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Johan Bijnens

Publications and source records attributed to Johan Bijnens.

At least 91 records · Page 5Linked to original sources
arXiv2010

Vector Formfactors in Hard Pion Chiral Perturbation Theory

We use three-flavour hard pion Chiral Perturbation Theory (HPChPT) in both the heavy meson and a relativistic formulation to calculate the chiral logarithms $m^2\log(m^2/μ^2)$ contributing to the formfactors of the $B_{(s)}\rightarrow π,K,η$ and $D_{(s)}\rightarrow π,K,η$ transitions at momentum transfer $q^2$ away from the endpoint $q^2_\mathrm{max}=(m_B-m_M)^2$. We compare our results with CLEO $D\toπ$ and $D\to K$ data. We also calculate the Isgur-Wise function of the $B_{(s)}\rightarrow D_{(s)}$ semileptonic decay away from the endpoint and the chiral logarithms for the pion and kaon electromagnetic formfactor. In two-flavour HPChPT we calculate the chiral logarithms for the pion vector and the scalar formfactors at $s\gg m_π^2$. This allows us to test hard pion ChPT using the existing two-loop calculations for these quantities.

hep-ph↗
arXiv2010

Hard Pion Chiral Perturbation Theory for $B\toπ$ and $D\toπ$ Formfactors

We use one-loop Heavy Meson Chiral Perturbation Theory (HMCHPT) as well as a relativistic formulation to calculate the chiral logarithms $m^2_π\log{\left(m^2_π/μ^2\right)}$ contributing to the formfactors of the semileptonic $B\rightarrow π$ decays at momentum transfer $q^2$ away from $q^2_\mathrm{max}=(m_B-m_π)^2$. We give arguments why this chiral behavior is reliable even in the energy regime with hard or fast pions. These results can be used to extrapolate the formfactors calculated on the lattice to lower light meson masses.

hep-ph↗
arXiv2010

The Massive O(N) Non-linear Sigma Model at High Orders

We extend our earlier work on the massive $O(N)$ nonlinear sigma model to other observables. We derive expressions at leading order in the large $N$ expansion at all orders in the loop expansion for the decay constant, vacuum expectation value, meson-meson scattering and the scalar and vector form factors. This is done using cactus diagram resummation using a generalized gap equation and other recursion relations. For general $N$ we derive the expressions for the $n$-th loop order leading logarithms $\left(M^2/F^2\log(μ^2/M^2)\right)^n$, up to five-loops for the decay constant and vacuum expectation value (VEV) and up to four-loops for meson-meson scattering, the scalar and vector form factors. We also quote our earlier result for the mass. The large $N$ results do not give a good approximation for the case $N=3$. We use our results to study the convergence of the perturbative series and compare with elastic unitarity.

hep-ph↗
arXiv2009

Technicolor and other QCD-like theories at next-to-next-to-leading order

We calculate the vacuum-expectation-value, the meson mass and the meson decay constant to next-to-next-to-leading-order in the chiral expansion for QCD-like theories with general $N_F$ degenerate flavours for the cases with a complex representation, a real and a pseudoreal representation, i.e. with global symmetry and breaking patters $SU(N_F)_L\times SU(N_F)_R\to SU(N_F)_V$, $SU(2N_F)\to SO(2N)$ and $SU(2N_F)\to Sp(2N_F)$. These calculations should be useful for lattice calculations for dynamical electroweak symmetry breaking and related cases.

hep-ph↗
arXiv2009

Leading Logarithms in the Massive O(N) Nonlinear Sigma Model

We review Buchler and Colangelo's result that leading divergences at any loop order can be calculated using only one-loop calculations and we provide an alternative proof. We then use this method to calculate the leading divergences of and thus the leading logarithmic corrections to the meson mass in the massive O(N) nonlinear sigma model to five-loop order. We also calculate the all-loop result to leading order in the large $N$ expansion by showing that only cactus diagrams contribute and by summing these via a generalized gap equation.

hep-ph↗
arXiv2009

Chiral perturbation theory in the meson sector

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 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 $η\to3π$ and the arguments for the existence of a ``hard pion ChPT'' and its application to $K\to2π$.

hep-ph↗
arXiv2009

Determination of Low Energy Constants and testing Chiral Perturbation Theory at order $p^6$ (NNLO)

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 $K_{l4}$ decay which have been evaluated numerically using fit 10 in \cite{Amoros:2001cp} for the NLO LECs. We also show some preliminary results for a new global fit of the NLO LECs

hep-ph↗
arXiv2009

$K\toππ$ Decays in SU(2) Chiral Perturbation Theory

We study the decays $K\toππ$ in one-loop two-flavour Chiral Perturbation Theory. We provide arguments why the calculation of the coefficient of the pionic chiral logarithm $\logm = M^2\log M^2$ is unique and then perform the calculation. As a check we perform the reduction of the known three-flavour result. The underlying arguments are expected to be valid for heavier particles and other processes as well.

hep-ph↗
arXiv2009

Relations at Order $p^6$ in Chiral Perturbation Theory

We report on a search of relations valid at order $p^6$ in Chiral Perturbation Theory. We have found relations between $ππ$, $πK$ scattering, $K_{\ell4}$ decays, masses and decay constants and scalar and vector form factors. In this paper we give the relations and a first numerical check of them.

hep-ph↗
arXiv2009

Determination of Low Energy Constants and testing Chiral Perturbation Theory at Next to Next to Leading Order

We present the results of a search for relations between observables that are independent of the Chiral Pertubation 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 $K_{l4}$ decay which have been evaluated numerically using the old fit (fit 10 in [1] of the NLO LECs.

hep-ph↗
arXiv2009

Status of Strong ChPT

The present status of Chiral Perturbation Theory (ChPT) in the strong mesonic sector is discussed. A very short introduction to ChPT is followed by an overview of existing two-loop calculations and the determination of the Low-Energy-Constants (LECs). I discuss the case of $η\toπππ$ decays in somewhat more detail and finish by mentioning some recent work on partially quenched ChPT and on the renormalization group in ChPT.

hep-ph↗
arXiv2007

Isospin breaking in $Kπ$ vector form-factors for the weak and rare decays $K_{\ell3}$, $K\toπν\barν$ and $K\toπ\ell^+\ell^-$

We calculate the two form-factors for the four Kaon to pion transitions via a vector current to order $p^6$ in Chiral Perturbation Theory to first order in isospin breaking via the quark masses. In addition we derive relations between these form-factors valid to first order in the up-down quark-mass difference but to all orders in Chiral Perturbation Theory. We present numerical results for all eight form-factors at $t=0$ and for varying $t$ and for the scalar form-factors at the Callan-Treiman point.

hep-ph↗
arXiv2007

Eta and Eta' physics

This talk describes the reasons why $η$ and $η^\prime$ decays are an interesting topic of study for both theory and experiment. The main part discusses the results of the recent calculation of $η\to3π$ 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 $η$ and $η^\prime$ decays for studying the anomaly.

nucl-th↗
arXiv2007

$η\to 3 π$ at Two Loops In Chiral Perturbation Theory

We calculate the decay $η\to3π$ at next-to-next-to-leading order or order $p^6$ 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 $Q=23.2$.

hep-ph↗
arXiv2007

Quark Mass dependence at Two Loops for Meson Properties

This talks contains a short introduction to Chiral Perturbation Theory and the existing calculations to two-loop order in the mesonic sector. I include a discussion on which quantities the expansion can be organized in. The present best values of the Low-Energy-Constants as determined from continuum physics are given as well as the assumptions underlying the fits to experimental data. I present plots of masses, decay constants and $f_+(0)$ in $K_{\ell3}$ as a function of quark or meson masses. The talk ends with a list of things for which it would be extremely useful to have good results from lattice QCD calculations.

hep-lat↗
arXiv2007

Radiative and semileptonic decays in Chiral Perturbation Theory

I give a short overview of what has been done in radiative and semileptonic Kaon decays in Chiral Perturbation Theory. This includes for semileptonic decays the work which has been done to order $p^6$ including preliminary results of isospin breaking to that order in $K_{\ell3}$. For the radiative decays I mainly present some results from recent work concerning $K_{\ell3γ}$.

hep-ph↗
arXiv2007

The Hadronic Light-by-Light Contribution to the Muon Anomalous Magnetic Moment: Where do we stand?

We review the status of the hadronic light-by-light contribution to the muon anomalous magnetic moment and critically compare recent calculations. We also study in detail which momentum regions the pi^0 exchange main contribution originates. We also argue that a_μ^{light-by-light} = (11 \pm 4) \times 10^{-10} encompasses the present understanding of this contribution and comment on some directions to improve on that.

hep-ph↗