Search results for "Roper resonance"
showing 10 items of 15 documents
A microscopic N N → N N*(1440) potential
2004
By means of a NN → N N* (1440) transition potential derived in a parameter-free way from a quark-model based N N potential, we determine simultaneously the πN N*(1440) and σ N N* (1440) coupling constants. We also present a study of the target Roper excitation diagram contributing to the p(d,d’) reaction.
Electromagnetic transition form factors of the Roper resonance in a phenomenological field theory
2014
We analyze the form factors of the electromagnetic nucleon-to-Roper-resonance transition in the framework of a low-energy phenomenological field theory. A systematic power-counting procedure is generated by applying the complex-mass scheme. Within this power counting we calculate the form factors to next-to-next-to-leading order and fit the results to empirical data.
The N*(1710) as a resonance in the ππN system
2008
We study the $\pi \pi N$ system by solving the Faddeev equations, for which the input two-body $t$-matrices are obtained by solving the Bethe-Salpeter equation in the coupled channel formalism. The potentials for the $\pi \pi$, $\pi N$ sub-systems and their coupled channels are obtained from chiral Lagrangians, which have been earlier used to study resonances in these systems successfully. In this work, we find a resonance in the $\pi\pi N$ system with a mass of $1704 - i 375/2$ MeV and with quantum numbers $I=1/2$, $J^\pi =1/2^+$. We identify this state with the $N^*(1710)$. This peak is found where the energies of the $\pi \pi$ sub-system fall in the region of the $\sigma$ resonance. We d…
Chiral unitary dynamics of hadrons and hadrons in a nuclear medium
2009
4th DAE-BRNS Workshop on Hadron Physics. Aligarh Muslim Univ, Dept Phys, Aligarh, INDIA, FEB 18-23, 2008
On the effect of excited states in lattice calculations of the nucleon axial charge
2017
Excited-state contamination is one of the dominant uncertainties in lattice calculations of the nucleon axial-charge, $g_A$. Recently published results in leading-order chiral perturbation theory (ChPT) predict the excited-state contamination to be independent of the nucleon interpolator and positive. However, empirical results from numerical lattice calculations show negative contamination (downward curvature), indicating that present-day calculations are not in the regime where the leading-order ChPT predictions apply. In this paper we show that, under plausible assumptions, one can reproduce the behavior of lattice correlators by taking into account final-state $N \pi$ interactions, in p…
Theoretical study of the NN → NNππ reaction
1998
Abstract We have developed a model for the NN → NNππ reaction and evaluated cross sections for the different charged channels. The low energy part of those channels where the pions can be in an isospin zero state is dominated by N ∗ excitation, driven by an isoscalar source recently found experimentally, followed by the decay N ∗ → N(ππ) S-wave T=0 . At higher energies, and in channels where the pions are not in T = 0, Δ excitation mechanisms become relevant. A rough agreement with the experimental data is obtained in most channels. Repercussions of the present findings for the ABC effect and the pp → ppπ0 reaction close to threshold are also suggested.
Two pion decay of the Roper resonance
2002
We evaluate the two pion decay of the Roper resonance in a model where explicit re-scattering of the two final pions is accounted for by the use of unitarized chiral perturbation theory. Our model does not include an explicit $\epsilon$ or $\sigma$ scalar-isoscalar meson decay mode, instead it generates it dynamically by means of the pion re-scattering. The two ways, explicit or dynamically generated, of introducing this decay channel have very different amplitudes. Nevertheless, through interference with the other terms of the model we are able to reproduce the same phenomenology as models with explicit consideration of the $\epsilon$ meson.
Multipole analysis of pion photoproduction based on fixed t dispersion relations and unitarity
1997
We have analysed pion photoproduction imposing constraints from fixed t dispersion relations and unitarity. Coupled integral equations for the S and P wave multipoles were derived from the dispersion relations and solved by the method of Omnes and Muskhelishvili. The free parameters were determined by a fit to the most recent data for \pi^{+} and \pi^{0} production on the proton as well as \pi^{-} production on the neutron, in the energy We have analysed pion photoproduction imposing constraints from fixed t dispersion relations and unitarity. Coupled integral equations for the S and P wave multipoles were derived from the dispersion relations and solved by the method of Omnes and Muskhelis…
PRODUCTION OF TWO PIONS INDUCED BY NEUTRINOS
2008
We study the threshold production of two pions induced by neutrinos in nucleon targets. The contribution of nucleon pole, pion and contact terms is calculated using a chiral Lagrangian. The contribution of the Roper resonance, neglected in earlier studies, has also been taken into account.
Chiral structure of the Roper resonance using complex-mass scheme
2010
The pole mass and the width of the Roper resonance are calculated as functions of the pion mass in the framework of low-energy effective field theory of the strong interactions. We implement a systematic power-counting procedure by applying the complex-mass scheme.