arXiv subjects
Publications and source records attributed to V. Barger.
We review some recent results and future prospects in the phenomenology of Supersymmmetry. We discuss the searches for superpartner states, the searches for Higgs bosons in the minimal SUSY model, and additional parameter constraints arising in SUSY-GUT models.
We elaborate on the production of the Standard Model Higgs particle at high-energy $e^+e^-$ colliders through the reaction $e^+e^- \rightarrow ZH$. Particular emphasis is put on the intermediate mass range. In addition to the signal we discuss in detail the background processes. Angular distributions which are sensitive to the spin and parity of the Higgs particle are analyzed.
In this paper we survey the signals and backgrounds for a strongly-interacting electroweak symmetry breaking sector at hadron supercolliders in the TeV region. We study the process pp->WWX, and compute the rates for the ``gold-plated'' channels, where W^{+/-}->l^{+/-}νand Z -> l^+l^- (l = e,μ), for a wide variety of models. Using a forward jet-tag, a central jet-veto and a back-to-back lepton cut to suppress the Standard Model backgrounds, we demonstrate that the SSC and LHC have substantial sensitivity to strong interactions in the electroweak symmetry breaking sector.
A survey is made of some recent ideas and progress in the phenomenological applications of Supersymmetry (SUSY). We describe the success of SUSY-GUT models, the expected experimental signatures and present limits on SUSY partner particles, and the phenomenology of Higgs bosons in the minimal SUSY model.}
We survey some recent ideas and progress in looking for particle physics beyond the Standard Model, connected by the theme of Supersymmetry (SUSY). We review the success of SUSY-GUT models, the expected experimental signatures and present limits on SUSY partner particles, and Higgs phenomenology in the minimal SUSY model.
We reanalyze the extraction of the heavy Higgs boson signal $H\rightarrow W^+W^-\rightarrow \bar\ellν,\ell\barν$ $(\ell=e\hbox{ or }μ)$ from the Standard Model background at hadron supercolliders, taking into account revised estimates of the top quark background. With new acceptance criteria the detection of the signal remains viable. Requiring a forward jet-tag, a central jet-veto, and a large relative transverse momentum of the two charged leptons yields $S/\sqrt B>6$ for one year of running at the SSC or LHC.
General issues in the renormalization group evolution of fermion masses and mixings is discussed. An effective fixed point in the top quark Yukawa coupling can strongly constrain its value at the electroweak scale. Predictions following from Yukawa coupling unification are affected by threshold corrections at the grand unified scale. The Landau pole translates into an upper limit on the strong gauge coupling $α_3(M_Z)$. Given the hierarchy in the fermion sector, the evolution of the Cabbibo-Kobayashi-Maskawa matrix can be expressed in terms of a single scaling parameter $S$. Using this scaling factor and analogous scaling factors for the quark and lepton masses, we outline a systematic strategy that readily yields electroweak predictions for any GUT scale texture.}
In minimal SUSY-GUT models with $M_{SUSY}\ltap 1$ TeV, the renormalization group equations have a solution dominated by the infrared fixed point of the top Yukawa coupling. This fixed point predicts $m_t=(200\; {\rm GeV})\sin β$; combined with the LEP results it excludes $m_t\ltap 130$ GeV. For $m_t$ in the range 130-160 GeV, we discuss the sensitivity of the $m_t$ fixed point result to GUT threshold corrections and point out the implications for Higgs boson searches. The lightest scalar $h$ has mass 60-85 GeV and will be detectable at LEPII. At SSC/LHC, each of the five scalars $h$, $H$, $A$, $H^{\pm }$ may be detectable, but not all of them together; in one parameter region none will be detectable.
The observation that the $b \rightarrow sγ$ decay rate is close to the Standard Model value implies a large mass for the charged-Higgs boson in the Minimum Supersymmetric Standard Model, that nearly closes the $t \rightarrow b H^+$ decay channel. For $m_t = 150$ GeV, the parameter region $m_A \ltap 130$ GeV is excluded; this largely pre-empts LEP II searches and also partially excludes a region that would be inaccessible to MSSM Higgs boson searches both at LEP II and at SSC/LHC.
We investigate the possibility of a multi-Higgs doublet model where the lightest neutral Higgs boson ($h^0$) decouples from the fermion sector. We are partially motivated by the four $\ell^+\ell^-γγ$ events with $M_{γγ}\simeq60$\,GeV recently observed by the L3 collaboration, which could be a signal for $Z\to (Z^*\to \ell^+\ell^-)+(h^0\to γγ)$. Collider signatures for the additional physical Higgs bosons present in such models are discussed.
We derive the two-loop evolution equations for the Cabibbo-Kobayashi-Maskawa matrix. We show that to leading order in the mass and CKM hierarchies the scaling of the mixings $|V_{ub}|^2$, $|V_{cb}|^2$, $|V_{td}|^2$, $|V_{ts}|^2$ and of the rephase-invariant CP-violating parameter $J$ is universal to all orders in perturbation theory. In leading order the other CKM elements do not scale. Imposing the constraint $λ_b=λ_τ$ at the GUT scale determines the CKM scaling factor to be $\simeq 0.58$ in the MSSM.
We make a numerical study of gauge and Yukawa unification in supersymmetric grand unified models and examine the quantitative implications of fermion mass ansätze at the grand unified scale. Integrating the renormalization group equations with $α_1(M_Z)$ and $α_2(M_Z)$ as inputs, we find $α_3(M_Z)\simeq 0.111 (0.122)$ for $M_{SUSY}^{}=m_t$ and $α_3(M_Z)\simeq 0.106 (0.116)$ for $M_{SUSY}^{}=1$ TeV at one-loop (two-loop) order. Including $b$ and $τ$ Yukawa couplings in the evolution, we find an upper limit $m_t\ltap 200$ GeV from Yukawa unification. For given $m_t\ltap 175$ GeV, there are two solutions for $β$, one with $\tan β> m_t/m_b$, and one with $\sin β\simeq 0.78(m_t/150\;{\rm GeV})$. Taking a popular ansatz for the mass matrices at the unified scale, we obtain a lower limit on the top quark mass of $m_t\gtap 150 (115)$ GeV for $α_3(M_Z)=0.11 (0.12)$ and an upper limit on the supersymmetry parameter $\tan β\ltap 50$ if $α_3(M_Z)=0.11$. The evolution of the quark mixing matrix elements is also evaluated.
The recently reported solar neutrino signal in the $^{71}$Ga GALLEX detector adds a new dimension to the solar neutrino puzzle, complementing the previously known signals in $^{37}$Cl and water-Cherenkov detectors. Possible explanations for this new signal in terms of matter-enhanced neutrino oscillations (MSW effect) are already awaiting in the literature. We point out here that long-wavelength vacuum oscillations can furnish an alternative explanation of all three signals simultaneously; such solutions give neutrino spectra with distinctive energy dependence and seasonal time dependence. %This is a Revtex file, which is Latex-based but depends upon inputting the %Revtex style files distributed by APS/Physical Review. For more information, %contact Peggy Sutherland at MIS@APSEDOFF.BITNET, phone (516) 349-7800 ext 674
The prospects for discovery of the five Higgs bosons of the minimal supersymmetric standard model are assessed for existing and planned future colliders, including LEP\,I, LEP\,II, LHC and SSC. As a benchmark for comparisons, we take a top-quark mass $m_t= 150\,$GeV and squark mass parameter $\tilde m= 1\,$TeV in evaluating one-loop radiative corrections; some results for other $m_t$ values are also given. Searches based on the most promising production and decay channels are taken into account. For large regions in parameter space, detectable signals are predicted for one or more of the Higgs bosons, but there remains a region for which no signals would be visible at the above colliders.
The lightest CP-even Higgs boson $h$ in the minimum supersymmetric standard model (MSSM) has a mass upper bound depending on the top quark and squark masses. An $e^+e^-$ collider with enough energy and luminosity to produce $h+Z$ at measurable rates up to the maximum $h$ mass would cover the entire MSSM parameter space, if $h+A$ production was also searched for. We explore the energy and/or luminosity needed for various top quark and squark masses. For $m_t=150$\,GeV and 1\,TeV SUSY mass scale, a 230\,GeV collider with 10\,fb$^{-1}$ luminosity would suffice.
We explore the potential of a future e^+ e^- collider in the 0.5 TeV center-of-mass energy range to detect intermediate or heavy Higgs bosons in the Standard Model. We first briefly assess the production cross sections and update the decay branching fractions for a Higgs boson of intermediate mass, with M_Z < m_H < 2M_W. We then study in detail the possibility of detecting a heavy Higgs boson, with m_H > 2M_W, through the production of pairs of weak bosons. We quantitatively analyze the sensitivity of the process e^+ e^- --> nu nubar W^+ W^- (ZZ) to the presence of a heavy Higgs-boson resonance in the Standard Model. We compare this signal to various backgrounds and to the smaller signal from e^+ e^- --> ZH --> mu^+ mu^- W^+ W^- (ZZ), assuming the weak-boson pairs to be detected and measured in their dominant hadronic decay modes W^+ W^- (ZZ) --> 4jets. A related Higgs-boson signal in 6-jet final states is also estimated. We show how the main backgrounds from e^+ e^- W^+ W^- (ZZ), e nu WZ, and t tbar production can be reduced by suitable acceptance cuts. Bremsstrahlung and typical beamstrahlung corrections are calculated. These corrections reduce Higgs-boson production by scattering mechanisms but increase production by annihilation mechanisms; they also smear out some dynamical features such as Jacobian peaks in p_T(H). With all these corrections included, we conclude that it should be possible to detect a heavy Higgs-boson signal in the nu nubar W^+ W^-(ZZ) channels up to mass m_H=350 GeV.
By evolution of fermion mass matrices of the Fritzsch and the Georgi-Jarlskog forms from the supersymmetric grand unified scale, DHR obtained predictions for the quark masses and mixings. Using Monte Carlo methods we test these predictions against the latest determinations of the mixings, the CP-violating parameter epsilon_K and the B_d^0--Bbar_d^0 mixing parameter r_d. The acceptable solutions closely specify the quark masses and mixings, but lie at the edges of allowed regions at 90% confidence level.