Pion decay constant
Encyclopedia
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 symmetry breaking
. The values are:
Beware: There are several conventions which differ by powers of
. The textbook by Weinberg uses the value 184 MeV. The textbook by Peskin and Schroeder uses the value 93 MeV.
Particle physics
Particle physics is a branch of physics that studies the existence and interactions of particles that are the constituents of what is usually referred to as matter or radiation. In current understanding, particles are excitations of quantum fields and interact following their dynamics...
, the pion decay constant is the square root
Square root
In mathematics, a square root of a number x is a number r such that r2 = x, or, in other words, a number r whose square is x...
of the coefficient in front of the kinetic term
Kinetic term
In physics, a kinetic term is the part of the Lagrangian that is bilinear in the fields , and usually contains two derivatives with respect to time ; in the case of fermions, the kinetic term usually has one derivative only...
for the pion
Pion
In particle physics, a pion is any of three subatomic particles: , , and . Pions are the lightest mesons and they play an important role in explaining the low-energy properties of the strong nuclear force....
in the low-energy effective action
Chiral perturbation theory
Chiral perturbation theory is an effective field theory constructed with a Lagrangian consistent with the chiral symmetry of quantum chromodynamics , as well as the other symmetries of parity and charge conjugation. ChPT is a theory which allows one to study the low-energy dynamics of QCD...
. It is dimensionally an energy scale and it determines the strength of the chiral symmetry breaking
Chiral symmetry breaking
In particle physics, chiral symmetry breaking is an example of spontaneous symmetry breaking affecting the chiral symmetry of gauge theory such as Quantum Chromodynamics. The origin may be described as a fermion condensate...
. The values are:
Beware: There are several conventions which differ by powers of
. The textbook by Weinberg uses the value 184 MeV. The textbook by Peskin and Schroeder uses the value 93 MeV.