# Tag Info

## New answers tagged quantum-chromodynamics

1

To start with, special relativity is necessary when describing elementary particles and hadrons composed by them. Special relativity defines the invariant mass of a particle or an ensemble of particles as the measure of the four momentum vector carried by the particle/ensemble. In the case of one elementary particle, an electron for example, it is ...

0

99.9% of the mass of a hadron or a meson comes from confinement in QCD. Confinement is a special feature of QCD due to its non abelian symmetry which leads to a negative beta function. It is confinement that also leads to a breaking of the chiral symmetry at about 200 MeV or the radius of a hadron (about 1 femto meter).

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A link would be useful to see the context of the quote One often hears the phrase "most of nuclear physics is in the low energy regime of QCD, where strong coupling constant is large ...", As it is it is wrong. This is correct The nuclear force is now understood as a residual effect of the even more powerful strong force, or strong interaction, ...

4

The dilaton $\sigma$ is the Goldstone boson of scale invariance. Scale transformations $x\rightarrow x/\lambda$ are generated non linearly, e.g. $$\sigma(x)\rightarrow \sigma(\lambda x)+f \log\lambda\,,\qquad \lambda>0$$ where $f$ is the dilaton decay constant (see below). An effective field theory for this Goldstone boson can be easily written with ...

2

Usually phase diagrams, e.g. of water, are shown as pressure vs temperature. However, we could just as well write a phase diagram as temperature vs density. This is because the equation of state of matter is a relation between pressure, density and temperature. The above phase diagram should be interpreted as showing: what is the state of matter at a certain ...

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