Search

We have previously studied the time-dependence of a B anti B meson mixture in terms of its density matrix. The requirement that the absolute value of the Stokes vector zeta(t) should evolve monotonically from its initial value zeta(0)=0 to its final value zeta(infinity)=1 was shown to lead to an upper bound on the CP violating overlap . In the present note we consider an entropy variable S as an alternative measure of mixing. We show that exactly the same upper bound emerges from the requirement that the flow of entropy is unidirectional (dS/dt<0). We compare the entropic current dS/dt with and without CP violation and identify certain physical features that appear when the bound on is violated., Comment: 8 pages, 4 figures. Typos corrected, comment on entropy added. To be published in Physical Review D

In a previous publication we noted that the time dependence of an incoherent $B^0-\bar{B}^0$ mixture undergoes a qualitative change when the magnitude of CP violation $\delta$ exceeds a critical value. Requiring, on physical grounds, that the system evolve from an initial incoherent state to a final pure state in a monotonic way, yields a new upper limit for $\delta$. The recent measurement of the wrong charge semileptonic asymmetry of $B_s^0$ mesons presented by the D0 collaboration is outside this bound by one standard deviation. If this result is confirmed it implies the existence of a new quantum mechanical oscillation phenomenon., Comment: 7 pages, 2 figures, version submitted for publication (Physical Review)

Coherent pi^+ and pi^0 production in low energy neutrino reactions is discussed in the framework of the partially conserved axial vector current theory (PCAC). The role of lepton mass effects in suppressing the pi^+ production is emphasized. Instead of using models of pion nucleus scattering, the available data on pion Carbon scattering are implemented for an analysis of the PCAC prediction. Our results agree well with the published upper limits for pi^+ production but are much below the recent MiniBooNE result for pi^0 production., Comment: 9 pages, 4 figures New reference added. Comment to fig. 1b and to ref. 16 added. Typos corrected. Version corresponds to the one submitted to Phys. Rev. D

For any inelastic process $v_{\ell} + I \to \ell^- + F$ with $m_{\ell} = 0$, the cross section at $\theta_{\ell} = 0$ is given by Adler's PCAC theorem. Inclusion of the lepton mass has a dynamical effect (``PCAC-screening'') caused by interference of spin-zero ($\pi^+$) and spin-one exchanges. This effect may be relevant to the forward suppression reported in recent experiments., Comment: 3 pages, 2 figures, presented at NuInt07, Fermilab, may 31 - june 3 2007

We reconsider the Feynman-Kislinger-Ravndal model applied to neutrino-excitation of baryon resonances. The effects of lepton mass are included, using the formalism of Kuzmin, Lyubushkin and Naumov. In addition we take account of the pion-pole contribution to the hadronic axial vector current. Application of this new formalism to the reaction nu(mu) + p --> mu + Delta at E(nu) approx 1 GeV gives a suppressed cross section at small angles, in agreement with the screening correction in Adler's forward scattering theorem. Application to the process nu(tau) + p --> tau + Delta at E(nu) approx 7 GeV leads to the prediction of right-handed tau polarization for forward-going leptons, in line with a calculation based on an isobar model. Our formalism represents an improved version of the Rein-Sehgal model, incorporating lepton mass effects in a manner consistent with PCAC., Comment: 14 pages, 5 figures. Typos in eq. 9 and 27 corrected. Numbers in table I for coherent cross sections (RSA and RSC) corrected (normalization error). Figs 3 and 4 changed accordingly. These corrections also apply to the published version PRD 76, 113004 (2007)

We study the evolution of a neutral $K$ meson prepared as an incoherent equal mixture of $K^0$ and $\bar{K^0}$. Denoting the density matrix by $\rho(t) = {1/2} N(t) [\1 + \vec{\zeta}(t) \cdot \vec{\sigma} ] $, the norm of the state $N(t)$ is found to decrease monotonically from one to zero, while the magnitude of the Stokes vector $|\vec{\zeta}(t)|$ increases monotonically from zero to one. This property qualifies these observables as arrows of time. Requiring monotonic behaviour of $N(t)$ for arbitrary values of $\gamma_L, \gamma_S$ and $\Delta m$ yields a bound on the CP-violating overlap $\delta = \braket{K_L}{K_S}$, which is similar to, but weaker than, the known unitarity bound. A similar requirement on $|\vec{\zeta}(t)|$ yields a new bound, $\delta^2 < {1/2} (\frac{\Delta \gamma}{\Delta m}) \sinh (\frac{3\pi}{4} \frac{\Delta \gamma}{\Delta m})$ which is particularly effective in limiting the CP-violating overlap in the $B^0$-$\bar{B^0}$ system. We obtain the Stokes parameter $\zeta_3(t)$ which shows how the average strangeness of the beam evolves from zero to $\delta$. The evolution of the Stokes vector from $|\vec{\zeta}| = 0$ to $|\vec{\zeta}| = 1$ has a resemblance to an order parameter of a system undergoing spontaneous symmetry breaking., Comment: 13 pages, 6 figures. Inserted conon "." in title; minor change in text. To appear in Physical review D

The K2K experiment, using a fine-grained detector in a neutrino beam of energy $ \sim 1.3 \mathrm{GeV}$ has observed two-track events that can be interpreted as a coherent reaction $\nu_\mu + \N \to \mu^- + \N + \pi^+ (\N = \rm{C}^{12})$ or an incoherent process $\nu_\mu + (p,n) \to \mu^- + \pi^+ + (p,n)$, the final nucleon being unobserved. The data show a significant deficit of forward-going muons in the interval $Q^2 \lesssim 0.1 \rm{GeV}^2$, where a sizeable coherent signal is expected. We attempt an explanantion of this effect, using a PCAC formula that includes the effect of the non-vanishing muon mass. A suppression of about 25 % is caused by a destructive interference of the axial vector and pseudoscalar (pion-exchange) amplitudes. The incoherent background is also reduced by 10 - 15 %. As a consequence the discrepancy between theory and observation is significantly reduced., Comment: 4 pages including 1 figure, changes in abstract and text; version to appear in Phys.Lett. B

Rare decays of K mesons are reviewed from the perspective of testing the ``ones'' and ``zeros'' of the standard model. Decays K^+ -> pi^+ nu anti-nu and K_L -> pi^0 nu anti-nu probe the one-loop effective Hamiltonian for s -> d nu anti-nu, and can constrain the rho, eta coordinates of the unitarity triangle. Decays such as K_L -> pi^0 l^+ l^-, K_L -> mu^+ mu^-, K^+ -> pi^+ l^+ l^- and K_L -> pi^+ pi^- e^+ e^- involve short-distance effects, as well as long-distance photon-induced contributions. Some comments are added on curious features of electroweak amplitudes in the ``gaugeless'' limit, and in the chiral electron limit m_e -> 0., Comment: 8 pages, Invited talk on DAFNE04 conference

We have recently shown that the large direct CP violation observed in the decay B^0 -> pi^+ pi^-, and the enhanced branching ratio for B^0 -> pi^0 pi^0, can be understood by invoking a small mixing of the pi pi system with the dominant D Dbar channel. We examine here the analogous effect of D Dbar <-> K Kbar mixing on the rare decays B^0 -> K^0 K^0bar, B^- -> K^- K^0 and B^0 -> K^+ K^-. We find (a) significant values for the asymmetry parameters C and S in B^0 / B^0bar -> K^0 K^0bar, (b) a possible enhancement of the suppressed mode B^0 -> K^+ K^-, (c) a correlation between the three decay channels following from a triangle relation between amplitudes A_{K^0 K^0bar} - A_{K^+ K^-} = A_{K^- K^0}. The pattern of asymmetries and branching ratios is compared with that derived from the short-distance QCD penguin interaction., Comment: 9 pages, 6 figures

We have studied in detail the spectrum of the decay mu^- -> e^- anti-nu_e nu_mu gamma as a function of the electron helicity, and verify the prediction of Sehgal (Phys.Lett. B569, 25 (2003)) that a significant fraction of the electrons in this decay is right-handed. These ``wrong-helicity'' electrons persist in the limit lambda = m_e / m_mu -> 0, and are connected with helicity-flip bremsstrahlung in QED. The longitudinal polarization of the electron is calculated as a function of the photon and electron energy, and deviates systematically from the naive V-A prediction P_L = -1. The right-handed component is concentrated in the collinear region theta <= m_e / E_e. In the limit lambda -> 0, we reproduce the results obtained in (Phys.Lett. B569, 25 (2003)) using the helicity-flip splitting function introduced by Falk and Sehgal., Comment: 11 pages, 7 figures; v2: shortened version to appear in Phys. Lett. B

We consider a model for the decay Bbar^0 -> rho^0 gamma in which the short-distance amplitude determined by the Hamiltonian describing b -> d gamma is combined with a typical long-distance contribution Bbar^0 -> D^+ D^- -> rho^0 gamma. The latter possesses a significant dynamical phase which induces a CP-violating asymmetry A_CP, as well as an important modification of the Stokes vector of the photon. The components S_1 and S_3 of the Stokes vector S = (S_1, S_2, S_3) can be measured in the decay Bbar^0 -> rho^0 gamma^* -> pi^+ pi^- e^+ e^- where they produce a characteristic effect in the angular distribution d Gamma / d phi, phi being the angle between the pi^+ pi^- and e^+ e^- planes. A similar analysis is carried out for the decays Bbar^0 -> Kbar^* gamma and Bbar^0 -> Kbar^* gamma^* -> pi^+ K^- e^+ e^-, Comment: 13 pages, 8 figures; v2: Some clarifying remarks added, together with additional references. Minor typos corrected. No change in results

Recent measurements of B^0 -> pi pi decays reveal two features that are in conflict with conventional calculations: the channel B^0 (Bbar^0) -> pi^+ pi^- shows a large direct CP-violating asymmetry, and the channel B^0 (B^0) -> pi^0 pi^0 has an unexpectedly high branching ratio. We show that both features can be understood in terms of strong-interaction mixing of pi pi and D Dbar channels in the isospin-zero state, an effect that is important because of the large experimentally observed ratio Gamma(B^0 / Bbar^0 -> D^+ D^-) / Gamma (B^0 / Bbar^0 -> pi^+ pi^-) approx. 50. Our dynamical model correlates the branching ratios and the CP-violating parameters C and S, for the decays B^0 (Bbar^0) -> pi^+ pi^-, B^0 (Bbar^0) -> pi^0 pi^0, B^0 (Bbar^0) -> D^+ D^- and B^0 (Bbar^0) -> D^0 Dbar^0., Comment: 10 pages, 2 figures, 1 table; v2: Misprint corrected in Eq. (12), second line: -a_m replaced by +a_m. To appear in Phys. Lett. B

Electrons emitted in the radiative decay mu^- -> e^- anti-nu_e nu_mu gamma have a significant probability of being right-handed, even in the limit m_e -> 0. Such ``wrong-helicity'' electrons, arising from helicity-flip bremsstrahlung, contribute an amount alpha/(4 pi) Gamma_0 to the muon decay width (Gamma_0 = G_F^2 m^5_mu/ (192 pi^3)). We use the helicity-flip splitting function D_hf (z) of Falk and Sehgal (Phys. Lett. B 325, 509 (1994)) to obtain the spectrum of the right-handed electrons and the photons that accompany them. For a minimum photon energy E_gamma = 10 MeV (20 MeV), approximately 4% (7%) of electrons in radiative mu-decay are right-handed., Comment: 8pages, 2 figures; v2: small correction in para (ii) of summary

We investigate the double Dalitz decays $B_s \to l^+ l^- l'^+ l'^-$ on the basis of the effective Hamiltonian for the transition $b \bar{s} \to l^+ l^-$, and universal form factors suggested by QCD. The correlated mass spectrum of the two lepton pairs in the decay $B_s \to e^+ e^- \mu^+ \mu^-$ is derived in an efficient way, using a QED result for meson decays mediated by two virtual photons: $B_s \to \gamma^* \gamma^* \to e^+ e^- \mu^+ \mu^-$. A comment is made on the correlation between the planes of the two lepton pairs. The conversion ratios $\rho_{lll'l'}= \frac{\Gamma(B_s \to l^+ l^- l'^+ l'^-)}{\Gamma(B_s \to \gamma \gamma)}$ are estimated to be $\rho_{eeee}=3 \times 10^{-4}, \rho_{ee\mu\mu}=9 \times 10^{-5} \text{and} \rho_{\mu\mu\mu\mu}=3 \times 10^{-5}$, and are enhanced relative to pure QED by $10-30 %$., Comment: Two typos corrected: (i) factor $1/\Gamma_{\gamma\gamma}$ inserted in Eq. (14), (ii) co-ordinate labels $x_{12},x_{34}$ inserted in Figs. 1-3. To appear in Physics Letters B

In the region of large mu^+ mu^- invariant mass, the decay spectrum of K_L -> mu^+ mu^- gamma deviates from the Dalitz pair spectrum, as a result of interference between conversion (K_L -> gamma^* gamma -> mu^+ mu^- gamma) and bremsstrahlung amplitudes. The latter is proportional to the K_L -> mu^+ mu^- matrix element, whose 2 gamma-absorptive part appears to dominate the observed K_L -> mu^+ mu^- decay rate. We examine the extent to which a scrutiny of the K_L -> mu^+ mu^- gamma spectrum in the end-point region could provide evidence on the real part of the K_L -> mu^+ mu^- amplitude. As a by-product, we obtain the absorptive part of the K_L -> gamma^* gamma form factor, using data on the K_L -> pi^+ pi^- gamma spectrum., Comment: 7 pages, 4 figures

We study the effects of a possible strong final state interaction among longitudinal W's in gamma.gamma --> W+W-. The relevant partial wave amplitudes are modified by an Omn\`es function approximated by a Breit-Wigner form factor. We study the fractional cross section f_{00} = \sigma_{LL}/\sigma_{Total} with both W's longitudinally polarised, in the presence of a J = 2 resonance (M = 2.5 TeV, Width = 500 GeV) or a J = 0 resonance (M = 1 TeV, Width = 1 TeV), whose parameters are scaled up from the f_2 and \sigma resonances in the \pi\pi system. We also examine the effects of final state interaction in the case of polarised photons (J_z = 0 or J_z = 2), and the impact on the Drell-Hearn-Gerasimov sum rule., Comment: 12 pages including figures

The decay (B^0)bar -> pi^+ pi^- gamma has a bremsstrahlung component determined by the amplitude for (B^0)bar -> pi^+ pi^-, as well as a direct component determined by the penguin interaction V_tb V^*_td c_7 O_7. Interference of these amplitudes produces a photon energy spectrum d Gamma/d x = a/x + b + c_1 x + c_2 x^2 + ... (x = 2 E_gamma/m_B) where the terms c_1,2 contain a dependence on the phase alpha_eff = pi - arg[(V_tb V^*_td)^* Amp((B^0)bar -> pi^+ pi^-)]. We also examine the angular distribution of these decays, and show that in the presence of strong phases, an untagged B^0/(B^0)bar beam can exhibit an asymmetry between the pi^+ and pi^- energy spectra., Comment: 11 pages, 4 figures, 1 table In abstract and in Eq. (17), a + b/x corrected to a/x + b. Slight improvement in Figs. 1b, 2c and 2d

We investigate the reaction e^+ e^- \to W^+ W^-, W^- \to l^- \bar{nu} in a strong coupling scenario as implemented in the BESS model. Energy and angle spectra of the secondary lepton are calculated and compared with the predictions of the Standard Model. These spectra provide a determination of the fraction f_0 of longitudinally polarized W's, and the backward fraction of secondary leptons, f_{back}. Assuming BESS parameters allowed by present data, we give numerical estimates of the effects to be expected at an e^+e^- collider of energy \sqrt{s} = 500- 800 GeV., Comment: 13 pages including figures

We consider the structure-dependent amplitude of the decay $B_s \to l^+ l^- \gamma$ $(l=e,\mu)$ in a model based on the effective Hamiltonian for $b \bar{s} \to l^+ l^-$ containing the Wilson coefficients $C_7,C_9$ and $C_{10}$. The form factors characterising the matrix elements $< \gamma | \bar{s} \gamma_\mu (1 \mp \gamma_5) b | \bar{B}_s>$ and $< \gamma | \bar{s} \sigma_{\mu\nu} (1 \mp \gamma_5) b | \bar{B}_s>$ are taken to have the universal form $f_V \approx f_A \approx f_T \approx f_{B_s} M_{B_s} R_s / (3 E_\gamma)$ suggested by recent work in QCD, where $R_s$ is a parameter related to the light cone wave function of the $B_s$ meson. Simple expressions are obtained for the charge asymmetry $A(x_\gamma)$ and the photon energy spectrum $d \Gamma/ d x_\gamma (x_\gamma = 2 E_\gamma/M_{B_s})$. The decay rates are calculated in terms of the decay rate of $B_s \to \gamma \gamma$. The branching ratios are estimated to be $Br(B_s \to e^+ e^- \gamma) = 2.0 \times 10^{-8}$ and $Br(B_s \to \mu^+ \mu^- \gamma) = 1.2 \times 10^{-8}$, somewhat higher than earlier estimates., Comment: sign of $f_T$ corrected; new table and figures

The epsilon-impurity of the K_L wave-function gives rise to a huge CP-violating effect in the decay K_L -> pi^+ pi^- gamma which is hidden in the polarization state (Stokes vector) of the photon. One component of the Stokes vector is CP-odd and T-even, and may be identified with circular polarization. Another component is CP-odd and T-odd (``oblique polarization'') and reveals itself as a large asymmetry (14%) in the decay K_L -> pi^+ pi^- e^+ e^-. Striking time-dependent effects are predicted in the angular distribution of the pi^+ pi^- e^+ e^- system emanating from an initial K^0 or K^0bar state., Comment: 5 pages, 6 figures, talk at International Conference on CP Violation Physics, 18-22 September 2000, Ferrara, Italy, minor typos corrected

We consider the decay K^0 (K^0 bar) -> pi^+ pi^- e^+ e^- of a neutral K meson prepared in a state of strangeness +1 (-1). The time evolution of the state produces remarkable time-dependent effects in the angular distribution of the pi^+ pi^- e^+ e^- system. These effects are correlated with the time-dependence of the photon polarization in the radiative decay K^0 (K^0 bar) -> pi^+ pi^- gamma. We study, in particular, the CP-odd, T-odd term in the distribution d Gamma / d phi of the angle between the pi^+ pi^- and the e^+ e^- planes. We also give the spectrum in the case that the decaying meson is an incoherent mixture of K^0 and K^0 bar, and discuss the case of K_S regeneration in a K_L beam., Comment: 16 pages, 8 figures, minor typos corrected, to appear in Phys. Lett. B

The origin of the large CP-odd and T-odd asymmetry observed in the decay K_L -> pi^+ pi^- e^+ e^- is traced to the polarization properties of the photon in the decay K_L -> pi^+ pi^- gamma. The Stokes vector of the photon S = (S_1, S_2, S_3) is studied as a function of the photon energy and found to possess CP-violating components S_1 and S_2 which are sizeable over a large part of the phase space, despite being proportional to the epsilon parameter of the K_L wave function. The component S_2 is T-even and manifests itself as a circular polarization of the photon, while S_1 is T-odd and gives rise to the asymmetry observed in K_L -> pi^+ pi^- e^+ e^-. The latter is shown to survive in the ``hermitian'' limit in which all unitarity phases are absent, and represents a genuine example of time reversal symmetry breaking in a CPT invariant theory., Comment: 4 pages including 2 figures

I review the theoretical basis of the prediction that the decay K_L -> pi+ pi- e+ e- should show a large CP- and T-violation, a prediction now confirmed by the KTeV experiment. The genesis of the effect lies in a large violation of CP- and T-invariance in the decay K_L -> pi+ pi- gamma, which is encrypted in the polarization state of the photon. The decay K_L -> pi+ pi- e+ e- serves as an analyser of the photon polarization. The asymmetry in the distribution of the angle phi between the pi+ pi- and e+ e- planes is a direct measure of the CP-odd, T-odd component of the photon's Stokes vector. A complete study of the angular distribution can reveal further CP-violating features, which probe the non-radiative (charge-radius and short-distance) components of the K_L -> pi+ pi- e+ e- amplitude., Comment: 8 pages including 1 figure, Talk at KAON 99 Conference, Chicago, June 21-26, 1999

The short-distance Hamiltonian describing b->s(d)e^-e^+ in the standard model is used to obtain the decay spectrum of \bar{B}->K^-pi^+e^-e^+ and \bar{B}->pi^-pi^+e^-e^+, assuming the Kpi and pipi systems to be the decay products of K^* and rho respectively. Specific features calculated are (i) angular distribution of K^- (or pi^-) in the K^-pi^+ (or pi^-pi^+) centre-of-mass (c.m.) frame; (ii) angular distribution of e^- in the e^-e^+ c.m. frame; and (iii) the correlation between the meson and lepton planes. We also derive CP-violating observables obtained by combining the above decays with the conjugate processes B->K^+pi^-e^-e^+ and B->pi^-pi^+e^-e^+., Comment: 19 pages, REVTeX, no figures. Equations (2.19a), (2.19b), (5.5)-(5.7) have been corrected; all results remain unchanged. These changes will appear in an Erratum submitted to Phys. Rev. D

Paper has been withdrawn by the authors., Comment: Paper has been withdrawn

The reaction $ e^+e^- \to W^+W^-$ produces a $W$-boson pair with a non-trivial spin correlation at threshold. This correlation leads to a characteristic angular correlation between the leptons produced in $W^{\pm} \to \ell ^{\pm} \nu$ (angles relative to the $e^-$ beam direction): $d \sigma /d \cos \theta_+ d \cos \theta_- \sim (1-\cos \theta_+) (1+ \cos \theta_-) (1+\cos \theta_- \cos \theta_+) $ . If only the $\ell^-$ is observed, its angular distribution is $d \sigma / d \cos \theta_- \sim (1+\cos \theta_-)(3-\cos \theta_-) $, implying a forward-backward asymmetry of 3/8. An analytic result is also given for the azimuthal correlation. These results are reproduced by a Monte Carlo program, that also enables us to study the effects of the $W$ decay width. The threshold behaviour, which stems from the dominance of $\nu$-exchange, is contrasted with that due to $\gamma$- and $Z$-exchange, which is relevant for annihilation in the helicity state $e^-_Re^+_L$., Comment: 10 pages, 6 figures, LaTeX, simpler derivation of main results, also added a comparison with Monte Carlo expectations

We have recently examined the static properties of the baryon octet (magnetic moments and axial vector coupling constants) in a generalized quark model in which the angular momentum of a polarized nucleon is partly spin $\langle S_z \rangle$ and partly orbital $\langle L_z \rangle$. The orbital momentum was represented by the rotation of a flux-tube connecting the three constituent quarks. The best fit is obtained with $\langle S_z \rangle = 0.08\pm 0.15$, $\langle L_z \rangle = 0.42\pm 0.14$. We now consider the consequences of this idea for the $q^2$-dependence of the magnetic and axial vector form factors. It is found that the isovector magnetic form factor $G_M^{\mathrm{isovec}}(q^2)$ differs in shape from the axial form factor $F_A(q^2)$ by an amount that depends on the spatial distribution of orbital angular momentum. The model of a rigidly rotating flux-tube leads to a relation between the magnetic, axial vector and matter radii, $\langle r^2 \rangle_{\mathrm{mag}} = f_{\mathrm{spin}} \langle r^2 \rangle_{\mathrm{axial}} + \frac{5}{2} f_{\mathrm{orb}} \langle r^2 \rangle_{\mathrm{matt}}$, where $f_{\mathrm{orb}}/ f_{\mathrm{spin}} = \frac{1}{3}\langle L_z \rangle / G_A$, $f_{\mathrm{spin}} + f_{\mathrm{orb}} = 1$. The shape of $F_A(q^2)$ is found to be close to a dipole with $M_A = 0.92\pm 0.06$ GeV., Comment: 18 pages, 5 ps-figures, uses RevTeX

We summarize the results of two papers in which we have studied CP violation in inclusive and exclusive decays b -> d e^+e^-. Two CP-violating effects are calculated: the partial rate asymmetry between b and \bar{b} decay, and the asymmetry between e^- and e^+ spectra for an untagged B/\bar{B} mixture. These asymmetries, combined with the branching ratio, can potentially determine the parameters (\rho, \eta) of the unitarity triangle. We also summarize a paper by Browder et al. on a possible CP-violating asymmetry in the inclusive reaction B -> K^-(K^{*-})X., Comment: 4 pages, LaTeX, 1 figure, uses prhep97.sty (included) and psfig.sty. Talk presented by L. M. Sehgal at the International Europhysics Conference on High Energy Physics, 19-26 August 1997, Jerusalem, Israel. To appear in the Proceedings

As a sequel to the calculation of the CP-violating asymmetry in the decay rates of b -> d l^+l^- and \bar{b} -> \bar{d} l^+l^-, we address in this paper the asymmetry in exclusive channels \bar{B} -> pi e^+e^- and \bar{B} -> rho e^+e^-, using form factors from two different models. In the invariant mass region 1GeV < \sqrt{s} < M_{J/psi}, the partial width asymmetry in the channel \bar{B} -> pi is -6% (-2%), and that in the channel \bar{B} -> rho, for one choice of form factors, is -5% (-2%), assuming CKM parameters eta = 0.34, rho = 0.3 (-0.3). We also calculate the forward-backward asymmetry A_{FB} of the e^- in the e^+e^- centre-of-mass system, and find average values (\bar{B} -> pi) \equiv 0, (\bar{B} -> rho)= -17 %, to be compared with the inclusive result (b -> d)= -9%. There is a CP-violating difference between A_{FB} and the corresponding asymmetry in the antiparticle channel \bar{A}_{FB}. Formulae are given that are applicable to any FCNC channel \bar{B} -> P_q (V_q) l^+l^-, q=s, d, with m_l \neq 0, including lepton spin effects. An approximate procedure is used to incorporate the rho, omega, and J/psi resonances., Comment: 34 pages, LaTeX2e, 8 figures, uses cite, psfig, and subeqn style files. Minor typos corrected, version to appear in Phys. Rev. D

The energy spectrum of leptons, produced by the decay of one or both W's in the reaction $e^+e^- \to W^+W^-$, is a significant probe of the helicity structure of this process. We calculate the energy spectrum $d \sigma /d E$ of a single decay lepton, as well as the two-dimensional energy distribution $d \sigma/d E_+dE_-$. We then consider a possible strong final state interaction in the longitudinally polarized state of the W^+W^- system, parametrized by a \rho -like resonance in the region of 1.8 TeV. We show that such a resonance produces measurable effects in the lepton spectrum at $\sqrt{s}=500$ GeV. The results are compared with those obtained from a non-resonant interaction approximated by a phase factor $e^{i \delta}$ in the l=1 part of the W^+_LW^-_L amplitude., Comment: LaTeX, 12 pages including 3 eps figures, uses amssym and epsf

The decay $b\to d e^+e^-$ has an amplitude containing comparable contributions proportional to $V_{tb}V_{td}^{*}$, $V_{cb}V_{cd}^{*}$ and $V_{ub}V_{ud}^{*}$. These pieces involve different unitarity phases produced by $c\bar{c}$ and $u\bar{u}$ loops. The simultaneous presence of different CKM phases and different dynamical phases leads to a calculable asymmetry in the partial widths of $b\to d e^+e^-$ and $\bar{b}\to \bar{d} e^+e^-$. Using the effective Hamiltonian of the standard model, we calculate this asymmetry as a function of the $e^+e^-$ invariant mass. The effects of $\rho$, $\omega$ and $J/\psi$ resonances are taken into account in the vacuum polarization of the $u\bar{u}$ and $c\bar{c}$ currents. As a typical result, an asymmetry of $- 5% (- 2%)$ is predicted in the nonresonant domain $1 GeV < m_{e^+e^-} < m_{J/\psi}$, assuming $\eta = 0.34$ and $\rho= 0.3 (-0.3)$. The branching ratio in this domain is $1.2\times 10^{-7} (3.3\times 10^{-7})$. Results are also obtained in the region of the $J/\psi$ resonance, where an asymmetry of $3\times 10^{-3}$ is expected, subject to certain theoretical uncertainties in the $b\to d J/\psi$ amplitude., Comment: 20 pages, LaTeX, 3 eps figures, uses cite.sty, epsf.sty, and amssym.sty. Version to appear in Phys. Rev. D, with some minor additions

We analyse the baryon magnetic moments in a model that relates them to the parton spins $\Delta u$, $\Delta d$, $\Delta s$, and includes a contribution from orbital angular momentum. The specific assumption is the existence of a 3-quark correlation (such as a flux string) that rotates with angular momentum $\langle L_z \rangle$ around the proton spin axis. A fit to the baryon magnetic moments, constrained by the measured values of the axial vector coupling constants $a^{(3)}=F+D$, $a^{(8)}=3F-D$, yields $\langle S_z \rangle = 0.08 \pm 0.13$, $\langle L_z \rangle = 0.39 \pm 0.09$, where the error is a theoretical estimate. A second fit, under slightly different assumptions, gives $\langle L_z \rangle = 0.37 \pm 0.09$, with no constraint on $\langle S_z \rangle$. The model provides a consistent description of axial vector couplings, magnetic moments and the quark polarization $\langle S_z \rangle$ measured in deep inelastic scattering. The fits suggest that a significant part of the angular momentum of the proton may reside in a collective rotation of the constituent quarks., Comment: 16 pages, 3 ps-figures, uses RevTeX. Abstract, Sec. II, III and IV have been expanded

The effective Hamiltonian for the decay $b\to s l^+ l^-$ predicts a characteristic polarization for the final state lepton, which can serve as an important test of the underlying theory. The lepton polarization has, in addition to a longitudinal component $P_L$, two orthogonal components $P_T$ and $P_N$, lying in and perpendicular to the decay plane which are proportional to $m_l/m_b$, and therefore significant for the $\tau^+\tau^-$ channel. The normal polarization component $P_N$ is a $T$-odd effect connected with the nonhermiticity of the effective Hamiltonian, arising mainly from $c\bar{c}$ intermediate states. We calculate all three polarization components for the decay $B\to X_s\tau^+\tau^-$ as a function of the lepton pair mass, and find average values $$ = -0.37, $$ = -0.63, $$ = 0.03. By comparison, the $\mu^-$ polarization is $$ = -0.77, $ = \approx 0$., Comment: 17 pages, LaTeX, 5 eps figures, uses epsf.sty and cite.sty

We consider the process $e^+e^-\to N_1N_2$, where $N_1$ and $N_2$ are heavy Majorana particles, with relative $CP$ given by $\eta_{CP}=+1$ or $-1$, decaying subsequently via $N_1,N_2\to W^{\pm}e^{\mp}$. We derive the energy and angle correlation of the dilepton final state, both for like-sign ($e^{\mp}e^{\mp}$) and unlike-sign ($e^-e^+$) configurations. Interesting differences are found between the cases $\eta_{CP}=+1$ and $-1$. The characteristics of unlike-sign $e^+e^-$ dileptons originating from a Majorana pair $N_1N_2$ are contrasted with those arising from the reaction $e^+e^-\to N\bar{N}\to W^+e^-W^-e^+$, where $N\bar{N}$ is a Dirac particle-antiparticle pair., Comment: 24 pages, RevTeX, 12 eps figures, uses epsf.sty

We consider the effects of quark-binding on the angular distribution and polarization characteristics of the inclusive decays $\Lambda_b \to X_s \gamma$ and $\Lambda_b \to X_c l \bar{\n}_l$ $(l=e, \tau)$, using the methods of heavy quark effective theory., Comment: 3 pages, LaTeX, 4 eps figures, uses epsfig.sty, subeqn.sty and wstwocl.sty. Presented by L. M. Sehgal at the EPS-HEP conference, Brussels, 1995. To appear in the proceedings

We study the angular distribution of photons produced in the inclusive decay of a polarized $\Lambda_b$, $\Lambda_b\to X_s\,\gamma$, using the technique of Heavy Quark Effective Theory. Finite non-perturbative corrections are obtained relative to the free quark decay $b\to s\gamma$. These corrections affect significantly the intensity and polarization of photons emitted at small angles relative to the $\Lambda_b$ spin direction., Comment: 10 pages, LaTeX, uses epsf, 2 figures appended as uuencoded, compressed eps tar-files

We discuss the longitudinal and transverse $\tau$-polarization in inclusive decays of hadrons containing $b$-quarks. The calculation is performed by means of an OPE in HQET. Some mathematical difficulties in calculating transverse polarizations are explained. Numerical results are presented for longitudinal and for transverse polarizations, both in and perpendicular to the decay plane., Comment: LATEX, 20 pages, 5 Postscript figures

The rare decays of the $K$ meson have had a long tradition as a laboratory for testing the symmetry properties of the weak interactions, and the manner in which these symmetries are broken by higher order effects. Present--day interest is focussed on decays that are suppressed by $CP$--symmetry or GIM symmetry. Such decays, in the standard theory, are sensitive to effects of the virtual top quark, and could also reveal new interactions transcending the standard model. In addition, the radiative decays of the $K$ meson have become a useful testing--ground for effective Lagrangians describing the low energy interactions of pions, kaons and photons., Comment: Invited Talk at the Third Workshop on High Energy Particle Physics (WHEPP 3) Madras, 1994, LaTex, 14 pages, 3 figures available upon request

It is shown that in the sequential decay $H\to ZZ\to (f_1\bar{f_1})+ (f_2\bar{f_2})$, the energy distribution of the final state particles provides a simple and powerful test of the $HZZ$ vertex. For a standard Higgs boson, the energy spectrum of any final fermion, in the rest frame of $H$, is predicted to be $d\Gamma /dx\sim 1+\beta^4-2(x-1)^2$, with $\beta = \sqrt{1-4m^2_Z/m^2_H}$ and $1-\beta \le x=4E/m_H\le 1+\beta $. By contrast, the spectrum for a pseudoscalar Higgs is $d\Gamma /dx \sim \beta^2+(x-1)^2$. There are characteristic energy correlations between $f_1$ and $f_2$ and between $f_1$ and $\bar{f_2}$. These considerations are applied to the ``gold--plated'' reaction $H\to ZZ\to \mu^+\mu^-\mu^+\mu^-$, including possible effects of CP--violation in the $HZZ$ coupling. Our formalism also yields the energy spectra and correlations of leptons in the decay $H\to W^+W^-\to l^+\nu_ll^- \bar{\nu_l}$., Comment: 14 pages + 4 figures

We study the energy correlation of charged leptons produced in the decay of a heavy Higgs particle $H\to t\bar t\to bl^+\nu_l\bar bl^-\bar{\nu}_l$ and $H\to W^+W^-\to l^+\nu_ll^-\bar{\nu}_l.$ The possible influence of $CP$--violation in the $Ht\bar t$ and $HW^+W^-$ vertices on the energy spectrum of the secondary leptons is analyzed. The energy distribution of the charged leptons in the decay $H\to W^+W^-\to l^+\nu_ll^-\bar{\nu}_l$ is sensitive to the $CP$--parity of the Higgs particle and yields a simple criterion for distinguishing scalar Higgs from pseudoscalar Higgs., Comment: 12 pages, + 4 uuencoded figures. report PITHA 94/25

We re-examine the question of a possible difference in the partial decay widths of $t$ and $\overline t$, induced by an intermediate scalar boson $H^+$ with $CP$-violating couplings. The interference of $W^+$ and $H^+$ exchanges is analysed by constructing the $2\times 2$ propagator matrix of the $W^+-H^+$ system, and determining its absorptive part in terms of fermion loops. Results are obtained for the partial rate difference in the channels $t\to bl^+\nu_l $ and $t\to bc\overline s$, which fulfil explicitly the constraints of $CPT$ invariance. These results are contrasted with those in previous work., Comment: 14 pages, report PITHA 94/19

The decays $K_{L,S} \to 3 \gamma $ are not forbidden by any selection rules or symmetry principles. However, gauge invariance and Bose statistics dictate that every photon pair in these transitions has at least two units of angular momentum. This gives rise to an extraordinary suppression. Using a simple model, we obtain the branching ratios $B(K_L \to 3 \gamma) \sim 3 \cdot 10^{-19}$, $B(K_S \to 3 \gamma) \sim 5 \cdot 10^{-22} $., Comment: LaTeX (1 figure appended as postscript file). A complete postscript file is available via anonymous ftp at ttpux2.physik.uni-karlsruhe.de (129.13.102.139) as pub/ttp93-39/ttp93-39.ps, Local preprint# TTP93-39 (December 1993)