Leanne D. Duffy

Axions as dark matter particles

We overview the current status of axions as dark matter. The axion is the pseudo-Nambu–Goldstone boson which arises from the Peccei–Quinn solution to the strong CP problem. Additionally, cold axion populations that can contribute to the dark matter of the universe will be generated via this mechanism. After reviewing these topics, we focus on constraints from the laboratory, astrophysics and cosmology. We discuss the current status of experimental searches and the consequences of the distribution of dark matter axions in the galactic halo for these searches. The axion remains an excellent candidate for the dark matter and future experiments, particularly the Axion Dark Matter eXperiment (ADMX), will cover a large fraction of the axion parameter space.

New X-ray free-electron laser architecture for generating high fluxes of longitudinally coherent 50 keV photons

Materials science needs to study dynamic properties of high-Z materials lead to a unique and challenging set of requirements for future X-ray free-electron lasers (XFELs), with single-pulse fluxes of up to 1012 50 keV X-rays that are both transversely and longitudinally coherent. These parameters cannot be met through an extension of the beam and FEL technologies used at existing and currently planned X-ray FEL facilities. We describe a novel technique to achieve higher fluxes by reducing the transverse beam emittance of high bunch charges and another to achieve longitudinal coherency by pre-modulating the electron beam current before it reaches the undulator. These techniques are investigated numerically and analytically, and also hold potential for increasing performance and decreasing cost of soft X-ray FELs.

New constraints for heavy axion-like particles from supernovae

We derive new constraints on the coupling of heavy pseudoscalar (axion-like) particles to photons, based on the gamma ray flux expected from the decay of these particles into photons. After being produced in the supernova core, these heavy axion-like particles would escape and a fraction of them would decay into photons before reaching the Earth. We have calculated the expected flux on Earth of these photons from the supernovae SN 1987A and Cassiopeia A and compared our results to data from the Fermi Large Area Telescope. This analysis provides strong constraints on the parameter space for axion-like particles. For a particle mass of 100 MeV, we find that the Peccei-Quinn constant, fa, must be greater than about 1015?GeV. Alternatively, for fa = 1012?GeV, we exclude the mass region between approximately 100?eV and 1?GeV.

Modulation sensitive search for nonvirialized dark-matter axions

Non-virialized dark-matter axions may be present in the Milky Way halo in the form of low-velocity-dispersion flows. The Axion Dark Matter eXperiment performed a search for the conversion of these axions into microwave photons using a resonant cavity immersed in a strong, static magnetic field. The spread of photon energy in these measurements was measured at spectral resolutions of the order of 1 Hz and below. If the energy variation were this small, the frequency modulation of any real axion signal due to the orbital and rotational motion of the Earth would become non-negligible. Conservative estimates of the expected signal modulation were made and used as a guide for the search procedure. The photon frequencies covered by this search are 812

Exploring Minimal Scenarios to Produce Transversely Bright Electron Beams Using the Eigen-Emittance Concept

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Using Emittance Partitioning Instead of a Laser Heater to Suppress the Microbunch Instability

852 and 858

The Milky Way’s Dark Matter Distribution and Consequences for Axion Detection

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USING AN EMITTANCE EXCHANGER AS A BUNCH COMPRESSOR

892 MHz, which correspond to an axion mass of 3.36

Arbitrary emittance partitioning between any two dimensions for electron beams

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MaRIE X-RAY FREE-ELECTRON LASER PRE-CONCEPTUAL DESIGN

3.52 and 3.55