| 1. |
- Afanasev, Andrei, et al.
(författare)
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Radiative corrections : from medium to high energy experiments
- 2024
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Ingår i: European Physical Journal A. - 1434-6001. ; 60:4
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Forskningsöversikt (refereegranskat)abstract
- Radiative corrections are crucial for modern high-precision physics experiments, and are an area of active research in the experimental and theoretical community. Here we provide an overview of the state of the field of radiative corrections with a focus on several topics: lepton–proton scattering, QED corrections in deep-inelastic scattering, and in radiative light-hadron decays. Particular emphasis is placed on the two-photon exchange, believed to be responsible for the proton form-factor discrepancy, and associated Monte-Carlo codes. We encourage the community to continue developing theoretical techniques to treat radiative corrections, and perform experimental tests of these corrections.
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| 2. |
- Baeza-Ballesteros, Jorge, et al.
(författare)
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The isospin-3 three-particle K-matrix at NLO in ChPT
- 2023
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Ingår i: Journal of High Energy Physics. - 1029-8479. ; 2023:5
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Tidskriftsartikel (refereegranskat)abstract
- The three-particle K-matrix, Kdf,3 , is a scheme-dependent quantity that parametrizes short-range three-particle interactions in the relativistic-field-theory three-particle finite-volume formalism. In this work, we compute its value for systems of three pions at maximal isospin through next-to-leading order (NLO) in Chiral Perturbation Theory (ChPT). We compare the values to existing lattice QCD results and find that the agreement between lattice QCD data and ChPT in the first two coefficients of the threshold expansion of Kdf,3 is significantly improved with respect to leading order once NLO effects are incorporated.
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| 3. |
- Baeza-Ballesteros, Jorge, et al.
(författare)
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The three-pion K-matrix at NLO in ChPT
- 2024
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Ingår i: Journal of High Energy Physics. - 1029-8479. ; 2024:3
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Tidskriftsartikel (refereegranskat)abstract
- The three-particle K-matrix, Kdf,3, is a scheme-dependent quantity that parametrizes short-range three-particle interactions in the relativistic-field-theory three-particle finite-volume formalism. In this work, we compute its value for systems of three pions in all isospin channels through next-to-leading order in Chiral Perturbation Theory, generalizing previous work done at maximum isospin. We obtain analytic expressions through quadratic order (or cubic order, in the case of zero isospin) in the expansion about the three-pion threshold.
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| 4. |
- Baeza-Ballesteros, Jorge, et al.
(författare)
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Three-pion scattering : From the chiral Lagrangian to the lattice
- 2023
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Ingår i: Nuclear and Particle Physics Proceedings. - 2405-6014.
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Tidskriftsartikel (refereegranskat)abstract
- In recent years, detailed studies of three-pion systems have become possible in lattice QCD. This has in turn led to interest in 3-to-3 scattering of pions in the chiral perturbation theory framework. In addition to being an interesting study of multi-meson dynamics in its own right, it provides a valuable handle on finite-volume effects and the pion mass dependence, thus complementing the lattice results. I present our derivation of the next-to-leading order amplitude for this process, as well as its conversion into the three-particle K-matrix, which enables direct comparison to the lattice. Our results significantly improve the agreement between theory and lattice, which was poor when only leading-order effects were taken into account.
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| 5. |
- Bijnens, Johan, et al.
(författare)
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Six-meson amplitude in QCD-like theories
- 2022
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Ingår i: Physical Review D. - 2470-0010. ; 106:5
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Tidskriftsartikel (refereegranskat)abstract
- We calculate the relativistic six-meson scattering amplitude at low energy within the framework of QCD-like theories with n degenerate quark flavors at next-to-leading order in the chiral counting. We discuss the cases of complex, real and pseudoreal representations, i.e. with global symmetry and breaking patterns SU(n)×SU(n)/SU(n) (extending the QCD case), SU(2n)/SO(2n), and SU(2n)/Sp(2n). In case of the one-particle-irreducible part, we obtain analytical expressions in terms of ten six-meson subamplitudes based on the flavor and group structures. We extend on our previous results obtained within the framework of the O(N+1)/O(N) nonlinear sigma model, with N being the number of meson flavors. This work allows for studying a number of properties of six-particle amplitudes at one-loop level.
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| 6. |
- Bijnens, Johan, et al.
(författare)
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Six-pion amplitude
- 2021
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Ingår i: Physical Review D. - 2470-0010. ; 104:5
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Tidskriftsartikel (refereegranskat)abstract
- Within the framework of the massive nonlinear sigma model extended to the next-to-leading order in the chiral counting [for corresponding to the two(-quark)-flavor Chiral Perturbation Theory], we calculate the relativistic six-pion scattering amplitude at low energy up to and including terms . Results for the pion mass, decay constant, and four-pion amplitude in the case of (meson) flavors at are also presented.
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| 7. |
- Cortina Gil, E., et al.
(författare)
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Measurement of the very rare K+→π+νν- decay
- 2021
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Ingår i: Journal of High Energy Physics. - 1029-8479. ; 2021:6
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Tidskriftsartikel (refereegranskat)abstract
- The NA62 experiment reports the branching ratio measurement BR(K+→π+νν¯)=(10.6−3.4+4.0|stat±0.9syst)×10−11 at 68% CL, based on the observation of 20 signal candidates with an expected background of 7.0 events from the total data sample collected at the CERN SPS during 2016–2018. This provides evidence for the very rare K+→π+νν¯ decay, observed with a significance of 3.4σ. The experiment achieves a single event sensitivity of (0.839 ± 0.054) × 10−11, corresponding to 10.0 events assuming the Standard Model branching ratio of (8.4 ± 1.0) × 10−11. This measurement is also used to set limits on BR(K+→ π+X), where X is a scalar or pseudo-scalar particle. Details are given of the analysis of the 2018 data sample, which corresponds to about 80% of the total data sample. © 2021, The Author(s).
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| 8. |
- Husek, Tomáš, et al.
(författare)
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Constraints on leptoquarks from lepton-flavour-violating tau-lepton processes
- 2022
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Ingår i: Journal of High Energy Physics. - 1029-8479. ; 2022:4
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Tidskriftsartikel (refereegranskat)abstract
- Leptoquarks are ubiquitous in several extensions of the Standard Model and seem to be able to accommodate the universality-violation-driven B-meson-decay anomalies and the (g −2)μ discrepancy interpreted as deviations from the Standard Model predictions. In addition, the search for lepton-flavour violation in the charged sector is, at present, a major research program that could also be facilitated by the dynamics generated by leptoquarks. In this article, we consider a rather wide framework of both scalar and vector leptoquarks as the generators of lepton-flavour violation in processes involving the tau lepton. We single out its couplings to leptoquarks, thus breaking universality in the lepton sector, and we integrate out leptoquarks at tree level, generating the corresponding dimension-6 operators of the Standard Model Effective Field Theory. In ref. [1] we obtained model-independent bounds on the Wilson coefficients of those operators contributing to lepton-flavour-violating hadron tau decays and ℓ–τ conversion in nuclei, with ℓ = e, μ. Hence, we use those results to translate the bounds into the couplings of leptoquarks to the Standard Model fermions.
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| 9. |
- Husek, Tomáš, et al.
(författare)
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Lepton-flavour violation in hadronic tau decays and l-τ conversion in nuclei
- 2021
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Ingår i: Proceedings of Science : 40th International Conference on High Energy Physics, ICHEP 2020 - 40th International Conference on High Energy Physics, ICHEP 2020. ; 390
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Konferensbidrag (refereegranskat)abstract
- Within the Standard Model Effective Field Theory framework, with operators up to dimension 6, we perform a model-independent analysis of the lepton-flavour-violating processes involving tau leptons. Namely, we study hadronic tau decays and l-t conversion in nuclei (l = e, µ). Based on available experimental limits, we establish constraints on the Wilson coefficients of the operators contributing to these processes. The related information from Belle II and foreseen future experiments can be easily incorporated into the resulting framework.
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| 10. |
- Husek, Tomas, et al.
(författare)
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Radiative corrections for the decay Sigma(0) -> Lambda e(+)e(-)
- 2020
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Ingår i: European Physical Journal C. - : SPRINGER. - 1434-6044 .- 1434-6052. ; 80:3
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Tidskriftsartikel (refereegranskat)abstract
- Electromagnetic form factors serve to explore the intrinsic structure of nucleons and their strangeness partners. With electron scattering at low energies the electromagnetic moments and radii of nucleons can be deduced. The corresponding experiments for hyperons are limited because of the unstable nature of the hyperons. Only for one process this turns to an advantage: the decay of the neutral Sigma hyperon to a Lambda hyperon and a real or virtual photon. Due to limited phase space the effects caused by the Sigma-to-Lambda transition form factors compete with the QED radiative corrections for the decay sigma 0 -> e+e-. These QED corrections are addressed in the present work, evaluated beyond the soft-photon approximation, i.e., over the whole range of the Dalitz plot and with no restrictions on the energy of the radiative photon.
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