A New Probe of Dark Matter and High-Energy Universe Using Microlensing

Ricotti, Massimo; Gould, Andrew

doi:10.1088/0004-637x/707/2/979

Cited by 171 publications

(284 citation statements)

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“…Primordial black holes (PBHs) are an alternative, disfavoured by their energetic evaporation, gravitational influence [6], and the large primordial density perturbations required for their production (δ 30%). For comparison, the initial density perturbations from inflation were δ ∼ 10 −5 .Ricotti & Gould [7] proposed a non-baryonic MACHO that avoids these constraints, and presents a promising new target for microlensing searches. Formation proceeds similarly to PBHs, whereby small-scale density perturbations in the early Universe collapse to a compact body.…”

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confidence: 99%

“…We present predicted fluxes and discuss prospects for detection with satellite missions and AirČerenkov telescopes (ACTs). In an appendix, we also give explicit predictions from a supersymmetric framework with a neutralino WIMP.Following matter-radiation equality, ultracompact minihalos accrete matter by radial infall [7] aswhere M h (z) is the total mass of the UCMH at redshift z, and z eq is the redshift of matter-radiation equality. We assume that UCMHs at z = 0 grew only until z = 10, because by this time structure formation would have progressed sufficiently far to prevent further accretion [10].…”

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confidence: 99%

“…Ricotti & Gould [7] proposed a non-baryonic MACHO that avoids these constraints, and presents a promising new target for microlensing searches. Formation proceeds similarly to PBHs, whereby small-scale density perturbations in the early Universe collapse to a compact body.…”

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confidence: 99%

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Gamma Rays from Ultracompact Primordial Dark Matter Minihalos

Scott

Sivertsson

2009

Phys. Rev. Lett.

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Ultracompact minihalos have recently been proposed as a new class of dark matter structure. These minihalos would be produced by phase transitions in the early Universe or features in the inflaton potential, and constitute non-baryonic massive compact halo objects (MACHOs) today. We examine the prospect of detecting ultracompact minihalos in gamma-rays if dark matter consists of self-annihilating particles. We compute present-day fluxes from minihalos produced in the e + e − annihilation epoch, and the QCD and electroweak phase transitions in the early Universe. Even at a distance of 100 pc, minihalos produced during the e + e − epoch should be eminently detectable today, either by the Fermi satellite, current AirČerenkov telescopes, or even in archival EGRET data. Within ∼1 pc, minihalos formed in the QCD phase transition would have similar predicted fluxes to the dwarf spheroidal galaxies targeted by current indirect dark matter searches, so might also be detectable by present or upcoming experiments.PACS numbers: 95.35.+d, 98.70.Rz, 98.80.Cq The identity of dark matter remains one of the key outstanding problems in physics. Weakly-interacting massive particles (WIMPs) provide a compelling solution [1] because their weak-scale masses and cross-sections make for a natural explanation of the observed abundance of dark matter. As most proposed WIMPs are their own antiparticles, high WIMP densities would also lead to high rates of self-annihilation. Annihilation products might then provide indirect evidence of the nature of dark matter. Gamma-rays are particularly attractive in this respect, as they do not suffer the same problems of deflection and attenuation as massive, charged species.It was proposed [2] that dark matter could be massive compact halo objects (MACHOs) of condensed baryons, e.g. brown dwarfs or faint stars. These are ruled out as the dominant component of dark matter by the cosmic microwave background (CMB; [3]), Big Bang Nucleosynthesis [4], and microlensing searches [5]. Primordial black holes (PBHs) are an alternative, disfavoured by their energetic evaporation, gravitational influence [6], and the large primordial density perturbations required for their production (δ 30%). For comparison, the initial density perturbations from inflation were δ ∼ 10 −5 .Ricotti & Gould [7] proposed a non-baryonic MACHO that avoids these constraints, and presents a promising new target for microlensing searches. Formation proceeds similarly to PBHs, whereby small-scale density perturbations in the early Universe collapse to a compact body. A small-scale power spectrum that is the same as observed on large scales [3] provides insufficient power for this to occur. Perturbations could however be enhanced by features in the inflaton potential, or phase transitions in the early Universe [8]. If a perturbation is small, matter will not be sufficiently compressed to form a black hole, leaving only a compact cloud of gas and dark matter. This mechanism requires density contrasts of just δ 10 −3 to proceed, so is fa...

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Gamma Rays from Ultracompact Primordial Dark Matter Minihalos

Scott

Sivertsson

2009

Phys. Rev. Lett.

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“…As can be read from (27), unlike δ m , δ r is sourced by both θ r and δ φ because there is steady production of radiation from φ. The corresponding isocurvature part becomes B iso k .…”

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confidence: 99%

Isocurvature Perturbation of Weakly Interacting Massive Particles and Small Scale Structure

2015

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The adiabatic perturbation of dark matter is damped during the kinetic decoupling due to the collision with relativistic component on sub-horizon scales. However the isocurvature part is free from damping and could be large enough to make a substantial contribution to the formation of small scale structure. We explicitly study the weakly interacting massive particles as dark matter with an early mater dominated period before radiation domination and show that the isocurvature perturbation is generated during the phase transition and leaves imprint in the observable signatures for small scale structure.

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“…PBHs have not been observed yet, and constraints from their non-observations have been used [14,[17][18][19][20][21] to place (currently weak) upper limits on the amplitude of the power spectrum over a very wide range of scales (from k ∼ 10 −2 Mpc −1 to k ∼ 10 23 Mpc −1 [14]). Similar arguments are behind another type of constraints on the power spectrum at small scales, namely those from the non-observations of ultra-compact minihalos of dark matter (UCMHs) [22,23] that are expected to have formed shortly after matterradiation equality when a perturbation with a very large amplitude but not large enough to collapse to a black hole enters the horizon [24][25][26].…”

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confidence: 77%

Uncertainties in primordial black-hole constraints on the primordial power spectrum

Akrami

Kühnel

Sandstad

2018

Physics of the Dark Universe

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The existence (and abundance) of primordial black holes (PBHs) is governed by the power spectrum of primordial perturbations generated during inflation. So far no PBHs have been observed, and instead, increasingly stringent bounds on their existence at different scales have been obtained. Up until recently, this has been exploited in attempts to constrain parts of the inflationary power spectrum that are unconstrained by cosmological observations. We first point out that the simple translation of the PBH non-observation bounds into constraints on the primordial power spectrum is inaccurate as it fails to include realistic aspects of PBH formation and evolution. We then demonstrate, by studying two examples of uncertainties from the effects of critical and non-spherical collapse, that even though they may seem small, they have important implications for the usefulness of the constraints. In particular, we point out that the uncertainty induced by non-spherical collapse may be much larger than the difference between particular bounds from PBH non-observations and the general maximum cap stemming from the condition Ω ≤ 1 on the dark-matter density in the form of PBHs. We therefore make the cautious suggestion of applying only the overall maximum dark-matter constraint to models of early Universe, as this requirement seems to currently provide a more reliable constraint, which better reflects our current lack of detailed knowledge of PBH formation. These, and other effects, such as merging, clustering and accretion, may also loosen constraints from non-observations of other primordial compact objects such as ultra-compact minihalos of dark matter.Keywords: primordial black holes, primordial power spectrum, dark matter Introduction -Cosmological observations, in particular those of the cosmic microwave background (CMB) anisotropies [1, 2], place tight constraints on the properties of the primordial density (or curvature) fluctuations on large scales through the accurate measurements of the primordial power spectrum [1,3]. These measurements, however, probe only a relatively small range of scales, ie., wave numbers between k ∼ 10 −3 Mpc −1 and k ∼ 1 Mpc −1 . Even though the measured power spectrum on these cosmological scales provides strong evidence in support of an inflationary phase [4][5][6][7] in the early Universe, and constrains various inflationary models and their parameters [3], it only probes a small region of the inflaton potential. It has therefore been of importance to try to extend the constraints on the curvature power spectrum to a wider range of scales using other cosmological and astrophysical measurements. Power-spectrum constraints have been extended to k ∼ 10 4 Mpc −1 through measurements of the CMB spectral distortions [8,9], and to k ∼ 10 4 Mpc −1 using constraints on entropy production between Big Bang nucleosynthesis and today [10], although these are currently only (fairly weak) upper bounds on the amplitude of the spectrum.One important set of such additional constraints on small scales has...

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A New Probe of Dark Matter and High-Energy Universe Using Microlensing

Cited by 171 publications

References 26 publications

Gamma Rays from Ultracompact Primordial Dark Matter Minihalos

Gamma Rays from Ultracompact Primordial Dark Matter Minihalos

Isocurvature Perturbation of Weakly Interacting Massive Particles and Small Scale Structure

Uncertainties in primordial black-hole constraints on the primordial power spectrum

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