202 research outputs found
Microscopic origin of pairing
A brief review of recent progress in the ab intio theory of nuclear pairing
is given. Nowdays several successful solutions of the ab intio BCS theory gap
equation were published which show that it is a promising first step in the
problem. However, the role of many-body correlations that go beyond the BCS
scheme remains uncertain and requires further investigations. As an
alternative, the semi-microscopic model is discussed in which the effective
pairing interaction calculated from the first principles is supplemented with a
small phenomenological addendum containing one phenomenological parameter
universal for all medium and heavy atomic nuclei.Comment: Contribution to the Volume 50 years of Nuclear BCS edited by World
Scientifi
Elementary excitations in homogeneous superfluid neutron star matter: Role of the proton component
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.Comment: Submitted for publicatio
Existence of nuclei with unusual neutron excess
Abstract A realistic model is suggested based on the quasiparticle Lagrange version of the self-consistent Finite Fermi Systems theory supplemented with the microscopically calculated surface parameters of the Landau–Migdal interaction amplitude. The latter are expressed in terms of the off-shell T -matrix of free NN -scattering and show a strong dependence on the chemical potential of a nucleus under consideration in the drip line vicinity. This effect could result in shifting the neutron drip line position to very large values of the neutron excess
Gluon condensation and deconfinement critical density in nuclear matter
An upper limit to the critical density for the transition to the deconfined
phase, at zero temperature, has been evaluated by analyzing the behavior of the
gluon condensate in nuclear matter. Due to the non linear baryon density
effects, the upper limit to the critical density, \rho_c turns out about nine
times the saturation density, rho_0 for the value of the gluon condensate in
vacuum =0.012 GeV^4. For neutron matter \rho_c \simeq 8.5
\rho_0. The dependence of the critical density on the value of the gluon
condensate in vacuum is studied.Comment: Published version, 11 pages, 2 eps figure
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