Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The blackness of the cosmic microwave background spectrum as a probe of
  the distance-duality relation   A violation of the reciprocity relation, which induces a violation of the
distance duality relation, reflects itself in a change in the normalisation of
the cosmic microwave spectrum in such a way that its spectrum is grey. We show
that existing observational constraints imply that the reciprocity relation
cannot be violated by more than 0.01% between decoupling and today. We compare
this effect to other sources of violation of the distance duality relations
which induce spectral distortion of the cosmic microwave background spectrum.

34
The categories of this paper are: chem-ph
28
The categories of this paper are: alg-geom
37
The categories of this paper are: supr-con
32
The categories of this paper are: atom-ph
12
The categories of this paper are: nucl-th
26
The categories of this paper are: bayes-an
14
The categories of this paper are: math-ph
31
The categories of this paper are: ao-sci
27
The categories of this paper are: comp-gas
15
The categories of this paper are: nucl-ex
30
The categories of this paper are: q-alg
4
The categories of this paper are: cond-mat
2
The categories of this paper are: math
3
The categories of this paper are: physics
8
The categories of this paper are: hep-ex
21
The categories of this paper are: adap-org