Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A Hamiltonian for the description of a non-relativistic spin-1/2 free
  particle   We propose a Hamiltonian for a nonrelativistic spin 1/2 \QTR{it}{free}
particle (e.g. an electron) and find that it contains information of its
internal degrees of freedom in the rest coordinate system. We comment on the
dynamical symmetry associated with the electron \QTR{it}{Zitterbewegung}.

30
The categories of this paper are: q-alg
33
The categories of this paper are: plasm-ph
23
The categories of this paper are: solv-int
5
The categories of this paper are: gr-qc
25
The categories of this paper are: patt-sol
24
The categories of this paper are: dg-ga
2
The categories of this paper are: math
6
The categories of this paper are: astro-ph
18
The categories of this paper are: econ
12
The categories of this paper are: nucl-th
21
The categories of this paper are: adap-org
27
The categories of this paper are: comp-gas
28
The categories of this paper are: alg-geom
35
The categories of this paper are: mtrl-th
19
The categories of this paper are: eess
31
The categories of this paper are: ao-sci