190 research outputs found
Discretising the velocity distribution for directional dark matter experiments
Dark matter (DM) direct detection experiments which are
directionally-sensitive may be the only method of probing the full velocity
distribution function (VDF) of the Galactic DM halo. We present an angular
basis for the DM VDF which can be used to parametrise the distribution in order
to mitigate astrophysical uncertainties in future directional experiments and
extract information about the DM halo. This basis consists of discretising the
VDF in a series of angular bins, with the VDF being only a function of the DM
speed within each bin. In contrast to other methods, such as spherical
harmonic expansions, the use of this basis allows us to guarantee that the
resulting VDF is everywhere positive and therefore physical. We present a
recipe for calculating the event rates corresponding to the discrete VDF for an
arbitrary number of angular bins and investigate the discretisation error
which is introduced in this way. For smooth, Standard Halo Model-like
distribution functions, only angular bins are required to achieve an
accuracy of around in the number of events in each bin. Shortly after
confirmation of the DM origin of the signal with around 50 events, this
accuracy should be sufficient to allow the discretised velocity distribution to
be employed reliably. For more extreme VDFs (such as streams), the
discretisation error is typically much larger, but can be improved with
increasing . This method paves the way towards an astrophysics-independent
analysis framework for the directional detection of dark matter.Comment: 36 pages, 11 figures. Matches version accepted in JCAP. Python code
for Radon transform calculation available from the autho
Earth-Scattering of super-heavy Dark Matter: updated constraints from detectors old and new
Direct searches for Dark Matter (DM) are continuously improving, probing down
to lower and lower DM-nucleon interaction cross sections. For
strongly-interacting massive particle (SIMP) Dark Matter, however, the
accessible cross section is bounded from above due to the stopping effect of
the atmosphere, Earth and detector shielding. We present a careful calculation
of the SIMP signal rate, focusing on super-heavy DM () for which the standard nuclear-stopping formalism is
applicable, and provide code for implementing this calculation numerically.
With recent results from the low-threshold CRESST 2017 surface run, we improve
the maximum cross section reach of direct detection searches by a factor of
around 5000, for DM masses up to . A reanalysis of the
longer-exposure, sub-surface CDMS-I results (published in 2002) improves the
previous cross section reach by two orders of magnitude, for masses up to
. Along with complementary constraints from SIMP
capture and annihilation in the Earth and Sun, these improved limits from
direct nuclear scattering searches close a number of windows in the SIMP
parameter space in the mass range GeV to GeV, of particular
interest for heavy DM produced gravitationally at the end of inflation.Comment: 12 pages, 7 figures. Code available at
https://github.com/bradkav/verne . Comments welcome. v2: Fixed references and
minor typos, corrected "-cleus" to "CRESST 2017 surface run". v3: Added
Appendix A with explicit expressions and coordinate system. v4: Added
discussion of variance in final DM speed. Version published in PR
Re-examining the significance of the 750 GeV diphoton excess at ATLAS
The excess seen in the diphoton channel at around 750 GeV by both ATLAS and
CMS has caused a great deal of excitement in the particle physics community.
However, there has recently been much discussion about uncertainties in the
significance of the peak seen by the ATLAS experiment. In this note, we aim to
estimate this significance using a range of possible parametrisations for the
smooth diphoton background. We obtain a local significance close to that
reported by ATLAS and further demonstrate that the significance of the excess
is not substantially reduced when more complicated background functions are
considered. In particular, the background contribution is strongly constrained
by the small numbers of events at large diphoton invariant mass. Future data
releases will improve constraints on the diphoton background, as well as
clarifying the true nature of the 750 GeV excess.Comment: 6 pages, 2 figures. Code available at
https://github.com/bradkav/ATLASfits/releases/latest . Additional references
and discussion on impact of using binned data added in v3. Comments very
welcom
You can hide but you have to run: direct detection with vector mediators
We study direct detection in simplified models of Dark Matter (DM) in which
interactions with Standard Model (SM) fermions are mediated by a heavy vector
boson. We consider fully general, gauge-invariant couplings between the SM, the
mediator and both scalar and fermion DM. We account for the evolution of the
couplings between the energy scale of the mediator mass and the nuclear energy
scale. This running arises from virtual effects of SM particles and its
inclusion is not optional. We compare bounds on the mediator mass from direct
detection experiments with and without accounting for the running. In some
cases the inclusion of these effects changes the bounds by several orders of
magnitude, as a consequence of operator mixing which generates new interactions
at low energy. We also highlight the importance of these effects when
translating LHC limits on the mediator mass into bounds on the direct detection
cross section. For an axial-vector mediator, the running can alter the derived
bounds on the spin-dependent DM-nucleon cross section by a factor of two or
more. Finally, we provide tools to facilitate the inclusion of these effects in
future studies: general approximate expressions for the low energy couplings
and a public code runDM to evolve the couplings between arbitrary energy
scales.Comment: 26 pages + appendices, 9 + 2 figures. The runDM code is available at
https://github.com/bradkav/runDM/. v2: references added, version published in
JHE
Signatures of Earth-scattering in the direct detection of Dark Matter
Direct detection experiments search for the interactions of Dark Matter (DM)
particles with nuclei in terrestrial detectors. But if these interactions are
sufficiently strong, DM particles may scatter in the Earth, affecting their
distribution in the lab. We present a new analytic calculation of this
`Earth-scattering' effect in the regime where DM particles scatter at most once
before reaching the detector. We perform the calculation self-consistently,
taking into account not only those particles which are scattered away from the
detector, but also those particles which are deflected towards the detector.
Taking into account a realistic model of the Earth and allowing for a range of
DM-nucleon interactions, we present the EarthShadow code, which we make
publicly available, for calculating the DM velocity distribution after
Earth-scattering. Focusing on low-mass DM, we find that Earth-scattering
reduces the direct detection rate at certain detector locations while
increasing the rate in others. The Earth's rotation induces a daily modulation
in the rate, which we find to be highly sensitive to the detector latitude and
to the form of the DM-nucleon interaction. These distinctive signatures would
allow us to unambiguously detect DM and perhaps even identify its interactions
in regions of the parameter space within the reach of current and future
experiments.Comment: 27 pages + appendices, 9 figures. Code (and animations) available at
https://github.com/bradkav/EarthShadow (Astrophysics Source Code Library,
record ascl:1611.012). v2: added references, matches version published in
JCA
Faint Light from Dark Matter: Classifying and Constraining Dark Matter-Photon Effective Operators
Even if Dark Matter (DM) is neutral under electromagnetism, it can still
interact with the Standard Model (SM) via photon exchange from
higher-dimensional operators. Here we classify the general effective operators
coupling DM to photons, distinguishing between Dirac/Majorana fermion and
complex/real scalar DM. We provide model-independent constraints on these
operators from direct and indirect detection. We also constrain various
DM-lepton operators, which induce DM-photon interactions via RG running or
which typically arise in sensible UV-completions. This provides a simple way to
quickly assess constraints on any DM model that interacts mainly via photon
exchange or couples to SM leptons.Comment: 32 pages + appendices, 9 + 1 figures, 2 + 1 tables. v2: some
clarifications and references added; conclusions unchanged; version published
in JHE
Primordial Black Holes as Silver Bullets for New Physics at the Weak Scale
Observational constraints on gamma rays produced by the annihilation of
weakly interacting massive particles around primordial black holes (PBHs) imply
that these two classes of Dark Matter candidates cannot coexist. We show here
that the successful detection of one or more PBHs by radio searches (with the
Square Kilometer Array) and gravitational waves searches (with LIGO/Virgo and
the upcoming Einstein Telescope) would set extraordinarily stringent
constraints on virtually all weak-scale extensions of the Standard Model with
stable relics, including those predicting a WIMP abundance much smaller than
that of Dark Matter. Upcoming PBHs searches have in particular the potential to
rule out almost the entire parameter space of popular theories such as the
minimal supersymmetric standard model and scalar singlet Dark Matter.Comment: 10 pages, 3 figures. Code available at
https://github.com/adam-coogan/pbhs_vs_wimps , archived at
https://zenodo.org/badge/latestdoi/169754838 . v2: Matches version published
in PR
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