11 research outputs found
Detecting axion dark matter beyond the magnetoquasistatic approximation
A number of proposals have been put forward for detecting axion dark matter
(DM) with grand unification scale decay constants that rely on the conversion
of coherent DM axions to oscillating magnetic fields in the presence of static,
laboratory magnetic fields. Crucially, such experiments \unicode{x2013}
including ABRACADABRA \unicode{x2013} have to-date worked in the limit that
the axion Compton wavelength is larger than the size of the experiment, which
allows one to take a magnetoquasistatic (MQS) approach to modeling the axion
signal. We use finite element methods to solve the coupled
axion-electromagnetism equations of motion without assuming the MQS
approximation. We show that the MQS approximation becomes a poor approximation
at frequencies two orders of magnitude lower than the naive MQS limit.
Radiation losses diminish the quality factor of an otherwise high- resonant
readout circuit, though this may be mitigated through shielding and minimizing
lossy materials. Additionally, self-resonances associated with the detector
geometry change the reactive properties of the pickup system, leading to two
generic features beyond MQS: there are frequencies that require an inductive
rather than capacitive tuning to maintain resonance, and the detector itself
becomes a multi-pole resonator at high frequencies. Accounting for these
features, competitive sensitivity to the axion-photon coupling may be extended
well beyond the naive MQS limit.Comment: 6+5 pages, 3+9 figure
Signatures of Primordial Energy Injection from Axion Strings
Axion strings are horizon-size topological defects that may be produced in
the early Universe. Ultra-light axion-like particles may form strings that
persist to temperatures below that of big bang nucleosynthesis. Such strings
have been considered previously as sources of gravitational waves and cosmic
microwave background (CMB) polarization rotation. In this work we show, through
analytic arguments and dedicated adaptive mesh refinement cosmological
simulations, that axion strings deposit a sub-dominant fraction of their energy
into high-energy Standard Model (SM) final states, for example, by the direct
production of heavy radial modes that subsequently decay to SM particles. This
high-energy SM radiation is absorbed by the primordial plasma, leading to novel
signatures in precision big bang nucleosynthesis, the CMB power spectrum, and
gamma-ray surveys. In particular, we show that CMB power spectrum data
constrains axion strings with decay constants GeV, up to
model dependence on the ultraviolet completion, for axion masses eV; future CMB surveys could find striking evidence of axion strings
with lower decay constants.Comment: 30 pages, 20 figures, Supplementary Animations at
https://goo.by/qHk9d, Video Abstract at https://youtu.be/Ae4AR46qKn
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Lumped-element axion dark matter detection beyond the magnetoquasistatic limit
HOW IMPORTANT ARE CSR COMPANIES FOR NATIONS’ GROWTH?
The paper provides new empirical evidence on the positive link between corporate social responsibility and income growth. Using available data for 26 countries over 2000–2008 we investigate cross-country growth differences by adding new variable (corporate social responsibility) to the standard growth regression model. We show that corporate social responsibility impact on growth is statistically significant but limited in size. Moreover, the inclusion of corporate social responsibility variable improves the fit of the regression. Countries with higher corporate social responsibility penetration as India achieve higher income growth rates. Evidence of the positive link between corporate social responsibility presented in this study encourage but further research on mechanism how socially responsible behavior affects growth is necessary