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     

Radiative effects in processes of diffractive vector meson electroproduction

The electromagnetic radiative correction to the cross section of the vector meson electroproduction is calculated. Explicit covariant formulae for the observed cross section are obtained. The dependence of the radiative correction on the experimental resolution and on the inelasticity cut is discussed. The FORTRAN code DIFFRAD, based on both exact (ultrarelativistic) and approximate sets of the formulae for the radiative correction to the cross section, is presented. Detailed numerical analysis for kinematical conditions of the recent experiments on the diffractive electroproduction of vector mesons is given. Received: 23 August 1998 / Published online: 15 April 1999     

Real time radiative corrections to charged particle decay laws

The real time exponential decay laws for meta-stable charged particles are shown to require radiative corrections. The methods employed are well known to be valid for radiatively correcting Breit-Wigner line shapes. Radiative corrections contribute substantially to precision life time measurements of muons and pions when initially stopped in condensed matter. Received: 21 February 1999 / Published online: 3 August 1999     

Laser influence on positron-antiproton radiative capture collision

The laser-assisted radiative capture between a positron and an antiproton is studied in detail. The theoretical results show that the cross-section for antihydrogen formation is significantly reduced with the application of a laser background. This effect is most marked when the laser polarization is parallelto the incident direction. Received: 13 November 1998 / Received in final form: 16 March 1999     

The low energy limit of the minimal nonlinear supersymmetric SU(5)-model; production and decay of Higgs particles

We consider the Higgssector in the low energy limit of the minimal nonlinear supersymmetric SU(5) model. We estimate radiative corrections to the Higgs masses using the effective potential. Furthermore Higgs boson decays are investigated and differences to the MSSM are discussed. Recieved: 28 October 1998 / Revised version: 17 December 1998 / Published online: 1 March 1999     

Screened-Coulomb ansatz for the nonfactorizable radiative corrections to off-shell W^+W^- production

We demonstrate that the results of the complete first-order calculation of the nonfactorizable QED corrections to the single-inclusive cross sections for fermions can be reproduced by a simple, physically motivated ansatz. The ansatz allows us to effectively take into account the screening role of the non-Coulomb radiative mechanisms by introducing a dampening factor in front of the width-dependent part of the known first-order Coulomb correction, the so-called screened-Coulomb ansatz. Received: 15 February 1999 / Published online: 18 June 1999     

Six-fermion production and Higgs boson physics at future e^+ e^- colliders

The six-fermion production processes , with all the lepton flavours and , relevant to the study of the intermediate-mass Higgs boson at future linear colliders are analysed. A Monte Carlo program, taking into account the whole set of tree-level scattering amplitudes and the relevant radiative effects, is developed to provide integrated cross-sections and generation of unweighted events. The complete calculation is compared with the available results of real Higgs production, and the opportunities of precision studies with event generation are discussed, demonstrating the relevance of a full six-fermion calculation. Numerical results for integrated cross-sections with various kinematical cuts and including radiative effects are given and commented. In the analysis of event samples, several distributions are studied and found to be sensitive to the presence and to the properties of the Higgs boson. Received: 20 December 1998 / Published online: 27 April 1999     

Alternative mass-shell renormalization for a minimal supersymmetric Higgs sector

An Aoki–Denner form of the renormalization scheme is suggested for the physical amplitudes in the minimal supersymmetric standard model. With the more explicit wave-function renormalization, the scheme is parameterized by the mass of the physical pseudoscalar () and the mass of heavy CP-even neutral Higgs () instead of the conventional , as input. The counterterm of is defined on mass shell perturbatively just within the Higgs sector. The renormalization of gauge-scalar mixings are fixed by proper Ward–Takahashi identities. The effect of the reparameterization is also probed to the radiative correction of the mass of the lightest Higgs. Received: 23 March 1999 / Published online: 16 November 1999     

Pion electroproduction in parity violating elastic ep scattering experiment

This study has been developed for electron-proton scattering experiments when only the scattered electrons are detected. Pion electroproduction on the proton including the cascade π⁰→ 2γ decay and the QED radiative corrections to elastic ep scattering are investigated. Our results are shown in the kinematical configuration of the parity violating electron scattering experiment planned at the Mainz Microtron (MAMI). Received: 20 April 1999 / Revised version: 4 June 1999     

Long-distance effects on the \mathrm{B}\to X_{\mathrm{s}}\gamma photon energy spectrum

We compute long-distance effects on the photon energy spectrum in inclusive radiative decays of B mesons using light-cone expansion and heavy-quark effective theory. We show that for sufficiently high photon energy, the leading nonperturbative QCD contribution is attributed to the distribution function. The distribution function is found to be universal in the sense that the same distribution function also encodes the leading nonperturbative contribution to inclusive semileptonic decays of B mesons at large momentum transfer. Some basic properties of the distribution function are deduced in QCD. Ways of extracting the distribution function directly from experiment and their implications are discussed. The theoretically clean methods for the determination of are described. Received: 7 June 1999 / Published online: 14 October 1999     

Straight-line path approximation for high energy elastic and inelastic scattering in quantum gravity

The asymptotic behavior of Planck energy elastic and inelastic amplitudes in quantum gravity is studied by means of the functional integration method. A straight-line path approximation is used to calculate the functional integrals which arise. Closed relativistically invariant expressions are obtained for the two “nucleons” elastic and inelastic amplitudes including the radiative corrections. Under the requirement of “softness” of the secondary gravitons a Poisson distribution for the number of particles emitted in the collision is found. Received: 6 December 1999 / Published online: 6 July 2000     

An efficient renormalization group improved implementation of the MSSM effective potential

In the context of MSSM, a novel improving procedure based on the renormalization group equation is applied to the effective potential in the Higgs sector. We focus on the one-loop radiative corrections computed in Landau gauge by using the mass independent renormalization scheme . Thanks to the decoupling theorem, the well-known multimass scale problem is circumvented by switching to a new effective field theory every time a new particle threshold is encountered. We find that, for any field configuration, there is a convenient renormalization scale at which the loop expansion respects the perturbation series hierarchy and the theory retains the vital property of stability. Received: 31 August 1999 / Revised version: 22 March 2000 / Published online: 23 October 2000     

Vacuum solutions of neutrino anomalies through a softly broken U(1) symmetry

We discuss an extended model which naturally leads to mass scales and mixing angles relevant for understanding both the solar and atmospheric neutrino anomalies in terms of the vacuum oscillations of the three known neutrinos. The model uses a softly broken –– symmetry and contains a heavy scale GeV. The –– symmetric neutrino masses solve the atmospheric neutrino anomaly while breaking of –– generates the highly suppressed radiative mass scale needed for the vacuum solution of the solar neutrino problem. All the neutrino masses in the model are inversely related to , thus providing seesaw-type of masses without invoking any heavy right-handed neutrinos. The possible embedding of the model into an SU(5) grand unified theory is discussed. Received: 5 August 1999 / Revised version: 18 November 1999 / Published online: 6 April 2000     

Photoluminescence in anatase titanium dioxide nanocrystals

Titanium dioxide (TiO₂) nanocrystals were prepared by a hydrolysis process of tetrabutyl titanate. X-ray diffraction and Raman scattering showed that the as-prepared TiO₂ nanocrystals have anatase structure of TiO₂, and that the monophase anatase nanocrystals can be achieved through a series of annealing treatments below 650 °C. We measured photoluminescence (PL) spectra of the TiO₂ nanocrystals. Under 2.41–2.71 eV laser irradiation, the TiO₂ nanocrystals displayed strong visible light emission with maxima of 2.15–2.29 eV even at excitation power as low as 0.06 W/cm². To identify the PL mechanism in the TiO₂ nanocrystals, the dependences of the PL intensity on excitation power and irradiation time were investigated. The experimental results indicated that the radiative recombination is mediated by localized levels related to surface defects residing in TiO₂ nanocrystallites. Received: 7 April 1999 / Revised version: 23 August 1999 / Published online: 30 November 1999     

Radiative return at $\Phi$ - and B-factories: FSR for muon pair production at next-to-leading order

Muon pair production through the radiative return is of importance for a measurement of the hadronic production cross section in two ways: it provides an independent calibration and it may give rise to an important background for the measurement of the pion form factor. With this motivation the Monte Carlo event generator PHOKHARA is extended to include next-to-leading order radiative corrections to the reaction . Furthermore, virtual ISR corrections to FSR from pions are introduced, which extends the applicability of the generator into a new kinematical regime. Finally, the effect of photon vacuum polarization is introduced into this new version of the generator.Received: 8 April 2004, Revised: 3 December 2004, Published online: 25 January 2005Work supported in part by BMBF under grant number 05HT9VKB0, EC 5th Framework Programme under contract HPRN-CT-2002-00311 (EURIDICE network), TARI project HPRI-CT-1999-00088, Polish State Committee for Scientific Research (KBN) under contract 2 P03B 017 24, BFM2002-00568, Generalitat Valenciana under grant GRUPOS03/013, and MCyT under grant FPA-2001-3031.     

Chiral Lagrangians and the Transition Amplitude for Radiative Muon Capture

 The transition operator for the radiative capture of mesons by protons is constructed starting from a chiral Lagrangian of the system obtained within the approach of hidden local symmetries. The transition operator is gauge invariant and its hadron radiative part satisfies exactly two relevant continuity equations. Received October 16, 1998; accepted for publication February 23, 1999     

Laser action in a cw diode-pumped Nd:Ca3Sc2Ge3O12 crystal

CW diode-pumped laser operation of Nd³⁺ in Ca₃Sc₂Ge₃O₁₂ (CaSGG) single garnet crystal has been demonstrated for the first time. We measured an 18% slope efficiency and 2.7-nm tunability with two different laser cavities. A spectroscopic characterization of our sample has also been performed including the absorption cross section in the 800-nm region and the emission cross section and radiative lifetime of the upper laser level. Received: 7 December 1999 / Revised version: 6 February 2000 / Published online: 27 April 2000     

Sensitivity of the Low-Energy p-d Capture Observables to the Nucleon-Nucleon Force Components

 Polarization observables in low-energy proton-deuteron radiative capture have been calculated using the Bonn-B nucleon-nucleon potential. Their sensitivity to the changes of the nucleon-nucleon force components has been studied. Modifications of these forces, which drastically diminished the permanent discrepancy between the data and theory for the vector-analyzing power in low-energy nucleon-deuteron elastic scattering, have only small effects on the pd capture observables. Received May 26, 1999; accepted for publication June 30, 1999     

Scanning of hadra]on cross section at DAΦNE by analysis of the initial-state radiative events

The initial-state radiative events in electron-positron annihilation into hadrons at DAΦNE are considered. The corresponding cross section with the full first-order radiative corrections is calculated. The analytical calculations take into account the actual angular acceptance and energy cutoff of the DAΦNE photon detector. Zh. éksp. Teor. Fiz. 69, No. 11, 769–775 (10 June 1999)