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Register a new userIs two-poles $Lambda(1405)$ one state or two?
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To understand the nature of two poles for the $Lambda(1405)$ state, we revisit the interactions of $bar{K}N$ and $piSigma$ with their coupled channels, where two-poles structure is found in the second Riemann sheet. We also dynamically generate two poles in the single channel interaction of $bar{K}N$ and $piSigma$, respectively. Moreover, we make a further study of two poles properties by evaluating the couplings, the compositeness, the wave functions, and the radii for the interactions of four coupled channels, two coupled channels and the single channel. Our results show that the nature of two poles is unique. The higher-mass pole is a pure $bar{K} N$ molecule, and the lower-mass one is a compositeness of mainly $pi Sigma$ with tiny component $bar{K} N$. From our results, one can conclude that the $Lambda(1405)$ state would be overlapped with two different states of the same quantum number.
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We discuss several aspects of the Lambda(1405) resonance in relation to the recent theoretical developments in chiral dynamics. We derive an effective single-channel KbarK N interaction based on chiral SU(3) coupled-channel approach, emphasizing the important role of the pi Sigma channel and the structure of the Lambda(1405) in Kbar N phenomenology. In order to clarify the structure of the resonance, we study the behavior with the number of colors (Nc) of the poles associated with the Lambda(1405), and argue the physical meaning of the renormalization procedure.
We investigate the photoproduction of Lambda(1405,1/2^-) = Lambda* off the proton target using the effective Lagrangian in the Born approximation. We observed that, depending on the choice of the K* N Lambda* coupling strength, the total cross section becomes 0.1 <~ sigma_Lambda* <~ 0.2 mu b near the threshold and starts to decrease beyond E_gamma ~ 1.6 GeV, and the angular dependence shows a mild enhancement in the forward direction. It turns out that the energy dependence of the total cross section is similar to that shown in the recent LEPS experiment. This suggests that the production mechanism of the Lambda* is dominated by the s-channel contribution.
It appears that there are two resonances with $J^P= 1/2^-$ quantum numbers in the energy region near the $Lambda(1405)$ hyperon. The nature of these states is a topic of current debate. To provide further insight we use Regge phenomenology to access how these two resonances fit the established hyperon spectrum. We find that only one of these resonances is compatible with a three-quark state.
We study the unitarized meson-baryon scattering amplitude at leading order in the strangeness $S=-1$ sector using time-ordered perturbation theory for a manifestly Lorentz-invariant formulation of chiral effective field theory. By solving the coupled-channel integral equations with the full off-shell dependence of the effective potential and applying subtractive renormalization, we analyze the renormalized scattering amplitudes and obtain the two-pole structure of the $Lambda(1405)$ resonance. We also point out the necessity of including higher-order terms.
We consider $Lambda$ and $bar{Lambda}$ production in a wide range of proton scattering experiments. The produced $Lambda$ and $bar{Lambda}$ may or may not contain a diquark remnant of the beam proton. The ratio of these two production mechanisms is found to be a simple universal function $r = [ kappa/(y_p - y) ]^i$ of the rapidity difference $y_p - y$ of the beam proton and the produced $Lambda$ or $bar{Lambda}$, valid over four orders of magnitude, from $r approx 0.01$ to $r approx 100$, with $kappa = 2.86 pm 0.03 pm 0.07$, and $i = 4.39 pm 0.06 pm 0.15$.
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