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We estimate the attainable limits on the coefficients of dimension--6 operators from the analysis of Higgs boson phenomenology, in the framework of a $SU_L(2) \times U_Y(1)$ gauge-invariant effective Lagrangian. Our results, based on the data sample already collected by the collaborations at Fermilab Tevatron, show that the coefficients of Higgs-vector boson couplings can be determined with unprecedented accuracy. Assuming that the coefficients of all ``blind'' operators are of the same magnitude, we are also able to impose more restrictive bounds on the anomalous vector-boson triple couplings than the present limit from double gauge boson production at the Tevatron collider.
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arxiv:hep-ph/9801250
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We establish the existence of a static, classically stable string solution in a region of parameters of the generic two-Higgs Standard Model. In an appropriate limit of parameters, the solution reduces to the well-known soliton of the O(3) non-linear sigma model.
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arxiv:hep-ph/9801263
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For a proper theoretical description of the top quark pair production cross section at the First Muon Collider in the kinematic regime away from the threshold the complete mass and energy dependence has to be taken into account. Two-loop calculations for the photon mediated total cross section are reviewed.
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arxiv:hep-ph/9801275
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In the framework of the hard pomeron model it is shown that at large $Q^2$ the diffractive contribution to the structure functions rises as $Q^{0.3362}$ and much slowlier than the total contribution rising as $Q$.
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arxiv:hep-ph/9801278
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To understand the short-distance vs long-distance final-state interactions, we have performed a detailed amplitude analysis for the two-body decay, J/psi into vector and pseudoscalar mesons. The current data favor a large relative phase nearly 90 degrees between the three-gluon and one-photon decay amplitudes. The source of this phase is apparently in the long-distance final-state interaction. Nothing anomalous is found in the magnitudes of the three-gluon and one-photon amplitudes. We discuss implications of this large relative phase in the weak decay of heavy particles.
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arxiv:hep-ph/9801284
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We discuss the possible generation of R-parity violating bilinear terms $ \mu_i\bar L_i H_2$ in both cases of gravity and gauge mediated supersymmetry breaking. Some phenomenological aspects are reviewed. In particular for scenario where $ \mu_i$ depend on the vacuum expectation values of some fields $S$, its fermionic partner $\tilde S$ plays the role of a sterile neutrino. This situation is quiet generic in the case of models arising from M-theory where $S$ is a modulus field. Observable effects are expected to be seen if the mass and mixing of $\tilde S$ with active neutrinos lie in an interesting region of parameters. This is naturally the case in gauge mediated supersymmetry breaking and some class of no-scale supergravity models where the gravitino mass is very small. For models with gravitino mass $m_{3/2}\sim$ TeV, we discuss the possibility that the modulino mass is of the order of $m^2_{3/2}/M_{Pl}$.
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arxiv:hep-ph/9801303
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The decay of disoriented chiral condensates into soft pions is considered within the context of a linear sigma model. Unlike earlier analytic studies, which focused on the production of pions as the sigma field rolled down toward its new equilibrium value, here we focus on the amplification of long-wavelength pion modes due to parametric resonance as the sigma field oscillates around the minimum of its potential. This process can create larger domains of pion fluctuations than the usual spinodal decomposition process, and hence may provide a viable experimental signature for chiral symmetry breaking in relativistic heavy ion collisions; it may also better explain physically the large growth of domains found in several numerical simulations.
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arxiv:hep-ph/9801307
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The odderon intercept $ \alpha $ is recalculated by the variational method based on conformal invariance. The final result is $\alpha=1-0.339 \alpha_s N/\pi$ in contrast to the published value above unity.
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arxiv:hep-ph/9801352
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Contributions to B - \bar B mixing from physics beyond the standard model may be detected from CP-violating asymmetries in B decays. There exists the possibility of large new contributions that cannot be detected by first generation experiments because of a discrete ambiguity. Some possible strategies for resolving this are discussed.
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arxiv:hep-ph/9801386
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The $\nu_{\mu} \to \nu_{\tau}$ and $\nu_{\mu} \to \nu_s$ solutions to the atmospheric neutrino problem are compared with SuperKamiokande data. The differences between these solutions due to matter effects in the Earth are calculated for the ratio of $\mu$-like to $e$-like events and for up-down flux asymmetries. These quantities are chosen because they are relatively insensitive to theoretical uncertainties in the overall neutrino flux normalisation and detection cross-sections and efficiencies. A $\chi^2$ analysis using these quantities is performed yielding $3\sigma$ ranges which are approximately given by $(0.725 - 1.0, 4 \times 10^{-4} - 2 \times 10^{-2} eV^2)$ and $(0.74 - 1.0, 1 \times 10^{-3} - 2 \times 10^{-2} eV^2)$ for $(\sin^2 2\theta,\Delta m^2)$ for the $\nu_{\mu} \to \nu_{\tau}$ and $\nu_{\mu} \to \nu_s$ solutions, respectively. Values of $\Delta m^2$ smaller than about $2 \times 10^{-3}$ eV$^2$ are disfavoured for the $\nu_{\mu} \to \nu_s$ solution, suggesting that future long baseline experiments should see a positive signal if this scenario is the correct one.
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arxiv:hep-ph/9801431
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Specific results of the computer simulation of dilepton production from expanding pion gas created in Pb+Pb 160 GeV/n collisions are presented. Azimuthal asymmetry of dilepton pairs in non-central collisions and interesting shape of the rapidity distribution of dilepton pairs are predicted. These results are understood on theoretical level as a consequence of momentum and space asymmetries in the initial state of pion gas without any assumption of thermalization. Implication on the production of dileptons in pre-hadronic phase of HIC is drawn.
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arxiv:hep-ph/9802207
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It is shown that the singular seesaw mechanism can simultaneously explain all the existing data supporting nonzero neutrino masses and mixing. The three mass-squared differences that are needed to accommodate the atmospheric neutrino data (through $\nu_\mu - \nu_s$ oscillation), the solar neutrino data via MSW mechanism (through $\nu_e - \nu_\tau$ oscillation), and the positive result of $\nu_\mu - \nu_e$ oscillation from LSND can be generated by this mechanism, whereas the vacuum oscillation solution to the solar neutrino problem is disfavored. We find that the electron and tau neutrino masses are of order $10^{-3}$ eV, and the muon neutrino and a sterile neutrino are almost maximally mixed to give a mass of order 1 eV. Two heavy sterile neutrinos have a mass of order 1 keV which can be obtained by the double seesaw mechanism with an intermediate mass scale $\sim 10^5$ GeV. A possible origin of such a scale is discussed.
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arxiv:hep-ph/9802209
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An eight-component formalism is proposed for the relativistic two-fermion problem. In QED, it extends the applicability of the Dirac equation with hyperfine interaction to the positronium case. The use of exact relativistic two-body kinematics entails a CP-invariant spectrum which is symmetric in the total cms energy. It allows the extension of recent \alpha^6 recoil corrections to the positronium case, and implies new recoil corrections to the fine and hyperfine structures and to the Bethe logarithm.
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arxiv:hep-ph/9802233
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An idea of possible anomalous contribution of non-perturbative origin to the nucleon spin was examined by analysing data on spin asymmetries in polarized deep inelastic scattering of leptons on nucleons. The region of high Bjorken x was explored. It was shown that experimental data available at present do not evidence for this effect.
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arxiv:hep-ph/9802266
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The dependence of the fractal behaviors of the pomeron induced system in deep inelastic lepton-nucleon scattering upon the diffractive kinematic variables is found rather robust and not sensitive to the distinct parameterization of the pomeron flux factor and structure function. A feasible experimental test of the phenomenological pomeron-exchanged model based on the fractal measurement in DESY $ep$ collider HERA is proposed.
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arxiv:hep-ph/9802269
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The ratios of partial rates for charged B decays to the recently observed $D^0 K$ mode and to the two $D_{CP}K$ final states (CP = $\pm$) are shown to constrain the weak phase $\gamma \equiv {\rm Arg} (V_{ub}^*)$. The smaller color-suppressed rate, providing further information about the phase, can be determined from these rates alone. Present estimates suggest that, while the first constraints can already be obtained in a high luminosity e^+e^- B factory, measuring the color-suppressed rate would require dedicated hadronic B production experiments.
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arxiv:hep-ph/9802315
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The two body non-leptonic $\Lambda_b$ decays are analyzed in factorization approximation, using quark model, $\xi = 1 / N_c$ as a free parameter. It is shown that the experimental branching ratio for $\Lambda_b \longrightarrow \Lambda {J/\psi}$ restricts $\xi$ and this ratio can be understood for a value of $\xi$ which lies in the range $ 0 \leq \xi \leq 0.5 $ suggested by two body B meson decays. The branching ratios for $\Lambda_b \longrightarrow \Lambda_{c} D^*_s(D_s) $ are predicted to be larger than the previous estimates. Finally it is pointed that CKM-Wolfenstein parameter $\rho^2 + \eta^2$, where $\eta$ is CP phase, can be determined from the ratio of widths of $\Lambda_b \longrightarrow \Lambda \bar{D}$ and $\Lambda_b \longrightarrow \Lambda {J/\psi}$ or that of $\Lambda_b \longrightarrow p D_s$ and $\Lambda_b \longrightarrow \Lambda_c D_s$ independent of the parameter $\xi$.
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arxiv:hep-ph/9802326
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We calculate the next-to-next-to-leading order correction to the cross section for top quark pair production in e+e- annihilation in the threshold region, resumming all O [ (alpha_s/beta)^n (alpha_s^2, beta^2, alpha_s beta) ] terms of perturbation series. We find that the magnitude of the NNLO correction is comparable to the size of the NLO corrections.
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arxiv:hep-ph/9802379
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A method developed from the Dualized Standard Model for calculating the quark CKM matrix and masses is applied to the parallel problem in neutrino oscillations. Taking the parameters determined from quarks and the masses of two neutrinos: $m_3^2 \sim 10^{-2} - 10^{-3} eV^2$ suggested by atmospheric neutrino data, and $m_2^2 \sim 10^{-10} eV^2$ suggested by the long wave-length oscillation (LWO) solution of the solar neutrino problem, one obtains from a parameter-free calculation all the mixing angles in reasonable agreement with existing experiment. However, the scheme is found not to accommodate comfortably the mass values $m_2^2 \sim 10^{-5} eV^2$ suggested by the MSW solution for solar neutrinos.
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arxiv:hep-ph/9802420
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We categorize general messenger and matter interactions in gauge-mediated SUSY breaking models by an R-parity for the messengers and study their phenomenological consequences. The new interactions may induce baryon- and lepton-number violating processes as well as flavor-changing neutral currents. Bounds on the couplings from low-energy data are generally weak due to the large messenger mass suppression, except for the constraint from proton decay. The soft masses for the scalar particles receive negative corrections from the new interactions. Consequently, in certain region of SUSY parameter space the \mu-parameter is greatly reduced. The pattern of radiative electroweak symmetry breaking, SUSY particle mass spectrum and decay channels are also affected, leading to observable experimental signature at the current and future colliders.
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arxiv:hep-ph/9802422
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Motivated by the need to understand hadron masses, we reexamine an old problem in QED - the composition of the electron mass - in a modern perspective. We find that in the unrenormalized QED, the vacuum subtraction plays an important role in understanding various sources of the electron mass. The same issue is also discussed in the modified minimal subtraction scheme with an emphasis on the scale and scheme dependence in the analysis.
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arxiv:hep-ph/9802437
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Approximately taking into account the higher-order effects due to multiple-gluon initial-state radiation, we extract from the latest Tevatron data of prompt J/psi hadroproduction the leading colour-octet matrix elements within the nonrelativistic-QCD (NRQCD) factorization formalism proposed by Bodwin, Braaten, and Lepage. We find that the matrix elements which describe the formation of J/psi mesons from colour-octet cc-bar pairs in the angular-momentum states ^{2S+1}L_J = ^1S_0 and ^3P_J, with J = 0,1,2, which are responsible for the excess of the predicted cross section of inelastic J/psi photoproduction over the existing HERA data at high values of the inelasticity variable z, are significantly reduced. We conclude that it is premature to proclaim a discrepancy between the Tevatron and HERA measurements of inclusive J/psi production in the NRQCD framework. We also consider J/psi mesons originating from the radiative feed down of promptly produced chi_{cJ} mesons.
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arxiv:hep-ph/9803256
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We generalize a previous construction of a fermiophobic model to the case of more than one extra $W$ and $Z$ gauge bosons. We focus in particular on the existence of screening configurations and their implication on the gauge boson mass spectrum. One of these configurations allows for the existence of a set of relatively light new gauge bosons, without violation of the quite restrictive bounds coming from the $\rho_{\rm NC}$ parameter. The links with Bess and degenerate Bess models are also discussed. Also the signal given here by this more traditional gauge extension of the SM could help to disentangle it from the towers of Kaluza-Klein states over $W$ and $Z$ gauge bosons in extra dimensions.
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arxiv:hep-ph/9803278
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We investigate the eigenvalue spectrum of the staggered Dirac matrix in SU(3) gauge theory and in full QCD on a $6^3\times 4$ lattice. As a measure of the fluctuation properties of the eigenvalues, we study the nearest-neighbor spacing distribution $P(s)$ for various values of $\beta$ both in the confinement and in the deconfinement phase. In both phases except far into the deconfinement region, the lattice data agree with the Wigner surmise of random-matrix theory which is indicative of quantum chaos. We do not find signs of a transition to Poisson regularity at the deconfinement phase transition.
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arxiv:hep-ph/9803285
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Using the Gell-Mann-Oakes-Renner (GOR) relation and semi-classical arguments, we show that the bulk quark spectrum in QCD exhibits a variety of regimes including the ergodic one described by random matrix theory. We analyze the quark spectral form-factor in the diffusive and ballistic regime. We suggest that a class of chiral transitions in QCD is possibly of the metal-insulator type, with a universal spectral statistics at the mobility edge.
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arxiv:hep-ph/9803289
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Large corrections to the quark mass matrices at the supersymmetric threshold allow the theory to have identical Yukawa matrices in the superpotential. We demonstrate that Up-Down unification can take place in a moderate quark-squark alignment scenario with an average squark mass of the order 1 TeV and with $\tan\beta>15$
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arxiv:hep-ph/9803354
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The ability of high energy lepton and photon colliders to probe the gauge couplings of the top-quark is summarized.
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arxiv:hep-ph/9803369
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The ability of present and future experiments to test the Standard Model in the $B$ meson sector is described. We examine the loop effects of new interactions in flavor changing neutral current $B$ decays and in $Z\to b\bar b$, concentrating on supersymmetry and the left-right symmetric model as specific examples of new physics scenarios. The procedure for performing a global fit to the Wilson coefficients which describe $b\to s$ transitions is outlined, and the results of such a fit from Monte Carlo generated data is compared to the predictions of our two sample new physics scenarios. A fit to the $Zb\bar b$ couplings from present data is also given.
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arxiv:hep-ph/9803370
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The alternative to the standard formulation of the quark-parton model is proposed. Our relativistically covariant approach is based on the solution of the master equations relating the structure and distribution functions, which consistently takes into account the intrinsic quark motion - in contradistinction to the standard infinite momentum approach, in which this motion is latently suppressed. The model well reproduces the experimental data on the both polarized and unpolarized structure functions, assuming that only the valence quarks term contributes to the nucleon spin. It is shown, the combined analysis of the polarized and unpolarized data can give an information about the effective masses and intrinsic motion of the quarks inside the nucleon. Simultaneously, it is shown that the rate of the nucleon energy carried by the quarks can be less, than estimated from the standard approach. As an addition, a prediction for the proton spin function $g_2$ is given.
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arxiv:hep-ph/9803443
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A fresh analysis of Left right symmetric supersymmetric models in the generic case where the scale of right handed symmetry breaking $M_R >> M_{SUSY}\sim M_W$ is presented. We conclude that the low energy effective theory for such models is essentially the MSSM with R parity (and therefore B,L symmetry) but the spectrum includes heavy conjugate neutrino supermultiplets that permit a seesaw mechanism and several characteristic charged supermultiplets over and above those of the MSSM.
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arxiv:hep-ph/9803461
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Muon colliders offer special opportunities to discover and study new physics. With the high intensity source of muons at the front end, orders of magnitude improvements would be realized in searches for rare muon processes, in deep inelastic muon and neutrino scattering experiments, and in long-baseline neutrino oscillation experiments. At a 100 to 500 GeV muon collider, neutral Higgs boson (or techni-particle) masses, widths and couplings could be precisely measured via s-channel production. Also, threshold cross-section studies of W+ W-, t t-bar, Zh and supersymmetric particle pairs would precisely determine the corrresponding masses and test supersymmetric radiative corrections. At the high energy frontier a 3 to 4 TeV muon collider is ideally suited for the study of scalar supersymmetric particles and extra Z-bosons or strong WW scattering.
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arxiv:hep-ph/9803480
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Recent calculations of heavy quark cross sections near threshold at next-to-next-to-leading order have found second-order corrections as large as first-order ones. We analyse long-distance contributions to the heavy quark potential in momentum and coordinate space and demonstrate that long-distance contributions in momentum space are suppressed as $\Lambda_{QCD}^2/q^2$. We then show that the long-distance sensitivity of order $\Lambda_{QCD} r$ introduced by the Fourier transform to coordinate space cancels to all orders in perturbation theory with long-distance contributions to the heavy quark pole mass. This leads us to define a subtraction scheme -- the `potential subtraction scheme' -- in which large corrections to the heavy quark potential and the `potential-subtracted' quark mass are absent. We compute the two-loop relation of the potential-subtracted quark mass to the $\bar{\rm MS}$ quark mass. We anticipate that threshold calculations expressed in terms of the scheme introduced here exhibit improved convergence properties.
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arxiv:hep-ph/9804241
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We discuss dilaton and Moduli dominant SUSY breaking scenarios in M-theory. In addition, for the nonperturbative superpotential from gaugino condensation, we discuss the soft terms in the simplest model (only S and T moduli fields) and in the $T^6/Z_{12}$ model from M-theory. From the phenomenology consideration, we suggest massless scalar SUSY breaking scenario.
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arxiv:hep-ph/9804243
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The lepton number violating process, $e^- e^- \to W^- W^-$ has been widely discussed in the Majorana neutrino exchange mechanism. Here, we discuss this process in a composite neutrino model where excited Majorana neutrinos are exchanged. We found several qualitatively different features from the neutrino exchange case: (1) The longitudinally polarized $W$'s are not produced, (2) the neutrinoless double beta decay does not constrain much and a much larger cross section is expected, and (3) CP violating phases may be explored because all excited neutrinos are heavy so that large mixings among them are expected.
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arxiv:hep-ph/9804245
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Non-perturbative lattice simulations have shown that there is no electroweak phase transition in the Standard Model for the allowed Higgs masses, m_H \gsim 75 GeV. In the Minimal Supersymmetric Standard Model, in contrast, it has been proposed that the transition should exist and even be strong enough for baryogenesis up to m_H ~ 105 GeV, provided that the lightest stop mass is in the range 100...160 GeV. However, this prediction is based on perturbation theory, and suffers from a noticeable gauge parameter and renormalization scale dependence. We have performed large-scale lattice Monte Carlo simulations of the MSSM electroweak phase transition. Extrapolating the results to the infinite volume and continuum limits, we find that the transition is in fact stronger than indicated by 2-loop perturbation theory. This guarantees that the perturbative Higgs mass bound m_H ~ 105 GeV is a conservative one, allows slightly larger stop masses (up to ~ 165 GeV), and provides a strong motivation for further studies of MSSM electroweak baryogenesis.
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arxiv:hep-ph/9804255
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Within an extended Skyrme soliton model for baryons the interplay between the collective radial motion and the SU(3)--flavor--rotations is investigated. The coupling between these modes is mediated by flavor symmetry breaking. Collective coordinates which describe the corresponding large amplitude fluctuations are introduced and treated canonically. When diagonalizing the resulting Hamiltonian flavor symmetry breaking is fully taken into consideration. As eigenstates not only the low--lying ${1/2}^+$ and ${3/2}^+$ baryons but also their radial excitations are obtained and compared to the empirical data. In particular the relevance of radial excitations for the penta--quark baryon $Z^+$ (Y=2, I=0, $J^\pi={1/2}^+$) is discussed. In this approach its mass is predicted to be $1.58{\rm GeV}$. Furthermore the widths for various hadronic decays are estimated which, for example, yields $\Gamma(Z^+\to NK)\sim 100{\rm MeV}$ for the only permissible decay process of the $Z^+$.
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arxiv:hep-ph/9804260
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ISAJET is a Monte Carlo event generator for $pp$, $\bar pp$, and $e^+e^-$ interactions at high energies. This document summarizes the physics underlying the program and describes how to use it.
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arxiv:hep-ph/9804321
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We review studies of the trilinear gauge boson couplings at the Tevatron proton-antiproton collider from data collected by the CDF and D0 collaborations during the period 1992--1996. The gauge boson couplings are a fundamental prediction of the standard model, resulting from the non-Abelian nature of the theory. Therefore, experimental tests of the couplings are of foremost importance. We introduce the experimental results by reviewing the effective Lagrangian formalism, the indirect constraints on the couplings from low-energy experiments, and the expected values of the couplings in theories beyond the standard model. Finally, we consider the prospects for future measurements.
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arxiv:hep-ph/9804322
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We introduce gauge-invariant quark and gluon angular momentum distributions after making a generalization of the angular momentum density operators. From the quark angular momentum distribution, we define the gauge-invariant and leading-twist quark {\it orbital} angular momentum distribution $L_q(x)$. The latter can be extracted from data on the polarized and unpolarized quark distributions and the off-forward distribution $E(x)$ in the forward limit. We comment upon the evolution equations obeyed by this as well as other orbital distributions considered in the literature.
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arxiv:hep-ph/9804337
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We investigate the effects of Yukawa couplings on the phenomenological predictions for a class of supersymmetric models which allows for the presence of complete SU(5) multiplets in addition to the Minimal Supersymmetric Standard Model spectrum. We develop a two loop analytical approach to quantify the predictions for gauge unification including Yukawa couplings. The effects of the heavy thresholds of the model are also included. In some cases accurate predictions can be made for the unification scale, irrespective of the initial (unknown) Yukawa couplings, so long as perturbation theory remains valid. We also consider the limit of a large number of extra states and compute the predictions in a resummed perturbation series approach to show that the results are stable in this limit. Finally we consider the possibility of making predictions for the case the gauge and Yukawa couplings enter the non-perturbative domain below the unification scale and estimate the errors which affect these predictions.
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arxiv:hep-ph/9804437
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We show that the fermion mass spectrum may naturally be understood in terms of flavour democratic fixed points in supersymmetric theories which have a large domain of attraction in the presence of "strong unification". Our approach provides an alternative to the approximate Yukawa texture zeroes of the Froggatt-Nielsen mechanism. We discuss a particular model based on a broken gauged $SU(3)_L\times SU(3)_R$ family symmetry which illustrates our approach.
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arxiv:hep-ph/9804446
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Fermion compositeness, and other types of new physics that can be described by the exchange of very massive particles, can manifest themselves as the result of an effective four-fermion contact interaction. In the case of the processes $e^+e^-\to \mu^+\mu^-,\tau^+\tau^-,\bar{b}b$ and $\bar{c}c$ at future $e^+e^-$ colliders with $\sqrt{s}=0.5-1$ TeV, we examine the sensitivity to four-fermion contact interactions of two new integrated observables, $\sigma_+$ and $\sigma_-$, conveniently defined for such kind of analysis. We find that, if longitudinal polarization of the electron beam were available, these observables would offer the opportunity to separate the helicity cross sections and, in this way, to derive model-independent bounds on the relevant parameters.
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arxiv:hep-ph/9805207
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We study the final-state interactions in $B \to \pi K$ decays through $B \to VV \to \pi K$ processes where the inelastic rescattering occurs via single pion exchange. The next-to-leading order low energy effective Hamiltonian and BSW model are used to evaluate the weak transition matrix elements and the final-state interactions. We found that the final-state interaction effects in $B \to \rho K^* \to \pi K$ processes are significant. The Fleischer-Mannel relation about the CKM angle $\gamma$ may be significantly modified.
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arxiv:hep-ph/9805260
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We extract diffractive parton densities from data on diffractive deep inelastic scattering (DIS) and on diffractive photoproduction of jets. We explore the results of several ansaetze for the functional form of the parton densities. Then we use the fitted parton densities to predict the diffractive production of jets and of W's and Z's in p-pbar collisions at the Tevatron. To fit the photoproduction data requires a large gluon density in the Pomeron. The predictions for the Tevatron cross sections are substantially higher than data; this signals a breakdown of hard-scattering factorization in diffractive hadron-hadron collisions.
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arxiv:hep-ph/9805268
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It is shown that the minimal Left-Right symmetric model admits cosmic string, domain wall and conditionally, monopole solutions. The strings arise when the $SU(2)_R$ is broken and can either be destabilized at the electroweak scale or remain stable through the subsequent breakdown to $U(1)_{EM}$. The monopoles and domain wall configurations exist in the $SU(2)_L\otimes U(1)_Y$ symmetric phase and disappear after subsequent symmetry breaking. Their destabilization provides new sources of non-equilibrium effects below the electroweak scale. Several defect-mediated mechanisms for low energy baryogenesis are shown to be realisable in this model.
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arxiv:hep-ph/9805276
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Data show that \tau_{B^{\pm}}\sim\tau_{B^0}, but \tau_{D^{\pm}}\sim 2\tau_{D^0}. The naive interpretation which attributes \tau_{D^{\pm}}\sim 2\tau_{D^0} to a destructive interference between two quark diagrams for D^{\pm} decays, definitely fails in the B-case. We investigate Close and Lipkin's suggestion that the phases for producing radially excited states \psi_{2s} in the decay products of B-mesons can possess an opposite sign to the integrals for \psi_{1s} decay products. Their contributions can partially compensate each other to result in \tau_{B^{\pm}}\sim\tau_{B^0}. Since D-mesons are much lighter than B-mesons, such possibilities do not exist in D-decays.
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arxiv:hep-ph/9805277
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We have calculated the KK bar --> KK bar scattering amplitude to next to leading order in Chiral Perturbation Theory. Then, making use of a unitarization procedure with one or several coupled channels (\pi\pi, KK bar in our case) we have calculated the \pi\pi --> \pi\pi, \pi\pi --> KK bar and KK bar --> KK bar S and P waves in good agreement with the experiment up to \sqrt{s}= 1.2 GeV. The \pi\pi scattering lengths with isospin and spin (I,J) equal to (0,0), (1,1) and (2,0) are also calculated in agreement with experiment and former Chiral Perturbation Theory calculations. Finally we have employed these amplitudes, making use of an Omnes representation, to calculate the scalar and the vector pion form factors, obtaining a good agreement with the available experimental data.
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arxiv:hep-ph/9805334
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We present the next-to-next-to-leading order relation between the moments of the $\Upsilon$ system spectral density and the inclusive $B$-meson semileptonic width. The perturbative series for the width as an explicit function of the moments is well convergent in three consequent orders in the strong coupling constant that provides solid and accurate theoretical estimate. As a result, the uncertainty of the value of $|V_{cb}|$ Cabibbo-Kobayashi-Maskawa matrix element is reduced.
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arxiv:hep-ph/9805344
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The relic abundance of stable neutralinos is investigated in $E_8 \times E_8'$ heterotic string theory when supersymmetry is spontaneously broken by hidden-sector gaugino condensates. In the weak coupling regime, very large scalar masses (compared to gaugino masses) are shown to lead to a too large relic abundance of the neutralinos, incompatible with cosmological observations in most of parameter space. The problem does not arise in the strong coupling regime (heterotic M-theory) because there scalar and gaugino masses are generically of the same order of magnitude.
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arxiv:hep-ph/9805397
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Combining three mechanisms, we reanalysis processes of $B \to \eta^{\prime} K(K^*),\eta K(K^*)$ and calculate their branching ratios. The results are compared with other mechanisms in the literature. The striking feature of the gluon fusion mechanism is emphasized and its experimental test is discussed.
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arxiv:hep-ph/9805451
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Broken chiral symmetry has become the basis for a unified treatment of hadronic interactions at low energies. After reviewing mechanisms for spontaneous chiral symmetry breaking, I outline the construction of the low--energy effective field theory of the Standard Model called chiral perturbation theory. The loop expansion and the renormalization procedure for this nonrenormalizable quantum field theory are developed. Evidence for the standard scenario with a large quark condensate is presented, in particular from high--statistics lattice calculations of the meson mass spectrum. Elastic pion--pion scattering is discussed as an example of a complete calculation to O(p^6) in the low--energy expansion. The meson--baryon system is the subject of the last lecture. After a short summary of heavy baryon chiral perturbation theory, a recent analysis of pion--nucleon scattering to O(p^3) is reviewed. Finally, I describe some very recent progress in the chiral approach to the nucleon--nucleon interaction.
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arxiv:hep-ph/9805500
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In this paper I review the theoretical progresses in studying the diffractive DIS in the colour--dipole approach.
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arxiv:hep-ph/9805504
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The current analysis of atmospheric neutrinos by the Super-Kamiokande Collaboration is based only on fully-contained one-ring events and partially contained events. We show that the up-down ratio of fully-contained, inclusive, multi-ring events gives an independent test of the atmospheric neutrino anomaly, without the need for particle identification. Moreover, this class of events is rich in neutral current events and hence gives crucial information for discriminating between oscillations of \nu_\mu into \nu_{e, \tau} and \nu_s.
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arxiv:hep-ph/9806218
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The renormalization group method in $R^2$-gravity without matter fields is discussed. A criterion for the existence of the renormalization constant for the metric has been found, two-loop higher order poles have been calculated, a relation which allows us to find the one-loop renormalization constant of the Newtonian constant has been suggested.
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arxiv:hep-ph/9806252
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We present a new, simple supersymmetry breaking model with direct gauge mediation. Supersymmetry breaking sector is based on the model with an Affine quantum moduli space. The model has no gauge messengers and no light scalars charged under the Standard Model which give a negative contribution to the soft masses. Large expectation value at the minimum is obtained by balancing the runaway potential and the dimension six nonrenormalizable term. This makes it easy to preserve the perturbative unification. Enough suppression of the supergravity contribution to the soft masses can also be shown.
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arxiv:hep-ph/9806273
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We evaluate the supersymmetry reach of the Large Hadron Collider within the gauge-mediated low energy supersymmetry breaking framework, assuming that a neutralino is the second lightest sparticle and that it decays promptly into a gravitino which escapes detection. We find that the maximum reach is obtained via a search for inclusive $\gamma\gamma+\eslt$ events coming dominantly from chargino and neutralino production. Assuming an integrated luminosity of 10~$fb^{-1}$, we find that LHC experiments will be able to probe values of the model parameter $\Lambda \alt 400$ TeV, corresponding to $m_{\tg} \leq 2.8$ TeV. A measure of the model parameter $\Lambda$ may be possible from the photon $p_T$ spectrum.
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arxiv:hep-ph/9806290
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We present a detailed study of photon production in hadronic events in electron-positron annihilation at LEP energies. We show that estimates of the inclusive photon spectrum using the quark-to-photon fragmentation function determined using the ALEPH `photon' +~1 jet data agree well with the observations of the OPAL collaboration. This agreement shows that the photon fragmentation function determined in this way can be used for inclusive observables. We also compare next-to-leading order and beyond leading logarithm predictions obtained using the numerically resummed solutions of the fragmentation function evolution equation of Bourhis, Fontannaz and Guillet and Gl\"uck, Reya and Vogt with the data. Moreover, in order to check the general behaviour of the fragmentation function, we consider an analytic series expansion in the strong coupling. We find that the parameterizations are inaccurate at large $x$ values. While the OPAL data is in broad agreement with estimates based on any of these approaches, the ALEPH data prefers the resummed BFG parameterization. Finally, there is some ambiguity as to whether the fragmentation function is treated as ${\cal O}(\alpha)$ or ${\cal O}(\alpha/\alpha_s)$. We show that at present this ambiguity affects mainly the prediction for the `photon' +~1 jet rate at large $z$.
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arxiv:hep-ph/9806316
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Recently, models proposing superheavy particles $X$ as source of ultrahigh energy cosmic rays have attracted some interest. The $X$-particles are either metastable relic particles from the early Universe or are released by topological defects. In these models, the detected air-showers are produced by primaries originating from the fragmentation of the $X$-particles. We present the fragmentation spectrum of superheavy particles calculated in SUSY-QCD. Then we discuss the status of the lightest supersymmetric particle as possible ultrahigh energy primary.
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arxiv:hep-ph/9806322
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In bilinear R-Parity violating models where a term \epsilon_3L_3H_2 is introduced in the superpotential, the tau lepton can mix with charginos. We show that this mixing is fully compatible with LEP1 precision measurements of the Z\tau\tau and W\tau\nu_\tau couplings even for large values of \epsilon_3 and of the induced vacuum expectation value v_3 of the tau-sneutrino. The single production of charginos at e+e- colliders is possible in this case and we present numerical values of the cross-section at LEP1, LEP2 and an NLC. We find maximum values of 10 pb at LEP1 and 1 fb at NLC, while the corresponding values at LEP2 are too small to observe.
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arxiv:hep-ph/9806382
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We compute the four-Fermi neutralino-quark interaction Lagrangian including contributions from the CP violating phases in the MSSM. We find that neutralino-nucleus scattering cross-sections relevant for direct detection experiments show a strong dependence on the value of the CP-violating phase associated with the $\mu$ parameter, $\theta_\mu$. In some cases, for a broad range of non-zero $\theta_\mu$, there are cancellations in the cross-sections which reduce the cross-section by more than an order of magnitude. In other cases, there may be enhancements as one varies $\theta_\mu$.
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arxiv:hep-ph/9806413
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Simple transformation formulas between fermion matrices and observables, and numerical values of quark matrices, are obtained on a particular weak basis with one quark matrix diagonal and the other with vanishing elements 1-1, 1-3 and 3-1, and with only the element 2-2 complex. When we choose $M_u$ diagonal, then $M_d$ shows intriguing numerical properties which suggest a four parameter description of it, which implies $V_{us}\simeq \sqrt{m_d/m_s}$, $V_{cb}\simeq (3/\sqrt{5})(m_s/m_b)$ and $V_{ub}\simeq (1/\sqrt{5})(\sqrt{m_d m_s}/m_b)$. Few comments on mass-mixing relations are added.
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arxiv:hep-ph/9806496
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The cross sections for the processes $\gamma \nu\to \gamma \gamma \nu$, $\gamma\gamma\to\gamma\nu\bar{\nu}$ and $\nu\bar{\nu}\to\gamma\gamma\gamma$ are calculated for a range of center of mass energies from below $m_e$ to considerably above $m_e$, but much less than $m_W$. This enables us to treat the neutrino--electron coupling as a four--Fermi interaction and results in amplitudes which are electron box diagrams with three real photons and one virtual photon at their vertices. These calculations extend our previous low--energy effective interaction results to higher energies and enable us to determine where the effective theory is reliable.
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arxiv:hep-ph/9806499
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A R-parity breaking SUSY model characterized by an effective bilinear violation with only $\tau$-lepton number breaking in the superpotential is outlined. The CP-odd Higgs boson masses and those of charged Higgs bosons are discussed. In the model, several interesting mass mixings else such as the mixing between $\tau$ lepton and charginos etc in the model are discussed too. Being one of example, we have computed the mixing production $e^{+} e^{-} \to \tau^{\mp} \tilde{\kappa}^{\pm}_{i} (i=1,2)$ in e^+ e^- colliders, where $\tau^{\mp}, \tilde{\kappa}^{\pm}_{i}(i=1,2)$ denote the physical $\tau$ lepton and charginos.
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arxiv:hep-ph/9806505
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The proton is formulated as a relativistic system of three constituent quarks interacting via a zero-range two-body force in the null-plane. The covariance of the null-plane Faddeev-like equation under kinematical front-form boosts is discussed. A simplified three-boson model of the nucleon wave-function is obtained numerically. The proton electric form-factor reproduces the experimental data for low momentum transfers and qualitatively describes the asymptotic region.
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arxiv:hep-ph/9806507
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We construct an effective three dimensional theory for the MSSM at high temperatures in the limit of large-$m_{A}$. We analyse the two-loop effective potential of the 3D theory for the case of a light right handed stop to determine the precise region in the $m_{h}$-$m_{\tilde{t}_{R}}$ plane for which the sphaleron constraint for preservation of the baryon asymmetry is satisfied. We also compare with results previously obtained usind 3D and 4D calculations of the effective potential. A two-stage phase transition still persists for a small range of values of $m_{\tilde{t}_{R}}$. The allowed region requires a value of $m_{\tilde{t}_{R}} \lsi m_{t}$ and $m_{h} \lsi 100$ (110) GeV for $m_{Q} = 300$ GeV (1 TeV).
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arxiv:hep-ph/9806519
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A model is constructed for a chiral abelian gauge-interaction of fermions and a potential of three higgses, so that the potential possesses a discrete symmetry of the vacuum state, which provides the introduction of three generations for the fermions. For the model including charged currents, a matrix of the flavor mixing is described, and a phase giving the violation of CP-invariance is determined. Some approximate relations connecting the values of mixing matrix to the mass ratios for the fermions in different generations are derived.
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arxiv:hep-ph/9806523
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Axions have been argued to form coherent axionic boson stars as well as incoherent axion gas. These are ones of most plausible candidates of dark matters. Since the axionic boson stars generate oscillating electric fields in an external magnetic field, they induce oscillating currents in magnetized conducting media, which result in emitting radiations. We show that colliding with a magnetic white dwarf, an axionic boson star can emit a monochromatic radiation with a frequency given by a mass of the axion.
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arxiv:hep-ph/9807232
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Low Q2 photon-proton cross sections are analysed using a simple, QCD-motivated parametrisation $\sigma_{\gamma^\star p}\propto 1/(Q^2+Q_0^2)$, which gives a good description of the data. The Q2 dependence of the gamma* p cross section is discussed in terms of the partonic transverse momenta of the hadronic state the photon fluctuates into.
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arxiv:hep-ph/9807268
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A fully realistic and systematic effective field theory model of a 3-brane universe is constructed. It consists of a six-dimensional gravitating spacetime, containing several, approximately parallel (3+1)-dimensional defects, or ``3-branes''. The Standard Model particles are confined to live on one of the 3-branes while different four-dimensional field theories may inhabit the others, in literally a case of ``parallel universes''. The effective field theory is valid up to the six-dimensional Planck scale, where it must be replaced by a more fundamental theory of gravity and 3-brane structure. Each 3-brane induces a conical geometry in the two dimensions transverse to it. Collectively, the curvature induced by the 3-branes can compactify the extra dimensions into a space of spherical topology. It is possible to take the six-dimensional Planck scale to be not much larger than the weak scale, and the compact space not much smaller than a millimeter, thereby realizing the recent proposal by Arkani-Hamed, Dimopoulos and Dvali for eliminating the Gauge Hierearchy Problem. In this case, an extra force is required to stabilize the compact space against collapse. This is provided by a six-dimensional (compact) U(1) gauge field with a magnetic flux quantum trapped in the compact space. The nature of the Cosmological Constant Problem in this scenario is discussed.
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arxiv:hep-ph/9807348
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We study the chiral phase transition of QCD at finite temperature and density by numerically solving Schwinger-Dyson equation for the quark propagator with the improved ladder approximation in the Landau gauge. Using the solution we calculate a pion decay constant from a generalized version of Pagels-Stokar formula. Chiral phase transition point is determined by analyzing an effective potential for the quark propagator. We find solutions for which chiral symmetry is broken while the value of the effective potential is larger than that for the chiral symmetric vacuum. These solutions correspond to meta-stable states, and the chiral symmetric vacuum is energetically favored. We present a phase diagram on the general temperature--chemical potential plane, and show that phase transitions are of first order in wide range.
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arxiv:hep-ph/9807408
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We analyze the partial rate asymmetry in $B^{\pm} \to P {\bar P} \pi^{\pm}$ decays ($ P = \pi^+, K ^+, \pi^0, \eta$) which results from the interference of the nonresonant decay amplitude and the resonant amplitude for $B^{\pm} \to \chi_{c0} \pi^{\pm} $ followed by the decay $\chi_{c0} \to P {\bar P} $. The CP violating phase $\gamma$ can be extracted from the measured asymmetry. We find that the partial rate asymmetry for $B^\pm \to \pi^+ \pi^- \pi^\pm$ is $0.33~sin \gamma$, while for $B^\pm \to K^+ K^-\pi^\pm$ it amounts $0.45~ sin \gamma$.
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arxiv:hep-ph/9807441
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Exclusive semileptonic $B$ decays into excited charmed mesons are studied with QCD sum rules in the leading order of heavy quark effective theory. Two universal Isgur-Wise functions \tau and \zeta for semileptonic B decays into four lowest lying excited $D$ mesons ($D_1$, $D_2^*$, $D'_0$, and $D'_1$) are determined. The decay rates and branching ratios for these processes are calculated.
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arxiv:hep-ph/9807461
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We analyze the general nonlinear evolution equations for multi gluon correlators derived in hep-ph/9709432 by restricting ourselves to a double logarithmic region. In this region our evolution equation becomes local in transverse momentum space and amenable to simple analysis. It provides a complete nonlinear generalization of the GLR equation. We find that the full double log evolution at high density becomes strikingly different from its linear doubly logarithmic DGLAP counterpart. An effective mass is induced by the nonlinear corrections which at high densities slows down the evolution considerably. We show that at small values of impact parameter the gluonic density grows as a logarithm of energy. At higher values of impact parameter the growth is faster, since the density of gluons is lower and nonlinearities are less important.
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arxiv:hep-ph/9807462
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We examine the current state of neutralino dark matter and consider how the LEP constraints on the Minimal Supersymmetric Standard Model parameters are squeezing the available dark matter regions. We also show how cosmological constraints augment bounds coming from collider searches to further constrain the MSSM parameter space.
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arxiv:hep-ph/9807481
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We consider the production of heavy quark jets at the $Z$-pole at the next-to-leading order (NLO) using the {\it Cambridge jet-algorithm}. We study the effects of the quark mass in two- and three-jet observables and the uncertainty due to unknown higher order corrections as well as due to fragmentation. We found that the three-jet observable has remarkably small NLO corrections, which are stable with respect to the change of the renormalization scale, when expressed in terms of the {\it running quark mass} at the $m_Z$-scale. The size of the hadronization uncertainty for this observable remains reasonably small and is very stable with respect to changes in the jet resolution parameter $y_c$.
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arxiv:hep-ph/9807489
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Recently a rephasing invariant definition of the CP-mixing parameter for Indirect CP Violation has been introduced. This is made possible by the explicit use of the CP operator into the analysis. The problem is then that of the determination of the CP operator for a CP violating scenario. We discuss it and provide a definite solution.
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arxiv:hep-ph/9808212
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The dynamical evolution of superconducting cosmic strings is much more complicated than that of simple Goto-Nambu strings. For this reason, there are only a few known analytical solutions and no numerical ones. The goal of this paper is to present numerical solutions for the dynamics of planar superconducting cosmic string loops. In most cases, a purely dynamical approach turns out to be insufficient to describe correctly the evolution of a loop due mainly to the appearance of shocks when spacelike currents are present and kinks for timelike currents, leading to yet unaccounted for quantum effects. The consequences of the quantum effects are mostly unknown at this time because the problem requires a dynamical field theory treatment. It is however likely that ultimately the result will be massive radiation in the form of charge carriers from the string.
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arxiv:hep-ph/9808222
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The suppression of photon bremsstrahlung due to a variety of in-medium effects is discussed. Different electrodynamic suppression effects are discussed, and compared with the related color analogs. Higher order effects are considered, and found to be important. Data from SLAC E-146 is discussed, and compared with theory. The effect of finite thickness targets is emphasized, since nuclear size is such an important limiting factor for the chromodynamics effects.
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arxiv:hep-ph/9808235
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Inspired by the recent proposal by Feldman and Cousins of a ``unified approach to the classical statistical analysis of small signals'' based on a choice of ordering in Neyman's construction of classical confidence intervals, I propose a new ordering principle for the classical statistical analysis of Poisson processes with background which minimizes the effect on the resulting confidence intervals of the observation of less background events than expected. The new ordering principle is applied to the calculation of the confidence region implied by the recent null result of the KARMEN neutrino oscillation experiment.
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arxiv:hep-ph/9808240
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We calculate a two-loop effective potential to the order of {\cal O}(\lambda_t^2\alpha_s) in the MSSM. We then study the corresponding two-loop corrections to the CP-even Higgs-boson mass for arbitrary \tan\beta and left-right top-squark mixings. We find that the lightest Higgs-boson mass is changed by at most a few GeV. We also show the improved scale dependence and compare to previous two-loop analyses.
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arxiv:hep-ph/9808299
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We calculate the two-body nonleptonic B decays using the factorization method. The recent measured decays by CLEO Collaboration can be explained in the factorization approach. We propose a number of ratios of branching ratios to determine the effective coefficients and the form factors.
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arxiv:hep-ph/9808329
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We consider the topological susceptibility for an SU(N) gauge theory in the limit of a large number of colors, $N \to \infty$. At nonzero temperature, the behavior of the topological susceptibility depends upon the order of the deconfining phase transition. The most interesting possibility is if the deconfining transition, at $T=T_d$, is of second order. Then we argue that Witten's relation implies that the topological susceptibility vanishes in a calculable fashion at $T_d$. As noted by Witten, this implies that for sufficiently light quark masses, metastable states which act like regions of nonzero $\theta$ --- parity odd bubbles --- can arise at temperatures just below $T_d$. Experimentally, parity odd bubbles have dramatic signatures: the $\eta'$ meson, and especially the $\eta$ meson, become light, and are copiously produced. Further, in parity odd bubbles, processes which are normally forbidden, such as $\eta \to \pi^0 \pi^0$, are allowed. The most direct way to detect parity violation is by measuring a parity odd global asymmetry for charged pions, which we define.
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arxiv:hep-ph/9808366
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General relativistic effects in the form of metric perturbations are usually neglected in the preheating era that follows inflation. We argue that in realistic multi-field models these effects are in fact crucial, and the fully coupled system of metric and quantum field fluctuations needs to be considered. Metric perturbations are resonantly amplified, breaking the scale-invariance of the primordial spectrum, and in turn stimulate scalar field resonances via gravitational rescattering. This non-gravitationally dominated nonlinear growth of gravitational fluctuations may have significant effects on the Doppler peaks in the cosmic background radiation, primordial black hole formation, gravitational waves and nonthermal symmetry restoration.
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arxiv:hep-ph/9808404
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The construction of an effective 3D theory at high temperatures for the MSSM as a model of electroweak baryogenesis is discussed. The analysis for a single light scalar field shows, that given the experimental constraints, there is no value of the Higgs mass for which a sufficiently first-order phase transition is obtained. A precise determination of the 3D parameters of the effective theory for the case of a light right-handed stop allows us to obtain an upper bound on the masses of the lightest Higgs and right-handed stop using the two-loop effective potential. A two-stage phase transition persists for a small range of values of $m_{\tilde{t}_{R}}$.
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arxiv:hep-ph/9808439
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In the semiclassical approach, inclusive and diffractive quark and gluon distributions are expressed in terms of correlation functions of Wilson loops. Each Wilson loop integrates the colour field strength in the area between the trajectories of two fast partons penetrating the proton. We introduce a specific model for averaging over the relevant colour field configurations. Within this model, all parton distributions at some low scale Q_0^2 are given in terms of three parameters. Inclusive and diffractive structure functions at higher values of Q^2 are determined in a leading-order QCD analysis. In both cases, the evolution is driven by a large gluon distribution. A satisfactory description of the structure functions F_2(x,Q^2) and F_2^D(3)(xi,beta,Q^2) is obtained. The observed rise of F_2^D(3) with xi is parametrized by a non-perturbative logarithmic energy dependence, compatible with unitarity. In our analysis, the observed rise of F_2 at small x is largely due to the same effect.
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arxiv:hep-ph/9808454
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We parametrize in a model-independent way possible departures from the minimal Standard Model predictions in the matter sector. We only assume the symmetry breaking pattern of the Standard Model and that new particles are sufficiently heavy so that the symmetry is non-linearly realized. Models with dynamical symmetry breaking are generically of this type. We review in the effective theory language to what extent the simplest models of dynamical breaking are actually constrained and the assumptions going into the comparison with experiment. Dynamical symmetry breaking models can be approximated at intermediate energies by four-fermion operators. We present a complete classification of the latter when new particles appear in the usual representations of the $SU(2)_L\times SU(3)_c$ group as well as a partial classification in the general case. We discuss the accuracy of the four-fermion description by matching to a simple `fundamental' theory. The coefficients of the effective lagrangian in the matter sector for dynamical symmetry breaking models (expressed in terms of the coefficients of the four-quark operators) are then compared to those of models with elementary scalars (such as the minimal Standard Model). Contrary to a somewhat widespread belief, we see that the sign of the vertex corrections is not fixed in dynamical symmetry breaking models. This work provides the theoretical tools required to analyze, in a rather general setting, constraints on the matter sector of the Standard Model.
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arxiv:hep-ph/9809237
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We investigate the total decay rate of the (ground state) $B_c$ meson within the framework of the relativistic constituent quark model formulated on the light-front (LF). The exclusive semileptonic (SL) and nonleptonic (NL) beauty and charm decays of the $B_c$ meson are described through vector and axial hadronic form factors, which are calculated in terms of the overlap of the parent and daughter LF wave functions. The latters are derived via the Hamiltonian LF formalism using as input the update version of the ISGW model. The inclusive SL and NL partial rates are calculated within a convolution approach inspired by the partonic model and involving the same $B_c$ wave function which is used for evaluation of the exclusive modes. We predict the partial rates for 74 exclusive SL and NL channels and 43 inclusive partial rates corresponding to the underlying $\bar{b}\to \bar{c}$ and $c\to s$ quark decays. Based on our approach we find $\Gamma^{\bar{b}}(B_c)= 0.52 \pm 0.02 ps^{-1}$, $\Gamma^{c}(B_c)= 0.98 \pm 0.07 ps^{-1}$, where the theoretical uncertainty is dominated by the uncertainty in the choice of the threshold values at which the hadron continuum starts. For the $B_c$ lifetime we obtain $\tau_{B_c}= 0.63 \pm 0.02 ps$ in a good agreement with the prediction obtained using the nonrelativistic operator product expansion. We also predict decay rates for many specific weak transitions of $B_c$. In particular, for the branching fractions of the $B^+_c \to J/\psi\mu^+\nu_{\mu}$, $B_c^+\to J/\psi\pi^+$ and $B_c^+ \to J/\psi+X $ decays we obtain 1.7%, 0.1 % and 13.2%, respectively.
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arxiv:hep-ph/9809249
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The BRS invariance of the electroweak gauge theory leads to relationships between amplitudes with external massive gauge bosons and amplitudes where some of these gauge bosons are replaced with their corresponding Nambu-Goldstone bosons. Unlike the equivalence theorem, these identities are exact at all energies. In this paper we discuss such identities which relate the process $e^+e^- \to W^+W^-$ to $W^\pm\chi^\mp$ and $\chi^+\chi^-$ production. By using a general form-factor decomposition for $e^+e^- \to W^+W^-$, $e^+e^- \to W^\pm \chi^\mp$ and $e^+e^- \to \chi^+\chi^-$ amplitudes, these identities are expressed as sum rules among scalar form factors. Because these sum rules may be applied order by order in perturbation theory, they provide a powerful test of higher order calculations. By using additional Ward-Takahashi identities we find that the various contributions are divided into separately gauge-invariant subsets, the sum rules applying independently to each subset. After a general discussion of the application of the sum rules we consider the one-loop contributions of scalar-fermions in the Minimal Supersymmetric Standard Model as an illustration.
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arxiv:hep-ph/9809256
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It is shown how the hard thermal loop approximation can be used in chiral perturbation theory to study some thermal properties of Goldstone bosons. Hard thermal effects are first studied in the non-linear sigma model. Then those results are used to obtain the thermal corrections to the transverse and longitudinal gauge field masses in the electroweak theory in the limit of a strongly interacting Higgs boson.
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arxiv:hep-ph/9809273
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We present the results of a study performed on the interactions of 10.6A GeV gold nuclei in nuclear emulsions. In a minimum bias sample of 1311 interac- tions, 5260 helium nuclei and 2622 heavy fragments were observed as Au projec- tile fragments. The experimental data are analyzed with particular emphasis of target separation interactions in emulsions and study of criticalexponents. Multiplicity distributions of the fast-moving projectile fragments are inves- tigated. Charged fragment moments, conditional moments as well as two and three -body asymmetries of the fast moving projectile particles are determined in terms of the total charge remaining bound in the multiply charged projectile fragments. Some differences in the average yields of helium nuclei and heavier fragments are observed, which may be attributed to a target effect. However, two and three-body asymmetries and conditional moments indicate that the breakup mechanism of the projectile seems to be independent of target mass. We looked for evidence of critical point observable in finite nuclei by study the resulting charged fragments distributions. We have obtained the values for the critical exponents gamma, beta and tau and compare our results with those at lower energy experiment (1.0A GeV data). The values suggest that a phase transition like behavior, is observed.
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arxiv:hep-ph/9809289
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We examine whether parameters related to the Higgs sector of the minimal supersymmetric standard model can be determined by detailed study of the production cross section and decay branching ratios of the Higgs boson. Assuming that only the light Higgs boson will be observed at a future $e^+e^-$ linear collider with $\sqrt{s}=300\sim500$ GeV, we show that values of $m_{susy}$ and $\tan\beta$ are restricted within a narrow region in the $m_{susy}$ versus $\tan\beta$ plane by the combined analysis of the light Higgs properties. It is also pointed out that, in some case, $\tan\beta$ may be restricted to a relatively small value, $\tan\beta=1\sim5$.
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arxiv:hep-ph/9809353
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Using the experimental result on b\to s\gamma and theoretical result on b\to sg, a four -generation SM is analysed to constrain the rephasing-invariant combinations of the CKM matrix and masses of the fourth generation quarks.
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arxiv:hep-ph/9809354
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The effects of the propagation of particles which have a finite life time and an according width in their mass spectrum are discussed in the context of transport descriptions. In the first part the coupling of soft photon modes to a source of charged particles is studied in a classical model which can be solved completely in analytical terms. The solution corresponds to a re-summation of certain field theory diagrams. The second part addresses the derivation of transport equations which also account for the damping width of the particles. The $\Phi$-derivable method of Baym is used to derive a self-consistent and conserving scheme. For this scheme a conserved energy-momentum tensor can be constructed. Furthermore, a kinetic entropy can be derived which besides the standard quasi-particle part also includes contributions from fluctuation.
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arxiv:hep-ph/9809419
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Neutrinos and antineutrinos of all three flavours are emitted during the post bounce phase of a core collapse supernova with $\numu/\nutau (\anumu/\anutau)$ having average energies more than that of $\nue(\anue)$. They can be detected by the new earth bound detector like SNO and Super-Kamiokande which are sensitive to neutrinos of all three flavours. In this letter we consider the effect of flavour oscillations on the neutrino flux and their expected number of events at the detector. We do a three-generation analysis and for the mass and mixing schemes we first consider the threefold maximal mixing model consistent with the solar and the atmospheric neutrino data and next a scenario with one $\Delta m^2 \sim 10^{-11} eV^2$ (solar range) and the other $\Delta m^2 \sim 10^{-18} eV^2$, for which the oscillation length is of the order of the supernova distance. In both these scenarios there are no matter effects in the resultant neutrino spectrum and one is concerned with vacuum oscillations. We find that though neutrino oscillations result in a depletion in the number of $\nue$ and $\anue$ coming from the supernova, the actual signals at the detectors are appreciable enhanced.
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arxiv:hep-ph/9809424
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We compute quark structure functions and the intrinsic Fock space distribution of sea quarks in a hadron wavefunction at small x. The computation is performed in an effective theory at small x where the gluon field is treated classically. At $Q^2$ large compared to an intrinsic scale associated with the density of gluons $\mu^2$, large compared to the QCD scale $\Lambda^2_{QCD}$, and large compared to the quark mass squared $M^2$, the Fock space distribution of quarks is identical to the distribution function measured in deep inelastic scattering. For $Q^2 \le M^2$ but $Q^2 >> \mu^2$, the quark distribution is computed in terms of the gluon distribution function and explicit expressions are obtained. For $Q^2 \le \mu^2$ but $Q^2 >> \Lambda_{QCD}^2$ we obtain formal expressions for the quark distribution functions in terms of the glue. An evaluation of these requires a renormalization group analysis of the gluon distribution function in the regime of high parton density. For light quarks at high $Q^2$, the DGLAP flavor singlet evolution equations for the parton distributions are recovered. Explicit expressions are given for heavy quark structure functions at small x.
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arxiv:hep-ph/9809427
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We revisit the work of K. Goeke, M. Harvey, F. Gr\"ummer, and J. N. Urbano (Phys. Rev. {\bf D37}, 754 (1988)) who considered a chiral model for the nucleon based on the linear sigma model with scalar-isoscalar scalar-isovector mesons coupled to quarks and solved using the coherent-pair approximation. In this way the quantum pion field can be treated in a non-perturbative fashion. In this work we review this model and the coherent pair approximation correcting several errors in the earlier work. We minimize the expectation value of the chiral hamiltonian in the ansatz coherent-pair ground state configuration and solve the resulting equations for nucleon quantum numbers. We calculate the canonical set of nucleon observables and compare with the Hedgehog model and experiment. Using the corrected equations yield slightly different values for nucleon observables but do not correct the large virial deviation in the $\pi$-nucleon coupling. Our results therefore do not significantly alter the conclusions of Goeke, et al..
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arxiv:hep-ph/9809473
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For the S-states of positronium and muonium, the terms of an expansion of energy levels in powers of the fine structure constant $\alpha$ are also members of a "recoil series". The first two terms of that series are calculated to all orders in $\alpha$.
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arxiv:hep-ph/9809533
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Within the context of massive N-component $\phi^4$ scalar field theory, we use asymptotic Pade-approximant methods to estimate from prior orders of perturbation theory the five-loop contributions to the coupling-constant beta-function $\beta_g$, the anomalous mass dimension $\gamma_m$, the vacuum-energy beta-function $\beta_v$, and the anomalous dimension $\gamma_2$ of the scalar field propagator. These estimates are then compared with explicit calculations of the five-loop contributions to $\beta_g$, $\gamma_m$, $\beta_v$, and are seen to be respectively within 5%, 18%, and 27% of their true values for $N$ between 1 and 5. We then extend asymptotic Pade-approximant methods to predict the presently unknown six-loop contributions to $\beta_g$, $\gamma_m$, and $\beta_v$. These predictions, as well as the six-loop prediction for $\gamma_2$, provide a test of asymptotic Pade-approximant methods against future calculations.
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arxiv:hep-ph/9809538
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We review standard applications of perturbative QCD to baryon production, and argue by examining data that it is generally relevant at high but experimentally feasible momentum transfers. Then we consider some new initiatives, particularly meson photoproduction off baryons and the seeming quagmire of Delta(1232) electroproduction.
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arxiv:hep-ph/9809595
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This talk discusses the sensitivity of electron-positron and proton-antiproton Penning-trap experiments to CPT- and Lorentz-violating effects in the context of an extension of the minimal standard model and quantum electrodynamics.
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arxiv:hep-ph/9809597
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