91 research outputs found
Shifting with
Precision measurements at the resonance agree well with the standard
model. However, there is still a hint of a discrepancy, not so much in by
itself (which has received a great deal of attention in the past several years)
but in the forward-backward asymmetry together with . The two
are of course correlated. We explore the possibilty that these and other
effects are due to the mixing of and 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 . We compute the ratio 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 parameter of
oblique corrections and . Under the natural assumption that the violation
of the 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 from the SM
prediction due to the FCNC's and the violation of the 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: inclusive,
jet and jets. We present the expected Run II limits on
the branching ratio of 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 --,
--, and -- planes. We find that
the new data enables us to make a stringent test on the correction to vertex. The variable is sensitive to the
couplings and thus plays a major role to give constraints on the nonuniversal
interaction effects. Upon imposing the new data on , we have the
allowed range of the model parameter at
1- level with GeV. Along with the minimal contact term, we
predict the new physics scale 1.6 TeV. By combining the
experimental results from all planes we obtain the allowed range of
: 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
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