Group-theoretical classification of orientable objects and particle phenomenology

Abstract: In our previous works, we have proposed a quantum description of relativistic orientable objects by a scalar field on the Poincar\'{e} group. This description is, in a sense, a generalization of ideas used by Wigner, Casimir and Eckart back in the 1930's in constructing a non-relativistic theory of a rigid rotator. The present work is a continuation and development of the above mentioned our works. The position of the relativistic orientable object in Minkowski space is completely determined by the position of a body-fixed reference frame with respect to the space-fixed reference frame, and can be specified by elements $q$ of the motion group of the Minkowski space - the Poincar\'e group $M(3,1)$. Quantum states of relativistic orientable objects are described by scalar wave functions $f(q)$ where the arguments $q=(x,z)$ consist of Minkowski space-time points $x$, and of orientation variables $z$ given by elements of the matrix $Z\in SL(2,C)$. Technically, we introduce and study the so-called double-sided representation $\boldsymbol{T}(\boldsymbol{g})f(q)=f(g_l^{-1}qg_r)$, $\boldsymbol{g}=(g_l,g_r)\in \boldsymbol{M}$, of the group $\boldsymbol{M}$, in the space of the scalar functions $f(q)$. Here the left multiplication by $g_l^{-1}$ corresponds to a change of space-fixed reference frame, whereas the right multiplication by $g_r$ corresponds to a change of body-fixed reference frame. On this basis, we develop a classification of the orientable objects and draw the attention to a possibility of connecting these results with the particle phenomenology. In particular, we demonstrate how one may identify fields described by linear and quadratic functions of $z$ with known elementary particles of spins $0$,$\frac{1}{2}$, and $1$. The developed classification does not contradict the phenomenology of elementary particles and, moreover, in some cases give its group-theoretic explanation.