601 research outputs found
Rational Conformal Field Theories With G_2 Holonomy
We study conformal field theories for strings propagating on compact,
seven-dimensional manifolds with G_2 holonomy. In particular, we describe the
construction of rational examples of such models. We argue that analogues of
Gepner models are to be constructed based not on N=1 minimal models, but on Z_2
orbifolds of N=2 models. In Z_2 orbifolds of Gepner models times a circle, it
turns out that unless all levels are even, there are no new Ramond ground
states from twisted sectors. In examples such as the quintic Calabi-Yau, this
reflects the fact that the classical geometric orbifold singularity can not be
resolved without violating G_2 holonomy. We also comment on supersymmetric
boundary states in such theories, which correspond to D-branes wrapping
supersymmetric cycles in the geometry.Comment: 20 pages, harvmac(b); v2: ref. adde
MHV Vertices And Tree Amplitudes In Gauge Theory
As an alternative to the usual Feynman graphs, tree amplitudes in Yang-Mills
theory can be constructed from tree graphs in which the vertices are tree level
MHV scattering amplitudes, continued off shell in a particular fashion. The
formalism leads to new and relatively simple formulas for many amplitudes, and
can be heuristically derived from twistor space.Comment: 27 p
The Googly Amplitudes in Gauge Theory
The googly amplitudes in gauge theory are computed by using the off shell MHV
vertices with the newly proposed rules of Cachazo, Svrcek and Witten. The
result is in agreement with the previously well-known results. In particular we
also obtain a simple result for the all negative but one positive helicity
amplitude when one of the external line is off shell.Comment: Latex file, 16 pages, 7 figures. Figures may bot display correctly in
ps file. Pls use pdf file instea
Cubic Twistorial String Field Theory
Witten has recently proposed a string theory in twistor space whose
D-instanton contributions are conjectured to compute N=4 super-Yang-Mills
scattering amplitudes. An alternative string theory in twistor space was then
proposed whose open string tree amplitudes reproduce the D-instanton
computations of maximal degree in Witten's model.
In this paper, a cubic open string field theory action is constructed for
this alternative string in twistor space, and is shown to be invariant under
parity transformations which exchange MHV and googly amplitudes. Since the
string field theory action is gauge-invariant and reproduces the correct cubic
super-Yang-Mills interactions, it provides strong support for the conjecture
that the string theory correctly computes N-point super-Yang-Mills tree
amplitudes.Comment: 19+1 pages, 4+1 EPS figures, JHEP3 LaTeX; v2: minor corrections,
references added; v3: the final version published in JHEP with a new footnote
on the d=0 on-shell contributio
Strong-coupling expansion of cusp anomaly and gluon amplitudes from quantum open strings in AdS_5 x S^5
An important ``observable'' of planar N=4 SYM theory is the scaling function
f(lambda) that appears in the anomalous dimension of large spin twist 2
operators and also in the cusp anomaly of light-like Wilson loops. The
non-trivial relation between the anomalous dimension and the Wilson
interpretations of f(lambda) is well-understood on the perturbative gauge
theory side of the AdS/CFT duality. In the first part of this paper we present
the dual string-theory counterpart of this relation, to all orders in
lambda^(-1/2) expansion. As a check, we explicitly compute the leading 1-loop
string sigma model correction to the cusp Wilson loop, reproducing the same
subleading coefficient in f(lambda) as found earlier in the spinning closed
string case. The same function f(lambda) appears also in the resummed form of
the 4-gluon amplitude as discussed at weak coupling by Bern, Dixon and Smirnov
and recently found at the leading order at strong coupling by Alday and
Maldacena (AM). Here we attempt to extend this approach to subleading order in
lambda^(-1/2) by computing the IR singular part of 1-loop string correction to
the corresponding T-dual Wilson loop. We discuss explicitly the 1-cusp case and
comment on apparent problems with the dimensional regularization proposal of AM
when directly applied order by order in strong coupling (inverse string
tension) expansion.Comment: 35 pages. v2: minor corrections, references adde
A Grassmannian Etude in NMHV Minors
Arkani-Hamed, Cachazo, Cheung and Kaplan have proposed a Grassmannian
formulation for the S-matrix of N=4 Yang-Mills as an integral over link
variables. In parallel work, the connected prescription for computing tree
amplitudes in Witten's twistor string theory has also been written in terms of
link variables. In this paper we extend the six- and seven-point results of
arXiv:0909.0229 and arXiv:0909.0499 by providing a simple analytic proof of the
equivalence between the two formulas for all tree-level NMHV superamplitudes.
Also we note that a simple deformation of the connected prescription integrand
gives directly the ACCK Grassmannian integrand in the limit when the
deformation parameters equal zero.Comment: 17 page
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