arXiv subjects

C. Schat

Publications and source records attributed to C. Schat.

5 recordsLinked to original sources

arXiv2014

Three-nucleon force at large distances: Insights from chiral effective field theory and the large-N_c expansion

We confirm the claim of Ref. [D.R. Phillips, C. Schat, Phys. Rev. C88 (2013) 3, 034002] that 20 operators are sufficient to represent the most general local isospin-invariant three-nucleon force and derive explicit relations between the two sets of operators suggested in Refs. [D.R. Phillips, C. Schat, Phys. Rev. C88 (2013) 3, 034002] and [H. Krebs, A.M. Gasparyan, E. Epelbaum, Phys.Rev. C87 (2013) 5, 054007]. We use the set of 20 operators to discuss the chiral expansion of the long- and intermediate-range parts of the three-nucleon force up to next-to-next-to-next-to-next-to-leading order in the standard formulation without explicit Delta(1232) degrees of freedom. We also address implications of the large-N_c expansion in QCD for the size of the various three-nucleon force contributions.

nucl-th↗

arXiv2008

S-wave γγ\to ππand f_0(980)\to ππ

We report on a dispersion relation for the γγ\to (ππ)_I S-wave in isospin I emphasizing the low energy region. The f_0(980) signal that emerges in γγ\to ππis also discussed. Our results could be used to distinguish between different ππisoscalar S-wave parameterizations. We also calculate the width of the σresonance to γγand obtain the value Γ(σ\toγγ)=(1.68\pm 0.15) KeV. Finally, we elaborate on the size of the f_0(980) coupling to ππand show that its smallness compared to the K\bar{K} one is not related to the OZI rule.

hep-ph↗

arXiv2007

Scalar radius of the pion and two photons into two pions. Strong S-wave final state interactions

The quadratic pion scalar radius, ^π_s, plays an important role for present precise determinations of ππscattering. The solution of the Muskhelishvili-Omnès equations for the non-strange null isospin (I) pion scalar form factor determines that ^π_s=(0.61\pm 0.04) fm^2. However, by using an Omnès representation of this form factor, Ynduráin recently obtains ^π_s=(0.75\pm 0.07) fm^2. A large discrepancy between both values, given the precision, then results. We show that Ynduráin's method is indeed compatible with the determinations from the Muskhelishvili-Omnès equations once a zero in the scalar form factor for some S-wave I=0 T-matrices is considered. Once this is accounted for, the resulting value is ^π=(0.63\pm 0.05) fm^2. On the other hand, we perform a theoretical study of the reaction γγ\to π^0π^0 based on dispersion relations. The large source of uncertainty for \sqrt{s}\gtrsim 0.5 GeV, due to variations in the phase used in the Omnès function above the K\bar{K} threshold, is removed by taking one more subtraction in the dispersion relation. This allows us to make sharper predictions for the cross section so that one could use this reaction to distinguish between different low energy ππparameterizations, once independent experiments are available. We also study the role played by the σor f_0(600) meson in this reaction and determine its width to two photons.

hep-ph↗

arXiv2004

Decays of Non-strange Negative Parity Baryons in the 1/Nc Expansion

The decays of non-strange negative parity baryons via the emission of single $π$ and $η$ mesons are analyzed in the framework of the $1/N_c$ expansion. A basis of spin-flavor operators for the partial wave amplitudes is established to order $1/N_c$ and the unknown effective coefficients are determined by fitting to the S- and D-wave partial widths as provided by the Particle Data Group. A set of relations between widths that result at the leading order, i.e. order $N_c^0$, is given and tested with the available data. Up to a few exceptions, a good description of the partial decays widths is already obtained at that order. Because of the rather large errors in the empirical input data the next to leading order fit fails to pin down with satisfactory accuracy the subleading effective coefficients. The hierarchy expected from the $1/N_c$ expansion is reflected in the results.

hep-ph↗

arXiv2003

Analysis of the [56,2^+] Baryon Masses in the 1/Nc Expansion

The mass spectrum of the positive parity [56,2^+] baryons is studied in the 1/Nc expansion up to and including O(1/Nc) effects with SU(3) symmetry breaking implemented to first order. A total of eighteen mass relations result, several of which are tested with the available data. The breaking of spin-flavor symmetry is dominated by the hyperfine interactions, while spin-orbit effects are found to be small.

hep-ph↗