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Article Dans Une Revue Classical and Quantum Gravity Année : 2009

What is a particle ?

Résumé

The notion of particle plays an essential role in quantum field theory (QFT). Some recent theoretical developments, however, have questioned this notion; for instance, QFT on curved spacetimes suggests that preferred particle states might not exist in general. Furthermore, a certain tension derives from the fact that QFT's particle states are intrinsically nonlocal, while experiments are localized. These considerations have lead some to suggest that in general QFT should not be interpreted in terms of particle states, but rather, say, in terms of eigenstates of local operators. On the other hand, it is not completely obvious how to reconcile this view with the empirically-observed ubiquitous particle-like behavior of quantum fields. We observe here that already in flat space there exist --strictly speaking-- two distinct notions of particles: globally defined n-particle Fock states and local particle states. The last describe the physical objects detected by the real finite-size particle detectors and are eigenstates of local field operators. In the limit in which the particle detectors are large compared, say, to the Compton wavelength, global and local particle states converge in a weak topology defined by physical measurements (but not in norm). This observation reconciles the two point of view and provides a local definition of particle state that remains well-defined even when the conventional global particle states are not defined. This definition could play an important role in quantum gravity, when asymptotic regions may not be available.

Dates et versions

hal-00004787 , version 1 (24-04-2005)

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Citer

Daniele Colosi, Carlo Rovelli. What is a particle ?. Classical and Quantum Gravity, 2009, 26 (2), pp.025002. ⟨hal-00004787⟩
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