138 research outputs found
Effect of stress and temperature on the optical properties of silicon nitride membranes at 1550 nm
Future gravitational-wave detectors operated at cryogenic temperatures are expected to be limited by thermal noise of the highly reflective mirror coatings. Silicon nitride is an interesting material for such coatings as it shows very low mechanical loss, a property related to low thermal noise, which is known to further decrease under stress. Low optical absorption is also required to maintain the low mirror temperature. Here, we investigate the effect of stress on the optical properties at 1,550 nm of silicon nitride membranes attached to a silicon frame. Our approach includes the measurement of the thermal expansion coefficient and the thermal conductivity of the membranes. The membrane and frame temperatures are varied, and translated into a change in stress using finite element modeling. The resulting product of the optical absorption and thermo-optic coefficient (dn/dT) is measured using photothermal common-path interferometry
Constraints on Light Majorana Dark Matter from Colliders
We explore model-independent collider constraints on light Majorana dark
matter particles. We find that colliders provide a complementary probe of WIMPs
to direct detection, and give the strongest current constraints on light DM
particles. Collider experiments can access interactions not probed by direct
detection searches, and outperform direct detection experiments by about an
order of magnitude for certain operators in a large part of parameter space.
For operators which are suppresssed at low momentum transfer, collider searches
have already placed constraints on such operators limiting their use as an
explanation for DAMA.Comment: 4 pages, 6 figure
Constraints on Dark Matter from Colliders
We show that colliders can impose strong constraints on models of dark
matter, in particular when the dark matter is light. We analyze models where
the dark matter is a fermion or scalar interacting with quarks and/or gluons
through an effective theory containing higher dimensional operators which
represent heavier states that have been integrated out of the effective field
theory. We determine bounds from existing Tevatron searches for monojets as
well as expected LHC reaches for a discovery. We find that colliders can
provide information which is complementary or in some cases even superior to
experiments searching for direct detection of dark matter through its
scattering with nuclei. In particular, both the Tevatron and the LHC can
outperform spin dependent searches by an order of magnitude or better over much
of parameter space, and if the dark matter couples mainly to gluons, the LHC
can place bounds superior to any spin independent search.Comment: 23 pages, 16 figure
QCD Baryogenesis
We explore a simple model which naturally explains the observed baryon
asymmetry of the Universe. In this model the strong coupling is promoted to a
dynamical quantity, which evolves through the vacuum expectation value of a
singlet scalar field that mixes with the Higgs field. In the resulting cosmic
history, QCD confinement and electroweak symmetry breaking initially occur
simultaneously close to the weak scale. The early confinement triggers the
axion to roll toward its minimum, which creates a chemical potential between
baryons and antibaryons through the interactions of the meson,
resulting in spontaneous baryogenesis. The electroweak sphalerons are sharply
switched off after confinement and the baryon asymmetry is frozen in.
Subsequently, evolution of the Higgs vacuum expectation value (which is
modified in the confined phase) triggers a relaxation to a Standard Model-like
vacuum. We identify viable regions of parameter space, and describe various
experimental probes, including current and future collider constraints, and
gravitational wave phenomenology.Comment: 23 pages, 8 figures. Published versio
‘Shall We Send a Panda?’ A Practical Guide to Engaging Schools in Research: Learning from Large-Scale Mental Health Intervention Trials
The substantial time that children and young people spend in schools makes them important sites to trial and embed prevention and early intervention programmes. However, schools are complex settings, and it can be difficult to maintain school engagement in research trials; many projects experience high levels of attrition. This commentary presents learning from two large-scale, mixed-methods mental health intervention trials in English schools. The paper explores the barriers and challenges to engaging schools in promotion or early intervention research and offers detailed recommendations for other researchers
Exploring how citizen science projects measuring beach plastic debris can support UN Sustainable Development Goals
Plastic debris within marine environments is an issue of global concern, leading to commitments at international, regional, and national scales to remove plastics from the environment and prevent further entry. The United Nations (UN) created a global framework of 17 Sustainable Development Goals (SDGs), with several goals to advance the environmental dimension of sustainable development, with global and country progress tracked by targets and their indicators. Countries voluntarily report their progress on the basis of guidance provided by the UN on what data is needed. SDG 14, Life Below Water, contains one target to significantly reduce marine pollution, with specific mention of plastic debris. To date, however, national information on plastic debris has been sparse, although citizen science projects have been collecting data at a spatial and temporal coverage relevant to SDG reporting. This paper provides an overview to clarify the data requirements for reporting on the SDG indicator of plastic debris density and the complex process in which data for SDGs is requested from and provided by countries. We then explore the potential for citizen science to assist countries in filling evidence gaps, through providing data on plastic pollution. We focus on the sub-indicator for beach debris, which accounts for most citizen science projects collecting data on plastic pollution. Then, we unpack the opportunities and challenges of augmenting SDG reporting with information gathered from citizen science communities. Lastly, we recommend ways for citizen science communities and governments to synergize efforts monitoring plastics to inform pathways for preventing and reducing such pollution ending up in our marine environments
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