Axion dark matter echo: A detailed analysis

It was recently shown that a powerful beam of radio/microwave radiation sent out to space can produce detectable backscattering via the stimulated decay of ambient axion dark matter. This echo is a faint and narrow signal centered at an angular frequency close to half the axion mass. In this article, we provide a detailed analytical and numerical analysis of this signal, considering the effects of the axion velocity distribution as well as the outgoing beam shape. In agreement with the original proposal, we find that the divergence of the outgoing beam does not affect the echo signal, which is only constrained by the axion velocity distribution. Moreover, our findings are relevant for the optimization of the experimental parameters in order to attain maximal signal-to-noise ratio or minimal energy consumption

The Echo Method for Axion Dark Matter Detection

The axion is a dark matter candidate arising from the spontaneous breaking of the Peccei–Quinn symmetry, introduced to solve the strong CP problem. It has been shown that radio/microwave radiation sent out to space is backscattered in the presence of axion dark matter due to stimulated axion decay. This backscattering is a feeble and narrow echo signal centered at an angular frequency very close to one-half of the axion mass. In this article, we summarize all the relevant results found so far, including analytical formulas for the echo signal, as well as sensitivity prospects for possible near-future experiments

Duration of Classicality of Homogeneous Condensates with Attractive Interactions

Dark matter axions and other highly degenerate bosonic fluids are commonly described by classical field equations. In a recent paper \cite{BECprop} we calculated the duration of classicality of homogeneous condensates with attractive contact interactions and of self-gravitating homogeneous condensates in critical expansion. According to their classical equations of motion, such condensates persist forever. In their quantum evolution parametric resonance causes quanta to jump in pairs out of the condensate into all modes with wavevector less than some critical value. We estimated in each case the time scale over which the condensate is depleted and after which a classical description is invalid.Comment: 5 pages, no figures, contributed to the 13th Patras Workshop on Axions, WIMPs and WISPs, Thessaloniki, May 15 to 19, 201

Anatomy of astrophysical echoes from axion dark matter

If the dark matter in the Universe is made of $\mu$eV axion-like particles (ALPs), then a rich phenomenology can emerge in connection to their stimulated decay into two photons. We discuss the ALP stimulated decay induced by electromagnetic radiation from Galactic radio sources. Three signatures, made by two echoes and one collinear emission, are associated with the decay, and can be simultaneously detected, offering a unique opportunity for a clear ALP identification. We derive the formalism associated with such signatures starting from first principles, and providing the relevant equations to be applied to study the ALP phenomenology. We then focus on the case of Galactic pulsars as stimulating sources and derive forecasts for future observations, which will be complementary to helioscopes and haloscopes resultsComment: 32 pages, 11 figures. Version accepted for publication in JCA

Constraining Below-threshold Radio Source Counts With Machine Learning

We propose a machine-learning-based technique to determine the number density of radio sources as a function of their flux density, for use in next-generation radio surveys. The method uses a convolutional neural network trained on simulations of the radio sky to predict the number of sources in several flux bins. To train the network, we adopt a supervised approach wherein we simulate training data stemming from a large domain of possible number count models going down to fluxes a factor of 100 below the threshold for source detection. We test the model reconstruction capabilities as well as benchmark the expected uncertainties in the model predictions, observing good performance for fluxes down to a factor of ten below the threshold. This work demonstrates that the capabilities of simple deep learning models for radio astronomy can be useful tools for future surveys.Comment: 15 pages, 10 figure

Duration of classicality of an inhomogeneous quantum field with repulsive contact self-interactions

Quantum fields with large degeneracy are often approximated as classical fields. Here, we show how the quantum and classical evolution of a highly degenerate quantum field with repulsive contact self-interactions differ fromeach other. Initially, the field is taken to be homogeneous except for a small plane-wave perturbation in only one mode. In quantum field theory, modes satisfying both momentum and energy conservation of the quasiparticles, grow exponentially with time. However, in the classical field approximation, the system is stable. We calculate the time scale after which the classical field description becomes invalid