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1.	Bernard, Claude, et al. (författare) Twisted finite-volume corrections to Kl3 decays with partially-quenched and rooted-staggered quarks 2017 Ingår i: Journal of High Energy Physics. - 1029-8479. ; 2017:3 Tidskriftsartikel (refereegranskat)abstract The determination of \|Vus\| from kaon semileptonic decays requires the value of the form factor f+(q2 = 0) which can be calculated precisely on the lattice. We provide the one-loop partially quenched chiral perturbation theory expressions both with and without including the effects of staggered quarks for all form factors at finite volume and with partially twisted boundary conditions for both the vector current and scalar density matrix elements at all q2. We point out that at finite volume there are more form factors than just f+ and f− for the vector current matrix element but that the Ward identity is fully satisfied. The size of the finite-volume corrections at present lattice sizes is small. This will help improve the lattice determination of f+(q2 = 0) since the finite-volume error is the dominant error source for some calculations. The size of the finite-volume corrections may be estimated on a single lattice ensemble by comparing results for various twist choices.
2.	Bijnens, Johan, et al. (författare) Chiral perturbation theory at finite volume and/or with twisted boundary conditions 2016 Ingår i: Proceedings of Science. ; Part F128557 Konferensbidrag (refereegranskat)abstract In this talk we discuss a number of ChPT calculations relevant for lattice QCD. These include the finite volume corrections at two-loop order for masses and decay constants. The second part is about hadronic vacuum polarization where we present the two-loop ChPT estimate for the disconnected and strange quark contributions. We also present the finite volume corrections at two-loop order. The final part is the one-loop finite volume with twisted boundary conditions contribution to f+(q2) and the full K&3 amplitude.
3.	Bijnens, Johan, et al. (författare) Connected, disconnected and strange quark contributions to HVP 2016 Ingår i: Journal of High Energy Physics. - 1029-8479. ; 2016:11 Tidskriftsartikel (refereegranskat)abstract We calculate all neutral vector two-point functions in Chiral Perturbation Theory (ChPT) to two-loop order and use these to estimate the ratio of disconnected to connected contributions as well as contributions involving the strange quark. We extend the ratio of −1/10 derived earlier in two flavour ChPT at one-loop order to a large part of the higher order contributions and discuss corrections to it. Our final estimate of the ratio disconnected to connected is negative and a few % in magnitude.
4.	Bijnens, Johan, et al. (författare) Constraining general two Higgs doublet models by the evolution of Yukawa couplings 2012 Ingår i: Journal of High Energy Physics. - 1029-8479. ; :5 Tidskriftsartikel (refereegranskat)abstract We study how general two Higgs doublet models can be constrained by considering their properties under renormalization group evolution of the Yukawa couplings. We take into account both the appearance of a Landau pole as well as off-diagonal Yukawa couplings leading to flavour changing neutral currents in violation with experimental constraints at the electroweak scale. We find that the latter condition can be used to limit the amount of Z(2) symmetry breaking allowed in a given model.
5.	Bijnens, Johan, et al. (författare) Constraining general two Higgs doublet models by the evolution of Yukawa couplings 2012 Ingår i: Proceedings of Science. Konferensbidrag (refereegranskat)abstract We analyse the constraints of the general two Higgs doublet models by evolving the Yukawa coupling constants to high energy under renormalization group. We consider the appearance of a Landau pole or large off-diagonal Yukawa couplings which cause tree level flavour changing neutral currents. Our study shows the latter condition can be used to answer how much Z 2 symmetry breaking can be allowed in a given 2HDM model.
6.	Bijnens, Johan, et al. (författare) Masses, decay constants and electromagnetic form-factors with twisted boundary conditions 2014 Ingår i: Journal of High Energy Physics. - 1029-8479. ; :5 Tidskriftsartikel (refereegranskat)abstract Using Chiral Perturbation Theory at one-loop we analyze the consequences of twisted boundary conditions. We point out that due to the broken Lorentz and reflection symmetry a number of unexpected terms show up in the expressions. We explicitly discuss the pseudo-scalar octet masses, axial-vector and pseudo-scalar decay constants and electromagnetic form-factors. We show how the Ward identities are satisfied using the momentum dependent masses and the non-zero vacuum-expectation-values values for the electromagnetic (vector) currents. Explicit expressions at one-loop are provided and an appendix discusses the needed one-loop twisted finite volume integrals.
7.	Bijnens, Johan, et al. (författare) Pion light-by-light contributions to the muon g − 2 2016 Ingår i: Journal of High Energy Physics. - 1029-8479. ; 2016:9 Tidskriftsartikel (refereegranskat)abstract This paper contains some new results on the hadronic light-by-light contribution (HLbL) to the muon g − 2. The first part argues that we can expect large effects from disconnected diagrams in present and future calculations by lattice QCD of HLbL. The argument is based on the dominance of pseudo-scalar meson exchange. In the second part, we revisit the pion loop HLbL contribution to the muon anomalous magnetic moment. We study it in the framework of some models studied earlier, pure pion loop, full VMD and hidden local symmetry for inclusion of vector mesons. In addition we study possible ways to include the axial-vector meson. The main part of the work is a detailed study of how the different momentum regions contribute. We derive a short distance constraint on the γγ → ππ amplitude and use this as a constraint on the models used for the pion loop. As a byproduct we present the general result for integration using the Gegenbauer polynomial method.
8.	Bijnens, Johan, et al. (författare) Scalar kinetic mixing and the renormalization group 2019 Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 792, s. 238-243 Tidskriftsartikel (refereegranskat)abstract Quantum field theories containing scalar fields with equal quantum numbers allow for a mixed kinetic term in the Lagrangian. It has been argued that this mixing must be taken into consideration when performing renormalization group (RG) analyses of such a theory. However, from the fact that scalar kinetic mixing does not correspond to a physical observable, we show that no extra parameters need to be introduced. Using a toy model, we explicitly derive the 1-loop RG equations (RGEs) in three different renormalization schemes to demonstrate how this issue can be dealt with. In schemes without kinetic mixing, either the fields mix during renormalization to produce non-diagonal anomalous dimensions or the RGEs explicitly depend on the scalar masses. Finally, we show how the different schemes are related to each other by scale dependent field redefinitions.
9.	Bijnens, Johan, et al. (författare) Vector two-point functions in finite volume using partially quenched chiral perturbation theory at two loops 2017 Ingår i: Journal of High Energy Physics. - 1029-8479. ; 2017:12 Tidskriftsartikel (refereegranskat)abstract We calculate vector-vector correlation functions at two loops using partially quenched chiral perturbation theory including finite volume effects and twisted boundary conditions. We present expressions for the flavor neutral cases and the flavor charged case with equal masses. Using these expressions we give an estimate for the ratio of disconnected to connected contributions for the strange part of the electromagnetic current. We give numerical examples for the effects of partial quenching, finite volume and twisting and suggest the use of different twists to check the size of finite volume effects. The main use of this work is expected to be for lattice QCD calculations of the hadronic vacuum polarization contribution to the muon anomalous magnetic moment.
10.	Relefors, Johan, et al. (författare) Masses, decay constants and electromagnetic form-factors with twisted boundary conditions 2015 Ingår i: Proceedings of Science. - 1824-8039. ; 29-June-2015 Tidskriftsartikel (refereegranskat)abstract We discuss some of the effects of twisted boundary conditions in finite volume using continuum SU(3) Chiral Perturbation Theory. We point out how broken cubic symmetry affects the definitions of quantities such as form-factors. Using the π+ as an example, we give one loop results for the mass, decay constants and electromagnetic form-factor and illustrate how the relevant Ward identities are satisfied.
11.	Alvarez, Benjamin, et al. (författare) NNLO positivity bounds on chiral perturbation theory for a general number of flavours 2022 Ingår i: Journal of High Energy Physics. - 1029-8479. ; 2022:3 Tidskriftsartikel (refereegranskat)abstract We present positivity bounds, derived from the principles of analyticity, unitarity and crossing symmetry, that constrain the low-energy constants of chiral perturbation theory. Bounds are produced for 2, 3 or more flavours in meson-meson scattering with equal meson masses, up to and including next-to-next-to-leading order (NNLO), using the second and higher derivatives of the amplitude. We enhance the bounds by using the most general isospin combinations posible (or higher-flavour counterparts thereof) and by analytically integrating the low-energy range of the discontinuities. In addition, we present a powerful and general mathematical framework for efficiently managing large numbers of positivity bounds.
12.	Alvarez, Benjamin, et al. (författare) NNLO Positivity Bounds on χPT for a General Number of Flavours 2024 Ingår i: Proceedings of Science. ; 413 Konferensbidrag (refereegranskat)abstract We present positivity bounds, derived from the principles of analyticity, unitarity and crossing symmetry, that constrain the low-energy constants of chiral perturbation theory. Bounds are produced for 2, 3 or more flavours with equal meson masses, up to and including next-to-next-to-leading order (NNLO), using the second and higher derivatives of the amplitude. We enhance the bounds by using the most general isospin combinations posible (or higher-flavour counterparts thereof) and by analytically integrating the low-energy range of the amplitude. In addition, we present a powerful and general mathematical framework for efficiently managing large numbers of positivity bounds.
13.	Ananthanarayan, B., et al. (författare) An analytic analysis of the pion decay constant in three-flavoured chiral perturbation theory 2017 Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 77:7 Tidskriftsartikel (refereegranskat)abstract A representation of the two-loop contribution to the pion decay constant in SU(3) chiral perturbation theory is presented. The result is analytic up to the contribution of the three (different) mass sunset integrals, for which an expansion in their external momentum has been taken. We also give an analytic expression for the two-loop contribution to the pion mass based on a renormalized representation and in terms of the physical eta mass. We find an expansion of Fπ and Mπ2 in the strange-quark mass in the isospin limit, and we perform the matching of the chiral SU(2) and SU(3) low-energy constants. A numerical analysis demonstrates the high accuracy of our representation, and the strong dependence of the pion decay constant upon the values of the low-energy constants, especially in the chiral limit. Finally, we present a simplified representation that is particularly suitable for fitting with available lattice data.
14.	Ananthanarayan, B., et al. (författare) An analytic approach to sunset diagrams in chiral perturbation theory : Theory and practice 2016 Ingår i: European Physical Journal A. - : Springer Science and Business Media LLC. - 1434-6001 .- 1434-601X. ; 52:12 Tidskriftsartikel (refereegranskat)abstract We demonstrate the use of several code implementations of the Mellin-Barnes method available in the public domain to derive analytic expressions for the sunset diagrams that arise in the two-loop contribution to the pion mass and decay constant in three-flavoured chiral perturbation theory. We also provide results for all possible two mass configurations of the sunset integral, and derive a new one-dimensional integral representation for the one mass sunset integral with arbitrary external momentum. Thoroughly annotated Mathematica notebooks are provided as ancillary files in the Electronic Supplementary Material to this paper, which may serve as pedagogical supplements to the methods described in this paper.
15.	Ananthanarayan, B., et al. (författare) Analytic representation of FK /Fπ in two loop chiral perturbation theory 2018 Ingår i: Physical Review D. - 2470-0010. ; 97:9 Tidskriftsartikel (refereegranskat)abstract We present an analytic representation of FK/Fπ as calculated in three-flavor two-loop chiral perturbation theory, which involves expressing three mass scale sunsets in terms of Kampé de Fériet series. We demonstrate how approximations may be made to obtain relatively compact analytic representations. An illustrative set of fits using lattice data is also presented, which shows good agreement with existing fits.
16.	Ananthanarayan, B., et al. (författare) Analytic representations of mK, FK, mη, and Fη in two loop SU (3) chiral perturbation theory 2018 Ingår i: Physical Review D. - 2470-0010. ; 97:11 Tidskriftsartikel (refereegranskat)abstract In this work, we consider expressions for the masses and decay constants of the pseudoscalar mesons in SU(3) chiral perturbation theory. These involve sunset diagrams and their derivatives evaluated at p2=mP2 (P=π, K, η). Recalling that there are three mass scales in this theory, mπ, mK and mη, there are instances when the finite part of the sunset diagrams do not admit an expression in terms of elementary functions, and have therefore been evaluated numerically in the past. In a recent publication, an expansion in the external momentum was performed to obtain approximate analytic expressions for mπ and Fπ, the pion mass and decay constant. We provide fully analytic exact expressions for mK and mη, the kaon and eta masses, and FK and Fη, the kaon and eta decay constants. These expressions, calculated using Mellin-Barnes methods, are in the form of double series in terms of two mass ratios. A numerical analysis of the results to evaluate the relative size of contributions coming from loops, chiral logarithms as well as phenomenological low-energy constants is presented. We also present a set of approximate analytic expressions for mK, FK, mη and Fη that facilitate comparisons with lattice results. Finally, we show how exact analytic expressions for mπ and Fπ may be obtained, the latter having been used in conjunction with the results for FK to produce a recently published analytic representation of FK/Fπ.
17.	Baeza-Ballesteros, Jorge, et al. (författare) The isospin-3 three-particle K-matrix at NLO in ChPT 2023 Ingår i: Journal of High Energy Physics. - 1029-8479. ; 2023:5 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.
18.	Baeza-Ballesteros, Jorge, et al. (författare) The three-pion K-matrix at NLO in ChPT 2024 Ingår i: Journal of High Energy Physics. - 1029-8479. ; 2024:3 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.
19.	Baeza-Ballesteros, Jorge, et al. (författare) Three-pion scattering : From the chiral Lagrangian to the lattice 2023 Ingår i: Nuclear and Particle Physics Proceedings. - 2405-6014. 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.
20.	Bernard, C., et al. (författare) Semileptonic kaon decay in staggered chiral perturbation theory 2014 Ingår i: Physical Review D (Particles, Fields, Gravitation and Cosmology). - 1550-2368. ; 89:5 Tidskriftsartikel (refereegranskat)abstract The determination of vertical bar V-us vertical bar from kaon semileptonic decays requires the value of the form factor f(+)(q(2) = 0), which can be calculated precisely on the lattice. We provide the one-loop partially quenched staggered chiral perturbation theory expressions that may be employed to analyze staggered simulations of f(+)(q(2)) with three light flavors. We consider both the case of a mixed action, where the valence and sea sectors have different staggered actions, and the standard case, where these actions are the same. The momentum transfer q(2) of the form factor is allowed to have an arbitrary value. We give results for the generic situation where the u, d, and s quark masses are all different, N-f = 1 + 1 + 1, and for the isospin limit, N-f = 2 + 1. The expression we obtain for f(+)(q(2)) is independent of the mass of the ( valence) spectator quark. In the limit of vanishing lattice spacing, our results reduce to the one-loop continuum partially quenched expression for f(+)(q(2)), which has not previously been reported in the literature for the N-f = 1 + 1 + 1 case. Our expressions have already been used in staggered lattice analyses of f(+)(0) and should prove useful in future calculations as well.
21.	Bijnens, Johan, et al. (författare) 2-loop short-distance constraints for the g − 2 HLbL 2022 Ingår i: Nuclear and Particle Physics Proceedings. - : Elsevier BV. - 2405-6014. ; 318-323, s. 182-186 Tidskriftsartikel (refereegranskat)abstract The recent experimental measurement of the muon g−2 at Fermilab National Laboratory, at a 4.2σ tension with the Standard Model prediction, highlights the need for further improvements on the theoretical uncertainties associated to the hadronic sector. In the framework of the operator product expansion in the presence of a background feld, the short-distance behaviour of the hadronic light-by-light contribution was recently studied. The leading term in this expansion is given by the massless quark-loop, which is numerically dominant compared to non-perturbative corrections. Here, we present the perturbative QCD correction to the massless quark-loop and estimate its size numerically. In particular, we fnd that for scales above 1 GeV it is relatively small, in general roughly −10% the size of the massless quark-loop. The knowledge of these short-distance constraints will in the future allow to reduce the systematic uncertainties in the Standard Model prediction of the hadronic light-by-light contribution to the g−2.
22.	Bijnens, Johan, et al. (författare) A new global fit of the L(i)(r) at next-to-next-to-leading order in Chiral Perturbation Theory 2012 Ingår i: Nuclear Physics, Section B. - : Elsevier BV. - 0550-3213. ; 854:3, s. 631-665 Tidskriftsartikel (refereegranskat)abstract Abstract in Undeterminednew fit is done to obtain numerical values for the order p(4) low-energy-constants L(i)(r) in Chiral Perturbation Theory. This includes both new data and new calculated observables. We take into account masses, decay constants, K(l4), pi pi and pi K scattering lengths and slopes and the slope of the pion scalar formfactor. We compare in detail where the changes w.r.t. the 10 years old "fit 10" come from. We discuss several scenarios for estimating the order p(6) constants C(i)(r) and search for possible values of them that provide a good convergence for the ChPT series. We present two such sets. One big change is that the fits do not have the expected behaviour in the limit of large N(c) as well as before. (C) 2011 Elsevier B.V. All rights reserved.
23.	Bijnens, Johan, et al. (författare) Analytical results for hadronic contributions to the muon g−2 2019 Ingår i: European Physical Society Conference on High Energy Physics (EPS-HEP2019). - Trieste, Italy : Sissa Medialab. - 1824-8039. ; 364 Konferensbidrag (refereegranskat)abstract This talk discusses two analytical calculations relevant for the Standard Model calculation of the muon g−2. The first part is the recent derivation of the quark-loop as the first term in a well-defined operator-product expansion for the short-distance part of the hadronic light-by-light contribution, as well as the calculation of the next term. The second part is the calculation of finite volume effects relevant for lattice QCD calculations of the electromagnetic contribution to the lowest-order hadronic vacuum-polarization contribution and the proof they only start at 1/L3
24.	Bijnens, Johan (författare) Chiral dynamics in the meson sector at two loops 2003 Ingår i: AIP Conference Proceedings. - : AIP. - 0094-243X .- 1551-7616. ; 698, s. 407-410 Konferensbidrag (refereegranskat)abstract I give a very short introduction to chiral perturbation theory and an overview of the next-to-next-to-leading order three-flavour calculations done. I discuss those relevant for an improvement in the accuracy of the measurement of Vus in more detail. One major conclusion is that all needed p6 low energy constants can be obtained from experiment via the scalar form-factor in Kl3 decays
25.	Bijnens, Johan (författare) Chiral Lagrangians 2002 Ingår i: INTERNATIONAL JOURNAL OF MODERN PHYSICS A. - 0217-751X. ; 17:23, s. 3154-3169 Konferensbidrag (refereegranskat)abstract An overview of the field of Chiral Lagrangians is given. This includes Chiral Perturbation Theory and resummations to extend, it to higher energies, applications to the muon anomalous magnetic moment, epsilon(1)/epsilon and others.
26.	Bijnens, Johan, et al. (författare) Chiral limit prediction for ε′/K/εK at NLO in 1/Nc 2001 Ingår i: Nuclear Physics B - Proceedings Supplements. - 0920-5632. ; 96:1-3, s. 354-363 Tidskriftsartikel (refereegranskat)abstract We report on a calculation of ε′K/εK at next-to-leading in the 1/Nc expansion and to lowest order in Chiral Perturbation Theory. We discuss the short-distance matching, the scale and scheme dependence as well as the long-distance short-distance matching. We include the two known chiral corrections to our result and discuss further order p4 corrections to it.
27.	Bijnens, Johan (författare) Chiral meson physics at two loops 2005 Ingår i: AIP Conference Proceedings. - : AIP. - 1551-7616 .- 0094-243X. ; 768, s. 153-159 Konferensbidrag (refereegranskat)abstract An overview of chiral perturbation theory calculations in the mesonic sector at the two loop level is given. Discussed in some detail are the partially quenched case relevant for lattice QCD, the general fitting procedures and ππ, πK scattering as well as the determination of Vus and K13 decays
28.	Bijnens, Johan (författare) Chiral perturbation theory and mesons 2012 Ingår i: Proceedings of Science. - 1824-8039. ; 2012-August Tidskriftsartikel (refereegranskat)abstract The talk contains a short introduction to mesonic Chiral Perturbation Theory (ChPT). In addition four disparate areas where some progress has been made in recent years are discussed. These are the last fit of the order p4 low-energy-constants Lri to data, hard pion ChPT, the recent twoloop work on EFT for QCD like theories and the high order leading logarithm calculations in the massive O(N) nonlinear sigma model.
29.	Bijnens, Johan, et al. (författare) Chiral perturbation theory at two loops and the measurement of V(us) 2003 Ingår i: XXXVIII Rencontres de Moriond. ; , s. 313-316 Konferensbidrag (refereegranskat)abstract I give an overview of the calculations done in three-flavour Chiral perturbation theory at next-to-next-to-leading order with an emphasis on those relevant for an improvement in the accuracy of the measurement of Vus. It is pointed out that all needed low energy constants can be obtained from experiment via the scalar form-factor in Kl3 decays
30.	Bijnens, Johan (författare) Chiral perturbation theory beyond one loop 2006 Ingår i: Progress in Particle and Nuclear Physics. - : Elsevier BV. - 1873-2224 .- 0146-6410. ; 58:2, s. 521-586 Forskningsöversikt (refereegranskat)abstract The existing Chiral Perturbation Theory (ChPT) calculations at order p6 are reviewed. The principles of ChPT and how they are used are introduced. The main part is a review of the two- and three-flavour full two-loop calculations and their comparison with experiment. We restrict the discussion to the mesonic purely strong and semileptonic sector. The review concludes by mentioning the existing results in finite volume, finite temperature and partially quenched ChPT
31.	Bijnens, Johan, et al. (författare) Chiral perturbation theory for neutron–antineutron oscillations 2017 Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 77:12 Tidskriftsartikel (refereegranskat)abstract We construct the Chiral Perturbation Theory operators for neutron–antineutron oscillations and use these to estimate chiral and finite volume corrections at one-loop order.
32.	Bijnens, Johan (författare) Chiral perturbation theory in the meson sector 2009 Ingår i: Proceedings of science. ; 86 Konferensbidrag (refereegranskat)abstract The present status of Chiral Perturbation Theory in the meson sector is discussed concentrating on recent developments. This write-up contains short discussions on a listing of a few historical papers, the principles behind ChPT, two-flavour ChPT including some comments about the Pion polarizability, three-flavour ChPT with a discussion of the recently found relations as tests of ChPT and preliminary results of a new fit of the NLO low-energy-constants (LECs). It discusses somewhat deeper η → 3π and the arguments for the existence of a “hard Pion ChPT” and its application to K → 2π.
33.	Bijnens, Johan, et al. (författare) Chiral symmetry and charmonium decays to two pseudoscalars 2011 Ingår i: European Physical Journal A. Hadrons and Nuclei. - : Springer Science and Business Media LLC. - 1434-6001. ; 47:11 Tidskriftsartikel (refereegranskat)abstract We apply hard pion Chiral Perturbation Theory to charmonium decays to pi pi, KK and eta eta. We first discuss why we expect to be able to provide results for the chiral logarithms in chi(c0) and chi(c2) decays to two pseudoscalars while for the decays from J/psi, psi(nS) and chi(c1) no simple prediction is possible. The leading chiral logarithm turns out to be absent for chi(c0), chi(c2) -> PP. This result is true for all fully chiral singlet states of spin zero and two.
34.	Bijnens, Johan (författare) CHIRON: a package for ChPT numerical results at two loops 2015 Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 75:1 Tidskriftsartikel (refereegranskat)abstract This document describes the package CHIRON which includes two libraries, chironitself and jbnumlib. chiron is a set of routines useful for two-loop numerical results in chiral perturbation theory (ChPT). It includes programs for the needed one-and two-loop integrals as well as routines to deal with the ChPT parameters. The present version includes everything needed for the masses, decay constants and quark-antiquark vacuum-expectation-values. An added routine calculates consistent values for the masses and decay constants when the pion and kaon masses are varied. In addition a number of finite volume results are included: one-loop tadpole integrals, two-loop sunset integrals and the results for masses and decay constants. The numerical routine library jbnumlib contains the numerical routines used in chiron. Many are to a large extent simple C++ versions of routines in the CERNLIB numerical library. Notable exceptions are the dilogarithm and the Jacobi theta function implementations. This paper describes what is included in CHIRON v0.50.
35.	Bijnens, Johan (författare) ChPT loops for the lattice : Pion mass and decay constant, HVP at finite volume and nn̄ -oscillations 2018 Ingår i: EPJ Web of Conferences. - : EDP Sciences. - 2101-6275 .- 2100-014X. ; 175 Tidskriftsartikel (refereegranskat)abstract I present higher loop order results for several calculations in Chiral perturbation Theory. 1) Two-loop results at finite volume for hadronic vacuum polarization. 2) A three-loop calculation of the pion mass and decay constant in two-flavour ChPT. For the pion mass all needed auxiliary parameters can be determined from lattice calculations of ππ-scattering. 3) Chiral corrections to neutron-anti-neutron oscillations.
36.	Bijnens, Johan, et al. (författare) Comment on the pion pole part of the light-by-light contribution to the muon g-2 2002 Ingår i: Nuclear Physics, Section B. - 0550-3213. ; 626:1-2, s. 410-411 Tidskriftsartikel (refereegranskat)abstract We comment on the recent calculations of the pion pole part of the light-by-light contribution to the muon anomalous magnetic moment and we point out where the analysis in our previous work was mistaken.
37.	Bijnens, Johan, et al. (författare) Constraints on the hadronic light-by-light in the Melnikov-Vainshtein regime 2023 Ingår i: Journal of High Energy Physics. - 1029-8479. ; 2023:2 Tidskriftsartikel (refereegranskat)abstract The muon anomalous magnetic moment continues to attract attention due to the possible tension between the experimentally measured value and the theoretical Standard Model prediction. With the aim to reduce the uncertainty on the hadronic light-by-light contribution to the magnetic moment, we derive short-distance constraints in the Melnikov-Vainshtein regime which are useful for data-driven determinations. In this kinematical region, two of the four electromagnetic currents are close in the four-point function defining the hadronic light-by-light tensor. To obtain the constraints, we develop a systematic operator product expansion of the tensor in question to next-to-leading order in the expansion in operators. We evaluate the leading in αs contributions and derive constraints for the next-to-leading operators that are also valid nonperturbatively.
38.	Bijnens, Johan, et al. (författare) Decay Constants of Pseudoscalar Mesons to Two Loops in Three-Flavor Partially Quenched ChPT 2005 Ingår i: Physical Review D (Particles, Fields, Gravitation and Cosmology). - 1550-2368. ; 71:9 Tidskriftsartikel (refereegranskat)abstract This paper presents a first study of the decay constants of the charged, or flavor-off-diagonal, pseudoscalar mesons to two loops for three flavors of sea quarks, in Partially Quenched Chiral Perturbation Theory (PQChPT). Explicit analytical expressions up to order p6 in the momentum expansion are given. The calculations have been performed within the supersymmetric formulation of PQChPT. We also present some numerical results to indicate the size of the corrections.
39.	Bijnens, Johan (författare) Decays of eta and eta ' and what can we learn from them? 2006 Ingår i: Acta Physica Slovaca. - 0323-0465. ; 56:3, s. 305-317 Tidskriftsartikel (refereegranskat)abstract A short overview of eta and eta' decays is given with an emphasis on what can be learned for the strong interaction from them. The talk consists of a short introduction to Chiral Perturbation Theory, a discussion of eta -> 3 pi beyond p(4) and some of the physics involved in eta' -> eta pi pi, 3 pi as well as an overview of anomalous processes.
40.	Bijnens, Johan, et al. (författare) Determination of Low Energy Constants and testing Chiral Perturbation Theory at Next to Next to Leading Order 2009 Ingår i: Proceedings of Science. ; PoS(EFT09):032 Konferensbidrag (refereegranskat)abstract We present the results of a search for relations between observables that are independent of the Chiral Perturbation Theory (ChPT) Next-to-Next-to-Leading Order (NNLO) Low-Energy Constants (LECs). We have found some relations between observables in $\pi\pi$, $\pi K$ scattering and $K_{l4}$ decay which have been evaluated numerically using the old fit (fit 10 in~\cite{Amoros:2001cp}) of the NLO LECs.
41.	Bijnens, Johan, et al. (författare) Determination of low energy constants and testing chiral perturbation theory at order p6 (NNLO) 2009 Ingår i: Proceedings of Science. ; 86 Konferensbidrag (refereegranskat)abstract We present the results of a search for relations between observables that are independent of the Chiral Perturbation Theory (ChPT) Next-to-Next-to-Leading Order (NNLO) Low-Energy Constants (LECs). We have found some relations between observables in ππ, πK scattering and Kl4 decay which have been evaluated numerically using fit 10 in [1] for the NLO LECs. We also show some preliminary results for a new global fit of the NLO LECs.
42.	Bijnens, Johan, et al. (författare) Electromagnetic corrections in partially quenched chiral perturbation theory 2007 Ingår i: Physical Review D (Particles, Fields, Gravitation and Cosmology). - 1550-2368. ; 75:1 Tidskriftsartikel (refereegranskat)abstract We introduce photons in partially quenched chiral perturbation theory and calculate the resulting electromagnetic loop-corrections at next-to-leading-order (NLO) for the charged meson masses and decay constants. We also present a numerical analysis to indicate the size of the different corrections. We show that several phenomenologically relevant quantities can be calculated consistently with photons which couple only to the valence quarks, allowing the use of gluon configurations produced without dynamical photons.
43.	Bijnens, Johan, et al. (författare) Electromagnetic finite-size effects to the hadronic vacuum polarization 2019 Ingår i: Physical Review D - Particles, Fields, Gravitation and Cosmology. - 2470-0010. ; 100:1 Tidskriftsartikel (refereegranskat)abstract In order to reduce the current hadronic uncertainties in the theory prediction for the anomalous magnetic moment of the muon, lattice calculations need to reach subpercent accuracy on the hadronic-vacuum-polarization contribution. This requires the inclusion of O(α) electromagnetic corrections. The inclusion of electromagnetic interactions in lattice simulations is known to generate potentially large finite-size effects suppressed only by powers of the inverse spatial extent. In this paper we derive an analytic expression for the QEDL finite-volume corrections to the two-pion contribution to the hadronic vacuum polarization at next-to-leading order in the electromagnetic coupling in scalar QED. The leading term is found to be of order 1/L3 where L is the spatial extent. A 1/L2 term is absent since the current is neutral and a photon far away thus sees no charge and we show that this result is universal. Our analytical results agree with results from the numerical evaluation of loop integrals as well as simulations of lattice scalar U(1) gauge theory with stochastically generated photon fields. In the latter case the agreement is up to exponentially suppressed finite-volume effects. For completeness we also calculate the hadronic vacuum polarization in infinite volume using a basis of 2-loop master integrals.
44.	Bijnens, Johan (författare) $\eta$ and $\eta'$ Physics 2008 Konferensbidrag (refereegranskat)abstract This talk describes the reasons why $\eta$ and $\eta^\prime$ decays are an interesting topic of study for both theory and experiment. The main part discusses the results of the recent calculation of $\eta\to3\pi$ at two-loop order in ChPT. Some puzzling aspects of the results compared to earlier dispersive calculations are highlighted. I also like to remind the reader of the use of $\eta$ and $\eta^\prime$ decays for studying the anomaly.
45.	Bijnens, Johan, et al. (författare) Eta decays at and beyond p(4) in Chiral Perturbation Theory 2002 Ingår i: PHYSICA SCRIPTA. - 0031-8949 .- 1402-4896. ; 99, s. 34-44 Konferensbidrag (refereegranskat)abstract An overview is given of Chiral Perturbation Theory and various applications to eta decays. In particular. the main decay eta --> 3pi is discussed at the one-loop level, and estimates of the higher order corrections are given. The importance of p(6) and higher order effects in double Dalitz and eta --> pi(0)gammagamma decays is pointed out. In all these cases the need for new experimental results is stressed.
46.	Bijnens, Johan, et al. (författare) eta Mass and NNLO three-flavor partially quenched chiral perturbation theory 2006 Ingår i: Physical Review D (Particles, Fields, Gravitation and Cosmology). - 1550-2368. ; 74:5 Tidskriftsartikel (refereegranskat)abstract We show how to resum neutral propagators to all orders in partially quenched chiral perturbation theory. We calculate the relevant quantities to next-to-next-to-leading order (NNLO). Using these results we show how to extend the proposal by Sharpe and Shoresh for determining the parameters relevant for the eta mass from partially quenched lattice QCD calculations to NNLO.
47.	Bijnens, Johan, et al. (författare) eta to 3 pi at Two Loops In Chiral Perturbation Theoryeta to 3 pi at Two Loops In Chiral Perturbation Theory 2007 Ingår i: Journal of High Energy Physics. - : Springer Science and Business Media LLC. - 1029-8479. ; 0711 Tidskriftsartikel (refereegranskat)abstract We calculate the decay eta to3 pi at next-to-next-to-leading order or order p6 in Chiral Perturbation Theory. The corrections are somewhat larger than was indicated by dispersive estimates. We present numerical results for the Dalitz plot parameters, the ratio r of the neutral to charged decay and the total decay rate. In addition we derive an inequality between the slope parameters of the charged and neutral decay. The experimental charged decay rate leads to central values for the isospin breaking quantities R=42.2 and Q=23.2.
48.	Bijnens, Johan, et al. (författare) Exploring light-cone sum rules for pion and kaon form factors 2002 Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 26:1, s. 67-79 Tidskriftsartikel (refereegranskat)abstract We analyze the higher-twist effects and the SU(3)-flavor symmetry breaking in the correlation functions used to calculate form factors of pseudoscalar mesons in the QCD light-cone sum rule approach. It is shown that the Ward identities for these correlation functions yield relations between twist-4 two-and three-particle distribution amplitudes. In addition to the relations already obtained from the QCD equations of motions, we have found a new one. With the help of these relations, the twist-4 contribution to the light-cone sum rule for the. pion electromagnetic form factor: is reduced to a very simple form. Simultaneously, we correct a sign error in an earlier calculation. The updated light-cone sum rule prediction for the pion form factor at intermediate momentum transfers is compared with the recent Jefferson Lab data. Furthermore, from the correlation functions with strange-quark currents the kaon electromagnetic form factor and the K --> pi weak transition form factors are predicted with O(m(s)) similar to O(m(K)(2)) accuracy.
49.	Bijnens, Johan, et al. (författare) Finite volume and partially quenched QCD-like effective field theories 2015 Ingår i: Journal of High Energy Physics. - 1029-8479. ; :11 Tidskriftsartikel (refereegranskat)abstract We present a calculation of the meson masses, decay constants and quark-antiquark vacuum expectation value for the three generic QCD-like chiral symmetry breaking patterns SU(N-F) x SU(N-F) -> SU(N-F)(V), SU(N-F) -> SO(N-F) and SU(2N(F)) -> Sp(2N(F)) in the effective field theory for these cases. We extend the previous two-loop work to include effects of partial quenching and finite volume. The calculation has been performed using the quark flow technique. We reproduce the known in finite volume results in the unquenched case. The analytical results can be found in the supplementary material. Some examples of numerical results are given. The numerical programs for all cases are included in version 0.54 of the CHIRON package. The purpose of this work is the use in lattice extrapolations to zero mass for QCD-like and strongly interacting Higgs sector lattice calculations.
50.	Bijnens, Johan, et al. (författare) Finite volume at two-loops in chiral perturbation theory 2015 Ingår i: Journal of High Energy Physics. - 1029-8479. ; :1 Tidskriftsartikel (refereegranskat)abstract We calculate the finite volume corrections to meson masses and decay constants in two and three flavour Chiral Perturbation Theory to two-loop order. The analytical results are compared with the existing result for the pion mass in two-flavour ChPT and the partial results for the other quantities. We present numerical results for all quantities.

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