In quantum chromodynamics (QCD), Brown–Rho (BR) scaling is an approximate scaling law for hadrons 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 stars.
[1] According to Gerald E. Brown and Mannque Rho in their 1991 publication in Physical Review Letters:[2] By using effective chiral Lagrangians with a suitable incorporation of the scaling property of QCD, we establish the approximate in-medium scaling law, m*σ/mσ ≈ m*N/mN ≈ m*ρ/mρ ≈ m*ω/mω ≈ f*π/fπ.
[5] For hadrons, a large part of their masses are generated by the chiral condensate.
Since the chiral condensate may vary significantly in hot and/or dense matter, hadron masses would also be modified.
Theoretically, a similar behavior is also found in the NJL model ... and the QCD sum rule ...[6]The hypothesis of Brown–Rho scaling is supported by experimental evidence on beta decay of 14C to the 14N ground state.