619 research outputs found
Composite Millicharged Dark Matter
We study a composite millicharged dark matter model. The dark matter is in
the form of pion-like objects emerging from a higher scale QCD-like theory. We
present two distinct possibilities with interesting phenomenological
consequences based on the choice of the parameters. In the first one, the dark
matter is produced non-thermally and it could potentially account for the 130
GeV Fermi photon line via decays of the "dark pions". We estimate the
self-interaction cross section which might play an important role both in
changing the dark matter halo profile at the center of the galaxy and in making
the dark matter warmer. In the second version the dark matter is produced via
the freeze-in mechanism. Finally we impose all possible astrophysical,
cosmological and experimental constraints. We study in detail generic
constraints on millicharged dark matter that can arise from anomalous isotope
searches of different elements and we show why constraints based on direct
searches from underground detectors are not generally valid.Comment: 10 pages, published versio
The Dark Side of Neutron Stars
We review severe constraints on asymmetric bosonic dark matter based on
observations of old neutron stars. Under certain conditions, dark matter
particles in the form of asymmetric bosonic WIMPs can be effectively trapped
onto nearby neutron stars, where they can rapidly thermalize and concentrate in
the core of the star. If some conditions are met, the WIMP population can
collapse gravitationally and form a black hole that can eventually destroy the
star. Based on the existence of old nearby neutron stars, we can exclude
certain classes of dark matter candidates.Comment: Presented at ICRC 2013, 5 pages, 1 figur
Probing Light Dark Matter via Evaporation from the Sun
Dark matter particles can be captured by the sun with rates that depend on
the dark matter mass and the DM-nucleon cross section. However, for masses
below GeV, the captured dark matter particles evaporate, leading to
an equilibrium where the rate of captured particles is equal to the rate of
evaporating ones. Unlike dark matter particles from the halo, the evaporating
dark matter particles have velocities that are not limited to values below the
escape velocity of the galaxy. Despite the fact that high velocities are
exponentially suppressed, I demonstrate here that current underground detectors
have the possibility to probe/constrain low dark matter parameter space by
(not)-observing the high energy tail of the evaporating dark matter particles
from the sun. I also show that the functional form of the differential rate of
counts with respect to the recoil energy in earth based detectors can identify
precisely the mass and the cross section of the dark matter particle in this
case.Comment: 5 pages, 1 figur
DaMaSCUS: The Impact of Underground Scatterings on Direct Detection of Light Dark Matter
Conventional dark matter direct detection experiments set stringent
constraints on dark matter by looking for elastic scattering events between
dark matter particles and nuclei in underground detectors. However these
constraints weaken significantly in the sub-GeV mass region, simply because
light dark matter does not have enough energy to trigger detectors regardless
of the dark matter-nucleon scattering cross section. Even if future experiments
lower their energy thresholds, they will still be blind to parameter space
where dark matter particles interact with nuclei strongly enough that they lose
enough energy and become unable to cause a signal above the experimental
threshold by the time they reach the underground detector. Therefore in case
dark matter is in the sub-GeV region and strongly interacting, possible
underground scatterings of dark matter with terrestrial nuclei must be taken
into account because they affect significantly the recoil spectra and event
rates, regardless of whether the experiment probes DM via DM-nucleus or
DM-electron interaction. To quantify this effect we present the publicly
available Dark Matter Simulation Code for Underground Scatterings (DaMaSCUS), a
Monte Carlo simulator of DM trajectories through the Earth taking underground
scatterings into account. Our simulation allows the precise calculation of the
density and velocity distribution of dark matter at any detector of given depth
and location on Earth. The simulation can also provide the accurate recoil
spectrum in underground detectors as well as the phase and amplitude of the
diurnal modulation caused by this shadowing effect of the Earth, ultimately
relating the modulations expected in different detectors, which is important to
decisively conclude if a diurnal modulation is due to dark matter or an
irrelevant background.Comment: 33 pages including 20 figures and 4 appendices. The DaMaSCUS code is
available at https://github.com/temken/ . v2: matches the published versio
On (Not)-Constraining Heavy Asymmetric Bosonic Dark Matter
Recently, constraints on bosonic asymmetric dark matter have been imposed
based on the existence of old neutron stars excluding the dark matter masses in
the range from keV up to several GeV. The constraints are based on the
star destruction scenario where the dark matter particles captured by the star
collapse forming a black hole that eventually consumes the host star. In
addition, there were claims in the literature that similar constraints can be
obtained for dark matter masses heavier than a few TeV. Here we argue that it
is not possible to extend to these constraints. We show that in the case of
heavy dark matter, instead of forming a single large black hole that consumes
the star, the collapsing dark matter particles form a series of small black
holes that evaporate fast without leading to the destruction of the star. Thus,
no constraints arise for bosonic asymmetric dark matter particles with masses
of a few TeV or higher
Growth of Black Holes in the interior of Rotating Neutron Stars
Mini-black holes made of dark matter that can potentially form in the
interior of neutron stars have been always thought to grow by accreting the
matter of the core of the star via a spherical Bondi accretion. However,
neutron stars have sometimes significant angulal velocities that can in
principle stall the spherical accretion and potentially change the conclusions
derived about the time it takes for black holes to destroy a star. We study the
effect of the star rotation on the growth of such black holes and the evolution
of the black hole spin. Assuming no mechanisms of angular momentum evacuation,
we find that even moderate rotation rates can in fact destroy spherical
accretion at the early stages of the black hole growth. However, we demonstrate
that the viscosity of nuclear matter can alleviate the effect of rotation,
making it possible for the black hole to maintain spherical accretion while
impeding the black hole from becoming maximally rotating.Comment: 9 page
Blocking the Hawking Radiation
Some severe constraints on asymmetric dark matter are based on the scenario
that certain types of WIMPs can form mini-black holes inside neutron stars that
can lead to their destruction. A crucial element for the realization of this
scenario is that the black hole grows after its formation (and eventually
destroys the star) instead of evaporating. The fate of the black hole is
dictated by the two opposite mechanics i.e. accretion of nuclear matter from
the center of the star and Hawking radiation that tends to decrease the mass of
the black hole. We study how the assumptions for the accretion rate can in fact
affect the critical mass beyond which a black hole always grows. We also study
to what extent degenerate nuclear matter can impede Hawking radiation due to
the fact that emitted particles can be Pauli blocked at the core of the star.Comment: 9 pages, 2 figure
Daily modulation and gravitational focusing in direct dark matter search experiments
We study the effect of gravitational focusing of the earth on dark matter. We
find that the effect can produce a detectable diurnal modulation in the dark
matter signal for part of the parameter space which for high dark matter masses
is larger than the diurnal modulation induced by the fluctuations in the flux
of dark matter particles due to the rotation of the earth around its own axis.
The two sources of diurnal modulation have different phases and can be
distinguished from each other. We demonstrate that the diurnal modulation can
potentially check the self-consistency of experiments that observe annual
modulated signals that can be attributed to dark matter. Failing to discover a
daily varying signal can result conclusively to the falsification of the
hypothesis that the annual modulation is due to dark matter. We also suggest
that null result experiments should check for a daily modulation of their
rejected background signal with specific phases. A potential discovery could
mean that dark matter collisions have been vetoed out.Comment: 8 pages, 4 figures (published version
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