560 research outputs found
Long-Range Forces in Direct Dark Matter Searches
We discuss the positive indications of a possible dark matter signal in
direct detection experiments in terms of a mechanism of interaction between the
dark matter particle and the nuclei occurring via the exchange of a light
mediator, resulting in a long-range interaction. We analyze the annual
modulation results observed by the DAMA and CoGeNT experiments and the observed
excess of events of CRESST. In our analysis, we discuss the relevance of
uncertainties related to the velocity distribution of galactic dark matter and
to the channeling effect in NaI. We find that a long-range force is a viable
mechanism, which can provide full agreement between the reconstructed dark
matter properties from the various experimental data sets, especially for
masses of the light mediator in the 10-30 MeV range and a light dark matter
with a mass around 10 GeV. The relevant bounds on the light mediator mass and
scattering cross section are then derived, should the annual modulation effects
be due to this class of long-range forces.Comment: 22 pages, 14 figures. v2: Matches version published on Phys.Rev.D;
analysis of CRESST to match the recent release of the new data updated,
discussion on astrophysical constraints on self-interacting dark matter
added, some typos corrected and some references added, conclusions unchanged.
v3: Few typos correcte
Can the flyby anomaly be attributed to earth-bound dark matter?
We make preliminary estimates to assess whether the recently reported flyby
anomaly can be attributed to dark matter interactions. We consider both elastic
and exothermic inelastic scattering from dark matter constituents; for
isotropic dark matter velocity distributions, the former decrease, while the
latter increase, the final flyby velocity. The fact that the observed flyby
velocity anomaly shows examples with both positive and negative signs, requires
the dominance of different dark matter scattering processes along different
flyby trajectories. The magnitude of the observed anomalies requires dark
matter densities many orders of magnitude greater than the galactic halo
density. Such a large density could result from an accumulation cascade, in
which the solar system-bound dark matter density is much higher than the
galactic halo density, and the earth-bound density is much higher than the
solar system-bound density. We discuss a number of strong constraints on the
hypothesis of a dark matter explanation for the flyby anomaly. These require
dark matter to be non-self-annihilating, with the dark matter scattering cross
section on nucleons much larger, and the dark matter mass much lighter, than
usually assumed.Comment: Latex, 21 pages. v3: substantially revised and expanded; v4: version
to appear in Phys. Rev.
Carbon Detonation and Shock-Triggered Helium Burning in Neutron Star Superbursts
The strong degeneracy of the 12C ignition layer on an accreting neutron star
results in a hydrodynamic thermonuclear runaway, in which the nuclear heating
time becomes shorter than the local dynamical time. We model the resulting
combustion wave during these superbursts as an upward propagating detonation.
We solve the reactive fluid flow and show that the detonation propagates
through the deepest layers of fuel and drives a shock wave that steepens as it
travels upward into lower density material. The shock is sufficiently strong
upon reaching the freshly accreted H/He layer that it triggers unstable 4He
burning if the superburst occurs during the latter half of the regular Type I
bursting cycle; this is likely the origin of the bright Type I precursor bursts
observed at the onset of superbursts. The cooling of the outermost shock-heated
layers produces a bright, ~0.1s, flash that precedes the Type I burst by a few
seconds; this may be the origin of the spike seen at the burst onset in 4U
1820-30 and 4U 1636-54, the only two bursts observed with RXTE at high time
resolution. The dominant products of the 12C detonation are 28Si, 32S, and
36Ar. Gupta et al. showed that a crust composed of such intermediate mass
elements has a larger heat flux than one composed of iron-peak elements and
helps bring the superburst ignition depth into better agreement with values
inferred from observations.Comment: 11 pages, 11 figures, accepted to ApJ; discussion about onset of
detonation discussed in new detail, including a new figur
An Improved Limit on Invisible Decays of Positronium
The results of a new search for positronium decays into invisible final
states are reported. Convincing detection of this decay mode would be a strong
evid ence for new physics beyond the Standard Model (SM): for example the
existence of extra--dimensions, of milli-charged particles, of new light gauge
bosons or of mirror particles. Mirror matter could be a relevant dark matter
candidate.
In this paper the setup and the results of a new experiment are presented. In
a collected sample of about orthopositronium decay
s, no evidence for invisible decays in an energy window [0,80] keV was found
and an upper limit on the branching ratio of orthopositronium \invdecay could
be set: \binvdecay<4.2\times 10^{-7} (90% C.L.)
Our results provide a limit on the photon mirror-photon mixing strength
(90% C.L.) and rule out particles lighter
than the electron mass with a fraction of the
electron charge. Furthermore, upper limits on the branching ratios for the
decay of parapositronium (90%
C.L.) and the direct annihilation (90% C.L.) could be set.Comment: 17 pages, 7 figures, added references, fixed limit on millicharged
particles and changed two plots accordingl
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