arXiv subjects

David Bowser-Chao

Publications and source records attributed to David Bowser-Chao.

17 recordsLinked to original sources

arXiv1998

On A New Class of Models for Soft CP Violation

We elaborate on a new class of models proposed recently by us and compare with another class proposed by Georgi and Glashow(GG). The models can be roughly classified as the righted-handed (or left-handed) models in our (or GG's) case. Both classes of models use softly broken CP symmetry to suppress tree level KM phase as well as the strong CP phase. The measured value of the CP-violating parameter $ε$ are accounted for by employing a new heavy sector of scalars and vectorial fermions. The models can be milliweak or superweak in nature depending on the scale of the heavy sector. We review the phenomenology of the right-handed models and compare with the left-handed models.

hep-ph↗

arXiv1998

Phase Effect of A General Two-Higgs-Doublet Model in $b\to sγ$

In a general two-Higgs-doublet model (2HDM), without the {\it ad hoc} discrete symmetries to prevent tree-level flavor-changing-neutral currents, an extra phase angle in the charged-Higgs-fermion coupling is allowed. We show that the charged-Higgs amplitude interferes destructively or constructively with the standard model amplitude depending crucially on this phase angle. The popular model I and II are special cases of our analysis. As a result of this phase angle the severe constraint on the charged-Higgs boson mass imposed by the inclusive rate of $b\to sγ$ from CLEO can be relaxed. We also examine the effects of this phase angle on the neutron electric dipole moment. Furthermore, we also discuss other constraints on the charged-Higgs-fermion couplings coming from measurements of $B^0-\bar{B^0}$ mixing, $ρ_0$, and $R_b$.

hep-ph↗

arXiv1998

Resonant Bound State Production at e- e- Colliders

Observation of a sequence of resonances at an e-e- collider would suggest bound states of strongly coupled constituents carrying lepton number. Obvious candidates for these exotic constituents are leptoquarks and leptogluons. We show that under reasonable assumptions, the existence of one leptogluon flavor of appropriate mass can give rise to sizeable ``leptoglueball'' production rates and observable resonance peaks. In contrast, one needs two leptoquark flavors in order to produce the analogous ``leptoquarkonium'' states. Moreover, cross-generational leptoquark couplings are necessary to give observable event rates in many cases, and leptoquarkonium mass splittings are too small to resolve with realistic beam energy resolutions.

hep-ph↗

arXiv1998

Lepto-mesons, Leptoquarkonium and the QCD Potential

We consider bound states of heavy leptoquark-antiquark pairs (lepto-mesons) as well as leptoquark-antileptoquark pairs (leptoquarkonium). Unlike the situation for top quarks, leptoquarks (if they exist) may live long enough for these hadrons to form. We study the spectra and decay widths of these states in the context of a nonrelativistic potential model which matches the recently calculated two-loop QCD potential at short distances to a successful phenomenological quarkonium potential at intermediate distances. We also compute the expected number of events for these states at future colliders.

hep-ph↗

arXiv1998

A Simple Charged Higgs Model of Soft CP Violation without Flavor Changing Neutral Currents

We propose a model of soft CP violation in which the CP violating mechanism naturally lies only in the charged Higgs sector. The charged Higgs mechanism not only accounts for the measured value of the CP-violating parameter $ε$ but also accommodates the current limits on $ε'/ε$. Our model naturally prevents tree-level Flavor-Changing Neutral Currents (FCNCs) of any kind. Unlike the Weinberg-Branco Three-Higgs Doublet Model, the deviation from the Standard Model rate for $b\to sγ$ is small. Furthermore, leading contributions to the electron (neutron) electric dipole moment are non-zero beginning at the three (two) loop level. Surprisingly similar to the Standard Kobayashi-Maskawa Model, our model is of milliweak character but with seemingly superweak phenomenology.

hep-ph↗

arXiv1998

Interplay Between Strong and Weak CP Phases

We discuss the subtle interplay between strong and weak CP phases that has often been ignored in the literature. We also point out the potentially important role that it plays in various models.

hep-ph↗

arXiv1997

Probing Anomalous Higgs Coupling through mu+ mu- --> H gamma

The process mu+ mu- --> H gamma, though small compared to the resonance process, could be observable at proposed muon colliders, given expected integrated luminosities. The apparently leading diagrams occur at tree-level, and are proportional to the Higgs-muon coupling. We show, however, that the one-loop contribution is comparable to the tree-level amplitude. Furthermore, the one-loop diagrams, unlike those at tree-level, could be greatly enhanced by possible anomalous Higgs-top quark or Higgs-gauge boson couplings. For a 500 GeV unpolarized muon collider, the total cross section for H-gamma associated production approaches 0.1 fb.

hep-ph↗

arXiv1997

Electron Electric Dipole Moment from CP Violation in the Charged Higgs Sector

The leading contributions to the electron (or muon) electric dipole moment due to CP violation in the charged Higgs sector are at the two-loop level. A careful analysis of the model-independent contribution is provided. We also consider specific scenarios to demonstrate how charged Higgs sector CP violation can naturally give rise to large electric dipole moments. Numerical results show that the electron electric dipole moment in such models can lie at the experimentally accessible level.

hep-ph↗

arXiv1997

CP Violation and Scalar Lepton Flavor Oscillation

Lepton flavor violation can be induced in supersymmetry by the mixing of two or more of the leptonic scalar partners, Krashnikov and Arkani-Hamed et al. pointed out that this effect may be observable at the Next Linear Collider, through slepton pair production with subsequent lepton flavor violating decays. If the slepton mixing involves all three generations, CP violation from the Cabibbo-Kobayashi-Maskawa phase could lead to CP violating asymmetries between the observed LFV decays. We lay down the formalism and give simple expressions for the CP violating asymmetry in the transition probabilities, and consider possible signals at future colliders.

hep-ph↗

arXiv1996

Radiative Higgs Boson Decays H -> f fbar gamma

Higgs boson radiative decays of the form $H\rightarrow f\bar{f}γ$ are calculated in the Standard Model using the complete one-loop expressions for the decay amplitudes. Contributions to the radiative width from leptons and light quarks are given. We also present $e\bar{e}$ invariant mass distributions for $H\rightarrow e\bar{e}γ$, which illustrate the importance of the photon pole contribution and the effects of the box diagrams.

hep-ph↗

arXiv1995

Higgs-photon associated production at $e\bar{e}$ colliders

We present complete analytical expressions for the amplitudes of the process $e\bar{e}\rightarrow Hγ$. The calculation is performed using nonlinear gauges, which significantly simplifies both the actual analytical calculation and the check of its gauge invariance. After comparing our results with a previous numerical calculation, we extend the range of Higgs masses and center of mass energies to those appropriate to LEP 200 and a future linear collider.

hep-ph↗

arXiv1994

Detecting the Intermediate-Mass Neutral Higgs Boson at the LHC Through $pp \to W H$

We examine the exclusive signature $pp \to WH \to \ell ν\;b \bar b$ at the LHC. Although the backgrounds, principally arising from top production and $Wjj$, are quite severe, it is shown that judicious application of phase-space cuts and the use of $b$-tagging can in fact greatly enhance the detectability of this channel. (Presented at the Eighth Meeting of the Division of Particles and Fields Albuquerque, New Mexico, August 2-6, 1994.)

hep-ph↗

arXiv1994

Signature of the Intermediate Mass Higgs Boson at the LHC With Flavor Tagging

We revisit the exclusive signature $e^\pm (μ^\pm) + b\bar b$ in the associated production of the intermediate mass Higgs boson with a $W$ boson. We show that it is feasible to use this signature to identify the Higgs boson in the lower intermediate mass region ($90$ to $130$ GeV) at the LHC with reasonable acceptance cuts by assuming effective bottom-jet identification. We further demonstrate that the background can be reduced with judicious cuts down to the level of the signal.

hep-ph↗

arXiv1993

Detecting an Intermediate Mass Charged Higgs at $γγ$ Colliders

The detection of an intermediate mass charged Higgs boson at $\gamgam$ colliders via the modes $\gamgam \to H^+ H^- \to ντ^+ \barν τ^-,~ c \bar{s} \bar{c} s,~$ and $ ντ^+ \bar{c}s + c \bar{s} \barν τ^-$ is considered. $W^+ W^-$ boson pair production is the dominant background for these modes. The three modes may be used in a complementary fashion to detect a charged Higgs boson. The mixed leptonic-hadronic mode may be used to determine the charged Higgs mass by reconstructing the invariant hadronic mass. The sensitivity of Br$(H^+ \rightarrow c\bar s,\,ντ^+)$ on the discovery limit of the charged Higgs boson is also discussed.

hep-ph↗

arXiv1993

The effects of a strongly interacting Higgs sector on $γ\,γ\rightarrow W_L^+\,W_L^-, Z_L^{\,0}\,Z_L^{\,0}$ scattering

We study the effects of a strongly interacting Higgs sector on the amplitudes for $γ\,γ\rightarrow W_L^+\,W_L^-, Z_L^{\,0}\,Z_L^{\,0}$ by unitarizing the $W_L^+\,W_L^-, Z_L^{\,0}\,Z_L^{\,0}, γ\,γ$ system using the $K$--matrix technique. Unitarization produces substantial corrections to the cross sections for gauge boson pair production by photon fusion when $m_H \agt 5-10\;$TeV.

hep-ph↗

arXiv1993

Detection of the heavy Higgs boson at $γγ$ colliders

We consider the possibility of detecting a heavy Higgs boson ($m_H>2m_Z$) in proposed $γγ$ colliders through the semi-leptonic mode $γγ\rightarrow H \rightarrow ZZ \rightarrow q\bar q \ell^+\ell^-$. We show that due to the non-monochromatic nature of the photon beams produced by the laser-backscattering method, the resultant cross section for Higgs production is much smaller than the on-resonance cross section and generally {\it decreases} with increasing collider energy. Although continuum $ZZ$ production is expected to be negligible, we demonstrate the presence of and calculate sizeable backgrounds from $γγ\rightarrow \ell^+\ell^-Z,\,q\bar qZ$, with $Z\rightarrow q\bar q,\,\ell^+\ell^-$, respectively, and $γγ\rightarrow t\bar t\rightarrow b\bar b\ell^+\ell^-ν\barν$. This channel may be used to detect a Higgs of mass $m_H$ up to around 350~GeV at a 0.5~TeV $e^+e^-$ collider, assuming a nominal yearly luminosity of 10--20~fb$^{-1}$.

hep-ph↗

arXiv1992

A Comparison of the Use of Binary Decision Trees and Neural Networks in Top Quark Detection

The use of neural networks for signal vs.~background discrimination in high-energy physics experiment has been investigated and has compared favorably with the efficiency of traditional kinematic cuts. Recent work in top quark identification produced a neural network that, for a given top quark mass, yielded a higher signal to background ratio in Monte Carlo simulation than a corresponding set of conventional cuts. In this article we discuss another pattern-recognition algorithm, the binary decision tree. We have applied a binary decision tree to top quark identification at the Tevatron and found it to be comparable in performance to the neural network. Furthermore, reservations about the "black box" nature of neural network discriminators do not apply to binary decision trees; a binary decision tree may be reduced to a set of kinematic cuts subject to conventional error analysis.

hep-ph↗