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mitchell porter
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- New standard model particle, or illusion of theorists?
This is an alert about a claim regarding the standard model, that got a burst of attention in the past two weeks.
The original paper came out last year:
"The electroweak η_W meson" by Gia Dvali, Archil Kobakhidze, Otari Sakhelashvili (2024)
The recent follow-up and other responses are
"η_W-meson from topological properties of the electroweak vacuum" by Dvali et al
"Hiding in Plain Sight, the electroweak η_W" by Giacomo Cacciapaglia, Francesco Sannino, Jessica Turner
"Astrophysical Consequences of an Electroweak η_W Pseudo-Scalar" by Hooman Davoudiasl
You can see the usual approach to the "electroweak theta term" in discussions here:
https://physics.stackexchange.com/search?q=electroweak+theta
If I was, say, a Quanta Magazine journalist writing about this, I'd want to start with an exposition of the theta or vacuum angle in QCD, the idea of topological susceptibility, and how it complicates the masses of the light-quark mesons. Specifically, all those mesons should themselves be light - as the Goldstone bosons of chiral symmetry breaking they should be massless, with some mass then coming from the quark masses. But one of them, the η' meson (eta prime), is heavy, and the reason is that it is the Goldstone boson of the axial part of chiral symmetry, and that symmetry is anomalous, i.e. does not actually hold, so the η' mass is not kept light by the symmetry. 't Hooft, Veneziano, and Witten all developed more detailed descriptions of where the mass comes from, in terms of the potentially CP-violating "theta term" of QCD, and the "topological susceptibility" which measures the sensitivity of the vacuum state to changes in the theta coupling.
The issue behind these new papers is whether there is a theta term in the electroweak interactions as well. The conventional view seems to be that it would somehow be rendered redundant by CP violation that already exists elsewhere in the electroweak sector. The idea that it might be there after all is at least thirty years old. This version is somehow an outgrowth of older ideas by Dvali on a gravitational theta term, and by Dvali and Funcke on the "gravi-majoron", an η_ν meson produced by the gravitational chiral anomaly and a neutrino condensate (work that I thought I had posted about here, years ago, but I can't find it now).
Of the two new papers by Dvali et al, one uses gravity to argue for an η_W meson, the other just uses the electroweak interaction. This may even be another occasion in which the possibility of a gauged SU(2) formulation of gravity hints at obscure relationships with the electroweak sector, but I would need to check that. Of the other two papers linked above, the one from Sannino's group claims that the η_W state is a superposition of a hydrogen atom and an antihydrogen atom (?!); while Davoudiasl sidesteps the theory issues and asks whether an η_W meson could explain dark matter or dark energy (as quintessence). He concludes, no.
The original paper came out last year:
"The electroweak η_W meson" by Gia Dvali, Archil Kobakhidze, Otari Sakhelashvili (2024)
The recent follow-up and other responses are
"η_W-meson from topological properties of the electroweak vacuum" by Dvali et al
"Hiding in Plain Sight, the electroweak η_W" by Giacomo Cacciapaglia, Francesco Sannino, Jessica Turner
"Astrophysical Consequences of an Electroweak η_W Pseudo-Scalar" by Hooman Davoudiasl
You can see the usual approach to the "electroweak theta term" in discussions here:
https://physics.stackexchange.com/search?q=electroweak+theta
If I was, say, a Quanta Magazine journalist writing about this, I'd want to start with an exposition of the theta or vacuum angle in QCD, the idea of topological susceptibility, and how it complicates the masses of the light-quark mesons. Specifically, all those mesons should themselves be light - as the Goldstone bosons of chiral symmetry breaking they should be massless, with some mass then coming from the quark masses. But one of them, the η' meson (eta prime), is heavy, and the reason is that it is the Goldstone boson of the axial part of chiral symmetry, and that symmetry is anomalous, i.e. does not actually hold, so the η' mass is not kept light by the symmetry. 't Hooft, Veneziano, and Witten all developed more detailed descriptions of where the mass comes from, in terms of the potentially CP-violating "theta term" of QCD, and the "topological susceptibility" which measures the sensitivity of the vacuum state to changes in the theta coupling.
The issue behind these new papers is whether there is a theta term in the electroweak interactions as well. The conventional view seems to be that it would somehow be rendered redundant by CP violation that already exists elsewhere in the electroweak sector. The idea that it might be there after all is at least thirty years old. This version is somehow an outgrowth of older ideas by Dvali on a gravitational theta term, and by Dvali and Funcke on the "gravi-majoron", an η_ν meson produced by the gravitational chiral anomaly and a neutrino condensate (work that I thought I had posted about here, years ago, but I can't find it now).
Of the two new papers by Dvali et al, one uses gravity to argue for an η_W meson, the other just uses the electroweak interaction. This may even be another occasion in which the possibility of a gauged SU(2) formulation of gravity hints at obscure relationships with the electroweak sector, but I would need to check that. Of the other two papers linked above, the one from Sannino's group claims that the η_W state is a superposition of a hydrogen atom and an antihydrogen atom (?!); while Davoudiasl sidesteps the theory issues and asks whether an η_W meson could explain dark matter or dark energy (as quintessence). He concludes, no.
