Category: General

Reducing the hassle with BibTeX

BibTeX is great for generating bibliographies, in particular combined with Inspire, but it also has its annoying aspects. This is a typical workflow to generate references for a paper:

  1. Find the texkey of a paper on Inspire and \cite it in the manuscript
  2. Copy & paste the bibtex entry into the .bib file
  3. Correct LaTeX code in the title (often missing the dollar signs or containing characters like “->”)
  4. After having completed the paper, check whether any of the preprints have been published in the meantime and add the journal reference.

In this list, step 1 is the only one requiring a brain, while steps 2-4 are increasingly annoying. This is why I have written a script that mostly automatizes these steps and I want to explain it in this post.

Spare me the details, tell me how to use it

Having completed step 1 above, you can compile your LaTeX document (let’s call it paper.tex) and a paper.aux file will be generated. This is the case even if you don’t have a bibliography file yet (and the compilation will thus fail). Installing my inspiretools script from GitHub, you can now execute the following command:

auxtobib paper.aux > bilbiography.bib

This command will download all the BibTeX entries from Inspire and save them to the .bib file. Step 2 has been automatized! When you add citations to the paper, just rerun the command. It will always fetch all the references anew, so if one of the references gets a journal reference added, your bibliography will be up to date. So step 4 is redundant as well!

What about step 3? Well, you could still do it manually, but all changes will be overwritten when you update the bibliography. The best way would be to change it on Inspire itself! And you can help doing that. The code contains a second script that you can invoke as

auxtoxml paper.aux > titles.xml

This will generate an XML file containing all the titles of the references in your bibliography. Correct all the LaTeX errors there and then send the XML file to The file is in the right format for the Inspire staff to quickly update the information in their database. This way, the change will not only persist when you update your references, but you will also have saved your colleagues some time!

How it works

The code uses the pyinspire script by Ian Huston (with some modifications by myself) that uses the Inspire API to fetch entries. It is written in Python.

In case you are wondering why I am taking the detour via the .aux file rather than directly extracting the references from the .tex file: I have found this to be more robust since it works with many different citation commands like \cite, \nocite, \autocites, and even with custom macros without the need to use complicated regular expressions.

Note that the current implementation is quite slow as it fetches each entry separately, which can take some time especially for long papers. In principle this could be sped up by fetching several entries simultaneously. If you want to improve on this, you are welcome to contribute to the repository.

New paper on composite Higgs

Today, a new paper entitled “Direct and indirect signals of natural composite Higgs models” by Christoph Niehoff, Peter Stangl and myself appeared on the preprint archive. Weighing 72 pages, it might be a good read on the beach in your well-deserved summer vacation!? Anyway, here is some information about why we made this analysis and what we found.

The idea of the Higgs boson being a composite particle is a compelling and fascinating solution to the electroweak hierarchy problem (also called the Higgs naturalness problem) and, according to many, is among the two most attractive solutions to this problem (the other one being supersymmetry). Many brilliant people have contributed to the construction of elaborate models that address a variety of challenges that arise when formulating a realistic theory implementing the composite Higgs idea. Given the plethora of experimental tests of the Standard Model, from precision electroweak measurements to flavour physics, direct searches for the production of heavy particles and precision measurements of the properties of the Higgs boson, it is not easy to determine whether a given model is viable, or what an experimental exclusion (or discovery!) in one observable implies for other observables.

In the past, many studies have either focused on a limited set of experimental tests – e.g. on Higgs physics, flavour physics or direct searches – or have studied the interplay between different tests in a qualitative way, while being as model-independent as possible. While this approach certainly has its advantages, to really study the correlations between different experimental tests of a new physics model (which is the overarching goal of our research group), one needs to select a specific model and perform a numerical analysis of all experimental constraints on its parameters. This is exactly what we have set out to do.

For several reasons (detailed in the paper), this turned out to be quite challenging on a technical level, and it was only thanks to a local computing cluster that we were able to obtain the results we were interested in. In the end, we think the results we got are interesting enough to justify the efforts. Just to mention two of the most exciting results of our analysis:

  • Some hints of a resonance at 2 TeV seen by ATLAS and CMS in diboson final states can be perfectly accomodated, while being in agreement with all other experimental constraints.
  • Deviations from Standard Model expectations in $B$ physics, in particular in angular observables in $B\to K^*\mu^+\mu^-$ and the branching ratio of $B_s\to\phi\mu^+\mu^-$, can be explained as well. To be honest, this came as a surprise to us! But most exciting about this is that it implies the existence of a neutral spin-1 resonance below 1 TeV which should show up soon in the dijet or $t\bar{t}$ mass distribution at LHC! And if it doesn’t show up, it’s clear that the models studied by us cannot explain these anomalies.

Many more big and small results can be found in the 61 plots and the accompanying text. Of course, having set up the analysis for one particular model (with four different flavour structures), we are now eager to apply this strategy also to other models or scenarios, and we are looking forward to discussing this with the community.

The $B\to K^*\mu^+\mu^-$ anomaly persists

tl;dr The $B\to K^*\mu^+\mu^-$ anomaly is still there, global fit prefers new physics in $C_9$ over SM by $3.7\sigma$, interpretation as hadronic effect not excluded though.

Two years ago the LHCb experiment measured a significant deviation from the Standard Model predictions in one of the angular observables of the $B\to K^*\mu^+\mu^-$ decay (prosaically called $P_5’$). This deviation caused a lot of discussion because it could in principle be a sign of physics beyond the Standard Model, but it has also been speculated that some mundane QCD effect not accounted for in the theoretical predictions for this (and other) observables is responsible for it.

Last year, another tantalizing announcement was made by the same experiment. Apparently, the decay rates of the two modes $B\to K\mu^+\mu^-$ and $B\to Ke^+e^-$ differ by something like 25% (their ratio, called $R_K$, was measured to be around 0.75). This is not possible in the Standard Model where electrons and muons are identical up to their different masses (which play no role in this decay). Interestingly, the two anomalies — dubbed $B\to K^*\mu^+\mu^-$ and $R_K$ anomalies — fit very nicely together if interpreted in terms of physics beyond the Standard Model. However, it was too early to draw a firm conclusion, with the $B\to K^*\mu^+\mu^-$ observables being potentially susceptible to poorly known QCD effects and the $R_K$ observation not being statistically very significant taken on its own.

Today at the conference Rencontres de Moriond in the Italian ski resort of La Thuile in the Aosta valley, one of the most important conferences in high energy physics, Christoph Langenbruch, on behalf of the LHCb collaboration, has presented their updated analysis of $B\to K^*\mu^+\mu^-$ angular observables and has shown that the tension with the Standard Model is still present (see the announcements here and here).

Thanks to the conference organizers as well as the LHCb collaboration, I was given the honour to be one of the theorists to give some initial interpretations of this measurement. Using the analysis developed with Wolfgang Altmannshofer for our recent paper and exploiting the $B\to K^*$ form factors obtained for a project with Roman Zwicky and Aoife Bharucha, in my talk I showed that in a global fit to all available experimental data, a new physics interpretation (in the so-called Wilson coefficient $C_9$, found already after the previous measurement) is preferred over the Standard Model by $3.7\sigma$ and even $4.3\sigma$ if $R_K$ is included.

While this is extremely interesting, unfortunately this is not yet evidence for the presence of “new” physics. It is still possible we are being fooled by an unexpected QCD effect. An interesting check of the QCD vs. new physics hypotheses is to consider the size of the deviation as a function of the invariant mass-squared of the muons, $q^2$. In the following plot, showing the values preferred by the data, a new physics effect would lead to boxes that align horizontally — i.e., no $q^2$ dependence — while a hadronic effect should have a different $q^2$ dependence. Indeed there seems to be an increasing trend when moving from the left towards the $J/\psi$ resonance (indicated by the first vertical gray line). However, at the moment it is fair to say that the situation is not yet conclusive and both hypotheses — new physics or an unexpectedly large hadronic effect — are still valid and both have interesting implications.


In the near future, it will be extremely intersting to see what LHCb has to say on the ratio of $B\to K^*\mu^+\mu^-$ vs. $B\to K^*e^+e^-$ observables. If muons and electrons indeed behave differently, this should have a visible impact there, even using data already taken in 2012 (but not yet analyzed). In the future, more precise measurements of processes like $B_s\to\mu^+\mu^-$ will certainly solve this puzzle.

[Technical comment: don’t be confused by the three different $3.7\sigma$ numbers here. The first ist the significance of the 2013 LHCb anomaly, which used a theory predictions that many (me included) considered as not conservative enough. The second is the significance of the new tension as obtained by LHCb. This is more conservative because it includes an important source of theory uncertainty (charm loops) not considered in the old analysis. The third is the pull of the $C_9$ new physics solution compared to the SM in our global fit. This uses many more processes and observables, while it does not use one of the bins where the tension observed by LHCb is largest, because we consider this bin to be theoretically unreliable. Using it as well, Joaquim Matias presented a pull of more than $4\sigma$ at the conference. In general, the agreement between the analyses presented by him and by me was very good, which is an important consistency check.]

New paper on $b\to s\nu\bar\nu$!

Today my collaborators Andrzej Buras, Jennifer Girrbach-Noe, Christoph Niehoff and I released our new paper on the decays $B\to K\nu\bar\nu$ and $B\to K^*\nu\bar\nu$. These two closely related decays are sensitive to physics beyond the Standard Model and will very likely be observed for the first time at the upcoming Belle-II experiment. It was about time to improve on the analysis of five years ago; especially interesting for us was the impact of the recent computation of $B\to K$ and $B\to K^*$ form factors on the lattice as well as the host of new measurements of observables in $b\to s\mu^+\mu^-$ transitions at LHC (remember the $B\to K^*\mu^+\mu^-$ anomaly?).

Here is just a selection of some of the main points of the paper that you might be interested in.

If you’re an experimentalist:

  • The central value of the Standard Model  prediction for the branching ratio of $B\to K^*\nu\bar\nu$ is now 40% higher – this is good news for Belle-II.
  • We show that, even if no new physics is discovered in $b\to s\mu^+\mu^-$ transitions at LHC, $b\to s\nu\bar\nu$ decays are still very interesting to probe new physics.
  • Even if there is no new physics, measuring these decays precisely is important to reduce theory uncertainties in other processes.

If you care about precise Standard Model predictions:

  • Using the information from the lattice and a recent full NLO calculation of electroweak corrections, we obtain relative uncertainties of about 10% on the branching ratios. (Details on the form factors will be discussed in an upcoming paper with Aoife Bharucha and Roman Zwicky.)

If you are interested in new physics:

  • We study the correlations between $b\to s\mu^+\mu^-$ and $b\to s\nu\bar\nu$ on a model-independent basis. Interestingly, if the current tensions in $b\to s\mu^+\mu^-$ are due to new physics, $b\to s\nu\bar\nu$ could help disentangle what kind of new physics is responsible for them.
  • We point out that if there is new physics (e.g. a $Z’$ boson) that only affects tau leptons (and tau neutrinos), $B\to K\nu\bar\nu$ and $B\to K^*\nu\bar\nu$ would be the first place to look for it.

Our new physics analysis is summarized in this plot, showing predictions of various scenarios in the plane of the $B\to K\nu\bar\nu$ and $B\to K^*\nu\bar\nu$ branching ratios, normalized to their SM values. If you are curious what it all means, have a look at the paper!