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1. One-loop electron mass and QED trace anomaly

   https://doi.org/10.1140/epjc/s10052-023-11535-6  

   Eides, Michael I. (May 2023, The European Physical Journal C)

   Abstract Electron mass is considered as a matrix element of the energy–momentum trace in the rest frame. The one-loop diagrams for this matrix element are different from the textbook diagrams for the electron mass renormalization. We clarify connection between the two sets of diagrams and explain analytically and diagrammatically why the results of both calculations coincide. 

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2. Landau-Khalatnikov-Fradkin Gauge Transformations for the Propagator and Vertex in QED and QED ₂

   https://doi.org/10.1088/1742-6596/2667/1/012023  

   Nicasio, José; Bashir, Adnan; Jentschura, Ulrich D; Edwards, James P (December 2023, Journal of Physics: Conference Series)

   Abstract The non-perturbative Landau-Khalatnikov-Fradkin (LKF) transformations describe how Green functions in quantum field theory transform under a change in the photon field’s linear covariant gauge parameter (denotedξ). The transformations are framed most simply in coordinate space where they are multiplicative. They imply that information on gauge-dependent contributions from higher order diagrams in the perturbative series is contained in lower order contributions, which is useful in multi-loop calculations. We study the LKF transformations for the propagator and the vertex in both scalar and spinor QED, in some particular dimensions. A novelty of our work is to derive momentum-space integral representations of these transformations; our expressions are also applicable to the longitudinal and transverse parts of the vertex. Applying these transformations to the tree-level Green functions, we show that the one-loop terms obtained from the LKF transformation agree with the gauge dependent parts obtained from perturbation theory. Our results will be presented in more comprehensive form elsewhere. 

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3. Parametric study of the polarization dependence of nonlinear Breit–Wheeler pair creation process using two laser pulses

   https://doi.org/10.1063/5.0165788  

   Qian, Qian; Seipt, Daniel; Vranic, Marija; Grismayer, Thomas E; Blackburn, Thomas G; Ridgers, Christopher P; Thomas, Alexander_G R (October 2023, Physics of Plasmas)

   With the rapid development of high-power petawatt class lasers worldwide, exploring physics in the strong field QED regime will become one of the frontiers for laser–plasma interactions research. Particle-in-cell codes, including quantum emission processes, are powerful tools for predicting and analyzing future experiments where the physics of relativistic plasma is strongly affected by strong field QED processes. The spin/polarization dependence of these quantum processes has been of recent interest. In this article, we perform a parametric study of the interaction of two laser pulses with an ultrarelativistic electron beam. The first pulse is optimized to generate high-energy photons by nonlinear Compton scattering and efficiently decelerate electron beam through the quantum radiation reaction. The second pulse is optimized to generate electron–positron pairs by the nonlinear Breit–Wheeler decay of photons with the maximum polarization dependence. This may be experimentally realized as a verification of the strong field QED framework, including the spin/polarization rates. 

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4. Fermion self-energy and damping rate in a hot magnetized plasma

   https://doi.org/10.1103/PhysRevD.109.096018  

   Ghosh, Ritesh; Shovkovy, Igor A. (May 2024, Physical Review D)

   We derive a general expression for the fermion self-energy in a hot magnetized plasma by using the Landau-level representation. In the one-loop approximation, the Dirac structure of the self-energy is characterized by five different functions that depend on the Landau-level index $n$and the longitudinal momentum $p_z$. We derive general expressions for all five functions and obtain closed-form expressions for their imaginary parts. The latter receive contributions from three types of on shell processes, which are interpreted in terms of Landau-level transitions, accompanied by a single photon (gluon) emission or absorption. By making use of the imaginary parts of the self-energy functions, we also derive the Landau-level dependent fermion damping rates ${\mathrm{\Gamma }}_n\left(p_z\right)$and study them numerically in a wide range of model parameters. We also demonstrate that the two-spin degeneracy of the Landau levels is lifted by the one-loop self-energy corrections. While the spin splitting of the damping rates is small, it may be important for some spin and chiral effects. We argue that the general method and the numerical results for the rates can have interesting applications in heavy-ion physics, astrophysics, and cosmology, where strongly magnetized QED or QCD plasmas are ubiquitous. Published by the American Physical Society2024 

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5. Locally finite two-loop amplitudes for off-shell multi-photon production in electron-positron annihilation

   https://doi.org/10.1007/JHEP04(2021)222  

   Anastasiou, Charalampos; Haindl, Rayan; Sterman, George; Yang, Zhou; Zeng, Mao (April 2021, Journal of High Energy Physics)

   null (Ed.)

   A bstract We study the singularity structure of two-loop QED amplitudes for the production of multiple off-shell photons in massless electron-positron annihilation and develop counterterms that remove their infrared and ultraviolet divergences point by point in the loop integrand. The remainders of the subtraction are integrable in four dimensions and can be computed in the future with numerical integration. The counterterms capture the divergences of the amplitudes and factorize in terms of the Born amplitude and the finite remainder of the one-loop amplitude. They consist of simple one- and two-loop integrals with at most three external momenta and can be integrated analytically in a simple manner with established methods. We uncover novel aspects of fully local IR factorization, where vertex and self energy subdiagrams must be modified by new symmetrizations over loop momenta, in order to expose their tree-like tensor structures and hence factorization of IR singularities prior to loop integration. This work is a first step towards isolating locally the hard contributions of generic gauge theory amplitudes and rendering them integrable in exactly four dimensions with numerical methods. 

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