We investigate gravitational microlensing signals produced by a spatially extended object transiting in front of a finite-sized source star. The most interesting features arise for lens and source sizes comparable to the Einstein radius of the setup. Using this information, we obtain constraints from the Subaru-HSC survey of M31 on the dark matter populations of nfw subhalos and boson stars of asteroid to Earth masses. These lens profiles capture the qualitative behavior of a wide range of dark matter substructures. We find that dark matter fractions down to $5\times {10}^{-3}$ may be probed, and that deviations from constraints on pointlike lenses (e.g., primordial black holes and machos) become visible for lenses of radius $0.1{\mathrm{R}}_{\odot }$ and larger, with the upper bound on lens masses weakening with increasing lens size.

Gas-rich dwarf galaxies located outside the virial radius of their host are relatively pristine systems and have ultralow gas cooling rates. This makes them very sensitive to heat injection by annihilation or decay of dark matter (DM). Such dwarfs are particularly sensitive to DM producing $e^{\pm }$ with energies 1–100 MeV or photons with energies 13.6 eV–1 keV, because these products can be efficiently thermalized in the neutral hydrogen gas of the dwarfs. Following the methodology of Wadekar and Farrar [ Phys. Rev. D 103, 123028 (2021)], we require the rate of heat injection by DM to not exceed the ultralow radiative cooling rate of gas in the Leo T dwarf galaxy. This gives model-independent bounds on (i) the decay lifetime of DM to $e^{\pm }$ (photons), which are stronger than all the previous literature for $m_{\mathrm{DM}}\sim 1–10\mathrm{MeV}$ ($m_{\mathrm{DM}}\sim 0.02–1\mathrm{keV}$), (ii) annihilation of DM to $e^{\pm }$ comparable to constraints from cosmic microwave background and $\mathrm{x}/\gamma$-ray surveys. We also translate our bounds for the case of the following DM models: axionlike particles (ALPs), sterile neutrinos, excited DM states, Higgs portal scalars, and dark baryons. Observations of gas-rich low-mass dwarfs from upcoming 21 cm and optical surveys can therefore be powerful probes of a multitude of models of DM.

Cold interstellar gas systems have been used to constrain dark matter (DM) models by the condition that the heating rate from DM must be lower than the astrophysical cooling rate of the gas. Following the methodology of Wadekar and Farrar [1], we use the interstellar medium of a gas-rich dwarf galaxy, Leo T, and a Milky Way-environment gas cloud, G33.4-8.0 to constrain DM. Leo T is a particularly strong system as its gas can have the lowest cooling rate among all the objects in the late Universe (owing to the low volume density and metallicity of the gas). Milky Way clouds, in some cases, provide complementary limits as the DM-gas relative velocity in them is much larger than that in Leo T. We derive constraints on the following scenarios in which DM can heat the gas: (i) interaction of axions with hydrogen atoms or free electrons in the gas, (ii) deceleration of relic magnetically charged DM in gas plasma, (iii) dynamical friction from compact DM, (iv) hard sphere scattering of composite DM with gas. Our limits are complementary to DM direct detection searches. Detection of more gas-rich low-mass dwarfs like Leo T from upcoming 21 cm and optical surveys can improve our bounds.

Damping properties in the free layers of tunnel magneto-resistance (TMR) readers were reported. The study used a free layer sample consisting of the same stacking structure as in TMR readers, involved comprehensive ferromagnetic resonance (FMR) measurements, and included numerical analysis of the FMR data. The results indicate that the free layer shows a Gilbert damping constant of 8.1 × 10⁻³. When the free layer is magnetized with a field which is not normal to the film plane, two-magnon scattering also occurs, although its contribution to the relaxation is at least 2.5 times smaller than the Gilbert contribution.

We investigate the astrophysical consequences of an attractive long-range interaction between dark matter and baryonic matter. Our study highlights the role of this interaction in inducing dynamical friction between dark matter and stars, which can significantly influence the evolution of compact stellar systems. Using the star cluster in Eridanus II as a case study, we derive a new stringent upper bound on the interaction strength α ˜ ≤ 314.5 for the interaction range λ = 1 pc . This constraint is independent of the dark matter mass and can improve the existing model-independent limits on α ˜ by a few orders of magnitude. Furthermore, we observe that the constraint is insensitive to the mass of the stellar system and the dark matter density in the stellar system as long as the system is dark matter dominated. This new approach can be applied to many other stellar systems, and we obtain comparable constraints from compact stellar halos observed in ultrafaint dwarf galaxies.

We investigate gravitational microlensing signals produced by a spatially extended object transiting in front of a finite-sized source star. The most interesting features arise for lens and source sizes comparable to the Einstein radius of the setup. Using this information, we obtain constraints from the Subaru-HSC survey of M31 on the dark matter populations of NFW subhalos and boson stars of asteroid to Earth masses. These lens profiles capture the qualitative behavior of a wide range of dark matter substructures. We find that deviations from constraints on point-like lenses (e.g. primordial black holes and MACHOs) become visible for lenses of radius 0.1 $R_\odot$ and larger, with the upper bound on lens masses weakening with increasing lens size.