Category High Energy Physics

Series on Axions, Part 6: Experimental Searches for Axions

In my earlier posts, I mentioned several times that axions don’t interact very much with the particles in the standard model, with the exception of photons. Awesomely enough, not only can axions decay to photons, but photons can decay to axions as well! This is called the Primakoff Effect (and Inverse Primakoff Effect): when axions […]

Series on Axions, Part 5: Axions, Dark Matter, and Cosmic Strings

In cosmology, the roles that axions play are pretty complicated, but I’m going to try to do my best to explain them. 80% of the matter in the universe is made up of “dark matter”, and we don’t really have any idea what it is. A lot of cosmologists think that, along with dark energy, […]

Series on Axions, Part 4: The Peccei-Quinn Mechanism

In 1977, two physicists named Roberto Peccei and Helen Quinn came along and proposed something radical: let’s add an additional U(1) symmetry to the standard model. This wouldn’t just be any symmetry, they said – it’ll be a global symmetry that we will force to be spontaneously broken, resulting in a new gauge boson that […]

2013 Nobel Prize in Physics: Lectures

Today, the Nobel Lectures were streamed live: Englert: The BEH mechanism and its scalar boson Higgs: Evading the Goldstone theorem You can find the video here: http://www.youtube.com/watch?v=6cEbfP1IDMU

Series on Axions, Part 3: The Strong CP Problem

Clearly, this U(1)a problem that Weinberg discovered needed to be solved, and so Gerard ‘t Hooft, a brilliant Dutch physicist, looked into it, and found the solution. There was no U(1)a problem, he said, because the vacuum of QCD is so complicated that there is no true U(1) a symmetry, even though the QCD Lagrangian […]

Series on Axions, Part 2: Weinberg and the U(1) Problem

Now we are back in 1975. Steven Weinberg, one of the greatest physicists of all time, realizes there is a big problem in the standard model, and he calls this problem “The U(1) Problem”. When you look at the equation that describes the way quantum chromodynamics acts – its Lagrangian – you find this global […]

Series on Axions, Part 1: Preliminaries

Our story begins in 1975, before axions were proposed. There was this big problem in Quantum Chromodynamics (QCD), which Weinberg named “The U(1) Problem”…before I describe it, let’s back up a little bit and decipher what all of this means, and we’ll get to it in the next post. To put it really simply, the […]