With a Title Unknown

I have a spare hour! This doesn't happen much these days unless I'm stuck somewhere dusty and highly populated. The evenings are currently filled with saying goodbye to old friends, saying goodbye to new friends and meeting a whole slew of new and interesting folk from all over the place. The days are steady and full at work too with this GUT project hopefully about to start properly. I'm slowly working my way through past results and asymptotically creeping towards the expected answers.

Today we had a very interesting lecture. This one should be in double italics as there are bits that I'm still to get my head around. So skip this if you're not versed in string theory.

The lecture was on the subject of D-branes, what they really mean and how we can generalise the formalism we have at the moment. The point being that through the many duality relations a descriptions of a fundamental string and a D-brane are in many ways equivalent. If we understand one, we can understand the other and D-branes are just as good a place to start as any.

The lecture was based on this paper which is semi-readable from my point of view having just relearned some of the topology that sinks into the abyss so quickly as I never actually get to use it.

The essence of the talk was that we have a description of D-branes in terms of a boundary conformal field theory, the open string description where the various dimensions in which the string ends live are given Dirichlet or Neumann boundary conditions. This description can be given in terms of the connection two form F living on the brane. However, what Dr Zheng wanted to point out was that the possible boundary conditions we have coming from this description are overly constrained and there should be many other classes of solution not given by this particular description. D-branes have several topological constraints, one of which is given by the cohomology class of the pullback of the flux, H, on the brane.

There's a second seemingly equivalent description of the geometry of the branes in terms of a certain orthogonal group (related to the pullback of the (1,1) forms onto the manifold), the significance of which I'm not clear on yet.
The important point is however that using this description instead of the usual one there is more freedom with which to define the brane, and branes embedded in sub manifolds of higher dimension branes are easily described in this formalism.

Conclusion: Using a mathematically different description of D-branes working from the boundary conditions up we can find new objects which are well defined in string theory and are not subject to the normal flux constraints of your average D-brane. OK, I stop because that's past the end of my understanding on this subject. In fact I don't know how rigorous any of this is, not having a good enough feel for things like De Rham Cohomologies. Fun nonetheless and nice to sit through a lecture where at least I understood all the words.

So, OK, no more physics/D-brane philosophy in this post.

Gastronomically speaking today I've overcome my food nemesis which has sat with me for the last decade. The only thing (as far as I remember) which I have failed to eat on squeemishness grounds was a conch. It arrived on my plate somewhere in the depths of a drizzly Normandy evening, cold, slimy and tasteless and I felt like Charlie Chaplin attempting to eat the rubber of his boots. However, the shoe was on the other foot today and I enjoyed a fine meal of spicy, well heated, thinly sliced conch which was a treat to behold.

On the literary front, there are many books still to talk about but for now I'll return to a favourite which I had the pleasure of reading whilst on holiday. 'To a God Unknown' was again an early Steinbeck but one which he slaved over for many years and is far more finely polished and honed than Tortilla flat, written at a similar time. The book chopped and changed so much (including the title shifting emphasis from 'To an unknown God' to 'To a God Unknown') that some of the original characters ended up in his book of short stories 'The Pastures of Heaven' - also a great read. 'To a God Unknown' is about a man who leaves his ancestral home to set up anew on fresh land with a renewed energy and enthusiasm. He picks his spot under a tree which he believes looks over the land as a God over his people and all safety and advice are drawn from the tree. The rest of the family come to settle on the land and in the course of time as in all Steinbeck's stories there are births, marriages and deaths and parties, each somehow seeded with a bitter pill which may or may not come to light through the book. The warmth from the tree turns to an unhealthy worship, frowned upon by many and it's no surprise that at a turning point in the book, things turn bad, the dry years arrive and the melancholy of his writing shows through just as powerfully as it did in his more mature work. I shan't give away the end, though generally the plot itself isn't the most important point about his books, the relationships and character traits are what give the relatively simple stories such depth. Another fine and satisfying read.

OK, I didn't quite have an hour and now time is almost up. I must make my ablution before heading out to a friend's leaving do.