Discrete Ambiguities in the Measurement of the Weak Phase Gamma

Several time-independent methods have been devised for measuring the phase gamma of the Cabibbo-Kobayashi-Maskawa unitarity triangle. It is shown that such measurements generally suffer from discrete ambiguity which is at least 8-fold, not 4-fold as commonly stated. This has serious experimental implications, which are explored in methods involving B->DK decays. The measurement sensitivity and new physics discovery potential are estimated using a full Monte Carlo detector simulation with realistic background estimates.Comment: 15 pages, 2 figures, fixed typ

Polarized Single Top Production at Leptonic Colliders from Broken R Parity Interactions Incorporating CP Violation

The contribution from the R parity violating interactions in the associated production of a top quark with a charm antiquark is examined for high energy leptonic colliders. We concentrate on the reactions associated with the semileptonic top decay. A set of characteristic dynamical distributions for the signal events is evaluated and the results contrasted against those from the standard model W-boson pair production background. Next, we turn to a study of a CP-odd observable, associated with the top spin, which leads to an asymmetry in the energy distribution of the emitted charged leptons for the pair of CP-conjugate final states, $b \bar l \nu \bar c$ and $\bar b l \bar \nu c$. A non vanishing asymmetry arises from a CP-odd phase, embedded in the R parity violating coupling constants, through interference terms between the R parity violating amplitudes at both the tree and loop levels.Comment: revtex file. 17 pages. 7 postscript figures. 1 table. The revised version includes an estimate of experimental uncertainties. Submitted to Phys. Rev.

The exclusive \bar{B} --> \pi e^+ e^- and \bar{B} --> \rho e^+ e^- decays in the two Higgs doublet model with flavor changing neutral currents

We calculate the leading logarithmic QCD corrections to the matrix element of the decay b --> d e^+ e^- in the two Higgs doublet model with tree level flavor changing currents (model III). We continue studying the differential branching ratio and the CP violating asymmetry for the exclusive decays B --> \pi e^+ e^- and B --> \rho e^+ e^- and analysing the dependencies of these quantities on the selected model III parameters, \xi^{U,D}, including the leading logarithmic QCD corrections. Further, we present the forward-backward asymmetry of dileptons for the decay B --> \rho e^+ e^- and discuss the dependencies to the model III parameters. We observe that there is a possibility to enhance the branching ratios and suppress the CP violating effects for both decays in the framework of the model III. Therefore, the measurements of these quantities will be an efficient tool to search the new physics beyond the SM.Comment: 27 pages, 14 Figure

Spin relaxation dynamics of radical-pair processes at low magnetic fields

We report measurements of room-temperature spin-relaxation times $T_1$ and $T_2$ of charge-carrier spins in a $\pi$-conjugated polymer thin film under bipolar injection and low (1\mbox{ mT}\lesssim B_0\lesssim 10\mbox{ mT}) static magnetic fields, using electrically detected magnetic resonant Hahn-echo and inversion-recovery pulse sequences. The experiments confirm the correlation between the magnetic-field sensitive observables of radical-pair processes, which include both the spin-dependent recombination currents in organic semiconductors and the associated spin-relaxation times when random local hyperfine fields and external magnetic fields compete in magnitude. Whereas a striking field dependence of spin-lattice relaxation exists in the low-field regime, the apparent spin decoherence time remains field independent as the distinction between the two is lifted at low fields.Comment: Manuscript: 14 pages, 4 figures; Supplemental Material: 13 pages, 7 figure

Extracting Weak Phase Information from B -> V_1 V_2 Decays

We describe a new method for extracting weak, CP-violating phase information, with no hadronic uncertainties, from an angular analysis of B -> V_1 V_2 decays, where V_1 and V_2 are vector mesons. The quantity $\sin^2 (2\beta + \gamma)$ can be cleanly obtained from the study of decays such as B_d^0(t) -> D^{*\pm} \rho^\mp, D^{*\pm} a_1^{\mp}, D^{*0} K^{*0}, etc. Similarly, one can use B_s^0(t) -> D_s^{*\pm} K^{*\mp} to extract $\sin^2 \gamma$. There are no penguin contributions to these decays. It is possible that $\sin^2 (2\beta + \gamma)$ will be the second function of CP phases, after $\sin 2\beta$, to be measured at B-factories.Comment: 4 pages, RevTeX, no figure

Three-photon electron spin resonances

We report the observation of a three-photon resonant transition of charge-carrier spins in an organic light-emitting diode using electrically detected magnetic resonance (EDMR) spectroscopy at room temperature. Under strong magnetic-resonant drive (drive field $B_1$ ~ static magnetic field $B_0$), a $B_0$-field swept EDMR line emerges when $B_0$ is approximately threefold the one-photon resonance field. Ratios of drive-induced shifts of this line to those of two- and one-photon shifts agree with analytical expressions derived from the Floquet Hamiltonian and confirm the nature of these three-photon transitions, enabling access of spin physics to a hitherto inaccessible domain of quantum mechanics.Comment: 32 pages, 18 figure

B-> K photon photon via intermediate eta'

We examine our previous conjecture that the eta' intermediate resonance has the dominant role in the long distance contributions to B decay into two photons and a strange final state hadron. We calculate the branching ratio of the exclusive B-> K eta'-> K photon photon decay using the nonspectator mechanism for eta' production in charmless hadronic B decays. It is shown that the obtained branching ratio B^eta'(B-> K\gamma\gamma)~ 8.7 X 10^{-7} is more than twice as large as the eta_c contribution to this decay mode.Comment: 6 pages, latex, no figure

Top quark electric and chromo electric dipole moments in the general two Higgs Doublet model

We study the electric and chromo electric dipole moment of top quark in the general two Higgs Doublet model (model III). We analyse the dependency of this quantity to the new phases coming from the complex Yukawa couplings and masses of charged and neutral Higgs bosons. We observe that the electric and chromo elecric dipole moments of top quark are at the order of 10^{-21} e cm and 10^{-20} g_s cm, which are extremely large values compared to ones calculated in the SM and also two Higgs Doublet model with real Yukawa couplings.Comment: 9 pages,10 figure

Single decay-lepton angular distributions in polarized e+e- --> t tbar and simple angular asymmetries as a measure of CP-violating top dipole couplings

In the presence of an electric dipole coupling of t-tbar to a photon, and an analogous "weak" dipole coupling to the Z, CP violation in the process e+e- --> t tbar results in modified polarization of the top and anti-top. This polarization can be analyzed by studying the angular distributions of decay charged leptons when the top or anti-top decays leptonically. Analytic expressions are presented for these distributions when either t or tbar decays leptonically, including O(alpha_s) QCD corrections in the soft-gluon approximation. The angular distributions are insensitive to anomalous interactions in top decay. Two types of simple CP-violating polar-angle asymmetries and two azimuthal asymmetries, which do not need the full reconstruction of the t or tbar, are studied. Independent 90% CL limits that may be obtained on the real and imaginary parts of the electric and weak dipole couplings at a linear collider operating at sqrt{s}=500 GeV with integrated luminosity 500 fb^{-1} and also at sqrt{s}=1000 GeV with integrated luminosity 1000 fb^{-1} have been evaluated. The effect of longitudinal electron and/or positron beam polarizations has been included.Comment: 26 pages, latex, figures included as latex files, version appearing in Pramana - Journal of Physics, minor corrections and note added in proo

TeV Strings and the Neutrino-Nucleon Cross Section at Ultra-high Energies

In scenarios with the fundamental unification scale at the TeV one expects string excitations of the standard model fields at accessible energies. We study the neutrino-nucleon cross section in these models. We show that duality of the scattering amplitude forces the existence of a tower of massive leptoquarks that mediate the process in the s-channel. Using the narrow-width approximation we find a sum rule for the production rate of resonances with different spin at each mass level. We show that these contributions can increase substantially the standard model neutrino-nucleon cross section, although seem insufficient in order to explain the cosmic ray events above the GZK cutoff energy.Comment: 10 pages, 1 figure, version to appear in PR