Neutral Pseudo Goldstone Bosons Research Articles

Exact formula of the spectrum of the pseudoscalar octet

Non-perturbative proof is presented of a generalized version of Goldstone theorem, where the Lagrangian conserves an approximate SU(3) chiral symmetry, that both quark masses and electromagnetism make contributions to the masses of spinless particles of pseudoscalar octet. We show that apart from what comes in the form of some projections of a two-body Bethe–Salpeter amplitude for which the photon lines like the gluon ones are all internal in the case of neutral pseudo-Goldstone bosons, the charged pseudoscalar mesons receive additional contributions that may be expressed in terms of the axial–vectorial projection of a three-body Bethe–Salpeter amplitude with an extra external photon line.

PGB pair production at LHC and ILC as a probe of the topcolor-assisted technicolor models

The topcolor-assisted technicolor (TC2) model predicts some light pseudo goldstone bosons (PGBs), which may be accessible at the LHC or ILC. In this work we study the pair productions of the charged or neutral PGBs at the LHC and ILC. For the productions at the LHC we consider the processes proceeding through gluon-gluon fusion and quark-antiquark annihilation, while for the productions at the ILC we consider both the electron-positron collision and the photon-photon collision. We find that in a large part of parameter space the production cross sections at both colliders can be quite large compared with the low standard model backgrounds. Therefore, in future experiments these productions may be detectable and allow for probing TC2 model.

Pseudo Goldstone boson effects intt¯productions at high energy hadron colliders and testing technicolor models

We study the top quark pair production process $pp(\overline{p})\ensuremath{\rightarrow}t\overline{t}$ in various kinds of technicolor (TC) models at the Fermilab Tevatron run II and the CERN LHC. The s-channel neutral pseudo Goldstone bosons (PGBs) contribute dominantly to the production amplitudes from their coupling to the gluons through the triangle loops of techniquarks and the top quark. Cross sections in different TC models with s-channel PGB contributions are calculated. It is shown that the PGB effects can be experimentally tested and different TC models under consideration can be distinguished at the LHC. Therefore, the $p\stackrel{\ensuremath{\rightarrow}}{p}t\overline{t}$ process at the LHC provides feasible tests of technicolor models.

Tt¯production rates at the Fermilab Tevatron and the CERN LHC in top-color-assisted multiscale technicolor models

We study the contributions of the neutral pseudo Goldstone bosons (technipions and top pions) to the t{bar t} production cross sections at the Fermilab Tevatron and the CERN LHC in top-color-assisted multiscale technicolor (TOPCMTC) models via the gluon-gluon fusion process from the loop-level couplings between the pseudo Goldstone bosons and the gluons. The MRS set A{sup {prime}} parton distributions are used in the calculation. It is shown that the new CDF datum on the t{bar t} production cross section gives constraints on the parameters in the TOPCMTC models. Models with a large portion of technicolor contributed top-quark mass are disfavored. With reasonable values of the parameters in TOPCMTC models, the cross section at the Tevatron is larger than that predicted by the standard model, and is consistent with the new CDF data. The enhancement of the cross section and the resonance peaks at the LHC are more significant, so that it is testable in future experiments. {copyright} {ital 1997} {ital The American Physical Society}

Production of neutral pseudo-Goldstone bosons at LEP II and NLC in multiscale walking technicolor models

Walking technicolor (WTC) models predict the existence of heavy neutral pseudo-Goldstone bosons (PGBs), whose masses are typically expected to be larger than 100 GeV. In this paper, we investigate the production and decay of these particles at the high energy e + e − experiments, LEP II and NLC. We find that, in WTC models, the production of neutral PGBs can be significantly enhanced, by one or two orders of magnitude, with respect to the predictions of traditional (QCD-like) TC models. The origin of such an enhancement is the existence of several low energy TC scales, that are likely to appear in WTC theories. This could allow the PGBs to be observed even at the energy and luminosity of the LEP II experiment. At LEP II, the PGBs are expected to be produced in the e + e − → Pγ channel, and, possibly, in the e + e − → Pe + e − channel, with a total rate that can be of the order of several tenths per year. Due to the typical large values of PGB masses, the relative branching ratios of PGB decays, in WTC theories, are different from those predicted in traditional TC models. In particular, a large fraction of these decays can occur in the P → γγ channel. In considering the PGB production, at LEP II, we find that, in most of the final states, the distinctive signatures of WTC events should allow the Standard Model background to be reduced to a negligible level. We also find that, at a 500 GeV NLC experiment, the production of neutral PGBs can occur in several channels, and can be of the order of 10 3 events per year. Instead, when we consider traditional TC models, we find that no PGB are typically predicted to be observed, both at LEP II and the NLC experiment.

THE EFFECT OF TOP QUARK LOOP ON THE NEUTRAL PSEUDO-GOLDSTONE BOSON PRODUCTION FROM Z DECAYS

The main production mechanism of neutral pseudo-Goldstone bosons, as predicted in technicolor models, is via their couplings to gauge bosons. We calculate the effect of top quark loop on the coupling. The result affects the prediction of the neutral pseudo-Goldstone boson production from Z decays.

Production and signatures of neutral pseudo-Goldstone bosons at the Z0 pole in technicolor and extended technicolor models

The existence of pseudo-Goldstone bosons (PGBs) is a common prediction of almost all non-minimal technicolor and extended technicolor models. In this paper we present a study of the production and decay of neutral PGBs at the Z 0 pole. We have expressed the couplings of the PGBs to ordinary particles in a form that is, to a large extent, model independent. This allows to obtain quite a general predictions of the theory for the various production and decay rates. The favorite channel in which neutral PGBs can be produced in Z 0 decays is usually represented by the simple Z 0 → Pγ decay. The main new result of this paper is an extensive analysis of the various Z 0 → P ƒƒ decays, where P is a PGB and ƒƒ is a fermion pair. The corresponding branching ratios are smaller than 10 −7 for almost all the possible values of the PGB mass, unless some specific theoretical assumptions are introduced. We also discuss the Z 0 → l + l − γ events with large photon invariant mass, recently observed by the L3 Collaboration at LEP, in the framework of ETC models.

The effect of top-loop on the coupling of P30a to the gluon-photon

The main production mechanism of colour octet isotriplet neutral pseudo-Goldstone bosons (denoted by P30a) is via g- gamma fusion. The total effective Lagrangian of P30a anomalous coupling to the gluon-photon is given. The effect of the top-quark loop on the coupling is calculated. Such an effect significantly changes the coupling strength. The net result is a more favourable situation for the detection of P30a at ep colliders (HERA and LEP/LHC).

Signatures of neutral pseudo Goldstone bosons from technicolor

Non-minimal technicolor models can contain neutral pseudo Goldstone bosons that can be produced in conjuction with a photon at LEP. We investigate all possible production and decay modes of such pseudo Goldstone bosons and show that all decay modes yield distinctive signatures for which one can readily search in current experiments. Possible signatures of this particle include three final state photons or single or double photons with missing energy. We also consider the possibility of searching for such particles at LEP II and hadron colliders.

The top mass and pseudo-Goldstone bosons at LHC/SSC

We consider models where the top mass is built up both from a top condensate and radiative contributions and mass generation in the weak boson sector is dynamical. As a consequence charged and neutral pseudo-Goldstone bosons appear. Their masses are estimated and found to be in a range accessible at LHC/SSC. Also they fall naturally in the region where the standard model requires new physics to appear. A brief qualitative discussion concerning their observability is added. Basically the search can be performed together with the search for charged and neutral Higgses. Particular important would be to discriminate them from SUSY charged Higgses. It is noted that the predicted scalar spectrum cannot be imitated by an extended Higgs sector of the standard model. Extension of the radiative mass generation to the τ-sector calls for the introduction of a new heavy lepton doublet with mass in the region 1–2 TeV.

Rho parameter and pseudo-Goldstone-boson couplings to the Z.

The possibility that neutral pseudo Goldstone bosons of "enhanced" technicolor theories can imitate neutral-Higgs-boson couplings to the $Z$ is considered in light of $\ensuremath{\rho}$-parameter constraints. A rough estimate indicates that couplings of neutral pseudo Goldstone bosons to the $Z$ induced by extended technicolor interactions are unlikely to be of conventional Higgs strength.

Production of neutral technicolor pseudo Goldstone bosons and QCD background at the Superconducting Super Collider.

The production of the neutral technicolor pseudo Goldstone bosons ${\mathrm{P}}^{0\ensuremath{'}}$ and ${\mathrm{P}}_{8}^{0\ensuremath{'}}$ at large transverse momentum in pp\ifmmode\bar\else\textasciimacron\fi{} collisions, pp\ifmmode\bar\else\textasciimacron\fi{}\ensuremath{\rightarrow}g(q)${\mathrm{P}}^{0\ensuremath{'}}$(${\mathrm{P}}_{8}^{0\ensuremath{'}}$)X, has been investigated at the Superconducting Super Collider (SSC) energy. The major two-body and three-body decay modes in tree diagrams are also investigated in detail. The tt\ifmmode\bar\else\textasciimacron\fi{} decay channel would dominate the decays of both ${\mathrm{P}}^{0\ensuremath{'}}$ and ${\mathrm{P}}_{8}^{0\ensuremath{'}}$ if it is allowed. Otherwise, gg and 3g will be the dominant decay modes unless the mass of the ${\mathrm{P}}^{0\ensuremath{'}}$ and ${\mathrm{P}}_{8}^{0\ensuremath{'}}$ are below 40 GeV, where bb\ifmmode\bar\else\textasciimacron\fi{} becomes dominant. The tt\ifmmode\bar\else\textasciimacron\fi{} channel will be the ideal signal for detecting these bosons since the signal is much larger than the QCD background. However, in the absence of the tt\ifmmode\bar\else\textasciimacron\fi{} channel, the \ensuremath{\tau}\ensuremath{\tau}\ifmmode\bar\else\textasciimacron\fi{} mode can be used to identify ${\mathrm{P}}^{0\ensuremath{'}}$ up to ${\mathrm{m}}_{\mathrm{P}}$=300 GeV in the transverse-momentum range ${\mathrm{P}}_{\mathrm{\ensuremath{\perp}}}$\ensuremath{\lesssim}100 GeV. Similarly, the bb\ifmmode\bar\else\textasciimacron\fi{} decay mode can serve as a useful signal for the identification of ${\mathrm{P}}_{8}^{0\ensuremath{'}}$ up to ${\mathrm{m}}_{\mathrm{P}}$=300 GeV for ${\mathrm{P}}_{\mathrm{\ensuremath{\perp}}}$ between 500 and 700 GeV. Our results show that these high-transverse-momentum production processes are useful in searching for the ${\mathrm{P}}^{0\ensuremath{'}}$ and ${\mathrm{P}}_{8}^{0\ensuremath{'}}$ at the SSC.