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Bastian Kubis

Publications and source records attributed to Bastian Kubis.

At least 109 records · Page 6Linked to original sources
arXiv2009

Cusps in eta' --> eta pi pi decays

The discovery of the cusp effect in the decay K+ --> pi+ pi0 pi0 has spurred the search for other decay channels, where this phenomenon, which is generated by strong final-state interactions, should also occur. A very promising candidate is eta' --> eta pi0 pi0. The cusp effect offers an excellent opportunity to experimentally extract pi pi S-Wave scattering lengths. We adapt and generalize the non-relativistic effective field theory framework developed for K --> 3 pi decays to eta' --> eta pi pi. The cusp effect is predicted to have an effect of more than 8 % on the decay spectrum below the pi+ pi- threshold. We also show that with our current theoretical information about eta' --> eta pi pi decays, it is not possible to extract pi eta threshold parameters.

hep-ph↗
arXiv2009

Electromagnetic effects in eta --> 3 pi

We re-evaluate the electromagnetic corrections to eta --> 3 pi decays at next-to-leading order in the chiral expansion, arguing that effects of order e^2(m_d-m_u) disregarded so far are not negligible compared to other contributions of order e^2 times a light quark mass. Despite the appearance of the Coulomb pole in eta --> pi+ pi- pi0 and cusps in eta --> 3 pi0, the overall corrections remain small.

hep-ph↗
arXiv2009

The cusp effect in eta' --> eta pi pi decays

Strong final-state interactions create a pronounced cusp in eta' --> eta pi0 pi0 decays. We adapt and generalize the non-relativistic effective field theory framework developed for the extraction of pi pi scattering lengths from K --> 3 pi decays to this case. The cusp effect is predicted to have an effect of more than 8% on the decay spectrum below the pi+ pi- threshold.

hep-ph↗
arXiv2009

Electromagnetic corrections in eta --> 3 pi decays

We re-evaluate the electromagnetic corrections to eta --> 3 pi decays at next-to-leading order in the chiral expansion, arguing that effects of order e^2(m_u-m_d) disregarded so far are not negligible compared to other contributions of order e^2 times a light quark mass. Despite the appearance of the Coulomb pole in eta --> pi+ pi- pi0 and cusps in eta --> 3 pi0, the overall corrections remain small.

hep-ph↗
arXiv2007

Hyperon decay form factors in chiral perturbation theory

We present a complete calculation of the SU(3)-breaking corrections to the hyperon vector form factors up to O(p^4) in covariant baryon chiral perturbation theory. Partial higher-order contributions are obtained, and we discuss chiral extrapolations of the vector form factor at zero momentum transfer. In addition we derive low-energy theorems for the subleading moments in hyperon decays, the weak Dirac radii and the weak anomalous magnetic moments, up to O(p^4).

hep-ph↗
arXiv2007

Investigation of a0-f0 mixing

We investigate the isospin-violating mixing of the light scalar mesons a0(980) and f0(980) within the unitarized chiral approach. Isospin-violating effects are considered to leading order in the quark mass differences and electromagnetism. In this approach both mesons are generated through meson-meson dynamics. Our results provide a description of the mixing phenomenon within a framework consistent with chiral symmetry and unitarity, where these resonances are not predominantly q q-bar states. Amongst the possible experimental signals, we discuss observable consequences for the reaction J/Psi -> phi pi0 eta in detail. In particular we demonstrate that the effect of a0-f0 mixing is by far the most important isospin-breaking effect in the resonance region and can indeed be extracted from experiment.

hep-ph↗
arXiv2006

T-odd correlations in radiative K_l3^+ decays and chiral perturbation theory

The charged kaon decay channel K_l3gamma^+ allows for studies of direct CP violation, possibly due to non-standard mechanisms, with the help of T-odd correlation variables. In order to be able to extract a CP-violating signal from experiment, it is necessary to understand all possible standard model phases that also produce T-odd asymmetries. We complement earlier studies by considering strong interaction phases in hadronic structure functions that appear at higher orders in chiral perturbation theory, and compare our findings to other potential sources of asymmetries.

hep-ph↗
arXiv2006

Aspects of radiative K^+_e3 decays

We re-investigate the radiative charged kaon decay K+- --> pi0 e+- nu_e gamma in chiral perturbation theory, merging the chiral expansion with Low's theorem. We thoroughly analyze the precision of the predicted branching ratio relative to the non-radiative decay channel. Structure dependent terms and their impact on differential decay distributions are investigated in detail, and the possibility to see effects of the chiral anomaly in this decay channel is emphasized.

hep-ph↗
arXiv2006

Isospin violation in the vector form factors of the nucleon

A quantitative understanding of isospin violation is an increasingly important ingredient for the extraction of the nucleon's strange vector form factors from experimental data. We calculate the isospin violating electric and magnetic form factors in chiral perturbation theory to leading and next-to-leading order respectively, and we extract the low-energy constants from resonance saturation. Uncertainties are dominated largely by limitations in the current knowledge of some vector meson couplings. The resulting bounds on isospin violation are sufficiently precise to be of value to on-going experimental studies of the strange form factors.

nucl-th↗
arXiv2006

Cusps in K --> 3 pi decays

The pion mass difference generates a pronounced cusp in K --> 3 pi decays. As has recently been pointed out by Cabibbo and Isidori, an accurate measurement of the cusp may allow one to pin down the S-wave pi pi scattering lengths to high precision. Here, we present and illustrate an effective field theory framework that allows one to determine the structure of this cusp in a straightforward manner. The strictures imposed by analyticity and unitarity are respected automatically.

hep-ph↗
arXiv2005

The Fubini-Furlan-Rosetti sum rule and related aspects in light of covariant baryon chiral perturbation theory

We analyze the Fubini-Furlan-Rosetti sum rule in the framework of covariant baryon chiral perturbation theory to leading one-loop accuracy and including next-to-leading order polynomial contributions. We discuss the relation between the subtraction constants in the invariant amplitudes and certain low-energy constants employed in earlier chiral perturbation theory studies of threshold neutral pion photoproduction off nucleons. In particular, we consider the corrections to the sum rule due to the finite pion mass and show that below the threshold they agree well with determinations based on fixed-t dispersion relations. We also discuss the energy dependence of the electric dipole amplitude E_{0+}.

nucl-th↗
arXiv2002

Analysis of the pion-kaon sigma-term and related topics

We calculate the one-loop contributions to the difference Δ_{πK} between the isoscalar on-shell pion-kaon scattering amplitude at the Cheng-Dashen point and the scalar form factor Γ_K (2M_π^2) in the framework of three flavor chiral perturbation theory. These corrections turn out to be small. This is further sharpened by treating the kaons as heavy fields (two flavor chiral perturbation theory). We also analyze the two-loop corrections to the kaon scalar form factor based on a dispersive technique. We find that these corrections are smaller than in the comparable case of the scalar form factor of the pion. This is related to the weaker final state interactions in the pion-kaon channel.

hep-ph↗
arXiv2001

Isospin violation in pion-kaon scattering

We consider strong and electromagnetic isospin violation in near-threshold pion-kaon scattering. At tree level, such effects are small for all physical channels. We work out the complete one-loop corrections to the process pi^- K^+ -> pi^0 K^0. They come out rather small. We also show that the corresponding radiative cross section is highly suppressed at threshold.

hep-ph↗
arXiv2001

Isospin violation in low-energy charged pion-kaon scattering

We evaluate the isospin breaking corrections to the scattering amplitude π^- K^+ -> π^- K^+ at threshold in the framework of chiral perturbation theory. This channel is of particular interest for the strong 2S-2P energy level shift in pion-kaon bound states. While a prediction of this level shift is hampered by a large uncertainty in the isoscalar scattering length, we find only a moderate uncertainty of about 3% in the electromagnetic corrections which are relevant for the extraction of the scattering lengths from experiment

hep-ph↗
arXiv2001

Virtual photons in the pion form factors and the energy-momentum tensor

We evaluate the vector and scalar form factor of the pion in the presence of virtual photons at next-to-leading order in two-flavor chiral perturbation theory. We also consider the scalar and tensor pion form factors of the energy-momentum tensor. We find that the intrinsic electromagnetic corrections are of the expected size for the vector form factor and very small for the charged pion scalar form factor. Detector resolution independent photon corrections reduce the vector radius by about one percent. The scalar radius of the neutral pion is reduced by two percent by isospin-breaking contributions. We perform infrared regularization by considering electron-positron annihilation into pions and the decay of a light Higgs boson into a pion pair. We discuss the detector resolution dependent contributions to the various form factors and pion radii.

hep-ph↗