116 research outputs found
Unification and Dark Matter in a Minimal Scalar Extension of the Standard Model
The six Higgs doublet model is a minimal extension of the Standard Model that
addresses dark matter and gauge coupling unification. Another Higgs doublet in
a 5 representation of a discrete symmetry group, such as S_6, is added to the
SM. The lightest components of the 5-Higgs are neutral, stable and serve as
dark matter so long as the discrete symmetry is not broken. Direct and indirect
detection signals, as well as collider signatures are discussed. The five-fold
multiplicity of the dark matter decreases its mass and typically helps make the
dark matter more visible in upcoming experiments.Comment: 10 pages, 7 figures; added references; corrected typo
Dark Matter Debris Flows in the Milky Way
We show that subhalos falling into the Milky Way create a flow of
tidally-stripped debris particles near the galactic center with characteristic
velocity behavior. In the Via Lactea-II N-body simulation, this unvirialized
component constitutes a few percent of the local density and has velocities
peaked at 340 km/s in the solar neighborhood. Such velocity substructure has
important implications for surveys of low-metallicity stars, as well as direct
detection experiments sensitive to dark matter with large scattering
thresholds.Comment: 4 pages, 3 figures; v2 includes new plots illustrating the radial and
tangential velocities of non-debris particles; v3 includes some additional
minor edit
Observation of the skin-depth effect on the Casimir force between metallic surfaces
We have performed comparative measurements of the Casimir force between a
metallic plate and a transparent sphere coated with metallic films of different
thicknesses. We have observed that, if the thickness of the coating is less
than the skin-depth of the electromagnetic modes that mostly contribute to the
interaction, the force is significantly smaller than that measured with a thick
bulk-like film. Our results provide the first direct evidence of the skin-depth
effect on the Casimir force between metallic surfaces.Comment: submitted for publication on Dec. 10, 2004. 3 figure
Parity Violation in Composite Inelastic Dark Matter Models
Recent experimental results indicate that the dark matter sector may have a
non-minimal structure with a spectrum of states and interactions. Inelastic
scattering has received particular attention in light of DAMA's annual
modulation signal. Composite inelastic dark matter (CiDM) provides a dynamical
origin for the mass splittings in inelastic dark matter models. We show that
higher dimensional operators in the CiDM Lagrangian lead to an admixture of
inelastic and elastic scattering in the presence of parity violation. This
scenario is consistent with direct detection experiments, even when parity
violation is nearly maximal. We present an effective field theory description
of such models and discuss the constraints from direct detection experiments.
The CiDM model with parity violation has non-trivial phenomenology because of
the multiple scattering channels that are allowed.Comment: 10 pages, 3 figure
Semi-visible Jets: Dark Matter Undercover at the LHC
The dark matter may be a composite particle that is accessible via a weakly
coupled portal. If these hidden-sector states are produced at the Large Hadron
Collider (LHC), they would undergo a QCD-like shower. This would result in a
spray of stable invisible dark matter along with unstable states that decay
back to the Standard Model. Such "semi-visible" jets arise, for example, when
their production and decay are driven by a leptophobic resonance; the
resulting signature is characterized by significant missing energy aligned
along the direction of one of the jets. These events are vetoed by the current
suite of searches employed by the LHC, resulting in low acceptance. This Letter
will demonstrate that the transverse mass---computed using the final-state jets
and the missing energy---provides a powerful discriminator between the signal
and the QCD background. Assuming that the couples to the Standard Model
quarks with the same strength as the , the proposed search can discover
(exclude) masses up to 2.5 TeV (3.5 TeV) with 100 fb of 14 TeV data
at the LHC.Comment: 5 pages, 3 figures. v3: Supplementary material and references added.
Model changed from scalar to fermionic dark quarks and figures updated
accordingly. Conclusions unchange
Dark-Matter Harmonics Beyond Annual Modulation
The count rate at dark-matter direct-detection experiments should modulate
annually due to the motion of the Earth around the Sun. We show that
higher-frequency modulations, including daily modulation, are also present and
in some cases are nearly as strong as the annual modulation. These higher-order
modes are particularly relevant if (i) the dark matter is light, O(10) GeV,
(ii) the scattering is inelastic, or (iii) velocity substructure is present;
for these cases, the higher-frequency modes are potentially observable at
current and ton-scale detectors. We derive simple expressions for the harmonic
modes as functions of the astrophysical and geophysical parameters describing
the Earth's orbit, using an updated expression for the Earth's velocity that
corrects a common error in the literature. For an isotropic halo velocity
distribution, certain ratios of the modes are approximately constant as a
function of nuclear recoil energy. Anisotropic distributions can also leave
observable features in the harmonic spectrum. Consequently, the higher-order
harmonic modes are a powerful tool for identifying a potential signal from
interactions with the Galactic dark-matter halo.Comment: 40 pages, 10 figures; v2 refs added, minor improvements; v3 refs
added, minor improvements, JCAP versio
Distinguishing Dark Matter from Unresolved Point Sources in the Inner Galaxy with Photon Statistics
Data from the Fermi Large Area Telescope suggests that there is an extended
excess of GeV gamma-ray photons in the Inner Galaxy. Identifying potential
astrophysical sources that contribute to this excess is an important step in
verifying whether the signal originates from annihilating dark matter. In this
paper, we focus on the potential contribution of unresolved point sources, such
as millisecond pulsars (MSPs). We propose that the statistics of the
photons---in particular, the flux probability density function (PDF) of the
photon counts below the point-source detection threshold---can potentially
distinguish between the dark-matter and point-source interpretations. We
calculate the flux PDF via the method of generating functions for these two
models of the excess. Working in the framework of Bayesian model comparison, we
then demonstrate that the flux PDF can potentially provide evidence for an
unresolved MSP-like point-source population.Comment: 27 pages, 8 figures; v2, reference added and other minor change
Measuring Anisotropies in the Cosmic Neutrino Background
Neutrino capture on tritium has emerged as a promising method for detecting
the cosmic neutrino background (CvB). We show that relic neutrinos are captured
most readily when their spin vectors are anti-aligned with the polarization
axis of the tritium nuclei and when they approach along the direction of
polarization. As a result, CvB observatories may measure anisotropies in the
cosmic neutrino velocity and spin distributions by polarizing the tritium
targets. A small dipole anisotropy in the CvB is expected due to the peculiar
velocity of the lab frame with respect to the cosmic frame and due to late-time
gravitational effects. The PTOLEMY experiment, a tritium observatory currently
under construction, should observe a nearly isotropic background. This would
serve as a strong test of the cosmological origin of a potential signal. The
polarized-target measurements may also constrain non-standard neutrino
interactions that would induce larger anisotropies and help discriminate
between Majorana versus Dirac neutrinos.Comment: 7 pages, 2 figure
- …