i.e., it transforms under the trivial (0, 0)-representation of the Lorentz group, leaving the value of the field at any spacetime point unchanged, in contrast to a vector or tensor field, or more generally, spinor-tensors, whose components undergo a mix under Lorentz transformations. Since particle or field spin by definition is determined by the Lorentz representation under which it transforms, all scalar (and pseudoscalar) fields and particles have spin zero, and are as such bosonic by the spin statistics theorem. See Weinberg 1995, Chapter 5 Weinberg, S. (1995). The Quantum Theory of Fields. Vol. I. Cambridge University Press. ISBN0-521-55001-7.
