Elementary excitations in homogeneous superfluid neutron star matter: Role of the proton component

Abstract

The thermal evolution of neuron stars depends on the elementary excitations affecting the stellar matter. In particular, the low-energy excitations, whose energy is proportional to the transfered momentum, can play a major role in the emission and propagation of neutrinos. In this paper, we focus on the density modes associated with the proton component in the homogeneous matter of the outer core of neutron stars (at density between one and three times the nuclear saturation density, where the baryonic constituants are expected to be neutrons and protons). In this region, it is predicted that the protons are superconductor. We study the respective roles of the proton pairing and Coulomb interaction in determining the properties of the modes associated with the proton component. This study is performed in the framework of the Random Phase Approximation, generalized in order to describe the response of a superfluid system.The formalism we use ensures that the Generalized Ward's Identities are satisfied. An important conclusion of this work is the presence of a pseudo-Goldstone mode associated with the proton superconductor in neutron-star matter. Indeed, the Goldstone mode, which characterizes a pure superfluid, is suppressed in usual superconductors due to the long-range Coulomb interaction, which only allows a plasmon mode. However, for the proton component of stellar matter, the Coulomb field is screened by the electrons and a pseudo-Goldstone mode occurs, with a velocity increased by the Coulomb interaction.

Submitted for publication

References in corpus (7)

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Cited by in corpus (10)

• Dark Matter Thermalization in Neutron Stars
• Axions from cooling compact stars: pair-breaking processes
• Viscosity of neutron star matter and $r$-modes in rotating pulsars
• Goldstone modes in the neutron star core
• Collective Modes in a Superfluid Neutron Gas within the Quasiparticle Random-Phase Approximation
• Vertex renormalization of weak interactions in compact stars: beyond leading order
• Response functions of cold neutron matter: density, spin and current fluctuations
• Collective Modes in the Superfluid Inner Crust of Neutron Stars
• Elementary excitations in homogeneous superfluid neutron star matter: role of the neutron-proton coupling
• Coupling between superfluid neutrons and superfluid protons in the elementary excitations of neutron star matter