1,075 research outputs found
In quest of "just" the Standard Model on D-branes at a singularity
In this note we explore the possibility of obtaining gauge bosons and
fermionic spectrum as close as possible to the Standard Model content, by
placing D3-branes at a ZN orbifold-like singularity in the presence of
D7-branes. Indeed, we find that this is plausible provided a sufficiently high
N is allowed for and the singular point is also fixed by an orientifold action.
If extra charged matter is not permitted then the singularity should
necessarily be non-supersymmetric. Correct hypercharge assignments require a
dependence on some Abelian gauge D7-groups. In achieving such a construction we
follow a recent observation made in Ref. [hep-th/0105155] about the possibility
that, the three left handed quarks, would present different U(2) transformation
properties.Comment: 18 pages, 1 table, no figures, v2: typos correcte
Effective Superpotentials via Konishi Anomaly
We use Ward identities derived from the generalized Konishi anomaly in order
to compute effective superpotentials for SU(N), SO(N) and
supersymmetric gauge theories coupled to matter in various representations. In
particular we focus on cubic and quartic tree level superpotentials. With this
technique higher order corrections to the perturbative part of the effective
superpotential can be easily evaluated.Comment: 17 pages, harvma
Universal structure of subleading infrared poles at strong coupling
Recently a concise expression for the subleading infrared singularity of
dimensional-regularized gauge theories has been proposed. For conformal
theories, such relation involves a universal eikonal contribution plus a
non-eikonal contribution, related to the subleading term in the anomalous
dimension of twist two operators with large spin. In this note we make use of
the AdS/CFT correspondence in order to check such conjecture at strong coupling
for the case of N=4 SYM.Comment: 13 page
Correlation functions, null polygonal Wilson loops, and local operators
We consider the ratio of the correlation function of n+1 local operators over
the correlator of the first n of these operators in planar N=4 super-Yang-Mills
theory, and consider the limit where the first n operators become pairwise null
separated. By studying the problem in twistor space, we prove that this is
equivalent to the correlator of a n-cusp null polygonal Wilson loop with the
remaining operator in general position, normalized by the expectation value of
the Wilson loop itself, as recently conjectured by Alday, Buchbinder and
Tseytlin. Twistor methods also provide a BCFW-like recursion relation for such
correlators. Finally, we study the natural extension where n operators become
pairwise null separated with k operators in general position. As an example, we
perform an analysis of the resulting correlator for k=2 and discuss some of the
difficulties associated to fixing the correlator completely in the strong
coupling regime.Comment: 34 pages, 6 figures. v2: typos corrected and references added; v3:
published versio
Some analytic results for two-loop scattering amplitudes
We present analytic results for the finite diagrams contributing to the
two-loop eight-point MHV scattering amplitude of planar N=4 SYM. We use a
recently proposed representation for the integrand of the amplitude in terms of
(momentum) twistors and focus on a restricted kinematics in which the answer
depends only on two independent cross-ratios. The theory of motives can be used
to vastly simplify the results, which can be expressed as simple combinations
of classical polylogarithms.Comment: 18 page
Contrast coding choices in a decade of mixed models
Contrast coding in regression models, including mixed-effect models, changes what the terms in the model mean. In particular, it determines whether or not model terms should be interpreted as main effects. This paper highlights how opaque descriptions of contrast coding have affected the field of psycholinguistics. We begin with a reproducible example in R using simulated data to demonstrate how incorrect conclusions can be made from mixed models; this also serves as a primer on contrast coding for statistical novices. We then present an analysis of 3384 papers from the field of psycholinguistics that we coded based upon whether a clear description of contrast coding was present. This analysis demonstrates that the majority of the psycholinguistic literature does not transparently describe contrast coding choices, posing an important challenge to reproducibility and replicability in our field
BRST Invariance of Non-local Charges and Monodromy Matrix of Bosonic String on AdS(5)xS(5)
Using the generalized Hamiltonian method of Batalin, Fradkin and Vilkovsky we
develop the BRST formalism for the bosonic string on AdS(5)xS(5) formulated as
principal chiral model. Then we show that the monodromy matrix and non-local
charges are BRST invariant.Comment: 26. page
Large spin systematics in CFT
20 pages; v2: version published in JHEPUsing conformal field theory (CFT) arguments we derive an infinite number of constraints on the large spin expansion of the anomalous dimensions and structure constants of higher spin operators. These arguments rely only on analiticity, unitarity, crossing-symmetry and the structure of the conformal partial wave expansion. We obtain results for both, perturbative CFT to all order in the perturbation parameter, as well as non-perturbatively. For the case of conformal gauge theories this provides a proof of the reciprocity principle to all orders in perturbation theory and provides a new "reciprocity" principle for structure constants. We argue that these results extend also to non-conformal theories.Peer reviewe
Differential equations for multi-loop integrals and two-dimensional kinematics
In this paper we consider multi-loop integrals appearing in MHV scattering
amplitudes of planar N=4 SYM. Through particular differential operators which
reduce the loop order by one, we present explicit equations for the two-loop
eight-point finite diagrams which relate them to massive hexagons. After the
reduction to two-dimensional kinematics, we solve them using symbol technology.
The terms invisible to the symbols are found through boundary conditions coming
from double soft limits. These equations are valid at all-loop order for double
pentaladders and allow to solve iteratively loop integrals given lower-loop
information. Comments are made about multi-leg and multi-loop integrals which
can appear in this special kinematics. The main motivation of this
investigation is to get a deeper understanding of these tools in this
configuration, as well as for their application in general four-dimensional
kinematics and to less supersymmetric theories.Comment: 25 pages, 7 figure
On correlation functions of Wilson loops, local and non-local operators
We discuss and extend recent conjectures relating partial null limits of
correlation functions of local gauge invariant operators and the expectation
value of null polygonal Wilson loops and local gauge invariant operators. We
point out that a particular partial null limit provides a strategy for the
calculation of the anomalous dimension of short twist-two operators at weak and
strong coupling.Comment: 29 pages, 8 figure
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