arXiv subjects

Peter Tinyakov

Publications and source records attributed to Peter Tinyakov.

At least 19 recordsLinked to original sources

arXiv2026

Gravitational waves from primordial black holes passing by neutron stars: observational prospects for the Galactic center

We investigate the gravitational wave (GW) signals emitted by planetary-mass primordial black holes (PBHs) passing nearby or traversing neutron stars (NSs). While previous studies mainly focused on the detailed waveforms of the signals, we estimate the rate of PBH-NS gravitational-wave events originating from the Galactic center and compute the probability of detecting a signal over 10 years of LIGO-Virgo-KAGRA observations. We examine in detail the case of PBHs bound to NSs, focusing on eccentric orbits that give rise to repeated GW bursts emitted in correlated series, each burst corresponding to a periastron passage. Despite the enhancement from the large number of bursts produced by a single PBH-NS pair, the total number of signals produced in this way remains subdominant to those due to random unbound encounters of PBHs with NSs. We also find that both types of signals have a very small probability $P\lesssim 10^{-8}$ to be detected in a 10 year period.

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arXiv2025

Bright Cosmic-Ray Source as a Solution to Auger-TA Tensions

The ultra-high-energy cosmic ray (UHECR) spectra measured by the Pierre Auger Observatory (Auger) and the Telescope Array (TA) agree very well below $10^{19.5}$ eV but differ significantly at higher energies. We show that these differences can be explained by a single nearby source superimposed on a nearly isotropic background. Taking into account deflections in Galactic and extragalactic magnetic fields, such a source can account for the excess in the TA spectrum without producing excessive anisotropy. The required hard spectrum of the source and intermediate-mass composition are consistent with previous fits of the Auger-only spectrum and composition. This scenario offers several additional advantages: (i) the source produces a broad excess partially overlapping the TA hotspots, suggesting their possible explanation; (ii) without additional tuning, it reproduces the $\sim90^\circ$ shift in dipole direction observed between the Auger-only and combined Auger-TA analyses; and (iii) the best-fit position of the source lies near M82, the brightest nearby starburst galaxy, making it a plausible source of the UHECR.

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arXiv2025

Constraints on asteroid-mass primordial black holes in dwarf galaxies using Hubble Space Telescope photometry

Primordial black holes (PBHs) in the asteroid-mass range remain a viable and until now unconstrained dark matter (DM) candidate. If such PBHs exist, they could be captured by stars in DM-dominated environments with low velocity dispersion such as ultra-faint dwarf galaxies (UFDs). The capture probability increases with the stellar mass, and captured PBHs would rapidly destroy their host stars. As a result, the presence of PBHs in UFDs would alter their stellar mass functions. Using photometric observations of three ultra-faint dwarf galaxies from the Hubble Space Telescope, we show that it is unlikely that their mass functions have been significantly modified by PBHs, and we place constraints on the PBH abundance. In the ultra-faint dwarf galaxy Triangulum II, PBHs around $10^{19}$g are excluded at the $2\sigma$ ($3\sigma$) level from constituting more than $\sim55\%$ ($\sim78\%$) of the dark matter, while the possibility that PBHs represent the entirety of the DM is excluded at the $3.7\sigma$ level.

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arXiv2025

UHECR deflections in the coherent Galactic magnetic field

We study the deflections of ultra-high-energy cosmic rays in several widely used models of the coherent Galactic magnetic field (GMF), including PT11 (Pshirkov et al. [1]), JF12 (Jansson and Farrar [2]), UF23 (Unger and Farrar [3]) and KST24 (Korochkin, Semikoz, and Tinyakov [4]). We propagate particles with rigidities of 5, 10, and 20 EV and analyze the differences in deflection predictions across these GMF models. We identify the GMF components responsible for deflections in various regions of the sky and discuss the uncertainties in modeling these components, as well as potential future improvements.

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arXiv2024

The coherent magnetic field of the Milky Way halo, Local Bubble and Fan Region

Recent catalog of Faraday rotation measures (RM) of extragalactic sources together with the synchrotron polarization data from WMAP and Planck provides us with a wealth of information on magnetic fields of the Galaxy. However, the integral character of these observables together with our position inside the Galaxy makes the inference of the coherent Galactic magnetic field (GMF) complicated and ambiguous. We combine several phenomenological components of the GMF -- the spiral arms, the toroidal halo, the X-shaped field and the field of the Local Bubble -- to construct a new model of the regular GMF outside the thin disk. To have control over the relative contributions of the RM and polarization data to the fit we pay special attention to the estimation of errors in data bins. To this end we develop a systematic method which is uniformly applicable to different data sets. This method takes into account individual measurement errors, the variance in the bin as well as fluctuations in the data at angular scales larger than the bin size. This leads to decrease of the errors and, as a result, to better sensitivity of the data to the model content. We cross checked the stability of our method with the new LOFAR data. We found that the four components listed above are sufficient to fit both the RM and polarization data over the whole sky with only a small fraction masked out. Moreover, we have achieved several important improvements compared to previous approaches. Due to account of our location inside of the Local Bubble our model does not require introduction of striated fields. For the first time we showed that the Fan Region can be modeled as a Galactic-scale feature. The pitch angle of the magnetic field in our fit converged to the value around 20 degrees. Interestingly, with value is very close to the direction of the arms inferred recently from Gaia data on upper main sequence stars.

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arXiv2024

Primordial black holes: the asteroid mass window

Primordial black holes (PBHs) are an attractive dark matter candidate, particularly if they can explain the totality of it. At PBH masses below $\sim 10^{17}$g and above $\sim 10^{23}$g this possibility is excluded from the variety of arguments and with different confidence. The range in between, often referred to as the "asteroid mass window", currently remains unconstrained. The most promising, in our view, way to probe this mass range is to use stars as the PBH detectors. If a star captures even a single PBH it starts being accreted onto it and eventually gets destroyed -- converted into a sub-solar mass black hole. This process may have a variety of signatures form a mere star disappearance to supernova-type explosions of a new kind. The viability of this approach depends crucially on the probability of PBH capture by stars. In this chapter we summarize the existing capture mechanisms and discuss their implications for constraining the abundance of (or perhaps discovering) PBHs in the asteroid mass window.

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arXiv2023

The impact of primordial black holes on the stellar mass function of ultra-faint dwarf galaxies

If primordial black holes constitute the dark matter, stars forming in dark-matter dominated environments with low velocity dispersions, such as ultra-faint dwarf galaxies, may capture a black hole at birth. The capture probability is non-negligible for primordial black holes of masses around $10^{20}$g, and increases with stellar mass. Moreover, infected stars are turned into virtually invisible black holes on cosmologically short timescales. Hence, the number of observed massive main-sequence stars in ultra-faint dwarfs should be suppressed if the dark matter was made of asteroid-mass primordial black holes. This would impact the measured mass distribution of stars, making it top-light (i.e. depleted in the high-mass range). Using simulated data that mimic the present-day observational power of telescopes, we show that already existing measurements of the mass function of stars in local ultra-faint dwarfs could be used to constrain the fraction of dark matter composed of primordial black holes in the -- currently unconstrained -- mass range of $10^{19}-10^{21}$g.

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arXiv2022

Constraints on primordial black holes from observation of stars in dwarf galaxies

We propose a way to constrain the primordial black hole (PBH) abundance in the range of PBH masses $m$ around $10^{20}$g based on their capture by Sun-like stars in dwarf galaxies, with subsequent star destruction. We calculate numerically the probability of a PBH capture by a star at the time of its formation in an environment typical of dwarf galaxies. Requiring that no more than a fraction $\xi$ of stars in a dwarf galaxy is destroyed by PBHs translates into an upper limit on the PBH abundance. For the parameters of Triangulum II and $\xi=0.5$, we find that no more than $\sim 35\%$ of dark matter can consist of PBHs in the mass range $10^{18} - \text{(a few)}\times 10^{21}$g. The constraints depend strongly on the parameter $\xi$ and may significantly improve if smaller values of $\xi$ are established from observations. An accurate determination of $\xi$ from dwarf galaxy modeling is thus of major importance.

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arXiv2021

Solar mass black holes from neutron stars and bosonic dark matter

Black holes with masses $\approx 1\, M_{\odot}$ cannot be produced via stellar evolution. A popular scenario of their formation involves transmutation of neutron stars - by accumulation of dark matter triggering gravitational collapse in the star centers. We show that this scenario can be realized in the models of bosonic dark matter despite the apparently contradicting requirements on the interactions of dark matter particles: on the one hand, they should couple to neutrons strongly enough to be captured inside the neutron stars, on the other, their loop-induced self-interactions impede collapse. Observing that these conflicting conditions are imposed at different scales, we demonstrate that models with efficient accumulation of dark matter can be deformed at large fields to make unavoidable its subsequent collapse into a black hole. Workable examples include weakly coupled models with bended infinite valleys.

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arXiv2021

The UHECR dipole and quadrupole in the latest data from the original Auger and TA surface detectors

The sources of ultra-high-energy cosmic rays are still unknown, but assuming standard physics, they are expected to lie within a few hundred megaparsecs from us. Indeed, over cosmological distances cosmic rays lose energy to interactions with background photons, at a rate depending on their mass number and energy and properties of photonuclear interactions and photon backgrounds. The universe is not homogeneous at such scales, hence the distribution of the arrival directions of cosmic rays is expected to reflect the inhomogeneities in the distribution of galaxies; the shorter the energy loss lengths, the stronger the expected anisotropies. Galactic and intergalactic magnetic fields can blur and distort the picture, but the magnitudes of the largest-scale anisotropies, namely the dipole and quadrupole moments, are the most robust to their effects. Measuring them with no bias regardless of any higher-order multipoles is not possible except with full-sky coverage. In this work, we achieve this in three energy ranges (approximately 8--16 EeV, 16--32 EeV, and 32--$\infty$ EeV) by combining surface-detector data collected at the Pierre Auger Observatory until 2020 and at the Telescope Array (TA) until 2019, before the completion of the upgrades of the arrays with new scintillator detectors. We find that the full-sky coverage achieved by combining Auger and TA data reduces the uncertainties on the north-south components of the dipole and quadrupole in half compared to Auger-only results.

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arXiv2021

UHECR arrival directions in the latest data from the original Auger and TA surface detectors and nearby galaxies

The distribution of ultra-high-energy cosmic-ray arrival directions appears to be nearly isotropic except for a dipole moment of order $6 \times (E/10~\mathrm{EeV})$ per cent. Nonetheless, at the highest energies, as the number of possible candidate sources within the propagation horizon and the magnetic deflections both shrink, smaller-scale anisotropies might be expected to emerge. On the other hand, the flux suppression reduces the statistics available for searching for such anisotropies. In this work, we consider two different lists of candidate sources: a sample of nearby starburst galaxies and the 2MRS catalog tracing stellar mass within $250~\mathrm{Mpc}$. We combine surface-detector data collected at the Pierre Auger Observatory until 2020 and the Telescope Array until 2019, and use them to test models in which UHECRs comprise an isotropic background and a foreground originating from the candidate sources and randomly deflected by magnetic fields. The free parameters of these models are the energy threshold, the signal fraction, and the search angular scale. We find a correlation between the arrival directions of $11.8\%_{-3.1\%}^{+5.0\%}$ of cosmic rays detected with $E \ge 38~\mathrm{EeV}$ by Auger or with $E \gtrsim 49~\mathrm{EeV}$ by TA and the position of nearby starburst galaxies on a ${15.5^\circ}_{-3.2^\circ}^{+5.3^\circ}$ angular scale, with a $4.2\sigma$ post-trial significance, as well as a weaker correlation with the overall galaxy distribution.

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arXiv2020

Revisiting primordial black holes capture into neutron stars

Primordial black holes (PBH), produced through a variety of processes in the early universe, could fill galactic halos accounting for a fraction or the totality of the dark matter. In particular, PBH with sub-stellar masses could be captured by stars, start to swallow their material, and eventually turn them into BH, hence originating a peculiar new type of stellar catastrophic event. Here we revisit this process in the most favorable case of PBH capture by neutron stars. We detail a number of novel features in the capture phase, during the settling within the star and mass growth of the PBH, and illustrate some phenomenological consequences. In particular, we point out that in the subsonic regime the PBH drag takes the form of a Bondi accretion. As a result, the onset of the final transmutation of the NS into a stellar sized BH is expected with the PBH seed in slight off-center position. We also compute the gravitational wave energy-loss and signals associated to different phases of the PBH-stellar interaction. In particular, the emission associated to the accretion phase is periodic with a few kHz frequency; in the rare case of a nearby Galactic event and for light PBH, it could constitute a warning of the forthcoming transmutation.

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arXiv2019

Constraints on Dark Matter from the Moon

New and complimentary constraints are placed on the spin-independent interactions of dark matter with baryonic matter. Similar to the Earth and other planets, the Moon does not have any major internal heat source. We derive constraints by comparing the rate of energy deposit by dark matter annihilations in the Moon to 12 mW/m$^2$ as measured by the Apollo mission. For light dark matter of mass $\mathcal{O}(10)$ GeV, we also examine the possibility of dark matter annihilations in the Moon limb. In this case, we place constraints by comparing the photon flux from such annihilations to that of the Fermi-LAT measurement of $10^{-4}$ MeV/cm$^2$s. This analysis excludes spin independent cross section $\gtrsim 10^{-37}$ $\rm{cm}^2$ for dark matter mass between 30 and 50 GeV.

hep-ph↗

arXiv2019

What is the nature and origin of the highest-energy particles in the universe?

This white paper was submitted to the US Astronomy and Astrophysics Decadal Survey (Astro2020) and defines the science questions to be answered in the next decade in the field of Ultra-High Energy Cosmic-Rays. Following a review of the recent experimental and theoretical advances in the field, the paper outlines strategies and requirements desirable for the design of future experiments.

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arXiv2018

Non-Primordial Solar Mass Black Holes

We propose a mechanism that can convert a sizeable fraction of neutron stars into black holes with mass $\sim 1M_\odot$, too light to be produced via standard stellar evolution. We show that asymmetric fermionic dark matter of mass $\sim$ TeV, with attractive self-interaction within the range that alleviates the problems of collisionless cold dark matter, can accumulate in a neutron star and collapse, forming a seed black hole that converts the rest of the star to a solar mass black hole. We estimate the fraction of neutron stars that can become black holes without contradicting existing neutron star observations. Like neutron stars, such solar mass black holes could be in binary systems, which may be searched for by existing and forthcoming gravitational wave detectors. The (non-)observation of binary mergers of solar mass black holes may thus test the specific nature of the dark matter.

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arXiv2017

How isotropic can the UHECR flux be?

Modern observatories of ultra-high energy cosmic rays (UHECR) have collected over 10^4 events with energies above 10 EeV, whose arrival directions appear to be nearly isotropically distributed. On the other hand, the distribution of matter in the nearby Universe -- and, therefore, presumably also that of UHECR sources -- is not homogeneous. This is expected to leave an imprint on the angular distribution of UHECR arrival directions, though deflections by cosmic magnetic fields can confound the picture. In this work, we investigate quantitatively this apparent inconsistency. To this end we study observables sensitive to UHECR source inhomogeneities but robust to uncertainties on magnetic fields and the UHECR mass composition. We show, in a rather model-independent way, that if the source distribution tracks the overall matter distribution, the arrival directions at energies above 30 EeV should exhibit a sizeable dipole and quadrupole anisotropy, detectable by UHECR observatories in the very near future. Were it not the case, one would have to seriously reconsider the present understanding of cosmic magnetic fields and/or the UHECR composition. Also, we show that the lack of a strong quadrupole moment above 10 EeV in the current data already disfavours a pure proton composition, and that in the very near future measurements of the dipole and quadrupole moment above 60 EeV will be able to provide evidence about the UHECR mass composition at those energies.

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arXiv2015

Tidal streams from axion miniclusters and direct axion searches

In some axion dark matter models a dominant fraction of axions resides in dense small-scale substructures, axion miniclusters. A fraction of these substructures is disrupted and forms tidal streams where the axion density may still be an order of magnitude larger than the average. We discuss implications of these streams for the direct axion searches. We estimate the fraction of disrupted miniclusters and the parameters of the resulting streams, and find that stream-crossing events would occur at a rate of about $1/(20 {\rm yr})$ for 2-3 days, during which the signal in axion detectors would be amplified by a factor $\sim 10$. These estimates suggest that the effect of the tidal disruption of axion miniclusters may be important for direct axion searches and deserves a more thorough study.

astro-ph.CO↗

arXiv2014

Adiabatic contraction revisited: implications for primordial black holes

We simulate the adiabatic contraction of a dark matter (DM) distribution during the process of the star formation, paying particular attention to the phase space distribution of the DM particles after the contraction. Assuming the initial uniform density and Maxwellian distribution of DM velocities, we find that the number $n(r)$ of DM particles within the radius $r$ scales like $n(r) \propto r^{1.5}$, leading to the DM density profile $ρ\propto r^{-1.5}$, in agreement with the Liouville theorem and previous numerical studies. At the same time, the number of DM particles $ν(r)$ with periastra smaller than $r$ is parametrically larger, $ν(r) \propto r$, implying that many particles contributing at any given moment into the density $ρ(r)$ at small $r$ have very elongated orbits and spend most of their time at distances larger than $r$. This has implications for the capture of DM by stars in the process of their formation. As a concrete example we consider the case of primordial black holes (PBH). We show that accounting for very eccentric orbits boosts the amount of captured PBH by a factor of up to $2\times 10^3$ depending on the PBH mass, improving correspondingly the previously derived constraints on the PBH abundance.

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