Shifting RbR_b with AFBbA^b_{FB}

Precision measurements at the $Z$ resonance agree well with the standard model. However, there is still a hint of a discrepancy, not so much in $R_b$ by itself (which has received a great deal of attention in the past several years) but in the forward-backward asymmetry $A^b_{FB}$ together with $R_b$. The two are of course correlated. We explore the possibilty that these and other effects are due to the mixing of $b_L$ and $b_R$ with one or more heavy quarks.Comment: 11 pages, 1 Figure, LaTex fil

Test of the chiral structure and FCNC in the quark sector by radiative B meson decays

We study the effects of a vector-like SU(2) quark doublet as a fourth generation. In this model we examine the chiral structure and the FCNC in the quark sector by using radiative B meson decays in the allowed region for parameters from $R_b = {\Gamma_{qq}}/{\Gamma_{had.}}$. We compute the ratio $R = {Br (b \to d \gamma)}/{Br (b \to s \gamma)}$ in the model which realizes a different chiral structure as well as FCNC. The constraints has been extracted from the experimental results of B meson decays, the $T_{new}$ parameter of oblique corrections and $R_b$. Under the natural assumption that the violation of the $V-A$ structure in the light-quark sector is small, we can determine the allowed region for most of the mixings parameters and the vector-like quark masses. We show that there will be significant deviations in $R$ from the SM prediction due to the FCNC's and the violation of the $V-A$ structure.Comment: 19 pages, figures included, revised version for publication (accepted in Int. Jour. Mod. Phys. A

An Elusive Z' Coupled to Beauty

By extending the standard gauge group to SU(3)_c \times SU(2)_L \times U(1)_Y \times U(1)_X with X charges carried only by the third family we accommodate the LEP measurement of R_b and predict a potentially measurable discrepancy in A_{FB}^{b} in e^+e^- scattering and that D^0\bar{D}^0 mixing may be near its experimental limit. The Z', which explicitly violates the GIM mechanism, can nevertheless be naturally consistent with FCNC constraints. Direct detection of the Z' is possible but challenging.Comment: 12 pages, plus 1 Postscript figure, uses revtex, Discussion of FCNC extende

Discovering a Light Higgs Boson with Light

We evaluate the prospects for detecting a non-standard light Higgs boson with a significant branching ratio to two photons, in Run II of the Fermilab Tevatron. We derive the reach for several channels: $2\gamma$ inclusive, $2\gamma+1$ jet and $2\gamma+2$ jets. We present the expected Run II limits on the branching ratio of $h\to\gamma\gamma$ as a function of the Higgs mass, for the case of ``bosonic'', as well as ``topcolor'' Higgs bosons.Comment: 11 pages, LaTeX, 7 figures, 4 tables, uses aipproc2.sty, contributed to the Physics at Run II Workshop, analysis redone with optimized cuts and improved background estimate, references adde

Resonant origin for density fluctuations deep within the Sun: helioseismology and magneto-gravity waves

We analyze helioseismic waves near the solar equator in the presence of magnetic fields deep within the solar radiative zone. We find that reasonable magnetic fields can significantly alter the shapes of the wave profiles for helioseismic g-modes. They can do so because the existence of density gradients allows g-modes to resonantly excite Alfven waves, causing mode energy to be funnelled along magnetic field lines, away from the solar equatorial plane. The resulting wave forms show comparatively sharp spikes in the density profile at radii where these resonances take place. We estimate how big these waves might be in the Sun, and perform a first search for observable consequences. We find the density excursions at the resonances to be too narrow to be ruled out by present-day analyses of p-wave helioseismic spectra, even if their amplitudes were to be larger than a few percent. (In contrast it has been shown in (Burgess et al. 2002) that such density excursions could affect solar neutrino fluxes in an important way.) Because solar p-waves are not strongly influenced by radiative-zone magnetic fields, standard analyses of helioseismic data should not be significantly altered. The influence of the magnetic field on the g-mode frequency spectrum could be used to probe sufficiently large radiative-zone magnetic fields should solar g-modes ever be definitively observed. Our results would have stronger implications if overstable solar g-modes should prove to have very large amplitudes, as has sometimes been argued.Comment: 18 pages, 6 figures; misprints correcte

What Precision Electroweak Physics Says About the SU(6)/Sp(6) Little Higgs

We study precision electroweak constraints on the close cousin of the Littlest Higgs, the SU(6)/Sp(6) model. We identify a near-oblique limit in which the heavy W' and B' decouple from the light fermions, and then calculate oblique corrections, including one-loop contributions from the extended top sector and the two Higgs doublets. We find regions of parameter space that give acceptably small precision electroweak corrections and only mild fine tuning in the Higgs potential, and also find that the mass of the lightest Higgs boson is relatively unconstrained by precision electroweak data. The fermions from the extended top sector can be as light as 1 TeV, and the W' can be as light as 1.8 TeV. We include an independent breaking scale for the B', which can still have a mass as low as a few hundred GeV.Comment: 52 pages, 16 figure

Signature for heavy Majorana neutrinos in hadronic collisions

The production and decay of new possible heavy Majorana neutrinos are analyzed in hadronic collisions. New bounds on the mixing of these particles with standard neutrinos are estimated according to a fundamental representation suggested by grand unified models. A clear signature for these Majorana neutrinos is given by same-sign dileptons plus a charged weak vector boson in the final state. We discuss the experimental possibilities for the future Large Hadron Collider (LHC) at CERN.Comment: Latex2e(epsfig), 12 pages, 8 figures, to appear Physical Review

Constraints on the parameters of the Left Right Mirror Model

We study some phenomenological constraints on the parameters of a left right model with mirror fermions (LRMM) that solves the strong CP problem. In particular, we evaluate the contribution of mirror neutrinos to the invisible Z decay width (\Gamma_Z^{inv}), and we find that the present experimental value on \Gamma_Z^{inv}, can be used to place an upper bound on the Z-Z' mixing angle that is consistent with limits obtained previously from other low-energy observables. In this model the charged fermions that correspond to the standard model (SM) mix with its mirror counterparts. This mixing, simultaneously with the Z-Z' one, leads to modifications of the \Gamma(Z --> f \bar{f}) decay width. By comparing with LEP data, we obtain bounds on the standard-mirror lepton mixing angles. We also find that the bottom quark mixing parameters can be chosen to fit the experimental values of R_b, and the resulting values for the Z-Z' mixing angle do not agree with previous bounds. However, this disagreement disappears if one takes the more recent ALEPH data.Comment: 7 pages, 2 figures, REVTe

Implications of the recent CERN LEP data on nonuniversal interactions with the precision electroweak tests

We explore the nonuniversal interaction effects in terms of the precision variables epsilons with the recent LEP data reported by the Electroweak Working Group. The epsilon variables with the nonuniversal interactions are calculated and constrained by the experimental ellipses in the $\epsilon_1$--$\epsilon_b$, $\epsilon_2$--$\epsilon_b$, and $\epsilon_3$--$\epsilon_b$ planes. We find that the new data enables us to make a stringent test on the correction to $Z \to b \bar{b}$ vertex. The $\epsilon_b$ variable is sensitive to the $Z b \bar b$ couplings and thus plays a major role to give constraints on the nonuniversal interaction effects. Upon imposing the new data on $\epsilon_b$, we have the allowed range of the model parameter $\kappa_L = 0.0063 \pm 0.0030$ at 1-$\sigma$ level with $m_t = 175$ GeV. Along with the minimal contact term, we predict the new physics scale $\Lambda \sim$ 1.6 TeV. By combining the experimental results from all planes we obtain the allowed range of $\kappa_L$ : $0.003 < \kappa_L < 0.010$ at 95 % C.L..Comment: 17 pages (including figs), ReVTeX, 5 .eps figs are included, to appear in Phys. Rev.

Is Vtb=1 ?

The strongest constraint on Vtb presently comes from the 3 x 3 unitarity of the CKM matrix, which fixes Vtb to be very close to one. If the unitarity is relaxed, current information from top production at Tevatron still leaves open the possibility that Vtb is sizably smaller than one. In minimal extensions of the standard model with extra heavy quarks, the unitarity constraints are much weaker and the EW precision parameters entail the strongest bounds on Vtb. We discuss the experimental perspectives of discovering and identifying such new physics models at the Tevatron and the LHC, through a precise measurement of Vtb from the single top cross sections and by the study of processes where the extra heavy quarks are produced.Comment: 19 pages, 8 figure