The $\gamma \gamma \rightarrow H^0 H^0$ decay in non-commutative quantum electrodynamics

We study the possibility of detecting non-commutative QED through neutral Higgs boson pair production at a collider. This is based on the assumption that H⁰ interacts directly with the photon as suggested by symmetry considerations. The sensitivity of the cross-section to the non-commutative scale and the Higgs mass is investigated. Received: 28 August 2002 / Revised version: 15 November 2002 / Published online: 19 February 2003     

Testing non-commutative QED \gamma\gamma\gamma and \gamma\gamma\gamma\gamma couplings at LHC

In this work, we investigate the sensitivity of the process at LHC for the photonic 3- and 4-point functions that appear in non-commutative QED. We show that this process serves to study the behavior of the space-space as well as of the space-time non-commutativity. We also show that this process can probe the non-commutative scale in the range of a few TeV.Received: 9 February 2004, Revised: 27 February 2004, Published online: 8 April 2004     

Radiative corrections to the decay H^+ \to W^+ A^0

Full one-loop electroweak corrections to the on-shell decay are computed in the framework of models with two Higgs doublets (THDM). Such a decay may be dominant for over a wide range of parameter space relevant at present and future colliders. We show that the corrections may approach 40% and in particular are sensitive to , which parameterizes the discrete symmetry breaking term. We suggest that a measurement of the branching ratio of may offer a possibility of measuring the magnitude of . Received:17 July 2000 / Revised version: 28 February 2001 / Published online: 3 May 2001     

The process\pi ^0 \to \lambda _\gamma \bar \lambda _\gamma as an alternative to\pi ^0 \to v\bar v

The process \(\pi ^0 \to \lambda _\gamma \bar \lambda _\gamma \) is investigated as an alternative to \(\pi ^0 \to v\bar v\) . It is shown that the experimental bound on the branching fraction for missing energy (in the form of \(\lambda _\gamma \bar \lambda _\gamma \) and/or \(v\bar v\) ) may be understood in terms of \(\pi ^0 \to \lambda _\gamma \bar \lambda _\gamma \) for the kinematically allowed photino mass, if the squark mass is >8 GeV.     

Yukawa coupling corrections to the decay H^+ \to W^+ A^0

We compute the fermionic radiative contributions to the decay in the framework of models with two Higgs doublets (2HDM), for the case of an on-shell and off-shell W. We show that, in the majority of the cases, current measurements of the parameter suggest and such decays could invalidate current charged Higgs searches or aid detection in the region . We find that the radiative corrections may approach 50% for small values of . Received: 22 April 1999 / Published online: 10 December 1999     

The reaction e^ + e^ - \to \gamma \pi ^0 \to \gamma v\overline v as a probe of neutrino mass

The reaction $e^ + e^ - \to \gamma \pi ^0 \to \gamma v\overline v $ is considered. It is shown that this reaction possesses a clear signature, producing in the resonance region practically monochromatic photons, which can easily be distinguished from background bremsstrahlung photons. Since the cross section of the reaction is proportional to the square of the neutrino mass, such a reaction can be used as a probe for neutrino mass.     

The \gamma \gamma \to \gamma \gamma process in the standard and SUSY models at high energies

We study the helicity amplitudes of the process at high energy, which in the standard and SUSY models first arise at the one-loop order. In the standard model (SM), the diagrams involve , charged-quark, and lepton loops, while in SUSY, we also have contributions from chargino-, charged-sfermion, and Higgs-loop diagrams. The SUSY contributions are most important in the region above the threshold for producing the supersymmetric partners; there, they interfere most effectively with the primarily imaginary SM amplitudes. Simple expressions for the relevant one-loop functions are given which provide a direct overview of the behaviour of the helicity amplitudes in the whole parameter space at high energies. The various characteristics of a large set of observables are studied in detail. Received: 3 February 1999 / Pulished online: 30 June 1999     

The \phi \to \gamma (a_0 (980) + f_0 (980)) \to \gamma {\rm K}\bar {\rm K} decays

We study the decay φ → γK ⁺ K ^? taking into account the scalar meson production φ → γ(a ₀+f ₀ → γK ⁺ K ^? and the final-state radiation. We note that the relative sign between the final-state radiation amplitude and the scalar-meson production amplitude is fixed in the K ⁺ K ^? loop model which describes data on the φ → γf ₀ → γππ and φ → γa ₀ → γπη decays. As consequence, this model predicts the definite interference between the final-state radiation and the scalar resonance production amplitudes. We calculate the mass spectra of the φ → γK ⁺ K ^? decay and the differential cross sections for $e^ + e^ - \to \phi \to \gamma {\rm K}^0 \bar {\rm K}^0 $ reactions.     

Towards a model-independent determination of the $\phi\to \gamma f_0$ coupling

A guide to the composition of the enigmatic f ₀(980) and a ₀(980) states is their formation in -radiative decays. Precision data are becoming available from the KLOE experiment at the DA NE machine at Frascati, as well as results from SND and CMD-2 at VEPP-2M at Novosibirsk. We show how the coupling of the f ₀(980) to this channel can be extracted from these, independently of the background provided by production. To do this we use the fact that the behaviour of both the f ₀(980) and cannot be determined by these data alone, but is strongly constrained by experimental results from other hadronic processes as required by unitarity. We find that the resulting coupling for the is GeV with a background that is quite unlike that assumed if unitarity is neglected. This provides an object lesson in how unitarity teaches us to add resonances. Not surprisingly the result is crucially dependent on the pole position of the f ₀(980), for which there are still sizeable uncertainties. At present this leads to an uncertainty in the branching ratio which can only be fixed by further precision data on the f ₀(980). Nevertheless, the is now the same order of magnitude as the experimental .Received: 25 March 2003, Published online: 5 September 2003