Search

Dark photons can be the ultralight dark matter candidate, interacting with Standard Model particles via kinetic mixing. We propose to search for ultralight dark photon dark matter (DPDM) through the local absorption at different radio telescopes. The local DPDM can induce harmonic oscillations of electrons inside the antenna of radio telescopes. It leads to a monochromatic radio signal and can be recorded by telescope receivers. Using the observation data from the FAST telescope, the upper limit on the kinetic mixing can already reach $10^{-12}$ for DPDM oscillation frequencies at $1-1.5$ GHz, which is stronger than the cosmic microwave background constraint by about one order of magnitude. Furthermore, large-scale interferometric arrays like LOFAR and SKA1 telescopes can achieve extraordinary sensitivities for direct DPDM search from 10 MHz to 10 GHz., 5 pages, 3 figures + appendix. Match the accepted version (PRL)

The recent measurement of helium-4 from the near-infrared spectroscopy of extremely metal-poor galaxies (EMPGs) by the Subaru Survey may point to a new puzzle in the Early Universe. We exploit this new helium measurement together with the percent-level determination of primordial deuterium, to assess indications for a non-vanishing lepton asymmetry during the Big Bang Nucleosynthesis (BBN) era, paying particular attention to the role of uncertainties in the nuclear reaction network. A cutting-edge Bayesian analysis focused on the role of the newly measured EMPGs, jointly with information from the Cosmic Microwave Background, suggests the existence of a nonzero lepton asymmetry at around the $2 \sigma$ level, providing a hint for cosmology beyond $\Lambda$CDM. We discuss conditions for a large total lepton asymmetry to be consistently realized in the Early Universe., Comment: Analysis updated with Astrophys.J. 941 (2022) 2, 167. 95% joint probability distribution now shown in Fig.1. Minor modifications of the text, conclusions unchanged. Version matches publication in Physical Review Letters

We identify examples of single field inflationary trajectories beyond the slow-roll regime which improve the fit to Planck 2018 data compared to baseline $\Lambda$CDM model with power law form of primordial spectrum and at the same time alleviate existing tensions between different data sets in the estimate of cosmological parameters such as $H_0$ and $S_8$. A damped oscillation in the first Hubble flow function - or equivalently a feature in the potential - and the corresponding localized oscillations in the primordial power spectrum partially mimic the improvement in the fit of Planck data due to $A_L$ or $\Omega_K$. Compared to the baseline model, this model can lead simultaneously to larger value of $H_0$ and a smaller value of $S_8$, a trend which can be enhanced when the most recent SH0ES measurement for $H_0$ is combined with Planck and BK18 data. Large scale structure data and more precise CMB polarization measurements will further provide critical tests of this intermediate fast roll phase., Comment: 8 pages, 4 figures and 1 table

We study the generation and evolution of second-order energy-density perturbations arising from primordial gravitational waves. Such "tensor-induced scalar modes" approximately evolve as standard linear matter perturbations and may leave observable signatures in the Large-Scale Structure of the Universe. We study the imprint on the matter power-spectrum of some primordial models which predict a large gravitational-wave signal at high frequencies. This novel mechanism in principle allows us to constrain or detect primordial gravitational waves by looking at specific features in the matter or galaxy power-spectrum, thereby allowing to probe them on a range of scales unexplored so far., Comment: v2. 8 pages, 2 figures. Figure 1 changed. Typos corrected. References added. Minor change of text. Conclusion unchanged. Published in Physical Review Letters

We explore the use of the mass spectrum of neutron stars and black holes in gravitational-wave compact binary sources as a cosmological probe. These standard siren sources provide direct measurements of luminosity distance. In addition, features in the mass distribution, such as mass gaps or peaks, will redshift, and thus provide independent constraints on their redshift distribution. We argue that the entire mass spectrum should be utilized to provide cosmological constraints. For example, we find that the mass spectrum of LIGO--Virgo--KAGRA events introduces at least five independent mass ``features'': the upper and lower edges of the pair instability supernova (PISN) gap, the upper and lower edges of the neutron star--black hole gap, and the minimum neutron star mass. We find that although the PISN gap dominates the cosmological inference with current detectors (2G), as shown in previous work, it is the lower mass gap that will provide the most powerful constraints in the era of Cosmic Explorer and Einstein Telescope (3G). By using the full mass distribution, we demonstrate that degeneracies between mass evolution and cosmological evolution can be broken, unless an astrophysical conspiracy shifts all features of the full mass distribution simultaneously following the (non-trivial) Hubble diagram evolution. We find that this self-calibrating ``spectral siren'' method has the potential to provide precision constraints of both cosmology and the evolution of the mass distribution, with 2G achieving better than $10\%$ precision on $H(z)$ at $z\lesssim1$ within a year, and 3G reaching $\lesssim1\%$ at $z\gtrsim2$ within one month., Comment: Matches PRL published version

The 21cm line emitted by neutral hydrogen (HI) during the Dark Ages carries imprints of pristine primordial correlations. In models of inflation driven by a single, canonical scalar field, we show that a phase of ultra-slow-roll can lead to a null in all the primordial correlations at a specific wavenumber $k_\textrm{dip}$. We consider scenarios wherein the null in the correlations occurs over wavenumbers $1 \lesssim k_\textrm{dip} \lesssim 10\,\mathrm{Mpc}^{-1}$, and examine the prospects of detecting such a damping in the HI signal due to the nulls at the level of power and bi-spectra in future observational missions., Comment: v1: 10 pages, 5 figures; v2: 11 pages, 5 figures including supplementary material, published in Phys. Rev. Lett

Dark Matter (DM) annihilation in our Galaxy may produce a linearly polarized synchrotron signal. We use, for the first time, synchrotron polarization to constrain the DM annihilation cross section by comparing theoretical predictions with the latest polarization maps obtained by the Planck satellite collaboration. We find that synchrotron polarization is typically more constraining than synchrotron intensity by about one order of magnitude, independently of uncertainties in the modeling of electron and positron propagation, or of the Galactic magnetic field. Our bounds compete with Cosmic Microwave Background limits in the case of leptophilic DM., Comment: 6+11 pages, 3+9 figures. Minor comments added, results unchanged. Matches the version accepted by PRL

Macroscopic dark matter is almost unconstrained over a wide "asteroid-like" mass range, where it could scatter on baryonic matter with geometric cross section. We show that when such an object travels through a star, it produces shock waves which reach the stellar surface, leading to a distinctive transient optical, UV and X-ray emission. This signature can be searched for on a variety of stellar types and locations. In a dense globular cluster, such events occur far more often than flare backgrounds, and an existing UV telescope could probe orders of magnitude in dark matter mass in one week of dedicated observation., 13 pages, 5 figures. v2: clarifications and references added, matches journal version

We study the effect of a first-order phase transition in a confining $SU(N)$ dark sector with heavy dark quarks. The baryons of this sector are the dark matter candidate. During the confinement phase transition the heavy quarks are trapped inside isolated, contracting pockets of the deconfined phase, giving rise to a second stage of annihilation that dramatically suppresses the dark quark abundance. The surviving abundance is determined by the local accidental asymmetry in each pocket. The correct dark matter abundance is obtained for $\mathcal{O}(1-100)$ PeV dark quarks, above the usual unitarity bound., 5 pages, 3 figures, comments are welcomed

If primordial black holes (PBHs) contribute more than 10 percent of the dark matter (DM) density, their energy density today is of the same order as that of the baryons. Such a cosmic coincidence might hint at a mutual origin for the formation scenario of PBHs and the baryon asymmetry of the Universe. Baryogenesis can be triggered by a sharp transition of the rolling rate of inflaton from slow-roll to (nearly) ultraslow-roll phases that produces large curvature perturbations for PBH formation in single-field inflationary models. We show that the baryogenesis requirement drives the PBH contribution to DM, along with the inferred PBH mass range, the resulting stochastic gravitational wave background frequency window, and the associated cosmic microwave background tensor-to-scalar ratio amplitude, into potentially observable regimes., Comment: 7 pages, 3 figures, version matched with publication (Editors' Suggestion)

Optimal transport theory has recently reemerged as a vastly resourceful field of mathematics with elegant applications across physics and computer science. Harnessing methods from geometry processing, we report on the efficient implementation for a specific problem in cosmology -- the reconstruction of the linear density field from low redshifts, in particular the recovery of the Baryonic Acoustic Oscillation (BAO) scale. We demonstrate our algorithm's accuracy by retrieving the BAO scale in noise-less cosmological simulations that are dedicated to cancel cosmic variance; we find uncertainties to be reduced by a factor of 4.3 compared with performing no reconstruction, and a factor of 3.1 compared with standard reconstruction., Accepted for publication in PRL. 7 pages incl. references; 2 figures; 1 table. v1 initial submission. v2 fixed affiliation. v3 matches published version, but larger figures

In many cosmologies dark matter clusters on subkiloparsec scales and forms compact subhalos, in which the majority of Galactic dark matter could reside. Null results in direct detection experiments since their advent four decades ago could then be the result of extremely rare encounters between the Earth and these subhalos. We investigate alternative and promising means to identify subhalo dark matter interacting with standard model particles: (1) subhalo collisions with old neutron stars can transfer kinetic energy and brighten the latter to luminosities within the reach of imminent infrared, optical, and ultraviolet telescopes; we identify new detection strategies involving single-star measurements and Galactic disk surveys, and obtain the first bounds on self-interacting dark matter in subhalos from the coldest known pulsar, PSR J2144–3933; (2) subhalo dark matter scattering with cosmic rays results in detectable effects; (3) historic Earth-subhalo encounters can leave dark matter tracks in Paleolithic minerals deep underground. These searches could discover dark matter subhalos weighing between gigaton and solar masses, with corresponding dark matter cross sections and masses spanning tens of orders of magnitude., Funded by SCOAP3.

Dark matter (DM) could be a relic of freeze-in through a light mediator, where the DM is produced by extremely feeble, IR-dominated processes in the thermal Standard Model plasma. In the simplest viable models with the DM mass below the MeV scale, the DM has a small effective electric charge and is born with a nonthermal phase-space distribution. This DM candidate would cause observable departures from standard cosmological evolution. In this work, we combine data from the cosmic microwave background (CMB), Lyman-$\alpha$ forest, quasar lensing, stellar streams, and Milky Way satellite abundances to set a lower limit on freeze-in DM masses up to $\sim 20\,$keV, with the exact constraint depending on whether the DM thermalizes in its own sector. We perform forecasts for the CMB-S4 experiment, the Hydrogen Epoch of Reionization Array, and the Vera Rubin Observatory, finding that freeze-in DM masses up to $\sim 80\,$keV can be explored. These cosmological probes are highly complementary with proposed direct-detection efforts to search for this DM candidate., Comment: 5+17 pages, 3+9 figures

Dark matter particles with Planck-scale mass ($\simeq10^{19}\text{GeV}/c^2$) arise in well-motivated theories and could be produced by several cosmological mechanisms. Using a blind analysis of data collected over a 813 d live time with DEAP-3600, a 3.3 t single-phase liquid argon-based dark matter experiment at SNOLAB, a search for supermassive dark matter was performed, looking for multiple-scatter signals. No candidate signal events were observed, leading to the first direct detection constraints on Planck-scale mass dark matter. Leading limits constrain dark matter masses between $8.3\times10^{6}$ and $1.2\times10^{19} \text{GeV}/c^2$, and cross sections for scattering on $^{40}$Ar between $1.0\times10^{-23}$ and $2.4\times10^{-18} \text{cm}^2$. These are used to constrain two composite dark matter models.

We propose a novel mechanism for enhancing the primordial gravitational waves without significantly affecting the curvature perturbations produced during inflation. This is achieved due to non-linear sourcing of resonantly amplified scalar field fluctuations. Our result is an explicit scale-dependent counter-example of the famous Lyth bound, which opens up a promising perspective of producing detectable inflationary tensor modes with low-scale inflation and a sub-Planckian field excursion. We explicitly demonstrate the testability of our mechanism with upcoming Cosmic Microwave Background B-mode observations., v1: 6 pages, 2 figures, comments are welcome. v2: 7 pages, 2 figures, updated references, minor modifications, accepted for publication in PRL

We present an alternative formation scenario for the gravitational wave event GW190521, that can be explained as the merger of central black holes from two ultra-dwarf galaxies of stellar mass $\sim 10^5-10^6 ~M_\odot$, which had themselves previously undergone a merger. The GW190521 components' masses of $85^{+21}_{-14}M_\odot$ and $66^{+17}_{-18}M_\odot$ challenge standard stellar evolution models, as they fall in the so-called mass gap. We demonstrate that the merger history of ultra-dwarf galaxies at high redshifts ($1\lesssim z \lesssim 2$) matches well the LIGO/Virgo inferred merger rate for black holes within the mass range of the GW190521 components, resulting in a likely time delay of $\lesssim 4$ Gyr considering the redshift of this event. We further demonstrate that the predicted time-scales are consistent with expectations for central black hole mergers, although with large uncertainties due to the lack of high-resolution simulations in low-mass dwarf galaxies. Our findings show that this black hole production and merging channel is viable and extremely interesting as a new way to explore galaxies' black hole seeds and galaxy formation. We recommend this scenario be investigated in detail with simulations and observations., 8 pages, 4 figures

We investigate the stochastic gravitational wave background (SGWB) from cosmic domain walls (DWs) caused by quantum fluctuations of a light scalar field $\phi$ during inflation. Perturbations of $\phi$ remain almost constant after leaving the Hubble horizon. The probabilities of the two domains depend on the averaged value of $\phi$ at each large scale region, leading to large scale perturbations of DW energy density and large anisotropies in the SGWB. We find that the angular power spectrum is scale-invariant and at least of the order of $10^{-2}$, which is expected to be detected by future gravitational-wave (GW) detectors. Since we have not detected primordial GWs yet, anisotropies of the SGWB could help us to verify the rationality of inflation and determine the energy scale of inflation., Comment: 6 pages, 2 figures

Unusual masses of black holes being discovered by gravitational wave experiments pose fundamental questions about the origin of these black holes. Black holes with masses smaller than the Chandrasekhar limit $\approx1.4\,M_\odot$ are essentially impossible to produce through stellar evolution. We propose a new channel for production of low mass black holes: stellar objects catastrophically accrete non-annihilating dark matter, and the small dark core subsequently collapses, eating up the host star and transmuting it into a black hole. The wide range of allowed dark matter masses allows a smaller effective Chandrasekhar limit, and thus smaller mass black holes. We point out several avenues to test our proposal, focusing on the redshift dependence of the merger rate. We show that redshift dependence of the merger rate can be used as a probe of the transmuted origin of low mass black holes., v2: 8 pages, 2 figures, Minor changes (Fig. 2 updated, text improved), Conclusions unchanged. Matches version published in Physical Review Letters

Solar-mass black holes with masses in the range of $\sim 1-2.5 M_{\odot}$ are not expected from conventional stellar evolution, but can be produced naturally via neutron star (NS) implosions induced by capture of small primordial black holes (PBHs) or from accumulation of some varieties of particle dark matter. We argue that a unique signature of such "transmuted" solar-mass BHs is that their mass distribution would follow that of the NSs. This would be distinct from the mass function of black holes in the solar-mass range predicted either by conventional stellar evolution or early Universe PBH production. We propose that analysis of the solar-mass BH population mass distribution in a narrow mass window of $\sim 1-2.5\,{\rm M}_\odot$ can provide a simple yet powerful test of the origin of these BHs. Recent LIGO/VIRGO gravitational wave (GW) observations of the binary merger events GW190425 and GW190814 are consistent with a BH mass in the range $\sim 1.5-2.6~M_{\odot}$. Though these results have fueled speculation on dark matter-transmuted solar-mass BHs, we demonstrate that it is unlikely that the origin of these particular events stems from NS implosions. Data from upcoming GW observations will be able to distinguish between solar-mass BHs and NSs with high confidence. This capability will facilitate and enhance the efficacy of our proposed test., Comment: 6 pages, 1 figure, 1 table

Pulsar timing data used to provide upper limits on a possible stochastic gravitational wave background (SGWB). However, the NANOGrav Collaboration has recently reported strong evidence for a stochastic common-spectrum process, which we interpret as a SGWB in the framework of cosmic strings. The possible NANOGrav signal would correspond to a string tension $G\mu \in (4 \times 10^{-11}, 10^{-10}) $ at the 68% confidence level, with a different frequency dependence from supermassive black hole mergers. The SGWB produced by cosmic strings with such values of $G\mu$ would be beyond the reach of LIGO, but could be measured by other planned and proposed detectors such as SKA, LISA, TianQin, AION-1km, AEDGE, Einstein Telescope and Cosmic Explorer., Comment: matches version published in PRL

We describe a new scenario for the formation of primordial black holes (PBHs). In the early Universe, the long-range forces mediated by the scalar fields can lead to formation of halos of heavy particles even during the radiation-dominated era. The same interactions result in the emission of scalar radiation from the motion and close encounters of particles in such halos. Radiative cooling due the scalar radiation allows the halos to collapse to black holes. We illustrate this scenario on a simple model with fermions interacting via the Yukawa forces. The abundance and the mass function of PBHs are suitable to account for all dark matter, or for some gravitational wave events detected by LIGO. The model relates the mass of the dark-sector particles to the masses and abundance of dark matter PBHs in a way that can explain why the dark matter and the ordinary matter have similar mass densities. The model also predicts a small contribution to the number of effective light degrees of freedom, which can help reconcile different measurements of the Hubble constant.

Modern cosmological analyses of galaxy-galaxy lensing face a theoretical systematic effect arising from the non-locality of the observed galaxy-galaxy lensing signal. Because the predicted tangential shear signal at a given separation depends on the physical modeling on all scales internal to that separation, systematic uncertainties in the modeling of non-linear small scales are propagated outwards to larger scales. Even in the absence of other limiting factors, this systematic effect alone can necessitate conservative small-scale cuts, resulting in significant losses of information in the tangential shear data vector. We construct a simple linear transformation of the observable that removes this non-locality, enabling more aggressive small-scale cuts for a given theoretical model. Our modified galaxy-galaxy lensing observable makes it possible to include observations on significantly smaller scales than those under the standard approach in cosmological analyses. More importantly, it ensures that the cosmological signal contained within the observable is exclusively drawn from well-understood physical scales., 6 pages, 3 figures

We propose a novel mechanism to test time variation of the propagation speed of gravitational waves (GWs) in light of GWs astronomy. As the stochastic GWs experience the whole history of cosmic expansion, they encode potential observational evidence of such variation. We report that, one feature of a varying GWs speed is that the energy spectrum of GWs will present resonantly-enhanced peaks if the GWs speed oscillates in time at high-energy scales. Such oscillatory behaviour arises in a wide class of modified gravity theories. The amplitude of these peaks can be at reach by current and forthcoming GWs instruments, hence making the underlying theories falsifiable. This mechanism reveals that probing the variation of GWs speed can be a promising way to search for new physics beyond general relativity., Comment: 6 pages, 2 figures

Gravitational waves (GWs) are subject to gravitational lensing in the same way as electromagnetic radiation. However, to date, no unequivocal observation of a lensed GW transient has been reported. Independently, GW observatories continue to search for the stochastic GW signal which is produced by many transient events at high redshift. We exploit a surprising connection between the lensing of individual transients and limits to the background radiation produced by the unresolved population of binary back hole mergers: we show that it constrains the fraction of individually resolvable lensed binary black holes to less than $\sim 4\times 10^{-5}$ at present sensitivity. We clarify the interpretation of existing, low redshift GW observations (obtained assuming no lensing) in terms of their apparent lensed redshifts and masses and explore constraints from GW observatories at future sensitivity. Based on our results, recent claims of observations of lensed events are statistically disfavoured., Comment: 9 pages, 6 figures, includes Supplemental material, published in Physical Review Letters

Low-mass structures of dark matter (DM) are expected to be entirely devoid of light-emitting regions and baryons. Precisely because of this lack of baryonic feedback, small-scale substructures of the Milky Way are a relatively pristine testing ground for discovering aspects of DM microphysics and primordial fluctuations on subgalactic scales. In this work, we report results from the first search for Galactic DM subhalos with time-domain astrometric weak gravitational lensing. The analysis is based on a matched-filter template of local lensing corrections to the proper motion of stars in the Magellanic Clouds. We describe a data analysis pipeline detailing sample selection, background subtraction, and handling outliers and other systematics. For tentative candidate lenses, we identify a signature based on an anomalous parallax template that can unequivocally confirm the presence of a DM lens, opening up prospects for robust discovery potential with full time-series data. We present our constraints on substructure fraction $f_l \lesssim 5$ at 90% CL (and $f_l \lesssim 2$ at 50% CL) for compact lenses with radii $r_l < 1\,\mathrm{pc}$, with best sensitivity reached for lens masses $M_l$ around $10^7$-$10^8\,M_\odot$. Parametric improvements are expected with future astrometric data sets; by end of mission, $Gaia$ could reach $f_l \lesssim 10^{-3}$ for these massive point-like objects, and be sensitive to lighter and/or more extended subhalos for $\mathcal{O}(1)$ substructure fractions., 9 pages, 11 figures

We propose a new non-thermal mechanism of dark matter production based on vacuum misalignment. A global $X$-charge asymmetry is generated at high temperatures, under which both the will-be Higgs and the dark matter are charged. At lower energies, the vacuum changes alignment and breaks the $U(1)_X$, leading to the emergence of the Higgs and of a fraction of charge asymmetry stored in the stable dark matter relic. This mechanism can be present in a wide variety of models based on vacuum misalignment, and we demonstrate it in a composite Higgs template model, where all the necessary ingredients are naturally present. A light pseudo-scalar $\eta$ is always predicted, with interesting implications for cosmology, future supernova observations and exotic $Z \to \gamma \eta$ decays., Comment: 6 pages, 1 figure, 1 table; accepted for publication in Physical Review Letters

Mysteries about the origin of high-energy cosmic neutrinos have deepened by the recent IceCube measurement of a large diffuse flux in the 10-100 TeV range. Based on the standard disk-corona picture of active galactic nuclei (AGN), we present a phenomenological model enabling us to systematically calculate the spectral sequence of multimessenger emission from the AGN coronae. We show that protons in the coronal plasma can be stochastically accelerated up to PeV energies by plasma turbulence, and find that the model explains the large diffuse flux of medium-energy neutrinos if the cosmic rays carry only a few percent of the thermal energy. We find that the Bethe-Heitler process plays a crucial role in connecting these neutrinos and cascaded MeV gamma rays, and point out that the gamma-ray flux can even be enhanced by the reacceleration of secondary pairs. Critical tests of the model are given by its prediction that a significant fraction of the MeV gamma-ray background correlates with about 10 TeV neutrinos, and nearby Seyfert galaxies including NGC 1068 are promising targets for IceCube, KM3Net, IceCube-Gen2, and future MeV gamma-ray telescopes., 7+6 pages, 4+6 figures, 0+2 tables, version to appear in PRL (submitted on Apr/08/2019), with clarifications and extended descriptions (including discussion on NGC 1068). Conclusions unchanged

We demonstrate that gravitational waves generated by efficient gauge preheating after axion inflation generically contribute significantly to the effective number of relativistic degrees of freedom $N_\mathrm{eff}$. We show that, with existing Planck limits, gravitational waves from preheating already place the strongest constraints on the inflaton's possible axial coupling to Abelian gauge fields. We demonstrate that gauge preheating can completely reheat the Universe regardless of the inflationary potential. Further, we quantify the variation of the efficiency of gravitational wave production from model to model and show that it is correlated with the tensor-to-scalar ratio. In particular, when combined with constraints on models whose tensor-to-scalar ratios would be detected by next-generation cosmic microwave background experiments, $r\gtrsim 10^{-3}$, constraints from $N_\mathrm{eff}$ will probe or rule out the entire coupling regime for which gauge preheating is efficient., Comment: v2: 6 pages, 2 figures; matches published version

Ultracompact dark matter (DM) minihalos at masses at and below $10^{-12}$ $M_\odot$ arise in axion DM models where the Peccei-Quinn (PQ) symmetry is broken after inflation. The minihalos arise from density perturbations that are generated from the non-trivial axion self interactions during and shortly after the collapse of the axion-string and domain-wall network. We perform high-resolution simulations of this scenario starting at the epoch before the PQ phase transition and ending at matter-radiation equality. We characterize the spectrum of primordial perturbations that are generated and comment on implications for efforts to detect axion DM. We also measure the DM density at different simulated masses and argue that the correct DM density is obtained for $m_a = 25.2 \pm 11.0$ $\mu\mathrm{eV}$., Comment: 6+17 pages, 4+14 figures; Supplementary Data at https://zenodo.org/record/2653964#.XPVFS9NKjOS with Supplementary Animation at https://youtu.be/1By1DMq1EpI

Primordial black holes (PBHs) are a viable candidate for dark matter if the PBH masses are in the currently unconstrained "sublunar" mass range. We revisit the possibility that PBHs were produced by nucleation of false vacuum bubbles during inflation. We show that this scenario can produce a population of PBHs that simultaneously accounts for all dark matter, explains the candidate event in Subaru Hyper Suprime-Cam (HSC) data, and contains both heavy black holes as observed by LIGO and very heavy seeds of supermassive black holes. We demonstrate with numerical studies that future observations of HSC, as well as other optical surveys, such as LSST, will be able to provide a definitive test for this generic PBH formation mechanism if it is the dominant source of dark matter., 7 pages, 3 figures; v2: published version

Certain anomalies in the CMB bring out a tension between the six-parameter flat $\Lambda$CDM model and the CMB data. We revisit the PLANCK analysis with loop quantum cosmology (LQC) predictions and show that LQC alleviates both the large-scale power anomaly and the tension in the lensing amplitude. These differences arise because, in LQC, the primordial power spectrum is scale dependent for small $k$, with a specific power suppression. We conclude with a prediction of larger optical depth and power suppression in the $B$-mode polarization power spectrum on large scales., Comment: 6 pages, 5 figures, 1 table. The version that appeared in PRL. A few clarifications and several references added

Line-intensity mapping (LIM) of emission form star-forming galaxies can be used to measure the baryon acoustic oscillation (BAO) scale as far back as the epoch of reionization. This provides a standard cosmic ruler to constrain the expansion rate of the Universe at redshifts which cannot be directly probed otherwise. In light of growing tension between measurements of the current expansion rate using the local distance ladder and those inferred from the cosmic microwave background, extending the constraints on the expansion history to bridge between the late and early Universe is of paramount importance. Using a newly derived methodology to robustly extract cosmological information from LIM, which minimizes the inherent degeneracy with unknown astrophysics, we show that present and future experiments can gradually improve the measurement precision of the expansion rate history, ultimately reaching percent-level constraints on the BAO scale. Specifically, we provide detailed forecasts for the SPHEREx satellite, which will target the H$\alpha$ and Lyman-$\alpha$ lines, and for the ground-based COMAP instrument---as well as a future stage-3 experiment---that will target the CO rotational lines. Besides weighing in on the so-called Hubble tension, reliable LIM cosmic rulers can enable wide-ranging tests of dark matter, dark energy and modified gravity., Comment: 7 pages; 3 figures

In simple inflationary cosmological scenarios the near-exponential growth can be followed by a long period in which the Universe is dominated by the oscillating inflaton condensate. The condensate is initially almost homogeneous, but perturbations grow gravitationally, eventually fragmenting the condensate if it is not disrupted more quickly by resonance or prompt reheating. We show that the gravitational fragmentation of the condensate is well-described by the Schr\"odinger-Poisson equations and use numerical solutions to show that large overdensities form quickly after the onset of nonlinearity. This is the first exploration of this phase of nonlinear dynamics in the very early universe, which can affect the detailed form of the inflationary power spectrum and the dark matter fraction when the dark sector is directly coupled to the inflaton., Comment: 4 pages, 3 figures (v2 added refs)

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/ INTEGRAL observation of the Galactic Center 511 keV gamma-ray line. Depending on the primordial black hole mass function and other astrophysical uncertainties, these constraints are the most stringent in the literature and show that primordial black holes contribute to less than 1\% of the dark matter density. Our technique also probes part of the mass range which was completely unconstrained by previous studies., v2: 8 pages, 2 figures. Published in Physical Review Letters

We study the post-inflation dynamics of multifield models involving nonminimal couplings using lattice simulations to capture significant nonlinear effects like backreaction and rescattering. We measure the effective equation of state and typical time-scales for the onset of thermalization, which could affect the usual mapping between predictions for primordial perturbation spectra and measurements of anisotropies in the cosmic microwave background radiation. For large values of the nonminimal coupling constants, we find efficient particle production that gives rise to nearly instantaneous preheating. Moreover, the strong single-field attractor behavior that was previously identified persists until the end of preheating, thereby suppressing typical signatures of multifield models. We therefore find that predictions for primordial observables in this class of models retain a close match to the latest observations., Comment: 6 pages, 7 figures. References added and minor edits made to match version to be published in Physical Review Letters

In hierarchical models of structure formation, the first galaxies form in low-mass dark matter potential wells, probing the behavior of dark matter on kiloparsec (kpc) scales. Even though these objects are below the detection threshold of current telescopes, future missions will open an observational window into this emergent world. In this Letter we investigate how the first galaxies are assembled in a `fuzzy' dark matter (FDM) cosmology where dark matter is an ultralight $\sim 10^{-22}$~eV boson and the primordial stars are expected to form along dense dark matter filaments. Using a first-of-its-kind cosmological hydrodynamical simulation, we explore the interplay between baryonic physics and unique wavelike features inherent to FDM. In our simulation, the dark matter filaments show coherent interference patterns on the boson de Broglie scale and develop cylindrical soliton-like cores which are unstable under gravity and collapse into kpc-scale spherical solitons. Features of the dark matter distribution are largely unaffected by the baryonic feedback. On the contrary, the distributions of gas and stars, which do form along the entire filament, exhibit central cores imprinted by dark matter -- a smoking gun signature of FDM., Comment: 6 pages, 2 figures, accepted to Phys. Rev. Lett

Dark matter comprises the bulk of the matter in the universe but its particle nature and cosmological origin remain mysterious. Knowledge of the dark matter density distribution in the Milky Way Galaxy is crucial to both our understanding of the standard cosmological model and for grounding direct and indirect searches for the particles comprising dark matter. Current measurements of Galactic dark matter content rely on model assumptions to infer the forces acting upon stars from the distribution of observed velocities. Here, we propose to apply the precision radial velocity method, optimized in recent years for exoplanet astronomy, to measure the change in the velocity of stars over time, thereby providing a direct probe of the local gravitational potential in the Galaxy. Using numerical simulations, we develop a realistic strategy to observe the differential accelerations of stars in our Galactic neighborhood with next-generation telescopes, at the level of $10^{-8}$ cm/s$^{2}$. Our simulations show that detecting accelerations at this level with an ensemble of $10^{3}$ stars requires the effect of stellar noise on radial velocity measurements to be reduced to $, 6 pages, 4 figures, Supplemental Material included as ancillary file

Observations of gravitational waves and their electromagnetic counterparts may soon uncover the existence of coalescing compact binary systems formed by a stellar-mass black hole and a neutron star. These mergers result in a remnant black hole, possibly surrounded by an accretion disk. The mass and spin of the remnant black hole depend on the properties of the coalescing binary. We construct a map from the binary components to the remnant black hole using a sample of numerical-relativity simulations of different mass ratios $q$, (anti)aligned dimensionless spins of the black hole ${a}_{\mathrm{BH}}$, and several neutron star equations of state. Given the binary total mass, the mass and spin of the remnant black hole can therefore be determined from the three parameters $(q,{a}_{\mathrm{BH}},\mathrm{\ensuremath{\Lambda}})$, where $\mathrm{\ensuremath{\Lambda}}$ is the tidal deformability of the neutron star. Our models also incorporate the binary black hole and test-mass limit cases and we discuss a simple extension for generic black-hole spins. We combine the remnant characterization with recent population synthesis simulations for various metallicities of the progenitor stars that generated the binary system. We predict that black-hole--neutron-star mergers produce a population of remnant black holes with masses distributed around $7\text{ }\text{ }{M}_{\ensuremath{\bigodot}}$ and $9\text{ }\text{ }{M}_{\ensuremath{\bigodot}}$. For isotropic spin distributions, nonmassive accretion disks are favored: no bright electromagnetic counterparts are expected in such mergers.

We show that a parity-breaking uniform (averaged over all directions on the sky) circular polarization of amplitude $V_{00} \simeq 2.6 \times 10^{-17}\, \Delta \chi (r/0.06)$ can be induced by chiral gravitational-wave (GW) background with tensor-to-scalar ratio $r$ and chirality parameter $\Delta\chi$ (which is $\pm1$ for a maximally chiral background). We also show, however, that a uniform circular polarization can arise from a realization of a non-chiral GW background that spontaneously breaks parity. The magnitude of this polarization is drawn from a distribution of root-variance $\sqrt{< V_{00}^2>} \simeq 1.5\times 10^{-18}\, (r/0.06)^{1/2}$ implying that the chirality parameter must be $\Delta \chi \gtrsim 0.12 (r/0.06)^{-1/2}$ to establish that the GW background is chiral. Although these values are too small to be detected by any experiment in the foreseeable future, the calculation is a proof of principle that cosmological parity breaking in the form of a chiral gravitational-wave background can be imprinted in the chirality of the photons in the cosmic microwave background. It also illustrates how a seemingly parity-breaking cosmological signal can arise from parity-conserving physics., Comment: 5 pages, v2: minor changes, version accepted for publication in PRL

The combination of multiple observational probes has long been advocated as a powerful technique to constrain cosmological parameters, in particular dark energy. The Dark Energy Survey has measured 207 spectroscopically--confirmed Type Ia supernova lightcurves; the baryon acoustic oscillation feature; weak gravitational lensing; and galaxy clustering. Here we present combined results from these probes, deriving constraints on the equation of state, $w$, of dark energy and its energy density in the Universe. Independently of other experiments, such as those that measure the cosmic microwave background, the probes from this single photometric survey rule out a Universe with no dark energy, finding $w=-0.80^{+0.09}_{-0.11}$. The geometry is shown to be consistent with a spatially flat Universe, and we obtain a constraint on the baryon density of $\Omega_b=0.069^{+0.009}_{-0.012}$ that is independent of early Universe measurements. These results demonstrate the potential power of large multi-probe photometric surveys and pave the way for order of magnitude advances in our constraints on properties of dark energy and cosmology over the next decade., Comment: 8 pages, 2 figures; v3 matches version accepted by PRL

The fuzzy dark matter (FDM) model treats DM as a bosonic field with astrophysically large de Broglie wavelength. A striking feature of this model is $\mathcal{O}(1)$ fluctuations in the dark matter density on time scales which are shorter than the gravitational timescale. Including for the first time the effect of core oscillations, we demonstrate how such fluctuations lead to heating of star clusters, and thus an increase in their size over time. From the survival of the old star cluster in Eridanus II we infer $m_a\gtrsim 0.6\rightarrow 1\times 10^{-19}\text{ eV}$ within modelling uncertainty if FDM is to compose all of the DM, and derive constraints on the FDM fraction at lower masses. The subhalo mass function in the Milky Way implies $m_a\gtrsim 0.8\times 10^{-21}\text{ eV}$ to successfully form Eridanus II. The window between $10^{-21}\text{ eV}\lesssim m_a\lesssim 10^{-20}\text{ eV}$ is affected by narrow band resonances, and the limited applicability of the diffusion approximation. Some of this window may be consistent with observations of Eridanus II and more detailed investigations are required., 6 pages, 2 figures; v2 comments and clarifications added, matches version accepted for publication in PRL

Cosmic Microwave Background temperature and polarization anisotropies from Planck have estimated a lower value of the optical depth to reionization ($\tau$) compared to WMAP. A significant period in the reionization history would then fall within $6, Comment: V1: 7 pages, 4 figures and 1 table; V2: Updated to Planck 2018 and recent astrophysical data

Massive fields in the primordial universe function as standard clocks and imprint clock signals in the density perturbations that directly record the scale factor of the primordial universe as a function of time, a(t). A measurement of such signals would identify the specific scenario of the primordial universe in a model-independent fashion. In this Letter, we introduce a new mechanism through which quantum fluctuations of massive fields function as standard clocks. The clock signals appear as scale-dependent oscillatory signals in the power spectrum of alternative scenarios to inflation., 8 pages; v3, LSS forecast added and other minor revisions. A slightly shortened version will appear in PRL

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, v2: small comments and references added, gamma-ray limits corrected in Fig. 2, matches journal version

We present a model where the inflaton can naturally account for all the dark matter in the Universe within the warm inflation paradigm. In particular, we show that the symmetries of the Warm Little Inflaton scenario (i) avoid large thermal and radiative corrections to the scalar potential, (ii) allow for sufficiently strong dissipative effects to sustain a radiation bath during inflation that becomes dominant at the end of the slow-roll regime, and (iii) enable a stable inflaton remnant in the post-inflationary epochs. The latter behaves as dark radiation until parametrically before matter-radiation equality, leading to a non-negligible contribution to the effective number of relativistic degrees of freedom during nucleosynthesis, becoming the dominant cold dark matter component in the Universe for inflaton masses in the $10^{-4}-10^{-1}$ eV range. Cold dark matter isocurvature perturbations, anti-correlated with the main adiabatic component, provide a smoking gun for this scenario that can be tested in the near future., Comment: 6 pages, 2 figures; Matches version published in Physical Review Letters

We show that the shape of the inflationary landscape potential may be constrained by analyzing cosmological data. The quantum fluctuations of fields orthogonal to the inflationary trajectory may have probed the structure of the local landscape potential, inducing non-Gaussianity (NG) in the primordial distribution of the curvature perturbations responsible for the cosmic microwave background (CMB) anisotropies and our Universe's large-scale structure. The resulting type of NG (tomographic NG) is determined by the shape of the landscape potential, and it cannot be fully characterized by 3- or 4-point correlation functions. Here we deduce an expression for the profile of this probability distribution function in terms of the landscape potential, and we show how this can be inverted in order to reconstruct the potential with the help of CMB observations. While current observations do not allow us to infer a significant level of tomographic NG, future surveys may improve the possibility of constraining this class of primordial signatures., Comment: v1: 6 pages, 3 figures; v2: references and clarifications added, published in Physical Review Letters

The nature of dark matter (DM) remains unknown despite very precise knowledge of its abundance in the universe. An alternative to new elementary particles postulates DM as made of macroscopic compact halo objects (MACHO) such as black holes formed in the very early universe. Stellar-mass primordial black holes (PBHs) are subject to less robust constraints than other mass ranges and might be connected to gravitational-wave signals detected by the Laser Interferometer Gravitational-Wave Observatory (LIGO). New methods are therefore necessary to constrain the viability of compact objects as a DM candidate. Here we report bounds on the abundance of compact objects from gravitational lensing of type Ia supernovae (SNe). Current SNe datasets constrain compact objects to represent less than 35.2% (Joint Lightcurve Analisis) and 37.2% (Union 2.1) of the total matter content in the universe, at 95% confidence-level. The results are valid for masses larger than $\sim 0.01M_\odot$ (solar-masses), limited by the size SNe relative to the lens Einstein radius. We demonstrate the mass range of the constraints by computing magnification probabilities for realistic SNe sizes and different values of the PBH mass. Our bounds are sensitive to the total abundance of compact objects with $M \lesssim 0.01M_\odot$ and complementary to other observational tests. These results are robust against cosmological parameters, outlier rejection, correlated noise and selection bias. PBHs and other MACHOs are therefore ruled out as the dominant form of DM for objects associated to LIGO gravitational wave detections. These bounds constrain early-universe models that predict stellar-mass PBH production and strengthen the case for lighter forms of DM, including new elementary particles., 16 pages, 9 figures. Discussion on finite SNe size and outliers expanded. Version accepted for publication in PRL

The epoch of the formation of the first stars, known as the cosmic dawn, has emerged as a new arena in the search for dark matter. In particular, the first claimed 21-cm detection exhibits a deeper global absorption feature than expected, which could be caused by a low baryonic temperature, and has been interpreted as a sign for electromagnetic interactions between baryons and dark matter. This hypothesis has a striking prediction: large temperature anisotropies sourced by the velocity-dependent cooling of the baryons. However, in order to remain consistent with the rest of cosmological observations, only part of the dark matter is allowed to be charged, and thus interactive. Here we compute, for the first time, the 21-cm fluctuations caused by a charged subcomponent of the dark matter, including both the pre- and post-recombination evolution of all fluids. We find that, for the same parameters that can explain the anomalous 21-cm absorption signal, any percent-level fraction of charged dark matter would source novel 21-cm fluctuations with a unique acoustic spectrum, and with an amplitude above any other known effects. These fluctuations are uncorrelated with the usual adiabatic anisotropies, and would be observable at high significance with interferometers such as LOFAR and HERA, thus providing a novel probe of dark matter at cosmic dawn., Comment: 6 pages, 4 figures. Updated to match PRL accepted version

We consider the 21cm absorption signal expected at high redshift in cosmologies with and without non-baryonic cold dark matter. The expansion of the early universe decelerates strongly with dark matter, but approximately coasts without it. This results in a different path length across the epochs when absorption is expected, with the consequence that the absorption is predicted to be a factor of $\sim 2$ greater without dark matter than with it. Observation of such a signal would motivate consideration of extended theories of gravity in lieu of dark matter., Comment: Accepted for publication in Phys. Rev. Letters. 9 pages (4 of which are bibliography), 1 figure. Model data available at http://astroweb.case.edu/ssm/models/

Cold Dark Matter (CDM) is a crucial constituent of the current concordance cosmological model. Having a vanishing equation of state (EoS), its energy density scales with the inverse cosmic volume and is thus uniquely described by a single number, its present abundance. We test the inverse cosmic volume law for Dark Matter (DM) by allowing its EoS to vary independently in eight redshift bins in the range $z=10^5$ and $z=0$. We use the latest measurements of the Cosmic Microwave Background radiation from the Planck satellite and supplement them with Baryon Acoustic Oscillation (BAO) data from the 6dF and SDSS-III BOSS surveys, and with the Hubble Space Telescope (HST) key project data. We find no evidence for nonzero EoS in any of the eight redshift bins. With Planck data alone, the DM abundance is most strongly constrained around matter-radiation equality $\omega^{\rm eq}_g = 0.1193^{+0.0036}_{-0.0035}$ (95% c.l.), whereas its present day value is more weakly constrained $\omega^{(0)}_g = 0.16^{+0.12}_{-0.10}$ (95% c.l.). Adding BAO or HST data does not significantly change the $\omega^{\rm eq}_g$ constraint, while $\omega^{(0)}_g$ tightens to $0.160^{+0.069}_{-0.065} $ (95% c.l.) and $0.124^{+0.081}_{-0.067}$ (95% c.l.) respectively. Our results constrain for the first time the level of "coldness" required of the DM across various cosmological epochs and show that the DM abundance is strictly positive at all times., Comment: 6 pages, 4 figures, changed color scheme for figures