Pulsar timing probes of primordial black holes and subhalos

Open Access

Pulsar timing probes of primordial black holes and subhalos

Jeff A. Dror, Harikrishnan Ramani, Tanner Trickle, and Kathryn M. Zurek

Phys. Rev. D 100, 023003 – Published 12 July 2019

Abstract

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 $10^{- 12} M_{⊙}$ to well above $100 M_{⊙}$ . 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 subcomponent reaching the subpercent 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.

Received 13 February 2019

DOI:https://doi.org/10.1103/PhysRevD.100.023003

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

Published by the American Physical Society

Physics Subject Headings (PhySH)

Gravitational lenses Hypothetical particle physics models Particle astrophysics

Gravitation, Cosmology & AstrophysicsParticles & Fields

Authors & Affiliations

Jeff A. Dror^1,2, Harikrishnan Ramani^1,2, Tanner Trickle ^1,2, and Kathryn M. Zurek^1,2,3

¹Theory Group, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
²Berkeley Center for Theoretical Physics, University of California, Berkeley, California 94720, USA
³Theoretical Physics Department, CERN, 1211 Geneva 23, Switzerland

Article Text

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Issue

Vol. 100, Iss. 2 — 15 July 2019

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Images

Figure 1
Normalized signal shape observable in pulsar timing data. In general the Doppler signal is a linear combination of the two shapes depending on the object’s trajectory, while the Shapiro signal shape is fixed.
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Figure 2
SKA projected constraints on the DM fraction $f$ for Doppler (blue) and Shapiro (red) signals contained in PBHs. The dynamic searches are shown in solid lines and static in dashed lines. Each search is labeled with the mass scalings corresponding to the analytic formulas given in Eqs. (30)–(35).
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Figure 3
PTA projected constraints on PBH-like DM compact objects of mass $M$ and DM fraction $f$ combining all proposed searches. The scenarios (labeled SC1-4) are described in the text and are roughly given by current capabilities (blue), current capabilities with 10 more years of measurement on the same pulsars (red), SKA capabilities (orange), and an optimistic scenario where SKA finds a large number of high performing pulsars (green). The dark gray region corresponds to the unphysical case of $f > 1$ . For reference we also show the constraint from lensing (dashed black).
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Figure 4
Sensitivity distance (as defined in the text) as a function of the compact object mass $M$ for PTA Doppler and Shapiro searches, as well as supernova and stellar lensing. The red curves in the left and right panels are the mass enclosed functions, $r_{enc}$ , for the NFW and UCMH-like profiles (defined in the text), respectively, for three different concentration parameters $c$ , and two different viral masses, $M_{vir} = 10^{- 7} M_{⊙}$ , $10^{- 1} M_{⊙}$ . Where these red curves intersect the sensitivity distance curves corresponds to the effective subhalo enclosed mass $M^{*}$ to which the various searches are sensitive. See text for more details.
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Figure 5
Comparison of the reach of pulsar timing data in scenario SC3 (red) to lensing (gray) experiments, for NFW halos of different concentration parameters, $c$ . With concentration parameters below $1 0^{8}$ , PTA searches rapidly become more sensitive than lensing searches. The PTA constraints are cut off when $r_{enc}$ never crosses the sensitivity radius for any $M$ . For the concentration parameters chosen, this only occurs for the Doppler dynamic search leading to a sharp rise in the constraints at $M_{vir} = 10^{- 9} M_{⊙}$ for $c = 100$ .
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Figure 6
Comparison of the analytic estimates (solid) and the full Monte Carlo approach (dashed) for SKA PTA parameters given in Table 1. The analytic estimate agrees with the numerical results to $O (1)$ corrections except on the left-hand side of the static constraints, where the closest-object approximation breaks down.
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