Muon g-2 Anomaly Gone?

I just learned some interesting news from Tommaso Dorigo’s blog. Go there for more details, but the news is the claim in these three papers that, accounting for GR effects on the precision measurement of the muon anomalous magnetic moment, the three sigma difference between experiment and theory goes away.

This sort of calculation needs to be checked by other experts in the field, and provides an excellent example of where you want good peer review. Presumably we’ll hear fairly soon whether the result holds up (the papers are not long or complicated). If this is right, it’s a fantastic example of our understanding of fundamental physics at work, with the muon g-2 experiments measuring something they weren’t even looking for, a subtle effect of general relativity.

Also interesting will be the implications for the ongoing experiment at Fermilab trying to achieve an even more precise g-2 measurement. I’m wondering whether there is any way for them to isolate the GR effect on their measurement.

The significance of this is that (setting aside questions about the neutrino sector), the muon g-2 measurement is the most prominent one I’m aware of where there has been a serious (three sigma) difference between experiment and Standard Model theory. This has often been interpreted as evidence for SUSY extensions of the SM. Projects producing “fits” that “predict” SUSY particles with masses somewhat too high to have been seen yet at the LHC use the g-2 anomaly as input. Tommaso ends by asking what happens to these fits if the g-2 anomaly goes away.

Update: For some recent things to read about the g-2 anomaly, before this latest news, see here and here.

Update: Rumor about a problem with this calculation here.

Update: According to this comment and this one, the g-2 collaboration has identified a problem with the calculation, making the predicted GR effect unobservably small. If the authors agree, presumably we’ll soon see a corrected version of the paper(s).

Looking for more information about this, I ran across two blogs I hadn’t seen before. String theorist Joe Conlon of Oxford has a blog called Fickle and Freckled. Not much there besides a posting supporting Brexit and denouncing the fact that nearly all of his colleagues disagree with him, which he fears will cost the university money. A second one is string/SUSY phenomenologist Mark Goodsell’s Real Self-Energy. Goodsell seems to be a Lubos fan, dealing with the current g-2 story by linking to his discussion and denouncing the authors as “effectively crackpots”. He also seems to be unhappy with a certain blogger:

I regularly read two or three physics blogs, since they report on the latest news (and rumours). Now, one of these blogs is very popular whose ostensible purpose is to persuade people that string theory is a misguided research topic. Obviously, this is something I disagree with. However, it also talks a lot about high-energy physics generally, and being rather well-connected it can be quite informative and useful. However, it pretty much uniformly takes a very pessimistic line about all concrete ideas for new physics. It is difficult to overstate how damaging this has been, in making physicists and scientists in neighbouring fields depressed about the future of high-energy physics, and opposing this trend is one of the reasons I would like to blog …

Goodsell has devoted his career to string and SUSY phenomenology, and seems to feel that this is the “future of high-energy physics”, and I’m responsible for making people discouraged about it. Perhaps he should stop advertising Lubos and denouncing crackpots, instead pay attention to the negative results from the LHC and the evidence they provide that his research program is a failure. Blaming his problems on me for pointing them out isn’t going to make them go away.

Update: As mentioned in the comments, Matt Visser now has a preprint criticizing the calculation in these articles.

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54 Responses to Muon g-2 Anomaly Gone?

  1. Dale says:

    Matt Visser’s rebuttal of the Japanese papers is based on the violation of the equivalence principle. The rebuttal is not based on any details of the experimental set-up. Surely if the Japanese disagree with Matt’s conclusions, they will post a reply to the rebuttal.

  2. Wyman says:

    I am having trouble understanding these objections based on the equivalence principle. The authors appear to be working in the Schwarzschild metric, and instead of referring to a quantity named like r_s / r they refer to the equivalent “gravitational potential of the Earth”, which is uniquely defined by identifying it with the term in the metric.

  3. vmarko says:


    They will reply if they find his rebuttal worthy of attention. If I were them, I wouldn’t.

    Best, 🙂

  4. A very brief arxiv paper ( from February the 13th may point quite educationally the erroneous tacit assumption made in the first Japanese paper namely taking a coordinate time for a physical one…

    “When we are moved … by a thirst for knowledge, then the error, like the pain or the sadness, passes us without ever being lost, and the trace of its passage is a renewed knowledge” (Alexander Grothendieck in “Harvests and Seeds”)

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