The double radiative annihilation of the heavy-light fermion bound states

We consider the double-radiative decays of heavy-light QED and QCD atoms, $\mu^+ e^- \to \gamma\gamma$ and $\bar{B}^{0}_s \to \gamma\gamma$. Especially, we take under scrutiny contributions coming from operators that vanish on the free-quark mass shell. We show that by field redefinitions these operators are converted into contact terms attached to the bound state dynamics. A net off-shell contribution is suppressed with respect to the effect of the well known flavour-changing magnetic-moment operator by the bound-state binding factor. The negligible off-shellness of the weakly bound QED atoms becomes more relevant for strongly bound QCD atoms. We analyze this off-shellness in model-approaches to QCD, one of them enabling us to keep close contact to the related effect in QED. We also comment on the off-shell effect in the corresponding process $\bar{B}_d \to K^* \gamma$, and discuss possible hindering of the claimed beyond-standard-model discovery in this decay mode.Comment: 24 pages, 5 figures; to be published in Fizika

Nucleon strangeness as the response to a strangeness-sensitive probe in a class of hadron models

On top of its valence quarks, the full nucleon ground state may contain appreciable admixture of s-\bar{s} pairs already at small momentum transfers. This paper discusses strangeness in the mean-field type of nucleon models, and exemplifies this by explicit calculations in the MIT bag model enriched by the presence of instantons. We calculate the instanton contribution to the strangeness in the MIT bag (on top of the standard contribution to strangeness found in that model). Although we do it in an essentially perturbative way, we present a detailed derivation of the formula expressing nucleon matrix elements of bilinear strange quark operators, in terms of a model valence nucleon state and interactions producing quark-antiquark fluctuations on top of that valence state. We do it in detail to clarify our argument that in the context of the mean-field type of quark models (where a Fock state expansion exists and where the nucleon state can be constructed out of single-quark states), the resulting formula acquires a significance beyond perturbation theory.The derivation combines the usage of the evolution operator containing a strangeness source, and Feynman-Hellmann theorem.Comment: LaTeX2e, 34 pages, 4 figures (included

On Distinguishing Non-Standard Interactions from Radiative Corrections in Neutrino-Electron Scattering

We present a contribution of higher order to neutrino-electron scattering that is a charged-current counterpart of both the anomalous axial-vector triangle and possible non-standard interaction contributions. It arises in the standard model with massive neutrinos, and renormalizes the nondiagonal axial-vector form-factor at low energies. We show that, due to the small size of radiative corrections, the neutrino-electron scattering still provides a discovery potential for some of the non-standard neutrino interactions proposed in the literature.Comment: 9 pages, 3 figures, change in title and context of the consideration, results of radiative corrections unchange

Stranost nukleona kao odziv na strano-osjetljivu probu u jednoj klasi hadronskih modela

On top of its valence quarks, the full nucleon ground state may contain appreciable admixture of ss¯ pairs already at small momentum transfers. This paper discusses strangeness in the mean–field type of nucleon models, and exemplifies this by explicit calculations in the MIT bag model enriched by the presence of instantons. We calculate the instanton contribution to the strangeness in the MIT bag (on top of the standard contribution to strangeness found in that model). Although we do it in an essentially perturbative way, we present a detailed derivation of the formula expressing nucleon matrix elements of bilinear strange quark operators, in terms of a model valence nucleon state and interactions producing quark-antiquark fluctuations on top of that valence state. We do it in detail to clarify our argument that in the context of the mean–field type of quark models (where a Fock state expansion exists and where the nucleon state can be constructed out of singlequark states), the resulting formula acquires a significance beyond perturbation theory. The derivation combines the usage of the evolution operator containing a strangeness source, and Feynman-Hellmann theorem.Pored valentnih kvarkova, cjelovito osnovno stanje nukleona može sadržavati znatnu primjesu parova ss¯ već pri malim prijenosima impulsa. Ovdje raspravljamo stranost u modelu nukleona sa srednjim poljem i provodimo eksplicitne račune u MIT modelu vreće uz prisutnost instantona. Računamo doprinos instantona stranosti u MIT vreći (povrh standardnog doprinosa stranosti u tom modelu). Iako se u biti primjenjuje račun smetnje, izlažemo podroban izvod izraza za nuklearne matrične elemente bilinearnih operatora stranih kvarkova, preko modelnog stanja valentnog nukleona i medudjelovanja koja tvore fluktuacije kvark-antikvark povrh onih od valentnog stanja. To se radi podrobno kako bismo objasnili da konačan izraz, dobiven u okviru kvarkovskih modela sa srednjim poljem (kada postoji Fockov razvoj i nukleonsko se stanje može složiti od jednokvarkovskih stanja), prelazi okvire računa smetnje. Primjenjuje se evolucijski operator koji sadrži izvore stranosti i FeynmanHellmannov teorem