Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A novel characterisation of gravitational radiation in asymptotically
  flat space-times   A novel criterion to determine the presence of gravitational radiation
arriving to, or departing from, null infinity of any weakly
asymptotically-simple space-time with vanishing cosmological constant is given.
The quantities involved are geometric, of tidal nature, with good gauge
behaviour and univocally defined at null infinity. The relationship with the
classical characterisation using the News tensor is analysed in detail. A new
balance law at infinity is presented, which may be useful to define `radiation
states'.

22
The categories of this paper are: chao-dyn
29
The categories of this paper are: funct-an
1
The categories of this paper are: cs
4
The categories of this paper are: cond-mat
8
The categories of this paper are: hep-ex
3
The categories of this paper are: physics
32
The categories of this paper are: atom-ph
37
The categories of this paper are: supr-con
30
The categories of this paper are: q-alg
34
The categories of this paper are: chem-ph
17
The categories of this paper are: q-fin
11
The categories of this paper are: hep-lat
20
The categories of this paper are: acc-phys
9
The categories of this paper are: nlin
28
The categories of this paper are: alg-geom
12
The categories of this paper are: nucl-th