Recent content by R.X.

.. because this loose set of different setups with shaky rules can't even be called mathematics...

No, K-theory plays a very small role, and even that is over-emphasized. Roughly K-theory is cohomology plus torsion, and since torsion is of minor importance in most practicial string computations, so is the difference between K-theory and cohomology. The K-theory story keeps flaoting around...

We had this discussed here before: there are simply no constituent "points" on a string. Namely how could one possibly ever measure or see those? One would need to do a scattering experiment and bounce something off that string. But all what one can do is to take another string and use it "as a...

Let's assume were are in a semi-classical regime, where quantum corrections are weak so that one has a smooth geometrical description; ie, a nice low energy effective lagrangian that involves classical gauge and Higgs fields, say. Then solitons correspond to solutions of the classical equations...

OK here an answer, upon request: D-branes are special cases of extended objects in string theory, ie higher dimensional p-branes which can be viewed as solitons (ie, non-perturbative configurations). D-branes are special in that they can be formulated in a "dual" way where a perturbative...

The "standard" heterotic string is not a direct product of a (left-moving) bosonic string with a (right-moving) superstring, but it is a "correlated" product. That's why the bosonic string tachyon does not need to appear, and in fact it cannot appear if the theory has space-time supersymmetry...

As if there wouldn't have been an answer to this old problem since a couple of years. Hawking himself conceded his bet lost, and now agrees with the string people that information is preserved. The point is that the Hawking radiation is not really thermal, but there are subtle correlations...

Hm.. I am not able to get hold a copy of that one... it appears not to have been submitted to arXiv, which is suspicious.. But at any rate, there is definitely no problem that QCD would be inconsistent due to local (gauge) anomalies. The whole particle physicist's world would be in turmoil...

What's wrong with this neat computational trick? It is simply a clever way to deal with gauge fixing. No one ever has claimed that FP ghosts would be more than ficticious degrees of freedom and be at the same level es eg electrons. The rules of QFT work so well so that one can call it the most...

Anomaly matching refers to chiral anomalies. But yours is a tricky question, because it has been suggested (from what I gather from Thiemann's and other's papers), that anomalies simply do not exist in LQG, due to the kind of quantization procedure applied there. One can only wonder how a...

Only too true.. that's why the Rishon model of Harari took a sudden nose dive, namely when it was realized by his student Nati Seiberg that the anomalies do not match. It simply disappered since then. This is what I thought til today. However, in the paper 0503213 mentioned above it made a...

Why on Earth should the holonomy group (of a manifold) coincide with the SM gauge group? Morally it is the complement of the gauge group in a larger group, and the larger the holonomy group becomes (ie the more curved the manifold is), the less symmetries will be preserved and the smaller the...

Pretty good characterization. Indeed closed string field theory has turned out to be extremely complex (non-polynomial), and while open strings are much simpler, it nevertheless seems hard to make progress towards a useful background independent formulation, using traditional methods. Probably a...

I plainly I don't have idea whether it would be helpful or not, as that approach has its own severe problems (which may or may not be overcome in the future). There may also be other kinds of background independent formulations that no one yet has thought of... at any rate my belief is that a...

It does not - the present formulation of string theory, as you and others including string physicists know and say, is background dependent, and finding a background independent formulation, or what else the relevant notion may precisely be, is one of the most important issues. No one says the...