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I report on recent theoretical developments at Quark Matter 2006.
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arxiv:hep-ph/0702004
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In a recent paper, we investigated the effects of the massive charged gauge bosons (bileptons) predicted by the minimal 331 model on the off-shell vertex WWV^* (V=gamma, Z) using a SU_L(2) X U_Y(1) covariant gauge-fixing term for the bileptons. We proceed along the same lines and calculate the effects of the gauge bosons predicted by the 331 model with right-handed neutrinos. It is found that the bilepton effects on the WWV^* vertex are of the same order of magnitude than those arising from the SM and several of its extensions, provided that the bilepton mass is of the order of a few hundred of GeVs. For heavier bileptons, their effects on the WWV^* vertex are negligible. The behavior of the form factors at high energies is also discussed as it is a reflect of the gauge invariance and gauge independence of the WWV^* Green function obtained via our quantization method.
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arxiv:hep-ph/0702081
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We give an overview of the current status of investigations of the polarization of gluons in the nucleon. We describe some of the physics of the spin-dependent gluon parton distribution and its phenomenology in high-energy polarized hadronic scattering. We also review the recent experimental results.
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arxiv:hep-ph/0702083
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DIS data from HERA show a striking regularity as \sigma^{\gamma^* p} is a function of the ratio \tau=Q^2/Q_s^2(x) only. The scaling function shows a break at \tau ~ 1, which has been taken as an indication for saturation. However, besides saturation also the transition between dominance of k_t-ordered (DGLAP) and k_t-non-ordered (BFKL) evolution contributes to a break around this value of \tau, as well as the suppression for small Q^2 due to finite quark masses and confinement. In this paper we use a dipole cascade model based on Mueller's dipole model, which also includes energy conservation and pomeron mergins, to investigate the contributions of these different effects to the scaling behaviour. As a result we predict that the scaling function for \tau < 1 will be modified when data for Q^2 > 1 GeV^2 become available. We also investigate the scaling properties of the charm contribution and the impact parameter dependence of the saturation scale.
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arxiv:hep-ph/0702087
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We exploit the Ward-Slavnov-Taylor identity relating the 3-gluons to the ghost-gluon vertices to conclude either that the ghost dressing function is finite and non vanishing at zero momentum while the gluon propagator diverges (although it may do so weakly enough not to be in contradiction with current lattice data) or that the 3-gluons vertex is non-regular when one momentum goes to zero. We stress that those results should be kept in mind when one studies the Infrared properties of the ghost and gluon propagators, for example by means of Dyson-Schwinger equations.
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arxiv:hep-ph/0702092
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We examine the amount of parameter tuning to make slow-roll inflation marginally eternal by considering an R-invariant chaotic inflation as an example of one-parameter tuning in supergravity. The primordial inflation turns out to be possibly marginal in such a setup.
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arxiv:hep-ph/0702127
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Meson Green's functions and decay constants $f_{\Gamma}$ in different channels $\Gamma$ are calculated using the Field Correlator Method. Both, spectrum and $f_\Gamma$, appear to be expressed only through universal constants: the string tension $\sigma$, $\alpha_s$, and the pole quark masses. For the $S$-wave states the calculated masses agree with the experimental numbers within $\pm 5$ MeV. For the $D$ and $D_s$ mesons the values of $f_{\rm P} (1S)$ are equal to 210(10) and 260(10) MeV, respectively, and their ratio $f_{D_s}/f_D$=1.24(3) agrees with recent CLEO experiment. The values $f_{\rm P}(1S)=182, 216, 438$ MeV are obtained for the $B$, $B_s$, and $B_c$ mesons with the ratio $f_{B_s}/f_B$=1.19(2) and $f_D/f_B$=1.14(2). The decay constants $f_{\rm P}(2S)$ for the first radial excitations as well as the decay constants $f_{\rm V}(1S)$ in the vector channel are also calculated. The difference of about 20% between $f_{D_s}$ and $f_D$, $f_{B_s}$ and $f_B$ directly follows from our analytical formulas.
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arxiv:hep-ph/0702157
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We study QED corrections to the chiral symmetry breaking in Nambu-Jona-Lasinio (NJL) model with two flavors of quarks. In the model the isospin symmetry is broken by differences of the current quark masses and the electromagnetic charges between up and down quarks. In the leading order of the 1/N expansion we calculate the effective potential of the model with one-loop QED corrections. Evaluating the effective potential, we study an influence of the isospin symmetry breaking on the orientation of chiral symmetry breaking. The current quark mass has an important contribution for the orientation of chiral symmetry breaking.
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arxiv:hep-ph/0702160
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We give an assessment of the three approaches, undertaken by the D$\emptyset$ experiment, to probe CP violation in $B_s$ mixing without measurement of $B_s$-$\bar B_s$ oscillations or tagging: dimuon charge asymmetry $A_{SL}$, untagged single muon charge asymmetry $A_{SL}^s$, and lifetime difference in untagged $B_s \to J/\psi\phi$ decay. The latter two approaches provide an alternative avenue, if not crosscheck, to the usual mixing-decay interference study in modes such as $B_s \to J/\psi\phi$. Prospects at the Tevatron, LHC and (Super) B factories are discussed.
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arxiv:hep-ph/0702163
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New physics (NP) in charmless strangeness-changing $B$ and $B_s$ decays, which are dominated by the $b \to s$ penguin amplitudes, can either preserve isospin or change it by one unit. A general formalism is presented studying pairs of processes related to each other by isospin reflection. We discuss information on $\Delta I$ in NP amplitudes, provided by time-integrated CP-violating rate asymmetries in $B^+$ and $B^0$ decays (or in $B_s$ decays), differences between rates for isospin-reflected processes, and coefficients $S$ of $\sin \Delta m t$ in time-dependent CP asymmetries. These four asymmetries in $B^+$ and $B^0$ decays (or five asymmetries in $B_s$ decays) are shown to determine the magnitude and CP-violating phase of a potential isovector NP amplitude, and the imaginary part of an isoscalar amplitude, assuming that strong phases in NP amplitudes are negligible. This information may be compared with predictions of specific models, for which we discuss a few examples.
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arxiv:hep-ph/0702193
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Braneworld modifications to the Friedmann expansion law can have an important effect on the cosmological evolution of the early universe. In particular, the primordial particle abundances crucially depend on the rate at which the universe expanded at early times. In this article, we study the production of stable and unstable gravitinos, both from thermal creation and from the decay of a heavy scalar, in the Randall-Sundrum II braneworld context. We conclude that, depending on the value of the 5D fundamental Planck mass, some of the usual standard cosmology constraints on the reheating temperature and on the mass of the heavy scalar can be evaded.
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arxiv:hep-ph/0702200
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We investigate a spectrum of a fermion, which we call a quark, above the critical temperature of the chiral phase transition in a gauge theory using the Schwinger-Dyson (SD) equation. The SD equation enables us to study the spectrum over a wide range of the gauge coupling. It is shown that the quark spectrum has two sharp peaks which correspond to the normal quasi-quark and the plasmino and is consistent with that obtained in the hard thermal loop approximation in the weak coupling region, while it has also two peaks but with smaller thermal masses and broader widths in the strong coupling region. Temperature-dependence of the quark spectrum is also discussed.
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arxiv:hep-ph/0702253
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The scale of fermion mass generation can, as shown by Appelquist and Chanowitz, be bounded from above by relating it to the scale of unitarity violation in the helicity nonconserving amplitude for fermion-anti-fermion pairs to scatter into pairs of longitudinally polarized electroweak gauge bosons. In this paper, we examine the process t tbar -> W_L W_L in a family of phenomenologically-viable deconstructed Higgsless models and we show that scale of unitarity violation depends on the mass of the additional vector-like fermion states that occur in these theories (the states that are the deconstructed analogs of Kaluza-Klein partners of the ordinary fermions in a five-dimensional theory). For sufficiently light vector fermions, and for a deconstructed theory with sufficiently many lattice sites (that is, sufficiently close to the continuum limit), the Appelquist-Chanowitz bound can be substantially weakened. More precisely, we find that, as one varies the mass of the vector-like fermion for fixed top-quark and gauge-boson masses, the bound on the scale of top-quark mass generation interpolates smoothly between the Appelquist-Chanowitz bound and one that can, potentially, be much higher. In these theories, therefore, the bound on the scale of fermion mass generation is independent of the bound on the scale of gauge-boson mass generation. While our analysis focuses on deconstructed Higgsless models, any theory in which top-quark mass generation proceeds via the mixing of chiral and vector fermions will give similar results.
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arxiv:hep-ph/0702281
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From a distance, the proton's weak charge is seen through the distorting effects of clouds of virtual particles. The effective weak charge can be calculated by starting with the measured weak coupling at the Z-pole and "running" the coupling to lower energy or, equivalently, longer distances. Because the "electroweak radiative corrections" or "loop diagrams" which give rise to the running depend not only on known particles, but on particles which have not yet been discovered, a difference between the calculated and measured weak charges may signal new physics. A measurement of Qweak to 4% will be sensitive to new physics at the few TeV scale. The Qweak experiment is based on the fact that the parity-violating longitudinal analyzing power, Az, in electron-proton scattering at low momentum transfer and small scattering angle, is proportional to the proton's weak charge. The experiment plans to measure the predicted Az of -0.3 ppm with a combined statistical and systematic uncertainty of 2.2%, corresponding to a total uncertainty of 4% of Qweak. This requires a statistical precision of 5 x 10^-9, which can be achieved in 2200 hours with an 85% polarized, 180 microamp electron beam incident on a 0.35 m liquid hydrogen target. A synchronous data acquisition system will integrate the detector current signals over each spin state and extract the helicity correlated, parity violating component.
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arxiv:hep-ph/0702283
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We examine supersymmetric models with mixed modulus-anomaly mediated SUSY breaking (MM-AMSB) soft terms which get comparable contributions to SUSY breaking from moduli-mediation and anomaly-mediation. The apparent (mirage) unification of soft SUSY breaking terms at Q=mu_mir not associated with any physical threshold is the hallmark of this scenario. The MM-AMSB structure of soft terms arises in models of string compactification with fluxes, where the addition of an anti-brane leads to an uplifting potential and a de Sitter universe, as first constructed by Kachru {\it et al.}. The phenomenology mainly depends on the relative strength of moduli- and anomaly-mediated SUSY breaking contributions, and on the Higgs and matter field modular weights, which are determined by the location of these fields in the extra dimensions. We delineate the allowed parameter space for a low and high value of tan(beta), for a wide range of modular weight choices. We calculate the neutralino relic density and display the WMAP-allowed regions. We show the reach of the CERN LHC and of the International Linear Collider. We discuss aspects of MM-AMSB models for Tevatron, LHC and ILC searches, muon g-2 and b->s \gamma branching fraction. We also calculate direct and indirect dark matter detection rates, and show that almost all WMAP-allowed models should be accessible to a ton-scale noble gas detector. Finally, we comment on the potential of colliders to measure the mirage unification scale and modular weights in the difficult case where mu_mir>>M_GUT.
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arxiv:hep-ph/0703024
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We study the energy loss of an energetic heavy quark produced in a high temperature quark-gluon plasma and travelling a finite distance before emerging in the vacuum. While the retardation time of purely collisional energy loss is found to be of the order of the Debye screening length, we find that the contributions from transition radiation and the Ter-Mikayelian effect do not compensate, leading to a reduction of the zeroth order (in an opacity expansion) energy loss.
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arxiv:hep-ph/0703095
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The pattern of a large approximate degeneracy of the excited hadron spectra (larger than the chiral restoration degeneracy) is present in the recent experimental report of Bugg. Here we try to model this degeneracy with state of the art quark models. We review how the Coulomb Gauge chiral invariant and confining Bethe-Salpeter equation simplifies in the case of very excited quark-antiquark mesons, including angular or radial excitations, to a Salpeter equation with an ultrarelativistic kinetic energy with the spin-independent part of the potential. The resulting meson spectrum is solved, and the excited chiral restoration is recovered, for all mesons with J > 0. Applying the ultrarelativistic simplification to a linear equal-time potential, linear Regge trajectories are obtained, for both angular and radial xcitations. The spectrum is also compared with the semi-classical Bohr-Sommerfeld quantization relation. However the excited angular and radial spectra do not coincide exactly. We then search, with the classical Bertrand theorem, for central potentials producing always classical closed orbits with the ultrarelativistic kinetic energy. We find that no such potential exists, and this implies that no exact larger degeneracy can be obtained in our equal-time framework, with a single principal quantum number comparable to the non-relativistic Coulomb or harmonic oscillator potentials. Nevertheless we find plausible that the large experimental approximate degeneracy will be modelled in the future by quark models beyond the present state of the art.
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arxiv:hep-ph/0703114
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Based on the nuclear attenuation data obtained by the HERMES experiment on nitrogen and krypton nuclei, it is shown that the nuclear attenuation $R_M^{h}$ can be parametrised in a form of a linear polynomial $P_1=a_{11}$ + $\tau a_{12}$, where $\tau$ is the formation time, which depends on the energy of the virtual photon $\nu$ and fraction of that energy $z$ carried by the final hadron. Three widely known parameterizations for $\tau$ were used for the performed fit. The fit parameters $a_{11}$ and $a_{12}$ do not depend on $\nu$ and $z$.
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arxiv:hep-ph/0703124
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The asymmetry of $D^-$ and $D^+$ meson production in $\pi^-N$ scattering observed by the E791 experiment is a typical phenomenon known as the leading particle effect in charm hadroproducton. We show that the phenomenon can be explained by the effect of light quark fragmentation into charmed hadrons (LQF). Meanwhile, the size of the LQF effect is estimated from data of the E791 experiment. A comparison is made with the estimate of the LQF effect from prompt like-sign dimuon rate in neutrino experiments. The influence of the LQF effect on the measurement of nucleon strange distribution asymmetry from charged current charm production processes is briefly discussed.
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arxiv:hep-ph/0703133
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Chiral symmetry breaking may exhibit significantly different patterns in two chiral limits: N_f=2 massless flavours (m_u=m_d=0, m_s physical) and N_f=3 massless flavours (m_u=m_d=0=m_s=0). Such a difference may arise due to vacuum fluctuations of s-bar{s} pairs related to the violation of the Zweig rule in the scalar sector, and could yield a numerical competition between contributions counted as leading order and next-to-leading in the chiral expansions of observables. We recall and extend Resummed Chiral Perturbation Theory (ReChPT), a framework that we introduced previously to deal with such instabilities: it requires a more careful definition of the relevant observables and their one-loop chiral expansions. We analyse the amplitudes for low-energy pi-pi and pi-K scatterings within ReChPT, which we match in subthreshold regions with dispersive representations obtained from the solutions Roy and Roy-Steiner equations. Using a frequentist approach, we constrain the quark mass ratio as well as the quark condensate and the pseudoscalar decay constant in the N_f=3 chiral limit. The results mildly favour significant contributions of vacuum fluctuations suppressing the N_f=3 quark condensate compared to its N_f=2 counterpart.
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arxiv:hep-ph/0703154
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We update the uncertainty analysis on $S$ parameter of the electroweak chiral Lagrangian (EWCL) by including the LEP-II W pair production data. We find that experimental data still allow a positive $S^{EXP}(1\textrm{TeV})$.
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arxiv:hep-ph/0703189
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Presented here is a technique of propagating uncertainties through the parton shower by means of an alternate event weight. This technique provides a mechanism to systematically quantify the effect of variations of certain components of the parton shower leading to a novel approach to probing the physics implemented in a parton shower code and understanding its limitations. Further, this approach can be applied to a large class of parton shower algorithms and requires no changes to the underlying implementation.
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arxiv:hep-ph/0703240
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We use Omnes representations of the form factors f_+ and f_0 for exclusive semileptonic B to pi decays, paying special attention to the treatment of the B* pole and its effect on f_+. We apply them to combine experimental partial branching fraction information with theoretical calculations of both form factors to extract |Vub|. The precision we achieve is competitive with the inclusive determination and we do not find a significant discrepancy between our result, |Vub| =(3.90+/-0.32+/-0.18)10^(-3), and the inclusive world average value, (4.45+/-0.20+/-0.26)10^(-3).
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arxiv:hep-ph/0703284
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The corrections of the gluon fusion to the BFKL equation in a unified partonic framework are studied. This modified BFKL equation predicts a stronger shadowing, which suppresses the gluon density and even leads to the gluon disappearance below the saturation region. We suggest that this unexpected effect is caused by a possible chaotic solution of the new equation.
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arxiv:hep-ph/0703309
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We present a class of models in which the top quark, by mixing with new physics at a higher energy scale, is naturally heavier than the other standard model particles. We take this new physics to be extended color. Our models contain new particles with masses between 100 GeV and 1 TeV, some of which may be just within the reach of the next generation of experiments. In particular one of our models implies the existence of two right handed top quarks. These models demonstrate the existence of a standard model-like theory consistent with experiment, and leading to new physics below the TeV scale, in which the third generation is treated differently than the first two.
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arxiv:hep-ph/9203205
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Using supersymmetric grand unified theories, we have recently invented a framework which allows the prediction of three quark masses, two of the parameters of the Kobayashi-Maskawa matrix and tan $\beta$, the ratio of the two vevs. These predictions are used to calculate $\epsilon$ and $\epsilon'$ in the kaon system, B meson mass mixing and the size of CP asymmetries in the decays of neutral B mesons to explicit final states of given CP.
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arxiv:hep-ph/9205240
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We propose a new mechanism for late cosmological baryon asymmetry in models with first order electroweak phase transition. Lepton asymmetry arises through the decay of particles produced out of equilbrium in bubble collisions and is converted into baryon asymmetry by sphalerons. Supersymmetric models with explicitly broken R-parity may provide a suiatble framework for the implementation of this mechanism.
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arxiv:hep-ph/9206212
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The basic tool for the study of the electroweak phase transition is $V_{eff} (\phi,T)$, the one-loop finite-temperature effective potential, improved by all-loop resummations of the most important infrared contributions. In this paper we perform, as a first step towards a full analysis of the Standard Model case, a detailed study of the effective potential of the scalar theory. We show that subleading corrections to the self-energies lead to spurious terms, linear in the field-dependent mass $m(\phi)$, in the daisy-improved effective potential. Consistency at subleading order requires the introduction of superdaisy diagrams, which prevent the appearance of linear terms. The resulting $V_{eff}(\phi,T)$ for the scalar theory hints at a phase transition which is either second-order or very weakly first-order.
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arxiv:hep-ph/9206227
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We discuss the Isgur-Wise function $\xi (y)$ in the small velocity (SV) limit within the QCD sum rule method. The behavior of $\xi (y)$ in the SV limit is sensitive to the particular form of the duality relations used to decontaminate the sum rule predictions from the continuum contribution. Peculiarities of the duality relations in the problem at hand are revealed. It is shown that the proper requirements of duality and angular isotropy for S wave states lead to an unambiguous form of the sum rules for the Isgur-Wise function. We illustrate the constraints due to these requirements using a toy model of the harmonic oscillator. The slope parameter and the shape of $\xi (y)$ are determined.
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arxiv:hep-ph/9207217
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We study $I=3/2$ elastic $K\pi $ scattering to Born order using nonrelativistic quark wavefunctions in a constituent-exchange model. This channel is ideal for the study of nonresonant meson-meson scattering amplitudes since s-channel resonances do not contribute significantly. Standard quark model parameters yield good agreement with the measured S- and P-wave phase shifts and with PCAC calculations of the scattering length. The P-wave phase shift is especially interesting because it is nonzero solely due to $SU(3)_f$ symmetry breaking effects, and is found to be in good agreement with experiment given conventional values for the strange and nonstrange constituent quark masses.
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arxiv:hep-ph/9207251
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The observed deficit of $\rm ^8B$ solar neutrinos may call for an improved standard model of the sun or an expanded standard model of particle physics ({\it e.g.,} with neutrino masses and mixing). In the former case, contemporary fluid motions and thermal fluctuations in the sun's core may modify nuclear reaction rates and restore agreement. To test this notion, we propose a search for short--term variations of the solar neutrino flux.
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arxiv:hep-ph/9208223
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We study the unknown coupling constants that appear at order $p^4$ in the Chiral Perturbation Theory analysis of $K \to \pi \gamma^* \to \pi l^+ l^-$, $K^{+-} \to \pi^{+-} \gamma \gamma$ and $K \to \pi \pi \gamma$ decays. To that end, we compute the chiral realization of the $\Delta S \, = \, 1$ Hamiltonian in the framework of the $1/N_c$-expansion of the low-energy action. The phenomenological implications are also discussed.
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arxiv:hep-ph/9209231
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In the standard scenario, the electroweak phase transition is a first order phase transition which completes by the nucleation of critical bubbles. Recently, there has been speculation that the standard picture of the electroweak phase transition is incorrect. Instead, it has been proposed that throughout the phase transition appreciable amounts of both broken and unbroken phases of $SU(2)$ coexist in equilibrium. I argue that this can not be the case. General principles insure that the universe will remain in a homogenous state of unbroken $SU(2)$ until the onset of critical bubble production.
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arxiv:hep-ph/9209258
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We examine multiphoton production in the electroweak sector of the Standard Model in the high energy limit using the equivalence theorem in combination with spinor helicity techniques. We utilize currents consisting of a charged scalar, spinor, or vector line that radiates $n$ photons. Only one end of the charged line is off shell in these currents, which are known for the cases of like-helicity and one unlike-helicity photons. We obtain a wide variety of helicity amplitudes for processes involving two pairs of charged particles by considering combinations of four currents. We examine the situation with respect to currents which have both ends of the charged line off-shell, and present solutions for the case of like-helicity photons. These new currents may be combined with two of the original currents to produce additional amplitudes involving Higgs, longitudinal $Z$ or neutrino pairs.
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arxiv:hep-ph/9210214
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We present a self-consistent calculation of the finite temperature effective potential for $\lambda \phi^4$ theory, using the composite operator effective potential in which an infinite series of the leading diagrams is summed up. Our calculation establishes the proper form of the leading correction to the perturbative one-loop effective potential.
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arxiv:hep-ph/9211211
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The so called Casimir energy embodies the O($(N_c)^0$) contribution to the skyrmion mass according to the semi-classical expansion theory of solitons. We claim that this contribution can be accurately estimated despite the fact that some of the counterterms, provided in principle by chiral perturbation theory, are not known in practice. Using $\zeta$ function techniques we show that $E_{cas}=E_{cas}(\mu)+E_{ct}(\mu)$ where $E_{cas}(\mu)>>E_{ct}(\mu)$ because it incorporates all the zero-mode contributions and it can be exactly calculated. Our results confirm that the fourth order Skyrme lagrangian does not seem to provide a correct description of the lightest baryons as solitons. We show that a simple extension to order six gives, on the contrary, good results without tuning the parameters of the chiral lagrangian.
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arxiv:hep-ph/9211229
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Contrary to the usual belief, by carefully examining the operation of parity transformation on the $(1,0)\oplus(0,1)$ mesons in the generalized canonical representation, we establish that the $(j,0)\oplus(0,j)$ meson-antimeson pair have {\it opposite} intrinsic parity. This opens up the possibility that while the particles without an internal structure may utilize one representation of the Lorentz group, phenomenologies of composite particles may exploit a different representation. As such (perhaps, only some of) the meson structures beyond the standard $q\,\overline {Q}$ may exploit the $(j,0)\oplus(0,j)$ generalized canonical representation of the Lorentz group -- this would result in a meson and the associated antimeson to manifest themselves in {\it different} partial waves. %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% CONSTRUCTIVE COMMENTS WELCOME, AS ALWAYS D. V. A. %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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arxiv:hep-ph/9211245
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We study the SU(3) extension of the Skyrme model with vector mesons in the collective quantization scheme. The parameters of the model are fixed in its mesonic sector. Fields which are excited by the collective rotation of the classical soliton are determined by a variational method. The resulting collective Hamiltonian which includes various symmetry breaking terms is diagonalized exactly. This yields reasonable predictions for the mass differences of the low-lying baryons. We furthermore investigate static properties of these baryons in this model by evaluating all relevant matrix elements using the exact eigenstates of the collective Hamiltonian. Electromagnetic observables are found to approximately obey the predictions obtained from SU(3) symmetry. Strong deviations from SU(3) symmetry are, however, found for the matrix elements of strange vector and scalar operators indicating a small amount of strangeness in the proton. The exploration of axial currents shows that the results of the EMC experiment may be explained with a small polarization of the strange sea of the proton without violating the successful Cabibbo model for semileptonic hyperon decays.
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arxiv:hep-ph/9211259
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The spectra and decay rates of $c \bar c$ and $b \bar b$ levels are well described, for the most part, by a power-law potential of the form $V(r)=\lambda(r^{\alpha}-1)/\alpha+{\rm const.}$, where $\alpha\simeq 0$. The results of an up-to-date fit to the data on spin-averaged levels are presented. Results on electric dipole transitions in systems bound by power law potentials are also presented, with applications to the bottomonium system.
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arxiv:hep-ph/9211313
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We present a new calculation of the CP violation parameter $\epsilon^{\prime}/ \epsilon$. The results reported in this paper have been obtained by using the $\Delta S=1$ effective Hamiltonian computed at the next-to-leading order, including QCD and QED penguins. The matrix elements of the relevant operators have been taken from lattice QCD, at a scale $\mu=2$ GeV. At this relatively large scale, the perturbative matching between the relevant operators and the corresponding coefficients is quite reliable. The effect of the next-to-leading corrections is to lower the prediction obtained at the leading order, thus favouring the experimental result of E731. We analyze different contributions to the final result and compare the leading and next-to-leading cases.
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arxiv:hep-ph/9212203
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A detailed numerical study of radiative corrections in the low $Q^2$ region at the HERA $ep$ collider was performed. The specific case of the total photoproduction cross section measurement was taken as an example. Two different programs, TERAD91 and HERACLES4.2, were used to get an estimation of the size of radiative effects. It was found that radiative corrections can be quite large in some points of the space of leptonic $(x,y)$ variables. However, after imposing experimentally feasible cuts on the radiated photon and the hadronic final state one gets corrections at the level of a few per cent.
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arxiv:hep-ph/9212222
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We use the analytical model recently introduced in Ref. \cite{lp92}, to investigate the statistics of temperature fluctuations on the cosmic microwave background (CMB), induced by topological defects. The cases of cosmic strings and textures are studied. We derive analytically the characteristic function of the probability distribution for ${\delta T}\over T$ and use it to obtain the lowest twelve moments including the skewness and the kurtosis. The distribution function is also obtained and it is compared with the Gaussian distribution thus identifying long non-Gaussian tails. We show that for both cosmic strings and textures all odd moments (including skewness) vanish while the relative deviation from the Gaussian for even moments increases with the order of the moment. The non-Gaussian signatures of textures, derived from the distribution function and the moments, are found to be much more prominent than the corresponding signatures for strings. We discuss the physical origin of this result.
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arxiv:hep-ph/9212228
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We point out that in a class of supersymmetric models where R-parity violation is induced by the spontaneous breaking of local $B-L$ symmetry, the R-parity violating $W$ decay $W\rightarrow\slep\gamma$ and $Z$ decay $Z\rightarrow\snu\gamma$, forbidden in the minimal supersymmetric standard model (MSSM), occur at an enhanced rate compared to other models with R-parity breaking. We find that the branching fractions for these modes can be of order $10^{-5}$ .
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arxiv:hep-ph/9212249
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The flow equations or exact RG equations for the Higgs Top System are solved to leading order in $1/N_c$. This allows to relate arbitrary bare actions with this field content continuously to effective low energy theories, and we find the flow converging towards general renormalizable models. The assumption of a bare action of the generalized Nambu-Jona-Lasinio type does not restrict the parameters of the low energy theory.
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arxiv:hep-ph/9212265
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In preon models based on chiral gauge theories, we show that light composite fermions can ensue as a result of gauging a subset of preons in a vector-like manner. After demonstrating how this mechanism works in a toy example, we construct a one generation model of quarks which admits a hierarchy between the up and down quark masses as well as between these masses and the compositeness scale. In simple extensions of this model to more generations we discuss the challenges of obtaining any quark mixing. Some possible phenomenological implications of scenarios where quarks and leptons which are heavier are also less pointlike are also considered.
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arxiv:hep-ph/9212275
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Analytic properties of hadronic amplitudes are discussed within the framework of QCD as formulated on the basis of the BRST algebra. Local, composite fields are introduced for hadrons. Given confinement, it is shown that hadronic amplitudes have no thresholds or structure singularities (anomalous thresholds) which are directly related to the underlying quark-gluon structure. In contrast, general amplitudes of QCD must have singularities in channels with non-zero color quantum number, which can be related to unphysical states.
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arxiv:hep-ph/9212292
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Intrinsic strangeness contributions to low-energy strange quark matrix elements of the nucleon are modelled using kaon loops and meson-nucleon vertex functions taken from nucleon-nucleon and nucleon-hyperon scattering. A comparison with pion loop contributions to the nucleon electromagnetic (EM) form factors indicates the presence of significant SU(3)-breaking in the mean-square charge radii. As a numerical consequence, the kaon loop contribution to the mean square Dirac strangeness radius is significantly smaller than could be observed with parity-violating elastic ep experiments planned for CEBAF, while the contribution to the Sachs radius is large enough to be observed with PV electron scattering from (0^+,0) nuclei. Kaon loops generate a strange magnetic moment of the same scale as the isoscalar EM magnetic moment and a strange axial vector form factor having roughly one-third magnitude extracted from nu p/nubar p elastic scattering. In the chiral limit, the loop contribution to the fraction of the nucleon's scalar density arising from strange quarks has roughly the same magnitude as the value extracted from analyses of Sigma_{\pi N}. The importance of satisfying the Ward-Takahashi Identity, not obeyed by previous calculations, is also illustrated, and the sensitivity of results to input parameters is analyzed.
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arxiv:hep-ph/9301229
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The implications of the deficit of solar neutrinos are discussed. If all of the experiments are taken literally the relative suppressions render an astrophysical explanation unlikely. Allowing MSW conversions, the data simultaneously determine the temperature of the core of the sun to within five percent. The implications of the atmospheric $\nu_\mu/\nu_e$ ratio are briefly discussed.
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arxiv:hep-ph/9301243
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We examine the possibility of fermion mass generation in 2+1- dimensional gauge theory from the current algebra point of view.In our approach the critical behavior is governed by the fluctuations of pions which are the Goldstone bosons for chiral symmetry breaking. Our analysis supports the existence of an upper critical number of Fermion flavors and exhibits the explicit form of the gap equation as well as the form of the critical exponent for the inverse correlation lenght of the order parameter
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arxiv:hep-ph/9301256
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We have evaluated the one loop correction to the bound on the lightest Higgs mass valid in the minimal, $ E_{6}$ based, supersymmetric $ \eta$ model. Under the assumption that the theory remains perturbative up to the $10^{16}$ GeV scale, we derive a conservative bound that decreases with the top mass for $M_t \leq 2 M_W$ and varies from $ \sim 160$ GeV to $\sim 145$ GeV when $90 \leq M_t \leq 200$ GeV.
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arxiv:hep-ph/9302218
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Classical vortex solutions in various two-Higgs systems are studied. The systems we consider include the standard model with two Higgs doublets, in which case the vortex appears as part of a string-like object. The Higgs potentials contain several different couplings in general and the spontaneous symmetry breaking involves with two different vacuum expectation values. In particular it is shown that the existence of such a solution in general requires a specific ratio of the two Higgs vacuum expectation values, i.e. $\tan\beta$, and some inequalities between different Higgs couplings. This ratio can be determined in terms of the couplings in the Higgs potential. The Higgs masses are also computed in this case. (1+2)-d solutions are topological so that they are topologically stable and the Bogomol'nyi bound is saturated for some couplings. Some comments on the stabilization of (1+3)-d solutions are also given. Thus, as long as such a defect can be formed in the early universe, stable or not, $\tan\beta$ is no longer an independent free parameter in the theory.
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arxiv:hep-ph/9302220
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If the electroweak symmetry-breaking sector becomes strongly interacting at high energies, it can be probed through longitudinal $W$ scattering. We present a model with many inelastic channels in the $W_L W_L$ scattering process, corresponding to the production of heavy fermion pairs. These heavy fermions affect the elastic scattering of $W_L$'s by propagating in loops, greatly reducing the amplitudes in some charge channels. We conclude that the symmetry-breaking sector cannot be fully explored by using, for example, the $W_L^\pm W_L^\pm$ mode alone, even when no resonance is present; all $W_L W_L \to W_L W_L$ scattering modes must be measured.
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arxiv:hep-ph/9302226
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The survival probability of large rapidity gaps in pp collisions is calculated for several different eikonal models of the Gaussian form. Results obtained for models based on partonic interactions are quite similar. The Regge-pole model predicts a higher value of $ < \vert S \vert^{2} > $ .
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arxiv:hep-ph/9302248
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We discuss the characteristic interference features of soft radiation in the threshold production of heavy unstable particles: soft gluon radiation in $\ee \to \tt$ and soft photon radiation in $\ee \to \ww$. We show that the heavy particle decay width controls the interference between the emission off the final state particles. As a result, the radiation pattern may provide a way of measuring the decay width of the heavy particles.
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arxiv:hep-ph/9302250
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The question of the renormalization scheme dependence of the $\tau$ semileptonic decay rate is revisited in response to a recent criticism. Particular attention is payed to a distinction between a consistent quantitative description of this dependence and the actual selection of a subset of ``acceptable'' renormalization schemes. It is argued that a reasonable universal measure of the renormalization scheme dependence can be formulated, which gives encouraging results when applied to various physical quantities, including the semileptonic $\tau$ decay rate.
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arxiv:hep-ph/9302264
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The coefficients appearing at leading and subleading order in the $1/m$ expansion of bilinear heavy quark currents are related to each other by imposing reparametrization invariance on both the effective current operators and the short-distance coefficient functions in the heavy quark effective theory. When combined with present knowledge about the leading order coefficients, the results allow to calculate all coefficients appearing at order $1/m$ to next-to-leading order in renormalization-group improved perturbation theory. They also provide a meaningful definition of the velocity transfer variable $v\cdot v'$ to order $1/m$.
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arxiv:hep-ph/9302269
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We have performed a QCD next-to-leading order (NLO) calculation for Deep Inelastic Scattering (DIS) retaining the full parton and hadron mass dependencies. We find that the gluon initiated contributions to DIS processes, such as charm production, are {\it comparable} in magnitude ({\it i.e.}, $30\%$ to $100\%$) to the ``leading-order'' (LO) sea-quark processes. The ``slow-rescaling" prescription and the full NLO formalism are compared in a quantitative manner. The use of DIS distributions and the inclusion of the charm mass via slow-rescaling are not sufficient to mimic the correct NLO physics. These results imply that previous analyses of charm production data to extract the strange and charm content of the nucleon, as well as the precise determination of Standard Model parameters based on these analyses (such as the Weinberg angle), need to be reassessed.
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arxiv:hep-ph/9302305
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The smallness of fermion masses and mixing angles has recently been been attributed to approximate global $U(1)$ symmetries, one for each fermion type. The parameters associated with these symmetry breakings are estimated here directly from observed masses and mixing angles. It turns out that although flavor changing reaction rates may be acceptably small in electroweak theories with several scalar doublets without imposing any special symmetries on the scalars themselves, such theories generically yield too much CP violation in the neutral kaon mass matrix. Hence in these theories CP must also be a good approximate symmetry. Such models provide an alternative mechanism for CP violation and have various interesting phenomenological features.
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arxiv:hep-ph/9303241
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A representative but not exhaustive review of the Schwinger-Dyson equation (SDE) approach to the nonperturbative study of QCD is presented. The main focus is the SDE for the quark self energy but studies of the gluon propagator and quark-gluon vertex are also discussed insofar as they are important to the quark SDE. The scope of this article is the application of these equations to the study of dynamical chiral symmetry breaking, quark confinement and the phenomenology of the spectrum and dynamics of QCD.
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arxiv:hep-ph/9303278
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We investigate the effects of the spontaneous CP violation at finite temperature in the Minimal Supersymmetric Standard Model on the baryogenesis at the weak scale. After a brief discussion of the case in which the electroweak phase transition is of the second order, we study in details the baryogenesis scenario when the transition proceeds via bubble nucleation. We show that the space-time dependent phase for the Higgs vacuum expectation values coming from the spontaneous CP violation can give rise to a efficient generation of baryon number inside the bubble walls if the superpotential parameters and the soft supersymmetry breaking ones are complex. However we find that in order to get the observed value for the baryon asymmetry of the universe the phases of such parameters can be as small as $10^{-5}$, giving rise to an electron dipole moment of the neutron well below the current experimental limit. Moreover a light Higgs pseudoscalar is needed, and an upper bound on its mass is obtained.
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arxiv:hep-ph/9304267
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Custodial $SU(2)$ breaking due to dynamical fermion masses is studied in a rather general context and it is shown how some well known limiting cases are correctly described. The type of ``gap equation'' which can systematically lead to extra negative contributions to the so--called $\rho$--parameter is emphasized. Furthermore general model independent features are discussed and it is shown how electro--weak precision measurements can be sensitive to the fermion content and/or dynamical features of a given theory.
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arxiv:hep-ph/9304269
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We compute the thermally averaged $\qq$--annihilation rate into two and three gluons in the early universe. We show that at very high temperatures $\qq\to ggg$ represents only a 3\%\ correction to $\qq\to gg$. Comparing the annihilation rate to the Hubble rate, corrected for particle interactions in the Standard Model gas, we find that quarks and gluons are not in chemical equilibrium when $T\gsim 3\times 10^{14}$ GeV.
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arxiv:hep-ph/9304273
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We consider in detail various theoretical uncertainties of the perturbative predictions for the decay width of $H^0\rightarrow b\overline{b}$ process in the region $50\ GeV< M_H\leq 2M_W$. We calculate the order $O(\alpha_s^2)$-contributions to the expression for $\Gamma_{Hb\overline{b}}$ through the pole quark mass and demonstrate that they are important for the elimination of the numerical difference between the corresponding expression and the one through the running $b$-quark mass. The order $O(\alpha\alpha_s)$ and $O(\alpha^2)$ massless and order $O(m_b^2/M_H^2)$ massive corrections to $\Gamma_{Hb\overline{b}}$ are also calculated. The importance of the latter contributions for modeling of the threshold effects is demonstrated. The troubles with identifying of the 4 recent L3 events $e^+e^-\rightarrow l^+l^-\gamma\gamma$ with the decay of a Standard Higgs boson are discussed.
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arxiv:hep-ph/9304282
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In previous work we have developed a relativistic quark model of mesons which is consistent with all QCD constraints at zeroth and first order in the heavy quark expansion. Here we obtain first order model predictions for the differential decay spectrum, the forward-backward asymmetry $A_{FB}$ and the $D^{\ast}$ polarization parameter $\alpha$ in the decay $B\to D^{\ast}\ell\nu$. We compare these with the predictions of QCD sum rules at first order. The model suggests why the corrections allowed at first order are small, concurrently with substantial corrections at second order.
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arxiv:hep-ph/9304309
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Mesonic fluctuations off the chiral soliton of the Nambu--Jona-Lasinio model are investigated. The hedgehog configuration is proven to represent a local extremum of the action. The method is applied to flavor SU(3) and the energy eigenvalue of the kaon bound state in the soliton background is evaluated which is the key ingredient for the Callan-Klebanov approach to hyperons. The energy eigenvalue of the corresponding strange-valence-quark is found to be 183MeV higher than the energy eigenvalue of the up-valence-quark when 400MeV is assumed for the up-quark constituent mass.
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arxiv:hep-ph/9304314
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We propose a way to reconcile the Standard Model of leptons with a purely vectorial theory. The observed neutrino is predicted to be massless. The unobservability of its partner and the $V-A$ structure of the weak currents are given the same origin.
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arxiv:hep-ph/9305212
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We calculate the baryon asymmetry of the Universe which would arise during a first order electroweak phase transition due to minimal standard model processes. It agrees in sign and magnitude with the observed baryonic excess, for resonable KM parameters and m$_t$ in the expected range, and plausible values of bubble velocity and other high temperature effects. A detailed version of this work (77pp) is being simultaneously submitted to the net. A shortened version of this recently appeared in Phys. Rev. Lett. {\bf 70}, 2833, 1993.
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arxiv:hep-ph/9305274
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In this paper there we describe the calculational background of deriving a strong meson Lagrangian from the Nambu--Jona-Lasinio quark model using the computer algebra systems FORM and REDUCE in recursive algorithms, based on the heat-kernel method for the calculation of the quark determinant.
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arxiv:hep-ph/9305329
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: We examine again the problem of the damping rate of a moving heavy fermion in a hot plasma within the resummed perturbative theory of Pisarski and Braaten. The ansatz for its evaluation which relates it to the imaginary part of the fermion propagator pole in the framework of a self-consistent approach is critically analyzed. As already pointed out by various authors, the only way to define the rate is through additional implementation of magnetic screening. We show in detail how the ansatz works in this case and where we disagree with other authors. We conclude that the self-consistent approach is not satisfactory.
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arxiv:hep-ph/9306219
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I discuss the absorption and dispersion of pions in hot matter. A two-loop calculation in the framework of chiral perturbation theory is presented and its result is compactly written in terms of the two- and three-particle forward $\pi \pi$ scattering amplitudes. At modest temperatures, $T \le 100$ MeV, the change in the pion mass is small and its dispersion law closely resembles the free space one. At these temperatures, all quantities of interest are given to a good degree of accuracy by the first term in the virial expansion which is linear in the density. (BUTP-93/16, uses espcrc1.sty from North-Holland Publishing)
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arxiv:hep-ph/9306275
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We present a detailed discussion of the elastic scattering of a supersymmetric neutralino off a nucleon or nucleus, with emphasis on the spin--independent interaction. We carefully treat QCD effects on the squark exchange contribution. In particular, we identify a class of terms that survive even in the absence of mixing in both the neutralino and squark sectors; the corresponding quark and gluon operators also appear in analyses of deep--inelastic lepton--nucleon scattering (``twist--2 operators''), so their hadronic matrix elements are well known. We also re--emphasize the importance of mixing between the superpartners of left-- and right--handed quarks, and of the contribution from the heavier scalar Higgs boson. We use our refined calculation of the scattering amplitude to update predictions of signal rates for cosmic relic neutralino searches with Germanium detectors. In general the counting rate varies strongly with the values (even the signs) of model parameters; typical results lie between a few times $10^{-4}$ and a few times $10^{-1}$ events/(kg$\cdot$day).
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arxiv:hep-ph/9307208
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Radiative Corrections to $W$ Pair Production and effects of finite width of the $W$ bosons are studied using the Monte Carlo {\tt WOPPER}. As an example the influence of QED radiative corrections on the reconstruction of the $W$ helicities at LEP 200 and a future 500 GeV $e^+ e^-$ collider is discussed.
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arxiv:hep-ph/9307282
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The process $ \bar{p} p \rightarrow e^{-} e^{+} $ is considered in the general case of polarized initial particles. A relation between the difference of the phases of the electromagnetic form factors $G_M$ and $G_E$ in the time-like region and measurable asymmetries is derived. It is shown that the moduli of the form factors can be determined from measurements of the total unpolarized cross section and of the integral asymmetry for longitudinally polarized (or transversely polarized) $\bar{p}$ and $p$. The behaviour of the proton form factors at high $q^2$ in the time-like region is also discussed. From the Phragm\'en-Lindel\"of's theorem it follows that the asymptotical behaviour of the form factors in the space-like and time-like regions must be the same. An analysis of experimental data in both regions based on perturbative QCD is presented.
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arxiv:hep-ph/9307314
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The zero four-momentum and equal mass limits are taken for the bubble diagram of scalar fields. It is seen that RTF and ITF are in complete agreement. However contributions from this diagram to both retarded and time-ordered functions do depend on the order of the limits and can be infinite in some cases. This shows explicitly that the relation between the free energy and a derivative expansion of a thermal effective action is generally much more complicated that is the case at zero temperature.
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arxiv:hep-ph/9307335
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We have used ISAJET 7.0/ISASUSY 1.0 to evaluate the rates and study distributions for trilepton events from the leptonic decays of charginos and neutralinos produced at the Fermilab Tevatron via the reaction, $p\bar p\rightarrow \tilde{W_1} \tilde{Z_2}$ + X for cuts inspired by the CDF and D0 experiments. We find that about 60\% of these events do not contain any jets, and so should be easily identifiable over Standard Model backgrounds from $t\bar{t}$ and WZ production, provided that the decay $\tilde{Z_2}\rightarrow\tilde{Z_1}Z$ is kinematically inaccessible. We further show that, with suitable cuts, these backgrounds can be reduced to less than 1-2 $fb$ even if $n_{jet} = 1$, effectively increasing the SUSY sample by 50\%. We confirm that the signal is only rate-limited, and that the Fermilab Tevatron after an accumulation of 100 $pb^{-1}$ of integrated luminosity will be able to explore parameters well beyond the range of LEP and, if sleptons are substantially lighter than squarks, close to the reach of LEP 200.
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arxiv:hep-ph/9307347
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We systematically analyse the gluonic penguin-induced charmless decays $B \ra K_X\phi$($K_X$ denotes the meson state $s\bar q \;(q=u\ {\rm or}\ d)$ ), in the standard model and the two-Higgs-doublet model. These processes, being induced at one-loop level, are of great importance in measuring the virtual top quark effect in the standard model, and also in searching for the non-standard signals in the low energy region. It is shown that the QCD effect is also significant in these processes, as in the weak radiative processes $B \ra X_s \gamma$. We also show that the charged Higgs contribution can not provide sizable enhancements for the decays $B \ra K_X\phi$, in contrast to the decays $B \ra K_X\gamma$. It is also found that processes such as $B \ra K_1(1400)\phi$ and $B \ra K(1460)\phi$ have large branching fractions among $B \ra K_X\phi$ decays.
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arxiv:hep-ph/9307370
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We observe that quantities like (f_{B_s}/f_B) / (f_{D_s} /f_D) are predicted to be unity both by heavy quark and by light quark flavor symmetries. Hence, the deviation from the symmetry prediction must be simultaneously small in both symmetry breaking parameters, i.e., order of the ratio of light to heavy quarks masses. We estimate the size of the correction. We observe that the ratio of (\Delta M/\Gamma) for B_s - \bar B_s to B - \bar B mixing can be expressed in terms of the measurable ratio f_{D_s} / f_D with good precision. We comment on applications of these ideas to other processes.
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arxiv:hep-ph/9308226
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The first-order bremsstrahlung emission spectrum is $\alpha d\omega/\omega$ at zero temperature. If the radiation is emitted into a region that contains a thermal distribution of photons, then the rate is increased by a factor $1+N(\omega)$ where $N(\omega)$ is the Bose-Einstein function. The stimulated emission changes the spectrum to $\alpha Td\omega/\omega^{2}$ for $\omega\ll T$. If this were correct, an infinite amount of energy would be radiated in the low frequency modes. This unphysical result indicates a breakdown of perturbation theory. The paper computes the bremsstrahlung rate to all orders of perturbation theory, neglecting the recoil of the charged particle. When the perturbation series is summed, it has a different low-energy behavior. For $\omega\ll\alpha T$, the spectrum is independent of $\omega$ and has a value proportional to $d\omega/\alpha T$ .
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arxiv:hep-ph/9308243
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The transport interaction rates of elastic scattering processes of thermal partons in the quark-gluon plasma are calculated beyond the leading logarithm approximation using the effective perturbation theory for QCD at finite temperatures developed by Braaten and Pisarski. The results for the ordinary and transport interaction rates obtained from the effective perturbation theory are compared to perturbative approximations based on an infrared cut-off by the Debye screening mass. The relevance of those interaction rates for a quark-gluon plasma possibly formed in ultrarelativistic heavy ion collisions are discussed.
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arxiv:hep-ph/9308257
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We consider a class of well motivated string-inspired flipped $SU(5)$ supergravity models which include four supersymmetry breaking scenarios: no-scale, strict no-scale, dilaton, and special dilaton, such that only three parameters are needed to describe all new phenomena $(m_t,\tan\beta,m_{\tilde g})$. We show that the LEP precise measurements of the electroweak parameters in the form of the $\epsilon_1$ variable, and the CLEOII allowed range for $\bsg$ are at present the most important experimental constraints on this class of models. For $m_t\gsim155\,(165)\GeV$, the $\epsilon_1$ constraint (at 90(95)\%CL) requires the presence of light charginos ($m_{\chi^\pm_1}\lsim50-100\GeV$ depending on $m_t$). Since all sparticle masses are proportional to $m_{\tilde g}$, $m_{\chi^\pm_1}\lsim100\GeV$ implies: $m_{\chi^0_1}\lsim55\GeV$, $m_{\chi^0_2}\lsim100\GeV$, $m_{\tilde g}\lsim360\GeV$, $m_{\tilde q}\lsim350\,(365)\GeV$, $m_{\tilde e_R}\lsim80\,(125)\GeV$, $m_{\tilde e_L}\lsim120\,(155)\GeV$, and $m_{\tilde\nu}\lsim100\,(140)\GeV$ in the no-scale (dilaton) flipped $SU(5)$ supergravity model. The $\bsg$ constraint excludes a significant fraction of the otherwise allowed region in the $(m_{\chi^\pm_1},\tan\beta)$ plane (irrespective of the magnitude of the chargino mass), while future experimental improvements will result in decisive tests of these models. In light of the $\epsilon_1$ constraint, we conclude that the outlook for chargino and selectron detection at LEPII and at HERA is quite favorable in this class of models.
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arxiv:hep-ph/9308266
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We study the decays of a scalar \stst\ bound state \sigst, where \st\ is the lighter stop eigenstate. If \st\ has no tree--level 2--body decays, the dominant decay modes of \sigst\ are $gg$ or, if $m_h < \mst \ll \mstt$, a pair of light scalar Higgs bosons $h$. The best signal for \sigst\ production at hadron colliders is probably its decay into two photons.
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arxiv:hep-ph/9308291
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We perform a systematic study of radiative corrections to the masses of the Higgs bosons in the minimal supersymmetric standard model (MSSM) augmented by a single gauge singlet, the so-called next-to-minimal supersymmetric standard model (NMSSM). Our method is based on the one-loop effective potential and includes effects of top quark, squark, Higgs and Higgsino loops. We discuss the renormalisation group flows of Yukawa couplings and the upper bound on the lightest CP-even neutral Higgs boson mass as a function of the heavier stop mass and top mass. We then give a general discussion of Higgs boson phenomenology including radiative corrections. We survey as much of the parameter space of the Higgs sector of the NMSSM as is practicable, and analyse the full spectrum of Higgs masses and couplings in these regions of parameter space. Characteristic signatures of the NMSSM such as light charged bosons and weakly coupled neutral scalars are discussed, as are the relative sizes of the various radiative corrections. The MSSM is also discussed as a limiting case of the NMSSM for comparison.
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arxiv:hep-ph/9308309
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The existence of a strongly interacting sector responsible for the electroweak symmetry breaking is assumed. As a consequence vector and axial-vector bound states may be formed. These resonances mix with the Standard Model gauge bosons and are of primary phenomenological importance for the LEP physics. The extended BESS model is an effective scheme based on the symmetry group $SU(8)_L\otimes SU(8)_R$, describing in a consistent way the interactions among the pseudo-Goldstone bosons, vector and axial-vector resonances and the standard gauge bosons. In a previous paper, the contribution from extended BESS to the electroweak oblique corrections was evaluated. However, only an estimate of the effects coming from mass and wave function renormalization of the new resonances, was given. Here we complete the evaluation by computing explicitly these effects. We confirm the previous result, that is, in spite of the great precision of the present LEP measurements, the extended BESS parameter space is not very much constrained.
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arxiv:hep-ph/9308366
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The single production of leptoquarks in $e^+e^-$, $e\gamma$ and $\gamma \gamma$ linear colliders is discussed. We show that these new particles could be seen in such machines even if their mass is close to the kinematic limit. (Invited talk given by G.B. at the ``Workshop on Physics and Experiments at Linear $e^+e^-$ Colliders'', Waikoloa, Hawaii, April 26-30, 1993.)
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arxiv:hep-ph/9309243
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We point out a connection between R symmetry and \susy\ breaking. We show that the existence of an R symmetry is a necessary condition for \susy\ breaking and a spontaneously broken R symmetry is a sufficient condition provided two conditions are satisfied. These conditions are: {\it genericity}, \ie\ the effective Lagrangian is a generic Lagrangian consistent with the symmetries of the theory (no fine tuning), and {\it calculability}, \ie\ the low energy theory can be described by a supersymmetric Wess-Zumino effective Lagrangian without gauge fields. All known models of dynamical supersymmetry breaking possess such a spontaneously broken R symmetry and therefore contain a potentially troublesome axion. However, we use the fact that genericity is {\it not} a feature of supersymmetric theories, even when nonperturbative renormalization is included, to show that the R symmetry can in many cases be explicitly broken without restoring supersymmetry and so the axion can be given an acceptably large mass.
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arxiv:hep-ph/9309299
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We have examined the consequences of assuming the existence of a light scalar boson, weakly coupled to neutrinos, and not coupled to any other light fermions. For a range of parameters, we find that this hypothesis leads to the development of neutrino clusters which form in the early Universe and which provide gravitational fluctuations on scales small compared to a parsec (i.e., the scale of solar systems). The existence of such clustering produces an effect which would appear as a negative mass squared for the electron neutrino in Tritium beta decay, without conflicting with other experiments. The neutrino masses arising in unified gauge theories would then be very much larger than the masses extracted from experiments within the solar system.
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arxiv:hep-ph/9309308
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We study the potential of the next-generation $e^+ e^-$ linear colliders with longitudinally polarized beams, to restrict the values of the anomalous trilinear couplings $WW\gamma$ and $WWZ$ from the measurement of the process $e^+ e^-\to W^+ W^-$. Along with initial $e^+e^-$ polarization, we account also for the possibilities offered by cross sections for polarized final $W$, in order to disentangle the constraints on the various constants. The results show the essential role of the initial beams polarization in improving the bounds obtained from the unpolarized case.
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arxiv:hep-ph/9309322
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We study vector boson pair production at $LHC$ and $SSC$, taking into account the effects generated by the anomalous vector boson and Higgs couplings induced by the operators ${\cal O}_W$ and ${\cal O}_{UW}$, which are the only dim=6 operators preserving $SU(2)_c$. These operators lead to enhanced production of transverse vector bosons, as opposed to the enhanced production of longitudinal gauge bosons, induced in case $M_H\gsim 1\ TeV$, by dim=4 terms already existing in the Standard Model lagrangian. For vector boson pair masses larger than $1\ TeV$, we establish very simple approximate expressions for the standard as well as the non-standard helicity amplitudes for $q\bar q$ annihilation and vector boson fusion, which accurately describe the physics. These expressions should simplify the experimental search for such interactions. We finally discuss the observability and the disentangling of these interactions.
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arxiv:hep-ph/9309324
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A two Higgs doublet model is employed to study the production of a CP-odd Higgs boson ($A$) associated with a large transverse momentum jet ($j$) at hadron supercolliders. The cross section of $pp \to jA+X$ is evaluated with four subprocesses: $gg \to gA$, $gq \to qA$, $g\bar{q} \to \bar{q}A$ and $q\bar{q} \to gA$. We find that $pp \to jA+X$ is a significant source of CP-odd Higgs bosons at future hadron supercolliders.
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arxiv:hep-ph/9310206
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The role lattice QCD can play in $B$ physics is surveyed. We include results for the decay constant, and discuss upcoming calculations of semileptonic form factors and neutral-meson mixing. Together with experimental measurements, these calculations can determine the unitarity triangle. Plenary talk presented at the Workshop on $B$ Physics at Hadron Accelerators, Snowmass, Colo., 21 June--2 July, 1993.
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arxiv:hep-ph/9310220
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We study a recent proposal to observe the disoriented chiral condensate in high energy collisions. In order to produce a large fluctuation in pion probability distribution, a large size of the correlated region is essential. We study the role of the intrinsic symmetry breaking and suggest that a negative (mass)^2 of mesons arising from a misaligned vacuum may be a candidate for such a mechanism. We further point out a possibility to observe unsuppressed strong $CP$ violation in the disoriented vacuum phase.
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arxiv:hep-ph/9310222
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A systematic study of possible deuteronlike two-meson bound states, {\it deusons}, is presented. Previous arguments that many such bound states may exist are elaborated with detailed arguments and numerical calculations including, in particular, the tensor potential. In the heavy meson sector one-pion exchange alone is strong enough to form at least deuteron-like $B\bar B^*$ and $B^*\bar B^*$ composites bound by approximately 50 MeV. Composites of $D\bar D^*$ and $D^*\bar D^*$ states bound by pion exchange alone are expected near the thresholds, while in the light meson sector one generally needs some additional short range attraction to form bound states. The quantum numbers of these states are I=0, In $B\bar B^*$ one predictss the states: $\eta_b(\approx 10545),\ \chi_{b1}(\approx 10562)$, and in $B^*\bar B^*$ one finds the states: $\eta_b(\approx 10590),\ \chi_{b0}(\approx 10582),\ h_b(\approx 10608),\ \chi_{b2}(\approx 10602)$. Near the $D\bar D^*$ threshold the states: $\eta_c(\approx 3870),\ \chi_{c0}(\approx 3870)$ are predicted, and near the $D^*\bar D^*$ threshold one finds the states: $\chi_{b0}(\approx 4015),\ \eta_{c}(\approx 4015),\ h_c(\approx 4015),\ \chi_{c2}(\approx 4015)$. Within the light meson sector pion exchange gives strong attraction for $P\bar V$ and $V\bar V$ systems with quantum numbers where the best non-$q\bar q$ candidates exist, although pion exchange alone is not strong enough to support such bound states.
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arxiv:hep-ph/9310247
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We construct new invariants and give several theorems which determine in general (i) the number of physically meaningful phases in quark mass matrices and (ii) which elements of these matrices can be rendered real by rephasings. We illustrate our results with simple models.
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arxiv:hep-ph/9310307
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The parton model, a zero-order approximation in many treatments, is shown to be a ``semiclassical" model whose results for certain averages also hold (correspondence principle) in quantum mechanics. Algebraic techniques developed for the M\"ossbauer effect exploit simple features of commutators to obtain sum rules showing the validity of the parton model for $b \rightarrow c$ semileptonic decays in the classical limit, $\hbar \rightarrow 0$, where all commutators vanish, and in general, even when binding effects are included, for the lowest moments of the lepton energy spectrum at fixed 3-momentum transfer. Interference between the $u \bar u$ and $d \bar d$ components of the $\rho^o$ and $\omega$ wave functions can be used as clues to contributions from small weak amplitudes and CP violation in decays to final states including these vector mesons.
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arxiv:hep-ph/9310318
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We derive the effective equations for the out of equilibrium time evolution of the order parameter and the fluctuations of a scalar field theory in spatially flat FRW cosmologies.The calculation is performed both to one-loop and in a non-perturbative, self-consistent Hartree approximation.The method consists of evolving an initial functional thermal density matrix in time and is suitable for studying phase transitions out of equilibrium. The renormalization aspects are studied in detail and we find that the counterterms depend on the initial state. We investigate the high temperature expansion and show that it breaks down at long times. We also obtain the time evolution of the initial Boltzmann distribution functions, and argue that to one-loop order or in the Hartree approximation, the time evolved state is a ``squeezed'' state. We illustrate the departure from thermal equilibrium by numerically studying the case of a free massive scalar field in de Sitter and radiation dominated cosmologies. It is found that a suitably defined non-equilibrium entropy per mode increases linearly with comoving time in a de Sitter cosmology, whereas it is {\it not} a monotonically increasing function in the radiation dominated case.
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arxiv:hep-ph/9310319
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We discuss spontaneous symmetry breaking of (1+1)-dimensional $\phi^4$ theory in light-front field theory using a Tamm-Dancoff truncation. We show that, even though light-front field theory has a simple vacuum state which is an eigenstate of the full Hamiltonian, the field can develop a nonzero vacuum expectation value. This occurs because the zero mode of the field must satisfy an operator valued constraint equation. In the context of (1+1)-dimensional $\phi^4$ theory we present solutions to the constraint equation using a Tamm-Dancoff truncation to a finite number of particles and modes. We study the behavior of the zero mode as a function of coupling and Fock space truncation. The zero mode introduces new interactions into the Hamiltonian which breaks the $Z_2$ symmetry of the theory when the coupling is stronger than the critical coupling.
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arxiv:hep-ph/9310330
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Little information is known about the polarization of gluons inside a longitudinally polarized proton. I report on the sensitivity of photoproduction experiments to it. Both jet and heavy quark production are considered.
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arxiv:hep-ph/9310351
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An introduction to the heavy quark effective theory and its symmetries is given. Some implications of the heavy quark spin and flavor symmetries are discussed. Recent results on fragmentation to quarkonium states are reviewed.
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arxiv:hep-ph/9311212
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Some results are presented indicating the distinct advantages that accrue from choosing a real representation for the generators of SU(N) rather than the usual and more popular Gell-Mann type matrices. A few examples in the context of quantum chromodynamics are used to serve as illustrations.
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arxiv:hep-ph/9311220
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We estimate the top quark, lightest sparticle (LSP) and scalar higgs masses within a supersymmetric grand unified framework in which $\tan\beta \simeq m_t/m_b$ and the electroweak symmetry is radiatively broken. The requirement that the calculated $b$ quark mass lie close to its measured value, together with the cosmological constraint $\Omega_{LSP} \approx 1$, fixes the top quark mass to be $m_t(m_t) \approx 170 \pm 15\ GeV$. The LSP (of bino purity $\stackrel{_>}{_\sim} 98\%)$ has mass $\sim 200 - 350\ GeV$. In the scalar higgs sector the CP-odd scalar mass $m_A \stackrel{_<}{_\sim} 220\ GeV$. With $m_A \stackrel{_>}{_\sim} M_Z$, as suggested by the decay $b \rightarrow s\gamma$, we find $M_Z \stackrel{_<}{_\sim} m_{h^0} (m_{H^0}) \stackrel{_<}{_\sim} 140 (220)\ GeV$ and $120\ GeV \stackrel{_<}{_\sim} m_{H^\pm} \stackrel{_<}{_\sim} 240\ GeV$.
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arxiv:hep-ph/9311225
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