A commonly conjectured form of the phase diagram is shown in the figure to the right. If we increase the quark density i.
Following this path corresponds to burrowing more and more deeply into a neutron star. At ultra-high densities we expect to find the color-flavor-locked CFL phase of color-superconducting quark matter. At intermediate densities we expect some other phases labelled "non-CFL quark liquid" in the figure whose nature is presently unknown,. If we heat up the system without introducing any preference for quarks over antiquarks, this corresponds to moving vertically upwards along the T axis. At first, quarks are still confined and we create a gas of hadrons pions , mostly. Following this path corresponds to travelling far back in time so to say , to the state of the universe shortly after the big bang where there was a very tiny preference for quarks over antiquarks.
Until recently it was also believed to be a boundary between phases where chiral symmetry is broken low temperature and density and phases where it is unbroken high temperature and density. It is now known that the CFL phase exhibits chiral symmetry breaking, and other quark matter phases may also break chiral symmetry, so it is not clear whether this is really a chiral transition line. The line ends at the "chiral critical point ", marked by a star in this figure, which is a special temperature and density at which striking physical phenomena, analogous to critical opalescence , are expected.
Reference for this section:,   . For a complete description of phase diagram it is required that one must have complete understanding of dense, strongly interacting hadronic matter and strongly interacting quark matter from some underlying theory e. However, because such a description requires the proper understanding of QCD in its non-perturbative regime, which is still far from being completely understood, any theoretical advance remains very challenging. The phase structure of quark matter remains mostly conjectural because it is difficult to perform calculations predicting the properties of quark matter.
The reason is that QCD, the theory describing the dominant interaction between quarks, is strongly coupled at the densities and temperatures of greatest physical interest, and hence it is very hard to obtain any predictions from it. Here are brief descriptions of some of the standard approaches.
The only first-principles calculational tool currently available is lattice QCD , i. Because QCD is asymptotically free it becomes weakly coupled at unrealistically high densities, and diagrammatic methods can be used.
At high temperatures, however, diagrammatic methods are still not under full control. To obtain a rough idea of what phases might occur, one can use a model that has some of the same properties as QCD, but is easier to manipulate. Many physicists use Nambu-Jona-Lasinio models , which contain no gluons, and replace the strong interaction with a four-fermion interaction. Mean-field methods are commonly used to analyse the phases. Another approach is the bag model , in which the effects of confinement are simulated by an additive energy density that penalizes unconfined quark matter.
Many physicists simply give up on a microscopic approach, and make informed guesses of the expected phases perhaps based on NJL model results. For each phase, they then write down an effective theory for the low-energy excitations, in terms of a small number of parameters, and use it to make predictions that could allow those parameters to be fixed by experimental observations.
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There are other methods that are sometimes used to shed light on QCD, but for various reasons have not yet yielded useful results in studying quark matter. It turns out that at high density the higher-order corrections are large, and the expansion gives misleading results. Adding scalar quarks squarks and fermionic gluons gluinos to the theory makes it more tractable, but the thermodynamics of quark matter depends crucially on the fact that only fermions can carry quark number, and on the number of degrees of freedom in general.
Experimentally, it is hard to map the phase diagram of quark matter because it has been rather difficult to learn how to tune to high enough temperatures and density in the laboratory experiment using collisions of relativistic heavy ions as experimental tools. However, these collisions ultimately will provide information about the crossover from hadronic matter to QGP.
It has been suggested that the observations of compact stars may also constrain the information about the high-density low-temperature region. Models of the cooling, spin-down, and precession of these stars offer information about the relevant properties of their interior.
As observations become more precise, physicists hope to learn more. One of the natural subjects for future research is the search for the exact location of the chiral critical point. Some ambitious lattice QCD calculations may have found evidence for it, and future calculations will clarify the situation. From Wikipedia, the free encyclopedia. Theorized phases of matter whose degrees of freedom include quarks and gluons. QCD in the non- perturbative regime: quark matter. The equations of QCD predict that a sea of quarks and gluons should be formed at high temperature and density.
What are the properties of this phase of matter?
The tale of the Hagedorn temperature – CERN Courier
Proceedings: A production scenario of Galactic strangelets and an estimation of their possible flux in solar neighborhood. Retrieved 11 October Bibcode : PhRvD.. Physical Review Letters. Bibcode : PhRvL. Retrieved 16 December Reviews of Modern Physics. Das Passwort muss mind.
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Startseite Physik, Astronomie Quantenphysik. Erschienen: Auf die Merkliste Drucken Weiterempfehlung. Softcover Springer. This has detoured our attention from the great enigmas posed by the dynamics and collective behavior of strongly interacting particles.