Friday 27 April 2012

How to explain the Higgs mechanism

Time and again I read/hear popular-level descriptions of the Higgs mechanism in which it is proclaimed that the Higgs field is "like molasses", offering resistance to particles moving through it. This is an awful analogy, and makes me cringe every time. Even non-physicists should immediately see why: a particle moving through molasses feels a drag force which will ultimately bring it to rest with respect to the molasses (in the absence of some persistent driving force). But the Higgs field fills all of spacetime, and thanks to Galileo and Newton, we know that in empty space, in the absence of forces, particles move with an arbitrary constant velocity (up to the speed limit imposed by Einstein, of course!).

The big difference is that the background value of the Higgs field is Lorentz-invariant — it doesn't define any absolute standard of rest.

Thursday 19 April 2012


I don't seem to be finding the time to write proper blog posts, so here is a dot-point rundown of a few things I have found interesting lately:

  • Bobby Acharya, Gordon Kane, and Piyush Kumar released a preprint last week in which they discuss 'generic' predictions of string theory for low energy physics. It is well worth a look, and represents a good review of some of the progress of the last ten years, but the word 'generic' concerns me quite a bit in this context; I don't even know a way to define a 'generic' member of a discrete set (of purported string vacua, for example). To be fair, the paper contains a number of caveats pointing out the various assumptions being made.

  • IceCube is a wonderful experiment, which uses the Antarctic ice sheet as a giant neutrino detector. The collaboration has just published a paper in which they report a null result in the search for neutrinos from almost 200 gamma ray bursts, allowing them to set a limit for neutrino production about four times below predictions. In particular, this basically rules out gamma ray bursts as the dominant source of very high energy cosmic rays. For a press-release-level overview, see here; the BBC has also covered the story.

Friday 6 April 2012

LHC back online for 2012

Yesterday, CERN announced that the proton-proton collisions are again underway at the LHC, for the first time since last year. One quantitative change is that the machine is now accelerating each beam to $4$ TeV per proton, compared to $3.5$ TeV in 2011. (For those who might not know, $1$ TeV is equivalent, by Einstein's famous relation $E = mc^2$, to approximately one thousand times the mass of a proton.)

This year could be a very significant one for particle physics. If the Higgs boson really is sitting at $\sim125$ GeV, then its discovery is likely to be announced, and if low-energy supersymmetry is part of the real world, then we might hope to see at least the first evidence of it.