Francesc Ferrer

We study the full-sky distribution of the radio emission from the stimulated decay of axions which are assumed to compose the dark matter in the Galaxy. Besides the constant extragalactic and CMB components, the decays are stimulated by a Galactic radio emission with a spatial distribution that we empirically determine from observations. We compare the diffuse emission to the counterimages of the brightest supernovæ remnants, and take into account the effects of free-free absorption. We show that, if the dark matter halo is described by a cuspy NFW profile, the expected signal from the Galactic center is the strongest. Interestingly, the emission from the Galactic anti-center provides competitive constraints that do not depend on assumptions on the uncertain dark matter density in the inner region. Furthermore, the anti-center of the Galaxy is the brightest spot if the Galactic dark matter density follows a cored profile …

A network of cosmic strings (CS), if present, would continue emitting gravitational waves (GW) as it evolves throughout the history of the Universe. This results in a characteristic broad spectrum making it a perfect source to infer the expansion history. In particular, a short inflationary period caused by a supercooled phase transition would cause a drop in the spectrum at frequencies corresponding to that event. However, the impact on the spectrum is similar to the ones caused by an early matter-dominated era or from particle production, making it difficult to disentangle these different physical origins. We point out that, in the case of a short inflationary period, the GW spectrum receives an additional contribution from the phase transition itself. This leads to a characteristic imprint of a peak on top of a wide plateau both visible at future GW observatories.

The flux of high energy neutrinos and photons produced in a blazar could get attenuated when they propagate through the dark matter spike around the central black hole and the halo of the host galaxy. Using the observation by IceCube of a few high-energy neutrino events from TXS 0506+ 056, and their coincident gamma ray events, we obtain new constraints on the dark matter-neutrino and dark matter-photon scattering cross sections. Our constraints are orders of magnitude more stringent than those derived from considering the attenuation through the intergalactic medium and the Milky Way dark matter halo. When the cross-section increases with energy, our constraints are also stronger than those derived from the CMB and large-scale structure.

A network of cosmic strings (CS), if present, would continue emitting gravitational waves (GW) as it evolves throughout the history of the Universe. This results in a characteristic broad spectrum making it a perfect source to infer the expansion history. In particular, a short inflationary period caused by a supercooled phase transition would cause a drop in the spectrum at frequencies corresponding to that event. However, the impact on the spectrum is similar to the ones caused by an early matter-dominated era or from particle production, making it difficult to disentangle these different physical origins. We point out that, in the case of a short inflationary period, the GW spectrum receives an additional contribution from the phase transition itself. This leads to a characteristic imprint of a peak on top of a wide plateau both visible at future GW observatories.

The 511 keV γ-ray emission from the galactic center region may fully or partially originate from the annihilation of positrons from dark matter particles with electrons from the interstellar medium. Alternatively, the positrons could be created by astrophysical sources, involving exclusively standard model physics. We describe here a new concept for a 511 keV mission called 511-CAM (511 keV gamma-ray camera using microcalorimeters) that combines focusing γ-ray optics with a stack of transition edge sensor microcalorimeter arrays in the focal plane. The 511-CAM detector assembly has a projected 511 keV energy resolution of 390 eV full width half maximum or better, and improves by a factor of at least 11 on the performance of state-of-the-art Ge-based Compton telescopes. Combining this unprecedented energy resolution with sub-arcmin angular resolutions afforded by Laue lens or channeling optics could make …

In the presence of radio waves having a wavelength equivalent to half of an axion mass, an axion undergoes a stimulated decay and emits two photons. Those two photons travel in opposite directions along the background radiation fields, and thus, the radio image and its counterimage of background fields would be enhanced. Assuming all the dark matter consists of axions, the radio signals from decays of an axion in the Milky Way stimulated by galactic, extragalactic, and CMB photons are computed. We also consider what could affect the signal: the time evolution of the flux from supernova remnants, the free-free absorption with Galactic electrons, the formation of dilute axion stars, and the mass segregation between dilute axion stars and ordinary stars. The resulting signal turns out to be bright enough to be detected by the first phase of the Square Kilometer Array for the axion-photon coupling g aγ~ 2-3× 10-11 …

Transition-edge sensor (TES) microcalorimeters have growing applications in X-ray and gamma-ray astronomy due to their high energy resolution and fast rates of time-stamping of individual photons. We are testing and optimizing a 32-pixels SLEDGEHAMMER (Spectrometer to Leverage Extensive Development of Gamma-ray TESs for Huge Arrays using Microwave Multiplexed Enabled Readout) detector developed by the quantum sensor group at the National Institute of Standards and Technology (NIST). TES arrays can achieve energy resolutions of 55 eV FWHM (Full Width Half Maximum) at 97 keV [Bennett et al. 2012]. This SLEDGEHAMMER detector has 32 microwave resonators inductively coupled with 32 Superconducting Quantum Interference Device (SQUIDs) and SQUIDs are coupled with 32 Mo-Au TESs. Each TES is thermally coupled to a 1.4× 1.4× 0.38 mm Sn absorber pixel to absorb gamma-ray …

We study the radio signals generated when an axion star enters the magnetosphere of a neutron star. As the axion star moves through the resonant region where the plasma-induced photon mass becomes equal to the axion mass, the axions can efficiently convert into photons, giving rise to an intense, transient radio signal. We show that a dense axion star with a mass∼ 10− 13 M⊙ composed of∼ 10 μ eV axions can account for most of the mysterious fast radio bursts.