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Radiation of gluons gives rise to extra jets in top quark events that can lead to complications in event reconstruction and mass measurement. I review recent results for gluon radiation in top quark production and decay, and discuss their implications for top quark physics.
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arxiv:hep-ph/9609354
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The cross section for Drell-Yan pair production in the limit of small $x$-target is derived in the rest frame of the target hadron. Our calculation is based on the fundamental quantity $\sigma(\rho)$, the cross section for the scattering of a $q\bar{q}$-pair with fixed transverse separation $\rho$ off a hadronic target. As in deep inelastic scattering the result can be given in terms of integrals of $\sigma(\rho)$. This is consistent with well known factorization theorems and also relates higher-twist terms in both processes. An analysis of the angular distribution of the produced lepton shows that additional integrals of $\sigma(\rho)$ can be obtained in the Drell-Yan process, which are not measurable in inclusive deep inelastic scattering.
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arxiv:hep-ph/9609384
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For large values of the Higgs mass the low energy structure of the gauged linear sigma model in the spontaneously broken phase can adequately be described by an effective field theory. We present a manifestly gauge-invariant functional technique to explicitly evaluate the corresponding effective Lagrangian from the underlying theory.
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arxiv:hep-ph/9609386
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We reanalyze the possibility of CP violation in the Higgs sector of the minimal supersymmetric standard model (MSSM). Contrary to the result of previous analysis, spontaneous CP violation can not occur by only chargino and neutralino radiative corrections since the vacuum does not stable. Top and stop radiative corrections are crucially needed. However even with this correction there is no experimentally allowed region in \tan \beta \geq 1. This situation is not remedied even if the stop left-right mixing is included. We also analyze explicit CP violation in the Higgs sector of the MSSM and show that the effect is too small to influence the phenomenology. We thus show that the Higgs sector can not, by itself, trigger CP violation in the MSSM.
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arxiv:hep-ph/9609395
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It is shown that if the sneutrino is the second lightest SUSY particle, then the decay products of squarks and gluinos produced at the TEVATRON collider tend to have i) more leptons, ii) smaller number of jets and iii) two or more carriers of missing E_T. This may relax the existing limits on the squark and gluino masses. This effect is likely to be even more striking as these limits improve with accumulation of data. Numerical results for signal cross sections are presented and compared with the ones obtained without a light sneutrino. The possibilities of accommodating this scenario in models motivated by N = 1 SUGRA are discussed.
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arxiv:hep-ph/9609413
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A study on effective anomalous interactions up to dimension 5 of the top quark with the electroweak gauge bosons is made in the non-linear Chiral Lagrangian approach. Bounds on the anomalous dimension four terms are obtained from their contribution to low energy data. Also, the potential contribution to the production of top quarks at hadron colliders (the Tevatron and the LHC) and the electron Linear Collider from both dimension 4 and 5 operators is analysed.
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arxiv:hep-ph/9609482
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The results are presented of a study of the accuracy one may achieve at HERA in measuring the strong coupling constant $\alpha_s$ and the gluon distribution $xg(x,Q^{2})$ using future data of the structure function $F_{2}(x,Q^{2})$ which are estimated to be accurate at the few % level over the full accessible kinematic region down to $x \simeq 10^{-5}$ and up to $Q^{2} \simeq 50000 GeV^{2}$. The analysis includes simulated proton and deuteron data, and the effect of combining HERA data with fixed target data is discussed.
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arxiv:hep-ph/9609489
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We review some selected topics in the decays of heavy flavours, beauty and charm, which are of principal interest at HERA-B and HERA. The topics in $B$ physics include: an update on the quark mixing matrix and CP violating phases, issues bearing on an improved resolution on the CP-violating phase $\Delta (sin 2 \beta)$, prospects of measuring radiative and semileptonic rare $B$ decays, the $B_s^{0}$ - $\overline{B_s^{0}}$ mixing ratio $x_s$, improved measurements of the $B_d^{0}$ - $\overline{B_d^{0}}$ mixing ratio $x_d$ and the $B$-hadron lifetimes, in particular $\tau(\Lambda_b)$. In the charm sector, we have focussed on rare decays and $D^0$- $\overline{D^0}$ mixing, whose measurements will signal physics beyond the standard model.
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arxiv:hep-ph/9609519
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We provide a new estimate of the long-distance component to the radiative transition $B \to \rho \gamma$. Our mechanism involves the soft-scattering of on-shell hadronic products of nonleptonic $B$ decay, as in the chain $B \to \rho\rho \to \rho\gamma$. We employ a phenomenological fit to scattering data to estimate the effect. The specific intermediate states considered here modify the $B \to \rho \gamma$ decay rate at roughly the $5 \to 8%$ level, although the underlying effect has the potential to be larger. Contrary to other mechanisms of long distance physics which have been discussed in the literature, this yields a non-negligible modification of the $B^0 \to \rho^0 \gamma$ channel and hence will provide an uncertainty in the extraction of $V_{td}$. This mechanism also affects the isospin relation between the rates for $B^- \to \rho^-\gamma$ and $B^0 \to \rho^0 \gamma$ and may generate CP asymmetries at experimentally observable levels.
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arxiv:hep-ph/9609530
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In this paper we investigate the dynamical properties of binary cosmic strings. We find extrinsic curvature dependence of the string action and show that kinks on binary strings are eroded while cusps can play a major role in their evolution.
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arxiv:hep-ph/9610201
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The radiative decay of the massive neutrino $\nu_i \rightarrow \nu_j \gamma$ is investigated in the framework of the Standard Model in external electromagnetic fields of various configurations: constant crossed field, constant uniform magnetic field, plane monochromatic wave's field. The effect of significant enhancement of the neutrino decay probability by the external field (electromagnetic catalysis) is discussed. An especially strong enhancement occurs in the case of the ultrarelativistic neutrino decay, since in this case the decay probability does not contain suppression caused by the smallness of the decaying neutrino mass. The ultrarelativistic neutrino decay catalysis is significant even in a relatively weak external field ($F/F_e << 1$, where $F_e$ is the critical Schwinger value). The expression for the photon splitting probability into the neutrino pair $\gamma \rightarrow \nu_i \bar\nu_j$ in the wave field is given. The estimations of a number of gamma-quanta produced in a volume filled with an electromagnetic field and the neutrino lifetime in a strong magnetic field are presented.
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arxiv:hep-ph/9610219
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Gauge theories broken by a single Higgs field are known to have first-order phase transitions in temperature if $\lambda/g^2 \ll 1$, where $g$ is the gauge coupling and $\lambda$ the Higgs self-coupling. If the theory is extended from one to $N$ Higgs doublets, with U($N$) flavor symmetry, the transition is known to be second order for $\lambda/g^2 \gtrsim 1$ in the $N\to\infty$ limit. We show that one can in principal compute the tricritical value of $\lambda/g^2$, separating first from second-order transitions, to any order in $1/N$. In particular, scalar fluctuations at the transition damp away the usual problems with the infrared behavior of high-temperature non-Abelian gauge theories. We explicitly compute the tricritical value of $\lambda/g^2$ for U(1) and SU(2) gauge theory to next-to-leading order in $1/N$.
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arxiv:hep-ph/9610226
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We study the impact of present and future $(g-2)_\mu$ measurements on supersymmetric models. The corrections to $(g-2)_\mu$ become particularly relevant in the presence of light sleptons, charginos and neutralinos, especially in the large $\tan\beta$ regime. For moderate or large values of $\tan\beta$, it is possible to rule out scenarios in which charginos and sneutrinos are both light, but nevertheless escape detection at the LEP2 collider. Furthermore, models in which supersymmetry breaking is transferred to the observable sector through gauge interactions can be efficiently constrained by the $(g-2)_{\mu}$ measurement.
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arxiv:hep-ph/9610233
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Abelian family symmetries provide a predictive framework for neutrino mass models. In seesaw models based on an abelian family symmetry, the structures of the Dirac and the Majorana matrices are derived from the symmetry, and the neutrino masses and mixing angles are determined by the lepton charges under the family symmetry. Such models can lead to mass degeneracies and large mixing angles as well as mass hierarchies, the squared mass difference between quasi-degenerate neutrinos being determined by the symmetry. We present two models illustrating this approach.
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arxiv:hep-ph/9610257
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We compute the branching fraction of the decays $B \to K \nu \bar\nu$ and $B \to K^* \nu \bar\nu$ in the Standard Model. We also comment on the experimental difficulties and procedures to detect such modes at B factories.
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arxiv:hep-ph/9610297
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The working group on jets and high-Et phenomena of the Future physics at HERA Workshop studied subjects ranging from next-to-leading order (NLO) corrections in deeply inelastic scattering (DIS) and photoproduction with the corresponding determinations of physical quantities, to the physics of instanton-induced processes, where a novel non-perturbative manifestation of QCD could be observed. Other centres of interest were the physics of the forward direction, the tuning of event generators and the development of a new generator which includes a consistent treatment of the small- and large-$x$ QCD evolution. The recommendations of the working group concerning detector upgrades and machine luminosity are summarized.
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arxiv:hep-ph/9610327
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Some recent developments in the phenomenology of the lightest scalar glueball are summarised. Tools for determining the gluonic content of a resonance of known mass, width and $J^{PC}$ from its branching fraction in radiative quarkonium decays and production cross section in $\gamma \gamma$ collisions are presented. Two $q\bar{q} - G$ mixing schemes for $J^{PC} = 0^{++}$, inspired by the lattice, are shown to lead to similar phenomenology that may be tested at BEPC and in $\gamma \gamma$ production at LEP2.
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arxiv:hep-ph/9610426
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We investigate azimuthal correlations in deep inelastic diffractive scattering, e + p -> e + \tilde{p} + X. The dependence of the ep cross section on the angle between the lepton plane and some direction in the hadronic final state can be written in a simple form; its measurement can be used to constrain the cross section for longitudinally polarised photons. Using the model of nonperturbative two-gluon exchange of Landshoff and Nachtmann we calculate the distribution of the azimuthal jet angle in diffractive dijet production and find that useful bounds on the longitudinal cross section for such events might be obtained from its measurement. We then discuss the predictions of this model for the dependence of the ep cross section on the azimuthal angle of the proton remnant \tilde{p}, which contains information about the helicity content of the pomeron.
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arxiv:hep-ph/9610430
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CERN collaboration NA50 has measured charmonium and Drell-Yan dimuon production in Pb+Pb collisions. Parton scattering broadens the transverse momentum, p_T, distributions for these processes. We predict that the average p_T^{2} will flatten in Pb+Pb collisions as a function of the neutral transverse energy of hadrons, E_T, in contrast to the almost-linear rise seen in S+U - psi +X. If seen, such a flattening will support hadronic explanations of charmonium suppression. Figures 2 and 5 are improved and numerous typographical errors are corrected.
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arxiv:hep-ph/9610432
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The radiative decay $\nu_H \to \nu_L + \gamma$ of massive neutrinos is analyzed in the framework of the standard model with lepton mixing for very strong magnetic fields $B\gg B_{cr} = m_e^2/e \sim 4.14 \times 10^{13}$G. The analysis is based on the approximate decay amplitude obtained by Gvozdev et al. Numerical results as well as analytical approximations for the decay rate are obtained for energies of the initial neutrino below and {\em above} the electron-positron pair creation threshold $2m_e$.
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arxiv:hep-ph/9610439
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Taking advantage of a semirelativistic and a full relativistic representation of the quark propagator in an external field we present an unified derivation of the semirelativistic potential and of a Bethe-Salpeter like equation for the quark-antiquark system. We consider three different models for the evaluation of the Wilson loop: the Modified Area Law model (MAL), the Stochastic Vacuum Model (SVM) and the Dual QCD (DQCD). We compare the corresponding potentials and show that they all agree at the short and the long distances. In the case of the Bethe-Salpeter equation we treat explicitly only the MAL model and give an expression for the kernel. Then we show that an effective mass operator can be obtained which agrees with the MAL potential in the semirelativistic limit. In the light quark mass limit this mass operator produces straight Regge trajectories with Nambu-Goto slope in agreement with the data. Finally we briefly discuss the mass independence of the hyperfine splitting in the heavy-light case.
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arxiv:hep-ph/9610530
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We develop quenched chiral perturbation theory for vector mesons made of light quarks, in the limit where the vector meson masses are much larger than the pion mass. We use this theory to extract the leading nonanalytic dependence of the vector meson masses on the masses of the light quarks. By comparing with analogous quantities computed in ordinary chiral perturbation theory, we estimate the size of quenching effects, observing that in general they can be quite large. This estimate is relevant to lattice simulations, where the $\rho$ mass is often used to set the lattice spacing.
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arxiv:hep-ph/9610532
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In 1992 Professor Ryszard R\c{a}czka started to work on formulation of a version of the Standard Model conformally coupled with gravity. Being his student I had got the honour to participate in those researches. The conformally invariant Higgs-Free Model was the result of our investigations. Ryszard R\c{a}czka passed away on 26 August 1996. I present here a short memorial survey of our results.
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arxiv:hep-ph/9610539
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The neutrino fluxes calculated from 14 standard solar models published recently in refereed journals are inconsistent with the results of the 4 pioneering solar neutrino experiments if nothing happens to the neutrinos after they are created in the solar interior. The sound speeds calculated from standard solar models are in excellent agreement with helioseismological measurements of sound speeds. Some statements made by Dar at Neutrino 96 are answered here.
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arxiv:hep-ph/9610542
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We examine the effects of SU(3) breaking in the matrix elements of the flavour-diagonal axial currents between octet baryon states and find that SU(3) breaking may be substantial for some matrix elements. We estimate the strange axial matrix element in the proton to be between -0.35 and 0 and the matrix element of the flavour-singlet current in the proton to be between -0.1 and +0.3 from the E-143 measurement g_1(x) . The up-quark content of the $\Xi^-$ is discussed and its implications for nonleptonic weak processes discussed. We also estimate the matrix element of the axial current coupling to the $Z^0$ between all octet baryon states. This may be important for neutrino interactions in dense nuclear environments, where hyperons may play an important role.
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arxiv:hep-ph/9611210
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Transverse polarization of ${}^3 S_1$ charmonium states, produced directly in $p\bar{p}$ collisions at asymptotically large transverse momentum p_t, has emerged as the most prominent test of color octet contributions and spin symmetry in quarkonium production. We present predictions for the polar angle distribution at moderate values of p_t \sim 4 - 20 GeV, covered by the Tevatron Run I data. We update the fits of NRQCD matrix elements and discuss their theoretical uncertainties. With our best fit values, no transverse polarization is expected at p_t \sim 5 GeV, but the angular distribution is predicted to change dramatically as p_t increases to 20 GeV.
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arxiv:hep-ph/9611218
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In view of the realistic possibility for operating high-energy polarized proton beams in future collider machines, it is highly desirable to propose for such beams, an absolute calibration allowing to measure accurately their degree of polarization. We consider more specifically one practical method based on pp elastic scattering near the forward direction and we discuss its limitations.
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arxiv:hep-ph/9611234
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To one-loop order and $O(\alpha_{em})$, the electromagnetic mass splittings of $\pi$, $a_1$, $K$, $K_1(1400)$, and $K^*(892)$ are calculated in the framework of $U(3)_L\times U(3)_R$ chiral field theory. The logarithmic divergences emerging in the Feynman integrations of the mesonic loops are factorized by using an intrinsic parameter $g$ of this theory. No other additional parameters or counterterms are introduced to absorb the mesonic loop divergences. When $f_\pi$,$m_\rho$ and $m_a$ are taken as inputs, the parameter $g$ will be determined and all the physical results are finite and fixed. Dashen's theorem is satisfied in the chiral SU(3) limit of this theory, and a rather large violation of the theorem is revealed at the order of $m_s$ or $m_K^2$. Mass ratios of light quarks have been determined. A relation for electromagnetic corrections to masses of axial-vector mesons is obtained. It could be regarded as a generalization of Dashen's theorem. Comparing with data, it is found that the non-electromagnetic mass difference of $K^*$ is in agreement with the estimation of Schechter, Subbaraman, Weigel.
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arxiv:hep-ph/9611297
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We compute the effective potential for $\phi^4$ theory with a squeezed coherent state type of construct for the ground state. The method essentially consists in optimising the basis at zero and finite temperatures. The gap equation becomes identical to resumming the infinite series of daisy and super daisy graphs while the effective potential includes multiloop effects and agrees with that obtained through composite operator formalism at finite temperature.
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arxiv:hep-ph/9611365
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We describe the state of the art in the field of radiative corrections for deep inelastic scattering. Different methods of calculation of radiative corrections are reviewed. Some new results for QED radiative corrections for polarized deep inelastic scattering at HERA are presented. A comparison of results obtained by the codes POLRAD and HECTOR is given for the kinematic regime of the HERMES experiment. Recent results on radiative corrections to deep inelastic scattering with tagged photons are briefly discussed.
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arxiv:hep-ph/9611426
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We discuss the case of simultaneous mixing of gauge bosons and mixing of fermions in a model independent way and for a variety of extra-fermion representations. In this context we analyze a class of lepton family violating processes, namely Z --> e tau, Z --> mu tau, Z --> e mu, mu --> e e e, tau --> e e e, tau --> mu mu mu, tau --> e mu mu and tau --> mu e e in the presence of one extra neutral gauge boson, Z', with universal, non-universal or family changing couplings. We derive bounds on the combined effect of Z-Z' mixing and ordinary--exotic lepton mixing.
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arxiv:hep-ph/9611442
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Introductory lectures on the phenomenology of the minimal supersymmetric Standard Model. The emphasis is on general signatures for supersymmetry and on the motivation for constructing supersymmetric models. These lectures are intended for experimental graduate students.
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arxiv:hep-ph/9612229
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We study the interactions of an elementary pion with a nucleon made of constituent quarks and show that the enforcement of chiral symmetry requires the use of a two-body operator, whose form does not depend on the choice of the pion-quark coupling. The coordinate space NN effective potential in the pion exchange channel is given as a sum of terms involving two gradients, that operate on both the usual Yukawa function and the confining potential. We also consider an application to the case of quarks bound by a harmonic potential and show that corrections due to the symmetry are important.
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arxiv:hep-ph/9612230
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We examine the prospects for determining $tan \beta$ from heavy Higgs scalar production in the minimal supersymmetric standard model at a future $e^+ e^-$ collider. Our analysis is independent of assumptions of parameter unification, and we consider general radiative corrections in the Higgs sector. Bounds are presented for $\sqrt{s} = 500$ GeV and 1 TeV, several Higgs masses, a variety of integrated luminosities and b-tagging efficiencies, and in scenarios with and without supersymmetric decays of the Higgs bosons. We find stringent constraints for $3 \alt tan \beta \alt 10$, and, for some scenarios, also interesting bounds on high $tan \beta$ through $tbH^{\pm}$ production. These bounds imply that simple Yukawa unifications may be confirmed or excluded. Implications for soft scalar mass determination and top squark parameters are also discussed.
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arxiv:hep-ph/9612333
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New experimental results on the spin dependent structure functions g_1 and g_2 which are determined from deep-inelastic scattering experiments at CERN, SLAC and DESY are reported. These results are used to evaluate the Bjorken sum rule and the singlet axial charge a_0. Results are discussed in the framework of next-to-leading order perturbative QCD. The role of the polarised gluons in the interpretation of the results on a_0 is emphasised. New experiments which aim to determine gluon polarisation are shortly described.
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arxiv:hep-ph/9612352
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We estimate the non-perturbative power-suppressed corrections to heavy flavour fragmentation and correlation functions in e^+e^- annihilation, using a model based on the analysis of one-loop Feynman graphs containing a massive gluon. This approach corresponds to the study of infrared renormalons in the large-n_f limit of QCD, or to the assumption of an infrared-finite effective coupling at low scales. We find that the leading corrections to the heavy quark fragmentation function are of order $\lambda/M$, where $\lambda$ is a typical hadronic scale ($\lambda\sim 0.4$ GeV) and M is the heavy quark mass. The inclusion of higher corrections corresponds to convolution with a universal function of M(1-x) concentrated at values of its argument of order $\lambda$, in agreement with intuitive expectations. On the other hand, corrections to heavy quark correlations are very small, of the order of $(\lambda/Q)^p$, where Q is the centre-of-mass energy and $p \ge 2$.
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arxiv:hep-ph/9612353
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The effects of light, long-lived gluinos on $2\to 2$ processes at hadron colliders are examined. Such particles can mediate single squark resonant production via $q\glu\to\sq\to q\glu$ which would significantly modify the dijet data sample. We find that squark masses in the range $130<m_{\tilde q}< 694, 595, 573$ GeV are excluded for gluino masses of $0.4, 1.3, 5.0$ GeV from existing UA2 and Tevatron data on dijet bump searches and angular distributions. Run II of the Tevatron has the capability of excluding this scenario for squark masses up to $\sim 1$ TeV.
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arxiv:hep-ph/9612377
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We present a QCD sum rule calculation of the strange-quark mass including four-loop QCD corrections to the correlator of scalar currents. We obtain $\bar m_s(1$ GeV$)=205.5\pm 19.1$ MeV.
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arxiv:hep-ph/9612394
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The production of soft dileptons in a thermal mesonic medium is discussed in the context of recent CERN experimental data reported by the CERES Collaboration. We do not intend to give a general and critical review, but instead concentrate mainly on our approach, however, incorporating many of the recent attempts in the literature. We calculate the contributions to the dilepton yield arising from pion annihilation and $\pi -\rho$ scattering. It is shown that thermal dileptons from $\pi -\rho$ scattering give a significant contribution to the low-mass yield, however, it can only partly account for the experimentally observed soft dilepton excess seen in S-Au and Pb-Au collisions at SPS energy. The out off-equilibrium effects as well as a dropping vector meson mass are discussed in the context of the thermal dilepton yield. We emphasize, following the results of Li, Ko, and Brown, that, until now, the best way to provide a quantitative explanation of the observed enhancement of low-mass dileptons by the CERN experiments is the assumption of a decreasing vector meson mass in a high density thermal medium.
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arxiv:hep-ph/9612448
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The energetic exclusive two-body nonleptonic decays of B mesons are investigated in the framework of the relativistic quark model within the factorization approximation. The heavy quark expansion is used for the calculation of form factors. The obtained results are in agrement with available experimental data.
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arxiv:hep-ph/9701218
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We calculate the top-quark-induced three-loop corrections of O(alpha_s^2 G_F M_t^2) to the Yukawa couplings of the first five quark flavours in the framework of the minimal standard model with an intermediate-mass Higgs boson, with mass M_H << 2M_t. The calculation is performed using an effective-Lagrangian approach implemented with the hard-mass procedure. As an application, we derive the O(alpha_s^2 G_F M_t^2) corrections to the H -> q q-bar partial decay widths, including the case q=b. The couplings of the Higgs boson to pairs of leptons and intermediate bosons being known to O(alpha_s^2 G_F M_t^2), this completes the knowledge of such corrections in the Higgs sector. We express the results both in the MS-bar and on-shell schemes of mass renormalization. We recover the notion that the QCD perturbation expansions exhibit a worse convergence behaviour in the on-shell scheme than they do in the MS-bar scheme.
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arxiv:hep-ph/9701277
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We propose a general scheme for constructing models in which the Standard Model (SM) gauge interactions are the mediators of supersymmetry breaking to the fields in the supersymmetric SM, but where the SM gauge groups couple directly to the sector which breaks supersymmetry dynamically. Despite the direct coupling, the models preserve perturbative unification of the SM gauge coupling constants. Furthermore, the supergravity contributions to the squark and slepton masses can be naturally small, typically being much less than 1% of the gauge mediated contributions. Both of these goals can be achieved without need of a fine-tuning or a very small coupling constant. This scheme requires run-away directions at the renormalizable level which are only lifted by non-renormalizable terms in the superpotential. To study the proposed scheme in practice, we develop a modified class of models based on $SU(N)\times SU(N-1)$ which allows us to gauge a $SU(N-2)$ global symmetry. However, we point out a new problem which can exist in models where the dynamical supersymmetry breaking sector and the ordinary sector are directly coupled -- the two-loop renormalization group has contributions which can induce negative $(mass)^2$ for the squarks and sleptons. We clarify the origin of the problem and argue that it is likely to be surmountable. We give a recipe for a successful model.
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arxiv:hep-ph/9701286
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The HQET/NRQCD Lagrangian is computed to order alpha/m^3. The computation is performed using dimensional regularization to regulate the ultraviolet and infrared divergences. The results are consistent with reparametrization invariance to order 1/m^3. Some subtleties in the matching conditions for NRQCD are discussed.
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arxiv:hep-ph/9701294
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In theories with gauge mediated supersymmetry breaking, the scalar tau, (${\tilde \tau_1}$) is the lightest superpartner for a large range of the parameter space. At the large electron positron collider (LEP 2) this scenario can give rise to events with four $\tau$ leptons and large missing energy. Two of the $\tau$'s ( coming from the decays of ${\tilde \tau_1}$'s ) will have large energy and transverse momentum, and can have similar sign electrical charges. Such events are very different from the usual photonic events that have been widely studied, and could be a very distinct signal for the discovery of supersymmetry.
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arxiv:hep-ph/9701341
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It is pointed out that the phase convention of the CKM matrix V affects texture analysis of the quark mass matrices (M_u, M_d) when we try to describe (M_u, M_d) by the observable quantities (quark masses and CKM matrix parameters) only. This is demonstrated for a case of the non-Hermitian Fritzsch-type mass matrix (tilde{M}_u, tilde{M}_d), which is a general expression of quark mass matrix (M_u, M_d) and is described by twelve parameters. We find that we can always choose a phase convention of V which yields tilde{M}_{u32} = 0, so that the remaining ten parameters in (tilde{M}_u, tilde{M}_d) can completely be expressed by the ten observable quantities.
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arxiv:hep-ph/9701345
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Consider a gauge singlet superfield S coupled to a pair of adjoint fields in a SUSY-GUT. If the tree-level vacuum is flat in S, the vev <S> which defines the GUT scale will be determined via dimensional transmutation at a scale M where the soft-breaking (mass)^2 vanishes as a result of running from $M_{Pl} = (8 \pi G_N)^{-1/2}$. Because of the large number of adjoint fields $N_A$ coupled to S, one finds that M can be generically close to $M_{GUT} = 2 \times 10^{16} GeV$: $M \simeq M_{Pl} \exp[-16 \pi^2 \log(3/2) / (N_A+4) \lambda^2]$, where $\lambda$ is a Yukawa $\sim$ 0.7. This work examines the symmetries and dynamical constraints required in a SUSY-GUT in order that the desired flatness in S is achieved, and that this flatness may survive in a supergravity framework.
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arxiv:hep-ph/9701373
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The study of the longitudinal polarization of Lambda and Lambda-bar hyperons produced in polarized deep inelastic scattering, neutrino scattering, and in Z0 decays allows to access the spin dynamics of the quark fragmentation process. Different phenomenological spin transfer mechanisms are considered and predictions for the Lambda and Lambda-bar longitudinal polarization in various processes using unpolarized and polarized targets are made. Current and future semi-inclusive deep inelastic scattering experiments will provide soon accurate enough data to study these phenomena and distinguish between various models for the spin transfer mechanisms.
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arxiv:hep-ph/9701384
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An explicit relativistic light-front quark model is presented which gives the momentum transfer dependent form factors of weak hadronic currents among heavy pseudoscalar and vector mesons in the whole accessible kinematic region $ 0\leq q^2 \leq q^2_{max} $. For the numerical investigations of the $ B \to D^* l \nu_l $, $ B \to \rho l \nu_l $, $ D\to K^* l \nu_l $ and $ D \to \rho l \nu_l $ semileptonic decays the equal time wave functions corresponding to the updated version of the ISGW model are adopted. Using the available experimental information on branching fractions $ BR(B \to D^* l \nu_l) $ and $ BR(B \to \rho l \nu_l) $ the CKM parameters $ V_{cb} $ and $ V_{ub} $ were estimated: $ |V_{cb}| = 0.036 \pm 0.004 $, $ |V_{ub}| = 0.0033 \pm 0.0004 $. The model is further tested by comparison with experimental data, QCD sum rules and lattice calculations.
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arxiv:hep-ph/9701388
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We calculate one-loop corrections to the single-top-quark production via $q\overline{q}' \to t\overline b$ at the Fermilab Tevatron from the Pseudo-Goldstone bosons ( PGBs ) in the framework of one generation technicolor model. The maximum correction to the total cross section for the single-top-quark production is found to reach -2.4% relative to the tree-level cross section, which may be observable at a high-luminosity Tevatron.
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arxiv:hep-ph/9701406
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Modern cosmology provides a connection between the physics of particles and fields and observational cosmology. Making use of this link, a wealth of new observational data can be utilized to explore and constrain theories of fundamental physics. Inflationary Universe models and topological defect theories are the most popular current paradigms for explaining the origin of structure in the Universe. In these lectures, I discuss various aspects of inflation and topological defects in which there has been interesting recent progress or in which there are outstanding problems. Particular emphasis is given to how baryogenesis scenarios can be influenced by inflation and topological defects.
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arxiv:hep-ph/9702217
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We discuss theoretical predictions for W-pair production and decay at LEP2 and higher energies in a form suitable for comparison with raw data. We present a practical framework for calculating uncertainties of predictions given by the KORALW and grc4f Monte Carlo programs. As an example we use observables in the $s\bar s c\bar c$ decay channel: the total four-quark (four-jet) cross section and two-quark/jet invariant-mass distribution and cross section, in the case when the other two may escape detection. Effects of QED bremsstrahlung, effective couplings, running W and Z widths, Coulomb interaction and the complete tree level set of diagrams are discussed. We also revisit the question of technical precision of the new version 1.21 of the KORALW Monte Carlo code as well as of version 1.2(26) of the grc4f one. Finally we find predictions of the two programs to have an overall physical uncertainty of 2%. As a side result we show, on the example of an $s\bar s$ invariant mass distribution, the strong interplay of spin correlations and detector cut-offs in the case of four-fermion final states.
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arxiv:hep-ph/9702249
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Pion and kaon observables are calculated using a Dyson-Schwinger Bethe-Salpeter formalism. It is shown that an infrared finite gluon propagator can lead to quark confinement via generation of complex mass poles in quark propagators. Observables, including electromagnetic form factors, are calculated entirely in Euclidean metric for spacelike values of bound state momentum and final results are extrapolated to the physical region.
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arxiv:hep-ph/9702251
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We present a massive Majorana neutrino model and see how it is constrained from the solar and atmospheric neutrino deficit experiments. This model incorporates the seesaw mechanism and Peccei-Quinn symmetry. Its consequence to the neutrinoless double beta decay is also discussed.
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arxiv:hep-ph/9702253
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We review the connection between m_t and the $Zb\bar b$ vertex in ETC models and discuss how data on R_b constrains ETC models. Theories in which the ETC and weak gauge groups do not commute are consistent with electroweak data and predict effects on single top production that will be visible at Fermilab.
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arxiv:hep-ph/9702261
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We have shown in hep-ph/9608266 that a neutrino magnetic moment form factor $\mu_{\nu} (q^2)$ could be considerably amplified at low momentum transfer,$q^2 \leq m_N^2$, at the cost of introducing an extra light neutral fermion $N$ with mass $m_N$ and nonzero magnetic moment. It was assumed that the magnetic moment of $N$ would originate in a renormalizable way at a heavy scale $M$. While the enhancement of the neutrino magnetic moment was unambiguous, we stressed that in this effective Lagrangian approach an uncertainty persisted about the behaviour of $\mu_{\nu} (q^2)$ in the interval $m_N^2 \ll q^2 \ll M^2$. This is not unexpected in presence of a nonrenormalizable effective theory (a particle with bare magnetic moment). We show in a simple renormalizable model for the magnetic moment of particle $N$ how a 2 loop calculation solves the ambiguity. In the domain $m_N^2 \ll q^2 \ll M^2$ we confirm the result obtained in hep-ph/9608266 using a sharp cut-off. It is amusing that the correct results are given, as expected, through dimensional regularization in the full theory, but not in the effective lagrangian approach.
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arxiv:hep-ph/9702317
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The method of differential renormalization is extended to the calculation of the one-loop graviton and gravitino corrections to $(g-2)_l$ in unbroken supergravity. Rewriting the singular contributions of all the diagrams in terms of only one singular function, U(1) gauge invariance and supersymmetry are preserved. We compare this calculation with previous ones which made use of momentum space regularization (renormalization) methods.
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arxiv:hep-ph/9702342
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We are presenting here the new formulae for Bose-Einstein correlations (BEC) which contain effects of final state interactions (FSI) of both strong (in $s$-wave) and electromagnetic origin. We demonstrate the importance of FSI in BEC by analysing data for $e^+e^-$ annihilation and for heavy collisions. The inclusion of FSI results in the practical elimination (at least in $e^+e^-$ data) of the so called degree of coherence parameter $\lambda$ (which becomes equal unity) and the long range parameter $\gamma$ (which is now equal zero).
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arxiv:hep-ph/9702346
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We evaluate the complete leading-order evolution kernels for the chiral-odd twist-3 distributions $e(x)$ and $\widetilde h_L(x)$ of the nucleon. We establish the connection between the evolution equations in light-cone position and light-cone fraction representations, which makes a correspondence between the non-local string operator product expansion and the QCD-inspired parton model. The compact expression obtained for the local anomalous dimension matrix coincides with previous calculations. In the multicolour QCD as well as in the large-$x$ limit the twist-3 distributions obey simple DGLAP equations. Combining these two limits, we propose improved DGLAP equations and compare them numerically with the solutions of the exact evolution equations.
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arxiv:hep-ph/9702354
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Recently, a semiclassical approach to diffraction has been proposed, which treats the proton as a classical colour field. The present paper demonstrates that this approach is consistent with the concept of diffractive parton distributions. The diffractive quark and gluon distributions are expressed through integrals of non-Abelian eikonal factors in the fundamental and adjoint representation respectively. As a by-product, previously calculated diffractive cross sections for processes with a final state gluon are rederived in a simpler way.
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arxiv:hep-ph/9702373
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We study the possibility of baryogenesis in the case of supersymmetry breaking with large mixing between the right-handed scalar charm and right-handed scalar top or right-handed scalar up and right-handed scalar top squarks resulting in one light right-handed up-type squark mass eigenstate. We argue that in this case the electroweak phase transition will be first order, and that large phases already present in the quark mass matrices can generate a baryon asymmetry of the correct magnitude without introducing any new phases specifically for this purpose. We study in detail a particular ansatz for supersymmetry breaking and CP violation where there is only one CP violating phase in the theory: in the up-type quark mass matrix. We study the constraints placed on this model by baryogenesis and flavor physics. This scenario has robust implications for low energy flavor phsyics including D-Dbar mixing and an electric dipole moment for the neutron that are close to the experimental bounds, and CP violation in the B-Bbar system that is different from that in the Standard Model.
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arxiv:hep-ph/9702423
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We present the analytical calculation in perturbative Quantum Chromodynamics of the (alpha_s)^3 contribution to the Ellis-Jaffe sum rule for the structure function g1 of polarized deep inelastic lepton-nucleon scattering.
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arxiv:hep-ph/9702435
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We analyze effects due to transverse degrees of freedom in QCD calculations of the fundamental hard exclusive amplitude of $\gamma^*\gamma \to \pi^0$ transition. A detailed discussion is given of the relation between the modified factorization approach (MFA) of Sterman et al. and standard factorization (SFA). Working in Feynman gauge, we construct basic building blocks of MFA from the one-loop coefficient function of the SFA, demonstrating that Sudakov effects are distinctly different from higher-twist corrections. We show also that the handbag-type diagram, contrary to naive expectations, does not contain an infinite chain of $(M^2/Q^2)^n$ corrections: they come only from diagrams with transverse gluons emitted from the hard propagator. A simpler picture emerges within the QCD sum rule approach: the sum over soft $\bar q G ... G q$ Fock components is dual to $\bar qq$ states generated by the local axial current. We combine the results based on QCD sum rules with pQCD radiative corrections and observe that the gap between our curves for the asymptotic and CZ distribution amplitudes is sufficiently large for an experimental discrimination between them.
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arxiv:hep-ph/9702443
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Exclusive semileptonic B decays into $D_1$ and $D_2^*$ mesons are investigated including order $\Lambda_{QCD}/m_{c,b}$ corrections using the heavy quark effective theory. At zero recoil, the $\Lambda_{QCD}/m_{c,b}$ corrections can be written in terms of the leading Isgur-Wise function for these transitions, $\tau$, and known meson mass splittings. We obtain an almost model independent prediction for the shape of the spectrum near zero recoil, including order $\Lambda_{QCD}/m_{c,b}$ corrections. We determine $\tau(1)$ from the measured $B\to D_1\ell\bar\nu$ branching ratio. Implications for B decay sum rules are discussed.
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arxiv:hep-ph/9703213
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We study the single production of heavy neutrinos via the processes $e^-e^+ \to \nu N$ and $e^-\gamma \to W^- N$ at future linear colliders. As a base of our considerations we take a wide class of models, both with vanishing and non-vanishing left-handed Majorana neutrino mass matrix $m_L$. We perform a model independent analyses of the existing experimental data and find connections between the characteristic of heavy neutrinos (masses, mixings, CP eigenvalues) and the $m_L$ parameters. We show that with the present experimental constraints heavy neutrino masses almost up to the collision energy can be tested in the future experiments.
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arxiv:hep-ph/9703215
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We develop a theory of the EPR-like effects due to neutrino oscillations in the $\pi \to \mu\nu$ decays. Its experimental implications are space-time correlations of neutrino and muon when they are both detected, while the pion decay point is not fixed. However, the more radical possibility of muon oscillations in experiments where only muons are detected (as it has been suggested in hep-ph/9509261), is ruled out. We start by discussing decays of monochromatic pions, and point out a few ``paradoxes''. Then we consider pion wave packets, solve the ``paradoxes'', and show that the formulas for $\mu nu$ correlations can be transformed into the usual expressions, describing neutrino oscillations, as soon as the pion decay point is fixed.
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arxiv:hep-ph/9703241
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A new evaluation of the universal $\pi\pi$ scattering length relation is used to extract the $\pi\pi$ $s$-wave scattering lengths from threshold pion production data. Previous work has shown that the chiral perturbation series relating threshold pion production to $\pi\pi$ scattering lengths appears to converge well only for the isospin-2 case, giving $a_2 = -0.031\pm 0.007 m_\pi^{-1}$. A model-independent and data-insensitive universal curve then implies $a_0 = 0.235\pm 0.03 m_\pi^{-1}$ for the isospin-0 scattering length.
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arxiv:hep-ph/9703247
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The combined absence of physical realizations of the UA(1) symmetry possessed by the classical QCD action in the chiral limit, and of an isoscalar Goldstone boson associated with its spontaneous breakdown, has been dubbed the UA(1) problem. A formal resolution of this problem proposed by 't Hooft relies on instantons to provide a mass to the would-be Goldstone boson (eta '). An alternate scheme for the generation of an eta ' mass proposed by Kogut and Susskind derives from quark annihilation into gluons and a strong infrared singularity in the gluon propagator associated with confinement. We demonstrate here how such diagrams are generated in quark based effective theories by including a certain class of diagrams which arise from correlated q qbar exchange and are of higher order 1/N_c. A low energy energy expansion of this corrections is of the form discussed by Witten, di Vecchia and Veneziano.
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arxiv:hep-ph/9703270
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The minimal supersymmetric standard model (MSSM), is perhaps the leading candidate for new physics beyond the standard model, but it encounters difficulties with string gauge unification and in addition does not shed any light on the question of fermion masses. We consider a scenario in which the MSSM is valid up to an energy scale of 10^16 GeV, but that above this scale the theory is supplemented by extra vector-like representations of the gauge group, plus a gauged U(1)_X family symmetry. In our approach the extra heavy matter above the scale 10^16 GeV is used in two different ways: (1) to allow (two-loop) gauge coupling unification at the string scale; (2) to mix with quarks, leptons and Higgs fields via spaghetti diagrams and so lead to phenomenologically acceptable Yukawa textures. We determine the most economical models in which the extra matter can satisfy both constraints simultaneously. We then give a general discussion of the infra-red fixed points of such models, pointing out the conditions for infra-red stability, then discuss two semi-realistic examples: a Higgs mixing model, and a quark mixing model.
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arxiv:hep-ph/9703293
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We look for a mechanism that removes without numerical fine tuning the strong constraint imposed by the flavor changing neutral current interaction of leptoquark exchange. If n x n degenerate leptoquarks couple universally to n generations of quarks and leptons in the weak basis, not only can the neutral current interactions be flavor diagonal, but also the charge current interaction takes exactly the same form as W exchange at low energies. Atomic parity violation still imposes tight constraints. Electroweak doublets with some left-right symmetry have the best chance to be the lightest leptoquarks.
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arxiv:hep-ph/9703316
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We calculate the decay constant ratios $f_{\eta_c}/f_{J/\psi}$ and $f_{\eta_b}/f_\Upsilon$. In the calculation we take into account the mock meson structures of the mesons, as well as the difference of the wave functions at origin of the vector and pseudoscalar mesons studied by Ahmady and Mendel. We find that the different spin structures of the mesons much affect the ratios. We incorporate our results in the prediction of the branching ratios of $B\to K \eta_c$.
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arxiv:hep-ph/9703364
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Starting from the relativistic gauge-invariant quark-antiquark Green function we obtain the relevant interaction in the one-body limit, which can be interpreted as the kernel of a non-perturbative Dirac equation. We study this kernel in different kinematic regions, reproducing, in particular, for heavy quark the potential case and sum rules results. We discuss the relevance of the result for heavy-light mesons and the relation with the phenomenological Dirac equations used up to now in the literature.
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arxiv:hep-ph/9703377
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If massive neutrinos possess magnetic moments, they can undergo spin flip in a magnetic field. The magnetic fields needed for a meaningful measurement of neutrino moments could be very high and may occur in astronomical objects such as some supernovae or active galactic nuclei: they are typically chaotic ones. We develop the general theory of the passage of neutrinos through such fields. We also develop a simple model which becomes solvable in the high energy limit. Both helicities occur with equal probability, independently of the initial distribution. Observational consequences are discussed.
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arxiv:hep-ph/9703382
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The isosinglet unpolarized and isovector polarized twist-2 quark distributions of the nucleon at low normalization point are calculated in the large-Nc limit. The nucleon is described as a soliton of the effective chiral theory. We derive the expressions for the distribution functions in the large-Nc limit starting from their definition as numbers of partons carrying momentum fraction x in the infinite momentum frame. We develop a numerical method for computation of the quark and antiquark distributions as sums over the quark single-particle levels in the pion field of the soliton. The contributions of the discrete bound-state level as well as the Dirac continuum are taken into account. The quark- and antiquark distributions obtained explicitly satisfy all general requirements. Results are in reasonable agreement with parametrizations of the data at low normalization point.
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arxiv:hep-ph/9703420
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The status of precision electroweak data, tests of the standard model, determination of its parameters, and constraints on new physics, are surveyed.
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arxiv:hep-ph/9703428
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The role that quasiparticles play in a strong interaction system with spontaneous symmetry breaking is examined. We find, using a non- perturbative cluster decomposition method, that the quasiparticles do not saturate the physical local observables at small distances. The fermion number density serves as a clearcut example. A component due to localized random quantum fluctuations of the order parameter(s) in the vacuum state and the contributions of ``quasiparticles'' corresponding to other local minima of the effective potential is needed. At large distances, the ordinary quasiparticle picture emerges in the response of the system to classical background fields but the above mentioned component acts as a source for them.
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arxiv:hep-ph/9704216
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We use Quark Combination Model to study baryon antibaryon rapidity correlation in e^+e^- annihilation and compare our predictions with the available data. We find that these results and relevant properties are all consistent with data. So the evidence to rule out Quark Combination Model which has long been cited in literatures does not exist.
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arxiv:hep-ph/9704271
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Available data on measured observables allow deriving estimates for some of the phenomenological parameters that characterize the time-evolution and decay of the neutral kaon system based on the hypothesis of complete positivity. The present experimental uncertainties are still too large to permit a full test of complete positivity.
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arxiv:hep-ph/9704283
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We provide a detailed, model-independent, study for CP violation effects due to the T-odd top-quark electric dipole moment (EDM) and weak dipole moment (WDM) in the top-quark pair production via $e^+e^-$ and two-photon annihilation at a next $e^+e^-$ linear collider (NLC). There are two methods in detecting CP violation effects in these processes. One method makes use of measurements of various spin correlations in the final decay products of the produced top-quark pair, while the other is to measure various CP-odd polarization asymmetry effects of the initial states. In the $e^+e^-$ case only the first method can be used, and in the $\gamma\gamma$ case both methods can be employed. We provide a complete classification of angular correlations of the $t$ and $\bar{t}$ decay products under CP and CP\tilde{T} which greatly faciliate CP tests in the $e^+e^-$ mode. Concentrating on the second method with the Compton back-scattered high-energetic laser light off the electron or positron beam in the two-photon mode, we construct two CP-odd and CP\tilde{T}-even initial polarization configurations and apply them to investigating CP-violating effects due to the top-quark EDM. With a typical set of experimental parameters at the NLC, we compare the 1-\sigma sensitivities to the top-quark EDM and WDM in the $e^+e^-$ mode and the two-photon mode. Some model expectation values of the T-odd parameters are compared with the results.
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arxiv:hep-ph/9704312
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The possibility that the mass hierarchy is intimately associated with the compositeness level of the matters is proposed in supersymmetric gauge theory. This implies, for instance, that the preons constituting top quark consists of the ``prepreons'' binded by the same gauge force making the charm quark out of another preons. The exemplifying toy model illustrates how the hierarchy in the yukawa coupling constants in the up-quark sector is generated from the underlying gauge dynamics. It is also indicated that the incorporation of down-type quarks as elementary objects leads to unpleasant results generically. Thus all the quarks as well as the leptons must also be regarded as composite in the present approach.
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arxiv:hep-ph/9704329
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J/\psi production associated with a hard photon in e^+e^- annihilation, being of QED nature, is invastigated thoroughly in the paper. To show its influence on the observation of the color-octet singnature in the e^+e^- annihilation via J/\psi inclusive production, the cross sections of the J/\psi productions through different mechanisms at various energies are compared quantatively by presenting them in figures together. The contribution from the production associated with a hard photon to the inclusive production of J/\psi is pointed out to be significant at the concerned energies, thus the influence from it on the observation of the color-octet signature should be dealt with carefully.
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arxiv:hep-ph/9704364
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We argue that diffractive DIS, dominated by soft interactions, is probably the unique process which allows us to observe unitarity effects in DIS. Guided by a close analogy between the diffractive dissociation of a highly virtual photon and the elastic scattering of hadrons we propose a specific procedure to analyse the data in order to detect the onset of the unitarity limit. Lacking appropriate data, we use the predictions of a realistic model as an input for our analysis, to demonstrate that the output unitarity signal is sufficiently large to be detectable.
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arxiv:hep-ph/9704372
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In this work we re-examine the opacity of the cosmic background radiation to the propagation of extremely high energy cosmic rays. We use the continuous energy loss approximation to provide spectral modification factors for several hypothesized cosmic ray sources. Earlier problems with this approximation are resolved including the effects of resonances other than the $\Delta$.
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arxiv:hep-ph/9704387
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Three-loop corrections to the scalar and pseudo-scalar current correlator are calculated. By applying the large momentum expansion mass terms up to order (m^2/q^2)^4 are evaluated analytically. As an application O(\alpha_s^2) corrections to the decay of a scalar and pseudo-scalar Higgs boson into top quarks are considered. It is shown that for a Higgs mass not far above the $t\bar{t}$ threshold these higher order mass corrections are necessary to get reliable results.
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arxiv:hep-ph/9704436
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The top quark data in the lepton plus $\tau$ channel offers a viable probe for the charged Higgs boson signal. We have analysed the recent Collider Detector at Fermilab (CDF) data in this channel to obtain a significant limit on the $H^\pm$ mass in the large $\tan\beta$ region.
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arxiv:hep-ph/9704442
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We have quantitatively reanalyzed the inclusive charmed-baryon decays. New ingredients are the Voloshin preasymptotic effects in semileptonic decays and the Cabibbo-subleading contributions to both semileptonic and nonleptonic decays. It has been found that the Cabbibo-subleading Voloshin contribution essentially improves the theoretical semileptonic branching ratio of $\Lambda_c^{+}$, in agreement with experiment. The semileptonic branching ratios for $\Xi_c^{+}$ and $\Omega_c^{0}$ are found to be large, i.e., of the order of 20%. The lifetimes hierarchy is in a good qualitative and even quantitative agreement with experiment except for the $\Xi_c^{+}$ lifetime, which is somewhat smaller than the experimental value. Future measurements, especially measurements of the semileptonic branching ratios for $\Omega_c^{0}$, $\Xi_c^{+}$ and $\Xi_c^{0}$ should be decisive for the check of this approach.
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arxiv:hep-ph/9704445
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The collimation $C$ of a hadronic event in the e^+e^- annihilation is defined as the average of $\cos\theta$, $C=<\cos\theta>$, where $\theta$ is the angle of each hadron measured from the thrust axis, and the average is over all the hadrons produced in an event. It is an infrared-stable event-shape parameter. $1-\bar C$, the difference between the unity and the average collimation at a given energy, is proportional to the anomalous dimension of the hadron multiplicity at the leading order in MLLA. Its next-to-leading order corrections are calculated.
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arxiv:hep-ph/9705238
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We present in analytic form the three-loop O(\alpha_s^2) correction to the H -> gg partial width of the standard-model Higgs boson with intermediate mass M_H << 2 M_t. Its knowledge is required because the O(\alpha_s) correction is so sizeable that the theoretical prediction to this order is unlikely to be reliable. For M_H=100 GeV, the resulting QCD correction factor reads $1+(215/12)\alpha_s^{(5)}(M_H)/\pi+150.419 (\alpha_s^{(5)}(M_H)/\pi)^2 \approx 1+0.66+0.21$. The new three-loop correction increases the Higgs-boson hadronic width by an amount of order 1%.
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arxiv:hep-ph/9705240
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New mechanism for the observed inclusive B -> \eta'X decay is suggested. We argue that the dominant contribution to this amplitude is due to the Cabbibo favored b -> \bar{c}cs process followed by the transition \bar{c}c -> \eta'. A large magnitude of the "intrinsic charm" component of \eta' is of critical importance in our approach. Our results are consistent with an unexpectedly large Br(B -> \eta'+X) \sim 10^{-3} recently announced by CLEO. We stress the uniqueness of this channel for 0^{-+} gluonia search.
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arxiv:hep-ph/9705251
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In this paper the three-loop polarization functions \Pi(q^2) are calculated for the cases of an external vector, axial-vector, scalar or pseudo-scalar current. Results are presented for the imaginary part which directly leads to the cross section $\sigma(e^+e^- \to Z \to hadrons)$ and to the Higgs decay rates, respectively.
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arxiv:hep-ph/9705254
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We present a model for the observed hierarchies among the Yukawa couplings of the standard model in the context of an effective low energy theory with an anomalous U(1) symmetry. This symmetry, a generic feature of superstring compactification, is a remnant of the Green-Schwarz anomaly cancellation mechanism. The gauge group is that of the standard model, augmented by X, the anomalous U(1), and two family-dependent phase symmetries $Y^{(1)}$ and $Y^{(2)}$. The correct hierarchies are reproduced only when $sin^2\theta_w=3/8$ at the cut-off. To cancel anomalies, right-handed neutrinos and other standard model singlets must be introduced. Independently of the charges of the right-handed neutrinos, this model produces the same neutrino mixing matrix and an inverted hierarchy of neutrino masses. The heaviest is the electron neutrino with a mass $\sim 1$ meV, and mixing of the order of $\lambda_c^3$ with each of the other two neutrinos.
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arxiv:hep-ph/9705270
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I review the ability of the LHC (large hadron collider), NLC (next linear lepton collider) and FMC (first muon collider) to detect and study Higgs bosons, with emphasis on the Higgs bosons of extended Higgs sectors, especially those of the minimal supersymmetric standard model (MSSM). Particular attention is given to means for distinguishing the lightest neutral CP-even Higgs boson of the MSSM from the single Higgs boson of the minimal Standard Model (SM).
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arxiv:hep-ph/9705282
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The low $x$ limit of deep inelastic electron proton scattering is considered using methods of perturbative QCD. In the first part we investigate the phenomenological consequences of the resummation of leading logarithms in $1/x$ given by the BFKL pomeron. We apply the BFKL pomeron to the inclusive structure function $F_2$, to the diffractive production of vector mesons at large momentum transfer, to inclusive photon diffractive dissociation in DIS and to quark-antiquark production with large transverse momenta in DIS diffractive dissociation. For the last process we perform extensive numerical calculations based on the double logarithmic approximation. The BFKL pomeron is known to violate unitarity. In the second part the first next-to-leading corrections which have to be taken into account to restore unitarity of the scattering amplitude are investigated. A compact configuration space representation of the two to four gluon transition vertex is derived. Conformal symmetry of the vertex is proven and its relation to a conformal covariant three point function is established. The important role of the spectral function $\chi_4$ of the four gluon state is pointed out. We relate this function to the twist expansion of the four gluon amplitude. Motivated by this relation we develop a method to perform the twist expansion of the amplitude. Based upon first results of our analysis we draw conclusions concerning the singularity structure of the function $\chi_4$.
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arxiv:hep-ph/9705288
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We show that QCD Minkowski observables such as the $e^{+}e^{-}$ R-ratio and the hadronic tau decay $R_{\tau}$ are completely determined by the effective charge (EC) beta-function, $\rho(x)$, corresponding to the Euclidean QCD vacuum polarization Adler D-function, together with the next-to-leading order (NLO) perturbative coefficient of D. An efficient numerical algorithm is given for evaluating R, $R_{\tau}$ from a weighted contour integration of $D(se^{i\theta})$ around a circle in the complex squared energy s-plane, with $\rho(x)$ used to evolve in s around the contour. The EC beta-function can be truncated at next-to-NLO (NNLO) using the known exact perturbative calculation or the uncalculated N^3 LO and higher terms can be approximated by the portion containing the highest power of b, the first QCD beta-function coefficient. The difference between the R, $R_{\tau}$ constructed using the NNLO and "leading-b" resummed versions of $\rho(x)$ provides an estimate of the uncertainty due to the uncalculated higher order corrections. Simple numerical parametrizations are given to facilitate these fits. For $R_{\tau}$ we estimate an uncertainty $\delta\alpha_{s}(m_{\tau}^{2})\simeq0.01$, corresponding to $\delta\alpha_{s}(M_{Z}^{2})\simeq0.002$. This encouragingly small uncertainty is much less than rather pessimistic estimates by other authors based on analogous all-orders resummations, which we demonstrate to be extremely dependent on the chosen renormalization scheme, and hence misleading.
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arxiv:hep-ph/9705314
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The recent calculation of the four-loop beta function in QCD provides further evidence that the Banks-Zaks expansion in 16half-n_f is sufficiently well behaved to be useful even for n_f=2 light flavours. This expansion inherently predicts "freezing" of the QCD couplant at low energies as a perturbative effect. We consider the e+e- and Bjorken-sum-rule cases as examples.
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arxiv:hep-ph/9705319
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We present the higher order QCD corrections to the fragmentation functions and the corresponding cross sections.
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arxiv:hep-ph/9705343
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We consider in this paper a Left-Right symmetric gauge model in which a global lepton-number-like symmetry is introduced and broken spontaneously at a scale that could be as low as 10^4 GeV or so. The corresponding physical Nambu-Goldstone boson, which we call majoron and denote J, can have tree-level flavour-violating couplings to the charged fermions, leading to sizeable majoron-emitting lepton-flavour-violating weak decays. We consider explicitly a leptonic variant of the model and show that the branching ratios for \mu -> e+J, \tau -> e + J and \tau -> \mu + J decays can be large enough to fall within the sensitivities of future \mu and \tau factories. On the other hand the left-right gauge symmetry breaking scale may be as low as few TeV.
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arxiv:hep-ph/9705394
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We present a brief description of the determination of the two-loop spin-dependent time-like splitting functions relevant for the NLO evolution of polarized fragmentation functions. Our calculation based on the analytic continuation of the corresponding space-like results obtained within the light-cone gauge method proposed by Curci, Furmanski, and Petronzio. As an application we present an analysis of polarized Lambda production in e+e- and ep collisions.
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arxiv:hep-ph/9705415
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Brooding over bosons, wave packets and Bose - Einstein correlations, we find that a generalization of the pion-laser model for the case of overlapping wave-packets is analytically solvable with complete n-particle symmetrization. The effective radius parameter of the two-particle correlation function is reduced for low values and enlargened for high values of the mean momentum in the rare gas limiting case, as compared to the case when multi-particle symmetrization effects are neglected. These results explicitly depend on the multiplicity, providing a theoretical basis for event-by-event analysis of high energy heavy ion reactions.
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arxiv:hep-ph/9705433
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CP violation in K and B decays is reviewed in the Standard Model (SM) and beyond the SM. In K decays, one is seeking first evidence for CP violation in direct $K\to \pi\pi$ decays. This would not give a precise quantitative test for the present explanation of CP violation in terms of a phase in the Cabibbo-Kobayashi-Maskawa (CKM) matrix. Such tests are provided by a variety of CP asymmetries in neutral and charged B decays. Certain features, characterizing CP violation beyond the standard model, are outlined in the B meson system.
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arxiv:hep-ph/9705440
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We consider diagonal and non-diagonal QCD sum rules for the ground state heavy baryons to leading order in $1/m_Q$ and at next-to-leading order in $\alpha_S$. In the non-diagonal case we evaluate the eight different two-loop diagrams which determine the perturbative $\alpha_S$-corrections to the Wilson coefficient of the quark condensate in the Operator Product Expansion. The QCD corrections to the non-diagonal sum rules are moderate compared to the QCD corrections in the diagonal case. We also consider constituent type sum rules using constituent type interpolating currents. The obtained results are in reasonable agreement with the corresponding results obtained in the diagonal case. As central values for the bound state energies we find $m(\Lambda_Q)-m_Q = 760 MeV$ and $m(\Sigma_Q)-m_Q = 940 MeV$. The central values for the residues are given by $F(\Lambda_Q) = 0.030 GeV^3$ and $F(\Sigma_Q) = 0.038 GeV^3$.
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arxiv:hep-ph/9705447
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