"Elementary excitations" VS. "Quasiparticles"

[timspac]

What's the difference between "Elementary exitations" and "Quasiparticle"?

Thanks!

[Bob_for_short]

What's the difference between "Elementary exitations" and "Quasiparticle"?

They are essentially the same things.

A quasi-particle is an entity to obey a particle-like equation. For example, the center of inertia R and the relative distance r between two particles obey particle-like equations but with non-particle masses: Mtot and µ (=m_reduced).

Elementary excitations are also simple "particle-like" entities used to describe the internal degrees of freedom (like r).