Abstract
Dense quark matter is expected to behave as a type-II superconductor at strong coupling. It was previously shown that if the strange quark mass m s is neglected, magnetic domain walls in the so-called 2SC phase are the energetically preferred magnetic defects in a certain parameter region. Computing the flux tube profiles and associated free energies within a Ginzburg–Landau approach, we find a cascade of multi-winding flux tubes as ‘remnants’ of the domain wall when m s is increased. These flux tubes exhibit an unconventional ring-like structure of the magnetic field. We show that flux tubes with winding numbers larger than one survive for values of m s up to about 20% of the quark chemical potential. This makes them unlikely to play a significant role in compact stars, but they may appear in the QCD phase diagram in the presence of an external magnetic field.
Highlights
Cold and dense matter is a color superconductor, in which certain color-magnetic fields are screened just like ordinary magnetic fields are screened in an electronic superconductor [1]
While in the massless case none of these phases appears in the phase diagram [17], we find that a window for this phase opens up in the presence of a strange quark mass, which was already observed in Refs. [30, 31]
We have shown that these domain walls – which can be viewed as flux tubes with infinite radius – turn into flux tubes with finite radius and high winding number as the strange quark mass is switched on
Summary
Cold and dense matter is a color superconductor, in which certain color-magnetic fields are screened just like ordinary magnetic fields are screened in an electronic superconductor [1]. In this paper we mostly focus on the so-called 2SC phase [11], where only up and down quarks participate in Cooper pairing, while the strange quarks and all quarks of one color remain unpaired In this phase, just like in the color-flavor-locked (CFL) phase [12], there is a certain combination of the photon and the gluons whose magnetic field penetrates the color superconductor unperturbed [13]. In the so-called semilocal approximation, where the SU (2) remains ungauged, these strings are described within an abelian Higgs model [44] In this context, the flux tube profiles are often calculated at the transition point between type-I and type-II superconductivity, referred to as the Bogomolny limit [45].
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