Thermodynamic of a onedimensional Bose gas at low temperature & superfluidity in neutronstar matter
 Date
 April 24 (Tue) at 15:30  16:30, 2018 (JST)
 Speaker

 Giulia De Rosi (The Institute of Photonic Sciences, Barcelona, Spain)
 Venue
 Language
 English
Ultracold atomic gases and neutronstar matter play a paramount importance in manybody physics, by exhibiting important analogies and differences. One of the most interesting phenomena shared by both systems is provided by superfluidity.
In the first part of the talk, I will show that the chemical potential of a onedimensional (1D) interacting Bose gas exhibits a nonmonotonic temperature dependence which is peculiar of superfluids. The effect is a direct consequence of the phononic nature of the excitation spectrum at large wavelengths exhibited by 1D Bose gases.
For low temperatures T, I demonstrate that the coefficient in the $T^2$ expansion of the chemical potential is defined by the zerotemperature density dependence of the sound velocity and it has been calculated along the crossover between the Bogoliubov weaklyinteracting gas and the TonksGirardeau gas of impenetrable bosons. The theoretical predictions along the crossover are confirmed by comparison with the exactly solvable YangYang model in which the finitetemperature equation of state is obtained numerically by solving Betheansatz equations.
In the second part of the talk, I will show the results of a study of the superfluid gap in pure neutron matter, associated with the formation of Cooper pairs in the $^1S_0$ channel. The interaction responsible of the onset of superfluidity is an effective interaction coming from a nuclear Hamiltonian strongly constrained by phenomenology and obtained from the correlated basis function (CBF) perturbation theory and the formalism of cluster expansions. The calculations have been carried out using an improved version of the CBF effective interaction, in which threenucleon forces are taken into account using a microscopic model. Our results show that the superfluid transition occurs at values of densities corresponding to the neutronstar inner crust.
References
 G. De Rosi, G. E. Astrakharchik and S. Stringari "Thermodynamic behavior of a onedimensional Bose gas at low temperature", Phys. Rev. A 96, 013613 (2017)
 O. Benhar and G. De Rosi "Superfluid Gap in Neutron Matter from a Microscopic Effective Interaction", J Low Temp Phys 189, 250 (2017)