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Screening and antiscreening of the pairing interaction in neutron matter
There are still large uncertainties about the density dependence of the critical temperature Tc for the onset of superfluidity in neutron matter. In this talk, I will revisit the effect of particle-hole (screening) corrections on the S-wave pairing at densities prevailing in the inner crust of neutron stars. At low densities, the repulsive effect of spin fluctuations leads to a strong reduction of Tc compared to the BCS result, also seen in quantum Monte-Carlo calculations. However, I will show that at densities above 0.01-0.02 fm−3, the attractive density fluctuations win against the repulsive spin fluctuations if realistic values for the Landau parameters are employed, leading to antiscreening rather than screening, i.e., to an enhancement of Tc. Then I will discuss the limit of low densities. In this limit, the celebrated Gorkov-Melik-Barkhudarov result, based on a weak-coupling formula, predicts a reduction of Tc by a factor of 0.45. However, if one wants to reproduce this result by solving the gap equation with the screened pairing interaction, it turns out to be necessary to use renormalization-group evolved interactions with cutoffs that scale with the Fermi momentum kF. Finally, I will briefly discuss the reduction of Tc c that one obtains by including, in addition to screening, the effect of pairing fluctuations in the framework of the Nozières-Schmitt-Rink theory.
Michaël Urban
IPN Orsay
04/04/2018 à 11:30
IPN Orsay, salle A015, bâtiment 100

Notes de dernières minutes :

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Institut de Physique Nucléaire Orsay - 15 rue Georges CLEMENCEAU - 91406 ORSAY (FRANCE)
UMR 8608 - CNRS/IN2P3

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