Cosmology and Nongalactic Astrophysics
Toward Detecting the Moving Lens Effect with Optical Spectroscopy
David Wittman, Rodrigo Stancioli and Christopher Hopp
Relativity predicts that sky-plane motion of a gravitational lens changes the wavelengths of lensed
photons. This moving lens effect is orders of magnitude smaller than cosmological and Doppler effects on the same
photons, but can be isolated by comparing different strongly lensed images of a given source. With a massive, fast-moving lens such as a
galaxy cluster falling into another cluster, lensed spectra of a given source could differ in wavelength by up to 1 part in $10^6$. We examine the feasibility of detecting this effect with optical spectroscopy, using Keck/Deimos data on the merging cluster RM J001938.7+033557.3 as a case study. We also quantify the predicted sky-plane motions of systems likely to be identified as merging clusters in a $\Lambda$CDM cosmology, and investigate how information on sky-plane motions could help constrain merger models. We find that measurement of the moving lens effect would disambiguate between models in which the subclusters are outbound after first pericenter and those in which the subclusters have returned to the same separation after first apocenter.
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Cosmology and Nongalactic Astrophysics
AdS - de Sitter transition in interacting dark energy models
Yifei Zhao, Jailson Alcaniz, Humberto A. Borges et al. (+2 more)
Recent cosmological results, including the persistent $H_0$ tension and indications of dynamical dark energy, have raised the possibility that the standard $\Lambda$-Cold Dark Matter ($\Lambda$CDM) model may be incomplete. At the same time, theoretical developments based on swampland
conjectures indicate that the realization of a stable de Sitter
vacuum within string theory is challenging. Motivated by these observational and theoretical considerations, we investigate an interacting $\Lambda$ scenario characterized by a general linear coupling in the dark sector. At the background level, this model naturally allows the dark energy density to evolve from negative to positive values, opening the possibility of a transition from an anti-de Sitter-like phase to the de Sitter-like phase inferred by current observations. We derive the analytic background solutions and perturbation equations, discuss the physically acceptable region of parameter space, and constrain the model with DES-Dovekie type Ia
supernovae, DESI BAO and CMB data. Our analysis suggests a parameter space allowing the dark energy density to change sign while maintaining positive dark matter density, motivating further investigation of an interaction-driven anti-de Sitter to de Sitter transition.
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All authors Yifei Zhao, Jailson Alcaniz, Humberto A. Borges, Saulo Carneiro, Rodrigo von Marttens
Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.IM
Fisher and DALI posterior approximations for testing gravity with gravitational waves
Felipe A. da Silva Barbosa, Davi C. Rodrigues, Josiel Mendonça Soares de Souza et al. (+1 more)
We investigate the accuracy and computational efficiency of posterior approximations for gravitational-wave (GW) parameter estimation based on Fisher
Matrix and its higher-order extension, the Derivative Approximation for LIkelihoods (DALI), in the context of tests of General Relativity using parameterized deviations in the inspiral waveforms (the TIGER formalism). We adopt the IMRPhenomD waveform and compare the exact posterior sampling to the following approximations in increasing order of complexity: the traditional Fisher
Matrix, the Fisher sampling (singlet-DALI), the doublet-DALI and the triplet-DALI. We find that both singlet and doublet-DALI are significantly faster than the exact posterior by factors between 20 and 1000, depending on the inspiral SNRs – larger gains correspond to larger SNRs. These gains are considerably larger for more complete waveforms, such as IMRPhenomHM. To evaluate the accuracy of the approximations, we use Jensen-Shannon divergence. We conclude that both singlet and doublet-DALI systematically improves over the standard Fisher
Matrix approximation, while triplet-DALI shows large variability, limiting its practical advantage. We also introduce a code with a new implementation of Fisher and DALI analysis (Symbolic DALI, SymDALI) which computes derivatives symbolically via Wolfram
Language.
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All authors Felipe A. da Silva Barbosa, Davi C. Rodrigues, Josiel Mendonça Soares de Souza, Miguel Quartin
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Constraints on Complex Electroweak WIMPs from Solar Capture
Juan P. Luengas, Maxim Pospelov and Harikrishnan Ramani
One of the most convincing realizations of particle dark matter is provided by models based on electroweak multiplets. The lightest neutral state of such a multiplet can be a stable Majorana
fermion or a real scalar, and its phenomenology is governed by two parameters: the dark matter mass and the mass splitting $\{m_\chi,\delta\}$. The sub-MeV range for $\delta$ is particularly important as it allows for a large inelastic scattering cross section. In this paper, we analyze solar capture, energy loss, and annihilation of scalar and fermionic electroweak multiplet dark matter, generalizing earlier results for the Higgsino to other representations. We find that, while the case of a doublet is somewhat special, higher representations behave in a self-similar way. For the higher multiplets, IceCube results constrain the splitting to $\delta \gtrsim 350$ keV for all dark matter masses up to $100$ TeV. Assuming thermal freeze-out and a Standard
Halo Model velocity distribution, this rules out most models of electroweak dark matter as a possible origin of the single high-recoil event reported by the LZ collaboration. We also show that a high-velocity tail in the dark matter distribution, such as that induced by the Large Magellanic Cloud, raises the splitting preferred by the LZ event above the solar bounds for many of the multiplets.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
How collective modes terminate in the dispersion relation of neutrino plasmas
Damiano F. G. Fiorillo
Neutrino plasmas support flavor waves, collective oscillations of flavor, that
neutrinos can resonantly emit or absorb when they fulfill the Cherenkov condition. For massless
neutrinos, this condition leads to singular features in the dispersion relation: Landau-damped modes, for example, disappear abruptly as their phase velocity approaches the speed of light. We investigate how these singularities change when nonzero
neutrino masses introduce a spread in velocities. We classify singular behavior of the frequency as a function of wavevector into i) degeneracy points, where two modes merge, and ii) abrupt mode termination, when the frequency approaches a branch cut of the flavor dielectric function. For each class, we derive a local expansion and determine where such behavior can occur. Degeneracy points, frequently encountered in axially symmetric dispersion relations in the fast limit, are not generic. Nonzero
neutrino masses lift the degeneracy along the
symmetry axis; in three-dimensional wavevector space, there might still be degeneracy lines, not necessarily intersecting the
symmetry axis. Abrupt mode termination, instead, persists generically, except for special energy distributions which are entire functions. As a byproduct of this study, we show that a collisionless
plasma with a Lorentzian
neutrino-frequency distribution is exactly equivalent to a monochromatic one with an effective collision rate. Approximating a general frequency distribution by a sum of Lorentzians therefore substantially simplifies the dispersion relation.
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Cosmology and Nongalactic Astrophysics
Testing Offsets Between Cluster-Scale Halos and BCGs in Strong Lensing Models Using the Jackknife Method
Sangjun Cha, Marceau Limousin and M. James Jee
Offsets between cluster-scale dark matter
halos and brightest cluster
galaxies (BCGs) inferred from strong
lensing (SL) models have been used to investigate cluster dynamics and dark matter physics. However, it is necessary to test whether these offsets are required by SL data themselves. We investigate whether allowing these offsets improves predictive accuracy and examine the effects on magnification, time-delay predictions, and critical curve positions. We evaluate lens models of Abell 370, RX J1347.5-1145, and MACS J0416.1-2403 using the jackknife method, which assesses predictions for source systems excluded from the lens reconstruction. Models are constructed with MrMARTIAN, which combines analytic mass profiles with a regularized grid that represents mass structure not captured by the profiles. We compare fixed and free
halo position models across regularization weights. The root mean square values averaged over excluded systems agree within bootstrap uncertainties, while the median paired differences remain close to zero across all three clusters and tested regularization weights. These results indicate comparable predictive accuracy between the fixed and free models. The total mass distributions remain broadly similar, although the magnitudes of fitted
halo offsets vary with regularization, showing that the mass decomposition is not unique. For these three clusters, offsets between BCGs and cluster-scale
halos in the lens models are not required by the SL data to improve predictive accuracy within the MrMARTIAN framework. The mass decomposition between the regularized grid and cluster-scale
halos is not uniquely determined. These findings limit physical interpretations based on fitted
halo positions alone. The model dependence of magnification and time-delay estimation can also affect the inferred intrinsic properties of high-
redshift sources or the Hubble constant.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Searching for BSM Experimental Signatures with Large Lagrangian Models
Ibrahim Elsharkawy, Victoria Knapp-Perez, Wahid Bhimji et al. (+1 more)
The search for physics Beyond the Standard Model (BSM) is generally limited not by the supply of theory descriptions but by the lack of discriminating experimental observations. A case in point is dark matter, where the overwhelming gravitational evidence only goes so far in distinguishing between models within a vast theory space. Exploring the space of testable model signatures may help identify overlooked experimental observables and indicate the utility of future experiments. A challenge is designing a search through model signatures outside what is found in the literature. Our primary contribution is hAIthem, a framework that combines the self-guided exploration of reinforcement learning (RL) with the broad literature-derived knowledge of LLMs. We build an RL
agent that learns to find which portions of a theory's high-dimensional parameter space are not excluded under some subset of constraints by playing a Battleship-style "game" against a suite of phenomenology tools. The
agent is built as a Large Lagrangian Model (LLaM), an autoregressive
transformer that reads a tokenized Lagrangian, is pretrained at scale (here on ~1 billion
tokens from ~10,000 Lagrangians), and is fine-tuned in a live environment. The framework then constructs a decision tree that separates RL-found regions using observables computed with established tools, and passes the remaining degenerate regions to a set of LLM
agents that compete to produce realistic signatures. In this proof of concept, RL-search outperforms an evolutionary-
algorithm baseline, finding more viable regions with greater physical diversity. In a restricted space of single dark scalar multiplet models, we find that hAIthem proposes interesting combinations of previously studied observables, such as the application of a
halo-independent kinematic ratio to paleo-detectors.
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All authors Ibrahim Elsharkawy, Victoria Knapp-Perez, Wahid Bhimji, Aishik Ghosh
Cosmology and Nongalactic Astrophysics
Close Pulsar Pairs See Dark Matter Substructure through the Gravitational-Wave Background
Abhiram Cherukupalli, Vincent S. H. Lee, Kim V. Berghaus et al. (+1 more)
Pulsar timing arrays detect signals from dark matter substructure, but a nanohertz gravitational-wave background (GWB) severely degrades their sensitivity. We show that timing
pulsar pairs separated by sub-parsec distances avoids this degradation. The GWB imprints nearly the same perturbation on both
pulsars and is suppressed in the difference of their residuals, whereas a nearby dark matter subhalo perturbs the two differently and survives. We find that an array with
pulsar pairs separated by $0.1\,\mathrm{pc}$ improves the sensitivity to subhalos of order $\sim10^{-6}$ solar masses by more than an order of magnitude, relative to an otherwise identical array of widely separated
pulsars. Dense globular clusters naturally host many such pairs, though the baryonic environment must be separated from a dark matter substructure signal.
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All authors Abhiram Cherukupalli, Vincent S. H. Lee, Kim V. Berghaus, Kathryn M. Zurek
Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
A Strong Cosmologically Coupled Mass Growth Solution in Linearized General Relativity
Kevin S. Croker, Joshua Cohon, Viktor T. Toth et al. (+13 more)
DESI Data Release 2 has heightened interest in cosmologically coupled black holes (CCBHs) as an explanation for accelerating late-time expansion, but known models for CCBHs grow too slowly to drive it. We construct at linear order a solution to General Relativity whose Hernandez-Misner-Sharp mass passively grows $\propto a^\kappa$ as the universe expands. The constant $\kappa$ enters all
eigenvalues of the Weyl and stress-tensor operators, so growth is unambiguously physical in both free-field and material sectors. The solution is causal over spacetime relevant for stellar collapse compact objects. A cloud of energized
vacuum emerges at $\kappa = 3$, complementing the $a^3$ scaling predicted elsewhere for the masses of energized
vacuum black holes. This first step toward $\kappa \sim 3$ CCBH exact solutions enables observational tests with
pulsar binaries.
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All authors Kevin S. Croker, Joshua Cohon, Viktor T. Toth, Massimiliano Rinaldi, Nicolas Fernandez, Joel L. Weiner, Duncan Farrah, Gregory Tarlé, Gustavo Niz, Christopher Cain, James W. Rohlf, Alejandro Aviles, Jake Summers, Leander Thiele, Rogier A. Windhorst, Joshua Grumski-Flores
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-th
Exact bispectra in strongly mixed multifield inflation
Lucas Pinol
Using the effective field theory of inflationary fluctuations extended by a massive isocurvature scalar, at unit sound speed, we compute the primordial bispectra generated by every cubic interaction of dimension four or less in the
unitary gauge, with the
curvature–isocurvature quadratic mixing resummed to all orders in the dimensionless mixing strength $\lambda=\rho/H$. Placing the mixing in the free
Hamiltonian [...], every scale-invariant tree-level bispectrum reduces to a single Schwinger-parameter integral over independent leg kernels, and what perturbation theory calls single, double and triple exchange are contact diagrams of the resummed theory. At strong mixing we unveil genuinely new, exact multifield bispectrum shapes with no correlation to the standard shapes used in data analyses. The squeezed limit carries a cosmological
collider signal with a universal frequency set by the dressed mass parameter $\mu_{\rm eff}$ at every exchange order. At weak mixing the clock coefficients are obtained in closed form and reduce [...] to the known perturbative single- and double-exchange results, exactly; the triple-exchange leading coefficient is obtained in closed form at every mass, in terms of hypergeometric functions, for the first time. At strong mixing the
collider amplitude scales as $e^{\pi(\lambda-2\mu_{\rm eff})/2}$ over the whole $(\lambda,\mu_{\rm eff})$ plane. This encompasses all previously studied regimes as particular cases [...]. A first confrontation of the six exact shapes with the Planck PR4 binned bispectrum shows a preference for strong mixing, where the cosmological
collider oscillations invade mildly squeezed configurations [...]. The shapes of all interactions over the whole plane [...] are released with the code that produced them, so that a template at any mixing and mass can be read off in milliseconds.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-th
CMB Injection Bounds on Moduli Fields
Naman Agarwal, Andrew R. Frey, Ratul Mahanta et al. (+3 more)
Light scalar fields with gravitational strength interactions (moduli) are ubiquitous in string, supergravity, and extra-dimensional models. If produced in the early universe with lifetimes exceeding the epoch of recombination, slowly decaying moduli inject energetic particles into the Standard Model
plasma, leaving distinct imprints on the
cosmic microwave background (CMB). In this paper we systematically derive CMB injection bounds on light moduli ($10^3\ {\rm eV}\leq m_{\rm{mod}}\leq 10^8\ {\rm eV}$) across the primary cosmological production channels:
vacuum misalignment, heavy scalar/inflaton decay, thermal emission from the primordial
plasma including production from a Hagedorn phase of hot strings. We show that these injection bounds impose stringent constraints that are complementary to both the standard cosmological moduli problem and fifth force bounds.
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All authors Naman Agarwal, Andrew R. Frey, Ratul Mahanta, Anshuman Maharana, Fernando Quevedo, Gonzalo Villa
Cosmology and Nongalactic Astrophysics
Gravitational-wave dark sirens as astrophysical probes: inferring galaxy-merger relations and identifying individual hosts
Alessandro Agapito and Michele Mancarella
Gravitational-wave (GW) “dark siren” techniques, namely the statistical association of GW events with a
galaxy catalog, have so far been used as a cosmological tool. Yet this association carries distinctive astrophysical information that remains unused—specifically, how compact binaries populate
galaxies and the identities of individual hosts. In this work, we turn the dark-siren program into an astrophysical probe by inferring both simultaneously within a single hierarchical framework. The method reduces the many potential hosts to a compact, probabilistically ranked target list, providing a direct follow-up decision tool. Applied blindly to GW170817, it recovers NGC~4993 as the highest-ranked host and constrains the
galaxy luminosity weighting, mildly favoring non-uniform host weights. Fixing the
galaxy weighting can instead degrade host identification and even favor the wrong host. This framework recasts dark sirens as a potentially unique probe of the astrophysics of electromagnetically dark compact-binary mergers.
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Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.GA
A Full-Sky SPHEREx Map of Integrated 3.3 and 3.4 {\mu}m PAH Emission
Roke Cepeda-Arroita, Clive Dickinson, J. Alberto Rubiño-Martín et al. (+4 more)
Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous in the interstellar medium and are among its smallest carbonaceous grains. Their infrared emission bands trace this small-grain population together with the interstellar radiation field that excites it, and are widely used to diagnose photodissociation regions, dust processing and
star formation. We present full-sky maps of the integrated radiance of the 3.3 $\mu$m aromatic C-H stretch and the adjacent 3.4-3.5 $\mu$m aliphatic complex, from SPHEREx QR2 Level-2 data. Existing all-sky PAH tracers are broadband, so the band emission can only be inferred as an excess over stellar and continuum emission; SPHEREx samples the spectrum finely enough for the bands to be fitted directly. We mask flagged detector pixels, subtract the per-pixel zodiacal-light model, subtract point sources with an empirically derived PSF, and coadd the results into inverse-variance-weighted HEALPix maps at 2.6' FWHM and Nside=4096 in 102 narrowband channels across Detector 4 (2.42-3.82 $\mu$m). At every sky pixel we fit a continuum and the two bands. The combined band radiance is the primary product; its decomposition into the aromatic and aliphatic components is released alongside it as an estimate, with its modelling systematic stated. These are the first full-sky maps of PAH band emission, resolving the 3.3 and 3.4-3.5 $\mu$m bands spectrally, and the first full-sky PAH maps from SPHEREx to be released. Because the 3.3 $\mu$m band is emitted preferentially by the smallest PAHs, the maps trace directly a grain population, including the candidate carriers of anomalous microwave emission, that broadband PAH proxies reach only indirectly. The maps and their associated products, including a reliability mask, are publicly available with an explanatory supplement at https://research.iac.es/proyecto/radioforegroundsplus/pages/data-products/spherex-pahs.php.
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All authors Roke Cepeda-Arroita, Clive Dickinson, J. Alberto Rubiño-Martín, Ricardo T. Génova-Santos, Gabriel A. Hoerning, Stuart E. Harper, Debabrata Adak
Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.HE
Shaping binary black hole merger efficiency with gravitational wave observations
Michele Bosi, Lumen Boco, Stefano Torniamenti et al. (+5 more)
Gravitational wave (GW) astronomy offers unprecedented insights into binary black hole (BBH) coalescence. However, many of the key quantities involved remain inaccessible to direct observations. The BBH merger rate density is deeply linked to both the merger efficiency and the distribution of delay time between binary formation and merger, neither of which is directly constrained by observations. Disentangling their impact on the merger rate represents a highly non-trivial endeavour. Here we present a semi-parametric BBH population model, based on population synthesis simulations of both isolated and dynamically-formed BBHs, anchored on an observation-driven,
metallicity-dependent
star formation history. We parametrise the merger efficiency of these two formation channels, fitting the model to GW events from the Gravitational-Wave Transient Catalog 5.0 within a hierarchical
Bayesian framework. Our analysis suggests that the isolated BBH merger efficiency should be lowered by a factor $\mathcal{O}(10)$ relative to standard population synthesis results. The dynamical channel requires an efficiency more than an order of magnitude larger than the isolated one to reproduce current GW observations. Nevertheless, we find that the two channels provide comparable contributions to the observed number of events. Finally, we introduce a parametrisation for the delay time distribution of the isolated BBHs. We derive a distribution consistent with the observed local merger rate and show its degeneracy with the merger efficiency.
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All authors Michele Bosi, Lumen Boco, Stefano Torniamenti, Stefano Rinaldi, Cecilia Sgalletta, Michela Mapelli, Carlo Baccigalupi, Andrea Lapi
Cosmology and Nongalactic Astrophysics
Carving out the Multifield Cosmological Collider Landscape
Denis Werth
We show that inflation with a large number of fields, as predicted by concrete ultraviolet
embeddings, generically produces almost-local cosmological
collider signals in the bispectrum squeezed limit. We construct the most general boost-breaking mixings between the
curvature perturbation and $N_{\rm f}$ additional fields, and extract the late-time scaling dimensions that dictate the soft limits of cosmological correlators. For a handful of fields, an enhanced squeezed limit (with potential oscillations) is a fine-tuned signal. At large $N_{\rm f}\sim100$, however, mixings generically drive the scaling dimensions toward the unitarity boundary. We show that this is a direct consequence of extreme value statistics and random-
matrix universality, turning an almost-local bispectrum shape into a generic prediction for almost any masses and mixings.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
The alternative scalar field dark sector of the Universe: Cosmological inflation, quintessence and ekpyrotic model in the framework of scalar-tensor cosmology
Marcin Postolak
This dissertation investigates scalar field descriptions of the dark sector (of the Universe), with emphasis on scalar-tensor cosmology, inflationary effective field theory, quintessence, and ekpyrotic/cyclic alternatives to inflation. The thesis first reviews scalar-tensor theories of
gravity, starting from Brans-Dicke theory and extending to general non-minimally coupled scalar fields. Particular
attention is paid to the interpretation of the scalar field, the relation between the Jordan and Einstein conformal frames, and the role of conformal transformations in cosmology. This provides the theoretical basis for treating scalar fields either as modified matter or as additional gravitational degrees of freedom. The second part discusses cosmological inflation from the viewpoint of effective field theory. The spontaneous breaking of time translations, the Goldstone description of adiabatic perturbations, higher-dimensional operators, radiative corrections and Planck-suppressed terms are analyzed in the context of ultraviolet sensitivity and the eta problem. The third part is devoted to quintessence as the simplest dynamical dark energy model. 'Tracking', 'scaling', 'thawing' and 'freezing' behaviors are discussed, together with observational diagnostics such as the statefinder parameters, the $(\omega_{\phi},\omega'_{\phi})$ plane and the $Om(z)$ diagnostic. The DESI DR2 results are used as motivation for considering time-dependent effective dark energy beyond a strict cosmological constant. The final part studies ekpyrotic and cyclic cosmologies. The ekpyrotic phase is analyzed as a smoothing mechanism based on an ultra-stiff scalar field equation of state. Perturbations, non-Gaussianity, tensor modes, bounce conditions,
entropy production, geodesic incompleteness and phase-resolved field-space distance bounds are discussed.
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Cosmology and Nongalactic Astrophysics
A halo-based intrinsic-alignment model for simulation-based inference
M. Gatti
Simulation-based inference and other field-level weak-
lensing analyses require intrinsic-
alignment (IA) models generating realistic intrinsic-ellipticity fields across two-point and non-Gaussian observables. We develop a
halo-based IA prescription with separate central and satellite components and test it against intrinsic
galaxy shapes in FLAMINGO. We jointly fit two-point and higher-order statistics involving the IA,
lensing, and density fields, including correlations between the intrinsic shapes of distinct
galaxies, and compare against field-level nonlinear-
alignment and density-weighted NLA prescriptions. We first evaluate the models at the positions of the original FLAMINGO
galaxies, fixing the
galaxy–matter connection and isolating the IA response. NLA and $\delta$NLA leave substantial discrepancies on nonlinear scales and across higher-order observables, whereas the
halo model provides a simultaneous description of all statistics. We then remove the FLAMINGO
galaxy catalogue and regenerate the source population from the
halo field using a low-dimensional
halo occupation model; the agreement is preserved even when the detailed occupation is only approximately reproduced. Much of this performance can be retained with a compact four-parameter portable model, and the same architecture transfers successfully to an independent
gravity-only N-body realization with different
halo definitions and shape measurements. These results show that nonlinear field-level IA modelling can be substantially improved over simple NLA-like prescriptions without introducing a large nuisance-parameter space. The
halo model therefore provides a promising route for incorporating intrinsic
alignments into simulation-based weak-
lensing inference, although further validation across
halo masses, hydrodynamical simulations, and realistic survey selections will be needed before application to data.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
The Irreversible Depletion of Dark Matter Spikes by Extreme-Mass-Ratio Inspirals
Charlie Sharpe, Yonadav Barry Ginat, Thomas F. M. Spieksma et al. (+2 more)
Dense dark matter spikes around massive black holes (MBHs) have been widely predicted to produce gravitational-wave dephasing in extreme-mass-ratio inspirals (EMRIs) that are potentially observable by LISA. We show that EMRIs, the very objects used to probe these spikes, also destroy them. Combining Fokker-Planck models of nuclear
star clusters with post-Newtonian three-body simulations of EMRI-dark matter encounters, we demonstrate that repeated gravitational slingshots irreversibly eject dark matter particles from the cluster's loss cone over gigayear time-scales. For MBHs at $z = 3$ with masses $\lesssim 10^5 \,M_\odot$, even conservative EMRI rates of $\mathcal{O}(1-10) \, \mathrm{Gyr}^{-1}$ suffice to deplete the spike density by orders of magnitude; for more realistic rates of $\mathcal{O}(100-300) \, \mathrm{Gyr}^{-1}$, the mass range extends to $\lesssim 10^6 \,M_\odot$. As a result, the gravitational-wave dephasing expected from such systems is greatly reduced, narrowing the prospects of detecting DM through this channel. Only heavy, high-
redshift systems with sufficiently low EMRI rates – for example, a $\sim 10^6 \,M_\odot$ MBH at $z \gtrsim 5$ with $\lesssim 100$ EMRIs per Gyr – can induce dephasing that exceeds one radian.
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All authors Charlie Sharpe, Yonadav Barry Ginat, Thomas F. M. Spieksma, Alexander Heger, Bence Kocsis
Cosmology and Nongalactic Astrophysics
Weak Lensing Measurements from the Lyman-$\alpha$ Forest
Anže Slosar
We attempt to measure the weak
lensing of the Lyman-$\alpha$ forest by projecting a quadratic
estimator of the forest-forest and
quasar-forest pair correlations, built from the DESI DR1 data, onto deflection templates constructed from low-
redshift galaxies and
quasars from DESI and BOSS. After validating deflection templates against the ACT DR6 and Planck PR4 CMB
lensing maps and testing the
estimator with injected displacements we measure the
lensing amplitude $A_L$ on the data. Consistent with predictions in the literature, the current generation of public data does not have sufficient signal-to-noise to measure this effect unequivocally: we find the
lensing amplitude $A_L=0.42\pm0.43$ from the forest auto-correlation and $0.87\pm0.48$ from the
quasar–forest cross-correlation. These two nearly independent measurements combine to $A_L=0.62\pm0.33$, consistent with both the fiducial value $A_L=1$ and with no
lensing.
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Cosmology and Nongalactic Astrophysics
Cross-correlating Squared kSZ and HI Intensity Fields: A Map-level ACT–MeerKAT Forecast
Yu-Er Jiang, Yun Liu, Yan Gong et al. (+5 more)
The kinetic Sunyaev–Zel'dovich (kSZ) effect probes the line-of-sight momentum of free electrons, but its blackbody spectrum and velocity-dependent sign make it difficult to isolate and cause conventional cross-correlations with density tracers to vanish. In this work, we investigate the cross-correlation of the squared kSZ field with the projected squared HI intensity field using mock ACT and MeerKAT observations constructed from a Jiutian-1G simulation lightcone. We generate
halo-based kSZ maps and MeerKAT-like HI brightness-temperature cubes over a $13.5^\circ\times13.5^\circ$ field. The simulations incorporate ACT beam smoothing and effective internal-linear-combination noise, together with the frequency-dependent MeerKAT beam, scanning strategy, map-making, and inhomogeneous thermal noise. We analyze signal-only, idealized amplitude-reconstructed, and Wiener-filtered kSZ maps. The resulting squared-field cross-correlations have diagnostic cumulative signal-to-noise ratios of approximately $3$-$4$. Our map-level results demonstrate the detectability of the ${\rm kSZ}^2\times {\rm HI}^2$ correlation in future joint ACT–MeerKAT observations.
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All authors Yu-Er Jiang, Yun Liu, Yan Gong, Zi-Yan Yuwen, Yin-Zhe Ma, Furen Deng, Xuelei Chen, Qi Guo
Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.GA
Population search for dark matter spikes in megamaser rotation curves
Gonzalo Herrera
A black hole growing adiabatically inside a dark matter
halo is expected to develop a dense spike, with a power-law slope between 1.5 and 2.5, depending on
redshift and baryonic activity. Direct dynamical tests of this prediction are almost non-existent. Here we show that water megamaser disks offer one; their masers orbit within a parsec of the black hole and are mapped individually with very long baseline interferometry, so the enclosed mass at each radius can be read off the rotation curve. We develop a search method and apply it to eleven megamaser disks with public kinematics. Compared with a black hole alone, a spike is preferred in NGC 1194 and NGC 4258 and moderately improves the fit in several others. Allowing the disks to warp removes this preference in all but NGC 4258 and NGC 6264. No combination of disks, warped or not, allows a spike heavier than about ten per cent of the black hole mass, a sensitivity validated with mock injection tests. Mapping the warps with maser accelerations and detecting fainter inner masers, where a spike and a tilt differ most, can break the remaining degeneracy. Megamaser disks open a window onto dark matter around supermassive black holes, and, importantly, one that enables population statistics.
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Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.GA
A 210 Megaparsec Ionized Structure at $z=6.8$ Revealed by an Astrophysics Foundation Model
Minghao Yue, Yongda Zhu, Jiani Ding et al. (+2 more)
Reionization is the last major transition in the Universe that transforms the intergalactic medium (IGM) from neutral to highly ionized, yet its spatial structure remains poorly constrained. Using an astrophysics foundation model trained for James Webb Space
Telescope datasets, we identify a luminous
galaxy at
redshift $z=7.567$ showing significant Ly$\alpha$ transmission at $z=6.80\pm0.07$. This transmission, named “the First Ly$\alpha$ transmission in the Reionization Epoch at $z\sim7$" (FL$\alpha$RE-z7), indicates a cosmological-scale ionized structure extending over $210.5^{+55.7}_{-53.5}$ comoving Megaparsecs at
cosmic dawn. The hydrogen neutral fraction of the ionized structure is $x_{\rm HI}=(2.07^{+0.29}_{-0.30})\times10^{-6}$, about $10^5$ times lower than the
cosmic mean at similar
redshifts $(x_{\rm HI}\approx0.4)$. Cosmological simulations suggest a probability of $\approx10^{-5}$ for a random sightline to reproduce the transmission. We find no significant
galaxy overdensity associated with the transmission region, in tension with canonical inside-out reionization models. FL$\alpha$RE-z7 severely challenges existing reionization models in the standard $\Lambda$CDM Universe, indicating extreme spatial fluctuation in ionizing radiation or IGM temperature. Our result marks the first example of a foundation model discovering a previously unpredicted astrophysical phenomenon, demonstrating the power of deep learning methods for mining large astronomical
datasets and finding unexpected new astrophysics.
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All authors Minghao Yue, Yongda Zhu, Jiani Ding, Xiaohui Fan, Yufeng Luo
Cosmology and Nongalactic Astrophysics
Everything Everywhere All At Once: A Hierarchical Framework for Mapping Anisotropies in the Local Universe
Aryan Bansal, Edward N. Taylor, Michelle Cluver et al. (+1 more)
We present a
Bayesian hierarchical forward model for mapping the local luminosity-density field from heterogeneous
redshift surveys. By dividing the survey volume into angular
cells and
redshift shells, we model the observed
galaxy distribution directly in apparent-magnitude and
redshift space. This allows us to infer
cell-level luminosity functions and densities while preserving each survey's unique selection function. Simultaneously, the ensemble of
cells constrains the
cosmic-mean luminosity function, its
redshift evolution, and the hyperparameters describing
cell-to-
cell variation. We apply the framework to 2MRS, 6dFGS, and GAMA over $0.005<z<0.065$, combining wide sky coverage with deeper and fainter
galaxy samples. The model successfully recovers global $J$-band luminosity-function parameters and a mean luminosity density consistent with previous low-
redshift measurements. The inferred luminosity-density scatter decreases with volume, consistent with the
cosmic-variance amplitude expected in a $\Lambda$CDM universe. Within the volume we probe, we find no evidence for a large coherent underdensity. Instead, the local Universe is broadly consistent with smooth
evolution and
cosmic variance. The nearest shell at $z \simeq 0.01$ is the clearest exception, lying $\simeq 0.12$~dex ($\simeq 25\%$) below the smooth global model, a $-2.6\sigma$ underdensity with a one-sided significance of $\simeq 99.5\%$. This framework offers a scalable architecture for mapping
cosmic density fields with next-generation wide and deep surveys.
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All authors Aryan Bansal, Edward N. Taylor, Michelle Cluver, Matthew Colless