quantum chromodynamics In theoretical physics, quantum chromodynamics (QCD) is the theory of the strong interaction between quarks mediated by gluons. Quarks are fundamental particles that make up composite hadrons such as the proton, neutron and pion. QCD is a type ...

(QCD), Brown–Rho (BR) scaling is an approximate scaling law for

hadron In particle physics, a hadron (; grc, ἁδρός, hadrós; "stout, thick") is a composite subatomic particle made of two or more quarks held together by the strong interaction. They are analogous to molecules that are held together by the ele ...

s in an ultra-hot, ultra-dense medium, such as hadrons in the

quark epoch In physical cosmology, the Quark epoch was the period in the evolution of the early universe when the fundamental interactions of gravitation, electromagnetism, the strong interaction and the weak interaction had taken their present forms, but th ...

during the first microsecond of the Big Bang or within

neutron star A neutron star is the collapsed core of a massive supergiant star, which had a total mass of between 10 and 25 solar masses, possibly more if the star was especially metal-rich. Except for black holes and some hypothetical objects (e.g. white ...

s. According to

Gerald E. Brown Gerald Edward Brown (born July 22, 1926 in Brookings, South Dakota; † May 31, 2013 in New York City) was an American theoretical physicist who worked on nuclear physics and astrophysics. Since 1968 he had been a professor at the Stony Brook Un ...

and Mannque Rho in their 1991 publication in ''

Physical Review Letters ''Physical Review Letters'' (''PRL''), established in 1958, is a peer-reviewed, scientific journal that is published 52 times per year by the American Physical Society. As also confirmed by various measurement standards, which include the ''Journa ...

'': refers to the pole mass of the ρ meson, whereas refers to the in-medium massarXiv preprint
/ref> (or running mass in the medium) of the ρ meson according to

QCD sum rules In quantum chromodynamics, the confining and strong coupling nature of the theory means that conventional perturbative techniques often fail to apply. The QCD sum rules (or Shifman– Vainshtein–Zakharov sum rules) are a way of dealing with t ...

. The

omega meson The omega meson () is a flavourless meson formed from a superposition of an up quark–antiquark and a down quark–antiquark pair. It is part of the vector meson nonet and mediates the nuclear force along with pions and rho mesons. Properti ...

, sigma meson, and

neutron The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the nuclei of atoms. Since protons and neutrons beh ...

are denoted by ω, σ, and N, respectively. The symbol denotes the free-space

pion decay constant In particle physics, the pion decay constant is the square root of the coefficient in front of the kinetic term for the pion in the low-energy effective action. It is dimensionally an energy scale and it determines the strength of the chiral symme ...

. (Decay constants have a "running time" and a "pole time" similar to the "running mass" and "pole mass" concepts, according to

special relativity In physics, the special theory of relativity, or special relativity for short, is a scientific theory regarding the relationship between space and time. In Albert Einstein's original treatment, the theory is based on two postulates: # The laws o ...

.) The symbol is also used to denote the pion decay constant.arXiv preprint
/ref> The hypothesis of Brown–Rho scaling is supported by experimental evidence on

beta decay In nuclear physics, beta decay (β-decay) is a type of radioactive decay in which a beta particle (fast energetic electron or positron) is emitted from an atomic nucleus, transforming the original nuclide to an isobar of that nuclide. For ...

of ¹⁴C to the ¹⁴N ground state.

References

Quantum chromodynamics {{particle-stub

See also

References