324 research outputs found
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
"Short" spinning strings and structure of quantum AdS_5 x S^5 spectrum
Using information from the marginality conditions of vertex operators for the
AdS_5 x S^5 superstring, we determine the structure of the dependence of the
energy of quantum string states on their conserved charges and the string
tension proportional to lambda^(1/2). We consider states on the leading Regge
trajectory in the flat space limit which carry one or two (equal) spins in
AdS_5 or S^5 and an orbital momentum in S^5, with Konishi multiplet states
being particular cases. We argue that the coefficients in the energy may be
found by using a semiclassical expansion. By analyzing the examples of folded
spinning strings in AdS_5 and S^5 as well as three cases of circular two-spin
strings we demonstrate the universality of transcendental (zeta-function) parts
of few leading coefficients. We also show the consistency with target space
supersymmetry with different states belonging to the same multiplet having the
same non-trivial part of the energy. We suggest, in particular, that a rational
coefficient (found by Basso for the folded string using Bethe Ansatz
considerations and which, in general, is yet to be determined by a direct
two-loop string calculation) should, in fact, be universal.Comment: 42p, Latex v2: Comments and summary table of coefficients added v3:
misprints corrected; dependence on winding number added in appendix
A Note on Twistor Gravity Amplitudes
In a recent paper, Witten proposed a surprising connection between
perturbative gauge theory and a certain topological model in twistor space. In
particular, he showed that gluon amplitudes are localized on holomorphic
curves. In this note we present some preliminary considerations on the
possibility of having a similar localization for gravity amplitudes.Comment: 14 pages, 6 figures. v2: minor changes, added referenc
One-Loop Maximal Helicity Violating Amplitudes in N=4 Super Yang-Mills Theories
One-loop maximal helicity violating (MHV) amplitudes in N=4 super Yang-Mills
(SYM) theories are analyzed, using the prescription of Cachazo, Svrcek, and
Witten (CSW). The relations between leading N_c amplitudes A_{n;1} and
sub-leading amplitudes A_{n;c} obtained by the CSW prescription are found to be
identical to those obtained from conventional field theory calculations.
Combining with existing results, this establishes the validity of the CSW
prescription to one-loop in the calculation of MHV amplitudes in N=4 SYM
theories of finite N_c.Comment: Minor changes and typos fixed. Published version in JHE
Magnon Bound-state Scattering in Gauge and String Theory
It has been shown that, in the infinite length limit, the magnons of the
gauge theory spin chain can form bound states carrying one finite and one
strictly infinite R-charge. These bound states have been argued to be
associated to simple poles of the multi-particle scattering matrix and to world
sheet solitons carrying the same charges. Classically, they can be mapped to
the solitons of the complex sine-Gordon theory.
Under relatively general assumptions we derive the condition that simple
poles of the two-particle scattering matrix correspond to physical bound states
and construct higher bound states ``one magnon at a time''. We construct the
scattering matrix of the bound states of the BDS and the AFS S-matrices. The
bound state S-matrix exhibits simple and double poles and thus its analytic
structure is much richer than that of the elementary magnon S-matrix. We also
discuss the bound states appearing in larger sectors and their S-matrices. The
large 't Hooft coupling limit of the scattering phase of the bound states in
the SU(2) sector is found to agree with the semiclassical scattering of world
sheet solitons. Intriguingly, the contribution of the dressing phase has an
independent world sheet interpretation as the soliton-antisoliton scattering
phase shift. The small momentum limit provides independent tests of these
identifications.Comment: 25 pages, Latex V2: clarifying comments added to footnote 1 and
footnote 10; references added V3: typos correcte
Beauty and the Twist: The Bethe Ansatz for Twisted N=4 SYM
It was recently shown that the string theory duals of certain deformations of
the N=4 gauge theory can be obtained by a combination of T-duality
transformations and coordinate shifts. Here we work out the corresponding
procedure of twisting the dual integrable spin chain and its Bethe ansatz. We
derive the Bethe equations for the complete twisted N=4 gauge theory at one and
higher loops. These have a natural generalization which we identify as twists
involving the Cartan generators of the conformal algebra. The underlying model
appears to be a form of noncommutative deformation of N=4 SYM.Comment: 28 pages, v2: reference flip corrected, v3: some typos in
(4.10,4.20,5.5) correcte
Quantum AdS_5 x S^5 superstring in the AdS light-cone gauge
We consider the AdS_5 x S^5 superstring in the light-cone gauge adapted to a
massless geodesic in AdS5 in the Poincare patch. The resulting action has a
relatively simple structure which makes it a natural starting point for various
perturbative quantum computations. We illustrate the utility of this AdS
light-cone gauge action by computing the 1-loop and 2-loop corrections to the
null cusp anomalous dimension reproducing in a much simpler and efficient way
earlier results obtained in conformal gauge. This leads to a further insight
into the structure of the superstring partition function in non-trivial
background.Comment: 21pages, Late
Topological B-Model on Weighted Projective Spaces and Self-Dual Models in Four Dimensions
It was recently shown by Witten on the basis of several examples that the
topological B-model whose target space is a Calabi-Yau (CY) supermanifold is
equivalent to holomorphic Chern-Simons (hCS) theory on the same supermanifold.
Moreover, for the supertwistor space CP^{3|4} as target space, it has been
demonstrated that hCS theory on CP^{3|4} is equivalent to self-dual N=4 super
Yang-Mills (SYM) theory in four dimensions. We consider as target spaces for
the B-model the weighted projective spaces WCP^{3|2}(1,1,1,1|p,q) with two
fermionic coordinates of weight p and q, respectively - which are CY
supermanifolds for p+q=4 - and discuss hCS theory on them. By using twistor
techniques, we obtain certain field theories in four dimensions which are
equivalent to hCS theory. These theories turn out to be self-dual truncations
of N=4 SYM theory or of its twisted (topological) version.Comment: 12 pages; v2: minor clarification, 3 references added, published
versio
A New Type of Stereoselectivity in Baeyer–Villiger Reactions: Access to E- and Z-Olefins
A new concept for accessing configurationally defined trisubstituted olefins has been developed. Starting from a common ketone precursor of the type 4-ethylidenecyclohexanone, Baeyer–Villiger monooxygenases are employed as catalysts in diastereoselective Baeyer–Villiger reactions leading to the corresponding E- or Z-configurated lactones. Wild-type cyclohexanone monooxygenase (CHMO) as catalyst delivers the E-isomers and a directed evolution mutant the opposite Z-isomers. Subsequent transition metal-catalyzed chemical transformations of a key product containing a vinyl bromide moiety provide a variety of different trisubstituted E- or Z-olefins. A model based on QM/MM sheds light on the origin of this unusual type of diastereoselectivity. In contrast to this biocatalytic approach, traditional Baeyer–Villiger reagents such as m-CPBA fail to show any selectivity, 1:1 mixtures of E- and Z-olefins being formed
Generalized scaling function from light-cone gauge AdS_5 x S^5 superstring
We revisit the computation of the 2-loop correction to the energy of a folded
spinning string in AdS_5 with an angular momentum J in S^5 in the scaling limit
log S, J >>1 with J / log S fixed. This correction gives the third term in the
strong-coupling expansion of the generalized scaling function. The computation,
using the AdS light-cone gauge approach developed in our previous paper, is
done by expanding the AdS_5 x S^5 superstring partition function near the
generalized null cusp world surface associated to the spinning string solution.
The result corrects and extends the previous conformal gauge result of
arXiv:0712.2479 and is found to be in complete agreement with the corresponding
terms in the generalized scaling function as obtained from the asymptotic Bethe
ansatz in arXiv:0805.4615 (and also partially from the quantum O(6) model and
the Bethe ansatz data in arXiv:0809.4952). This provides a highly nontrivial
strong coupling comparison of the Bethe ansatz proposal with the quantum AdS_5
x S^5 superstring theory, which goes beyond the leading semiclassical term
effectively controlled by the underlying algebraic curve. The 2-loop
computation we perform involves all the structures in the AdS light-cone gauge
superstring action of hep-th/0009171 and thus tests its ultraviolet finiteness
and, through the agreement with the Bethe ansatz, its quantum integrability. We
do most of the computations for a generalized spinning string solution or the
corresponding null cusp surface that involves both the orbital momentum and the
winding in a large circle of S^5.Comment: 50 pages, late
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