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

TREE DIAGRAMS IN WITTEN’S SUPERSTRING FIELD THEORY

1989 ◽  
Vol 04 (21) ◽  
pp. 2063-2071
Author(s):  
GEORGE SIOPSIS
Keyword(s):  
Field Theory ◽  
Scattering Amplitudes ◽  
Invariant Theory ◽  
Higher Order ◽  
Contact Term ◽  
Tree Level ◽  
Gauge Invariant

It is shown that the contact term discovered by Wendt is sufficient to ensure finiteness of all tree-level scattering amplitudes in Witten’s field theory of open superstrings. Its inclusion in the action also leads to a gauge-invariant theory. Thus, no additional higher-order counterterms in the action are needed.

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 PROBING THE FROISSART BOUND FOR MODELS WITH CHARGED VECTOR FIELDS IN D=3

1994 ◽  
Vol 09 (18) ◽  
pp. 1695-1700 ◽  
Author(s):  
O.M. DEL CIMA
Keyword(s):  
Asymptotic Behavior ◽  
Scattering Amplitudes ◽  
Gauge Field ◽  
Vector Fields ◽  
Three Dimensional ◽  
Tree Level ◽  
Abelian Gauge ◽  
Gauge Invariant ◽  
Maxwell Fields ◽  
Chern Simons

One discusses the tree-level unitarity and presents asymptotic behavior of scattering amplitudes for three-dimensional gauge-invariant models where complex Chern- Simons-Maxwell fields (with and without a Proca-like mass) are coupled to an Abelian gauge field.

scholarly journals PION FORM FACTORS AT INTERMEDIATE MOMENTUM TRANSFER IN A COVARIANT APPROACH

1996 ◽  
Vol 11 (04) ◽  
pp. 655-675 ◽  
Author(s):  
ADAM SZCZEPANIAK ◽  
ANTHONY G. WILLIAMS
Keyword(s):  
Wave Function ◽  
Form Factor ◽  
Momentum Transfer ◽  
Transition Form Factor ◽  
Form Factors ◽  
Transition Form ◽  
Gauge Invariant ◽  
Pion Wave Function ◽  
Covariant Gauge ◽  
Text Component

We study the pion electromagnetic and γ*+π0→γ transition form factors at intermediate momentum transfer. We calculate soft, nonperturbative corrections to the leading perturbative amplitudes which arise from the [Formula: see text] component of the pion wave function. We work in Minkowski space and use a Lorentz-covariant, gauge-invariant generalized perturbative integral representation for the [Formula: see text] amplitudes. For the transition form factor we find relative insensitivity to the detailed nonperturbative structure of the wave function for |q2|≳10 GeV 2, whereas considerable sensitivity is found for the electromagnetic form factor.

scholarly journals NONLOCAL REGULARIZATION OF ABELIAN MODELS WITH SPONTANEOUS SYMMETRY BREAKING

2001 ◽  
Vol 16 (17) ◽  
pp. 1117-1127 ◽  
Author(s):  
M. A. CLAYTON
Keyword(s):  
Symmetry Breaking ◽  
Spontaneous Symmetry Breaking ◽  
Form Factors ◽  
Original Formulation ◽  
Gauge Bosons ◽  
Gauge Invariant ◽  
Brst Invariance ◽  
Nonlocal Regularization

We demonstrate how nonlocal regularization is applied to gauge-invariant models with spontaneous symmetry breaking. Motivated by the ability to find a nonlocal BRST invariance that leads to the decoupling of longitudinal gauge bosons from physical amplitudes, we show that the original formulation of the method leads to a nontrivial relationship between the nonlocal form factors that can appear in the model.

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 THE SCALAR SECTOR IN 331 MODELS

2003 ◽  
Vol 18 (09) ◽  
pp. 1573-1586 ◽  
Author(s):  
M. B. TULLY ◽  
G. C. JOSHI
Keyword(s):  
Symmetry Breaking ◽  
Scalar Potential ◽  
Lepton Number ◽  
Tree Level ◽  
Gauge Bosons ◽  
Gauge Invariant ◽  
Mass Matrices ◽  
Scalar Mass ◽  
Scalar Sector ◽  
General Gauge

We calculate the exact tree-level scalar mass matrices resulting from symmetry breaking using the most general gauge-invariant scalar potential of the 331 model, both with and without the condition that the lepton number is conserved. Physical masses are also obtained in some cases, as well as couplings to standard and exotic gauge bosons.

scholarly journals LOOP VARIABLES AND GAUGE INVARIANCE IN CLOSED BOSONIC STRING THEORY

2004 ◽  
Vol 19 (38) ◽  
pp. 2857-2870 ◽  
Author(s):  
B. SATHIAPALAN
Keyword(s):  
Gauge Invariance ◽  
Open String ◽  
Closed String ◽  
Bosonic String ◽  
Tree Level ◽  
Gauge Invariant ◽  
Open Strings ◽  
Invariant Description ◽  
String Amplitudes ◽  
Closed Bosonic String

We extend an earlier proposal for a gauge-invariant description of off-shell open strings (at tree level), using loop variables, to off-shell closed strings (at tree level). The basic idea is to describe the closed string amplitudes as a product of two open string amplitudes (using the technique of Kawai, Lewellen and Tye). The loop variable techniques that were used earlier for open strings can be applied here mutatis mutandis. It is a proposal for a theory whose on-shell amplitudes coincide with those of the closed bosonic string in 26 dimensions. It is also gauge-invariant off-shell. As was the case with the open string, the interacting closed string looks like a free closed string thickened to a band.

NUCLEON ELECTROMAGNETIC FORM FACTORS AND CHIRAL SINGULARITIES

1999 ◽  
Vol 08 (04) ◽  
pp. 355-379
Author(s):  
C. D. JOHNSON ◽  
R. TEGEN
Keyword(s):  
Closed Form ◽  
Scattering Amplitude ◽  
Form Factors ◽  
Electromagnetic Form Factors ◽  
Threshold Behaviour ◽  
Gauge Invariant ◽  
Meson Loop ◽  
Loop Approximation ◽  
Quark Substructure

Chiral singularities in both nucleon isovector radii are calculated in closed form. Within a one-meson-loop approximation we implement in an explicitly gauge invariant manner quark substructure in the γ π π and πNN vertex functions. The coefficients of log mπ and [Formula: see text] terms are directly related to gA and to the threshold behaviour of the πN amplitude A(-)(ν,0) which are 1 and 0, respectively, if only the N pole is considered in the πN scattering amplitude. This result is remarkably independent of the cut-off procedure. If mesonic substructure at the γ π π vertex is included, however, gA becomes slightly smaller than 1 and [Formula: see text] becomes moderately negative. This hints at important contributions to both gA and [Formula: see text] from the Δ(1232) and possibly other N*, Δ* resonances in this approach.

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