Pulsars act as accurate clocks, sensitive to gravitational redshift and acceleration induced by transiting clumps of matter. We study the sensitivity of pulsar timing arrays (PTAs) to single transiting compact objects, focusing on primordial black holes and compact subhalos in the mass range from $10^{-12} M _{\odot}$ to well above $100~M_\odot$. We find that the Square Kilometer Array can constrain such objects to be a subdominant component of the dark matter over this entire mass range, with sensitivity to a dark matter sub-component reaching the sub-percent level over significant parts of this range. We also find that PTAs offer an opportunity to probe substantially less dense objects than lensing because of the large effective radius over which such objects can be observed, and we quantify the subhalo concentration parameters which can be constrained.
The distribution of galaxies displays anisotropy on different scales and it is often referred as galaxy alignment. To understand the origin of galaxy alignments on small scales, one must investigate how galaxies were accreted in the early universe and quantify their primordial anisotropic at the time of accretion. In this paper we use N-body simulations to investigate the accretion of dark matter subhaloes, focusing on their alignment with the host halo shape and the orientation of mass distribution on large scale, defined using the hessian matrix of the density field. The large/small (e1/e3) …
Dark matter substructure on small scales is currently weakly constrained, and its study may shed light on the nature of the dark matter. In this work we study the gravitational effects of dark matter substructure on measured pulsar phases in pulsar timing arrays (PTAs). Due to the stability of pulse phases observed over several years, dark matter substructure around the Earth-pulsar system can imprint discernible signatures in gravitational Doppler and Shapiro delays. We compute pulsar phase correlations induced by general dark matter substructure, and project constraints for a few models such…
We investigate the primordial curvature perturbation by the observation of dark matter substructure. Assuming a bump in the spectrum of the curvature perturbation in the wavenumber of k>1 Mpc^{-1}, we track the evolution of the host halo and subhalos in a semi-analytic way. Taking into account possible uncertainties in the evaluation of the tidal stripping effect on the subhalo growth, we find a new robust bound on the curvature perturbation with a bump from the number of observed dwarf spheroidal galaxies in our Galaxy and the observations of the stellar stream. The upper limit on the amplitu…
We investigate the capability of pulsar timing arrays (PTAs) as a probe of primordial black holes (PBHs), which might constitute the Galactic dark matter. A PBH passing nearby the Earth or a pulsar gives an impulse acceleration and induces residuals on otherwise orderly pulsar timing data. We show that the timing residuals induced at pulsars are optimal for searching heavier PBHs than those at the Earth, and the two probes are highly complemental. Future facilities like SKA could detect PBHs with masses around 10^(22-28) g even if only a small fraction (< 1%) of the Galactic dark matter consis…
The gravitational waves measured at LIGO are presumed here to come from merging primordial black holes. We ask how these primordial black holes could arise through inflationary models while not conflicting with current experiments. Among the approaches that work, we investigate the opportunity for corroboration through experimental probes of gravitational waves at pulsar timing arrays. We provide examples of theories that are already ruled out, theories that will soon be probed, and theories that will not be tested in the foreseeable future. The models that are most strongly constrained are th…
A lower bound on primordial power spectrum from halo substructure
University of Amsterdam（阿姆斯特丹大学）；Kavli Institute for the Physics and Mathematics of the Universe, University of Tokyo（东京大学宇宙起源研究科）；Yokohama National University（横滨国立大学）；RIKEN Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS)（理化学研究所交叉理论数学科学部）；Institute for Theoretical Physics, Kanazawa University（金泽大学理论物理研究所）；Saga University（佐贺大学）
The recent discovery of gravitational waves from merging black holes has generated interest in primordial black holes as a possible component of the dark matter. In this paper, we show that pulsar timing may soon have sufficient data to constrain $1$-$1000\,M_{\odot}$ primordial black holes via the non-detection of a third-order Shapiro time delay as the black holes move around the Galactic halo. We present the results of a Monte Carlo simulation which suggests that future data from known pulsars may be capable of constraining the PBH density more stringently than other existing methods in the…
Pulsar Timing Sensitivity to Dark Matter Substructure in the Presence of a Stochastic Gravitational-Wave Background
California Institute of Technology（加州理工学院）；University of California, Berkeley（加利福尼亚大学伯克利分校）；University of California, San Diego（加利福尼亚大学圣地亚哥分校）；Karlsruhe Institute of Technology (KIT)（卡尔斯鲁厄理工学院）
In two previous papers (Salvador-Solé 2012a,b), it was shown that: i) the typical structural and kinematic properties of haloes in (bottom-up) hierarchical cosmologies endowed with random Gaussian density perturbations of dissipationless collisionless dark matter emerge naturally from the typical properties of peaks in the primordial density field and ii) halo statistics are well described by the peak formalism. In the present paper, we use these results to model halo substructure. Specifically, making use of the peak formalism and the fact that accreting haloes evolve from the inside-out, we …
Primordial black holes (PBHs) are one of the candidates to explain the gravitational wave (GW) signals observed by the LIGO detectors. Among several phenomena in the early Universe, cosmic inflation is a major example to generate PBHs from large primordial density perturbations. In this paper, we discuss the possibility to interpret the observed GW events as mergers of PBHs which are produced by cosmic inflation. The primordial curvature perturbation should be large enough to produce a sizable amount of PBHs and thus we have several other probes to test this scenario. We point out that the cur…
Implications of Pulsar Timing Array Data for Scalar-Induced Gravitational Waves and Primordial Black Holes: Primordial Non-Gaussianity $f_{\mathrm{NL}}$ Considered
Small-scale dark matter structure within the Milky Way is expected to affect pulsar timing. The change in gravitational potential induced by a dark matter halo passing near the line of sight to a pulsar would produce a varying delay in the light travel time of photons from the pulsar. Individual transits produce an effect that would either be too rare or too weak to be detected in 30-year pulsar observations. However, a population of dark matter subhalos would be expected to produce a detectable effect on the measured properties of pulsars if the subhalos constitute a significant fraction of t…
We demonstrate that the perturbations of strongly lensed images by low-mass dark matter subhalos are significantly impacted by the concentration of the perturbing subhalo. For subhalo concentrations expected in $Λ$CDM, significant constraints on the concentration can be obtained at HST resolution for subhalos with masses larger than about $10^{10}M_\odot$. Constraints are also possible for lower mass subhalos, if their concentrations are higher than the expected scatter in CDM. We also find that the concentration of lower mass perturbers down to $\sim 10^8M_\odot$ can be well-constrained with …
Close Pulsar Pairs See Dark Matter Substructure through the Gravitational-Wave Background
California Institute of Technology（加州理工学院）；University of California, Berkeley（加州大学伯克利分校）；University of California, San Diego（加州大学圣地亚哥分校）；Karlsruhe Institute of Technology (KIT)（卡尔斯鲁厄理工学院）
Probing Primordial Black Hole Mergers in Clusters with Pulsar Timing Data
a Service de Physique Th\'eorique, Brussels Laboratory of the Universe BLU-ULB, Universit\'e Libre de Bruxelles, Boulevard du Triomphe, CP225, 1050 Brussels, Belgium
In this paper, the criterion used to determine whether a density perturbation will collapse to form a primordial black hole (PBH) is re-examined, in respect of its use to determine the abundance of PBHs. There is particular focus on which parameter to use, the time at which the abundance should be calculated, and the use of different smoothing functions. It is concluded that, with the tools currently available, the smoothed density contrast should be used rather than the peak value, and should be calculated from the time-independent component of the density contrast in the super-horizon limit …
Models of Dark Matter (DM) can leave unique imprints on the Universe's small scale structure by boosting density perturbations on small scales. We study the capability of Pulsar Timing Arrays to search for, and constrain, subhalos from such models. The models of DM we consider are ordinary adiabatic perturbations in $Λ$CDM, QCD axion miniclusters, models with early matter domination, and vector DM produced during inflation. We show that $Λ$CDM, largely due to tidal stripping effects in the Milky Way, is out of reach for PTAs (as well as every other probe proposed to detect DM small scale struc…
The NANOGrav, Parkes, European, and International Pulsar Timing Array (PTA) Collaborations have reported evidence for a common-spectrum process that can potentially correspond to a stochastic gravitational wave background (SGWB) in the 1--100 nHz frequency range. We consider the scenario in which this signal is produced by magnetohydrodynamic (MHD) turbulence in the early Universe, induced by a nonhelical primordial magnetic field at the energy scale corresponding to the quark confinement phase transition. We perform MHD simulations to study the dynamical evolution of the magnetic field and co…
Ultracompact Minihalos (UCMHs) have been proposed as a type of dark matter sub-structure seeded by large-amplitude primordial perturbations and topological defects. UCMHs are expected to survive to the present era, allowing constraints to be placed on their cosmic abundance using observations within our own Galaxy. Constraints on their number density can be linked to conditions in the early universe that impact structure formation, such as increased primordial power on small scales, generic weak non-Gaussianity, and the presence of cosmic strings. We use new constraints on the abundance of UCM…
Impact on time delays due to milli-lensing by subhalos on lensed gravitational waves
Department of Physics, Dr. Vishwanath Karad MIT World Peace University（德拉·维斯瓦纳特·卡拉德麻省理工学院世界和平大学物理系）；Inter-University Centre for Astronomy and Astrophysics（大学间天文学和天体物理学中心）；Kavli IPMU (WPI), UTIAS, The University of Tokyo（卡弗里宇宙物理学与数学起源研究所（WPI），东京大学宇宙射线研究所）；Department of Physics, Indian Institute of Science Education and Research（印度科学教育与研究机构物理系）
Primordial black hole (PBH) mergers have been proposed as an explanation for the gravitational wave events detected by the LIGO collaboration. Such PBHs may be formed in the early Universe as a result of the collapse of extremely rare high-sigma peaks of primordial fluctuations on small scales, as long as the amplitude of primordial perturbations on small scales is enhanced significantly relative to the amplitude of perturbations observed on large scales. One consequence of these small-scale perturbations is generation of stochastic gravitational waves that arise at second order in scalar pert…
In the axion monodromy inflation, the inflation is driven by the axion with super-Planckian field values in a monomial potential with superimposed sinusoidal modulations. The coupling of the axion to massless gauge fields can induce copious particle production during inflation, resulting in large non-Gaussian curvature perturbation that leads to the formation of primordial black holes. In this paper, we explore the parameter space in the axion monodromy inflation model that favors the formation of primordial black holes with masses ranging from $10^8$ grams to $20$ solar masses. We also study …
The recent observations of the gravitational waves (GWs) by LIGO-Virgo collaboration infer the increasing possibility of the primordial black holes (PBHs). Recently it was pointed out that sufficient PBHs are produced by the Affleck-Dine mechanism where inhomogeneous baryogenesis takes place due to change of the Hubble induced mass during and after inflation and forms high baryon bubbles (HBBs). The produced HBBs have large density contrasts through the QCD phase transition or stable Q-ball formation, which leads to formation of the LIGO PBHs. Furthermore, in this model stringent constraints f…
We revise primordial black hole (PBH) formation in the axion-like curvaton model and investigate whether PBHs formed in this model can be the origin of the gravtitational wave (GW) signals detected by the Advanced LIGO. In this model, small-scale curvature perturbations with large amplitude are generated, which is essential for PBH formation. On the other hand, large curvature perturbations also become a source of primordial GWs by their second-order effects. Severe constraints are imposed on such GWs by pulsar timing array (PTA) experiments. We also check the consistency of the model with the…
In this letter, we propose a novel scenario which simultaneously explains $\mathcal{O}(10)M_\odot$ primordial black holes (PBHs) and dark matter in the minimally supersymmetric standard model. Gravitational waves (GWs) events detected by LIGO-Virgo collaboration suggest an existence of black holes as heavy as $\sim 30M_\odot$. In our scenario, as seeds of the PBHs, we make use of the baryon number perturbations which are induced by the special type of Affleck-Dine mechanism. Furthermore, the scenario does not suffer from the stringent constraints from CMB $μ$-distortion due to the Silk damping…
The NANOGrav collaboration for the pulsar timing array (PTA) observation recently announced evidence of an isotropic stochastic process, which may be the first detection of the stochastic gravitational-wave (GW) background. We discuss the possibility that the signal is caused by the second-order GWs associated with the formation of solar-mass primordial black holes (PBHs). This possibility can be tested by future interferometer-type GW observations targeting the stochastic GWs from merger events of solar-mass PBHs as well as by updates of PTA observations.
If the black holes detected by LIGO/VIRGO are primordial black holes (PBHs) sourcing from a large primordial curvature perturbation on small scales, the corresponding induced gravitational waves (GWs) would peak at nanohertz that is detectable by the current and future observations of pulsar timing array (PTA). In this paper we show that with the mass function estimated from the merger rate of LIGO O1 and O2 events, the induced GWs from such a curvature perturbation with a Gaussian narrow peak at some small scale would be in a seemingly mild tension with current constraints from PTA. However, …
