String creation and destruction

atyy

Can strings be created and destroyed (like particles)?

tom.stoer

You mean the whole string, not the vibration?

The string worldsheet would look like a 2-sphere; I have never seen something like that, but it's a good idea.

In a path integral in QFT this would be something like a disconnected Greens function which can be eliminated.

atyy

Yes.

Ben Niehoff

Yes. Whole strings are created and destroyed in string field theory.

tom.stoer

How do these "disconnected vacuum bubbles contribute"?

Ben Niehoff

Eh? I don't know much about string field theory, but I think vacuum bubble diagrams do not contribute.

But when you include interaction vertices, strings can join and split.

atyy

What's up with string field theory these days? It seems to have been quite popular about 5 pr 6 years ago, but at least casual browsing of arxiv doesn't seem to turn up much recent. Any good reviews you know of?

atyy

http://arxiv.org/abs/hep-th/0605202
String Field Theory
Washington Taylor (MIT, Stanford)
(Submitted on 19 May 2006 (v1), last revised 28 Jun 2006 (this version, v2))
This elementary introduction to string field theory highlights the features and the limitations of this approach to quantum gravity as it is currently understood. String field theory is a formulation of string theory as a field theory in space-time with an infinite number of massive fields. Although existing constructions of string field theory require expanding around a fixed choice of space-time background, the theory is in principle background-independent, in the sense that different backgrounds can be realized as different field configurations in the theory. String field theory is the only string formalism developed so far which, in principle, has the potential to systematically address questions involving multiple asymptotically distinct string backgrounds. Thus, although it is not yet well defined as a quantum theory, string field theory may eventually be helpful for understanding questions related to cosmology in string theory.

http://arxiv.org/abs/0901.3386
Regularizing Cubic Open Neveu-Schwarz String Field Theory
Nathan Berkovits, Warren Siegel
(Submitted on 22 Jan 2009 (v1), last revised 27 May 2009 (this version, v2))
After introducing non-minimal variables, the midpoint insertion of Y\bar Y in cubic open Neveu-Schwarz string field theory can be replaced with an operator N_\rho depending on a constant parameter \rho. As in cubic open superstring field theory using the pure spinor formalism, the operator N_\rho is invertible and is equal to 1 up to a BRST-trivial quantity. So unlike the linearized equation of motion Y\bar Y QV=0 which requires truncation of the Hilbert space in order to imply QV=0, the linearized equation N_\rho QV=0 directly implies QV=0.