Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A theory of electromagnetism with uniquely defined potential and
  covariant conserved spin   A theory of electromagnetism is proposed that is based on the Fermi
Lagrangian, which is symmetric under electromagnetic spin rotation. Its
features are: - the four-potential is unambiguously determined by the
inhomogeneous wave equation and boundary conditions at infinity. - the Lorenz
condition and minimal coupling then follow from charge conservation. -
electromagnetic spin is conserved and spin operators can be defined without
sacrificing covariance. - quantisation is fully covariant, without redefining
the metric. - all experimental predictions are the same as in the standard
theory. This result proves that electromagnetic gauge invariance is redundant
as a fundamental principle of physics.

26
The categories of this paper are: bayes-an
21
The categories of this paper are: adap-org
12
The categories of this paper are: nucl-th
17
The categories of this paper are: q-fin
37
The categories of this paper are: supr-con
22
The categories of this paper are: chao-dyn
8
The categories of this paper are: hep-ex
36
The categories of this paper are: cmp-lg
16
The categories of this paper are: stat
29
The categories of this paper are: funct-an
33
The categories of this paper are: plasm-ph
25
The categories of this paper are: patt-sol
11
The categories of this paper are: hep-lat
6
The categories of this paper are: astro-ph
35
The categories of this paper are: mtrl-th
4
The categories of this paper are: cond-mat