## Archive for April, 2007

### Part III Demographics

28Apr07

In what I can only imagine was a moment of inspired procrastination, Steffen, my friend and fellow Part III student, did a demographic survey of this year’s Part III theoretical physicists (hep/gr). There’s some small wiggle room for error in the data, but the rough results are as follows: Total number of Part III theoretical […]

### Silly Symmetry Factors

24Apr07

A few months ago some of the Part III students were having a good time calculating the symmetry factors of silly Feynman diagrams. Perhaps there are others out there who would be amused by the game. References For those who don’t spend much time thinking about symmetry factors, section 9 of Mark Srednicki’s QFT book […]

### Orbifolding out of the 5D Chirality Problem

22Apr07

How to get left/right-handed 4D theories from an ambidexterous 5D theory… demote the 5th dimension from a manifold to an orbifold. In a previous post I introduced the 5D chirality problem. The problem was that there is no such thing as a 5D parity operator, and hence 5D spinors are Dirac spinors. In other words, […]

### On the Virginia Tech slayings

17Apr07

This post is not about physics; the post on orbifolding in extra dimensions has been delayed. This is also a post on a current event and possibly a sensitive/political subject. My intent is to discuss, hopefully without causing any offense. Topics in this post came from a conversation with a colleague in Los Angeles. The […]

### The 5D Chirality Problem

15Apr07

Message from the 5th dimension: “We’re ambidexterous up here. Why are you left/right-handed?” There are lots of neat little problems that pop up when you play with models of extra dimensions. One such problem that one might not have expected is how to write down a 4D chiral theory. For simiplicity let’s play with a […]

### Gravity Probe B: Geodetic effect within 1%

15Apr07

The NASA/Stanford University Gravity Probe B (GPB) team has made its first public announcement at the 2007 American Physical Society April Meeting, and they have announced that the geodetic effect predicted by general relativity has been confirmed to within 1%. Analysis on the `frame-dragging’ effect is ongoing, complete results are expected to be announced in […]

### When a `theory’ is not a theory

14Apr07

My good friend Adam is a postgrad at the Cambridge Institute of Astronomy. He’s active in science outreach and is good at identifying key points where the general public and practicing scientists often misunderstand one another. One particular point that has come up several times is the use of the word “theory” in high energy […]

### On a Tangent [Frame]

12Apr07

Spacetime is like a sweet sixteen party. Fermions are the teenagers who get to propagate and interact on this spacetime. Based on what little I know about sweet sixteen parties, they involve a teenager dancing around, then changing into a different dress, and then dancing around some more. The tangent space is like the dressing […]

### April Fooled at the LHC

02Apr07

The title of this post is a pun. Yesterday was marked by several of the usual April Fools jokes on the Internet. The best post I found was by Dr. Tommaso Dorigo, who played off of the actual news of a failed LHC high-pressure magnet test to `leak’ [false] news that the LHC would be […]