Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Fakeons versus Lee-Wick ghosts: physical Pauli-Villars fields, finite
  QED and quantum gravity   We reconsider the Lee-Wick (LW) models and compare their properties to the
properties of the models that contain purely virtual particles. We argue
against the LW premise that unstable particles can be removed from the sets of
incoming and outgoing states in scattering processes. The removal leads to a
non-Hermitian classical limit, besides clashing with the observation of the
muon. If, on the other hand, all the states are included, the LW models have an
unbounded Hamiltonian or negative norms. Purely virtual particles, on the
contrary, lead to a Hermitian classical limit and are absent from the sets of
incoming and outgoing states without implications on the observation of
long-lived unstable particles. We give a vademecum to summarize the properties
of most options. We study a method to remove the LW ghosts only partially, by
saving the physical particles they contain. Specifically, we replace a LW ghost
with a certain superposition of a fakeon and an observable particle, and drop
only the former from the sets of the external states. The trick can be used to
make the Pauli-Villars fields consistent and observable, without sending their
masses to infinity, or build a finite QED, by tweaking the original Lee-Wick
construction. However, it has issues with general covariance, so it cannot be
applied as is to quantum gravity, where a manifestly covariant decomposition
requires the introduction of a massive spin 2 multiplet.

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The categories of this paper are: hep-lat
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The categories of this paper are: chem-ph
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The categories of this paper are: chao-dyn
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The categories of this paper are: q-fin
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The categories of this paper are: dg-ga
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The categories of this paper are: nlin
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The categories of this paper are: eess
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The categories of this paper are: econ
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The categories of this paper are: alg-geom
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The categories of this paper are: bayes-an
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The categories of this paper are: adap-org
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The categories of this paper are: nucl-th
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The categories of this paper are: funct-an
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The categories of this paper are: supr-con
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The categories of this paper are: nucl-ex
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The categories of this paper are: math-ph