889 research outputs found
Probing Kaluza-Klein Dark Matter with Neutrino Telescopes
In models in which all of the Standard Model fields live in extra universal
dimensions, the lightest Kaluza-Klein (KK) particle can be stable. Calculations
of the one-loop radiative corrections to the masses of the KK modes suggest
that the identity of the lightest KK particle (LKP) is mostly the first KK
excitation of the hypercharge gauge boson. This LKP is a viable dark matter
candidate with an ideal present-day relic abundance if its mass is moderately
large, between 600 to 1200 GeV. Such weakly interacting dark matter particles
are expected to become gravitationally trapped in large bodies, such as the
Sun, and annihilate into neutrinos or other particles that decay into
neutrinos. We calculate the annihilation rate, neutrino flux and the resulting
event rate in present and future neutrino telescopes. The relatively large mass
implies that the neutrino energy spectrum is expected to be well above the
energy threshold of AMANDA and IceCube. We find that the event rate in IceCube
is between a few to tens of events per year.Comment: 13 pages, 3 figures, LaTeX; typos fixed, version to appear in PR
Galactic Cosmic Strings as Sources of Primary Antiprotons
A possible signature of a class of superconducting cosmic strings trapped in
the Milky Way plasma is the emission of low energy antiprotons due to baryon
number violating processes on the string. We find the terrestrial flux and the
energy spectrum of such antiprotons. Current observational bounds on the flux
of low energy antiprotons place a {\it lower} bound on the string tension which
is comparable to that given by the electroweak scale.Comment: 11 pages; added reference to recent observations of low energy
antiproton
Final state interactions in the decay
In this article, we study the final-state rescattering effects in the decay
, the numerical results indicate the corrections are
comparable with the contribution from the naive factorizable amplitude, and the
total amplitudes can accommodate the experimental data.Comment: 11 pages, 1 figure, revised version, to appear in EPJ
QGP flow fluctuations and the characteristics of higher moments
The dynamical development of expanding Quark-gluon Plasma (QGP) flow is
studied in a 3+1D fluid dynamical model with a globally symmetric, initial
condition. We minimize fluctuations arising from complex dynamical processes at
finite impact parameters and from fluctuating random initial conditions to have
a conservative fluid dynamical background estimate for the statistical
distributions of the thermodynamical parameters. We also avoid a phase
transition in the equation of state, and we let the matter supercool during the
expansion.
Then central Pb+Pb collisions at TeV are studied in an
almost perfect fluid dynamical model, with azimuthally symmetric initial state
generated in a dynamical flux-tube model. The general development of
thermodynamical extensives are also shown for lower energies.
We observe considerable deviations from a thermal equilibrium source as a
consequence of the fluid dynamical expansion arising from a least fluctuating
initial state
Constraints on the SU(3) Electroweak Model
We consider a recent proposal by Dimopoulos and Kaplan to embed the
electroweak SU(2)_L X U(1)_Y into a larger group SU(3)_W X SU(2) X U(1) at a
scale above a TeV. This idea is motivated by the prediction for the weak mixing
angle sin^2 theta_W = 1/4, which naturally appears in these models so long as
the gauge couplings of the high energy SU(2) and U(1) groups are moderately
large. The extended gauge dynamics results in new effective operators that
contribute to four-fermion interactions and Z pole observables. We calculate
the corrections to these electroweak precision observables and carry out a
global fit of the new physics to the data. For SU(2) and U(1) gauge couplings
larger than 1, we find that the 95% C.L. lower bound on the matching (heavy
gauge boson mass) scale is 11 TeV. We comment on the fine-tuning of the high
energy gauge couplings needed to allow matching scales above our bounds. The
remnants of SU(3)_W breaking include multi-TeV SU(2)_L doublets with electric
charge (+-2,+-1). The lightest charged gauge boson is stable, leading to
cosmological difficulties.Comment: 17 pages, LaTeX, 4 figures embedded, uses JHEP.cl
Theory of coherent acoustic phonons in InGaN/GaN multi-quantum wells
A microscopic theory for the generation and propagation of coherent LA
phonons in pseudomorphically strained wurzite (0001) InGaN/GaN multi-quantum
well (MQW) p-i-n diodes is presented. The generation of coherent LA phonons is
driven by photoexcitation of electron-hole pairs by an ultrafast Gaussian pump
laser and is treated theoretically using the density matrix formalism. We use
realistic wurzite bandstructures taking valence-band mixing and strain-induced
piezo- electric fields into account. In addition, the many-body Coulomb
ineraction is treated in the screened time-dependent Hartree-Fock
approximation. We find that under typical experimental conditions, our
microscopic theory can be simplified and mapped onto a loaded string problem
which can be easily solved.Comment: 20 pages, 17 figure
Follicular Oocytes Better Support Development in Rabbit Cloning Than Oviductal Oocytes
This study was conducted to determine the effect of rabbit oocytes collected from ovaries or oviducts on the developmental potential of nuclear transplant embryos. Donor nuclei were obtained from adult skin fibroblasts, cumulus cells, and embryonic blastomeres. Rabbit oocytes were flushed from the oviducts (oviductal oocytes) or aspirated from the ovaries (follicular oocytes) of superovulated does at 10, 11, or 12-h post-hCG injection. The majority of collected oocytes were still attached to the sites of ovulation on the ovaries. We found that follicular oocytes had a significantly higher rate of fusion with nuclear donor cells than oviductal oocytes. There was no difference in the cleavage rate between follicular and oviductal groups, but morula and blastocyst development was significantly higher in the follicular group than in the oviductal group. Two live clones were produced in follicular group using blastomere and cumulus nuclear donors, whereas one live clone was produced in the oviductal group using a cumulus nuclear donor. These results demonstrate that cloned rabbit embryos derived from follicular oocytes have better developmental competence than those derived from oviductal oocytes.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90481/1/cell-2E2011-2E0030.pd
A High Statistics Search for Ultra-High Energy Gamma-Ray Emission from Cygnus X-3 and Hercules X-1
We have carried out a high statistics (2 Billion events) search for
ultra-high energy gamma-ray emission from the X-ray binary sources Cygnus X-3
and Hercules X-1. Using data taken with the CASA-MIA detector over a five year
period (1990-1995), we find no evidence for steady emission from either source
at energies above 115 TeV. The derived upper limits on such emission are more
than two orders of magnitude lower than earlier claimed detections. We also
find no evidence for neutral particle or gamma-ray emission from either source
on time scales of one day and 0.5 hr. For Cygnus X-3, there is no evidence for
emission correlated with the 4.8 hr X-ray periodicity or with the occurrence of
large radio flares. Unless one postulates that these sources were very active
earlier and are now dormant, the limits presented here put into question the
earlier results, and highlight the difficulties that possible future
experiments will have in detecting gamma-ray signals at ultra-high energies.Comment: 26 LaTeX pages, 16 PostScript figures, uses psfig.sty to be published
in Physical Review
Women Under Kuomintang R ule Variations on the Feminine Mystique
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/68360/2/10.1177_009770047500100101.pd
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