Pion excitations in a nucleonic medium may be pertinent to the luminosity of neutron stars

The luminosity per unit volume from the modified URCA process and from some new single-nucleon processes proposed here can be increased by several orders of magnitude by systematically taking into account collective effects in a dense nucleonic medium. These new single-nucleon processes involve thermal excitations of the pion field in the nucleonic medium. The increase in luminosity is probably sufficient to explain the existing experimental upper limits on the surface temperatures of neutron stars