Abstract
Topological fluctuations change their nature in the different phases of strong interactions, and the interrelation of topology, chiral symmetry and confinement at high temperature has been investigated in many lattice studies. This review is devoted to the much less explored subject of topology in dense matter. After a short overview of the status at zero density, which will serve as a baseline for the discussion, we will present lattice results for baryon rich matter, which, due to technical difficulties, has been mostly studied in two-color QCD, and for matter with isospin and chiral imbalances. In some cases, a coherent pattern emerges, and in particular the topological susceptibility seems suppressed at high temperature for baryon and isospin rich matter. However, at low temperatures the topological aspects of dense matter remain not completely clear and call for further studies.
Highlights
In broad outline, the general framework of this review is Quantum Chromodynamics (QCD) and its several phases and critical phenomena depending on temperature, baryonic, isospin and chiral densities
We can still ’see’ topological fluctuations in the quark sector. These observations are at the root of the discovery of the so-called Chiral Magnetic Effect (CME) [49]: electric charge separation in the presence of an external magnetic field that is induced by the chirality imbalance
In the previous Section we have argued that one may expect some significant differences in topology in the different phases, and have shown a summary of results at zero density
Summary
The general framework of this review is Quantum Chromodynamics (QCD) and its several phases and critical phenomena depending on temperature, baryonic, isospin and chiral densities. At lower temperatures and increasing baryonic density, one encounters nuclear matter first, a transition to a dense deconfined phase of quarks and gluons. This phase of matter is realised in the interior of neutron stars, extremely compact stellar objects produced in the supernova explosions. Chiral symmetry breaking occurs via a space-homogeneous condensate At high temperature this is known to dissolve, while for low temperatures and high-density different pairing phenomena result in a rich, and still not entirely explored phase diagram [4,5,6]. A non-zero density—be it due to baryon, isospin or chiral imbalances—is an important probe for the interplay of chiral symmetry, confinement and topology, and may shed some light on its general aspects
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