The International Gamma-Ray Astrophysics Laboratory (INTEGRAL) satellite has yielded unprecedented measurements of the soft gamma-ray spectrum of our Galaxy. Here we use those measurements to set constraints on dark matter (DM) that decays or annihilates into photons with energies $E\approx 0.02-2$ MeV. First, we revisit the constraints on particle DM that decays or annihilates to photon pairs. In particular, for decaying DM, we find that previous limits were overstated by roughly an order of magnitude. Our new, conservative analysis finds that the DM lifetime must satisfy $τ\gtrsim 5\times 10^{26}\,{\rm s}\times (m_χ/\rm MeV)^{-1}$ for DM masses $m_χ=0.054-3.6$ MeV. For MeV-scale DM that annihilates into photons INTEGRAL sets the strongest constraints to date. Second, we target ultralight primordial black holes (PBHs) through their Hawking radiation. This makes them appear as decaying DM with a photon spectrum peaking at $E\approx 5.77/(8πG M_{\rm PBH})$, for a PBH of mass $M_{\rm PBH}$. We use the INTEGRAL data to demonstrate that, at 95\% C.L., PBHs with masses less than $1.2\times 10^{17}$ g cannot comprise all of the DM, setting the tightest bound to date on ultralight PBHs.
Light, asteroid-mass primordial black holes, with lifetimes in the range between hundreds to several millions times the age of the universe, are well-motivated candidates for the cosmological dark matter. Using archival COMPTEL data, we improve over current constraints on the allowed parameter space of primordial black holes as dark matter by studying their evaporation to soft gamma-rays in nearby astrophysical structures. We point out that a new generation of proposed MeV gamma-ray telescopes will offer the unique opportunity to directly detect Hawking evaporation from observations of nearby …
The mechanism of the generation of dark matter and dark radiation from the evaporation of primordial black holes is very interesting. We consider the case of Kerr black holes to generalize previous results obtained in the Schwarzschild case. For dark matter, the results do not change dramatically and the bounds on warm dark matter apply similarly: in particular, the Kerr case cannot save the scenario of black hole domination for light dark matter. For dark radiation, the expectations for $ΔN_{eff}$ do not change significantly with respect to the Schwarzschild case, but for an enhancement in th…
The radiation emitted by horizonless exotic compact objects (ECOs), such as wormholes, 2-2-holes, fuzzballs, gravastars, boson stars, collapsed polymers, superspinars etc., is expected to be strongly suppressed when compared to the radiation of black holes. If large primordial curvature fluctuations collapse into such objects instead of black holes, they do not evaporate or evaporate much slower than black holes and could thus constitute all of the dark matter with masses below $M < 10^{-16}M_\odot.$ We reevaluate the relevant experimental constraints for light ECOs in this mass range and show…
We derive the strongest constraint on the fraction of dark matter that can be composed of low mass primordial black holes by using the observation of the Galactic Center 511 keV gamma-ray line. Primordial black holes of masses $\lesssim$ 10$^{15}$ kg will evaporate to produce $e^\pm$ pairs. The positrons will lose energy in the Galactic Center, become non-relativistic, and then annihilate with the ambient electrons. We derive robust and conservative bounds by assuming that the rate of positron injection via primordial black hole evaporation is less than what is required to explain the SPI/ INT…
We investigate photon signatures of general decaying dark-matter particles in halos of primordial black holes. We derive the halo-profile density and the total decay rate for these combined dark-matter scenarios. For the case of axion-like particles of masses below $\mathcal{O}( 1 )\,$keV, we find strong bounds on the decay constant which are several orders of magnitude stronger than the strongest existing bounds, for all halo masses above $\mathcal{O}( 10^{-5} )$ solar masses. Using future X-ray measurements, it will be possible to push these bounds on such combined dark-matter scenarios even…
Models of Co-Decaying dark matter lead to an early matter dominated epoch -- prior to BBN -- which results in an enhancement of the growth of dark matter substructure. If these primordial structures collapse further they can form primordial black holes providing an additional dark matter candidate. We derive the mass fraction in these black holes (which is not monochromatic) and consider observational constraints on how much of the dark matter could be comprised in these relics. We find that in many cases they can be a significant fraction of the dark matter. Interestingly, the masses of these…
The structure and evolution of Primordial Antimatter domains and Dark matter objects are analysed. Relativistic low-density antimatter domains are described. The Relativistic FRW perfect-fluid solution is found for the characterization of i) ultra-high density antimatter domains, ii) high-density antimatter domains, and iii) dense anti-matter domains. The possible sub-domains structures is analyzed. The structures evolved to the time of galaxy formation are outlined. Comparison is given with other primordial celestial objects. The features of antistars are outlined. In the case of WIMP dark ma…
Primordial black holes are produced in a minimal UV extension to the Higgs inflation with an included $R^2$ term. We show that for parameters consistent with Standard Model measurements and Planck observation results lead to $M_{\rm PBH} \in (10^{-16}, 10^{-15}) M_\odot$ primordial black holes with significant abundance, which may consist the majority of dark matter.
Combining constraints from microlensing and Lyman-$α$ forest, we provide a simple argument to show that large spatial clustering of stellar-mass primordial black holes at the time of formation, such as the one induced by the presence of large non-Gaussianities, is ruled out. Therefore, it is not possible to evade existing constraints preventing stellar-mass primordial black holes to be a dominant constituent of the dark matter by boosting their initial clustering.
Primordial black holes (PBHs) are expected to accrete particle dark matter around them to form ultracompact minihalos (UCMHs), if the PBHs themselves are not most of the dark matter. We show that if most dark matter is a thermal relic, then the inner regions of UCMHs around PBHs are highly luminous sources of annihilation products. Flux constraints on gamma rays and neutrinos set strong abundance limits, improving previous limits by orders of magnitude. Assuming enough particle dark matter exists to form UCMHs, we find that Omega_PBH <~ 10^-4 (for m_DM c^2 ~ 100 GeV) for a vast range in PBH ma…
We revisit constraints on small-scale primordial power from annihilation signals from dark matter minihalos. Using gamma rays and neutrinos from extragalactic minihalos and assuming the delta-function primordial spectrum, we show the dependence of the constraints on annihilation modes, the mass of dark matter, and the annihilation cross section. We report both conservative constraints by assuming minihalos are fully destructed when becoming part of halos originating from the standard almost-scale invariant primordial spectrum, and optimistic constraints by neglecting destruction.
Primordial black holes and secondary gravitational waves can be used to probe the small scale physics at very early time. For secondary gravitational waves produced after the horizon reentry, we derive an analytical formula for the time integral of the source and analytical behavior of the time dependence of the energy density of induced gravitational waves is obtained. By proposing a piecewise power law parametrization for the power spectrum of primordial curvature perturbations, we use the observational constraints on primordial black hole dark matter to obtain an upper bound on the power sp…
The NANOGrav Collaboration has recently published a strong evidence for a stochastic common-spectrum process that may be interpreted as a stochastic gravitational wave background. We show that such a signal can be explained by second-order gravitational waves produced during the formation of primordial black holes from the collapse of sizeable scalar perturbations generated during inflation. This possibility has two predictions: $i$) the primordial black holes may comprise the totality of the dark matter with the dominant contribution to their mass function falling in the range $(10^{-15}÷10^{…
We demonstrate that adiabatic dark matter can be generated by gravity induced symmetry breaking during inflation. We study a $Z_2$ symmetric scalar singlet that couples to other fields only through gravity and for which the symmetry is broken by the spacetime curvature during inflation when the non-minimal coupling $ξ$ is negative. We find that the symmetry breaking leads to the formation of adiabatic dark matter with the observed abundance for the singlet mass $m\sim{\rm MeV}$ and $|ξ|\sim 1$.
The evaporation of primordial black holes with a mass in the $1\ {\rm gram}\lesssim M_{\rm PBH}\lesssim$1000 kg range can lead to the production of dark matter particles of almost any mass in the range $0.1\ {\rm MeV}\lesssim m_{\rm DM}\lesssim 10^{18}$ GeV with the right relic density at very early times, $τ\lesssim 10^{-10}$ s. We calculate, as a function of the primordial black holes mass and initial abundance, the combination of dark matter particle masses and number of effective dark degrees of freedom leading to the right abundance of dark matter today, whether or not evaporation stops a…
We consider a general class of axion models, including the QCD and string axion, in which the PQ symmetry is broken before or during inflation. Assuming the axion is the dominant component of the dark matter, we discuss axion star formation in virialized dark minihalos around primordial black holes through gravitational Bose-Einstein condensation. We determine the conditions for minihalos to kinetically produce axion stars before galaxy formation. Today, we expect up to $\sim 10^{17}$ ($\sim 10^9$) axion stars in a radius of 100 parsecs around the Sun for the case of the QCD (string) axion.
We report on a study of the natural warm inflationary paradigm (WNI). We show two important new results arise in this model. One is that the observational constraints on the primordial power spectrum from the cosmic microwave background (CMB) can be satisfied without going beyond the Planck scale of the effective field theory. The second is that WNI can inevitably provide perfect conditions for the production of primordial black holes (PBHs) in the golden window of black-hole mass range ($10^{-16} -10^{-11}M_{\odot}$) where it can account for all of the the dark matter content of the universe …
Primordial black holes (PBHs) in the asteroid-mass range $(10^{-17}$--$10^{-12})~M_{\odot}$ almost entirely escape constraints as dark matter candidates. In the early universe, however, the Schwarzschild metric is no longer applicable and we must carefully consider PBH metrics with a proper cosmological embedding. In particular, the Thakurta solution stands out as perhaps the most adequate such solution. Notably, the Thakurta metric contains a time-dependent apparent horizon, proportional to the cosmological scale-factor. We show that this implies the PBHs are hotter than in the standard Schwa…
Primordial black holes in the mass range from $10^{-5}$ to $10^9$ g might have existed in the early universe. Via their evaporation mechanism (completed before Big Bang Nucleosynthesis), they might have released stable particles beyond the Standard Model. We reconsider the possibility that such particles might constitute the main part or a fraction of the dark matter observed today, updating the impact on this scenario from warm dark matter constraints. If sufficiently light, stable particles from primordial black holes evaporation might also provide a significant contribution to dark radiatio…
The idea of dark matter in the form of primordial black holes has seen a recent revival triggered by the LIGO detection of gravitational waves from binary black hole mergers. In this context, it has been argued that a large initial clustering of primordial black holes can help alleviate the strong constraints on this scenario. In this work, we show that on the contrary, with large initial clustering the problem is exacerbated and constraints on primordial black hole dark matter become overwhelmingly strong.
For the current central values of the Higgs and top masses, the Standard Model Higgs potential develops an instability at a scale of the order of $10^{11}$ GeV. We show that a cosmological signature of such instability could be dark matter in the form of primordial black holes seeded by Higgs fluctuations during inflation. The existence of dark matter might not require physics beyond the Standard Model.
We show that primordial (nearly) extremal black holes with a wide range of masses from the Planck scale to around $10^9$ g could be cosmologically stable and explain dark matter, given a dark electromagnetism and a heavy dark electron. For individual black holes, Hawking radiation and Schwinger discharge processes are suppressed by near-extremality and the heaviness of the dark electron, respectively. In contrast, the merger events of binary systems provide an opportunity to directly observe Hawking radiation. Because the merger products are not extremal, they rapidly evaporate and produce tra…
We review the formation and evaporation of primordial black holes (PBHs) and their possible contribution to dark matter. Various constraints suggest they could only provide most of it in the mass windows $10^{17}$ - $10^{23}\,$g or $10$ - $10^{2}\,M_{\odot}$, with the last possibility perhaps being suggested by the LIGO/Virgo observations. However, PBHs could have important consequences even if they have a low cosmological density. Sufficiently large ones might generate cosmic structures and provide seeds for the supermassive black holes in galactic nuclei. Planck-mass relics of PBH evaporatio…
The primordial black hole (PBH) comprising full dark matter (DM) abundance is currently allowed if its mass lies between $10^{-16}M_{\odot} \lesssim M \lesssim 10^{-11} M_{\odot}$. This lightest mass range is hard to be probed by ongoing gravitational lensing observations. In this paper, we advocate that an old idea of the lensing parallax of Gamma-ray bursts (GRBs), observed simultaneously by spatially separated detectors, can probe the unconstrained mass range; and that of nearby stars can probe a heavier mass range. In addition to various good properties of GRBs, astrophysical separations a…
Primordial black holes can have substantial spin -- a fundamental property that has a strong effect on its evaporation rate. We conduct a comprehensive study of the detectability of primordial black holes with non-negligible spin, via the searches for the neutrinos and positrons in the MeV energy range. Diffuse supernova neutrino background searches and observation of the 511 keV gamma-ray line from positrons in the Galactic center set competitive constraints. Spinning primordial black holes are probed up to a slightly higher mass range compared to non-spinning ones. Our constraint using neutr…
We consider light dark matter candidates originated from the evaporation of Schwarzschild primordial black holes, with masses in the range $10^{-5}-10^9$ g. These candidates are beyond Standard Model particles with negligible couplings to the other particles, so that they interact only gravitationally. Belonging to the category of warm dark matter, they nevertheless spoil structure formation, with a softer impact for increasing values of the candidate spin. Requiring such candidates to fully account for the observed dark matter, we find that the scenario of black hole domination is ruled out f…
If light enough primordial black holes (PBH) account for dark matter, then its density decreases with time as they lose mass via Hawking radiation. We show that this time-dependence of the matter density can be formulated as an equivalent $w(z)$ dark energy model and we study its implications on the expansion history. Using our approach and comparing with the latest cosmological data, including the supernovae type Ia, Baryon Acoustic Oscillations, Cosmic Microwave Background and the Hubble expansion H(z) data, we place observational constraints on the PBH model. We find that it is statisticall…
We consider the possibility that the majority of dark matter in our Universe consists of black holes of primordial origin. We determine the conditions under which such black holes may have originated from a single-field model of inflation characterized by a quartic polynomial potential. We also explore the effect of higher-dimensional operators. The large power spectrum of curvature perturbations that is needed for a large black hole abundance sources sizable second order tensor perturbations. The resulting stochastic background of primordial gravitational waves could be detected by the future…
Primordial black holes (PBHs) are not as exotic as once thought and constitute a compelling non-particle dark matter (DM) candidate. We present a novel general PBH formation mechanism from scalar field fragmentation, which does not suffer from the inflaton potential fine-tuning that plagues many of the standard PBH formation models. We discuss how interactions of compact stars with very small sub-lunar/asteroid-size PBHs, which reside in the open window of parameter space where PBHs can constitute all of DM, allow for a slew of new astrophysical signatures that could shed light on PBH DM and a…
Primordial Black Holes (PBHs) with a mass $M \lesssim {10^{17}}$g are expected to inject sub-GeV electrons and positrons in the Galaxy via Hawking radiation. These cosmic rays are shielded by the solar magnetic field for Earth-bound detectors, but not for Voyager-1, which is now beyond the heliopause. We use its data to constrain the fraction of PBHs to the dark matter in the Galaxy, finding that PBHs with $M<10^{16}$g cannot contribute more than 0.1% (or less for a lognormal mass distribution). Our limits are based on local galactic measurements and are thus complementary to those derived fro…
We investigate the effects of producing dark matter by Hawking evaporation of primordial black holes (PBHs) in scenarios that may have a second well-motivated dark matter production mechanism, such as freeze-out, freeze-in, or gravitational production. We show that the interplay between PBHs and the alternative sources of dark matter can give rise to model-independent modifications to the required dark matter abundance from each production mechanism, which in turn affect the prospects for dark matter detection. In particular, we demonstrate that for the freeze-out mechanism, accounting for eva…
We show that current cosmic acceleration can be explained by an almost massless scalar field experiencing quantum fluctuations during primordial inflation. Provided its mass does not exceed the Hubble parameter today, this field has been frozen during the cosmological ages to start dominating the universe only recently. By using supernovae data, completed with baryonic acoustic oscillations from galaxy surveys and cosmic microwave background anisotropies, we infer the energy scale of primordial inflation to be around a few TeV, which implies a negligible tensor-to-scalar ratio of the primordia…
X-ray signals converted from high-frequency gravitational waves emitted by spinning light primordial black hole dark matter
Kobe University（神户大学）；National Astronomical Observatory of Japan（日本国立天文台）；The University of Tokyo（东京大学）；SOKENDAI（综合研究大学院大学）；KEK（高能加速器研究机构）；Kavli IPMU (WPI), UTIAS, The University of Tokyo（卡弗里宇宙物理学起源研究所（世界顶尖科学研究中心），东京大学宇宙边疆机构）
Dark matter(DM) is the only possible candidate which would be apart from the thermal equilibrium before Big Bang nucleosynthesis(BBN) in accordance with current DM searches. In this work, we report a generic scenario that primordial perturbation of dark matter(PPDM) can be, effectively, generated and encoded with primordial information of very early universe up to the reheating era. We present an analytical solution of the whole evolution of PPDM. A novel and strong constraint on the reheating process imposed by primordial gravitational wave(PGW) is obtained for the first time. It indicates th…
Constraining the inflationary epoch is one of the aims of modern cosmology. In order to fully exploit current and future small-scale observations, it is necessary to devise tools to directly relate them to the early universes dynamics. We present here a novel reverse engineer approach able to connect fundamental late-time observables to consistent inflationary dynamics and, eventually, to the inflaton potential. Employing this procedure, we are able to describe which conditions can give rise to a raised plateau in the power spectrum of curvature perturbations at small scales, which are not con…
Light black holes could have formed in the very early universe through the collapse of large primordial density fluctuations. These primordial black holes (PBHs), if light enough, would have evaporated by now because of the emission of Hawking radiation; thus they could not represent a sizable fraction of dark matter today. However, they could have left imprints in the early cosmological epochs. We will discuss the impact of massless graviton emission by (rotating) PBHs before the onset of big bang nucleosynthesis (BBN) and conclude that this contribution to dark radiation is constrained by th…
We argue that primordial dark matter halos could be generated during radiation domination by long range attractive forces stronger than gravity. In this paper we derive the conditions under which these structures could dominate the dark matter content of the Universe while passing microlensing constraints and cosmic microwave background energy injection bounds. The dark matter particles would be clumped in objects in the solar mass range with typical sizes of the order of the solar system. Consequences for direct dark matter searches are important.
We argue that a primordial black hole is a natural and unique candidate for all dark matter. We show that, in a smooth-hybrid new double inflation model, a right amount of the primordial black holes, with a sharply-defined mass, can be produced at the end of the smooth-hybrid regime, through preheating. We first consider masses < 10^(-7)M_sun which are allowed by all the previous constraints. We next discuss much heavier mass 10^5 M_sun hinted at by entropy, and galactic size evolution, arguments. Effects on the running of the scalar spectral index are computed.
We calculate the early universe evolution of perturbations in the dark matter energy density in the context of simple dark sector models containing a GeV scale light mediator. We consider the case that the mediator is long lived, with lifetime up to a second, and before decaying it temporarily dominates the energy density of the universe. We show that for primordial perturbations that enter the horizon around this period, the interplay between linear growth during matter domination and collisional damping can generically lead to a sharp peak in the spectrum of dark matter density perturbation.…
In light of our previous work \cite{Liu:2019xhn}, we investigate the possibility of the formation of a primordial black hole in the second inflationary process induced by the oscillation of curvaton. By adopting the instability of the Mathieu equation, one could utilize the $δ$ function to fully describe the power spectrum. Due to the running of curvaton mass, we can simulate the value of abundance of primordial black holes nearly covering all of the mass ranges, in which we have given three special cases. One case could account for the dark matter in some sense since the abundance of a primor…
The redshifted 21cm radio signal has emerged as an important probe for investigating the dynamics of the dark age Universe (recombination to reionization). In the current analysis, we explore the combined effect of primordial black hole (PBH) evaporation and the baryon-dark matter (DM) interaction in the 21cm scenario. The variation of brightness temperature shows remarkable dependence on the DM masses ($m_χ$) and the baryon-DM cross-sections ($\overlineσ_0$) besides the influences of the PBH parameters (mass $\mathcal{M_{\rm BH}}$ and initial mass fraction $β_{\rm BH}$). We address both upper…
Ultra-light primordial black holes with masses $M_{BH}<10^9$~g evaporate before big-bang nucleosynthesis producing all matter fields, including dark matter, in particular super-heavy dark matter: $M_{DM}\gtrsim 10^{10}$ GeV. If the dark matter gets its mass via $U(1)$ symmetry-breaking, the phase transition that gives a mass to the dark matter also produces cosmic strings which radiate gravitational waves. Because the symmetry-breaking scale $Λ_{CS}$ is of the same order as $M_{DM}$, the gravitational waves radiated by the cosmic strings have a large enough amplitude to be detectable across al…
We compute the primordial mirror helium He' mass fraction emerging from Big Bang nucleosynthesis in the mirror sector of particles in the presence of kinetic mixing between photons and mirror photons. We explore the kinetic mixing parameter (epsilon) values relevant for cosmology and which are also currently probed by the dark matter direct detection experiments. In particular, we find that for epsilon \sim 10^{-9}, as suggested by the DAMA/Libra and other experiments, a large He' mass fraction (Y_{He'} \approx 90%) is produced. Such a large value of the primordial He' mass fraction will have …
Hawking evaporation of primordial black holes (PBH) with masses ranging from $\sim 10^{-1}$ to $\sim 10^9$ g can generate the whole observed dark matter (DM) relic density. However, a second DM production mechanism, like freeze-out or freeze-in, could have also been active in the early universe. Here we study the interplay of these mechanisms, focusing on the scenario where PBHs dominate the energy density of the universe, leading to a nonstandard cosmological era. For concreteness, we use the singlet scalar DM model as an example for this analysis.
