scispace - formally typeset
Search or ask a question

Showing papers on "Elementary particle published in 1993"


Journal ArticleDOI
TL;DR: This paper describes an approach to model building with supersymmetry broken at comparatively low energies which solves these problems, and gives a realistic example.
Abstract: Conventional approaches to supersymmetric model building suffer from several naturalness problems: they do not explain the large hierarchy between the weak scale and the Planck mass, and they require fine-tuning to avoid large flavor-changing neutral currents and particle electric dipole moments. The existence of models with dynamical supersymmetry breaking, which can explain the hierarchy, has been known for some time, but efforts to build such models have suffered from unwanted axions and difficulties with asymptotic freedom. In this paper we describe an approach to model building with supersymmetry broken at comparatively low energies which solves these problems, and give a realistic example.

790 citations


Journal ArticleDOI
TL;DR: In this paper, it was shown that the azimuthal dependence of the distribution of hadrons in a quark jet is a probe of the transverse spin of the quark initiating the jet.

695 citations


Journal ArticleDOI
TL;DR: A large relic neutralino density is found, and the requirement that relic neutralinos do not overclose the Universe does not lead to upper bounds on SUSY-breaking parameters that are strictly valid for all combinations of parameters and of interest for existing or planned collider experiments.
Abstract: We compute the cosmic relic (dark-matter) density of the lightest supersymmetric particle (LSP) in the framework of minimal [ital N]=1 supergravity models with radiative breaking of the electroweak gauge symmetry. To this end, we recalculate the cross sections for all possible annihilation processes for a general, mixed neutralino state with arbitrary mass. Our analysis includes effects of all Yukawa couplings of third-generation fermions, and allows for a fairly general set of soft supersymmetry- (SUSY-) breaking parameters at the Planck scale. We find that a cosmologically interesting relic density emerges naturally over wide regions of parameter space. However, the requirement that relic neutralinos do not overclose the Universe does not lead to upper bounds on SUSY-breaking parameters that are strictly valid for all combinations of parameters and of interest for existing or planned collider experiments; in particular, gluino and squark masses in excess of 5 TeV cannot strictly be excluded. On the other hand, in the generic'' case of a gauginolike neutralino whose annihilation cross sections are not accidentally'' enhanced by a nearby Higgs boson or [ital Z] pole, all sparticles should lie within the reach of the proposed [ital pp] and [ital e][sup +][ital e[minus]] supercolliders. We also find thatmore » requiring the LSP to provide all dark matter predicted by inflationary models imposes a strict lower bound of 40 GeV on the common scalar mass [ital m] at the Planck scale, while the lightest sleptons would have to be heavier than 100 GeV. Fortunately, a large relic neutralino density does not exclude the possibility that charginos, neutralinos, gluinos, and squarks are all within the reach of the CERN [ital e][sup +][ital e[minus]] collider LEP 200 and the Fermilab Tevatron.« less

600 citations


Journal ArticleDOI
TL;DR: Using a linear realization of the Goldstone bosons, a complete set of dimension-six operators which are SU(2)[times]U(1) gauge invariant and conserve [ital C] and [ital P] are considered to study effects of new physics which originates above 1 TeV and the Higgs boson mass dependence of the results can be investigated.
Abstract: Novel strong interactions in the electroweak bosonic sector are expected to induce effective interactions between the Higgs doublet field and the electroweak gauge bosons which lead to anomalous $\mathrm{WWZ}$ and $\mathrm{WW}\ensuremath{\gamma}$ vertices once the Higgs field acquires a vacuum expectation value. Using a linear realization of the Goldstone bosons, we consider a complete set of dimension-six operators which are SU(2)\ifmmode\times\else\texttimes\fi{}U(1) gauge invariant and conserve $C$ and $P$. This approach allows us to study effects of new physics which originates above 1 TeV and the Higgs boson mass dependence of the results can be investigated. Four of the dimension-six operators affect low energy and present CERN LEP experiments at the tree level. Another five influence neutral and charged current experiments at the one-loop level and three of these lead to anomalous $\mathrm{WWZ}$ and $\mathrm{WW}\ensuremath{\gamma}$ vertices. Their loop contributions are at most logarithmically divergent, and these logarithmic divergences can be understood as renormalizations of the four operators which contribute at the tree level. Constraints on the remaining five operators can be obtained if one assumes the absence of cancellations between the tree level and one-loop contributions. The resulting bounds on anomalous triple gauge boson couplins are modest, which emphasizes the importance of direct measurements of the triple gauge boson vertices, e.g., in ${W}^{+}{W}^{\ensuremath{-}}$ production at LEP II.

447 citations


Journal ArticleDOI
TL;DR: The QCD corrections to the fusion cross section for arbitrary Higgs boson and top quark mass values are presented and they increase the cross section σ (pp→H) by about a factor of 1.5 to 1.7.
Abstract: Gluon fusion is the main production mechanism for Higgs bosons with masses up to several hundred GeV in pp collisions at the CERN large Hadron Collider and Superconducting Super Collider. We present the QCD corrections to the fusion cross section for arbitrary Higgs boson and top quark mass values: gg → H(g), gq → Hq, and qq → Hg. The QCD corrections are positive and they increase the cross section σ (pp→H) by about a factor of 1.5 to 1.7. The analysis applies to the production of Higgs particles in the standard model and also to the production of the CP-even Higgs particles in extensions of the Higgs sectors are required, for example, by supersymmetric theories

333 citations


Journal ArticleDOI
TL;DR: A class of terms that survive even in the absence of mixing in both the neutralino and squark sectors are identified; 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.
Abstract: 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 reemphasize 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 ${10}^{\ensuremath{-}4}$ and a few times ${10}^{\ensuremath{-}1}$ events/(kg day).

330 citations


Journal ArticleDOI
TL;DR: In this article, the electroweak breaking mechanism in the minimal supersymmetric standard model (MSSM) using the complete one-loop effective potential V1 was examined and the region of the whole MSSM parameter space that leads to a successful SU(2) × U(1) breaking with an acceptable top-quark mass.

278 citations


Journal ArticleDOI
TL;DR: In hadron-hadron collisions, production of Higgs bosons and other color-singlet systems can occur via fusion of electroweak bosons, occasionally leaving a ``rapidity gap'' in the underlying-event structure, which is studied to see whether it serves as a signature for detection of the Higgs Bosons, etc.
Abstract: In hadron-hadron collisions, production of Higgs bosons and other color-singlet systems can occur via fusion of electroweak bosons, occasionally leaving a ``rapidity gap'' in the underlying-event structure. This observation, due to Dokshitzer, Khoze, and Troyan, is studied to see whether it serves as a signature for detection of the Higgs bosons, etc. We find it is a very strong signature at subprocess c.m. energies in excess of a few TeV. The most serious problem with this strategy is the estimation of the fraction of events containing the rapidity gap; most of the time the gap is filled by soft interactions of spectator degrees of freedom. We also study this question and estimate this ``survival probability of the rapidity gap'' to be of order 5%, with an uncertainty of a factor 3. Ways of testing this estimate and further discussion of the underlying hard-diffraction physics are presented.

275 citations


Journal ArticleDOI
TL;DR: In this paper, the authors present an explicit example in which the whole particle spectrum is given as a function of the top quark mass, and the existence of Kaluza-Klein excitations for gauge bosons and higgses is predicted.

241 citations


Journal ArticleDOI
TL;DR: A revised and complete list of the electroweak chiral Lagrangian operators up to dimension four and the connection to the [ital S], [ital T], and [ital U] parameters and the parameters describing the triple gauge boson vertices is made.
Abstract: A revised and complete list of the electroweak chiral Lagrangian operators up to dimension four is provided. The connection of these operators to the $S$, $T$, and $U$ parameters and the parameters describing the triple gauge boson vertices $\mathrm{WW}\ensuremath{\gamma}$ and $\mathrm{WWZ}$ is made, and the size of these parameters from new heavy physics is estimated using a one flavor-doublet model of heavy fermions. The coefficients of the chiral Lagrangian operators are also computed in this model.

177 citations


Journal ArticleDOI
TL;DR: The mechanism, which implements natural doublet-triplet splitting using the adjoint Higgs boson, converts these dimension-5 operators effectively into dimension 6 by explicitly computing the Higgs spectrum and the resulting threshold uncertainties.
Abstract: In supersymmetric grand unified theories, proton decay mediated by the color-triplet Higgsino is generally problematic and requires some fine-tuning of parameters. We present a mechanism which naturally suppresses such dimension-5 operators in the context of SUSY SO(10). The mechanism, which implements natural doublet-triplet splitting using the adjoint Higgs boson, converts these dimension-5 operators effectively into dimension 6. By explicitly computing the Higgs spectrum and the resulting threshold uncertainties we show that the successful prediction of ${{sin}^{2}\ensuremath{\theta}}_{W}$ is maintained as a prediction in this scheme. It is argued that only a weak suppression of the Higgsino-mediated proton decay is achievable within SUSY SU(5) without fine-tuning, in contrast to a strong suppression in SUSY SO(10).

Journal ArticleDOI
TL;DR: This work derives general formulas for the oblique-correction parameters [ital S], [ital T], and [ital U] in an extension of the standard model with an arbitrary number of vectorlike singlet and vectorlike doublet quarks, or with mirror quarks which mix with the standard quarks of the same electric charge.
Abstract: We derive general formulas for the oblique-correction parameters $S$, $T$, and $U$ in an extension of the standard model with an arbitrary number of vectorlike singlet and vectorlike doublet quarks, or with mirror quarks, which mix with the standard quarks of the same electric charge. We analyze numerically the oblique corrections caused by some simple structures of exotic quarks, paying special attention to the decoupling properties.

Journal ArticleDOI
TL;DR: The first three years of the L3 detector at the Large Electron Positron collider (LEP) achieved ( ΔE / E 0 ≃ 1.4% for electrons and photons at E = 45 GeV and ( Δp / p ) ≃ 2.5% for muons at p = 45 geV as discussed by the authors.

Journal ArticleDOI
TL;DR: It is shown that only in the extremely relativistic limit can the usual quantum mechanical oscillation probability be factored out of the time-averaged cross section.
Abstract: We discuss neutrino oscillations in the framework of the quantum field theory without introducing the concept of neutrino weak eigenstates. The external particles are described by wave packets and the different mass eigenstate neutrinos propagate between the production and detection interactions, which are macroscopically localized in space-time. The time-averaged cross section, which is the measurable quantity in the usual experimental setting, is calculated. It is shown that only in the extremely relativistic limit can the usual quantum mechanical oscillation probability be factored out of the cross section.

Journal ArticleDOI
TL;DR: In this paper, a lower bound to the Higgs mass for a given top quark mass is given for α s (M z ) = 0.117, where α s is the number of top quarks in the model.

Journal ArticleDOI
TL;DR: It is found that the present limit on [mu][r arrow][ital e][gamma] implies that, in the Cheng-Sher scenario of multi-Higgs-doublet models, all neutral Higgs bosons possess flavor-changing couplings proportional to [radical][ital m][sub [ital i]m[ital j]m] .
Abstract: The two-loop mechanism of Bjorken and Weinberg is used to constrain flavor-changing neutral Higgs bosons. We calculate the complete set of two-loop diagrams for the rare decay $\ensuremath{\mu}\ensuremath{\rightarrow}e+\ensuremath{\gamma}$ induced by such neutral Higgs bosons, for arbitrary Higgs boson and top quark masses. The analytic result is used to set limits on Higgs boson masses for some recent models with a specific ansatz about the flavor-changing couplings. For example, in the Cheng-Sher scenario of multi-Higgs-doublet models, all neutral Higgs bosons possess flavor-changing (${f}_{i}\ensuremath{\leftrightarrow}{f}_{j}$) couplings proportional to $\sqrt{{m}_{i}{m}_{j}}$. We find that the present limit on $\ensuremath{\mu}\ensuremath{\rightarrow}e\ensuremath{\gamma}$ implies that, in such a scheme, these neutral Higgs bosons should be heavier than 200 GeV.

Journal ArticleDOI
TL;DR: In this paper, the QCD radiative corrections to the γγ decay widths of scalar and pseudoscalar Higgs particles in multi-doublet extensions of the Higgs sector, as realized for instance in supersymmetric theories are presented.

Journal ArticleDOI
TL;DR: In this article, a very weakly interacting keV majoron is considered as a dark matter particle (DMP), which provides both the critical density δcr = 1.88 × 10−29h2 g/cm3 and the galactic scale Mgal ∼ mPl3 /mJ2 ∼ 1012M ⊙ (mJ/1 keV)−2 for galaxy formation.

Journal ArticleDOI
TL;DR: In this paper, a detailed description of the calculation in the Standard Model of all the m t 4 radiative correction effects to the electroweak precision observables for arbitrary values of the Higgs mass is given.

Journal ArticleDOI
TL;DR: In this article, the weak interactions of pseudoscalar mesons with meson resonances with spin 0, 1 to lowest order in the derivative expansion were considered and the resonance contributions to the O( p 4 ) weak coupling constants were determined.

Journal ArticleDOI
TL;DR: In this paper, the authors present the QCD corrections to the gluon fusion processes of the scalar Higgs particles h, H, and the pseudoscalar higgs particle A in the minimal supersymmetric extension of the Standard Model, which are in general large and positive, increasing the production cross section up to factors of about 2.

Journal ArticleDOI
TL;DR: In this paper, an effective lagrangian including negative and positive parity heavy mesons containing a heavy quark, light pseudoscalars, and light vector resonances, with their allowed interactions, was introduced.

Journal ArticleDOI
TL;DR: In this paper, the potential of LEP2 to measure the trilinear couplings of the vector bosons, Z 0 W + W − and γW+ W − among one another, was investigated.

Journal ArticleDOI
TL;DR: In this paper, the authors considered a general supersymmetric standard model with arbitrary Higgs sectors and showed that the allowed region in the (mh,mt) plane depends on the scale �, below which the theory remains perturbative.

Journal ArticleDOI
TL;DR: In this paper, the authors derived constraints on the relic abundance of a generic particle of mass ∼ 1−1014 TeV which decays into neutrinos at cosmological epochs, using data from the Frejus and IMB nucleon decay detectors and the Fly's Eye air-shower array.

Journal ArticleDOI
TL;DR: In this article, a modified quark-quark interaction is applied to study the nucleon-nucleon interaction, which is suggested by instanton models and includes pion ( pi ) and sigma ( sigma ) exchanges as non-perturbative components and the one-gluon exchange as a perturbative one.
Abstract: A modified quark-quark interaction is applied to study the nucleon-nucleon interaction. The quark potential is suggested by instanton models and includes pion ( pi ) and sigma ( sigma ) exchanges as non-perturbative components and the one-gluon exchange as a perturbative one. The nucleon-nucleon potential derived from this model presents short-range repulsion and medium-range attraction besides the usual pion tail. Using this interaction the nucleon-nucleon phase shifts within the resonating group method have been calculated. They agree reasonably well with experimental values.

Journal ArticleDOI
TL;DR: A calculable upper limit on the mass of the lightest Higgs boson is derived in perturbatively valid supersymmetric theories with arbitrary Higgs sectors with standard model gauge symmetry and a supersymmetry spectrum around or below 1 TeV.
Abstract: We derive a calculable upper limit on the mass of the lightest Higgs boson in perturbatively valid supersymmetric theories with arbitrary Higgs sectors. We assume a supersymmetry spectrum around or below 1 TeV and the standard model gauge symmetry, but place no restrictions on the Higgs sector. We estimate m h o<146 GeV for M t ≥100 GeV from all effects except possible additional heavy fermions beyond top (which could increase the limit approximately 12 GeV per extra family); for 60≤M t ≤100 GeV we and m h o<156 GeV. In most explicitly constructed models the lightest Higgs boson mass does not saturate the upper limit

Journal ArticleDOI
TL;DR: In this paper, the sensitivity of the mt fixed point result to GUT threshold corrections and point out the implications for Higgs boson searches is discussed, and the lightest scalar h has mass 60-85 GeV and will be detectable at LEP II.

Journal ArticleDOI
TL;DR: In this article, it was shown that the present experimental limits on μ-e conversion in nuclei give a nuclear-model-independent bound on the Z-e-μ vertex which is twice as strong as that obtained from μ → eee.

Journal ArticleDOI
TL;DR: A wide class of neutrino physics motivated models are characterized by the spontaneous violation of a global U(1) lepton number symmetry at or below the electroweak scale by an SU(2)⊗U( 1) singlet vacuum expectation value as discussed by the authors.