Gauge invariance of the dual Meissner effect in QCD
  The dual Meissner effect is described and numerically observed in a gauge-invariant way in lattice Monte-Carlo simulations of pure SU(2) QCD.   A gauge-invariant Abelian-like field strength is defined in terms of a unit-vector in color space which is constructed by a non-Abelian field strength itself. A gauge-invariant monopole-like quantity is defined by a violation of the Bianchi identity with respect to the Abelian-like field strength. The squeezing of the non-Abelian electric field $\sqrt{\sum_a(E^a_i)^2}$ between a pair of static quark and anti-quark occurs due to the solenoidal current coming from the gauge-invariant monopole-like quantity. An equation similar to the dual London equation is confirmed approximately in the long-range region. 
Tsuneo Suzuki, Katsuya Ishiguro, Yoshifumi Nakamura and Toru Sekido