Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: On the energy of physical states in QED in the convariant gauge   In quantum field theory it is generally assumed that there is a lower bound
to the energy of a quantum state. Here, it will be shown that there is no lower
bound to the energy of physical states in QED in a manifestly covariant gauge.

16
The categories of this paper are: stat
24
The categories of this paper are: dg-ga
31
The categories of this paper are: ao-sci
25
The categories of this paper are: patt-sol
23
The categories of this paper are: solv-int
12
The categories of this paper are: nucl-th
6
The categories of this paper are: astro-ph
36
The categories of this paper are: cmp-lg
14
The categories of this paper are: math-ph
10
The categories of this paper are: q-bio
21
The categories of this paper are: adap-org
20
The categories of this paper are: acc-phys
4
The categories of this paper are: cond-mat
37
The categories of this paper are: supr-con
8
The categories of this paper are: hep-ex
33
The categories of this paper are: plasm-ph