Wednesday, 4 July 2012


CMS and ATLAS both now have conclusive evidence of a Higgs-like particle with a mass of around $125-127$ GeV; this will be covered all over the internet, so I won't go into details here. I will say that it's a thrilling moment, and that we all eagerly await more data, to elucidate the detailed properties of this particle.

But the main reason for this post is to publicly congratulate everybody involved in this work. There are (at least) two distinct groups of people to highlight:

  • The LHC is an extraordinary machine, and has been performing phenomenally well; this discovery is only possible now because the machine has delivered so much integrated luminosity so quickly. It represents an unparallelled engineering achievement, so congratulations to the team who have worked so hard to get it to this stage.

Tuesday, 3 July 2012

Professor Higgs, your boson is ready

As has already been discussed extensively by many bloggers (including Jester, Tommaso, Shaun, and especially Peter Woit), CERN are holding a special seminar and press conference tomorrow morning, to announce the latest results on the hunt for the Higgs boson. It is widely rumoured that the evidence of a $\sim 125$ GeV Higgs from last year has strengthened to the point of being conclusive.

The plausibility of said rumours was only increased by a press release, which came out yesterday, giving the final results from the Higgs search at the Tevatron; the paper itself is available here.

String Phenomenology: Days 4 & 5

Well, my blogging momentum ran out towards the end of last week, but I will wrap up the String Pheno series with some points of note from the last two days.

In a day dominated by F-theory talks (at least in the plenary sessions), I thought the best of the lot was from Eran Palti, who discussed 'ultra-local' model-building in F-theory. The idea is to focus on the neighbourhood of a single point in the compact geometry, where all the important interactions are supported. His main point was that in many string models, we don't actually have enough control to calculate physical coupling constants; often an overall proportionality factor is missing, and simply assumed to be 'of order one' (i.e. of magnitude between about .1 and 10). I think this is a very important point; 'string phenomenology' as it stands is a bit of a misnomer, because as far as I know, nobody has yet been able to do an honest calculation of all quantities like masses and coupling constants in a realistic string model.

Friday, 29 June 2012

String Phenomenology: Day 3

As you will have noticed if you visit this blog, I've not done a very good job of blogging this conference. In order to keep things in order, let me post the only thing I wrote about day 3, so I can move on to the later days!

Mariana Graña discussed the consistency of putative string theory solutions which break supersymmetry via anti-D3-branes in a warped throat (I briefly discussed this in a previous post). She was fairly adamant that this setup is inconsistent, due to induced singularities in the three-form fluxes supporting the throat. The most important approximation she and her collaborators have used seems to be to 'smear' the anti-D3-branes — replace the point-like branes with a continuous charge distribution. This misses one possible resolution of the singularities, which is polarisation of the anti-D3-branes into NS5-branes, but they have arguments to suggest that this won't solve the problem. I doubt that the controversy will be resolved any time soon.

(The latest paper by Graña et al. went on the arXiv the day after this talk.)

Edit: I suppose it's reasonable to also flag my own talk, in which I spoke about my paper from May, which I already mentioned here. I wasn't particularly happy with the talk, although it went okay, and I had a fair-sized audience who seemed to pay attention, so no complaints!

Wednesday, 27 June 2012

String Phenomenology: Day 2

Here are some of the highlights from day 2 of the conference, as I saw it.

Gordy Kane continued to describe his recent collaboration with Bobby Acharya and others (see the post about day 1), focussing on their prediction of the Higgs mass. Specifically, they claim to predict that the Higgs should sit between about 122 and 129 GeV, and most likely at about 125 GeV. This time, the animosity towards these claims was a lot more apparent.

Tuesday, 26 June 2012

String Phenomenology: Day 1

Here is a brief overview of the more interesting points of day 1. I will link to the abstracts of each talk; hopefully, in time, the same pages will also include the slides and video from the talks.

Ben Allanach kicked things off by describing some of the lates experimental results, and what they might mean for supersymmetry (SUSY) in particular (and hence for string model building, basically all of which is supersymmetric). His most important points (I think) were the following:

  • Discovery of a standard-model-like Higgs, with a mass of around 125 GeV, could be just around the corner. In many popular realisations of SUSY breaking, a Higgs mass of 125 GeV is right at, or just beyond, the maximum possible value, assuming that superpartner masses are kept below several TeV.
  • There is an unexplained anomaly in the Tevatron data, in the 'forward-backward asymmetry' in the production of top-anti-top pairs. The Tevatron collided protons and anti-protons, and this variable measures the number of tops which are produced travelling in the same direction as the initial proton, compared to the number travelling in the direction of the anti-proton. The measured value disagrees with the standard model prediction by something like $3\sigma$.

Monday, 25 June 2012

String Phenomenology 2012

This week I am in Cambridge for this year's String Phenomenology conference, and it seems like a good excuse to do some blogging. There are five days of what should be quite interesting talks, and I will try to summarise and pass comment on at least some of them every day. Watch this space!