Some indications that lepton universality (i.e. the propositions that leptons are identical to each other in their weak force decay behavior except that they are different in mass), is violated in b quark decays, which shouldn't happen in the Standard Model of Particle Physics, has created the latest cottage industry of "new physics" models that could explain this phenomena. But, it turns out that most of these models are tightly constrained or ruled out entirely by other data.

Also, more accurate calculations of the Standard Model prediction in the "non-perturbative" regime governed by lattice QCD make the observed anomalies appear smaller than they had seemed using only perturbative QCD Standard Model predictions near the edge of their domain of applicability.

One of the latest papers reviewing these constraints, from a month ago, has the following abstract:

"Many new physics models that explain the intriguing anomalies in the

**New non-perturbative calculations point, however, in the direction of a small discrepancy in this observable. Using up-to-date inputs to determine**

ΔMSMs , we find a severe reduction of the allowed parameter space of Z′ and leptoquark models explaining the B -anomalies. Remarkably, in the former case the upper bound on the Z′

**mass approaches dangerously close to the energy scales already probed by the LHC.**We finally identify some model building directions in order to alleviate the tension with

Luca Di Luzio, Matthew Kirk and Alexander Lenz, "One constraint to kill them all?" (December 18, 2017).

Another paper from two weeks ago also constrains potential remedies for these anomalies by another means:

**We perform a comprehensive model-independent analysis of new physics in**

b→cℓν , considering vector, scalar, and tensor interactions, including for the first time differential distributions of B→D∗ℓν

**angular observables. We show that these are valuable in constraining non-standard interactions.**Specifically, the zero-recoil endpoint of the

**we present**

Vcb determinations from exclusive B

**decays, both with frequentist and Bayesian statistics, leading to compatible results.**The entire numerical analysis is based on open source code, allowing it to be easily adapted once new data or new form factors become available.

In short, the evidence continues to mount that the observed b decay anomalies are a fluke or arise either from experimental errors or inaccuracies in theoretical Standard Model predictions, rather than from "new physics."

## 7 comments:

Deur has another paper on the arXiv

Thanks for the heads up. I'm always interest in those papers (but a bit surprised that I missed it after looking through today's batch).

Did a search and can't find it. Did you mean a different one than https://arxiv.org/abs/1709.02481 ?

I blogged the September paper at https://dispatchesfromturtleisland.blogspot.com/2017/09/deur-considers-dark-energy-as-form-of.html

Ah! It looks like v.2 of the September paper came out on January 14, 2018.

I had missed v.1 and did not notice that what I was viewing was v.2. It appears there are significant changes to v.2. So anyway, you now have the correct paper. Sorry I have been slow in getting back to you. My DSL has been down.

No sweat. Thanks in any case.

Post a Comment