Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Gauge invariance and time symmetry breaking   Employing an arbitrary velocity gauge transformation this contribution argues
that the breaking of time symmetry is a natural consequence of irreversibility.

10
The categories of this paper are: q-bio
36
The categories of this paper are: cmp-lg
33
The categories of this paper are: plasm-ph
16
The categories of this paper are: stat
4
The categories of this paper are: cond-mat
2
The categories of this paper are: math
15
The categories of this paper are: nucl-ex
23
The categories of this paper are: solv-int
34
The categories of this paper are: chem-ph
32
The categories of this paper are: atom-ph
8
The categories of this paper are: hep-ex
13
The categories of this paper are: quant-ph
24
The categories of this paper are: dg-ga
5
The categories of this paper are: gr-qc
37
The categories of this paper are: supr-con
7
The categories of this paper are: hep-th