perusmassa

Perusmassa is a term used in theoretical physics to denote a proposed intrinsic component of the rest mass of a composite system. The word derives from Finnish, where perus means base or fundamental and massa means mass. In discussions of mass decomposition, perusmassa is treated as representing the intrinsic rest-mass contribution carried by the system’s constituents.

In a mass-decomposition framework, the total invariant mass M of a system is written as M = P + E, where P is the perusmassa and E aggregates all other energy contributions, such as binding energy and field energy. Perusmassa is intended to represent the intrinsic rest-mass portion arising from the constituents themselves, and is associated with the system’s rest-frame properties, though its exact value depends on the chosen decomposition scheme.

Proponents argue that separating a baseline, intrinsic mass from interaction-energy terms can help compare theoretical models of hadron and nuclear structure with experimental rest masses. Critics note that the division is model-dependent and can be ill-defined outside a specific theoretical framework, limiting its universal applicability.

Perusmassa is primarily discussed in contexts such as hadron physics, lattice quantum chromodynamics, and nuclear-structure theory, where mass budgets of composite particles are analyzed. It is distinct from conventional notions of rest mass and does not represent a separate physical observable in standard measurements, but rather a bookkeeping construct within a given model.

See also: Mass, Rest mass, Binding energy, Constituent quark model, Lattice QCD.