The detection of primordial black holes (PBHs) would mark a major breakthrough, with far-reaching implications for early universe cosmology, fundamental physics, and the nature of dark matter. Gravitational wave observations have recently emerged as a powerful tool to test the existence and properties of PBHs, as these objects leave distinctive imprints on the gravitational waveform. Notably, there are no known astrophysical processes that can form sub-solar mass black holes, making their discovery a compelling signal of new physics.In addition to PBHs, we consider other exotic compact object (ECO) candidates — such as strange quark stars and boson stars — which can produce similar gravitational signatures and potentially mimic PBHs.In this work, we employ the Fisher matrix formalism to explore a broad parameter space, including binary masses, spins, and different nuclear and quark matter equations of state. Our goal is to assess the ability of next-generation gravitational wave detectors — specifically Cosmic Explorer and the Einstein Telescope — to distinguish PBHs from ECOs, stellar BHs and neutron stars. We compute the maximum luminosity distances (LDs) at which confident (≥ 3σ) detections of sub-solar masses or tidal effects are possible, providing quantitative benchmarks for PBH identification or exclusion under various observational scenarios.Our results indicate that next-generation detectors will be capable of probing sub-solar mass PBHs out to cosmological distances of z ∼ 3. For heavier objects with masses up to M ≲ 2 M ⊙, we show that PBHs can be distinguished from neutron stars via their lack of tidal effects up to redshifts of z ∼ 0.2.

Resolving mass ordering is an important issue in the neutrino physics. In Ref. [1] the authors investigate the phenomenology of a unified neutrino mixing framework and reveal that the predicted sum of neutrino masses derived from an approximate [Formula: see text] reflection symmetric flavor neutrino mass matrix based on the unified neutrino mixing with an inverted mass ordering, is excluded from DESI2024 and Supernova Ia luminosity distance data. We note that in Ref. [1] an error is present in Eq.(20), i.e., the expression for [Formula: see text], a similar error also appears in Eq.(26) for [Formula: see text]. That is, the condition that [Formula: see text] and [Formula: see text] are real is omitted. We impose this condition and analyze its consequences. Using the newest data [2], it is obtained that the predicted sm derived from the approximate [Formula: see text] reflection symmetric neutrino mass matrices [Formula: see text] for both NO and IO are allowed. We note also that their conclusion is invalid, as it is based on outdated data.

Abstract The Nancy Grace Roman Space Telescope (Roman) will provide a revolutionary measurement of the Universe’s expansion kinematics, driven by dark matter and dark energy, out to z ≈ 3. The accuracy of this measurement is predicated on the assumption that standardized Type Ia supernova (SN Ia) luminosities do not evolve with redshift. If present, SN Ia luminosity evolution is expected to be most detectable in the dark-matter-dominated era of the Universe ( z ≳ 1.5), with its effects becoming more easily distinguishable from dark energy variation at increasing redshift. We present JWST NIRCam and NIRSpec observations of SN 2025ogs, a normal SN Ia at z = 2.05 ± 0.01. This supernova offers a key point of comparison for interpreting future high-redshift SN Ia samples. The NIRCam light curve indicates a blue color ( B − V = −0.27 ± 0.06 mag) and a moderately fast decline (Δ m 15 ( B ) = 1.55 ± 0.15 mag), both within standard criteria for inclusion in cosmological analyses. Its luminosity distance is in 1.0 σ agreement with the standard flat ΛCDM model, as well as with current cosmological constraints from the Dark Energy Survey (5 yr) and Pantheon+. The NIRSpec spectrum displays all of the hallmark absorption features of a normal SN Ia observed at peak brightness. We find that the rest-frame optical color, rest-frame near-UV properties, and Si ii line strengths are all consistent with the moderately fast decline inferred from the light curve. Multiple absorption features (Ca ii H and K, O i λ 7774, and the Ca ii near-infrared triplet) all appear at a lower blueshift relative to a sample of low- z SNe Ia. Together, these results suggest that SN Ia standardization remains robust at z ≈ 2, and also highlight the importance of JWST spectroscopy for uncovering evolutionary effects that could impact Roman’s high-precision cosmology.

Abstract We present a new measurement of the Hubble constant, H 0 , following the gravitational-wave event GW170817 and Dark Energy Spectroscopic Instrument (DESI) observations. A standard siren measurement with a nearby (luminosity distance ∼40 Mpc) event such as GW170817 is typically sensitive to the peculiar motion of the host galaxy owing to local dynamics. Previous measurements from this event have taken advantage of peculiar velocity measurements of nearby galaxies, including a handful of objects in the galaxy group that the host of the event, NGC 4993, has been associated with. Still, the group’s properties and NGC 4993’s membership were debated. We present DESI observations of thousands of galaxies in the vicinity of NGC 4993, resulting in 39 group galaxies and a fivefold increase in galaxies compared to previous observations, with many contributing to a peculiar velocity measurement. Examining the local dynamics, our observations support the presence of a galaxy group of which NGC 4993 is a part with a halo mass of order ∼10 13 M ⊙ . Using peculiar velocity measurements from our fundamental plane galaxy observations, we find H 0 = 70 . 9 − 8.5 + 6.4 km s −1 Mpc −1 . In addition, using a peculiar velocity measurement for NGC 4993 from surface brightness fluctuations in Cosmicflows-4, we find H 0 = 73 . 4 − 3.9 + 3.3 km s −1 Mpc −1 . We study the impact of different galaxy selection criteria on the determination of the peculiar velocity and, in turn, on the H 0 measurement. Our results demonstrate the value of multiplexed spectroscopic observations for probing the local environments of gravitational-wave events used in standard siren measurements.

Abstract We present a bar-informed kinematic-distance (BIKD) method to reconstruct face-on molecular-gas maps of the inner Milky Way from position–position–velocity data, relaxing the standard assumption of axisymmetric circular rotation that can generate severe artifacts in barred regions. BIKD replaces the rotation curve with a nonaxisymmetric streaming field extracted from hydrodynamical simulations in an observationally constrained barred Galactic potential, and infers a discrete distance posterior along each sightline using a Gaussian likelihood in line-of-sight velocity. To mitigate multimodality, we adopt posterior-weighted map-making via posterior sampling (a soft-assignment scheme), including a reweighting to reduce velocity-crowding bias. We validate the full pipeline in closed-loop tests on the simulations, showing that the recovered large-scale morphology is only weakly sensitive to simple distance priors and remains stable across plausible variations in bar angle, snapshot time, and pattern speed. We then apply BIKD to a Galactic CO(1–0) survey to obtain a face-on $\Sigma _{\mathrm{H_2}}$ map. Compared to a standard axisymmetric kinematic-distance (KD) reconstruction, BIKD strongly suppresses line-of-sight–elongated finger-of-God features and robustly recovers a bar-aligned, quadrant-asymmetric inner-Galaxy morphology under model marginalization. The model-marginalized radial profiles show an approximately exponential decline beyond ${\sim }4$ kpc, a pronounced deficit at $R\sim 0.5$–3.5 kpc (a bar gap), and a central concentration consistent with Central Molecular Zone surface densities. Finally, we compare prominent ridge-shaped overdensities in the BIKD map with independent spiral-arm loci traced by high-mass star-forming region masers with very long baseline interferometry (VLBI) trigonometric parallaxes and by Classical Cepheids with period–luminosity distances. Several maser-parallax segments are qualitatively consistent with the dominant BIKD ridges, whereas the Cepheid loci do not coincide with them within their recommended azimuth range. Overall, BIKD provides a practical, model-marginalized face-on reconstruction of molecular gas in the inner Milky Way that can be compared directly with modern stellar maps.

Recent observational evidence of axially symmetric anisotropies in the local cosmic expansion rate motivates an investigation of whether they can be accounted for within the Lemaître– Tolman-Bondi (LTB) framework with an off-center observer. Within this setting, we compute the exact relativistic luminosity distance via the Sachs equation and compare it with the approximate expression obtained from the covariant cosmographic approach (including Hubble, deceleration, jerk and curvature parameters).This comparison allows us to identify the regimes in which the covariant cosmographic method remains reliable.In addition, we compare the LTB relativistic distance for small inhomogeneities with the corresponding result derived from linear perturbation theory (LPT) in the standard cosmological model. This analysis establishes a precise correspondence between the LTB and LPT approaches, offering a consistent dictionary for the interpretation of the observed anisotropies of the large-scale gravitational field.We test luminosity distance reconstructions in a spherically symmetric overdensity with an off-center observer. For moderate central density contrasts (δc ≲ 1), LPT reproduces the exact distance within 10% for observers inside the typical size of the structure. However, Covariant Cosmography (CC) extends this regime of validity upto δc ≲ 2.5. At larger radii, the situation reverses: for observers at three times the characteristic size, LPT remains accurate up to δc ≲ 3, while CC already exceeds 10% error for δc ≳ 1.5. At sufficiently large distances from the structure, both methods converge to the exact solution. Thus, CC is essential for accurate distance estimates near dense regions, while LPT remains reliable at larger separations.This analysis will be instrumental in interpreting expansion-rate anisotropies, facilitating investigations of the local Universe beyond the FLRW framework with a fully non-perturbative metric approach.

Classical physics and visible matter are insufficient to account for cosmic phenomena such as flat galactic rotation curves or the apparent acceleration of the Universe, leading to the conventional introduction of dark matter and dark energy. However, their persistent invisibility suggests that these effects may stem not from hidden components but from deeper physical principles. Here, we propose that the dark-sector phenomenology emerges from nonlinear quantum forces absent in classical dynamics, originating from the infinite hierarchy of quantum corrections in the Wigner–Moyal phase-space formulation. Previous studies have shown that these higher-order corrections vanish under coarse resolution yet grow exponentially when the system is resolved more finely. We reinterpret this resolution-dependent quantum complexity as a relativistic effect amplified by gravitational potential, whose normalization reproduces spacetime curvature in the weak-field limit and generates additional forces on cosmic scales. When the mass distribution can be described as a macroscopic wave packet, the resulting quantum-corrected force naturally reproduces galactic rotation curves without invoking dark matter. Conversely, when the background potential defining the quantum corrections is tied to the observer’s causal horizon, it weakens with distance, causing the quantum terms to diminish and the dynamics to gradually converge toward classical behavior — making the faraway Universe appear to contain less dark matter. This horizon-dependent suppression naturally reduces the inferred luminosity distances of distant galaxies, accounting for the Pantheon[Formula: see text] Type Ia supernova data without invoking dark energy and giving the impression of an accelerating Universe. Our results suggest that the combined phenomenology of relativity, dark matter, and dark energy may arise from gravitationally regulated quantum statistical dynamics, offering a unified and observationally consistent alternative to the standard dark-sector paradigm.

Abstract We present a comprehensive forecast for cosmological constraints using the joint observation of the cosmic shear signal from the Chinese Space Station Survey Telescope (CSST) and the clustering signal from the next-generation gravitational wave (GW) detector networks, e.g., Einstein Telescope and Cosmic Explorer. By leveraging the angular clustering of astrophysical gravitational wave sources (AGWS) from the third-generation detectors and CSST’s weak lensing surveys, we develop a theoretical framework to compute auto- and cross-angular power spectra of AGWS clustering, cosmic shear, and their cross correlation. Mock data sets are generated by considering the detector-specific selection functions, uncertainties in luminosity distance, and weak lensing systematics. We employ the Markov Chain Monte Carlo methods to constrain the ΛCDM cosmological parameters, AGWS bias parameters, and star formation rate parameters under three detector configurations. Our results demonstrate that the joint observation can achieve sub-5% precision on H 0 (2.19%) and w (5.7%). In addition, the AGWS clustering bias parameters can be constrained to a precision of 4%–5%, enabling the differentiation between stellar-origin compact binaries and primordial black hole scenarios. This multimessenger approach can also be helpful to resolve mass-redshift degeneracies in the dark siren methods, providing independent validation for Hubble tension. Our work indicates that the joint observation of the third-generation GW detectors and the CSST can be a powerful probe of large-scale structure and the cosmic expansion history.

Without making any assumption on the underlying geometry and metric of the local Universe, we provide ameasurement of the expansion rate fluctuation field using the Cosmicflows-4 and Pantheon+ samples in the redshift range 0.01 < z < 0.1 (30 h -1 Mpc < R < 300 h -1 Mpc).The amplitude of the anisotropic fluctuations is found to be of order a few percent relative to the monopole of the expansion rate.We further decompose the expansion rate fluctuation field into spherical harmonic components and analyze their evolution with redshift across the studied redshift range.At low redshift, the dipole is clearly dominant, with an amplitude of ∼ (2.2 ± 0.15) × 10-2, significantly larger than the higher-ordermodes. As redshift increases, the dipole amplitude steadily decreases, reaching roughly half its value in the highest redshift bin investigated. The quadrupoleis also significant, at about half the dipole amplitude, and persists across all redshift bins, with no clear decreasing trend, although uncertainties grow at higher redshift. A nonzero octupole is detected at low redshift with asignal-to-noise ratio of ∼ 3, but it becomes unconstrained at higher redshift. The dipole, quadrupole, and octupole components are found to be aligned, exhibiting axial symmetry around a common axis (l = 295°, b = 5°).We interpret the observed fluctuations in the expansion rate within the framework of covariant cosmography. Our results indicate that the multipoles of the expansion rate fluctuation field are primarily driven by a strong quadrupole in the covariant Hubble parameter, together with dipole and octupole contributions from the covariant deceleration parameter. These few parameters suffice to reconstruct the luminosity distance with high precision out to z ∼ 0.1, in a manner that is model-independent, non-perturbative, and free from assumptions about peculiar velocities.Finally, we find that the CMB frame is not locally comoving with the matter fluid, and that a matter fluid element, roughly a spherical region of sizein the range 38 ≲ R (Mpc) ≲ 100centered on the observer position, moves relative to the CMB frame with a velocity of 188 ± 22 km/s, along the axis of symmetry.

Abstract In this draft, we investigate the propagation and observational imprints of gravitational waves (GWs) from compact binary inspirals in f ( T ) theory, a torsion based extension of general relativity (GR). In this theory, modifications to the underlying dynamics alter the effective luminosity distance of GWs relative to the standard electromagnetic counterpart, introducing a redshift dependent damping effect. We consider exponential corrections of f ( T ) theory to analyze the impact on the propagation of tensor modes and the corresponding GW signals, by using post-Newtonian waveform templates and Fisher matrix forecasts. We assess the ability of current and future ground based interferometers, such as Advanced LIGO (aLIGO) and the Einstein Telescope (ET), to constrain the additional parameters introduced by these models. Current detectors already constrain deviations from GR, while next-generation observatories will improve these bounds by up to two orders of magnitude, underscoring the power of GW observations to test torsion based gravity models.

The coming decade will be crucial for determining the final design and configuration of a global network of next-generation (XG) gravitational-wave detectors, including the Telescope (ET) and Cosmic Explorer (CE). In this study, and for the first time, we assessed the performance of various network configurations using neural posterior estimation (NPE) implemented in Einstein Dingo-IS ---a method based on normalizing flows and importance sampling that enables fast and accurate inference. We focused on a specific science case involving short-duration, massive and high-redshift binary black hole mergers with detector-frame chirp masses $( _ )$ $&gt; 100 _⊙$. These systems encompass early-Universe stellar and primordial black holes, as well as intermediate-mass black hole binaries, for which XG observatories are expected to deliver major discoveries. Validation against standard Bayesian inference demonstrates that NPE robustly reproduces complex and disconnected posterior structures across all network configurations. For a network of two misaligned L-shaped ET detectors (2L MisA), the posterior distributions on luminosity distance can become multimodal and degenerate with the sky position, leading to less precise distance estimates compared to the triangular ET configuration. However, the number of sky-location multimodalities is substantially lower than the eight expected with the triangular ET, resulting in improved sky and volume localization. Adding CE to the network further reduces sky-position degeneracies, and the better performance of the 2L MisA configuration over the triangle remains evident. M d M

In the gravity quantum theory, the quantization of spacetime may lead to the modification of the dispersion relation between the energy and the momentum and the Lorentz invariance violation (LIV). High energy and long-distance gamma-ray bursts (GRBs) observations in the universe provide a unique opportunity to test the possibility of LIV. In this work, we use 88 time delays from GRBs ($0.117 &lt; z &lt; 6.29$), and provide a cosmological model-independent approach based on the luminosity distance data from 174 GRBs to test LIV. Combining the observation data from multiband of GRBs provides us with an opportunity to mitigate the potential systematic errors arising from variations in the physical characteristics among diverse object populations, and to add a higher redshift dataset for testing the energy-dependent velocity caused by the corrected dispersion relationship of photons. These robust limits of the energy scale for the linear and quadratic LIV effects are $E_{\mathrm{QG},1} \ge 1.5\times 10^{15}$ GeV, and $E_{\mathrm{QG},2} \ge 8.5\times 10^{9}$ GeV, respectively. It exhibits a significantly reduced value compared to the energy scale of Planck in both scenarios of linear and quadratic LIV.

Abstract We present a joint test of cosmic curvature, Ω k 0 , and the cosmic distance–duality relation (CDDR) using the Etherington relation, which connects the luminosity and angular diameter distances at the same redshift. In this work, we combine the angular diameter distance measurements from recent Baryon acoustic oscillation (BAO) observations with luminosity distances reconstructed from cosmic chronometers data of Hubble parameter H ( z ) using a nonparametric technique, Gaussian process. A key part of our analysis is the systematic comparison of different BAO measurements—two dimensional (2D) BAO, three-dimensional (3D) BAO, and 3D Dark Energy Spectroscopic Instrument BAO—to determine whether any potential tension between angular and anisotropic BAO data affects constraints on the distance duality parameter η ( z ) and Ω k 0 . We adopt four representative parameterizations of η ( z ) to examine the correlation between η ( z ) and Ω k 0 . Our results show no evidence for violation of the CDDR, with η ( z ) consistent with unity at the 99% confidence level for all BAO datasets and parameterizations. In all scenarios, the best-fit values of Ω k 0 mildly favor a nonflat universe, although a spatially flat universe remains compatible at the 95% confidence level. The constraints on η 1 and Ω k 0 indicate slight variations across different BAO datasets, but the discrepancies between the 2D and 3D BAO measurements do not introduce any significant bias, and no statistically meaningful tension is observed. Our work provides robust constraints on cosmic curvature and the validity of the CDDR based on nonparametric distance reconstruction.

This study sought to investigate how Binary Black Hole (BBH) parameters—chirp mass, mass ratio, and luminosity distance—influence key Gravitational Wave (GW) signal features maximum frequency, and signal-to-noise ratio (SNR). Examining GWs enables the study of the dynamics of BBH systems as their physical properties can reflect observable signal characteristics. A quantitative research is conducted utilizing a set of 16 high-SNR events from the Gravitational-Wave Transient Catalogs. For each event, physical parameters were extracted from catalog data, and maximum frequencies were obtained from previous discovery papers or estimated through Q-transform visualizations of strain time-series. With these data, five parameter pairs—chirp mass vs. maximum frequency, mass ratio vs. maximum frequency, distance vs. maximum frequency, chirp mass vs. SNR, mass ratio vs. SNR—are analyzed by Pearson and Spearman correlations. Analyses revealed generally weak relationships between BBH parameters and GW signal characteristics, suggesting the subtle influence of BBH parameters on GW signal features and the potential role of untested variables, like spin, orbital orientation. Future work should focus on strengthening the precision of GW data analysis by incorporating methods such as bootstrapping, expanding the range of examined signal characteristics, and improved signal-extraction tools. This research can help deepen the understanding of how fundamental black hole properties impact the signals we observe.

Abstract Within a Bayesian statistical framework, we jointly estimate the source and lens parameters and evaluate the relative evidence between the lensed and unlensed models. We investigate the wave-optics effects induced by a point-mass lens on gravitational waves (GWs) from massive binary black holes with comparable component masses ( q = 0.9) and assess the capability of the space-based GW detector Taiji to detect such effects. Specifically, we investigate the impact of the redshifted lens mass M Lz ∈ [3 × 10 5 , 3 × 10 7 ] M ⊙ , the dimensionless impact parameter y is scaled in terms of the Einstein radius of the lens with y ∈ [10, 50], the source redshift z s ∈ [4, 6], and the total source mass M s ∈ [10 5 , 10 7 ] M ⊙ on parameter estimation and model selection. Our results indicate that larger M Lz values reduce the fitting factor ( F F ), thereby amplifying the waveform residual and its associated residual signal-to-noise ratio ( SNR res ), which enhances the ability to distinguish between lensed and unlensed models. Conversely, for y ≥ 50, the F F approaches 1 and SNR res becomes too small to allow effective model discrimination. For y ≤ 30, the degeneracy between the luminosity distance d L and M Lz can be effectively broken. While the Bayes factor decreases with increasing source redshift z s , lensing signatures remain identifiable up to z s = 6. The influence of the total source mass M s depends on the overlap of the GW signal with the detector’s sensitive band. Overall, effective model discrimination generally requires an SNR res ≥ 5 (corresponding to F F ≤ 0.9999994 for the results presented in this work).

The Cosmic Distance Duality Relation (CDDR) connects the angular diameter distance ($d_A$) and the luminosity distance ($d_L$) at a given redshift. This fundamental relation holds in any metric theory of gravity, provided that photon number is conserved and light propagates along null geodesics. A deviation from this relation could indicate new physics beyond the standard cosmological model. In this work, we test the validity of the CDDR at very low redshifts ($z &lt; 0.04$) by combining $d_A$ from the Megamaser Cosmology Project with $d_L$ from the Pantheon+ sample of Type Ia Supernovae (SNIa). We further incorporate high-redshift Baryon Acoustic Oscillation (BAO)-based $d_A$ measurements from DESI DR2 in combination with SNIa data, highlighting the critical role of the $r_d-M_b$ (early-late) calibration in testing the CDDR using these two probes. Assuming CDDR holds, we perform a Bayesian analysis to derive model-independent constraints on the calibration parameters. Using only BAO and SNIa data, we observe a strong degeneracy between $r_d$ and $M_b$. However, the inclusion of calibration-free Megamaser measurements breaks this degeneracy, enabling independent constraints without relying on a specific cosmological model or distance-ladder techniques. Additionally, we present a forecast incorporating the expected precision from future Megamaser and SNIa observations, demonstrating their potential to significantly tighten constraints on early-late calibration parameters, under the assumption of validity of CDDR.

The distance duality relation (DDR) relates two independent ways of measuring cosmological distances, namely the angular diameter distance and the luminosity distance. These can be measured with baryon acoustic oscillations (BAO) and Type Ia supernovae (SNe Ia), respectively. Here, we use recent DESI DR1, Pantheon+, SH0ES and DES-SN5YR data to test this fundamental relation. We employ a parametrised approach and also use model-independent Generic Algorithms (GA), which are a machine learning method where functions evolve loosely based on biological evolution. When we use DESI and Pantheon+ data without Cepheid calibration or big bang nucleosynthesis (BBN), there is a 2σ discrepancy with the DDR in the parametrised approach. Then, we add high-redshift BBN data and the low-redshift SH0ES Cepheid calibration. This reflects the Hubble tension since both data sets are in tension in the standard cosmological model ΛCDM. In this case, we find a significant violation of the DDR in the parametrised case at 6σ. Replacing the Pantheon+ SNe Ia data by DES-SN5YR, we find similar results. For the model-independent approach, we find no deviation in the uncalibrated case and a small deviation with BBN and Cepheids which remains at 1σ. This shows the importance of considering model-independent approaches for the DDR.

Gravitational wave dark sirens are a powerful tool for cosmology and inference of compact object population hyperparameters. They allow for a measurement of the luminosity distance to the source, but not their redshift. Galaxy catalogues in the source localization volume can be used to infer the redshift of the source in a statistical manner. Catalogues are, however, limited by their incompleteness, which can be significant at redshifts corresponding to current GW events. In this work, we detail how to implement in practice variance completion, a novel galaxy completion method which uses knowledge of the large scale structure to optimize the potential of dark sirens analyses. We compress the prediction for the missing number of galaxies into a ratio between the predictions of variance completion and the standard homogeneous completion method. This ratio format can be easily incorporated into existing line of sight computations used in dark sirens software; we demonstrate this procedure using the GLADE+ galaxy catalogue and the gwcosmo software package. We discuss the robustness of the method, and apply it to well-localized event GW190814 as a proof of concept. Finally, we apply the method to data from the third observing run of LIGO-Virgo-KAGRA, finding that it yields results that are consistent with homogeneous completion. We also discuss the prospects for an improvement if the GW localization volume shrinks.

We carry out a detailed analytical investigation of the propagation of gravitational waves in ghost-free bimetric gravity in a late-time de Sitter epoch. In this regime, the dynamical equations for the massless and massive graviton modes can be decoupled and solved exactly. We provide uniform approximations for the modes in terms of elementary functions, which are valid on all scales and for all viable mass windows. We identify different dynamical regimes for the system, depending on the propagation properties of the massive graviton, and whether the massless and massive components of the signal can be temporally resolved or not. In each regime, we compute the gravitational-wave luminosity distance as a function of redshift and study the propagation of wave packets. This allows for the derivation of a new observational bound for the ghost-free bimetric theory using the event GW170817. Further, by an explicit computation, we show that the massless and massive components of the signal retain their coherence also in the regime where they can be temporally resolved, even when couplings to incoherent matter degrees of freedom are included.

Abstract In this work, we revisit/reinterpret/extend the model-independent analysis method (which we now call spread—luminosity distance fitting) from our previous work. We apply it to the updated supernova type Ia catalog, Pantheon+ and recent gamma ray bursts compilations. The procedure allows us, using only Friedmann-Lemaitre-Robertson-Walker (FLRW) assumption, to construct good approximations for expansion history of the Universe, re-confirming its acceleration to be a robust feature. When we also assume general relativity (GR), we can demonstrate, without any matter/energy model in mind, the need for (possibly nonconstant) generalized dark energy (GDE). We find hints for positive pressure of GDE at z &gt; 1 with implications on either the complexity of dark energy, or the validity of one of the cosmological principle, interpretation of SN Ia data, or GR.