Color superconductivity
The color superconductivity of the quantum field theory is a theory of the quantum expected (QCD) phase of a gas from quark and Gluons .
Phases like color superconductivity arise at
- very high densities of more than 10 times the typical density of atomic nuclei and at the same time
- Temperatures below about 10 M eV (in particle physics the temperature is usually given in electron volts , 1 MeV corresponds to about 10 10 Kelvin).
In heavy ion - collision experiments , such densities can not be achieved - but probably even higher temperatures, as some time for the investigation of quark-gluon plasma can be used. This is expected at the typical atomic nucleus density and from around 170 MeV.
history
The possibility that a color superconducting phase could form in the QCD was already considered in the 1970s. The term color superconductivity ( english color superconductivity ) in 1977 at Caltech by Steven Frautschi embossed and his doctoral Bertrand Barrois. In the 2000s, the were using methods many-body theory of condensed matter physics new theoretical insights gained through the phases of QCD.
description
A color superconducting phase is formed from quark-quark pairs, which attract each other through the exchange of gluons. This is analogous to the Cooper pairs of electrons in the metallic superconductor according to the BCS theory , which attract each other by means of phonons . Analogously, the color-charged gluons are given a mass so that their range is limited, like that of the magnetic fields in solid-state superconductors (“ Meissner effect ”). The color-neutral gluons, on the other hand, remain massless in many color superconducting phases and also form new mixed states with the electromagnetic photon (“rotated photon”).
Several varieties
In contrast to normal superconductors, there are different types of color superconductivity, since quarks with their quantum numbers of flavor and color occur in more variations than electrons. For the borderline case of infinitely high density, perturbation-theoretical calculations can be made in QCD , which show the preference for a color-flavor-locked phase (CFL) for three quark flavors ; In it, the associated color combinations are defined ( locked ) for quark pairs of certain flavor combinations . It is more difficult to make predictions for other areas of the phase diagram , since the grid calculations otherwise used in QCD can not be applied to the area of high densities.
Occurrence in neutron stars
Very dense matter may exist inside neutron stars , the relics of supernovae . Their matter is usually imagined as nuclear matter made up of nucleons (here Fermigas ) and mesons . In addition, a color superconducting phase could also be present under appropriate conditions. The effects would be very subtle and, as the theorists hope, would manifest themselves in effects such as the cooling rate of the neutron star or in its rotational behavior. Theoretically, one expects that the color superconducting state is a superfluid , i. H. exhibits vanishing internal friction , which is generally believed to lead to a rapid decay of the star rotation. In nature, on the other hand, one observes many pulsars with relatively stable periods of rotation, some in the millisecond range.
Web links
- J. Cheyne, G. Cowan, M. Alford: Superconducting quarks. (No longer available online.) In: Frontiers website. UK PPARC , February 25, 2002, archived from the original on March 12, 2007 ; accessed on July 11, 2016 .
- Hands: The phase diagram of QCD . 2001, arxiv : physics / 0105022
- arxiv : 0709.4635
- Rajagopal, Wilczek: The condensed matter phases of QCD . In: Handbook of QCD . 2001, arxiv : hep-ph / 0011333
- Alford: QCD at high temperature / density . 2002, arxiv : hep-ph / 0209287
Individual evidence
- ↑ Barrois. In: Nuclear Physics B , 129, 1977, p. 390, part of his dissertation