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LISA bright sirens as a tiebreaker among cosmologies in tension

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M. F. A. Medeiros, F. C. Carvalho, L. L. Sales

Cosmology and Nongalactic Astrophysics · Submitted 28 Sep 2026 · 62 references

Pith's verdict: The tiebreaker framing and the 3x3 grid give LISA forecasting a genuinely useful new question, and the statistical execution is careful and unusually honest; the one operative claim that is actually untested is the small-catalogue exclusion, which rests on random thinning rather than redshift-dependent counterpart selection.

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arXiv ID2609.35317 (version 1)
Pith ID2LBRN5VN, Pith's permanent record of this paper and its review
CitationF. C. Carvalho, L. L. Sales, M. F. A. Medeiros. "LISA bright sirens as a tiebreaker among cosmologies in tension." arXiv:2609.35317 (2026). https://pith.science/paper/2LBRN5VN
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The paper

The paper claims

This paper claims that a future LISA bright-siren catalogue built under the Cepheid-calibrated Pantheon+SH0ES cosmology would be inconsistent with every real-data background at a significance far beyond 5 sigma, while the Planck-2018 and…

The reading

This paper asks a different question from a standard forecast: not how tightly LISA will constrain one cosmology, but which of the cosmologies currently in dispute over the Hubble constant a future LISA bright-siren dataset would render most self-consistent. The authors build mock LISA catalogues of massive black hole binary mergers under three fiducial cosmologies drawn from the Planck-2018 CMB, the Union3 supernova compilation, and the Cepheid-calibrated Pantheon+SH0ES, each catalogue carrying an error budget from instrumental noise, weak lensing, and host peculiar velocities. They then compare the LISA-only posterior with a real-data background of Type Ia supernovae, DESI baryon acoustic oscillations, cosmic chronometers, and the compressed Planck CMB, in the ($H_0,\Omega_m$) plane. The tension runs from 2.08$\sigma$ to far beyond 5$\sigma$ depending almost entirely on which fiducial the catalogue was simulated under: the Cepheid-calibrated universe is inconsistent with every background tested, while the Planck and Union3 universes, separated by only 0.24 km/s/Mpc in $H_0$, cannot be told apart at any catalogue size. The upshot is that LISA bright sirens are a sharp arbiter of the Cepheid-calibrated scenario and silent between the other two.

What carries the argument

The central object is the LISA bright siren: a massive black hole binary coalescence whose luminosity distance comes directly from the gravitational-wave waveform, with the redshift fixed by an identified electromagnetic counterpart. The analysis runs a three-step protocol per fiducial — simulate a mock catalogue of detected events (signal-to-noise ratio above 8) at the fiducial ($H_0,\Omega_m$), take a fixed real-data background, and compare their posteriors — and quantifies the tension with the Raveri–Hu difference-in-mean statistic $Q_{\rm DM}$, built from the difference between the two posterior means and the sum of their covariances and converted to an $n\sigma$ value through the $\chi^2$ distribution with two degrees of freedom. Each event's distance error combines an instrumental term ($\approx 2\,d_L/\rho$, the factor of two covering the distance–inclination correlation), a weak-lensing dispersion, and a peculiar-velocity term, added in quadrature. Because both the LISA-only and background posteriors are strongly elongated along the $H_0$–$\Omega_m$ degeneracy while the offset between them runs across it, the two-dimensional statistic carries the discriminating information that the one-dimensional marginals hide.

Extended reading notes

Core claim

The central claim, on the paper's own terms, is that LISA bright sirens offer sharply asymmetric discriminating power as a tiebreaker in the Hubble tension. A catalogue generated in a Pantheon+SH0ES universe — $H_0\approx 73$ km/s/Mpc, the Cepheid-calibrated end — is inconsistent with every real-data background the authors test, at significance far beyond 5$\sigma$ for the 768 simulated events, still above 5$\sigma$ at 50 bright sirens, and at 3–5$\sigma$ by Fisher estimate for the 10–20 counterpart events expected from recent population models. The exclusion is carried by the two-dimensional offset running across the $H_0$–$\Omega_m$ degeneracy, so the one-dimensional marginals understate it badly. By contrast, the Planck-2018 and Union3 fiducials, separated by only 0.24 km/s/Mpc in $H_0$, differ in their tension from a common background (2.1$\sigma$ versus 3.3$\sigma$) by less than the $\pm 0.4\sigma$ scatter between noise realisations and cannot be separated by enlarging the catalogue, which tightens both equally. The paper argues this asymmetry — not any ranking of the three — is the result that carries forward. It also shows the waveform supplies no prior of its own: catalogues built at $H_0$ from 35 to 115 km/s/Mpc are recovered with essentially the same fractional precision, so rejecting an implausible expansion history is done entirely by the electromagnetic comparison.

Load-bearing premise

The load-bearing premise is that every detected massive black hole binary has an identified electromagnetic counterpart giving a measured redshift: the LISA-only posterior width, and hence the tension against every background, scales directly with how many bright sirens with known redshift the catalogue contains, and the authors themselves acknowledge (Section 6) that realistic counterpart fractions are considerably smaller and that a redshift-dependent counterpart fraction would be the proper treatment.

Editorial extensions

If this is right

  • A LISA bright-siren catalogue with roughly 50 or more events carrying measured redshifts would decisively exclude a Cepheid-calibrated expansion history ($H_0\approx 73$ km/s/Mpc) at beyond 5$\sigma$, settling whether the local distance-ladder value is a real feature of the Universe.
  • The exclusion does not rest on the CMB: removing CMB information entirely (BBN-calibrated BAO ruler, no compressed CMB shift parameter) still leaves the Pantheon+SH0ES fiducial above 5$\sigma$, though removing the absolute calibration of the BAO ruler drops it to 2.8$\sigma$.
  • The Planck-2018 and Union3 scenarios are not separately resolvable by LISA bright sirens of any plausible size on this error budget, so LISA will not decide which of those two low-$H_0$ histories is right.
  • The tension between LISA-only and background data is dominated by the assumed fiducial (the supernova compilation moves it by at most 1.2$\sigma$), so the informative comparison is across fiducials at fixed compilation, not within a scenario paired with its own supernovae.
  • Because the waveform supplies no prior of its own on $H_0$ — catalogues from 35 to 115 km/s/Mpc recover their fiducial with nearly identical fractional precision — the rejection of an implausible cosmology is a statement about the electromagnetic data, not about LISA physics.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • The paper's tiebreaker is implicitly a test of the early-Universe calibration chain: because the real-data background's absolute distance scale is set by the BAO sound horizon and the Planck CMB, a 'consistent' LISA result under this protocol is one agreeing with a Planck-like $H_0$, so the exercise assumes the early-Universe anchor rather than adjudicating between it and the local ladder.
  • If the realistic bright-siren yield with identified counterparts is small (order 10–20 events), a single-mission exclusion stays in the 3–5$\sigma$ range; stacking LISA events with galaxy-catalogue statistical (dark siren) redshifts could raise the effective event count and push the test past 5$\sigma$ — an extension the paper does not itself pursue.
  • A LISA result that instead lands near the Cepheid value (near 73 km/s/Mpc) would, on this paper's own logic, point to a systematic error in the early-Universe-anchored reference chain rather than to new physics, because LISA alone cannot distinguish the two; resolving such a surprise would require a genuinely ladder-independent late-time probe.
  • The uniform fractional recovery across $H_0 = 35$–115 km/s/Mpc implies the most informative LISA statement is not its precision but its location: a near-Planck agreement would corroborate the early-Universe anchor, and a near-Cepheid agreement would indict it.
Original abstract

Gravitational waves from massive black hole binaries detected by LISA will deliver luminosity distances without any astrophysical calibration, offering a probe of the expansion history independent of the cosmic distance ladder. Rather than asking how tightly LISA will constrain a single fiducial cosmology, we ask which of several mutually discrepant present-day cosmologies a future LISA dataset would render most self-consistent. We build mock catalogues of LISA bright sirens under three fiducial cosmologies drawn from datasets that participate in the current $H_0$ discrepancy (Planck 2018, Union3 and Pantheon+SH0ES), with a self-consistent error budget from instrumental noise, weak lensing and host peculiar velocities. We compare the posterior from the simulated LISA data alone with that of a real-data combination of Type Ia supernovae, DESI baryon acoustic oscillations, cosmic chronometers and the compressed Planck 2018 CMB, and quantify their internal tension in the $(H_0,\Omega_m)$ plane, crossing each fiducial with three SN Ia compilations. The fiducial drives the tension, from $2.08\sigma$ to well beyond $5\sigma$, while the supernova compilation changes it by at most $1.2\sigma$. The discriminating power is strongly asymmetric: a Pantheon+SH0ES universe is inconsistent with every background we test, at a significance far in excess of $5\sigma$ and still at $3$-$5\sigma$ for the $10$-$20$ events expected from recent population models, whereas the Planck 2018 and Union3 fiducials, which differ by only $0.24$ km/s/Mpc in $H_0$, cannot be separated by any catalogue size. LISA bright sirens are therefore a sharp arbiter of the Cepheid-calibrated scenario and, on this error budget, silent between the other two.

The compiled record

The paper's own sentences, arranged, kept beside the review and separate from it. Each label is drawn from a closed vocabulary; the number beside it is the probability the classifier gave that label. Numbers in the tables are the authors', checked by code. No sentence in this record was written by a model.

Compiled by classifier-1.13.0 via TypeSafe API, question bank abstract-p1-20260923, 2026-09-29: 1 request, 6,154 input tokens.

What the abstract itself states, as probabilities: claims first 0.04 · states limitation 0.87 · human participants 0.02 · controlled comparison 0.37 · randomized assignment 0.01 · states quantitative result 0.98 · compares with prior results 0.79 · mentions code or data availability 0.03.

The abstract, sentence by sentence

arXiv listing abstract v1. Results and the main claim are underlined; .

Gravitational waves from massive black hole binaries detected by LISA will deliver luminosity distances without any astrophysical calibration, offering a probe of the expansion history independent of the cosmic distance ladder. Rather than asking how tightly LISA will constrain a single fiducial cosmology, we ask which of several mutually discrepant present-day cosmologies a future LISA dataset would render most self-consistent. We build mock catalogues of LISA bright sirens under three fiducial cosmologies drawn from datasets that participate in the current $H_0$ discrepancy (Planck 2018, Union3 and Pantheon+SH0ES), with a self-consistent error budget from instrumental noise, weak lensing and host peculiar velocities. We compare the posterior from the simulated LISA data alone with that of a real-data combination of Type Ia supernovae, DESI baryon acoustic oscillations, cosmic chronometers and the compressed Planck 2018 CMB, and quantify their internal tension in the $(H_0,\Omega_m)$ plane, crossing each fiducial with three SN Ia compilations. The fiducial drives the tension, from $2.08\sigma$ to well beyond $5\sigma$, while the supernova compilation changes it by at most $1.2\sigma$. The discriminating power is strongly asymmetric: a Pantheon+SH0ES universe is inconsistent with every background we test, at a significance far in excess of $5\sigma$ and still at $3$-$5\sigma$ for the $10$-$20$ events expected from recent population models, whereas the Planck 2018 and Union3 fiducials, which differ by only $0.24$ km/s/Mpc in $H_0$, cannot be separated by any catalogue size. LISA bright sirens are therefore a sharp arbiter of the Cepheid-calibrated scenario and, on this error budget, silent between the other two.

background contribution method result interpretation main claim

What the classifier reports for each sentence. The number is the probability it gave the label.
#sentencerolethe authors' own workstates the main conclusionstrength
s0 Gravitational waves from massive black hole binaries detected by LISA will deliver luminosity distances without any astrophysical calibration, offering a probe of the expansion history independent of the cosmic distance ladder. background 0.98 0.09 0.03 asserted 0.78
s1 Rather than asking how tightly LISA will constrain a single fiducial cosmology, we ask which of several mutually discrepant present-day cosmologies a future LISA dataset would render most self-consistent. contribution 0.91 0.33 0.04 asserted 0.60
s2 We build mock catalogues of LISA bright sirens under three fiducial cosmologies drawn from datasets that participate in the current $H_0$ discrepancy (Planck 2018, Union3 and Pantheon+SH0ES), with a self-consistent error budget from instrumental noise, weak lensing and host peculiar velocities. method 0.98 0.94 0.02 asserted 0.98
s3 We compare the posterior from the simulated LISA data alone with that of a real-data combination of Type Ia supernovae, DESI baryon acoustic oscillations, cosmic chronometers and the compressed Planck 2018 CMB, and quantify their internal tension in the $(H_0,\Omega_m)$ plane, crossing each fiducial with three SN Ia compilations. method 0.97 0.93 0.03 asserted 0.97
s4 The fiducial drives the tension, from $2.08\sigma$ to well beyond $5\sigma$, while the supernova compilation changes it by at most $1.2\sigma$. result 1.00 0.92 0.10 asserted 1.00
s5 The discriminating power is strongly asymmetric: a Pantheon+SH0ES universe is inconsistent with every background we test, at a significance far in excess of $5\sigma$ and still at $3$-$5\sigma$ for the $10$-$20$ events expected from recent population models, whereas the Planck 2018 and Union3 fiducials, which differ by only $0.24$ km/s/Mpc in $H_0$, cannot be separated by any catalogue size. result 1.00 0.93 0.51 asserted 1.00
s6 LISA bright sirens are therefore a sharp arbiter of the Cepheid-calibrated scenario and, on this error budget, silent between the other two. interpretation 0.98 0.88 0.87 asserted 1.00

What kind of paper the classifier reports this is: simulation study 1.00 · evidence from simulation or computation 1.00.

What was examined, and what was not

sources read
  • arXiv listing abstract v1
not examined
  • full text
  • figures and tables
  • references and citing sentences
  • relations to other papers
levels run
  • P abstract
not run
  • S sections
  • T body sentences
  • C citations
  • R cross-paper relations

Every quoted sentence on this record is the authors'. Every label is from Pith's closed vocabulary, with the probability shown beside it. Every number in the measurements table is the authors', checked by code. Record as JSON

Figures
Figure 1. Decomposition of the per-event distance uncertainty. Left: median fractional error of each term against redshift, with the interquartile band; the instrumental term scatters widely because the signal-to-noise ratio depends on the drawn masses and orientation. Right: share of the total variance carried by each term, in redshift bins. The step at z = 1 follows the population model, whose component-mass range changes there. 4 Datasets We test three fiducial cosmologies, each drawn from a dataset that participates in the current H0 discrepancy: the Planck 2018 baseline [5], Union3 [29],…
Figure 2. summarises the catalogue: the redshift distribution that follows from Eq. (4.1), and the signal-to-noise ratio of the same events evaluated under each fiducial. Because the fiducial only rescales the redshift-to-distance mapping, the three SNR sets nearly coincide
Figure 3. Simulated LISA bright-siren Hubble diagrams, one per fiducial scenario. Error bars are 1σ from the combined instrumental, weak-lensing, and peculiar-velocity budget of Eq. (3.10). The three panels contain the same intrinsic binaries observed in different universes: only the redshift-to-distance mapping changes, which isolates the effect of the cosmology from the sampling noise of the population. where d obs L is the simulated distance, dL(zi ; ·) the model prediction, and σdL,i the total error of Eq. (3.10). 4.2 Real electromagnetic data We combine the LISA mock with real probes th
Figure 4. Recovery of the injected fiducial over 300 independent noise realisations per scenario. Points scatter along the H0–Ωm,0 degeneracy, which is why a deviation that looks large in the one￾dimensional marginals can be unremarkable in two dimensions. The mean recovered value (cross) sits on the injected fiducial (star) in all three cases. 5.2 LISA as a tiebreaker The central result is the consistency between the simulated LISA data and the real mea￾surements, quantified by the two-dimensional tension nσ in the (H0, Ωm,0) plane between the LISA-only and real-data posteriors
Figure 5. Planck18 fiducial. Marginalised (H0, Ωm,0) posteriors, with 68% and 95% contours. Filled: the LISA-only mock (purple) and the three real-data backgrounds, each being one SN Ia compilation combined with DESI-DR2, cosmic chronometers and Planck-18: Pantheon+SH0ES (orange), Union3 (green), DES-Dovekie (blue). Dashed: the joint posterior of the mock with each background, drawn in the colour of the compilation that entered it. The star marks the fiducial at which the mock was generated. The offset between the purple contour and each coloured one is the internal tension of
Figure 6. Union3 fiducial; colours and line styles as in
Figure 7. Pantheon+SH0ES fiducial; colours and line styles as in
Figure 8. Behaviour at deliberately unphysical fiducials, with Ωm,0 held at the Planck value and only H0 varied. The shaded band marks the range spanned by present measurements; dotted lines mark the fiducials tabulated in the text. Left: fraction of the catalogue still above the detection threshold ρ = 8. Lowering H0 lengthens every distance, lowers the signal-to-noise ratio and removes events; raising it costs nothing. Centre: fractional precision on H0, which varies only weakly, so the mock recovers whatever fiducial it was built on. Right: internal tension against the fixed real-data…
Figure 9. Discriminating power against catalogue size. Left: precision on H0; each point averages 25 random subsamples of the catalogue. Right: tension between the LISA-only posterior at each fiducial and the fixed real-data reference. The shaded band marks the range of bright sirens forecast for a five-year mission in [23]; more recent models predict fewer [61]. 6 Conclusions We have forecast the cosmological reach of LISA bright sirens, treating the mission not as a stand-alone ruler but as a tiebreaker among cosmological scenarios that are currently in tension. We built mock catalogues of…

Figures reproduced from arXiv:2609.35317 by the authors.

References

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