21,981 research outputs found

### Can Heavy WIMPs Be Captured by the Earth?

If weakly interacting massive particles (WIMPs) in bound solar orbits are
systematically driven into the Sun by solar-system resonances (as Farinella et
al. have shown is the case for many Earth-crossing asteroids), then the capture
of high-mass WIMPs by the Earth would be affected dramatically because
high-mass WIMPs are captured primarily from bound orbits. WIMP capture would be
eliminated for M_x>630 GeV and would be highly suppressed for M_x>~150 GeV.
Annihilation of captured WIMPs and anti-WIMPs is expected to give rise to
neutrinos coming from the Earth's center. The absence of such a neutrino signal
has been used to place limits on WIMP parameters. At present, one does not know
if typical WIMP orbits are in fact affected by these resonances. Until this
question is investigated and resolved, one must (conservatively) assume that
they are. Hence, limits on high-mass WIMP parameters are significantly weaker
than previously believed.Comment: 8 pages + 1 figure. Submitted to Ap

### No Death Star -- For Now

A star passing within \sim 10^4 \au of the Sun would trigger a comet shower
that would reach the inner solar system about 0.18 Myr later. We calculate a
prior probability of ~0.4% that a star has passed this close to the Sun but
that the comet shower has not yet reached the Earth. We search the HIPPARCOS
catalog for such recent close-encounter candidates and, in agreement with
Garcia-Sanchez et al. (1997), find none. The new result reported in this Letter
is an estimation of the completeness of the search. Because of the relatively
bright completeness limit of the catalog itself, V~8, the search is sensitive
to only about half the stars that could have had such a near encounter. On the
other hand, we show that the search is sensitive to nearly all of the past
encounters that would lead to a major shower in the future and conclude that it
is highly unlikely that one will occur during the next 0.5 Myr.Comment: 10 pages, 1 figure. In press at The Astrophysical Journal Letter

### Measuring the Rotation Speed of Giant Stars From Gravitational Microlensing

During some gravitational lensing events, the lens transits the face of the
star. This causes a shift in the apparent radial velocity of the star which is
proportional to its rotation speed. It also changes the magnification relative
to what would be expected for a point source. By measuring both effects, one
can determine the rotation parameter $v\sin i$. The method is especially useful
for K giant stars because these have turbulent velocities that are typically
large compared with their rotation speed. By making a series of radial velocity
measurements, one can typically determine $v\sin i$ to the same accuracy as the
individual radial velocity measurements. There are approximately 10
microlensing transit events per year which would be suitable to make these
measurements.Comment: 11 pages including 1 embedded figur

### Lax Operator for the Quantised Orthosymplectic Superalgebra U_q[osp(2|n)]

Each quantum superalgebra is a quasi-triangular Hopf superalgebra, so
contains a \textit{universal $R$-matrix} in the tensor product algebra which
satisfies the Yang-Baxter equation. Applying the vector representation $\pi$,
which acts on the vector module $V$, to one side of a universal $R$-matrix
gives a Lax operator. In this paper a Lax operator is constructed for the
$C$-type quantum superalgebras $U_q[osp(2|n)]$. This can in turn be used to
find a solution to the Yang-Baxter equation acting on $V \otimes V \otimes W$
where $W$ is an arbitrary $U_q[osp(2|n)]$ module. The case $W=V$ is included
here as an example.Comment: 15 page

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