scholarly journals All tree-level MHV form factors in N $$ \mathcal{N} $$ = 4 SYM from twistor space

2016 ◽  
Vol 2016 (6) ◽  
Author(s):  
Laura Koster ◽  
Vladimir Mitev ◽  
Matthias Staudacher ◽  
Matthias Wilhelm
Keyword(s):  
Twistor Space ◽  
Form Factors ◽  
Tree Level

scholarly journals The connected prescription for form factors in twistor space

2016 ◽  
Vol 2016 (11) ◽  
Author(s):  
A. Brandhuber ◽  
E. Hughes ◽  
R. Panerai ◽  
B. Spence ◽  
G. Travaglini
Keyword(s):  
Twistor Space ◽  
Form Factors

scholarly journals On the zero-crossing of the three-gluon Green’s function from lattice simulations

2018 ◽  
Vol 175 ◽  
pp. 12012 ◽  
Author(s):  
Andreas Athenodorou ◽  
Philippe Boucaud ◽  
Feliciano de Soto ◽  
José Rodríguez-Quintero ◽  
Savvas Zafeiropoulos
Keyword(s):  
Green’S Function ◽  
Green's Function ◽  
Large Volume ◽  
Form Factors ◽  
Tree Level ◽  
Zero Crossing ◽  
Zero Momentum ◽  
Made In

We report on some efforts recently made in order to gain a better understanding of some IR properties of the 3-point gluon Green’s function by exploiting results from large-volume quenched lattice simulations. These lattice results have been obtained by using both tree-level Symanzik and the standard Wilson action, in the aim of assessing the possible impact of effects presumably resulting from a particular choice for the discretization of the action. The main resulting feature is the existence of a negative log-aritmic divergence at zero-momentum, which pulls the 3-gluon form factors down at low momenta and, consequently, yields a zero-crossing at a given deep IR momentum. The results can be correctly explained by analyzing the relevant Dyson-Schwinger equations and appropriate truncation schemes.

scholarly journals On form factors and correlation functions in twistor space

2017 ◽  
Vol 2017 (3) ◽  
Author(s):  
Laura Koster ◽  
Vladimir Mitev ◽  
Matthias Staudacher ◽  
Matthias Wilhelm
Keyword(s):  
Correlation Functions ◽  
Twistor Space ◽  
Form Factors

Study of Λb → Λℓ+ℓ− (ℓ = e,μ,τ) decays in the G(221) model

2016 ◽  
Vol 31 (36) ◽  
pp. 1650197
Author(s):  
Shuai-Wei Wang
Keyword(s):  
Sum Rules ◽  
Branching Ratio ◽  
Form Factors ◽  
New Physics ◽  
Tree Level ◽  
Decay Channels ◽  
Flavor Changing ◽  
The Standard Model ◽  
Lepton Polarization ◽  
Text Model

We study respectively the baryonic semilepton decays [Formula: see text][Formula: see text] in the [Formula: see text] model, which includes the tree-level flavor-changing-neutral-currents (FCNCs) induced by [Formula: see text] and [Formula: see text] bosons and modifies the Wilson coefficients [Formula: see text] and [Formula: see text]. For the form factors, we use the results of QCD light-cone sum rules (LCSR) in the low [Formula: see text] region and lattice QCD in the high [Formula: see text] region, respectively. We consider the effects of this new physics (NP) model on some measured physical observables, like the differential branching ratio, the longitudinal polarization of the dilepton system, the lepton-side forward–backward asymmetry and the baryon-side forward–backward asymmetry, and find, obvious differences occur in some observables between the Standard Model (SM) and this NP model. Meanwhile, we also discuss the double lepton polarization asymmetries of these decay channels, and find, [Formula: see text], [Formula: see text] and [Formula: see text] of these decay channels are sensitive to the contribution of this NP model.

scholarly journals Gauge-invariant tree-level photoproduction amplitudes with form factors

1998 ◽  
Vol 58 (1) ◽  
pp. R40-R44 ◽  
Author(s):  
H. Haberzettl ◽  
C. Bennhold ◽  
T. Mart ◽  
T. Feuster
Keyword(s):  
Form Factors ◽  
Tree Level ◽  
Gauge Invariant

scholarly journals Ambidextrous light transforms for celestial amplitudes

2022 ◽  
Vol 2022 (1) ◽  
Author(s):  
Atul Sharma
Keyword(s):  
Fourier Transforms ◽  
Twistor Space ◽  
Tree Level ◽  
Positive Energy ◽  
Helicity State ◽  
Negative Helicity ◽  
Energy Constraints

Abstract Low multiplicity celestial amplitudes of gluons and gravitons tend to be distributional in the celestial coordinates z,$$ \overline{z} $$ z ¯ . We provide a new systematic remedy to this situation by studying celestial amplitudes in a basis of light transformed boost eigenstates. Motivated by a novel equivalence between light transforms and Witten’s half-Fourier transforms to twistor space, we light transform every positive helicity state in the coordinate z and every negative helicity state in $$ \overline{z} $$ z ¯ . With examples, we show that this “ambidextrous” prescription beautifully recasts two- and three-point celestial amplitudes in terms of standard conformally covariant structures. These are used to extract examples of celestial OPE for light transformed operators. We also study such amplitudes at higher multiplicity by constructing the Grassmannian representation of tree-level gluon celestial amplitudes as well as their light transforms. The formulae for n-point Nk−2MHV amplitudes take the form of Euler-type integrals over regions in Gr(k, n) cut out by positive energy constraints.

YANG-MILLS AMPLITUDES FROM STRING THEORY IN TWISTOR SPACE

2005 ◽  
Vol 20 (15) ◽  
pp. 3416-3419 ◽  
Author(s):  
MARCUS SPRADLIN
Keyword(s):  
Scattering Amplitudes ◽  
String Theory ◽  
Twistor Space ◽  
Mathematical Structure ◽  
Feynman Diagrams ◽  
Tree Level ◽  
Algebraic Equations ◽  
Yang Mills

Tree-level gluon scattering amplitudes in Yang-Mills theory frequently display simple mathematical structure which is completely obscure in the calculation of Feynman diagrams. We describe a novel way of calculating these amplitudes, motivated by a conjectured relation to twistor space, in which the problem of summing Feynman diagrams is replaced by the problem of solving a certain set of algebraic equations.

scholarly journals $$ \mathcal{N} $$ = 7 On-shell diagrams and supergravity amplitudes in momentum twistor space

2021 ◽  
Vol 2021 (1) ◽  
Author(s):  
Connor Armstrong ◽  
Joseph A. Farrow ◽  
Arthur E. Lipstein
Keyword(s):  
Scattering Amplitudes ◽  
Twistor Space ◽  
Tree Level ◽  
Yang Mills

Abstract We derive an on-shell diagram recursion for tree-level scattering amplitudes in $$ \mathcal{N} $$ N = 7 supergravity. The diagrams are evaluated in terms of Grassmannian integrals and momentum twistors, generalising previous results of Hodges in momentum twistor space to non-MHV amplitudes. In particular, we recast five and six-point NMHV amplitudes in terms of $$ \mathcal{N} $$ N = 7 R-invariants analogous to those of $$ \mathcal{N} $$ N = 4 super-Yang-Mills, which makes cancellation of spurious poles more transparent. Above 5-points, this requires defining momentum twistors with respect to different orderings of the external momenta.

scholarly journals Precision calculations of the double radiative bottom-meson decays in soft-collinear effective theory

2020 ◽  
Vol 2020 (12) ◽  
Author(s):  
Yue-Long Shen ◽  
Yu-Ming Wang ◽  
Yan-Bing Wei
Keyword(s):  
Equations Of Motion ◽  
Form Factors ◽  
Bottom Meson ◽  
Photon Radiation ◽  
Effective Theory ◽  
Tree Level ◽  
Meson Decay ◽  
Neutral Meson ◽  
Power Correction ◽  
Soft Collinear Effective Theory

Abstract Employing the systematic framework of soft-collinear effective theory (SCET) we perform an improved calculation of the leading-power contributions to the double radiative Bd,s-meson decay amplitudes in the heavy quark expansion by including the perturbative resummation of enhanced logarithms of mb/ΛQCD at the next-to-leading-logarithmic accuracy. We then construct the QCD factorization formulae for the subleading power contributions arising from the energetic photon radiation off the constituent light-flavour quark of the bottom meson at tree level. Furthermore, we explore the factorization properties of the subleading power correction from the effective SCET current "Image missing" at $$ \mathcal{O}\left({\alpha}_s^0\right) $$ O α s 0 by virtue of the operator identities due to the classical equations of motion. The higher-twist contributions to the Bd,s→ γγ helicity form factors from the two-particle and three-particle bottom-meson distribution amplitudes are evaluated with the perturbative factorization technique, up to the twist-six accuracy. In addition, the subleading power weak-annihilation contributions from both the current-current and QCD penguin operators are taken into account at the one-loop accuracy. We proceed to apply the operator-production-expansion-controlled dispersion relation for estimating the power-suppressed soft contributions to the double radiative Bd,s-meson decay form factors, which cannot be factorized into the light-cone distribution amplitudes of the heavy-meson and the resolved photon as well as the hard-scattering kernel calculable in perturbation theory canonically. Phenomenological explorations of the radiative Bd,s→ γγ decay observables in the presence of the neutral-meson mixing, including the CP-averaged branching fractions, the polarization fractions and the time-dependent CP asymmetries, are carried out subsequently with an emphasis on the numerical impacts of the newly computed ingredients together with the theory uncertainties from the shape parameters of the HQET bottom-meson distribution amplitudes.

TREE-LEVEL LONG-DISTANCE CONTRIBUTIONS TO K+→π+ ℓ+ℓ-

2014 ◽  
Vol 29 (01) ◽  
pp. 1450001 ◽  
Author(s):  
DAO-NENG GAO ◽  
YI-CONG YU
Keyword(s):  
Form Factor ◽  
Axial Vector ◽  
Form Factors ◽  
Tree Level ◽  
Additional Contribution ◽  
Long Distance ◽  
Tree Diagram ◽  
Level Transition ◽  
Pseudoscalar Form Factor

We study a new contribution, which is a tree-level transition from long-distance dynamics, to K+→π+ℓ+ℓ- (ℓ = e, μ) decays. It is found that this tree-diagram can be calculated unambiguously and would generate the additional contribution to the vector, axial-vector, scalar and pseudoscalar form factor of the decay. Our analysis shows that these form factors are strongly suppressed and this long-distance contribution is well under control.

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