Structure formation during an early period of matter domination

Dark matter may be in the form of non-baryonic structures such as compact subhalos and boson stars. Structures weighing between asteroid and solar masses may be discovered via gravitational microlensing, an astronomical probe that has in the past helped constrain the population of primordial black holes and baryonic machos. We investigate the non-trivial effect of the size of and density distribution within these structures on the microlensing signal, and constrain their populations using the eros- and ogle-iv surveys. Structures larger than a solar radius are generally constrained more weakly than point-like lenses, but stronger constraints may be obtained for structures with mass distributions that give rise to caustic crossings or produce larger magnifications.

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“…Finally, it would be interesting to investigate the effect on our constraints of varying the magnification threshold in Eq. (6).…”

Section: Discussionmentioning

confidence: 99%

Gravitational microlensing by dark matter in extended structures

2020

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“…The relativistic decay products of the scalar field inherit this inhomogeneity; subhorizon perturbations in the radiation density grow during an EMDE, but that growth is lost when the Universe becomes radiation dominated [51]. When dark matter annihilations are added to scenarios in which dark matter is primarily produced during scalar decays, the dark matter perturbations still grow linearly during the EMDE, but they decrease slightly when much of the dark matter annihilates during the transition to radiation domination [53,54].…”

Section: B Perturbation Evolutionmentioning

confidence: 99%

The dark matter annihilation boost from low-temperature reheating

Erickcek

2015

Phys. Rev. D

185

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The evolution of the Universe between inflation and the onset of Big Bang Nucleosynthesis is difficult to probe and largely unconstrained. This ignorance profoundly limits our understanding of dark matter: we cannot calculate its thermal relic abundance without knowing when the Universe became radiation dominated. Fortunately, small-scale density perturbations provide a probe of the early Universe that could break this degeneracy. If dark matter is a thermal relic, density perturbations that enter the horizon during an early matter-dominated era grow linearly with the scale factor prior to reheating. The resulting abundance of substructure boosts the annihilation rate by several orders of magnitude, which can compensate for the smaller annihilation cross sections that are required to generate the observed dark matter density in these scenarios. In particular, thermal relics with masses less than a TeV that thermally and kinetically decouple prior to reheating may already be ruled out by Fermi-LAT observations of dwarf spheroidal galaxies. Although these constraints are subject to uncertainties regarding the internal structure of the microhalos that form from the enhanced perturbations, they open up the possibility of using gamma-ray observations to learn about the reheating of the Universe.

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“…In this article, we study the growth of small-scale struc-ture in hidden sector dark matter scenarios and discuss the impact of such structure on the prospects for indirect detection. During an early matter-dominated era (EMDE), matter density perturbations grow linearly, in contrast to the logarithmic growth that occurs during standard radiation domination [29][30][31][32]. This rapid growth enhances small-scale inhomogeneity and can trigger the formation of numerous sub-earth-mass microhalos long before structure would form in the absence of an EMDE.…”

Section: Introductionmentioning

confidence: 99%

Annihilation signatures of hidden sector dark matter within early-forming microhalos

et al. 2019

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If the dark matter is part of a hidden sector with only very feeble couplings to the Standard Model, the lightest particle in the hidden sector will generically be long-lived and could come to dominate the energy density of the universe prior to the onset of nucleosynthesis. During this early matter-dominated era, density perturbations will grow more quickly than otherwise predicted, leading to a large abundance of sub-earth-mass dark matter microhalos. Since the dark matter does not couple directly to the Standard Model, the minimum halo mass is much smaller than expected for weakly interacting dark matter, and the smallest halos could form during the radiation-dominated era. In this paper, we calculate the evolution of density perturbations within the context of such hidden sector models and use a series of N -body simulations to determine the outcome of nonlinear collapse during radiation domination. The resulting microhalos are extremely dense, which leads to very high rates of dark matter annihilation and to large indirect detection signals that resemble those ordinarily predicted for decaying dark matter. We find that the Fermi Collaboration's measurement of the high-latitude gamma-ray background rules out a wide range of parameter space within this class of models. The scenarios that are most difficult to constrain are those that feature a very long early matter-dominated era; if microhalos form prior to the decay of the unstable hidden sector matter, the destruction of these microhalos effectively heats the dark matter, suppressing the later formation of microhalos.

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Structure formation during an early period of matter domination

Cited by 53 publications

References 23 publications

Gravitational microlensing by dark matter in extended structures

Gravitational microlensing by dark matter in extended structures

The dark matter annihilation boost from low-temperature reheating

Annihilation signatures of hidden sector dark matter within early-forming microhalos

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