Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: On Physical Equivalence between Nonlinear Gravity Theories   We argue that in a nonlinear gravity theory, which according to well-known
results is dynamically equivalent to a self-gravitating scalar field in General
Relativity, the true physical variables are exactly those which describe the
equivalent general-relativistic model (these variables are known as Einstein
frame). Whenever such variables cannot be defined, there are strong indications
that the original theory is unphysical. We explicitly show how to map, in the
presence of matter, the Jordan frame to the Einstein one and backwards. We
study energetics for asymptotically flat solutions. This is based on the
second-order dynamics obtained, without changing the metric, by the use of a
Helmholtz Lagrangian. We prove for a large class of these Lagrangians that the
ADM energy is positive for solutions close to flat space. The proof of this
Positive Energy Theorem relies on the existence of the Einstein frame, since in
the (Helmholtz--)Jordan frame the Dominant Energy Condition does not hold and
the field variables are unrelated to the total energy of the system.

27
The categories of this paper are: comp-gas
13
The categories of this paper are: quant-ph
37
The categories of this paper are: supr-con
32
The categories of this paper are: atom-ph
23
The categories of this paper are: solv-int
20
The categories of this paper are: acc-phys
6
The categories of this paper are: astro-ph
21
The categories of this paper are: adap-org
26
The categories of this paper are: bayes-an
7
The categories of this paper are: hep-th
31
The categories of this paper are: ao-sci
11
The categories of this paper are: hep-lat
9
The categories of this paper are: nlin
14
The categories of this paper are: math-ph
8
The categories of this paper are: hep-ex
12
The categories of this paper are: nucl-th