arXiv subjects
T. G. Rizzo
Publications and source records attributed to T. G. Rizzo.
Bulk Gauge Fields in the Randall-Sundrum Model
We explore the consequences of placing the Standard Model gauge fields in the bulk of the recently proposed localized gravity model of Randall and Sundrum. We find that the Kaluza Klein excitations of these fields are necessarily strongly coupled and we demonstrate that current precision electroweak data constrain the lowest states to lie above $\simeq 23$ TeV. Taking the weak scale to be $\sim 1$ TeV, the resulting implications on the model parameters force the bulk curvature, $R_5$, to be larger than the higher dimensional Planck scale, $M$, violating the consistency of the theory. In turn, to preserve $|R_5|\lsim M^2$, the weak scale must be pushed to $\gsim 100$ TeV. Hence we conclude that it is disfavored to place the Standard Model gauge fields in the bulk of this model as it is presently formulated.
Warped Phenomenology
We explore the phenomenology associated with the recently proposed localized gravity model of Randall and Sundrum where gravity propagates in a 5-dimensional non-factorizable geometry and generates the 4-dimensional weak-Planck scale hierarchy by an exponential function of the compactification radius, called a warp factor. The Kaluza-Klein tower of gravitons which emerge in this scenario have strikingly different properties than in the factorizable case with large extra dimensions. We derive the form of the graviton tower interactions with the Standard Model fields and examine their direct production in Drell-Yan and dijet events at the Tevatron and LHC as well as the KK spectrum line-shape at high-energy linear \epem colliders. In the case where the first KK excitation is observed, we outline the procedure to uniquely determine the parameters of this scenario. We also investigate the effect of KK tower exchanges in contact interaction searches. We find that present experiments can place meaningful constraints on the parameters of this model.
Resonant Slepton Production at Hadron Colliders in R-parity Violating Models
Single $s$-channel production of sleptons, such as $\tilde τ$'s and/or $\tilde ν_τ$, with their subsequent decay into purely leptonic or dijet final states is possible in hadronic collisions via R-parity violating couplings. We examine the impact of slepton production on bump searches in both the Drell-Yan and dijet channels and examine whether the lepton charge asymmetry in the $\ellν$ channel provides for additional search sensitivity. As a consequence, search reaches in the slepton mass-R-parity violating coupling plane are obtained for both the Tevatron and LHC. The possibility of using the leptonic angular distributions and the lepton charge asymmetry to distinguish slepton resonances from new gauge bosons is also analyzed.
$b \to s\ell^+\ell^-$ in the Left-Right Symmetric Model
We begin to analyze and contrast the predictions for the decay $b\to s\ell^+\ell^-$ in the Left-Right Symmetric Model(LRM) with those of the Standard Model(SM). In particular, we show that the forward-backward asymmetry of the lepton spectrum can be used to distinguish the SM from the simplest manifestation of the LRM. [To appear in the Proceedings of the 2nd International Conference on B Physics and CP Violation, Honolulu, HI, 24-27 March 1997]
NEW PARTICLES AND INTERACTIONS
We analyze the manifestations of new matter particles predicted by models of new physics beyond the Standard Model, at present and future high--energy colliders. We consider both the production of these new particles and some of their indirect signatures at $pp$ and $eP$ colliders as well as TeV $\ee$ colliders with their $\ee, e γ, γγ$ and $e^- e^-$ modes. The report is arranged into four main sections plus an overview. These sections will deal separately with exotic and excited fermions, difermions, and new interactions.
Model Dependence of $W_R$ Searches at the Tevatron
We explore the sensitivity of the on-going Tevatron search for charged, right-handed gauge bosons, $W_R^{\pm}$, to various model dependent assumptions such as the magnitude of the $SU(2)_R$ gauge coupling, the values of the right-handed Kobayashi-Maskawa mixing matrix elements, $(V_R)_{ij}$, and the nature of the right-handed neutrino. These results also have important implications for HERA searches for right-handed currents.
Summary of the Extensions of the Standard Model Working Group
We summarize the results of the extended gauge group working group of the Madison-Argonne Workshop on Present and Future Colliders. Contributions are described on the previously unexamined two photon fusion production of heavy leptons, new studies of $Z'$ couplings to $ν\barν$ and $q\bar{q}$, and previously unexplored vector leptoquark production. More detailed accounts of these studies can be found in individual contributions.
Using `Invisible' Decay Modes as Probes of Z' Couplings
We explore the possibility that $Z'$ couplings can be probed using decay modes which involve neutrinos once Standard Model backgrounds are directly determined by the data itself. For some models, sufficient statistics are available at either the SSC or LHC to render these modes useful for coupling determinations, provided the mass of the $Z'$ is not much larger than 1 TeV, if we assume other new physics background sources are absent.
Extraction of $Z'$ Coupling Data From $Z' \to jj$ at the LHC and SSC
A recent analysis has shown that it may be possible at the SSC to extract information about $Z'$ couplings via the decay $Z' \to jj$. This technique was found to be useful for some extended electroweak models provided the $Z'$ is relatively light. In the present paper, we generalize this procedure to the LHC and to $Z'$'s which are more massive than 1 TeV. (Contributed to the {\it Proceedings of the Workshop on Physics at Current Accelerators and the Supercollider}, Argonne National Laboratory, June 2-5, 1993.)
Inverse Neutrinoless Double $β$-Decay at the NLC?
The NLC may allow us to search for the `inverse' process to neutrinoless double-$β$ decay, $e^-e^-\to W^-W^-$, which probes the existence of Majorana masses for neutrinos. Expectations for the observation of this process in both the Standard Model and its extension, the Left-Right Symmetric Model, are examined. (Talk given at the {\it {Workshop on Physics and Experiments at Linear $e^+e^-$ Colliders}}, Waikoloa, Hawaii.)
Using $b \to sγ$ to Probe Top Quark Couplings
Possible anomalous couplings of the top-quark to on-shell photons and gluons are constrained by the recent results of the CLEO Collaboration on both inclusive and exclusive radiative $B$ decays. We find that the process \bsg\ can lead to reasonable bounds on both the anomalous electric and magnetic dipole moments of the top-quark, while essentially no limits are obtained on the corresponding chromoelectric and chromomagnetic moments, which enter the expression for the decay rate only through operator mixing.
A Model of Universality Violation Revisited
The possibility that the interactions of the third generation of quarks and leptons may violate universality by a small amount remains an open experimental question. The model of Li and Ma, which naturally accommodates such violations, is found to be highly constrained by newly obtained, high precision electroweak and $τ$-lepton data once full Standard Model radiative corrections are incorporated into the analysis. A comparison of the predictions of this model with existing data and the expectations for future colliders is presented.
Constraints on Anomalous Gauge Boson Couplings From $b \to sγ$
The recent results of the CLEO Collaboration on both inclusive and exclusive radiative $B$ decays are combined with those of the UA2 Collaboration on $Wγ$ production to highly constrain the anomalous trilinear gauge couplings of the $W$. The theoretical analysis of the $b \to sγ$ process employs, next-to-leading order operator coefficient evolution as well as QCD bremsstrahlung and appropriate phase space corrections.
Extraction of Coupling Information From $Z' \to jj$
An analysis by the ATLAS Collaboration has recently shown, contrary to popular belief, that a combination of strategic cuts, excellent mass resolution, and detailed knowledge of the QCD backgrounds from direct measurements can be used to extract a signal in the $Z' \to jj$ channel in excess of $6σ$ for certain classes of extended electroweak models. We explore the possibility that the data extracted from $Z$ dijet peak will have sufficient statistical power as to supply information on the couplings of the $Z'$ provided it is used in conjunction with complimentary results from the $Z' \to \ell^+ \ell^-$ `discovery' channel. We show, for a 1 TeV $Z'$ produced at the SSC, that this technique can provide a powerful new tool with which to identify the origin of $Z'$'s.
Radiative $W$ and $Z$ Decays and Spontaneous R-Parity Violation
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 $W\rightarrow\slepγ$ and $Z$ decay $Z\rightarrow\snuγ$, 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 $10^{-5}$ .
SO(10) Grand Unification with a Low-Energy $M_R$
Contrary to commonly held belief, we show that one can obtain a low value for $M_R$, the $SU(2)_R$ breaking scale, in grand unification theories based on $SO(10)$. This possibility emerges in the supersymmetric version of $SO(10)$ with a judicious choice of Higgs content. The unification scale is found to be consistent with the constraint from proton decay. This result is first explicitly demonstrated using the one loop renormalization group equations, and then a full two loop analysis is carried out.
Lepton Number Violating Radiative $W$ Decay in Models with R-parity Violation
Models with explicit R-parity violation can induce new rare radiative decay modes of the $W$ boson into single supersymmetric particles which also violate lepton number. We examine the rate and signature for one such decay, $W\rightarrow \tilde lγ$, and find that such a mode will be very difficult to observe, due its small branching fraction, even if the lepton number violating coupling in the superpotential is comparable in strength to electromagnetism. This parallels a similar result obtained earlier by Hewett in the case of radiative $Z$ decays.