293 research outputs found
Note on the pseudo-Nambu-Goldstone Boson of Meta-stable SUSY Violation
Many models of meta-stable supersymmetry (SUSY) breaking lead to a very light
scalar pseudo-Nambu Goldstone boson (PNGB), P, associated with spontaneous
breakdown of a baryon number like symmetry in the hidden sector. Current
particle physics data provide no useful constraints on the existence of P. For
example, the predicted decay rates for both K --> pi + P, b--> s + P and
Upsilon --> photon + P are many orders of magnitude below the present
experimental bounds. We also consider astrophysical implications of the PNGB
and find a significant constraint from its effect on the evolution of red
giants. This constraint either rules out models with a hidden sector gauge
group larger than SU(4), or requires a new intermediate scale, of order at most
10^{10} GeV, at which the hidden sector baryon number is explicitly broken.Comment: 17 pages, 3 figures. Version 2: minor typographical errors fixed.
Version 3: a more reliable estimate for the decay rate of K-->pi+PNGB is
provided, and the predicted rate for b-->s+PNGB is now include
Experimental limits on massive neutrinos from e(+)e(-) annihilations at 29 GeV
This is the publisher's version, also available electronically from http://journals.aps.org/prd/abstract/10.1103/PhysRevD.37.577.A search was made in 29-GeV e(+)e(-) annihilations for massive neutrinos decaying to e(±)X(∓)(ν) where X is a muon or meson. A 300-pb(-1) data sample yielded just one candidate event with a mass m(e)X>1.8 GeV. Significant limits are found for new neutrinos with masses from 1.8 to 6.7 GeV and with mixing parameters in the range 3×10(-6)<‖U‖(2)<1. .A
Improved measurement of the K+->pi+nu(nu)over-bar branching ratio
An additional event near the upper kinematic limit for K+-->pi(+)nu(nu) over bar has been observed by experiment E949 at Brookhaven National Laboratory. Combining previously reported and new data, the branching ratio is B(K+-->pi(+)nu(nu) over bar)=(1.47(-0.89)(+1.30))x10(-10) based on three events observed in the pion momentum region 211<P<229 MeV/c. At the measured central value of the branching ratio, the additional event had a signal-to-background ratio of 0.9
Intrinsic spin Hall torque in a moire Chern magnet
In spin torque magnetic memories, electrically actuated spin currents are
used to switch a magnetic bit. Typically, these require a multilayer geometry
including both a free ferromagnetic layer and a second layer providing spin
injection. For example, spin may be injected by a nonmagnetic layer exhibiting
a large spin Hall effect, a phenomenon known as spin-orbit torque. Here, we
demonstrate a spin-orbit torque magnetic bit in a single two-dimensional system
with intrinsic magnetism and strong Berry curvature. We study AB-stacked
MoTe2/WSe2, which hosts a magnetic Chern insulator at a carrier density of one
hole per moire superlattice site. We observe hysteretic switching of the
resistivity as a function of applied current. Magnetic imaging using a
superconducting quantum interference device reveals that current switches
correspond to reversals of individual magnetic domains. The real space pattern
of domain reversals aligns precisely with spin accumulation measured near the
high-Berry curvature Hubbard band edges. This suggests that intrinsic spin- or
valley-Hall torques drive the observed current-driven magnetic switching in
both MoTe2/WSe2 and other moire materials. The switching current density of
10^3 Amps per square centimeter is significantly less than reported in other
platforms paving the way for efficient control of magnetic order
Improved Measurement of the K+ to pi+ nu nubar Branching Ratio
An additional event near the upper kinematic limit for K+ to pi+ nu nubar has
been observed by Experiment E949 at Brookhaven National Laboratory. Combining
previously reported and new data, the branching ratio is B(K+ to pi+ nu nubar)=
1.47 (+1.30, - 0.89) x 10-10 based on three events observed in the pion
momentum region 211<P<229 MeV/c. At the measured central value of the branching
ratio, the additional event had a signal-to-background ratio of 0.9
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