Samuel J. Witte
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View article: Searching for Axion Dark Matter Near Relaxing Magnetars
Searching for Axion Dark Matter Near Relaxing Magnetars Open
Axion dark matter passing through the magnetospheres of magnetars can undergo hyper-efficient resonant mixing with low-energy photons, leading to the production of narrow spectral lines that could be detectable on Earth. Since this is a re…
View article: Stepping up superradiance constraints on axions
Stepping up superradiance constraints on axions Open
Light feebly-coupled bosonic particles can efficiently extract the rotational energy of rapidly spinning black holes on subastrophysical timescales via a phenomenon known as black hole superradiance. In the case of light axions, the feeble…
View article: Stepping Up Superradiance Constraints on Axions
Stepping Up Superradiance Constraints on Axions Open
Light feebly-coupled bosonic particles can efficiently extract the rotational energy of rapidly spinning black holes on sub-astrophysical timescales via a phenomenon known as black hole superradiance. In the case of light axions, the feebl…
View article: A systematic study of hidden sector dark matter: application to the gamma-ray and antiproton excesses
A systematic study of hidden sector dark matter: application to the gamma-ray and antiproton excesses Open
In hidden sector models, dark matter does not directly couple to the particle content of the Standard Model, strongly suppressing rates at direct detection experiments, while still allowing for large signals from annihilation. In this pape…
View article: Pulsar Nulling and Vacuum Radio Emission from Axion Clouds
Pulsar Nulling and Vacuum Radio Emission from Axion Clouds Open
Nonrelativistic axions can be efficiently produced in the polar caps of pulsars, resulting in the formation of a dense cloud of gravitationally bound axions. Here, we investigate the interplay between such an axion cloud and the electrodyn…
View article: Numerical analysis of resonant axion-photon mixing
Numerical analysis of resonant axion-photon mixing Open
Many present-day axion searches attempt to probe the mixing of axions and photons, which occurs in the presence of an external magnetic field. While this process is well understood in a number of simple and idealized contexts, a strongly v…
View article: Numerical Analysis of Resonant Axion-Photon Mixing: Part I
Numerical Analysis of Resonant Axion-Photon Mixing: Part I Open
Many present-day axion searches attempt to probe the mixing of axions and photons, which occurs in the presence of an external magnetic field. While this process is well-understood in a number of simple and idealized contexts, a strongly v…
View article: The Growth and Evolution of Axion Clouds around Pulsars
The Growth and Evolution of Axion Clouds around Pulsars Open
Axions can be efficiently produced from the dynamical evolution of the electromagnetic fields in the polar caps of neutron stars. If the axion mass lies roughly in the range $10^{-10} \\, {\\rm eV} \\lesssim m_a \\lesssim 10^{-4}$ eV, a si…
View article: Pulsar Nulling and Vacuum Radio Emission from Axion Clouds
Pulsar Nulling and Vacuum Radio Emission from Axion Clouds Open
Non-relativistic axions can be efficiently produced in in the polar caps of pulsars, resulting in the formation of a dense cloud of gravitationally bound axions. Here, we investigate the interplay between such an axion cloud and the electr…
View article: Generalized ray tracing for axions in astrophysical plasmas
Generalized ray tracing for axions in astrophysical plasmas Open
Ray tracing plays a vital role in black hole imaging, modeling the emission mechanisms of pulsars, and deriving signatures from physics beyond the Standard Model. In this work we focus on one specific application of ray tracing, namely, pr…
View article: Adiabatic Axion-Photon Mixing Near Neutron Stars
Adiabatic Axion-Photon Mixing Near Neutron Stars Open
One of the promising new proposals to search for axions in astrophysical environments is to look for narrow radio lines produced from the resonant conversion of axion dark matter falling through the magnetospheres of neutron stars. For suf…
View article: Generalized Ray Tracing for Axions in Astrophysical Plasmas
Generalized Ray Tracing for Axions in Astrophysical Plasmas Open
Ray tracing plays a vital role in black hole imaging, modeling the emission mechanisms of pulsars, and deriving signatures from physics beyond the Standard Model. In this work we focus on one specific application of ray tracing, namely, pr…
View article: Novel Constraints on Axions Produced in Pulsar Polar-Cap Cascades
Novel Constraints on Axions Produced in Pulsar Polar-Cap Cascades Open
Axions can be copiously produced in localized regions of neutron star magnetospheres where the ambient plasma is unable to efficiently screen the induced electric field. As these axions stream away from the neutron star they can resonantly…
View article: Constraining the X-ray heating and reionization using 21-cm power spectra with Marginal Neural Ratio Estimation
Constraining the X-ray heating and reionization using 21-cm power spectra with Marginal Neural Ratio Estimation Open
Cosmic Dawn (CD) and Epoch of Reionization (EoR) are epochs of the Universe which host invaluable information about the cosmology and astrophysics of X-ray heating and hydrogen reionization. Radio interferometric observations of the 21-cm …
View article: Axion Clouds around Neutron Stars
Axion Clouds around Neutron Stars Open
Recent work has shown that axions can be efficiently produced via non-stationary pair plasma discharges in the polar cap region of pulsars. Here, we point out that for axion masses $10^{-9} \, {\rm eV} \lesssim m_a \lesssim 10^{-4} \, \rm …
View article: Precision CMB constraints on eV-scale bosons coupled to neutrinos
Precision CMB constraints on eV-scale bosons coupled to neutrinos Open
The cosmic microwave background (CMB) has proven to be an invaluable tool for studying the properties and interactions of neutrinos, providing insight not only into the sum of neutrino masses but also the free streaming nature of neutrinos…
View article: Transient radio lines from axion miniclusters and axion stars
Transient radio lines from axion miniclusters and axion stars Open
Gravitationally bound clumps of dark matter axions in the form of 'miniclusters' or even denser 'axion stars' can generate strong radio signals through axion-photon conversion when encountering highly magnetised neutron star magnetospheres…
View article: Constraining the X-ray heating and reionization using 21-cm power spectra with Marginal Neural Ratio Estimation
Constraining the X-ray heating and reionization using 21-cm power spectra with Marginal Neural Ratio Estimation Open
Cosmic Dawn (CD) and Epoch of Reionization (EoR) are epochs of the Universe which host invaluable information about the cosmology and astrophysics of X-ray heating and hydrogen reionization. Radio interferometric observations of the 21-cm …
View article: Extraterrestrial Axion Search with the Breakthrough Listen Galactic Center Survey
Extraterrestrial Axion Search with the Breakthrough Listen Galactic Center Survey Open
Axion dark matter (DM) may efficiently convert to photons in the magnetospheres of neutron stars (NSs), producing nearly monochromatic radio emission. This process is resonantly triggered when the plasma frequency induced by the underlying…
View article: Revisiting constraints on WIMPs around primordial black holes
Revisiting constraints on WIMPs around primordial black holes Open
While primordial black holes (PBHs) with masses MPBH10-11 M cannot comprise the entirety of dark matter, the existence of even a small population of these objects can have profound astrophysical consequences. A subdominant population of PB…
View article: Novel Constraints on Axions Produced in Pulsar Polar-Cap Cascades
Novel Constraints on Axions Produced in Pulsar Polar-Cap Cascades Open
Axions can be copiously produced in localized regions of neutron star magnetospheres where the ambient plasma is unable to efficiently screen the induced electric field. As these axions stream away from the neutron star they can resonantly…
View article: Fast and credible likelihood-free cosmology with truncated marginal neural ratio estimation
Fast and credible likelihood-free cosmology with truncated marginal neural ratio estimation Open
Sampling-based inference techniques are central to modern cosmological data analysis; these methods, however, scale poorly with dimensionality and typically require approximate or intractable likelihoods. In this paper we describe how Trun…
View article: Revisiting constraints on WIMPs around primordial black holes
Revisiting constraints on WIMPs around primordial black holes Open
While Primordial Black Holes (PBHs) with masses $M_{\rm PBH} \gtrsim 10^{-11} \, M_\odot$ cannot comprise the entirety of dark matter, the existence of even a small population of these objects can have profound astrophysical consequences. …
View article: Astrophysical and Cosmological Probes of Dark Matter
Astrophysical and Cosmological Probes of Dark Matter Open
While astrophysical and cosmological probes provide a remarkably precise and consistent picture of the quantity and general properties of dark matter, its fundamental nature remains one of the most significant open questions in physics. Ob…
View article: Extraterrestrial Axion Search with the Breakthrough Listen Galactic Center Survey
Extraterrestrial Axion Search with the Breakthrough Listen Galactic Center Survey Open
Axion dark matter (DM) may efficiently convert to photons in the magnetospheres of neutron stars (NSs), producing nearly monochromatic radio emission. This process is resonantly triggered when the plasma frequency induced by the underlying…
View article: Axion-photon conversion in neutron star magnetospheres: The role of the plasma in the Goldreich-Julian model
Axion-photon conversion in neutron star magnetospheres: The role of the plasma in the Goldreich-Julian model Open
The most promising indirect search for the existence of axion dark matter uses radio telescopes to look for narrow spectral lines generated from the resonant conversion of axions in the magnetospheres of neutron stars. Unfortunately, a lar…
View article: Fast and Credible Likelihood-Free Cosmology with Truncated Marginal Neural Ratio Estimation
Fast and Credible Likelihood-Free Cosmology with Truncated Marginal Neural Ratio Estimation Open
Sampling-based inference techniques are central to modern cosmological data analysis; these methods, however, scale poorly with dimensionality and typically require approximate or intractable likelihoods. In this paper we describe how Trun…
View article: Exploring the origin of supermassive black holes with coherent neutrino scattering
Exploring the origin of supermassive black holes with coherent neutrino scattering Open
Collapsing supermassive stars ($M \gtrsim 3 \times 10^4 M_{\odot}$) at high redshifts can naturally provide seeds and explain the origin of the supermassive black holes observed in the centers of nearly all galaxies. During the collapse of…