Gravitons, if they exist, are generally considered to be virtual particles within the framework of quantum field theory.
In quantum field theory, particles are described as excitations or quanta of their corresponding fields. The electromagnetic force, for example, is mediated by virtual photons, which are the quanta of the electromagnetic field. Similarly, the weak force is mediated by virtual W and Z bosons.
Gravitons are postulated as the hypothetical particles that mediate the gravitational force. However, it's important to note that the full understanding of quantum gravity, which describes the quantum behavior of gravitational interactions, is still an area of ongoing research and remains elusive. a complete and consistent theory of quantum gravity that incorporates gravitons has not yet been established.
In the current framework of quantum field theory, virtual particles are mathematical entities that arise during calculations and do not correspond to directly measurable or observable particles. They represent intermediate states in Feynman diagrams, which depict particle interactions and calculations of scattering amplitudes. Virtual particles are not directly detected because they violate energy-momentum conservation and have properties that differ from real, on-shell particles.
However, it is important to note that the precise nature of gravitons, their existence, and their properties are still subjects of active research and remain to be experimentally confirmed. The full understanding of quantum gravity, including the role of gravitons as virtual or potentially real particles, is an ongoing pursuit in theoretical physics.