Following up on the recent work of Cachazo, He and Yuan \cite{arXiv:1503.04816 [hep-th]}, we derive the double soft graviton theorem in perturbative gravity. We show that the double soft theorem derived using CHY formula precisely matches with the perturbative computation involving Feynman diagrams. In particular, we find how certain delicate limits of Feynman diagrams play an important role in obtaining this equivalence.
In this letter, we show a nilpotent matrix representation of the exterior derivative operator in noncommutative geometry (NCG), by translating the noncommutative relations of the algebraic formalization into the original one. As a result, we can construct the extended gauge theory without complicated algebraic rules nor excessively large differential algebra and non-monomorphic representation.
This is the first of a series of two papers where decoupling of unphysical states in the minimal pure spinor formalism is investigated. The multi-loop amplitude prescription for the minimal pure spinor superstring formulated in hep-th/0406055 involves the insertion of picture changing operators in the path integral. These operators are BRST closed in a distributional sense and depend on a number of constant tensors. One can trace the origin of these insertions to gauge fixing, so the amplitudes are formally independent of the constant tensors. We show however by explicit tree-level and one-loop computations that the picture changing operators are not BRST closed inside correlators and the amplitudes do depend on these constant tensors. This is due to the fact that the gauge fixing condition implicit in the existing minimal amplitude prescription is singular and this can lead to Lorentz violation and non-decoupling of BRST exact states. As discussed in hep-th/0406055, a manifestly Lorentz invariant prescription can be obtained by integrating over the constant tensors and in the sequel to this paper, it is shown that when one includes these integrations unphysical states do decouple to all orders despite the fact that the PCO's are not BRST closed inside correlators.
We study baryons of arbitrary isospin in a stringy holographic QCD model. In this D4-D8 holographic setting, the flavor symmetry is promoted to a gauge symmetry in the bulk, and produces, as KK modes of the gauge field, pions and spin one mesons of low energy QCD. Baryons of arbitrary isospins are represented as instanton solitons with isospin and spin quantum numbers locked, in a manner similar to the Skyrmion model. The soliton picture leads to a natural effective field theory of arbitrary baryons interacting with mesons. Couplings of baryons to axial mesons, including pions, are dominated in the large $N_c$ limit by a direct coupling to the flavor field strength in five dimensions. We delineate the relevant couplings and determine their strengths. This work generalizes part of hep-th/0701276 and arXiv:0705.2632 [hep-th] to all excited baryons. Due to technical difficulties in introducing relativistic higher spin fields, we perform all computations in the nonrelativistic regime, which suffices for the leading $N_c$ predictions.
We will present a new extension of the standard model of particle physics in its almost-commutative formulation. This extension has as its basis the algebra of the standard model with four summands (Iochum et al 2004 J. Math. Phys. 45 5003 (Preprint hep-th/0312276), Jureit J-H and Stephan C 2005 J. Math. Phys. 46 043512 (Preprint hep-th/0501134), Schucker T 2005 Krajewski diagrams and spin lifts Preprint hep-th/0501181, Jureit et al 2005 J. Math. Phys. 46 072303 (Preprint hep-th/0503190), Jureit J-H and Stephan C 2006 On a classification of irreducible almost commutative geometries: IV (Preprint hep-th/0610040)), and enlarges only the particle content by an arbitrary number of generations of left–right symmetric doublets which couple vectorially to the U(1)Y × SU(2)w subgroup of the standard model. As in the model presented in Stephan (2007 Almost-commutative geometries beyond the standard model: II. New Colours Preprint hep-th/0706.0595), which introduced particles with a new colour, grand unification is no longer required by the spectral action. The new model may also possess a candidate for dark matter in the hundred TeV mass range with neutrino-like cross section.
Abstract The hierarchy of conformally invariant kth powers of the Laplacian acting on a scalar field with scaling dimensions Δ ( k ) = k − d / 2 , k = 1 , 2 , 3 , as obtained in the recent work [R. Manvelyan, D.H. Tchrakian, Phys. Lett. B 644 (2007) 370, hep-th/0611077 ] is rederived using the Fefferman–Graham ( d + 2 ) -dimensional ambient space approach. The corresponding mysterious “holographic” structure of these operators is clarified. We explore also the ( d + 2 ) -dimensional ambient space origin of the Ricci gauging procedure proposed by A. Iorio, L. O'Raifeartaigh, I. Sachs and C. Wiesendanger as another method of constructing the Weyl invariant Lagrangians. The corresponding gauged ambient metric, Fefferman–Graham expansion and extended Penrose–Brown–Henneaux transformations are proposed and analyzed.
Abstract We modify a recently proposed heterotic model hep-th/0703210 , giving three net-generations of Standard Model fermions, to get rid of an additional U ( 1 ) factor in the gauge group. The method employs a stable SU ( 5 ) bundle on a Calabi–Yau threefold admitting a free involution. The bundle has to be built as a deformation of the direct sum of a stable SU ( 4 ) bundle and the trivial line bundle.
This proceeding is based on hep‐th/0605225 and it shows that the most general anomaly related effective action contains Stückelberg, axionic and Chern‐Simons‐like couplings. Such couplings are generically non‐trivial in orientifold string vacua. A similar analysis in quantum field theories provides similar couplings. These Chern‐Simons couplings generate new signals which might be visible at LHC.