Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Singular Instantons in Eddington-inspired-Born-Infeld Gravity   In this work, we investigate $O(4)$-symmetric instantons within the
Eddington-inspired-Born-Infeld gravity theory (EiBI). We discuss the regular
Hawking-Moss instanton and find that the tunneling rate reduces to the General
Relativity (GR) value, even though the action value is different by a constant.
We give a thorough analysis of the singular Vilenkin instanton and the
Hawking-Turok instanton with a quadratic scalar field potential in the EiBI
theory. In both cases, we find that the singularity can be avoided in the sense
that the physical metric, its scalar curvature and the scalar field are regular
under some parameter restrictions, but there is a curvature singularity of the
auxiliary metric compatible with the connection. We find that the on-shell
action is finite and the probability does not reduce to its GR value. We also
find that the Vilenkin instanton in the EiBI theory would still cause the
instability of the Minkowski space, similar to that in GR, and this is
observationally inconsistent. This result suggests that the singularity of the
auxiliary metric may be problematic at the quantum level and that these
instantons should be excluded from the path integral.

4
The categories of this paper are: cond-mat
26
The categories of this paper are: bayes-an
25
The categories of this paper are: patt-sol
34
The categories of this paper are: chem-ph
32
The categories of this paper are: atom-ph
23
The categories of this paper are: solv-int
2
The categories of this paper are: math
36
The categories of this paper are: cmp-lg
20
The categories of this paper are: acc-phys
13
The categories of this paper are: quant-ph
3
The categories of this paper are: physics
9
The categories of this paper are: nlin
14
The categories of this paper are: math-ph
24
The categories of this paper are: dg-ga
27
The categories of this paper are: comp-gas
15
The categories of this paper are: nucl-ex