quantum chromodynamics In theoretical physics, quantum chromodynamics (QCD) is the study 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 of ...

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

hadron In particle physics, a hadron is a composite subatomic particle made of two or more quarks held together by the strong nuclear force. Pronounced , the name is derived . They are analogous to molecules, which are held together by the electri ...

s in an ultra-hot, ultra-dense medium, such as hadrons in the quark epoch during the first microsecond of the Big Bang or within

neutron star A neutron star is the gravitationally collapsed Stellar core, core of a massive supergiant star. It results from the supernova explosion of a stellar evolution#Massive star, massive star—combined with gravitational collapse—that compresses ...

s. According to Gerald E. Brown 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. The journal is considered one of the most prestigious in the field of physics ...

'': 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 color confinement, confining and strong coupling nature of the theory means that conventional perturbative techniques often fail to apply. The QCD sum rules (or Mikhail Shifman, Shifman–Arkady Vainshtein, Vainshtei ...

. The omega meson, sigma meson, and

neutron The neutron is a subatomic particle, symbol or , that has no electric charge, and a mass slightly greater than that of a proton. The Discovery of the neutron, neutron was discovered by James Chadwick in 1932, leading to the discovery of nucle ...

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 sym ...

. (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 of the relationship between Spacetime, space and time. In Albert Einstein's 1905 paper, Annus Mirabilis papers#Special relativity, "On the Ele ...

.) 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 an atomic nucleus emits a beta particle (fast energetic electron or positron), transforming into an isobar of that nuclide. For example, beta decay of a neutron ...

of ¹⁴C to the ¹⁴N ground state.

References

Quantum chromodynamics {{particle-stub

See also

References