6533b826fe1ef96bd1284d3e

RESEARCH PRODUCT

The sigma K coupling in the chiral unitary approach and the isoscalar (K)over-barN , (K)over-barA interaction

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We evaluate the 'σ' exchange contribution to the K¯N→K¯N scattering within a chiral unitary approach. We show that the chiral transition potentials for ππ→KK¯ in the t-channel lead to a 'σ' contribution that vanishes in the K¯ forward direction and, hence, would produce a null 'σ' exchange contribution to the K− optical potential in nuclear matter in a simple impulse approximation. This is a consequence of the fact that the leading order chiral Lagrangian gives an I=0 ππ→KK¯ amplitude proportional to the squared momentum transfer, q2. This finding poses questions on the meaning or the origin of 'σ' exchange potentials used in relativistic mean field approaches to the K− nuclear selfenergy. This elementary 'σ' exchange potential in K¯N→K¯N is compared to the Weinberg-Tomozawa term and is found to be smaller than present theoretical uncertainties but will be relevant in the future when aiming at fitting increasingly more accurate data.