\tau\rightarrow\omegA3\pi\nu decays

A theoretical study of the anomalous decay mode is presented. The theoretical value of the branching ratio of agrees well with the data. The branching ratio of is predicted. It is found that the vertices of and play a dominant role in these two decay modes. CVC is satisfied, and there is no adjustable parameter. Received: 30 July 2001 / Published online: 21 November 2001     

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     

B\to \pi \rho, \pi \omega decays in perturbative QCD approach

We calculate the branching ratios and CP-asymmetries for , and decays, in the perturbative QCD approach. In this approach, we calculate non-factorizable and annihilation type contributions, in addition to the usual factorizable contributions. Our result is in agreement with the branching ratio of , measured by the CLEO and BABAR collaborations. We also predict large CP-asymmetries in these decays. These channels are useful to determine the CKM angle . Received: 5 November 2001 / Published online: 8 February 2002     

\left\langle {:\bar \psi \psi :} \right\rangle and three-point functions in QCD

We calculate the coefficients of to leading order in _s in the operator product expansion of the fundamental three-point functions of QCD in the deep Euclidean region. We demonstrate that these coefficients satisfy the Ward identities.Supported by BMFT 0233 REB4     

Three-body baryonic $\overline B\to \Lambda \bar p \pi$ decays and such

We study the decay rates and spectra of , , , , and modes in the factorization approach. The baryon pairs are produced through vector, axial vector, scalar and pseudoscalar operators. Previous predictions, including ours, are an order of magnitude too small compared to experiment. By incorporating QCD counting rules and studying the asymptotic behavior, we find an earlier relation between the pseudoscalar and axial vector form factors to be too restrictive. Instead, the pseudoscalar and scalar form factors are related asymptotically. Following this approach, the measured rate () and spectrum can be understood, and should be dominantly left-hand polarized, while we expect . These results and other predictions can be checked soon. Received: 27 February 2003 / Published online: 5 May 2003     

CP violation in \Lambda_b \to p \pi^- decay

Using the next-to-leading order QCD corrected effective Hamiltonian, scale and scheme independent Wilson coefficients, we have estimated the branching ratio and CP violating asymmetries for the decay mode in the Standard Model using the framework of generalized factorization. The effects of nonfactorizable contributions are taken into account by treating the effective no. of colors as a free parameter. The form factors are evaluated in the nonrelativistic quark model. The estimated branching ratio is found to be which lies below the current experimental upper limit and the CP violating asymmetries are and . Received: 15 February 2000 / Published online: 8 June 2000     

The exclusive B_s\rightarrow \phi \ell^+ \ell^- decay in the two Higgs doublet models

We study the differential branching ratio, the branching ratio and the forward-backward asymmetry for exclusive decay in the two Higgs doublet model. We analyze the dependences of these quantities on the model parameters and show that these observables are highly sensitive to new physics and hence may provide a powerful probe of the SM and beyond. Received: 27 March 2002 / Revised version: 3 July 2002 / Published online: 20 September 2002 RID="a" ID="a" e-mail: gurerk@newton.physics.metu.edu.tr RID="b" ID="b" e-mail: gsevgur@metu.edu.tr     

Gluonic penguin contribution to B \rightarrow \pi \pi decays

We use the light-cone sum rule technique to calculate the contribution of the gluonic penguin operator O _8g to the decay of the B-meson to two pions. Leading-order perturbative and non-perturbative corrections are included, corresponding to hard and soft exchanged gluons, respectively. While the overall contribution of this operator to the decay is small as expected before, we find that the so-called soft-gluon part of this contribution is of the order of the hard-gluon one. This implies that the inclusion of soft gluons in the calculation of matrix elements may be important.Received: 30 September 2002, Published online: 22 October 2003PACS: 13.25.Hw Hadronic decays of mesons: Decays of bottom mesons - 11.55.Hx Sum rules     

Determination of radiative widths of scalar mesons from experimental results on \gamma\gamma\to\pi\pi

The scalar mesons in the 1 GeV region constitute the Higgs sector of the strong interactions. They are responsible for the masses of all light flavour hadrons. However, the composition of these scalar states is far from clear, despite decades of experimental effort. The two photon couplings of the 's are a guide to their structure. Two photon results from Mark II, Crystal Ball and CELLO prompt a new Amplitude Analysis of , cross-sections. Despite their currently limited angular coverage and lack of polarized photons, we use a methodology that provides the nearest one can presently achieve to a model-independent partial wave separation. We find two distinct classes of solutions. Both have very similar two photon couplings for the and . Hopefully these definitive results will be a spur to dynamical calculations that will bring us a better understanding of these important states. Received: 10 Decmeber 1998 / Published online: 27 April 1999     

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     

A kinematically complete measurement of K^+ \to \pi^+ \pi^0 \pi^0 decays

In a kinematically complete setting, the decays of stopped were measured. In the frame work of the Weinberg polynomial expansion, the coefficients up to quadratic terms were deduced. The results are in good agreement with previous measurements and consistent with CP conservation expectations. The empirical rule is violated. Received: 16 October 1999 / Published online: 27 January 2000     

\mu\rightarrow e\gamma decay in the left-right supersymmetric model

We calculate the dipole amplitude for the decay and related processes in the left-right supersymmetric model when parity breaking occurs at a considerably large scale. The low-energy flavor violation in the model originates either from the nonvanishing remnants of the left-right symmetry in the slepton mass matrix or from the direct flavor changing lepton-slepton-neutralino interaction. The result is found to be large and already accessible with current experimental accuracy for supersymmetric masses not far above the electroweak scale. It also provides nontrivial constraints on the lepton mixing in the model. Received: 8 June 1998 / Published online: 15 October 1998     

\pi\pi correlations in \gamma + A reactions

Preliminary differential cross-sections of the reactions and with A = ¹ H, ¹² C, and ^nat Pb are presented. A significant nuclear-mass dependence of the invariant-mass distribution is found in the channel. The dependence is not observed in the channel. The in-medium observation in the channel is consistent with an in-medium modification of the interaction in the I = J = 0 channel, changing width and pole position of a resonant state.Received: 30 September 2002, Published online: 22 October 2003PACS: 13.60.Le Meson production - 21.65. + f Nuclear matterJ.G. Messchendorp: For the TAPS and A2 Collaborations     

The \gamma \gamma \to Z Z process and the search for virtual SUSY effects at a \gamma \gamma Collider

We study the helicity amplitudes of the process in the Standard Model at high energy. These amplitudes receive contributions from the W and charged quark and lepton loops, analogous to those encountered in the cases studied before. But also receives contributions from the Higgs s-channel poles involving the effective Higgs- vertex. At energies , the amplitudes in all three processes are mainly helicity-conserving and almost purely imaginary; which renders them a very useful tool in searching for New Physics. As an example, a SUSY case is studied, and the signatures due to the virtual effects induced by a chargino-, charged slepton- or a lightest stop-loop in , are explored. These signatures, combined with the analogous ones in and , should help identifying the nature of possible New Physics particles. Received: 3 September 1999 / Published online: 3 February 2000     

Partial wave analysis of $\bar pp \to \bar \Lambda \Lambda$

A partial wave analysis of PS185 data for is presented. A ³ S ₁ cusp is identified in the inverse process at threshold, using detailed balance to deduce cross sections from . Partial wave amplitudes for ³ P ₀, ³ F ₃, ³ D ₃ and ³ G ₃ exhibit a behaviour very similar to resonances observed in Crystal Barrel data. With this identification, the data then provide evidence for a new I = 0, J ^PC = 1^- resonance with mass MeV, MeV, coupling to both ³ S ₁ and ³ D ₁.Received: 4 June 2004, Published online: 9 July 2004     

\sigma-\omega model and compressible bag model

Compressible bag model is formulated on the basis of lagrangian field theory. A specific application is done in conjunction with - model. The results are similar to Chin-Walecka model and almost reproduce our previous results. The effective nucleon mass does not become so small owing to the compressibility, in contrast to Chin-Walecka model. Received: 12 May 1998 / Revised version: 9 July 1998 / Published online: 8 September 1998     

Multi-ring signatures of the oscillation $\nu_\mu \rightarrow \nu_e$ in a water Cherenkov detector

Multi-ring signatures of appearance via the oscillation are formulated for a water Cherenkov detector. These signatures are appropriate for long-baseline neutrino experiments operating at relatively high neutrino energies GeV that emphasize the matter effect. The NC background is less for selected multi-ring events than for 1e-like events, and may be directly estimated from the data. Our results suggest that best sensitivity to and to the sign of can be reached with baselines over some 6000 km.Received: 14 April 2003, Revised: 19 June 2003, Published online: 26 September 2003M.A. Kubantsev: Now at Department of Physics and Astronomy, Northwestern University, Evanston, IL 60208, USA     

Analyticity of \eta \pi isospin-violating form factors and the \tau \rightarrow \eta \pi \nu second-class decay

We consider the evaluation of the \(\eta \pi \) isospin-violating vector and scalar form factors relying on a systematic application of analyticity and unitarity, combined with chiral expansion results. It is argued that the usual analyticity properties do hold (i.e. no anomalous thresholds are present) in spite of the instability of the \(\eta \) meson in QCD. Unitarity relates the vector form factor to the \(\eta \pi \rightarrow \pi \pi \) amplitude: we exploit progress in formulating and solving the Khuri–Treiman equations for \(\eta \rightarrow 3\pi \) and in experimental measurements of the Dalitz plot parameters to evaluate the shape of the \(\rho \) -meson peak. Observing this peak in the energy distribution of the \(\tau \rightarrow \eta \pi \nu \) decay would be a background-free signature of a second-class amplitude. The scalar form factor is also estimated from a phase dispersive representation using a plausible model for the \(\eta \pi \) elastic scattering \(S\) -wave phase shift and a sum rule constraint in the inelastic region. We indicate how a possibly exotic nature of the \(a_0(980)\) scalar meson manifests itself in a dispersive approach. A remark is finally made on a second-class amplitude in the \(\tau \rightarrow \pi \pi \nu \) decay.     

The processes \gamma\gamma\to Z H in SM and MSSM

The process first arises at the one loop level, and as such it provides us with remarkable tests of the structure of the electroweak Higgs sector. These tests are complementary to those in the gauge sector involving . We show that in the standard model (SM) where , as well as in the supersymmetric case where or , observables exist (like e.g. the energy dependence, angular distribution, photon polarization dependence or final Z polarization) which present rather spectacular properties. Such properties involve strong threshold effects with steps, bumps or peaks, reflecting the type of Higgs and heavy quarks and chargino masses and couplings predicted by the SM and supersymmetric models. Received: 13 March 2001 / Published online: 13 June 2001