A model for the γp→ π+π−p reaction

Theoretical study of the NN → NNππ reaction

“…This reaction is interesting because the N * excitation with N * → N(ππ) T =0 S−wave decay shown in diagrams (4) and (5), which were dominant in the pp → ppπ + π − reaction, do not exist now. Diagrams (6) and (7) still contribute, but they are very small because they involve one N * Nπ p-wave coupling, which vanishes at threshold and also σ exchange is not allowed. Indeed the π + π 0 system can only be in T = 1, 2 but not in T = 0.…”

“…In the γN → ππN reaction, which has also been the subject of study at threshold as a further test of chiral symmetry [4,5], one of the most interesting results is the role of the N * (1520, J π = 3/2 − ) resonance [6]. The mechanism of N * (1520) photoexcitation followed by the decay into ∆π interferes with the dominant Kroll Ruderman ∆Nπγ term and allows one to obtain information about the N * (1520) → ∆π decay amplitudes, additional to the one obtained from the analysis of the πN → ππN reaction [7], and which poses new challenges to quark models of baryons [8].…”

ρ→ππ decay in nuclear medium

“…The constants g 1 and G 1 are adjusted in such a way, that in the nonrelativistic limit we recover the couplings [61,62], where k is the spin index of the ρ. The comparison, with the explicit form of the Rarita-Schwinger spinors and the matrices T ∆ and S ∆ (see…”

Helicity asymmetries in double pion photoproduction on the proton

“…The photoproduction of two pions on nucleons at low and intermediate energies (up to E γ ∼ 1 GeV) has been the subject of intense experimental [1][2][3][4][5][6] and theoretical [7][8][9][10][11][12][13][14][15][16][17][18][19] study. The works have been mainly motivated to understand the role of the many baryonic resonances involved in the process.…”