We summarize recent developments in our understanding of low-mass quark-antiquark excitations in hadronic matter under various different conditions. This includes the ther-modynamics of the chiral condensate, pions as Goldstone bosons in normal nuclear matter, and excursions into extreme territory of the QCD phase diagram: lepton pair production from a fireball expanding through the transition ...

A code is -quasi-cyclic ( -QC) if there is an integer such that cyclic shift of a codeword by -positions is also a codeword. For = 1, cyclic codes are obtained. A dyadic code is a code which is closed under all dyadic shifts. An -QC dyadic ( -QCD) code is one which is both -QC and dyadic. QCD codes with = 1 give codes that are cyclic and dyadic (CD). In this correspondence, we obtain a simple c...

We study instanton effects in QCD at very high baryon density. In this regime instantons are suppressed by a large power of (ΛQCD/μ), where ΛQCD is the QCD scale parameter and μ is the baryon chemical potential. Instantons are nevertheless important because they contribute to several physical observables that vanish to all orders in perturbative QCD. We study, in particular, the chiral condensa...

The Perturbative QCD Potential and the t ¯ t Threshold Abstract We include the full second-order corrections to the static QCD potential in the analysis of the t ¯ t threshold cross section. There is an unexpectedly large difference between the QCD potential improved by the renormalization-group equation in momentum space and the potential improved by the renormalization-group equation in coord...