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1. Electroweak precision pseudo-observables at the e+e− Z-resonance peak

   https://doi.org/10.22323/1.390.0663  

   Dubovyk, Ievgen; Freitas, Ayres; Gluza, Janusz; Grzanka, Krzysztof; Riemann, Tord; Usovitsch, Johann (January 2021, 40th International Conference on High Energy Physics (ICHEP2020))

   null (Ed.)

   Phenomenologically relevant electroweak precision pseudo-observables related to Z-boson physics are discussed in the context of the strong experimental demands of future e+e− colliders. The recent completion of two-loop Z-boson results is summarized and a prospect for the 3-loop Standard Model calculation of the Z-boson decay pseudo-observable is given. 

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2. Mixed EW-QCD leading fermionic three-loop corrections at $$ \mathcal{O} $$(αsα2) to electroweak precision observables

   https://doi.org/10.1007/JHEP03(2021)215  

   Chen, Lisong; Freitas, Ayres (March 2021, Journal of High Energy Physics)

   null (Ed.)

   A bstract Measurements of electroweak precision observables at future electron-position colliders, such as the CEPC, FCC-ee, and ILC, will be sensitive to physics at multi-TeV scales. To achieve this sensitivity, precise predictions for the Standard Model expectations of these observables are needed, including corrections at the three- and four-loop level. In this article, results are presented for the calculation of a subset of three-loop mixed electroweak-QCD corrections, stemming from diagrams with a gluon exchange and two closed fermion loops. The numerical impact of these corrections is illustrated for a number of applications: the prediction of the W-boson mass from the Fermi constant, the effective weak mixing angle, and the partial and total widths of the Z boson. Two alternative renormalization schemes for the top-quark mass are considered, on-shell and $$ \overline{\mathrm{MS}} $$ MS ¯ . 

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3. Locally finite two-loop QCD amplitudes from IR universality for electroweak production

   https://doi.org/10.1007/JHEP05(2023)242  

   Anastasiou, Charalampos; Sterman, George (June 2023, Journal of High Energy Physics)

   A bstract We describe the implementation of infrared subtractions for two-loop QCD corrections to quark-antiquark annihilation to electroweak final states. The subtractions are given as form-factor integrands whose integrals are known. The resulting subtracted amplitudes are amenable to efficient numerical integration. Our procedure is based on the universality of infrared singularities and requires a relatively limited set of subtractions, whose number grows as the number of two-loop diagrams, rather than with the number of singular regions of integration. 

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4. Ab initio electron-two-phonon scattering in GaAs from next-to-leading order perturbation theory

   https://doi.org/10.1038/s41467-020-15339-0  

   Lee, Nien-En; Zhou, Jin-Jian; Chen, Hsiao-Yi; Bernardi, Marco (March 2020, Nature Communications)

   Abstract Electron-phonon (e–ph) interactions are usually treated in the lowest order of perturbation theory. Here we derive next-to-leading ordere–ph interactions, and compute from first principles the associated electron-two-phonon (2ph) scattering rates. The derivations involve Matsubara sums of two-loop Feynman diagrams, and the numerical calculations are challenging as they involve Brillouin zone integrals over two crystal momenta and depend critically on the intermediate state lifetimes. Using Monte Carlo integration together with a self-consistent update of the intermediate state lifetimes, we compute and converge the 2ph scattering rates, and analyze their energy and temperature dependence. We apply our method to GaAs, a weakly polar semiconductor with dominant optical-mode long-rangee–ph interactions. We find that the 2ph scattering rates are as large as nearly half the value of the one-phonon rates, and that including the 2ph processes is necessary to accurately predict the electron mobility in GaAs from first principles. 

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5. Integrating three-loop modular graph functions and transcendentality of string amplitudes

   https://doi.org/10.1007/JHEP02(2022)019  

   D’Hoker, Eric; Geiser, Nicholas (February 2022, Journal of High Energy Physics)

   A bstract Modular graph functions (MGFs) are SL(2 , ℤ)-invariant functions on the Poincaré upper half-plane associated with Feynman graphs of a conformal scalar field on a torus. The low-energy expansion of genus-one superstring amplitudes involves suitably regularized integrals of MGFs over the fundamental domain for SL(2 , ℤ). In earlier work, these integrals were evaluated for all MGFs up to two loops and for higher loops up to weight six. These results led to the conjectured uniform transcendentality of the genus-one four-graviton amplitude in Type II superstring theory. In this paper, we explicitly evaluate the integrals of several infinite families of three-loop MGFs and investigate their transcendental structure. Up to weight seven, the structure of the integral of each individual MGF is consistent with the uniform transcendentality of string amplitudes. Starting at weight eight, the transcendental weights obtained for the integrals of individual MGFs are no longer consistent with the uniform transcendentality of string amplitudes. However, in all the cases we examine, the violations of uniform transcendentality take on a special form given by the integrals of triple products of non-holomorphic Eisenstein series. If Type II superstring amplitudes do exhibit uniform transcendentality, then the special combinations of MGFs which enter the amplitudes must be such that these integrals of triple products of Eisenstein series precisely cancel one another. Whether this indeed is the case poses a novel challenge to the conjectured uniform transcendentality of genus-one string amplitudes. 

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