The quest for purely virtual quanta: fakeons versus Feynman-Wheeler particles

Abstract

The search for purely virtual quanta has attracted interest in the past. We consider various proposals and compare them to the concept of fake particle, or "fakeon". In particular, the Feynman-Wheeler propagator, which amounts to using the Cauchy principal value inside Feynman diagrams, violates renormalizability, unitarity and stability, due to the coexistence of the prescriptions ±iǫ. We contrast the Feynman, fakeon and Feynman-Wheeler prescriptions in ordinary as well as cut diagrams. The fakeon does not have the problems of the Feynman-Wheeler propagator and emerges as the correct concept of purely virtual quantum. It allows us to make sense of quantum gravity at the fundamental level, and places it on an equal footing with the standard model. The resulting theory of quantum gravity is perturbative up to an incredibly high energy.

Predictions of quantum gravity in inflationary cosmology: effects of the Weyl-squared term

“…What about a particle that is always virtual and can never become real? We can think of it as a purely virtual quantum [28] or a fake particle, i.e., a particle that mediates interactions among other particles, but is invisible to our detectors. And by that we mean invisible in principle, not just in practice.…”

Finite Quantum Gravity Amplitudes: No Strings Attached

“…These constraints constitute challenges for many quantum gravity programs. For instance, Stelle gravity [12,13] resolves the growth of the amplitudes at high energy at the expense of unitarity or causality [14,15], while Lee-Wick-type gravity models [16][17][18][19][20][21] break causality at sub-Planckian scales (also see Refs. [22,23] for a related discussion of massive ghost modes in nonlocal gravity models).…”

Quantum field theories of arbitrary-spin massive multiplets and Palatini quantum gravity

“…However, these approaches do not address the renormalizability issue, so the problem of embedding the Proca, Pauli-Fierz and Rarita-Schwinger fields into a renormalizable, unitary framework has remained essentially open, so far. In this paper, we offer a solution by means of purely virtual particles [16]. The key concept, inspired by the theory of quantum gravity formulated in [14], is the idea JHEP07(2020)176…”

“…A recent account of how this works, with calculations and comparison with alternative concepts, in particular a suggestion [18] based on the Feynman-Wheeler absorber-emitter theory [19,20], can be found in ref. [16]. For the proofs to all orders the reader is referred to ref.…”