spinless

Spinless describes particles or models that have zero intrinsic angular momentum, or systems in which spin degrees of freedom are neglected. In quantum mechanics, a particle with spin quantum number s = 0 is called spinless; such particles are scalars in relativistic quantum field theory and are examples of spin-0 bosons.

In particle physics and related fields, spinless often refers to real scalar particles. The Higgs boson is the best known example of a spin-0 particle. Spin-0 mesons, such as pions, also have zero spin. In many theoretical contexts, the term is used when discussing properties that do not rely on spin, or when spin degrees of freedom are not included in the model.

In condensed matter physics and statistical mechanics, spinless models are used to study charge and density dynamics without spin interactions. A spinless fermion model treats electrons as fermions without spin, so each orbital can be occupied by at most one fermion, emphasizing charge transport and correlation effects. Spinless boson models describe spin-0 bosons and are relevant for lattice boson systems and Bose-Einstein condensates.

Notes: due to the spin-statistics theorem in relativistic theory, intrinsically spin-zero particles are bosons, though in non-relativistic or effective theories, the label “spinless” may simply indicate that the spin degree of freedom has been removed from the description. Spinless descriptions help isolate the roles of charge, statistics, and spatial symmetries in theoretical analyses.