5,683 research outputs found
Low-luminosity Extragalactic Water Masers toward M82, M51, and NGC4051
Sub-arcsecond observations using the Very Large Array (VLA) are presented for
low-luminosity water maser in M82, M51, and NGC4051. New maser features have
been detected within the M82 starburst complex. They are largely associated
with star-forming activity, such as optically identified starburst-driven
winds, H II regions, or the early phase of star formation in the galaxy. The
water maser in M51 consists of blueshifted and redshifted features relative to
thesystemic velocity of the galaxy. The redshifted features are measured to the
northwest of the nuclear radio source, while the location of the blueshifted
counterpart is displaced by about 2" from the radio source. A small velocity
gradient closely aligned with the radio jet is detected from the redshifted
features. The redshifted maser most likely amplifies the background radio
continuum jet, while the blueshifted counterpart marks off-nuclear star
formation in the galaxy. All of the detected maser features in the narrow-line
Seyfert 1 galaxy NGC 4051 remain unresolved by new VLA observations. Due to the
low luminosity of the maser, the maser excitation is not directly related to
the active galactic nucleus.Comment: 20 pages, 10 figures. Accepted for publication in AJ (17/Oct/2006
Search for a Higgs Boson Decaying into Two Photons with the L3 Detector at LEP
A search is performed for a Higgs boson, decaying into two photons, using the
L3 data collected at centre of mass energies between = 189 and 202
GeV, corresponding to an integrated luminosity of 400 pb. The processes
, , are considered. The observed data are found to be consistent with the
expected background from standard physics processes. Limits on the branching
fraction of the Higgs boson decay into two photons as a function of the Higgs
mass are shown and a lower mass limit on a fermiophobic Higgs is derived.Comment: 3 pages, 2 postscript figures, Presented at the DPF2000 Conference,
August 9-12, 2000, The Ohio State University, Columbus, Ohi
Light bottom squark and gluino confront electroweak precision measurements
We address the compatibility of a light sbottom (mass 2\sim 5.5 \gev) and a
light gluino (mass 12\sim 16 \gev) with electroweak precision measurements.
Such light particles have been suggested to explain the observed excess in the
quark production cross section at the Tevatron. The electroweak observables
may be affected by the sbottom and gluino through the SUSY-QCD corrections to
the vertex. We examine, in addition to the SUSY-QCD corrections, the
electroweak corrections to the gauge boson propagators from the stop which are
allowed to be light from the SU(2) symmetry. We find that this scenario is
strongly disfavored from electroweak precision measurements unless the heavier
sbottom mass eigenstate is lighter than 180\gev and the left-right mixing in
the stop sector is sufficiently large. This implies that one of the stops
should be lighter than about 98\gev.Comment: 4 pages, revtex, 2 figures. Reference added, version to appear in
Phys.Rev.Let
Analyticity, crossing and the absorptive parts of the one-loop contributions to the quark-quark-gluon gauge boson four-point function
Starting from the known one-loop result for the -annihilation
process with
massless quarks we employ analyticity and crossing to determine the absorptive
parts of the corresponding one-loop contributions in Deep Inelastic Scattering
(DIS) and in the Drell-Yan process (DY). Whereas the
absorptive parts generate a non-measurable phase factor in the
-annihilation channel one obtains measurable phase effects from the
one-loop contributions in the deep inelastic and in the Drell-Yan case. We
compare our results with the results of previous calculations where the
absorptive parts in DIS and in the DY process were calculated directly in the
respective channels. We also present some new results on the dispersive and
absorptive contributions of the triangle anomaly graph to the DIS process.Comment: 23 pages, 5 figures, typos corrected. Version to appear in Phys. Rev.
Search for MSSM Higgses at the Tevatron
We present an overview of searches for MSSM Higgs at the Tevatron,
concentrating on searches probing the high tan(beta) region. We discuss the
search for A/H -> tau tau which is soon to be completed in the Run I data and
review the new tau triggers implemented by CDF and D0 in Run II, which will
greatly impact this analysis. We also present the results of a Run I search for
A/H bb -> bbbb performed by CDF and highlight expected improvements in this
channel by both experiments in Run II.Comment: 3 pages with 1 figure, to be published in "Proceedings of the 31st
International Conference on High Energy Physics ICHEP 2002
Phase diagram of a frustrated mixed-spin ladder with diagonal exchange bonds
Using exact numerical diagonalization and the conformal field theory
approach, we study the effect of magnetic frustrations due to diagonal exchange
bonds in a system of two coupled mixed-spin Heisenberg chains. It
is established that relatively moderate frustrations are able to destroy the
ferrimagnetic state and to stabilize the critical spin-liquid phase typical for
half-integer-spin antiferromagnetic Heisenberg chains. Both phases are
separated by a narrow but finite region occupied by a critical
partially-polarized ferromagnetic phase.Comment: 5 PRB pages, 7 eps figures, to appear in Phys. Rev.
Probing the Weak Boson Sector in
We study possible deviations from the standard model in the reaction at a 500 GeV collider. As a photon source we use a
laser backscattered photon beam. We investigate the most general and vertices including operators up to
energy-dimension-six which are Lorentz invariant. These vertices require four
extra parameters; two are CP-conserving, and , and two are
CP-violating, and . We present analytical expressions of
the helicity amplitudes for the process for arbitrary
values of anomalous couplings. Assuming Standard Model values are actually
measured we present the allowed region in the () plane at the
90\% confidence level. We then show how the angular correlation of the
decay products can be used to extract detailed information on the anomalous
(especially CP-violating) and couplings.Comment: Latex, 25 pages, 12 figures (not included). One compressed postscript
file including all the figures available at
ftp://ftp.kek.jp/kek/preprints/TH/TH-420/kekth420.ps.g
Prospects of Measuring General Higgs Couplings at e^+e^- Linear Colliders
We examine how accurately the general HZV couplings, with V=Z,gamma, may be
determined by studying e^+e^- --> Hff-bar processes at future e^+e^- linear
colliders. By using the optimal-observable method, which makes use of all
available experimental information, we find out which combinations of the
various HZV coupling terms may be constrained most efficiently with high
luminosity. We also assess the benefits of measuring the tau-lepton helicities,
identifying the bottom-hadron charges, polarizing the electron beam and running
at two different collider energies. The HZZ couplings are generally found to be
well constrained, even without these options, while the HZ-gamma couplings are
not. The constraints on the latter may be significantly improved by beam
polarization.Comment: 28 pages (LaTeX), 5 figures (axodraw and eps
One-loop contributions of charginos and neutralinos to W-pair production in E+ E- collisions
We study the one-loop effects of charginos and neutralinos on the helicity
amplitudes for \eeww in the minimal supersymmetric standard model. The
calculation is tested by using two methods. First, the sum rule for the form
factors between \eeww and the process where the external bosons are
replaced by the corresponding Goldstone bosons is employed to test
the analytic expression and the accuracy of the numerical program. Second, the
decoupling property in the large mass limit is used to test the overall
normalization of the amplitudes. These two tests are most effectively carried
out when the amplitudes are expanded in terms of the modified minimal
subtraction () couplings of the standard model. The resulting
perturbation expansion is valid at collider energies below and around the
threshold of the light supersymmetric particles. We find that the corrections
to the cross section of the longitudinally polarized -pair production can be
as large as -1.4% at the threshold of the light chargino-pair production for
large scattering angles. We also study the effects of the CP-violating phase in
the chargino and neutralino sectors on the helicity amplitudes. We find that
the resulting CP-violating asymmetries can be at most 0.1%.Comment: 30 pages, 25 figures, Final verision, To appear in Physical Review D,
Several sentences are improve
The coupling constants for an electroweak model with a unification symmetry
We introduce the sequence of spontaneous symmetry breaking of a coupling
between Pati-Salam and electroweak symmetries
in order to establish a mathematically consistent relation among the coupling
constants at grand unification energy scale. With the values of baryon minus
lepton quantum numbers of known quarks and leptons, by including right-handed
neutrinos, we can find the mixing angle relations at different energy levels up
to the electromagnetic scale.Comment: 8 page
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