2$ matrices that different elements acquire in this formalism. Using this procedure we calculate the analytic (single component) thermal amplitude for the pion pole term in the ensemble average of two axial-vector currents to two loops in chiral perturbation theory. The general expressions obtained for the effective mass and decay constants of the pion are evaluated in the chiral and the nonrelativistic limits. We also investigate the effect of massive states on these effective parameters.Comment: 17 pages TeX and 9 eps figure