| 1. |
- Bijnens, Johan, et al.
(författare)
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Higher-order tree-level amplitudes in the nonlinear sigma model
- 2019
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Ingår i: Journal of High Energy Physics. - 1029-8479. ; 2019:11
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Tidskriftsartikel (refereegranskat)abstract
- We present a generalisation of the flavour-ordering method applied to the chiral nonlinear sigma model with any number of flavours. We use an extended Lagrangian with terms containing any number of derivatives, organised in a power-counting hierarchy. The method allows diagrammatic computations at tree-level with any number of legs at any order in the power-counting. Using an automated implementation of the method, we calculate amplitudes ranging from 12 legs at leading order, O(p2), to 6 legs at next-to- next-to-next-to-leading order, O(p8). In addition to this, we generalise several properties of amplitudes in the nonlinear sigma model to higher orders. These include the double soft limit and the uniqueness of stripped amplitudes.
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| 2. |
- Bijnens, Johan, et al.
(författare)
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Leading logarithms for mesons and nucleons
- 2015
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Ingår i: Proceedings of Science. - 1824-8039.
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Tidskriftsartikel (refereegranskat)abstract
- This talk describes the work done in calculating leading logarithms in massive effective field theories. We discuss shortly leading logarithms in renormalizable theories and how they can be calculated using only one-loop calculations in effective field theories. The remainder of the talk discusses masses, decay constants, condensates and anomalous processes in mesonic effective field theories like Chiral Perturbation Theory and the expansion of the nucleon mass.
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| 3. |
- Bijnens, Johan, et al.
(författare)
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Leading logarithms in N-flavour mesonic Chiral Perturbation Theory
- 2013
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Ingår i: Nuclear Physics, Section B. - : Elsevier BV. - 0550-3213. ; 873:1, s. 137-164
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Tidskriftsartikel (refereegranskat)abstract
- We extend earlier work on leading logarithms in the massive nonlinear O(n) sigma model to the case of SU(N) x SU(N)/SU(N) which coincides with mesonic Chiral Perturbation Theory for N flavours of light quarks. We discuss the leading logarithms for the mass and decay constant to six loops and for the vacuum expectation value ((q) over barq) to seven loops. For dynamical quantities the expressions grow extremely large much faster such that we only quote the leading logarithms to five loops for the vector and scalar form factor and for meson-meson scattering. The last quantity we consider is the vector-vector to meson-meson amplitude where we quote results up to four loops for a subset of quantities, in particular for the pion polarizabilities. As a side result we provide an elementary proof that the factors of N appearing at each loop order are odd or even depending on the order and the remaining traces over external flavours. (C) 2013 Published by Elsevier B.V.
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| 4. |
- Bijnens, Johan, et al.
(författare)
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Leading logarithms in the anomalous sector of two-flavour QCD
- 2012
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Ingår i: Nuclear Physics, Section B. - : Elsevier BV. - 0550-3213. ; 860:2, s. 245-266
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Tidskriftsartikel (refereegranskat)abstract
- We add the Wess-Zumino-Witten term to the N = 3 massive nonlinear sigma model and study the leading logarithms in the anomalous sector. We obtain the leading logarithms to six loops for pi(0) -> gamma*gamma* and to five loops for y*pi pi pi. In addition we extend the earlier work on the mass and decay constant to six loops and the vector form factor to five loops. We present numerical results for the anomalous processes and the vector form factor. In all cases the series are found to converge rapidly. (C) 2012 Elsevier B.V. All rights reserved.
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| 5. |
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| 6. |
- Husek, Tomas, et al.
(författare)
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Radiative corrections to the η(') Dalitz decays
- 2018
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Ingår i: Physical Review D. - 2470-0010 .- 2470-0029. ; 97:9
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Tidskriftsartikel (refereegranskat)abstract
- We provide the complete set of radiative corrections to the Dalitz decays eta(()'()) -> l(+)l(-)gamma beyond the softphoton approximation, i. e., over the whole range of the Dalitz plot and with no restrictions on the energy of a radiative photon. The corrections inevitably depend on the eta(()'()) -> gamma*gamma(*) transition form factors. For the singly virtual transition form factor appearing, e.g., in the bremsstrahlung correction, recent dispersive calculations are used. For the one-photon-irreducible contribution at the one-loop level (for the doubly virtual form factor), we use a vector-meson-dominance-inspired model while taking into account the eta-eta' mixing.
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| 7. |
- Kadavy, Tomas, et al.
(författare)
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Contribution of QCD condensates to the OPE of Green functions of chiral currents
- 2019
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Ingår i: EPJ Web of Conferences. - : EDP Sciences. - 2100-014X. ; 199
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Tidskriftsartikel (refereegranskat)abstract
- A framework of operator product expansion (OPE) allows us to study high-energy behaviour of Green functions. A calculation of such Green functions within chiral perturbation theory (PT) or resonance chiral theory (RT) and subsequent matching of the result to the OPE enables us to determine constraints for unknown parameters of the effective theories. We present such procedure for Green functions in the odd-intrinsic parity sector of QCD.
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| 8. |
- Kampf, Karol, et al.
(författare)
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Analytical dispersive construction of eta -> 3 pi amplitude: First order in isospin breaking
- 2011
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Ingår i: Physical Review D (Particles, Fields, Gravitation and Cosmology). - 1550-2368. ; 84:11
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Tidskriftsartikel (refereegranskat)abstract
- Because of their small electromagnetic corrections, the isospin-breaking decays n -> 3 pi seem to be good candidates for extracting isospin-breaking parameters similar to(m(d) - m(u)). This task is unfortunately complicated by large chiral corrections and the discrepancy between the experimentally measured values of the Dalitz parameters describing the energy dependence of the amplitudes of these decays and those predicted from chiral perturbation theory. We present two methods based on an analytic dispersive representation that use the information from the NNLO chiral result and the one from the measurement of the charged n -> 3 pi decay by KLOE together in a harmonized way in order to determine the value of the quark mass ratio R. Our final result is R = 37.7 +/- 2.2. This value supplemented by values of m(s)/(m) over cap or even (m) over cap and m(s) from other methods (as sum-rules or lattice) enables us to obtain further quark mass characteristics. For instance the recent lattice value for m(s)/(m) over cap similar to 27: 5 leads to Q = 23.1 +/- 0.7. We also quote the corresponding values of the current masses m(u) and m(d).
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| 9. |
- Kampf, Karol
(författare)
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Odd sector of QCD
- 2011
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Ingår i: Nuclear Physics B Proceedings supplements. - : Elsevier BV. - 0920-5632. ; 219, s. 64-67
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Konferensbidrag (refereegranskat)abstract
- A systematic study of the odd-intrinsic parity sector of QCD is presented. We briefly describe different applications including pi(0) -> gamma gamma decay, muonic g -2 factor and test of new holographic conjectures.
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| 10. |
- Kampf, Karol
(författare)
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On decays of light unflavoured pseudoscalar mesons
- 2011
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Ingår i: 2nd International Workshop on the Physics of Fundamental Symmetries and Interactions (PSI). - : Elsevier BV. - 1875-3892. ; 17
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Konferensbidrag (refereegranskat)abstract
- The ongoing and planned experimental activities with direct reference to light unflavoured pseudoscalar mesons motivate a new theoretical study regarding their properties. An overview including details on new precise calculations is presented.
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