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arXiv:2604.26271

Galilean Reeh--Schlieder Obstruction

Leonardo A. Pachon

quant-phgr-qcmath-phSubmitted Apr 29, 2026• Announced Apr 30, 2026
v1 · Apr 29, 2026v2 · Oct 2, 2026
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Abstract

We prove that the standard Galilean Haag--Kastler axioms, augmented by Bargmann mass superselection, are inconsistent with the Reeh--Schlieder property: no such net admits a vacuum that is cyclic and separating for every local field algebra. Two ingredients combine: Galilean Schrödinger fields annihilate the Fock vacuum, and Bargmann mass superselection forbids the Hermitian-combination evasion that keeps relativistic axioms consistent. The result extends beyond the Fock-representation hypothesis: any Galilean Haag--Kastler net whose canonical fields carry definite Bargmann mass charges and admit time-zero restrictions on a field-algebra-stable common dense domain is incompatible with Reeh--Schlieder. The bounded-below mass spectrum and the vacuum-at-spectral-minimum, usually imposed as separate axioms, are derived consequences -- of positive-energy boost positivity and a Bose-CCR algebraic descent, respectively. The Tomita--Takesaki modular flow is consequently unavailable on Galilean local field algebras. We identify the Reeh--Schlieder property as the precise structural ingredient distinguishing relativistic from Galilean algebraic quantum field theory: relativistic AQFT has it as a theorem, Galilean AQFT cannot.

Comments
16 pages, 3 figures

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We prove that the standard Galilean Haag--Kastler axioms, augmented by Bargmann mass superselection, are inconsistent with the Reeh--Schlieder property: no such net admits a vacuum that is cyclic and separating for every local field algebra. Two ingredients combine: Galilean Schrödinger fields annihilate the Fock vacuum, and Bargmann mass superselection forbids the Hermitian-combination evasion that keeps relativistic axioms consistent. The result extends beyond the Fock-representation hypothesis: any Galilean Haag--Kastler net whose canonical fields carry definite Bargmann mass charges and admit time-zero restrictions on a field-algebra-stable common dense domain is incompatible with Reeh--Schlieder. The bounded-below mass spectrum and the vacuum-at-spectral-minimum, usually imposed as separate axioms, are derived consequences -- of positive-energy boost positivity and a Bose-CCR algebraic descent, respectively. The Tomita--Takesaki modular flow is consequently unavailable on Galilean local field algebras. We identify the Reeh--Schlieder property as the precise structural ingredient distinguishing relativistic from Galilean algebraic quantum field theory: relativistic AQFT has it as a theorem, Galilean AQFT cannot.
We ask which kinematical groups allow local algebras of canonical quantum fields to commute at unequal times. The Galilei group acts transitively on pairs of non-simultaneous events with a given time separation, so a Galilean-invariant commutation relation between sharp-time algebras at unequal times also holds at coincident positions; at arbitrarily short separations it contradicts the canonical commutation relations, with no spectral assumption. Under unitary Bargmann covariance and positivity of the energy modulo the central mass, the vacuum is annihilated by the annihilation fields, hence not separating for local algebras, and the vacuum two-point function of a canonical field factorises into the free Schrödinger propagator and the characteristic function of an internal-energy distribution. Sharp-time algebras at unequal times then commute only at a closed null set of time separations, bounded below by the Mandelstam-Tamm and Margolus-Levitin times and empty for sharp or generic internal energy; any finite set of separations occurs. Algebras of open spacetime regions containing time-smeared fields never commute. Positivity cannot be dropped: without it, commutation can hold at all separations beyond any given one. Among spatially isotropic homogeneous spacetimes with absolute time, only the galilean ones are transitive at fixed time separation, up to discrete exceptions in the two oscillating cases, realised by a harmonic trap in the Newton-Hooke one. Non-commutation transfers from the vacuum to every representation of a simple C*-algebra on which the dynamics acts by automorphisms, including free Bose and Fermi gases at all temperatures and the Galilei-covariant cutoff dynamics of interacting fermions of Narnhofer and Thirring; without such a vacuum representation it can fail even in thermal equilibrium.
Many of the "counterintuitive" features of relativistic quantum field theory have their formal root in the Reeh-Schlieder theorem, which in particular entails that local operations applied to the vacuum state can produce any state of the entire field.It is of great interest then that I.E.Segal and, more recently, G. Fleming (in a paper entitled "Reeh-Schlieder meets Newton-Wigner") have proposed an alternative "Newton-Wigner" localization scheme that avoids the Reeh-Schlieder theorem.In this paper, I reconstruct the Newton-Wigner localization scheme and clarify the limited extent to which it avoids the counterintuitive consequences of the Reeh-Schlieder theorem.I also argue that there is no coherent interpretation of the Newton-Wigner localization scheme that renders it free from act-outcome correlations at spacelike separation.
Many of the “counterintuitive” features of relativistic quantum field theory have their formal root in the Reeh-Schlieder theorem, which in particular entails that local operations applied to the vacuum state can produce any state of the entire field. It is of great interest then that I. E. Segal and, more recently, G. Fleming (in a paper entitled “Reeh-Schlieder meets Newton-Wigner”) have proposed an alternative “Newton-Wigner” localization scheme that avoids the Reeh-Schlieder theorem. In this paper, I reconstruct the Newton-Wigner localization scheme and clarify the limited extent to which it avoids the counterintuitive consequences of the Reeh-Schlieder theorem. I also argue that there is no coherent interpretation of the Newton-Wigner localization scheme that renders it free from act-outcome correlations at spacelike separation.
The nature and properties of the vacuum as well as the meaning and localization properties of one or many particle states have attracted a fair amount of attention and stirred up sometimes heated debate in relativistic quantum field theory over the years. I will review some of the literature on the subject and will then show that these issues arise just as well in non-relativistic theories of extended systems, such as free bose fields. I will argue they should as such not have given rise either to surprise or to controversy. They are in fact the result of the misinterpretation of the vacuum as ``empty space'' and of a too stringent interpretation of field quanta as point particles. I will in particular present a generalization of an apparently little known theorem of Knight on the non-localizability of field quanta, Licht's characterization of localized excitations of the vacuum, and explain how the physical consequences of the Reeh-Schlieder theorem on the cyclicity and separability of the vacuum for local observables are already perfectly familiar from non-relativistic systems of coupled oscillators.
The Reeh-Schlieder theorem asserts the vacuum and certain other states to be spacelike superentangled relative to local quantum fields. This motivates an inquiry into the physical status of various concepts of localization. It is argued that a covariant generalization of Newton-Wigner localization is a physically illuminating concept. When analyzed in terms of nonlocally covariant quantum fields, creating and annihilating quanta in Newton-Wigner localized states, the vacuum is seen to not possess the spacelike superentanglement that the Reeh-Schlieder theorem displays relative to local fields, and to be locally empty as well as globally empty. Newton-Wigner localization is then shown to be physically interpretable in terms of a covariant generalization of the center of energy, the two localizations being identical if the system has no internal angular momentum. Finally, some of the counterintuitive features of Newton-Wigner localization are shown to have close analogues in classical special relativity.