Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Ghosts & Matter Couplings in Massive (bi-&multi-)Gravity   Recently, several works have investigated the coupling to matter in
ghost-free massive (bi-&multi-)gravity and a new effective coupling to matter
has been proposed. In this note we clarify some confusion on the existence and
the implications of a ghost above the strong coupling scale. We confirm that
the standard constraint which is otherwise typically present in this type of
theories disappears on generic backgrounds as soon as this new coupling is
considered. This implies the re-emergence of the Boulware-Deser ghost.
Nevertheless the absence of ghost in the decoupling limit implies that the
cut-off scale (if identified with the scale at which the ghost enters) is
higher than the strong coupling scale. Therefore there is a valid interesting
region of applicability for these couplings at scales below the cut-off.

23
The categories of this paper are: solv-int
37
The categories of this paper are: supr-con
3
The categories of this paper are: physics
32
The categories of this paper are: atom-ph
12
The categories of this paper are: nucl-th
13
The categories of this paper are: quant-ph
34
The categories of this paper are: chem-ph
26
The categories of this paper are: bayes-an
2
The categories of this paper are: math
14
The categories of this paper are: math-ph
0
The categories of this paper are: hep-ph
29
The categories of this paper are: funct-an
16
The categories of this paper are: stat
24
The categories of this paper are: dg-ga
9
The categories of this paper are: nlin
10
The categories of this paper are: q-bio