  The quantum chromodynamics (QCD) Kondo effect is a quantum phenomenon in
which heavy quarks ($c$, $b$) exist as impurity particles in quark matter
composed of light quarks ($u$, $d$, $s$) at extremely high density. This is
analogous to the famous Kondo effect in condensed matter physics. In the
present paper, we show theoretically the existence of the "QCD Kondo excitons",
i.e., the bound states of light quarks and heavy quarks, as the
lowest-excitation modes above the ground state of the quark matter governed by
the QCD Kondo effect. These are neutral for color and electric charges,
similarly to the Kondo excitons in condensed matter, and they are new type of
quasiparticles absent in the normal phase of quark matter. The QCD Kondo
excitons have various masses and quantum numbers, i.e., flavors and spin
parities (scalar, pseudoscalar, vector, and axialvector). The QCD Kondo
excitons lead to the emergence of the neutral currents in transport phenomena,
which are measurable in lattice QCD simulations. The study of the QCD Kondo
excitons will provide us with understanding of new universal properties shared
by quark matter and condensed matter.
