Dense Matter Physics

George Y. C. Leung

University of Massachusetts Dartmouth

Dense matter physics is the study of the physical properties of material substance compressed to high density. The density range begins with hundreds of grams per cubic centimeter and extends to values ten to fiften orders of magnitudes higher. Although such dense matter does not occur terrestrially, it exists inside stellar objects such as the white dwarf stars, neutron stars, and black holes, and possibly existed during the early phase of the universe. Dense matter physics therefore provides the scientific basis for the investigation of these objects.

GLOSSARY

Adiabat

Equation of state of matter that relates the pressure to the density of the system under a constant entropy.

Baryons

Elementary particles belonging to a type of fermions that includes the nucleons, hyperons, delta particles, and others. Each baryon is associated with a baryon number of one, which is a quantity conserved in all nuclear reactions.

Bosons

Elementary particles are divided into two classes called bosons and fermions. The bosons include the photons, phonons, and mesons. At thermal equilibrium, the energy distribution of identical bosons follows the Bose-Einstein distribution.

Degenerate electrons

System of electrons that occupy the lowest allowable momentum states of the system, thus constituting the absolute ground state of such a system.

Fermions

Class of elementary particlesthat includes the electrons, neutrinos, nucleons, and other baryons. Identical fermions obey Pauli's exclusion principle and follow the Fermi-Dirac distribution at thermal equilibrium.

Isotherm

Equation of state of matter which relates the pressure to the density of the system at constant temperature.

Neutrinos

Neutral massless fermions that interact with matter through the weak interaction. Neutrinos are produced, for example, in the decay of the neutrons.

Neutronization

Form of nuclear reaction in which the neutron content of the reaction product is always higher than that of the reaction ingredient. It occurs in dense matter as its density increases from 107 to 1012 g/cm3.

Nuclear matter

Matter substance forming the interior of a nucleus. Its density is approximately 2.8 x1012 g/cm3 which is relatively independent of the nuclear species. It is composed of nearly half neutrons and half protons.

Phonons

Lattice vibrations of a solid may be decomposed into a set of vibrational modes of definite frequencies. Each frequency mode is composed of an integral number of quanta of definite energy and momentum. These quanta are called phonons. They are classified as bosons.

Photons

Particle-wave duality is an important concept of quantum theory. In quantum theory, electromagnetic radiation may be treated as a system of photons endowed with particle properties such as energy and momentum. A photon is a massless boson of unit spin.

Quarks

Subparticle units that form the elementary particles. There are several species of quarks, each of which possesses, in addition to mass and electric charge, other fundamental attributes such as c-charge (color) and f-charge (flavor).

Superconductivity

Electrical resistance of a superconductor disappears completely when it is cooled below the critical temperature. The phenomenon is explained by the fact that due to the presence of an energy gap in the charge carriers' (electrons or protons) energy spectrum, the carriers cannot be scattered very easily, and the absence of scattering leads to superconductivity.

Superfluidity

Superfluidity is the complete absence of viscosity. The conditions leading to superconductivity also lead to superfluidity in the proton or electron components of the substance. In the case of neutron matter, the neutron component may turn superfluid due to the absence of scattering. The critical temperatures for the proton and neutron components in neutron matter need not be the same.