scholarly journals Two-loop fermion self-energy in reduced quantum electrodynamics and application to the ultrarelativistic limit of graphene

2014 ◽  
Vol 89 (6) ◽  
Author(s):  
A. V. Kotikov ◽  
S. Teber
Keyword(s):  
Quantum Electrodynamics ◽  
Self Energy ◽  
Ultrarelativistic Limit

scholarly journals Quantum electrodynamics with self-conjugated equations with spinor wave functions for fermion fields

2021 ◽  
pp. 2150086
Author(s):  
V. P. Neznamov ◽  
V. E. Shemarulin
Keyword(s):  
Cross Sections ◽  
Magnetic Moment ◽  
Anomalous Magnetic Moment ◽  
Quantum Electrodynamics ◽  
Lamb Shift ◽  
Wave Functions ◽  
Self Energy ◽  
Fermion Fields ◽  
Spinor Wave

Quantum electrodynamics (QED) with self-conjugated equations with spinor wave functions for fermion fields is considered. In the low order of the perturbation theory, matrix elements of some of QED physical processes are calculated. The final results coincide with cross-sections calculated in the standard QED. The self-energy of an electron and amplitudes of processes associated with determination of the anomalous magnetic moment of an electron and Lamb shift are calculated. These results agree with the results in the standard QED. Distinctive feature of the developed theory is the fact that only states with positive energies are present in the intermediate virtual states in the calculations of the electron self-energy, anomalous magnetic moment of an electron and Lamb shift. Besides, in equations, masses of particles and antiparticles have the opposite signs.

scholarly journals On the electrodynamic self-energy of the electron

1948 ◽  
Vol 195 (1041) ◽  
pp. 163-173
Keyword(s):  
Perturbation Theory ◽  
Wave Equation ◽  
Quantum Electrodynamics ◽  
Energy State ◽  
Energy Eigenvalue ◽  
Expansion Method ◽  
Negative Energy ◽  
The Self ◽  
Variation Principle ◽  
Self Energy

The stationary-state wave equation for an electron at rest in a negative-energy state in interaction with only its own electromagnetic field is considered. Quantum electrodynamics, single-electron theory and a ‘cut-off’ procedure in momentum-space are used. Expressions in the form of expansions in powers of e 2 /hc are derived for the wave function ψ and the energy-eigenvalue E by a method which (unlike perturbation theory) is not based on the assumption that the self-energy is small. The convergence of the expansion for E is not proved rigorously but the first few terms are shown to decrease rapidly. For low cut-off frequencies K 0 the expression for E behaves as the equivalent perturbation expression but for large K 0 it behaves as — J(e 2 /hc) hK0. The variation principle is applied to an approximation (obtained from the expansion method) for r/r, and it is proved rigorously that for large K 0 the self-energy is algebraically less than or equal to —J(e 2 /hc) hK 0 . Hence, if the electron wave-equation is considered as the limiting case of the ‘cut-off’ equation as K 0 ->ao, it is established that the divergences obtained are not merely due to improper use of perturbation theory and that the self-energy is indeed infinite.

ON THE POSSIBLE EXISTENCE OF A DERIVATIVE COUPLING IN QUANTUM ELECTRODYNAMICS

1959 ◽  
Vol 37 (12) ◽  
pp. 1339-1343
Author(s):  
F. A. Kaempffer
Keyword(s):  
Cross Section ◽  
Quantum Electrodynamics ◽  
Mass Difference ◽  
Large Mass ◽  
The Self ◽  
Nucleon Mass ◽  
Muon Scattering ◽  
Derivative Coupling ◽  
Self Energy ◽  
Classical Analogue

Within the framework of quantum electrodynamics there exists the possibility of a derivative coupling between source and photon field, referred to as eΛ-charge, which has no classical analogue. For calculations the usual graph technique can be used, provided the factor eγμ contributed by each vertex in a conventional graph is replaced by ieΛkμ, where Λ is a length characteristic of the new interaction. Using as cutoff the nucleon mass M one finds for a bare source of electronic mass m the self-energy in second order to be Λm/m ≈ 200, if Λ−1 ≈ 60 M. It is argued that the large mass difference between muon and electron may be due to this effect, assuming muon and electron to differ only in that the muon has eΛ-charge whereas the electron has not. An estimate is made of the muon–muon scattering cross section caused by the presence of eΛ-charge on the muon, and it is found that the existence of this derivative coupling may have escaped observation.

scholarly journals Convergence in Quantum Field Theory without Use of Renormalization

2019 ◽  
Author(s):  
Biswaranjan Dikshit
Keyword(s):  
Field Theory ◽  
Quantum Field Theory ◽  
Quantum Electrodynamics ◽  
Ad Hoc ◽  
Probability Amplitude ◽  
Quantum Field ◽  
Counter Term ◽  
Self Energy ◽  
Calculated Probability ◽  
Conventional Methods

In quantum field theory (QFT), it is well known that when Feynman diagrams containing loops are evaluated to account for self interactions, probability amplitude comes out to be infinite which is physically not admissible. So, to make the QFT convergent, various renormalization methods are conventionally followed in which an additional (infinite) counter term is postulated which neutralizes the original infinity generated by diagram. The resulting finite values of amplitudes have agreed with experiments with surprising accuracy. However, proponents of renormalization methods acknowledged that this ad-hoc procedure of subtraction of infinity from infinity to reach at a finite value is not at all satisfactory and there is no physical basis for bringing in the counter term. So, it is desirable to establish a method in QFT which does not generate any infinite term (thus not requiring renormalization), but which predicts same results as conventional methods do. In this paper, we describe such a technique taking self interaction quantum electrodynamics diagram representing electron or photon self energy. In our method, no problem of infinity arises and hence renormalization is not necessary. Still, the dependence of calculated probability amplitude on physical variables in our technique comes out to be same as conventional methods. Using similar procedure, we hope, the problem of non-renormalizability of quantum gravity may be solved in future.

scholarly journals Some recent advances in bound-state quantum electrodynamics

2005 ◽  
Vol 83 (4) ◽  
pp. 375-386 ◽  
Author(s):  
U D Jentschura ◽  
J Evers
Keyword(s):  
Effective Field Theories ◽  
Quantum Electrodynamics ◽  
Lamb Shift ◽  
Recent Progress ◽  
Bound State ◽  
Effective Field ◽  
Field Theories ◽  
Nonrelativistic Quantum ◽  
Self Energy ◽  
Bound Electron

We discuss recent progress in various problems related to bound-state quantum electrodynamics: the bound-electron g factor, two-loop self-energy corrections, and the laser-dressed Lamb shift. The progress relies on various advances in the bound-state formalism, including ideas inspired by effective field theories such as nonrelativistic quantum electrodynamics. Radiative corrections in dynamical processes represent a promising field for further investigations. PACS Nos.: 31.15.–p, 12.20.Ds

scholarly journals Quantum Electrodynamics in Strong Magnetic Fields. IV. Electron Self-energy

1987 ◽  
Vol 40 (1) ◽  
pp. 1 ◽  
Author(s):  
AJ Parle
Keyword(s):  
Magnetic Field ◽  
Fine Structure ◽  
Quantum Electrodynamics ◽  
Mass Shell ◽  
Mass Operator ◽  
Structure Constant ◽  
Fine Structure Constant ◽  
Strong Magnetic Fields ◽  
Self Energy ◽  
Cyclotron Emission

The electron self-energy in a magnetic field is calculated with the effect of the field included exactly. A new representation of the wavefunctions and other quantities is defined, in which the mass operator has a particularly simple form. After renormalisation, the form of the mass operator allows corrections to the Dirac equation, wavefunctions, vertex function and the electron propagator close to the mass shell to be calculated to lowest order in the fine structure constant. The probability for an electron to change spin while remaining in the same Landau level is calculated, and is found to be much less than the probability of cyclotron emission.

Generalized quantum electrodynamics: One-loop correction

2021 ◽  
Author(s):  
David Montenegro
Keyword(s):  
Quantum Electrodynamics ◽  
Loop Correction ◽  
Interaction Picture ◽  
Perturbative Approach ◽  
Self Energy ◽  
Higher Derivative ◽  
Consistent Extension ◽  
Point Correlation ◽  
The Stability

In this paper, we give an update on divergent problems concerning the radiative corrections of quantum electrodynamics in (3[Formula: see text]+[Formula: see text]1) dimensions. In doing so, we introduce a geometric adaptation for the covariant photon propagator by including a higher derivative field. This derivation, so-called generalized quantum electrodynamics, is motivated by the stability and unitarity features. This theory provides a natural and self-consistent extension of the quantum electrodynamics by enlarging the space parameter of spinor-gauge interactions. In particular, Haag’s theorem undermines the perturbative characterization of the interaction picture due to its inconsistency on quantum field theory foundations. To circumvent this problem, we develop our perturbative approach in the Heisenberg picture and use it to investigate the behavior of the operator current at one-loop. We find the two- and three-point correlation functions are ultraviolet finite, electron self-energy and vertex corrections, respectively. On the other hand, we also explain how the vacuum polarization remains ultraviolet divergent only at [Formula: see text] order. Finally, we evaluate the anomalous magnetic moment, which allows us to specify a lower bound value for the Podolsky parameter.

Screening masses of photons interacting with a two-species fermionic system in relativistic BCS–BEC crossover

2017 ◽  
Vol 31 (11) ◽  
pp. 1750078
Author(s):  
Xun Huang ◽  
Wei-Min Cai ◽  
Hao Guo
Keyword(s):  
Mechanical Stability ◽  
Nonrelativistic Limit ◽  
Superfluid Density ◽  
Einstein Condensation ◽  
Number Density ◽  
Fermionic System ◽  
Self Energy ◽  
Ultrarelativistic Limit ◽  
Bose Einstein ◽  
Electromagnetic Instability

We address the behavior of Debye and Meissner masses of photons in a condensate of fermion pairs in the presence of number density asymmetry. Our formalism applies to a two-species fermionic system with number density asymmetry in BCS–Bose–Einstein condensation (BEC)–relativistic BEC crossover and with variable rapidity. Our results recover the known results of the photon self-energy in the ultrarelativistic limit and the superfluid density in the nonrelativistic limit. We further consider the electromagnetic stability of the condensate and show that the Meissner mass squared can become negative in the weakly coupling BCS regime and the strongly coupling relativistic BEC regime. The electromagnetic instability is compared to the mechanical stability discussed in previous works.

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