Researchers have proposed a mechanism for the confinement of the "massive ghost" within the framework of quadratic gravity. This hypothetical massive particle, which emerges in certain formulations of quantum gravity, poses a fundamental problem: it violates the unitarity of the physical S-matrix, implying a loss of probability and theoretical inconsistency. Quadratic gravity, an extension of general relativity that includes quadratic terms in the curvature tensor, is a candidate for a quantum theory of gravity, but must resolve this massive ghost challenge to be viable.

The work is based on a manifestly covariant and local canonical operator formalism. First, the manifestly covariant quantization of quadratic gravity in the De Donder gauge (or harmonic gauge) was re-examined from the perspective of dipole fields. Subsequently, an effective Lagrangian for the asymptotic fields of a BRST quartet was derived. It was found that the asymptotic field corresponding to the massive ghost obeys a dipole field equation, similar to that observed in the Froissart model, which is a key characteristic of this formalism.

To understand the quantum aspects of the theory, a manifestly covariant quantization of the effective Lagrangian was performed using two distinct methods: one based on the three-dimensional Fourier transform and another on the four-dimensional Fourier transform. Both approaches yielded the same result: the quantum Fock space is spanned by multipole states. This finding suggests that the massive ghost could be confined, thereby avoiding unitarity violations and opening a path towards the consistency of quadratic gravity as a quantum theory of gravity.