Antihydrogen and Fundamental Physics by Michael Charlton & Stefan Eriksson & Graham M. Shore

Author:Michael Charlton & Stefan Eriksson & Graham M. Shore
Language: eng
Format: epub
ISBN: 9783030517137
Publisher: Springer International Publishing

3.1.2 Theoretical Principles

Of course, Lorentz and symmetry does imply that the charges of and H should be the same. However, charge neutrality of antihydrogen is not really a test of in the sense that even in the Lorentz and violating effective theories described in Chap. 2, the charges of the proton and antiproton, and the electron and positron, are still required to be equal and opposite. In fact, this is a much deeper property of relativistic QFT which ultimately is necessary for causality.

As explained in Sect. 2.​1, the existence of antiparticles with precisely the same mass and opposite charge is a requirement of causality, necessary to ensure the vanishing of the relevant correlators for spacelike separation (microcausality). It is therefore almost impossible to see how any difference in magnitude of the charge of the electron and positron could be compatible with our present understanding of QFT.

Even if we momentarily set these structural issues aside and continue to entertain the idea that the electron and positron charges could be different, further difficulties proliferate. Given the existence of the coupling of the photon to an pair, either the photon would be charged or, in contradiction to a huge body of experimental evidence, electric charge conservation would be violated. In the former case, an accelerating electron would lose charge by synchrotron radiation, leading to further paradoxes. Indeed, experimental limits on the charge of the photon are extremely strong, the PDG quoting a bound of [93].

A second issue, which would apply equally to hydrogen, is then the equality of the magnitude of the charges of the antiproton and positron (or equivalently, the proton and electron). In the standard model, this is again ensured by a deep principle, in this case unitarity. As discussed in Sect. 2.​6, the absence of anomalies in gauged currents imposes a set of constraints on the charges of the fermions which appear as internal lines in the 3-current triangle diagrams. This imposes a precise balance between the quark and lepton charges. If this is broken, we would lose conservation of a gauged current, which in turn would lead to a loss of unitarity in the QFT.

We see, therefore, that the experimental measurement of charge neutrality of antihydrogen should be viewed as a test of causality and unitarity in the standard model QFT. While invariance does imply the equality of the charge of hydrogen and antihydrogen, charge neutrality would still be required even in a -violating QFT.

The only remaining loophole would seem to be our assumption that the measured charge of the bound states is given precisely by the sum of the charges of their constituents, either the antiproton and positron for the antihydrogen atom or the valence quarks for the antiproton. This is referred to as the “assumption of charge superposition” in [31]. It could conceivably be possible to imagine some sort of charge screening mechanism which could invalidate this for a particular experimental measurement. However, such a screening effect would have had to avoid detection everywhere else in the

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