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Register a new userN-body simulations of dark matter with frequent self-interactions
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Self-interacting dark matter (SIDM) models have the potential to solve the small-scale problems that arise in the cold dark matter paradigm. Simulations are a powerful tool for studying SIDM in the context of astrophysics, but it is numerically challenging to study differential cross-sections that favour small-angle scattering, as in light-mediator models. Here, we present a novel approach to model frequent scattering based on an effective drag force, which we have implemented into the N-body code gadget-3. In a range of test problems, we demonstrate that our implementation accurately models frequent scattering. Our implementation can be used to study differences between SIDM models that predict rare and frequent scattering. We simulate core formation in isolated dark matter haloes, as well as major mergers of galaxy clusters and find that SIDM models with rare and frequent interactions make different predictions. In particular, frequent interactions are able to produce larger offsets between the distribution of galaxies and dark matter in equal-mass mergers.
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We revisit constraints on annihilating dark matter based on the global 21cm signature observed by EDGES. For this purpose, we used the numerical data of the latest N-body simulation performed by state-of-art standard in order to estimate the boost factor at high redshifts ($z$ = 10 - 100), which enhances the annihilation of dark matter in course of structure formation. By taking into account to what fraction injected energy from dark matter annihilation contributes to ionization, excitation and heating of intergalactic medium during dark ages, we estimated how large the global 21cm absorption can be. By assuming the thermal freezeout scenario, we find that $m_{rm DM} < 15$ GeV and $m_{rm DM} < 3$ GeV have been excluded at 95$%$ C.L. for the annihilation modes into $bbar{b}$ and $e^+ e^-$, respectively.
Dark matter particles may decay, emitting photons. Drawing on the EAGLE family of hydrodynamic simulations of galaxy formation -- including the APOSTLE and C-EAGLE simulations -- we assess the systematic uncertainties and scatter on the decay flux from different galaxy classes, from Milky Way satellites to galaxy clusters, and compare our results to studies of the 3.55~keV line. We demonstrate that previous detections and non-detections of this line are consistent with a dark matter interpretation. For example, in our simulations the width of the the dark matter decay line for Perseus-analogue galaxy clusters lies in the range 1300-1700~kms. Therefore, the non-detection of the 3.55~keV line in the centre of the Perseus cluster by the {it Hitomi} collaboration is consistent with detections by other instruments. We also consider trends with stellar and halo mass and evaluate the scatter in the expected fluxes arising from the anisotropic halo mass distribution and from object-to-object variations. We provide specific predictions for observations with {it XMM-Newton} and with the planned X-ray telescopes {it XRISM} and {it ATHENA}. If future detections of unexplained X-ray lines match our predictions, including line widths, we will have strong evidence that we have discovered the dark matter.
We study the density structures of dark matter subhalos for both cold dark matter and self-interacting dark matter models using high-resolution cosmological $N$-body simulations. We quantify subhalos central density at 150 pc from the center of each subhalo at the classical dwarf spheroidal and ultrafaint dwarf scales. By comparing them with observations, we find that the self-interacting scattering cross-section of $sigma/m<3 rm{cm^{2}g^{-1}}$ is favored. Due to the combination of hosts tide and self-interactions, the central density of subhalos with small pericenter shows a noticeable difference between the cold and the self-interacting models, indicating that dwarf satellites with small pericenter are ideal sites to further constrain the nature of dark matter by future large spectroscopic surveys.
We present a general framework for obtaining robust bounds on the nature of dark matter using cosmological $N$-body simulations and Lyman-alpha forest data. We construct an emulator of hydrodynamical simulations, which is a flexible, accurate and computationally-efficient model for predicting the response of the Lyman-alpha forest flux power spectrum to different dark matter models, the state of the intergalactic medium (IGM) and the primordial power spectrum. The emulator combines a flexible parameterization for the small-scale suppression in the matter power spectrum arising in non-cold dark matter models, with an improved IGM model. We then demonstrate how to optimize the emulator for the case of ultra-light axion dark matter, presenting tests of convergence. We also carry out cross-validation tests of the accuracy of flux power spectrum prediction. This framework can be optimized for the analysis of many other dark matter candidates, e.g., warm or interacting dark matter. Our work demonstrates that a combination of an optimized emulator and cosmological effective theories, where many models are described by a single set of equations, is a powerful approach for robust and computationally-efficient inference from the cosmic large-scale structure.
Observations show that supermassive black holes (SMBHs) with a mass of $sim10^9 M_odot$ exist when the Universe is just $6%$ of its current age. We propose a scenario where a self-interacting dark matter halo experiences gravothermal instability and its central region collapses into a seed black hole. The presence of baryons in protogalaxies could significantly accelerate the gravothermal evolution of the halo and shorten collapse timescales. The central halo could dissipate its angular momentum remnant via viscosity induced by the self-interactions. The host halo must be on high tails of density fluctuations, implying that high-$z$ SMBHs are expected to be rare in this scenario. We further derive conditions for triggering general relativistic instability of the collapsed region. Our results indicate that self-interacting dark matter can provide a unified explanation for diverse dark matter distributions in galaxies today and the origin of SMBHs at redshifts $zsim6-7$.
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