Wednesday, February 18, 2009

Dyonic Giant Magnons on CP^3

Kalousios et al. posted a paper (arXiv:0902.3179) today investigating a new dyonic magnon solution on CP^3. Fans of twistor theory will recall that CP^3 is actually projective twistor space. However, here the context is N=6 superconformal Chern-Simons theory with SU(N)xSU(N) symmetry, which in the large N,k limit is dual to type IIA string theory on AdS_4 x CP^3. The present paper generalizes Maldacena's giant magnon construction where it is a particular open string configuration on an R x S^2 subset of AdS_5 x S^5. This is done by noticing the equations of motion for a string on R x CP^3 are classically integrable, and supplementing them with the Virasoro constraints. Various solutions are given, such as a pointlike string moving along the equator of an S^2 in CP^3 and another on a CP^1 which is a rotation of the ordinary Hofman-Maldacena giant magnon.

Looking back at twistor string theory, Witten wanted to consider the open string B-model on CP^3, but was hindered by the fact that CP^3 is not a Calabi-Yau manifold, hence giving an anomalous R-symmetry. For this reason he considered supermanifolds of the form CP^{3|N}, which is Calabi-Yau if and only if N=4.

In the present case, type IIA string theory has no such restrictions, so it might be that Kalousios et al. have laid the foundation for a new twistor string theory on ordinary CP^3, where the perturbative expansion of the superconformal N=6 theory could be related to a D-instanton expansion of the dual string theory on AdS_4 x CP^3.

Friday, February 06, 2009

Wednesday, February 04, 2009

Blackfolds, Twistor Strings and Cosmic Strings

Today's (Wed. Feb 4th) new arxiv HEP papers included some noteworthy topics, such as black holes with novel horizon geometries, N=8 twistor supergravity and cosmic superstrings. The abstracts are as follows (feel free to comment):


We argue that the main feature behind novel properties of higher-dimensional black holes, compared to four-dimensional ones, is that their horizons can have two characteristic lengths of very different size. We develop a long-distance worldvolume effective theory that captures the black hole dynamics at scales much larger than the short scale. In this limit the black hole is regarded as a blackfold: a black brane (possibly boosted locally) whose worldvolume spans a curved submanifold of the spacetime. This approach reveals black objects with novel horizon geometries and topologies more complex than the black ring, but more generally it provides a new organizing framework for the dynamics of higher-dimensional black holes.

New Twistor String Theories Revisited

A gauged version of Berkovits twistor string theory featuring the particle content of N=8 supergravity was suggested by Abou-Zeid, Hull and Mason. The equations of motion for a particular multiplet in the modified theory are examined on the level of basic twistor fields and thereby shown to imply the vanishing of the negative helicity graviton on-shell. Additionally, the restrictions emerging from the equation of motion for the new gauge field \bar{B} reveal the chiral nature of interactions in theories constructed in this manner. Moreover, a particular amplitude in Berkovits open string theory is shown to be in agreement with the corresponding result in Einstein gravity.

Cosmic Strings and Cosmic Superstrings

In these lectures, I review the current status of cosmic strings and cosmic superstrings. I first discuss topological defects in the context of Grand Unified Theories, focusing in particular in cosmic strings arising as gauge theory solitons. I discuss the reconciliation between cosmic strings and cosmological inflation, I review cosmic string dynamics, cosmic string thermodynamics and cosmic string gravity, which leads to a number of interesting observational signatures. I then proceed with the notion of cosmic superstrings arising at the end of brane inflation, within the context of brane-world cosmological models inspired from string theory. I discuss the differences between cosmic superstrings and their solitonic analogues, I review our current understanding about the evolution of cosmic superstring networks, and I then briefly describe the variety of observational consequences, which may help us to get an insight into the stringy description of our Universe.