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A cosmological model treating dark matter as a coherent quantum wave agrees well with conventional dark-matter theory on an astronomical scale. But on smaller scales, the quantum nature of wave-like dark matter can explain dark-matter cores that are observed in dwarf galaxies, which standard theory cannot. The conventional cold-particle interpretation of dark matter (known as ‘cold dark matter’, or CDM) still lacks laboratory support and struggles with the basic properties of common dwarf galaxies, which have surprisingly uniform central masses and shallow density profiles 1 , 2 , 3 , 4 , 5 . In contrast, galaxies predicted by CDM extend to much lower masses, with steeper, singular profiles 6 , 7 , 8 , 9 . This tension motivates cold, wavelike dark matter (ψDM) composed of a non-relativistic Bose–Einstein condensate, so the uncertainty principle counters gravity below a Jeans scale 10 , 11 , 12 . Here we achieve cosmological simulations of this quantum state at unprecedentedly high resolution capable of resolving dwarf galaxies, with only one free parameter, m B , the boson mass. We demonstrate the large-scale structure is indistinguishable from CDM, as desired, but differs radically inside galaxies where quantum interference forms solitonic cores surrounded by extended haloes of fluctuating density granules. These results allow us to determine eV using stellar phase-space distributions in dwarf spheroidal galaxies. Denser, more massive solitons are predicted for Milky Way sized galaxies, providing a substantial seed to help explain early spheroid formation. The onset of galaxy formation is substantially delayed relative to CDM, appearing at redshift z ≲ 13 in our simulations.

Fuzzy dark matter (FDM), consisting of ultralight bosons, is an intriguing alternative to cold dark matter. Numerical simulations solving the Schrödinger–Poisson (SP) equation, which governs FDM dynamics, show that FDM halos consist of a central solitonic core (representing the ground state of the SP equation), surrounded by a large envelope of excited states. Wave interference gives rise to density fluctuations of order unity throughout the envelope and causes the soliton to undergo density oscillations and execute a confined random walk in the central region of the halo. The resulting gravitational potential perturbations are an efficient source of dynamical heating. Using high-resolution numerical simulations of a 6.6 × 109 M ⊙ FDM halo with boson mass m b = 8 × 10−23 eV, we investigate the impact of this dynamical heating on the structure and kinematics of spheroidal dwarf galaxies of a fixed mass but different initial sizes and ellipticities. The galaxies are set up in equilibrium in the time-and-azimuthally averaged halo potential and evolved for 10 Gyr in the live FDM halo. We find that they continuously increase their sizes and central velocity dispersions. In addition, their kinematic structures become strongly radially anisotropic, especially in the outskirts. Dynamical heating also causes initially ellipsoidal galaxies to become more spherical over time from the inside out and gives rise to distorted, nonconcentric isodensity contours. These telltale characteristics of dynamical heating of dwarf galaxies in FDM halos can potentially be used to constrain the boson mass.

The Fermi Gamma-Ray Space Telescope reveals two large bubbles in the Galaxy, extending nearly symmetrically ∼50° above and below the Galactic center (GC). Previous simulations of bubble formation invoking active galactic nucleus (AGN) jets have assumed that the jets are vertical to the Galactic disk; however, in general, the jet orientation does not necessarily correlate with the rotational axis of the Galactic disk. Using three-dimensional special relativistic hydrodynamic simulations including cosmic rays (CRs) and thermal gas, we show that the dense clumpy gas within the Galactic disk disrupts jet collimation (“failed jets” hereafter), which causes the failed jets to form hot bubbles. Subsequent buoyancy in the stratified atmosphere renders them vertical to form the symmetric Fermi and eROSITA bubbles (collectively, Galactic bubbles). We find that (1) despite the relativistic jets emanating from the GC at various angles ≤45° with respect to the rotational axis of the Galaxy, the Galactic bubbles nonetheless appear aligned with the axis; (2) the edge of the eROSITA bubbles corresponds to a forward shock driven by the hot bubbles; (3) followed by the forward shock is a tangling contact discontinuity corresponding to the edge of the Fermi bubbles; (4) assuming a leptonic model we find that the observed gamma-ray bubbles and microwave haze can be reproduced with a best-fit CR power-law spectral index of 2.4; The agreements between the simulated and the observed multiwavelength features suggest that forming the Galactic bubbles by oblique AGN failed jets is a plausible scenario.

The cold dark matter (CDM) paradigm successfully explains the cosmic structure over an enormous span of redshifts. However, it fails when probing the innermost regions of dark matter halos and the properties of the Milky Way’s dwarf galaxy satellites. Moreover, the lack of experimental detection of Weakly Interacting Massive Particle (WIMP) favors alternative candidates such as light axionic dark matter that naturally arise in string theory. Cosmological N-body simulations have shown that axionic dark matter forms a solitonic core of size of ≃150 pc in the innermost region of the galactic halos. The oscillating scalar field associated to the axionic dark matter halo produces an oscillating gravitational potential that induces a time dilation of the pulse arrival time of ≃400 ns/(m B /10 − 22 eV) for pulsar within such a solitonic core. Over the whole galaxy, the averaged predicted signal may be detectable with current and forthcoming pulsar timing array telescopes.

Unveiling the true nature of dark matter, which manifests itself only through gravity, is one of the principal quests in physics. Leading candidates for dark matter are weakly interacting massive particles or ultralight bosons (axions), at opposite extremes in mass scales, that have been postulated by competing theories to solve deficiencies in the Standard Model of particle physics. Whereas dark matter weakly interacting massive particles behave like discrete particles (ϱDM), quantum interference between dark matter axions is manifested as waves (ψDM). Here, we show that gravitational lensing leaves signatures in multiply lensed images of background galaxies that reveal whether the foreground lensing galaxy inhabits a ϱDM or ψDM halo. Whereas ϱDM lens models leave well documented anomalies between the predicted and observed brightnesses and positions of multiply lensed images, ψDM lens models correctly predict the level of anomalies remaining with ϱDM lens models. More challengingly, when subjected to a battery of tests for reproducing the quadruply lensed triplet images in the system HS 0810+2554, ψDM is able to reproduce all aspects of this system whereas ϱDM often fails. The ability of ψDM to resolve lensing anomalies even in demanding cases such as HS 0810+2554, together with its success in reproducing other astrophysical observations, tilt the balance toward new physics invoking axions.Modelling of the gravitationally lensed system HS 0810+2554 with wavelike dark matter resolves brightness and position anomalies remaining after the standard massive-particle dark matter treatment.

In a low-bit sampling digital correlator for wide-bandwidth interferometry observations, nonuniform spectra of the analog input can degrade the correlator efficiency. In this work we evaluate this issue in detail, particularly for correlators having fine spectral resolution. We find the degradation to be due to nonlinear transfer of noise among different frequency channels, thereby altering the per channel signal-to-noise ratio (S/N) in an unfavorable manner with low-power channels having worse S/N and high-power channels, better S/N. (The favorable S/N in high-power channels arise primarily from effective oversampling.) To the leading order, the favorable and unfavorable S/N at different channels can largely cancel and the S/N degradation occurs as a second-order effect. However, when the two input spectra for correlation deviate from each other, such a cancellation mechanism may be suppressed.

Wave (fuzzy) dark matter (\\(\\)DM) consists of ultralight bosons, featuring a solitonic core within a granular halo. Here we extend \\(\\)DM to two components, with distinct particle masses \\(m\\) and coupled only through gravity, and investigate the resulting soliton-halo structure via cosmological simulations. Specifically, we assume \\(\\)DM contains \\(75\\) per cent major component and \\(25\\) per cent minor component, fix the major-component particle mass to \\(m_ major=110^-22\\, eV\\), and explore two different minor-component particle masses with \\(m_ major:m_ minor=3:1\\) and \\(1:3\\), respectively. For \\(m_ major:m_ minor=3:1\\), we find that (i) the major- and minor-component solitons coexist, have comparable masses, and are roughly concentric. (ii) The soliton peak density is significantly lower than the single-component counterpart, leading to a smoother soliton-to-halo transition and rotation curve. (iii) The combined soliton mass of both components follows the same single-component core-halo mass relation. In dramatic contrast, for \\(m_ major:m_ minor=1:3\\), a minor-component soliton cannot form with the presence of a stable major-component soliton; the total density profile, for both halo and soliton, is thus dominated by the major component and closely follows the single-component case. To support this finding, we propose a toy model illustrating that it is difficult to form a soliton in a hot environment associated with a deep gravitational potential. The work demonstrates the extra flexibility added to the multi-component \\(\\)DM model can resolve observational tensions over the single-component model while retaining its key features.

Soliton in the hostile turbulent wave dark matter (\\(\\)DM) halo of a galaxy agitates with various kinds of excitation, and the soliton even breathes heavily under great stress. A theory of collective excitation for a \\(\\)DM soliton is presented. The collective excitation has different degrees of coupling to negative energy modes, where lower-order excitation generally necessitates more negative energy coupling. A constrained variational principle is developed to assess the frequencies and mode structures of small-amplitude perturbations. The predicted frequencies are in good agreement with those found in simulations. Soliton breathing at amplitudes on the verge of breakup is also a highlight of this work. Even in this extreme nonlinear regime, the wave function perturbation amplitudes are moderate. The simulation data shows a stable oscillation with frequency weakly dependent on the oscillation amplitude, and hints a self-consistent quasi-linear model for the wave function that accounts for modifications in the ground state wave function and the equilibrium density. The mock solution, constructed from the simulation data, can shed lights on the dynamics of the large-amplitude breathing soliton and supports the quasi-linear model, as evidenced by its ability to well predict the nonlinear eigenfrequency shifts and large-amplitude breathing frequency observed in simulations.

We investigate nonlinear structure formation in the fuzzy dark matter (FDM) model in comparison to cold dark matter (CDM) models from a weak lensing perspective using perturbative methods. We use Eulerian perturbation theory (PT) up to fourth order to compute the tree-level matter trispectrum and the one-loop matter spectrum and bispectrum from consistently chosen initial conditions. In addition, we predict the non-linear matter power spectra using \\(N\\)-body simulations with CDM and FDM initial conditions. We go on to derive the respective lensing spectra, bispectra and trispectra in CDM and FDM in the context of a Euclid-like weak lensing survey. Finally, we compute the attainable cumulative signal-to-noise ratios and an estimate of the attainable \\(^2\\)-functionals for distinguishing FDM from CDM at particle masses \\(m=10^-21\\) eV, \\(m = 10^-22\\) eV and \\(m = 10^-23\\) eV. We find that PT predictions cannot be used to reliably distinguish the three models in a weak lensing survey. Assuming that \\(N\\)-body simulations overestimate the late-time small-scale power in the FDM model, future weak lensing survey might be used to distinguish between the FDM and CDM cases up to a mass of \\(m = 10^-23\\) eV. However, observations probing the local high-\\(z\\) universe are probably more suited to constrain the FDM mass.

The evolution of cosmic perturbations in a two-component ultralight axionic universe is investigated. We present the first spectral computation of perturbations in multi-component universes. A particular case composed of light extreme axions and free massive particles offers a possibility for the formation of very high-redshift massive galaxies, which are typically required to host massive early quasars. Our computation retains the information of perturbed velocities for individual axion components, opening a new avenue for setting up initial conditions for future axion dark matter simulations.