scholarly journals Finite calculation of divergent self-energy diagrams

2003 ◽  
Vol 81 (12) ◽  
pp. 1433-1445 ◽  
Author(s):  
A Aste ◽  
D Trautmann
Keyword(s):  
Perturbation Theory ◽  
Dispersion Relation ◽  
Imaginary Part ◽  
Feynman Diagram ◽  
Feynman Diagrams ◽  
Energy Diagram ◽  
The Real ◽  
Self Energy ◽  
Single Integral ◽  
Analytic Expression

Using dispersive techniques, it is possible to avoid ultraviolet divergences in the calculation of Feynman diagrams, making subsequent regularization of divergent diagrams unnecessary. We give a simple introduction to the most important features of such dispersive techniques in the framework of the so-called finite causal perturbation theory. The method is also applied to the "divergent" general massive two-loop sunrise self-energy diagram, where it leads directly to an analytic expression for the imaginary part of the diagram in accordance with the literature, whereas the real part can be obtained by a single integral dispersion relation. It is pointed out that dispersive methods have been known for decades and have been applied to several nontrivial Feynman diagram calculations.PACS Nos.: 11.10.–z, 11.15.Bt, 12.20.Ds, 12.38.Bx

scholarly journals GAP EQUATION IN SCALAR FIELD THEORY AT FINITE TEMPERATURE

1999 ◽  
Vol 14 (04) ◽  
pp. 257-266
Author(s):  
KRISHNENDU MUKHERJEE
Keyword(s):  
Field Theory ◽  
Perturbation Theory ◽  
Scalar Field ◽  
Imaginary Part ◽  
Finite Temperature ◽  
Thermal Mass ◽  
Scalar Field Theory ◽  
Gap Equation ◽  
The Real

We investigate the two-loop gap equation for the thermal mass of hot massless g2ϕ4 theory and find that the gap equation itself has a nonzero finite imaginary part. This implies that it is not possible to find the real thermal mass as a solution of the gap equation beyond g2 order in perturbation theory. We have solved the gap equation and obtained the real and imaginary parts of the thermal mass which are correct up to g4 order in perturbation theory.

COMPLEXITY OF HADRONIC AMPLITUDES VIA QUARK LOOPS

1993 ◽  
Vol 02 (01) ◽  
pp. 219-232 ◽  
Author(s):  
A.N. MITRA ◽  
I. SANTHANAM ◽  
A. ESSAGHOLIAN
Keyword(s):  
Wave Function ◽  
Dispersion Relation ◽  
Imaginary Part ◽  
Vertex Function ◽  
Proper Understanding ◽  
The Real ◽  
Loop Integral ◽  
Model Based ◽  
Structure Formula ◽  
Transition Amplitudes

The structure of hadronic transition amplitudes h→h′+h″ via quark triangle loops is investigated in terms of hadron quark vertex functions [Formula: see text], using for illustration the case of the ρ→ππ transition. A Bethe-Salpeter model based on the Covariant-Instantaneity-Ansatz (CIA) for its kernel which provides an exact interconnection between the 3D and 4D forms the BS wave function, determines the structure [Formula: see text]. The nonlocality feature inherent in the vertex function causes the imaginary part of gρππ calculated from the loop integral to be generally different from its dispersion relation value which would be obtained from analyticity of gρππ in the ρ-mass. Pending a proper understanding of this nonlocality (associated with confining interactions) only the real part of gρππ is found unambiguous while the imaginary part is model-dependent.

COMPUTATION OF 1-LOOP CONTRIBUTIONS IN Y.M. THEORIES WITH CLASS III NONRELATIVISTIC GAUGES

1992 ◽  
Vol 03 (02) ◽  
pp. 321-335 ◽  
Author(s):  
A. BURNEL ◽  
H. CAPRASSE
Keyword(s):  
Feynman Diagram ◽  
Class Iii ◽  
High Complexity ◽  
Energy Diagram ◽  
Careful Choice ◽  
Self Energy ◽  
Limited Memory ◽  
Intermediate Results

A program to compute the gluon self-energy diagram in class III nonrelativistic gauges has been constructed. It succeeded to show that axial gauges do not exhibit nonlocal counterterms. The high complexity of the calculations, the need to be able to control intermediate steps of calculations and the necessity to work inside a limited memory of a few Mbytes led us to give it special features which may serve outside the specific application for which it has been designed. The structure of the program and its salient working features are described. It is divided into four modules, which are almost independent except that they are linked by their respective output. Files containing intermediate results of calculations are automatically generated. The amount of algebraic manipulations has been greatly reduced thanks to a careful choice of the representation of the expression adapted to each stage of the calculation. The adaptative character of this program is discussed as well as the generalization it needs to cover other types of Feynman diagram calculations.

Transversality of the resummed thermal gluon self-energy

1993 ◽  
Vol 71 (5-6) ◽  
pp. 256-261 ◽  
Author(s):  
G. Kunstatter
Keyword(s):  
Quantum Chromodynamics ◽  
Imaginary Part ◽  
The Self ◽  
Ward Identities ◽  
Generating Functional ◽  
The Real ◽  
Self Energy ◽  
Gauge Fixing

The perturbative Ward identities obeyed by the effective vertices and propagators for thermal quantum chromodynamics (QCD) have recently been used to prove to order g2T the on-shell transversality of the imaginary part of the (resummed) gluon self-energy in all linear gauges. Here the same result is derived for both the real and imaginary parts of the self-energy using the nonperturbative gauge-fixing identities obeyed by the generating functional for QCD.

scholarly journals Opacity from Loops in AdS

2021 ◽  
Vol 2021 (2) ◽  
Author(s):  
Alexandria Costantino ◽  
Sylvain Fichet
Keyword(s):  
Imaginary Part ◽  
Quantum Dynamics ◽  
Model Building ◽  
Asymptotic Properties ◽  
The Self ◽  
Effective Theory ◽  
Self Energy ◽  
Higher Dimensional ◽  
Timelike Region ◽  
Spectral Representations

Abstract We investigate how quantum dynamics affects the propagation of a scalar field in Lorentzian AdS. We work in momentum space, in which the propagator admits two spectral representations (denoted “conformal” and “momentum”) in addition to a closed-form one, and all have a simple split structure. Focusing on scalar bubbles, we compute the imaginary part of the self-energy ImΠ in the three representations, which involves the evaluation of seemingly very different objects. We explicitly prove their equivalence in any dimension, and derive some elementary and asymptotic properties of ImΠ.Using a WKB-like approach in the timelike region, we evaluate the propagator dressed with the imaginary part of the self-energy. We find that the dressing from loops exponentially dampens the propagator when one of the endpoints is in the IR region, rendering this region opaque to propagation. This suppression may have implications for field-theoretical model-building in AdS. We argue that in the effective theory (EFT) paradigm, opacity of the IR region induced by higher dimensional operators censors the region of EFT breakdown. This confirms earlier expectations from the literature. Specializing to AdS5, we determine a universal contribution to opacity from gravity.

scholarly journals Stochastic computation of g − 2 in QED

2021 ◽  
Vol 2021 (5) ◽  
Author(s):  
Ryuichiro Kitano ◽  
Hiromasa Takaura ◽  
Shoji Hashimoto
Keyword(s):  
Perturbation Theory ◽  
Numerical Computation ◽  
Magnetic Moment ◽  
Anomalous Magnetic Moment ◽  
Stochastic Perturbation ◽  
Higher Order ◽  
Feynman Diagrams ◽  
Perturbative Series ◽  
Physical Quantities

Abstract We perform a numerical computation of the anomalous magnetic moment (g − 2) of the electron in QED by using the stochastic perturbation theory. Formulating QED on the lattice, we develop a method to calculate the coefficients of the perturbative series of g − 2 without the use of the Feynman diagrams. We demonstrate the feasibility of the method by performing a computation up to the α3 order and compare with the known results. This program provides us with a totally independent check of the results obtained by the Feynman diagrams and will be useful for the estimations of not-yet-calculated higher order values. This work provides an example of the application of the numerical stochastic perturbation theory to physical quantities, for which the external states have to be taken on-shell.

scholarly journals MASSLESS TWO-LOOP SELF-ENERGY DIAGRAM: HISTORICAL REVIEW

2012 ◽  
Vol 27 (19) ◽  
pp. 1230018 ◽  
Author(s):  
A. G. GROZIN
Keyword(s):  
Historical Review ◽  
Energy Diagram ◽  
Self Energy

This class of diagrams has numerous applications. Many interesting results have been obtained for it.

scholarly journals Feynman diagrams and rooted maps

Open Physics ◽  
2018 ◽  
Vol 16 (1) ◽  
pp. 149-167 ◽  
Author(s):  
Andrea Prunotto ◽  
Wanda Maria Alberico ◽  
Piotr Czerski
Keyword(s):  
Single Particle ◽  
Feynman Diagram ◽  
Feynman Diagrams ◽  
Topological Properties ◽  
Many Body ◽  
Perturbative Order ◽  
Original Definition ◽  
Many Body Systems ◽  
Definition Of ◽  
Particle Propagator

Abstract The rooted maps theory, a branch of the theory of homology, is shown to be a powerful tool for investigating the topological properties of Feynman diagrams, related to the single particle propagator in the quantum many-body systems. The numerical correspondence between the number of this class of Feynman diagrams as a function of perturbative order and the number of rooted maps as a function of the number of edges is studied. A graphical procedure to associate Feynman diagrams and rooted maps is then stated. Finally, starting from rooted maps principles, an original definition of the genus of a Feynman diagram, which totally differs from the usual one, is given.

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