Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Field-theoretical space-time position operator of the Dirac electron   A field-theoretical space-time position operator can be properly introduced
for the Dirac field, it plays the role of a generalized Noether charge
associated with a local symmetry, and its second-quantized form shows that
quantum fields possess zero-point time, which implies that a zero-point
fluctuation of energy must be accompanied with a zero-point fluctuation of
time, and then in agreement with the time-energy uncertainty principle. In
practice, some possible physical effects owing to zero-point time remain to be
found.

10
The categories of this paper are: q-bio
17
The categories of this paper are: q-fin
6
The categories of this paper are: astro-ph
21
The categories of this paper are: adap-org
0
The categories of this paper are: hep-ph
37
The categories of this paper are: supr-con
5
The categories of this paper are: gr-qc
2
The categories of this paper are: math
34
The categories of this paper are: chem-ph
9
The categories of this paper are: nlin
30
The categories of this paper are: q-alg
35
The categories of this paper are: mtrl-th
1
The categories of this paper are: cs
15
The categories of this paper are: nucl-ex
11
The categories of this paper are: hep-lat
3
The categories of this paper are: physics