Hierarchical Formation of Dark Matter Halos and the Free Streaming Scale

Ishiyama, Tomoaki

doi:10.1088/0004-637x/788/1/27

Cited by 117 publications

(202 citation statements)

References 66 publications

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“…[6] estimated the resulting boost to the annihilation rate by assuming that all microhalos present at a certain redshift have NFW profiles and that the central regions of these microhalos survive to the present day. All the microhalos were assumed to have the same concentration, c = 2, which is the lowest concentration seen in simulations of microhalo formation [20,21]. This assumption effectively implies that all the microhalos are newly formed at the redshift z f at which the microhalo population is evaluated and therefore provides a conservative estimate of the boost factor.…”

Section: Resultsmentioning

confidence: 99%

Bringing isolated dark matter out of isolation: Late-time reheating and indirect detection

2016

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In standard cosmology, the growth of structure becomes significant following matter-radiation equality. In non-thermal histories, where an effectively matter-dominated phase occurs due to scalar oscillations prior to Big Bang Nucleosynthesis, a new scale at smaller wavelengths appears in the matter power spectrum. Density perturbations that enter the horizon during the early matter-dominated era (EMDE) grow linearly with the scale factor prior to the onset of radiation domination, which leads to enhanced inhomogeneity on small scales if dark matter thermally and kinetically decouples during the EMDE. The microhalos that form from these enhanced perturbations significantly boost the self-annihilation rate for dark matter. This has important implications for indirect detection experiments: the larger annihilation rate may result in observable signals from dark matter candidates that are usually deemed untestable. As a proof of principle, we consider Binos in heavy supersymmetry with an intermediate extended Higgs sector and all other superpartners decoupled. We find that these isolated Binos, which lie under the neutrino floor, can account for the dark matter relic density and decouple from the Standard Model early enough to preserve the enhanced small-scale inhomogeneity generated during the EMDE. If early-forming microhalos survive as subhalos within larger microhalos, the resulting boost to the annihilation rate for Bino dark matter near the pseudoscalar resonance exceeds the upper limit established by Fermi-LAT's observations of dwarf spheroidal galaxies. These DM candidates motivate the N -body simulations required to eliminate uncertainties in the microhalos' internal structure by exemplifying how an EMDE can enable Fermi-LAT to probe isolated dark matter.

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Section: Resultsmentioning

confidence: 99%

Bringing isolated dark matter out of isolation: Late-time reheating and indirect detection

2016

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“…Computing the merger rate in the small halos discussed above requires us to extrapo-late both the halo mass function and the concentrationmass relation around six orders of magnitude in mass beyond the smallest halos present in the calibration simulations. High-resolution simulations of 10 −4 M cold dark matter micro-halos [31,32] suggest that our assumed concentration-mass relations underestimate the internal density of these halos, making our rates conservative.…”

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confidence: 95%

Did LIGO Detect Dark Matter?

et al. 2016

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We consider the possibility that the black-hole (BH) binary detected by LIGO may be a signature of dark matter. Interestingly enough, there remains a window for masses 20 M M bh 100 M where primordial black holes (PBHs) may constitute the dark matter. If two BHs in a galactic halo pass sufficiently close, they radiate enough energy in gravitational waves to become gravitationally bound. The bound BHs will rapidly spiral inward due to emission of gravitational radiation and ultimately merge. Uncertainties in the rate for such events arise from our imprecise knowledge of the phase-space structure of galactic halos on the smallest scales. Still, reasonable estimates span a range that overlaps the 2 − 53 Gpc −3 yr −1 rate estimated from GW150914, thus raising the possibility that LIGO has detected PBH dark matter. PBH mergers are likely to be distributed spatially more like dark matter than luminous matter and have no optical nor neutrino counterparts. They may be distinguished from mergers of BHs from more traditional astrophysical sources through the observed mass spectrum, their high ellipticities, or their stochastic gravitational wave background. Next generation experiments will be invaluable in performing these tests.The nature of the dark matter (DM) is one of the most longstanding and puzzling questions in physics. Cosmological measurements have now determined with exquisite precision the abundance of DM [1, 2], and from both observations and numerical simulations we know quite a bit about its distribution in Galactic halos. Still, the nature of the DM remains a mystery. Given the efficacy with which weakly-interacting massive particlesfor many years the favored particle-theory explanationhave eluded detection, it may be warranted to consider other possibilities for DM. Primordial black holes (PBHs) are one such possibility [3-6].Here we consider whether the two ∼ 30 M black holes detected by LIGO [7] could plausibly be PBHs. There is a window for PBHs to be DM if the BH mass is in the range 20 M M 100 M [8,9]. Lower masses are excluded by microlensing surveys [10][11][12]. Higher masses would disrupt wide binaries [9,13,14]. It has been argued that PBHs in this mass range are excluded by CMB constraints [15,16]. However, these constraints require modeling of several complex physical processes, including the accretion of gas onto a moving BH, the conversion of the accreted mass to a luminosity, the self-consistent feedback of the BH radiation on the accretion process, and the deposition of the radiated energy as heat in the photon-baryon plasma. A significant (and difficult to quantify) uncertainty should therefore be associated with this upper limit [17], and it seems worthwhile to examine whether PBHs in this mass range could have other observational consequences.In this Letter, we show that if DM consists of ∼ 30 M BHs, then the rate for mergers of such PBHs falls within the merger rate inferred from GW150914. In any galactic halo, there is a chance two BHs will undergo a hard scatter, lose energy to a s...

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“…When using c h V we have no parametrization for field halos and only have information for subhalos. Nevertheless, as we discussed above, the concentration in the calibration bin agrees very well with the concentration of field halos, so we use these results along with the concentration of the more massive halos from the BolshoiP simulation (Klypin et al 2011) and that of microhalos from Ishiyama (2014). In order to compute c h V from c h 200 in P12, we assume an NFW profile and use Eq.…”

mentioning

confidence: 95%

“…Some of the reasons have to do with the difficulty in defining and assigning concentrations to subhalos in simulations. As a result, for computing the substructure boost to the DM annihilation signal, a common practice in the past has been the use of the concentration derived from field halos as the concentration of subhalos of the same mass (see, e.g., Lavalle et al (2008); Kuhlen et al (2008);Charbonnier et al (2011);Pinzke et al (2011);Gao et al (2012); Nezri et al (2012); Anderhalden & Diemand (2013);Sánchez-Conde & Prada (2014);Ishiyama (2014)). Although this assumption represents a reasonable first order approximation, the current status of the field is calling for a more refined substructure boost model that relies on more accurate subhalo concentration values.…”

Section: Introductionmentioning

confidence: 99%

“…In order to reduce the uncertainties when extrapolating outside the range probed by these simulations, we also use the results for more massive halos obtained from the BolshoiP simulation (Klypin et al 2011) and those for microhalos obtained by Ishiyama (2014). Formally, the way we add these halos in our subhalo fit is by assuming the subhalo concentration at x sub = 1 to be equal to the concentration of halos of the same mass.…”

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confidence: 99%

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Characterization of subhalo structural properties and implications for dark matter annihilation signals

Moliné

Sánchez‐Conde

Palomares‐Ruiz

et al. 2017

Mon. Not. R. Astron. Soc.

160

295

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A prediction of the standard ΛCDM cosmological model, also confirmed by N-body simulations, is that dark matter (DM) halos are teeming with numerous self-bound substructure, or subhalos. The precise properties of these subhalos represent important probes of the underlying cosmological model. In this work, we use data from the N-body Via Lactea II and ELVIS Milky Way-size simulations to learn about the structure of subhalos with masses 10 6 − 10 11 h −1 M . Thanks to a superb subhalo statistics, by taking a profileindependent approach, we study subhalo properties as a function of the distance to the host halo center and subhalo mass, and provide a set of fits that, including both dependences, accurately describe the subhalo structure. With this at hand, we also investigate the role of subhalos on the search for DM via its annihilation products. Indeed, previous work has shown that subhalos are expected to boost the DM signal of their host halos significantly. Yet, these works have traditionally assumed that subhalos exhibit similar structural properties than those of field halos of the same mass, while it is well known from simulations that subhalos are more concentrated. Building upon the results from our N-body data analysis, we refine the substructure boost model of Sánchez-Conde & Prada (2014). We find boost values that are a factor 2 − 3 higher than previous ones. We further refine our boost model to include unavoidable tidal stripping effects on the subhalo population. For field halos, this only introduces a moderate (∼ 20% − 30%) suppression of the boost. Yet, for subhalos like those hosting the dwarf satellite galaxies of the Milky Way, tidal stripping does play a critical role, the total boost for these objects being only at the level of a few tens of percent in the most optimistic cases. Finally, we provide a parametrization of the boost factor for field halos that can be safely applied over a wide halo mass range.

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Hierarchical Formation of Dark Matter Halos and the Free Streaming Scale

Cited by 117 publications

References 66 publications

Bringing isolated dark matter out of isolation: Late-time reheating and indirect detection

Bringing isolated dark matter out of isolation: Late-time reheating and indirect detection

Did LIGO Detect Dark Matter?

Characterization of subhalo structural properties and implications for dark matter annihilation signals

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