ar X iv : h ep - t h / 07 01 18 2 v 1 1 9 Ja n 20 07 Twistorial and space - time descriptions of D = 4 string models ∗

ar X iv : h ep - t h / 05 01 14 3 v 1 1 9 Ja n 20 05 CCNY - HEP - 05 / 1 January 2005 A Note on MHV Amplitudes for Gravitons

We show how the maximally helicity violating (MHV) scattering amplitudes for gravitons can be related to current correlators and vertex operators in twistor space. This is similar to what happens in Yang-Mills theory and raises the possibility of a direct twistor-string-like construction for N = 8 supergravity.

ar X iv : h ep - t h / 04 01 06 4 v 2 1 4 M ar 2 00 4 BITWISTOR FORMULATION OF SPINNING PARTICLE 1

Twistorial formulation of a particle of arbitrary spin has been constructed. Equations of twistor transformation are obtained for massive and massless spinning particles. Twistor space of the massive particle is formed by two twistors and two complex scalars. In the massive case, integral transformations relating twistor fields with usual space–time fields have been constructed.

ar X iv : h ep - t h / 96 12 20 0 v 2 9 J an 1 99 7 1 Perturbative gravitational couplings and Siegel modular forms in D = 4 , N = 2 string models

We consider four-parameter D = 4, N = 2 string models with Hodge numbers (4, 214 − 12n) and (4, 148), and we express their perturbative Wilsonian gravitational coupling F1 in terms of Siegel modular forms.

ar X iv : h ep - t h / 06 12 12 9 v 3 1 1 Ja n 20 07 STRING COSMOLOGY

ar X iv : h ep - t h / 02 01 03 3 v 2 1 4 Ja n 20 02 String with noncommutative world - sheet and stringy instantons

The model of the bosonic string with the noncommutative world-sheet geometry is proposed in the framework of Fedosov's deformation quantization. The re-interpretation of the model in terms of bosonic string coupled to infinite multiplet of background fields is given and the link to the W-symmetry is discussed. For the case of d=4 Euclidean target space, the stringy counterparts of the Yang-Mill...