203,465 research outputs found
On the fraction of dark matter in charged massive particles (CHAMPs)
From various cosmological, astrophysical and terrestrial requirements, we
derive conservative upper bounds on the present-day fraction of the mass of the
Galactic dark matter (DM) halo in charged massive particles (CHAMPs). If dark
matter particles are neutral but decay lately into CHAMPs, the lack of
detection of heavy hydrogen in sea water and the vertical pressure equilibrium
in the Galactic disc turn out to put the most stringent bounds. Adopting very
conservative assumptions about the recoiling velocity of CHAMPs in the decay
and on the decay energy deposited in baryonic gas, we find that the lifetime
for decaying neutral DM must be > (0.9-3.4)x 10^3 Gyr. Even assuming the
gyroradii of CHAMPs in the Galactic magnetic field are too small for halo
CHAMPs to reach Earth, the present-day fraction of the mass of the Galactic
halo in CHAMPs should be < (0.4-1.4)x 10^{-2}. We show that redistributing the
DM through the coupling between CHAMPs and the ubiquitous magnetic fields
cannot be a solution to the cuspy halo problem in dwarf galaxies.Comment: 21 pages, 2 figures. To appear in JCA
Constraints on long-lived electrically charged massive particles from anomalous strong lens systems
We investigate anomalous strong lens systems, particularly the effects of
weak lensing by structures in the line of sight, in models with long-lived
electrically charged massive particles (CHAMPs). In such models, matter density
perturbations are suppressed through the acoustic damping and the flux ratio of
lens systems are impacted, from which we can constrain the nature of CHAMPs.
For this purpose, first we perform -body simulations and develop a fitting
formula to obtain non-linear matter power spectra in models where cold neutral
dark matter and CHAMPs coexist in the early Universe. By using the observed
anomalous quadruple lens samples, we obtained the constraints on the lifetime
() and the mass density fraction () of CHAMPs. We
show that, for , the lifetime is bounded as yr (95% confidence level), while a longer lifetime yr is allowed when at the 95% confidence level.
Implications of our result for particle physics models are also discussed.Comment: 20 pages, 6 figure
Bounds on long-lived charged massive particles from Big Bang nucleosynthesis
The Big Bang nucleosynthesis (BBN) in the presence of charged massive
particles (CHAMPs) is studied in detail. All currently known effects due to the
existence of bound states between CHAMPs and nuclei, including possible
late-time destruction of Li6 and Li7 are included. The study sets conservative
bounds on CHAMP abundances in the decay time range 3x10^2 sec - 10^12 sec. It
is stressed that the production of Li6 at early times T ~ 10keV is
overestimated by a factor ~ 10 when the approximation of the Saha equation for
the He4 bound state fraction is utilised. To obtain conservative limits on the
abundance of CHAMPs, a Monte-Carlo analysis with ~ 3x10^6 independent BBN runs,
varying reaction rates of nineteen different reactions, is performed (see
attached erratum, however). The analysis yields the surprising result that
except for small areas in the particle parameter space conservative constraints
on the abundance of decaying charged particles are currently very close to
those of neutral particles. It is shown that, in case a number of heretofore
unconsidered reactions may be determined reliably in future, it is conceivable
that the limit on CHAMPs in the early Universe could be tightened by orders of
magnitude. An ERRATUM gives limits on primordial CHAMP densities when the by
Ref. Kamimura et al. recently more accurately determined CHAMP reaction rates
are employed.Comment: includes Erratum showing most up to date limits after determination
of the most important reaction rate
On the density of singular hyperbolic three-dimensional vector fields: a conjecture of Palis
In this note we announce a result for vector fields on three-dimensional
manifolds: those who are singular hyperbolic or exhibit a homoclinic tangency
form a dense subset of the space of -vector fields. This answers a
conjecture by Palis. The argument uses an extension for local fibered flows of
Ma\~n\'e and Pujals-Sambarino's theorems about the uniform contraction of
one-dimensional dominated bundles.
Sur la densit\'e de l'hyperbolicit\'e singuli\`ere pour les champs de
vecteurs en dimension trois : une conjecture de Palis
Dans cette note, nous annon\c{c}ons un r\'esultat portant sur les champs de
vecteurs des vari\'et\'es de dimension : ceux qui v\'erifient
l'hyperbolicit\'e singuli\`ere ou qui poss\`edent une tangence homocline
forment un sous-ensemble dense de l'espace des champs de vecteurs . Ceci
r\'epond \`a une conjecture de Palis. La d\'emonstration utilise une
g\'en\'eralisation pour les flots fibr\'es locaux des th\'eor\`emes de Ma\~n\'e
et Pujals-Sambarino traitant de la contraction uniforme de fibr\'es
unidimensionnels domin\'es
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