Instrumentation and Methods for Astrophysics
Massive Stars in the Thirties: awaiting new Hubble discoveries
Lidia M. Oskinova, Sylvia Ekström, Miriam Garcia et al. (+4 more)
Massive
stars play a fundamental role in shaping the
evolution of
galaxies through feedback, chemical enrichment, and their end products as
neutron stars and black holes. Despite major progress in the last decade, key uncertainties remain in the physics of massive
stars, particularly in mass loss, internal mixing, binary interactions, and the upper end of the initial mass function. These uncertainties directly affect our understanding of
stellar populations, gravitational wave progenitors, and the young Universe probed by JWST. HST is uniquely capable to address these open questions. UV diagnostics are essential for determining
stellar parameters, tracing
stellar winds, and identifying interacting binaries and stripped-envelope
stars. Long-term spectroscopic monitoring further enables constraints on variability, wind structure, and presupernova mass loss. We outline a set of questions which need to be addressed in 2030s by combining UV - optical spectroscopy, time - domain monitoring, and archival baseline exploitation of massive
stars and
star forming regions. These observations will target massive
stars across a range of
metallicities, resolve the most luminous
stellar populations, and identify compact-object binaries and post-interaction systems. Together, these efforts will pave the way to HWO and secure the long-term legacy of HST in massive
star astrophysics.
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All authors Lidia M. Oskinova, Sylvia Ekström, Miriam Garcia, Takashi Moriya, Andreas A.C. Sander, Sergio Simón-Díaz, Aida Wofford
Astrophysics of Galaxies
Supermassive black holes in six triaxial galaxies: Insights from SINFONI and MUSE observations
Sabine Thater, Avinash Chaturvedi, Davor Krajnovic et al. (+5 more)
Dynamical modelling can be used to constrain the masses of central black holes; however, modelling massive
galaxies is challenging due to their complexity. In this work, we report six new supermassive black hole mass measurements of massive early-type
galaxies from
stellar kinematics, which were extracted from adaptive optics-assisted SINFONI and MUSE observations. We combine the
stellar kinematics with HST photometry to build DYNAMITE triaxial Schwarzschild orbit-superposition models. Our Schwarzschild models can recover the complex triaxial features of the
galaxies and constrain the black hole masses of all six
galaxies. We find that strong triaxial kinematic features can bias the mass measurements and correct for this effect. The derived black hole masses are (1.14^{+0.41}_{-0.63}) * 10^9 Msun for NGC 3706, (1.19^{+1.34}_{-0.80}) * 10^9$ Msun for NGC 3923, (1.14^{+1.08}_{-0.95}) * 10^9 Msun for NGC 4261, (4.68^{+2.99}_{-4.26}) * 10^8 Msun for NGC 4636, (3.51^{+3.37}_{-2.57}) * 10^9 Msun for IC 4296, and (2.43^{+1.53}_{-1.65}) * 10^9 Msun for IC 4329 at 3sigma confidence level. We compare our measurements with published results from axisymmetric Schwarzschild modelling and with our Jeans Anisotropic Models (JAM), and obtain mostly consistent black hole masses. Most of our black hole mass estimates can be well constrained using only MUSE observations. All of our mass measurements are in agreement with local black hole scaling relations.
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All authors Sabine Thater, Avinash Chaturvedi, Davor Krajnovic, Michele Cappellari, Sadegh Khochfar, Thorsten Naab, Marc Sarzi, Glenn van de Ven
Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
Antoine Dierckx, Sébastien Clesse and Francesca Vidotto
The possibility that Dark Matter (DM) is partially or totally constituted by stable Planckian remnants of light
Primordial Black Holes (PBHs), suggested for instance by Loop
Quantum Gravity (LQG), is investigated. Distinct phenomenological regimes are identified, including scenarios that trigger an early matter-dominated epoch. New constraints are derived on the initial PBH and final remnant abundances. We show that a significant initial abundance of PBHs lighter than $10^3$ kg would overproduce Planckian relics, implying that any observational evidence for such PBHs would challenge models with quasi-stable remnants. Conversely, the products of Hawking radiation from PBHs with masses between $10^3$ and $10^{12}$ kg impose that Planckian relics could only be a highly subdominant DM component. We identify a PBH mass around $10^3$ kg for which Hawking evaporation naturally reheats the Universe while the remnants entirely constitute the present-day DM. Such a scenario does not require fine-tuning the initial abundance of PBH of this mass, which could range from $10^{-10}$ to order one. These early-Universe cosmologies yield distinct observational signatures: scalar-induced gravitational waves sourced by
primordial or Poisson fluctuations that are amplified by the early PBH-dominated era. Current and future observations of LIGO/Virgo/KAGRA, the Einstein
Telescope and LISA, as well as probes of the effective number of relativistic degrees of freedom, can be used to probe and constrain the initial PBH abundance and the present-day abundance of Planckian relics.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc
When the Ringing Stops: Purely Imaginary Modes in the Ringdown Spectrum of Dynamical Black Holes
Lodovico Capuano, Thomas Lovo, Gorka Prieto-Varela et al. (+4 more)
We extend the frequency-domain analysis of quasinormal modes in a dynamical, spherically symmetric black hole spacetime undergoing constant-rate mass
evolution. In particular, we report a novel feature of the spectrum: the presence of purely imaginary
eigenvalues in addition to the usual light-ring modes. We study the frequencies of these modes both analytically and numerically. The analytical calculation uses a novel formalism based on recent advances in connection coefficients of Heun functions. We then compute the frequencies numerically using a spectral method on hyperboloidal slices and find excellent agreement between the two approaches. Finally, we validate the frequency-domain results against an independent set of time-domain simulations. Our analysis shows that the purely imaginary modes govern the late-time signal through exponentially decaying tails. In the Schwarzschild limit, both frequency- and time-domain studies consistently show that the purely imaginary modes give rise to the familiar Schwarzschild power-law tail.
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All authors Lodovico Capuano, Thomas Lovo, Gorka Prieto-Varela, Subhodeep Sarkar, Adrien Kuntz, Enrico Barausse, Dawood Kothawala
Astrophysics of Galaxies
Closing the UV Gap: Rest-frame EUV science from high-redshift QSOs as a legacy-defining capability
Rongmon Bordoloi and J. Michael Shull
The Hubble Space
Telescope is the only high-resolution ultraviolet spectroscopic facility that will exist until the Habitable Worlds Observatory (HWO) achieves first light in the mid-2040s. We describe a coherent class of science, coupling rest-frame extreme-ultraviolet (EUV; 1–4 Ryd, 228–912 Å) absorption and continuum spectroscopy of intermediate-
redshift quasars at $z = 1-2$, shifting the rest-frame EUV
photons into the HST/COS far-UV bandpass. This science on
quasars and gas in the IGM and CGM is doubly perishable. The COS detector sensitivity is declining, just as new
quasars are found (Milliquas, UVQS, and soon Rubin, Roman, and Euclid). Thus, the window to reach UV-bright
quasars at $z>1$ QSOs narrows with every deferred orbit. Expanding HST UV orbit allocations in the 2030s would deliver a step-change in warm-hot CGM/IGM science and produce the first systematic, empirical EUV SED census of QSOs. These
datasets will serve as the foundational low-
redshift anchor for HWO science. This recommendation makes the scientific and strategic case for an expansion of the HST/COS spectroscopic data base on intermediate
redshift AGN in their rest-frame EUV.
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High Energy Astrophysical Phenomena
Dust grain chemistry in the diffuse ISM towards the black hole transient GX 339-4
I. Psaradaki, L. Corrales, E. Costantini et al. (+10 more)
We present results on X-ray absorption and the
dust grain chemistry in the diffuse interstellar medium (ISM), based on a new Cycle 25 Chandra High Energy Transmission Grating Spectrometer (HETGS) observational campaign targeting the black hole transient GX 339-4. The X-ray source offers an optimal combination of moderate hydrogen column density and high X-ray flux, enabling the first detailed simultaneous fitting of the photoabsorption edges of Fe, O, Si, and Mg which are key elemental constituents of interstellar
dust. We performed a joint spectral analysis of Chandra/HETGS data and archival observations from the Reflection Grating Spectrometer (RGS) on board XMM-Newton. We found that the
dust grain chemical composition along this diffuse
Galactic line of sight is best described by the silicate Mg-rich amorphous pyroxene (Mg0.75Fe0.25SiO3) and metallic iron. We also discuss the elemental abundances and depletions of Fe, O, Si, and Mg, and the presence of absorption features in the X-ray spectrum of this source associated with highly ionised
plasma.
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All authors I. Psaradaki, L. Corrales, E. Costantini, P. Draghis, J. A. García, E. Gatuzz, P. Kosec, G. Mastroserio, M. Mehdipour, F. Paerels, D. Rogantini, N. Schulz, S. Zeegers
High Energy Astrophysical Phenomena
Impact of the equation of state on core collapse supernovae I: the low-$T/|W|$ instability
Marco Cusinato, Martin Obergaulinger and Miguel Ángel Aloy
Rapidly rotating core-collapse
supernovae are promising sources of multimessenger emission, as non-axisymmetric dynamics in the newly formed proto-
neutron star can leave characteristic imprints on both gravitational waves and
neutrinos. We present three-dimensional
neutrino-magnetohydrodynamics simulations of the collapse of a rapidly rotating $35\,\mathrm{M}_\odot$ progenitor, performed with five different finite-temperature
nuclear equations of state, to investigate how dense-matter physics affects the development of the low-$T/|W|$ instability and its associated multimessenger signatures. We find that the low-$T/|W|$ instability develops in all equation of state models considered, indicating that its occurrence is robust for this rapidly rotating progenitor. However, its onset time, dominant azimuthal structure, lifetime, and characteristic multimessenger frequencies vary among models, reflecting differences in the evolving proto-
neutron star structure and rotation profile. The instability produces large-scale spiral modes that generate quasi-periodic gravitational wave emission and modulate the
neutrino luminosities, especially along directions close to the equatorial plane. The dominant gravitational wave frequency associated with the instability correlates with the effective stiffness and compactness of the proto-
neutron star: models with more compact/stiffer configurations emit at higher frequencies. This suggests that, in rapidly rotating core-collapse
supernovae, the frequency of the low-$T/|W|$ instability-driven gravitational wave signal may provide a diagnostic of the dense-matter equation of state, complementary to the information carried by the
neutrino signal.
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Cosmology and Nongalactic Astrophysics
Dominated-Convergence Failure in Cosmological Perturbation Theory and a Numerical Foundation for BBGKY+ZA
Svetlin V. Tassev
A common ingredient in cosmological perturbation theory (PT) is the expansion of the dark matter overdensity $\delta$ in the Lagrangian displacement $s$, which amounts to enforcing mass conservation perturbatively. In Eulerian PT (EPT), that expansion occurs already at the level of the continuity equation; in Lagrangian PT (LPT) it is done in the Poisson equation. We show that the resulting perturbative solutions for $\delta$ can diverge not because of the expansion in $s$ per se, but because of an exchange of an infinite sum with a
Fourier integral that violates the conditions of Lebesgue's dominated-convergence (DC)
theorem. We show that this DC obstruction (DCO) is one clear reason why the convergence of EPT is controlled by advection terms beyond the linear $\delta$. The same DCO underlies LPT: LPT's region of validity is the resummation region of a DC-violating series, bounded by shell crossing on one side and severely underdense regions on the other. Effective field theories (EFT) of large-scale structure need to smooth at short scales just to recover from that DCO, independent of whether non-linearities beyond mass conservation are important or not. An alternative is to never expand $\delta$ in $s$: instead evolve phase-space cumulants using the BBGKY hierarchy, initialized with the Zel'dovich approximation (ZA). The DCO is then absent by construction, so an EFT of BBGKY can focus on physics beyond mass conservation, which may allow pushing PT beyond shell crossing. The trade-off is the need for a closure relation, for which one can again use the ZA. We provide the building blocks for such a BBGKY+ZA recipe. A bottleneck for implementing it has been the ZA phase-space two-point function $\mathcal{P}$, which we successfully integrate numerically; we then write the higher ZA phase-space correlators needed for closure as products and convolutions of $\mathcal{P}$.
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Astrophysics of Galaxies
A 1% distance to the Large Magellanic Cloud measured by population-II pulsating stars using Gaia Data Release 3
Bastian Lengen, Richard I. Anderson and Mauricio Cruz Reyes
Population-II pulsating
stars provide a route to extragalactic distances that is independent of the classical Cepheid distance scale and complementary to
geometric and tip-of-the-red-
giant-branch (TRGB) methods. We apply optical Wesenheit Leavitt laws for RR Lyrae and type II Cepheid
stars calibrated with
Gaia DR3 data and anchored by homogeneous globular-cluster distances based on trigonometric parallaxes to variable
stars in the Large Magellanic Cloud (LMC). We adopt RRab
stars as the baseline tracer because they define the absolute zero point of the calibration, dominate the LMC sample, and provide robust classifications. The uncertainty budget propagates the full covariance
matrix of the calibration parameters, treating calibration uncertainties as correlated systematics rather than independent
star-by-
star errors. Using 12,193 RRab
stars after outlier rejection, we determine mu_LMC = 18.423 +/- 0.002 (stat) +/- 0.020 (syst) mag. This combines the statistical uncertainty on the mean and the systematic uncertainty of the absolute calibration, which currently limits the total precision. Our result is lower than the detached-eclipsing-binary
benchmark by 0.054 mag, corresponding to an approximately 1.7 sigma offset, and agrees with the TRGB distance obtained from the same globular-cluster scale to within 0.024 mag. RRc and T2Cep
stars provide useful consistency checks, although the relative RRc-RRab and T2Cep-RRab offsets measured in the LMC differ from those calibrated in globular clusters.
Geometric corrections between tracer barycenters and external reference positions are below 0.003 mag. Individual RRab distances map the three-dimensional structure of the LMC across a broad 10-degree-radius field. A planar model reproduces the dominant distance gradient and yields i = 21.3 +/- 0.7 deg and Theta = 145.2 +/- 2.2 deg, in agreement with previous determinations.
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Astrophysics of Galaxies
Too many protoclusters? Reconciling the overabundance of cluster progenitors within the first billion years of the Universe
Callum Witten, Jake S. Bennett, Pascal A. Oesch et al. (+8 more)
JWST has revealed an overabundance of apparent (`Coma'-like) cluster progenitors at $z>5$ that is $\sim$ two (300) times in excess of, and in $2.3\sigma$ ($4\sigma$) tension with, the number density of such objects at present day and theoretical predictions from $\Lambda$CDM. We present an analysis of protocluster candidates between $5<z<9$ from the literature, and in the TNG-Cluster and TNG300 simulations, aimed at resolving this tension. We first identify an inconsistency in how protocluster candidates are characterised: observational
halo masses are estimated by summing the
stellar mass over very large apertures ($\gtrsim 50\, R_{\rm vir}$), but are compared to the
halo mass within the virial radius from simulations. In addition, these
halo masses are commonly compared to the backward-tracked
halo mass
evolution of clusters, whereas a forward-tracked
evolution of massive high-
redshift haloes is more appropriate. Correcting these inconsistencies, while accounting for the merging of coincident protoclusters and the fluctuations associated with
cosmic variance, entirely alleviates the tension. Ultimately, we find that $64\%$ of the protocluster candidates are instead likely to be proto-groups (i.e., $M_{200c}<10^{14}\, {\rm M_{\odot}}$) and none appear likely to become Coma-like clusters (i.e., $M_{200c}>10^{15}\, {\rm M_{\odot}}$) by $z=0$. Although some of these overdensities may not become clusters, they still trace extreme nodes of the
cosmic web that may host early environmental effects, drive the first ionised regions, and contribute significantly to the
cosmic star-formation rate density. These results demonstrate the need for more careful comparisons between observations and simulations of high-
redshift protoclusters, and that improved selection criteria, potentially using the summation of the
halo mass on Lagrangian scales, are vital for high-
redshift protocluster science.
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All authors Callum Witten, Jake S. Bennett, Pascal A. Oesch, Seunghwan Lim, Chamilla Terp, Jakob M. Helton, Kasper E. Heintz, Romain A. Meyer, William McClymont, Thomas Herard-Demanche, Emma Giovinazzo
High Energy Astrophysical Phenomena
Itai Linial, Brian D. Metzger and Andrei M. Beloborodov
A growing fraction of
tidal disruption events (TDEs) exhibit
radio emission that rises only years after the optical or infrared
flare, indicating delayed
outflow activity. In some events the
outflow is inferred to be slow ($\sim 0.02 \, c$) and massive ($\gtrsim 0.01-0.1 M_{\odot}$), challenging models such as delayed jets and disk state transitions. We propose a new mechanism for such delayed
outflows: repeated collisions between a TDE
accretion disk and a pre-existing
stellar extreme-mass-ratio-inspiral (EMRI) orbiting the black hole. In this scenario, the delay reflects the viscous time required for the initially compact TDE disk to expand and intercept the EMRI orbit, rather than delayed jet launching or off-axis viewing effects. Once
star-disk collisions commence, repeated impacts eject
outflows with velocities comparable to the orbital speed, $v_{\rm w} \sim 0.02-0.1c$. We develop a time-dependent model for the coupled
evolution of the spreading disk and EMRI-induced mass-loss, identifying regimes where the
outflow is dominated by disk material or ablated
stellar debris. Depending on disk viscosity, orbital period, and collision efficiency, masses $\sim (10^{-3}-1) \, \rm M_\odot$ can be launched with energies up to $10^{51} \rm \, erg$, years after the TDE. These
outflows produce
radio emission through interaction with circumnuclear material or earlier TDE ejecta, consistent with observed late-time
radio re-brightening. This model predicts a connection between delayed
radio flares and EMRI-hosting systems, potentially including those exhibiting quasi-periodic eruptions (QPEs) powered by
star-disk collisions, though the conditions for bright
radio flares may not always match those necessary for detectable QPEs.
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Earth and Planetary Astrophysics
Assessing Ariel's capabilities to observe free-floating brown dwarfs
Roman Akhmetshyn, Nicolas B Cowan and Sarah Casewell
The primary goal of the Ariel space
telescope is to conduct the biggest spectroscopic survey of transiting
exoplanets to characterize their atmospheres and weather. We propose to extend the Ariel survey to another domain of alien atmospheres - rogue
planets and free-floating brown
dwarfs. Their isolated nature means the observations are uncontaminated by light from a host
star, and their short rotation periods, often similar to hot Jupiter orbital periods, provide an opportunity to study time-varying meteorology. Phase curve observations would especially help scientists understand atmospheric dynamics at the L/T transition, where multiple cloud species at different altitudes influence the time-varying spectra of brown
dwarfs. Inferring timescales and length scales of these atmospheric features is key to understanding the meteorology of sub-
stellar objects. We quantify how many isolated cool objects that Ariel's fine guidance sensor (FGS) is able to guide on. Among 2744 selected targets, none are bright enough under the planned 10 Hz FGS cadence; however, with a "slow" fine guidance mode of 1 Hz, Ariel could study 98 L0- to L5-type brown
dwarfs. We simulate single-epoch and time-series spectroscopic observations of the brightest isolated brown
dwarfs given currently known instrumental specifications. We show that the resolution and sensitivity of Ariel instruments in the 1.1-7.8 micron regime can measure cloud-induced variability at the sub-percent level. A survey of brown
dwarf phase curve observations, unavailable to ground-based
telescopes, would be the perfect complement to Ariel's survey of atmospheric variability in hot Jupiters.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Minimal dark $SU(2)$ origin of a massless Dirac neutrino
P. S. Bhupal Dev, Julia Gehrlein, Amartya Sengupta et al. (+1 more)
We propose a gauge-
symmetry origin of a rank-two Dirac
neutrino mass
matrix that enforces one exactly massless
neutrino, while being consistent with the oscillation data, as well as cosmological constraints. The mechanism relies on a minimal dark $SU(2)_D$ gauge
symmetry under which one right-handed-
neutrino-like Weyl
fermion is charged, thereby forbidding its Standard Model Yukawa coupling.
Quantum consistency then fixes the minimal dark-sector completion: Cancellation of the Witten anomaly requires a second fermionic $SU(2)_D$ doublet, while a discrete $Z_4$
symmetry that forbids Majorana masses allows the two dark doublets to form a vectorlike pair. This anomaly-free completion gives rise to a secluded, confining dark sector with a viable dark matter candidate, linking the protected
neutrino texture to dark infrared dynamics.
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All authors P. S. Bhupal Dev, Julia Gehrlein, Amartya Sengupta, Amarjit Soni
Instrumentation and Methods for Astrophysics
Photometry is all you need: supernova classification as a mixing problem
Ana Sofía M. Uzsoy and V. Ashley Villar
In the era of large-scale photometric surveys, scalable and robust methods for classifying
supernova (SN) populations are increasingly necessary. Often, spectroscopy is essential in addition to photometry to reliably classify SNe; however, complete spectroscopic follow-up is infeasible for all of the millions of transient light curves being collected by facilities such as the Vera C. Rubin Observatory. Using light curves of SNe Ia and Ibc observed with the Zwicky Transient Facility, we frame the classification of large SN populations as a mixing problem. We fit all objects using a semi-analytical SN model powered by radioactive decay, and we model the resulting distributions of fit parameters with a Gaussian Mixture model to optimize the shared population mixing fraction. This approach allows us to reliably constrain the ratio of the populations and classify SNe Ia and Ibc with $\geq$ 90% accuracy without any need for labeled training data, i.e., a spectroscopic
dataset. We validate this method for varying population mixing fractions and explore the impact of including spectroscopic, photometric, or no
redshift information, and a small amount of known labels. Overall, this method allows for fast and accurate SN classification and population characterization using only photometry.
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Astrophysics of Galaxies
The incidence and star-formation properties of X-ray active galactic nuclei across the star-forming main sequence in DESI-eRASS1: the role of host-galaxy morphology
G. Mountrichas, F. J. Carrera, V. A. Masoura et al. (+3 more)
The interplay between
star formation and supermassive black-hole growth is central to
galaxy evolution, but how host-
galaxy morphology regulates
star-formation enhancement and AGN triggering across the
star-forming main sequence remains unclear. We investigate the
star-formation properties and incidence of X-ray AGN across the
star-forming main sequence using the DESI-eRASS1
dataset, focusing on host structure. Our analysis includes 1171 X-ray selected AGN and 45374 non-AGN
star-forming
galaxies at $z\le1.5$. We quantify
star formation in AGN hosts relative to matched control samples using ${\rm SFR}_{norm}$ and examine its dependence on X-ray luminosity ($L_X$) and specific
accretion rate ($\lambda_{sBHAR}$). We measure AGN incidence as a function of distance from the
star-forming main sequence ($\Delta_{\rm MS}$), separating disk- and spheroid-dominated systems based on Sersic index. ${\rm SFR}_{norm}$ remains close to unity at low to intermediate $L_X$ and increases at higher luminosities, with the transition shifting toward higher $L_X$ in more massive systems. This trend depends on morphology: in the
stellar-mass range $10.5\le\log(M_\star/M_\odot)<11.5$, disk-dominated AGN hosts exhibit enhanced ${\rm SFR}_{norm}$ at moderate $L_X$, while spheroid-dominated systems remain consistent with unity. No comparable morphology dependence is found when using $\lambda_{sBHAR}$. The incidence of X-ray AGN increases strongly with $\Delta_{\rm MS}$ in both
redshift bins, with a steeper dependence at higher
redshift. The $\Delta_{\rm MS}$-incidence relation is also morphology-dependent and evolves with
redshift. The connection between
star formation and AGN activity is governed by global gas availability but modulated by host-
galaxy structure and
cosmic epoch. Absolute AGN power is more tightly linked to host-wide
star formation than
accretion efficiency normalised by
stellar mass.
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All authors G. Mountrichas, F. J. Carrera, V. A. Masoura, S. Mateos, M. Siudek, A. Corral
Instrumentation and Methods for Astrophysics
Agentic AI for Gravitational Wave Data Analysis: A Head-to-Head Comparison of Coding Agents Executing a Matched Filter Pipeline on Einstein Telescope Simulated Data
Gianluca Inguglia
We report a methodological study of agentic AI in gravitational-wave data analysis: two systems, Claude Code (Anthropic) and Codex (OpenAI), autonomously executed the same simple end-to-end pipeline on Einstein
Telescope (ET) simulated data, on shared infrastructure and without human intervention. The object of study is the behaviour, reliability and auditability of the
agents, not the physics output, used here as a controlled test case. The pipeline comprises power spectral density estimation from simulated ET noise,
geometric template bank generation with IMRPhenomD waveforms, matched-filter recovery of 100 binary black hole injections, results generation, and LLM-assisted production of a LaTeX manuscript in Physical Review D style. Both
agents received identical specifications and resources. The experiment was run twice: first with unrealistically loud injections, then with signals rescaled to a physically motivated SNR range. In both runs the results converged, with comparable detection efficiency and template bank size. The
agents, however, behaved very differently: Claude Code finished in about 3.4 minutes with silent deviations from the specification, while Codex needed about 16 minutes across explicit self-correcting restarts, including an unsolicited optimization of the matched-filter inner loop. In the second run, a subtle difference in interpreting the SNR-range instruction produced a genuine scientific divergence: Claude Code silently raised the SNR floor to 8 (100% efficiency), while Codex followed the specification literally down to SNR 7 and recorded one missed detection. We discuss the implications - speed versus auditability, silent deviation versus explicit self-correction, instruction interpretation, and intermediate data representations in multi-model pipelines - for agentic AI in scientific workflows, within the limits of a single-pipeline, two-run
benchmark.
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Cosmology and Nongalactic Astrophysics
The energy conditions and model selection in the local Universe
Namit Chandak, Fulvio Melia and Junjie Wei
The four principal energy conditions (ECs) in general relativity prohibit negative energies, repulsive
gravity and superluminal energy flows. One must invoke exotic matter to violate any one of these, yet $\Lambda$CDM does so quite prominently during inflation and in the epoch of dark energy dominance. In this paper, we carry out model selection between the standard model and the $R_{\rm h}=ct$ universe using a combination of HII
galaxy and
cosmic chronometer measurements in the local Universe, and directly compare the results to the constraints imposed by the ECs. We find that the latter cosmology is not only strongly favored by these data, with a likelihood of $\sim 92\%$ versus only $\sim 8\%$ for the former, but that its optimized fit is fully compliant with all four ECs, while $\Lambda$CDM's best fit violates the so-called strong energy condition at $z\lesssim 2$.
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Cosmology and Nongalactic Astrophysics
Fewer simulations, sharper covariances: Reducing mock covariance noise with Zeldovich approximation control variates
Boryana Hadzhiyska and Martin White
We present a control-variate method for reducing the variance of power spectrum covariance
matrix estimates from simulations of large-scale structure. The idea is to pair each mock simulation with a cheap Zeldovich-approximation realization sharing the same initial conditions, and to use the known statistical properties of the Zeldovich field to remove correlated sample variance from the covariance
estimator. Under a Gaussian disconnected approximation, we derive fully analytic expressions for both the optimal control-variate coefficient, $\beta(k,\ell;k',\ell')$, and the corresponding correlation, $\rho(k,\ell;k',\ell')$, in terms of the auto- and cross-power spectra of the target and control fields. In the monopole case, the correlation takes the simple form $\rho(k,k') = r^2(k),r^2(k')$, where $r(k)$ is the standard cross-correlation coefficient between the target and Zeldovich fields, implying that covariance estimation remains highly efficient whenever the two fields are strongly correlated. For masked
redshift-space lognormal mocks, resembling LRGs from DESI, we find that the control-variate
estimator reduces the variance of the covariance
matrix by approximately an order of magnitude on large scales, $k\lesssim 0.05\,h\,{\rm Mpc}^{-1}$, precisely where accurate covariance estimation is most challenging. The gains are smaller for higher $k$ but typically accelerate convergence by a factor of 2-3, substantially lowering the computational cost of covariance estimation for current and upcoming large-scale structure surveys. After a cheap parametric-bootstrap calibration of the precision-
matrix bias, the control-variate covariance yields a $\chi^2$ distribution consistent with the expected number of degrees of freedom. This method is readily implementable in current imaging and spectroscopic surveys (e.g., DESI, Euclid, LSST, PFS, SPHEREx).
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Cosmology and Nongalactic Astrophysics
Whispers of Supergravity in Gravitational Wave Backgrounds: Determining the Gravitino Mass from Cosmic Thermal History
Angus Spalding and Stephen F. King
Gravitino masses above the electroweak scale provide the simplest solution to the gravitino problem, but such large mass scales lie far beyond the reach of
collider experiments. We show that the
stochastic gravitational wave background offers a direct probe of this otherwise inaccessible regime. Despite decaying before Big-Bang Nucleosynthesis (BBN), these gravitinos naturally generate a period of early matter domination in the early universe. This non-standard epoch leaves a characteristic imprint on any
primordial gravitational wave background, characterised by two frequencies corresponding to the onset and end of this phase. We demonstrate that, when early matter domination occurs while the gravitational-wave background is freely propagating, its spectral features enable the direct inference of both the gravitino mass and initial abundance, while more generally, even when the background is sourced during the early matter-dominated epoch, the gravitino mass can still be determined. Future gravitational wave observatories span a vast frequency range, enabling sensitivity to gravitino masses from the BBN bound of $\mathcal{O}(100) \text{TeV}$ up to $\mathcal{O}(10^{10}) \text{TeV}$. Already, the signal reported by NANOGrav, if
primordial in origin, offers a potential probe of gravitino masses in the range $500$-$10^4 \text{TeV}$. Gravitational wave observables therefore probe an enormous region of parameter space, far beyond the reach of
collider experiments. We are entering an era in which supergravity can be probed through gravitational wave backgrounds alongside
collider experiments.
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Cosmology and Nongalactic Astrophysics
Entropic backreaction from cosmic structure formation: a thermodynamic approach to the late-time cosmological tensions
Biswajit Pandey
High-precision cosmological observations have revealed persistent tensions within the standard $\Lambda$CDM paradigm, most notably the discrepancy in the Hubble constant and the lower than predicted amplitude of late-time matter clustering quantified by $S_8$. We propose a unified thermodynamic framework in which entropic backreaction generated during
cosmic structure formation modifies both the background expansion history and the growth of matter perturbations. As gravitational instability drives the growth of
cosmic structures, the configuration
entropy associated with the matter distribution decreases through the nonlinear redistribution of gravitational binding energy. The resulting entropic energy density contributes a late-time backreaction that enhances the
cosmic expansion rate without altering early-Universe physics or the CMB sound horizon. Simultaneously, the same irreversible
entropy dissipation process induces a dissipative correction within the
cosmic velocity flow, suppressing the efficiency of coherent gravitational clustering at late times. The framework operates entirely within standard General Relativity: the Einstein field equations, Poisson equation, and gravitational coupling remain unmodified, and no new propagating degrees of freedom or fifth forces are introduced. Entropic backreaction therefore provides a thermodynamically motivated, theoretically conservative, and observationally testable mechanism that may simultaneously alleviate the major late-time cosmological tensions.
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High Energy Astrophysical Phenomena · Cross-listed from nucl-th
Three-dimensional orbital-free density functional theory description of nuclear pasta in the inner crust of neutron stars
Yo Nakamura and Kazuyuki Sekizawa
Background: In the bottom layer of the inner crust of
neutron stars, various crystalline structures are expected to emerge that are collectively called “
nuclear pasta.” It is desirable to know properties of
nuclear pasta in a wide variety of conditions for astrophysical applications. However, three-dimensional fully-microscopic calculations require huge computational effort that makes it still challenging to carry out systematic calculations. Purpose: In this paper, we propose an efficient method to calculate various
nuclear pasta configurations in a non-empirical manner, based on three-dimensional orbital-free density functional theory (OF-DFT). We demonstrate the feasibility of the proposed approach by applying it to densities across the inner crust of
neutron stars. Methods: As a first application of OF-DFT for
nuclear pasta, we employ the second-order extended Thomas-
Fermi (ETF) expansion of Skyrme energy density functional (EDF) to construct an EDF that depends only on
neutron and
proton number densities. Based on the variational principle, we derive Euler-Lagrange equations to determine optimal
neutron and
proton density distributions and solve them self-consistently. In this work, we call this approach the self-consistent ETF (SC-ETF) method. Results: We perform three-dimensional SC-ETF calculations with various box sizes. We successfully obtain various pasta structures, depending on given average nucleon number densities, consistent with earlier studies. Moreover, we find other exotic structures, such as bending and/or connected rods, slabs with a hole, etc., underlining the advantage of the self-consistent formalism. Conclusions: We demonstrate that the SC-ETF method proposed in this study, which can be regarded as a realization of OF-DFT, is a promising tool that can efficiently describe complex pasta structures without empirical assumptions on
geometric shapes.
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Astrophysics of Galaxies
The formation of supermassive black holes from Population III.1 seeds. IV. Self-regulated seeding from supermassive star ionizing feedback
Maya A. Petkova, Jonathan C. Tan, Jasbir Singh et al. (+5 more)
Supermassive Population III.1
stars, i.e., formed from pristine, metal-free gas leading to conditions where dark matter annihilation heating is significant, have been proposed as the progenitors of supermassive black holes (SMBHs) in the early universe ($z \sim 20-40$). Since such Pop III.1
stars only form from non-irradiated gas in dark matter minihalos, they are predicted to appear isolated from each other and other sources of feedback. The previous papers in this series used the isolation distance of Pop III.1
stars as a free parameter to seed SMBH in cosmological simulations of dark matter
halos. Here we develop a feedback-regulated model of Pop III.1 isolation, based on the growth of HII regions around each Pop III.1
star and lower-mass, irradiated Pop III.2
stars. Our model considers the time delay between the formation of a minihalo and its Pop III.1
star, R-type expansion of HII regions that expand into the intergalactic medium (IGM), and the
redshift dependence of Strömgren spheres for longer-lived ionizing sources. For a fiducial Pop III.1
star H-ionizing
photon luminosity of $10^{53}\:{\rm s}^{-1}$ and lifetime of $10\:$Myr we find an R-type HII region radius of $R_{\rm R}\simeq1.3\:$cMpc, approximately independent of
redshift. The median formation
redshift is $\sim20$, with the process essentially complete by $z\sim16$. The overall number density of SMBHs produced in this model is then $n_{\rm SMBH}\simeq 3 \phi_V/(4\pi R_{\rm R}^3)\simeq 0.2\:{\rm cMpc}^{-3}$. We also discuss predictions for the abundance of binary SMBHs, which may appear as dual active
galactic nuclei (AGN; $\lesssim 0.3\%$ for $z>6$), and SMBH binary merger rates, measurable by the forthcoming LISA mission.
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All authors Maya A. Petkova, Jonathan C. Tan, Jasbir Singh, Vieri Cammelli, Mahsa Sanati, Benjamin Keller, Pierluigi Monaco, Devesh Nandal
Solar and Stellar Astrophysics
Evolution of the dusty nova QY Mus from eruption to quiescence
Mohit Singh Bisht, A. Raj, F.M. Walter et al. (+3 more)
We present a comprehensive study of the spectrophotometric
evolution of the classical nova QY Mus from eruption to quiescence. The light curve shows a notable
dust dip, classifying it as a D (137)-type nova, with
dust formation beginning at $\sim$123 days post-outburst and reaching a maximum optical depth of $\tau \sim 3.2$. We classify QY Mus as a slow nova with $t_2 = 87 \pm 6$ days, and derive an absolute magnitude of $M_V = -6.55 \pm 0.54$ using the MMRD relation. The spectroscopic
evolution, traced from 94 to 1348 days, shows prominent P-Cygni profiles in Balmer and Fe II lines during the early decline, consistent with an Fe II-type nova. The transition to the nebular phase occurs around $\sim$233 days, marked by the emergence of [O III] emission. Photoionization modeling using Cloudy of 41 emission lines on day 590 yields a central source temperature of $(7.08 \pm 0.20)\times10^{5}$ K, with enhanced nitrogen and oxygen abundances and moderate neon enrichment, suggesting that QY Mus is not a neon nova. Mid-infrared WISE observations at $\sim$502 days indicate the presence of cool
dust at $\sim$400 K. Using a
Gaia-based color magnitude diagram constructed in this work for 34 quiescent novae, we find that QY Mus occupies a region consistent with systems hosting main-sequence or subgiant secondaries; its orbital period further supports a subgiant companion. These results establish QY Mus as a slow,
dust-forming nova with well-characterized
evolution and a subgiant secondary.
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All authors Mohit Singh Bisht, A. Raj, F.M. Walter, D. Bisht, K. Belwal, S. Biswas
Instrumentation and Methods for Astrophysics
The unique ability of the Hubble Space Telescope to characterize young exoplanet environments
Keighley E. Rockcliffe, Allison Youngblood, Kevin France et al. (+10 more)
The chemical and mass
evolution of
exoplanet atmospheres is shaped by their specific X-ray through ultraviolet (5 - 3200 Angstroms) irradiance history. X-ray and EUV (5 - 911 Angstroms) radiation largely contributes to atmospheric heating via photoionization, while far- and near-UV emission (912 - 3200 Angstroms) drives photochemistry. The (uncharacterized) variance between young
star spectra in this wavelength range for the same spectral type causes significant uncertainty in interpreting present-day transmission spectra of young
exoplanets, directly impacting the science return of the James Webb Space
Telescope and other programs. Additionally, the lack of direct X-ray through UV characterization for
stars of all ages leads to large uncertainties in the high-energy irradiance history of all planetary systems, propagating into uncertainties in their chemical and mass
evolution. This influences current and future observing programs, as well as the goal of the future flagship Habitable Worlds Observatory to find and characterize habitable
exoplanets. There are less than a handful of young
planet hosts with well-characterized X-ray through UV environments. The Hubble Space
Telescope is the only observatory capable of measuring the UV spectrum and enabling the characterization of
exoplanet high-energy environments. We advocate for an observing program to measure the UV, estimate the EUV, and measure the X-ray where possible and needed of all amenable young
planet hosts, addressing the Space
Telescope Science Institute's call for Building a Roadmap for Hubble Science into the 2030s.
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All authors Keighley E. Rockcliffe, Allison Youngblood, Kevin France, Cynthia Froning, P. C. Schneider, Elisabeth Newton, David J. Wilson, Vighnesh Nagpal, Sarah Peacock, Seth Redfield, Mayumi Liz de Andrade Miyazato, Hans-R. Müller, Aylin García Soto
Astrophysics of Galaxies
Cluster-centric trends in bar size and pattern speed: the case of Abell 2199
Chandan Watts, Sudhanshu Barway, Mousumi Das et al. (+1 more)
We investigate how the environment of a dynamically unrelaxed
galaxy cluster influences the structure and dynamics of
stellar bars. In particular, we examine cluster-centric variations in normalised bar size and bar pattern speed in Abell 2199. Our analysis is based on 578 spectroscopically confirmed members of Abell 2199, including a master sample of 325
galaxies with homogeneous
stellar mass and
star formation rate measurements. We identify 39 barred
galaxies and measure their structural properties using isophotal ellipse fitting and three-component (bulge+disc+bar) photometric decompositions. For 22 barred
galaxies with MaNGA integral-field spectroscopy, we estimate bar pattern speeds using the Tremaine-Weinberg method, obtaining robust measurements for 12
galaxies.
Stellar population age and projected specific angular momentum are analysed using $D4000_{R_{\mathrm{e}}}$ and $\lambda_{R_{\mathrm{e}}}$ from the MaNGA Pipe3D catalogue. Abell2199 exhibits
star formation-density and morphology-density relations despite its non-relaxed dynamical state. Early-type spiral (ETS) barred
galaxies show systematic cluster-centric variations in normalised bar size, with relatively larger bars towards the cluster centre and smaller bars at intermediate radii. A corresponding variation in bar pattern speed with cluster-centric distance is also observed. These trends motivate a division at $\sim$0.5$R_{\mathrm{vir}}$, within which morphology-dependent environmental signatures become clearer, as barred
galaxies in the inner region tend to host older
stellar populations and lower projected angular momentum than those in the outskirts, with ETS+Bar
galaxies retaining higher angular momentum compared to S0+Bar
galaxies at comparable radii.
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All authors Chandan Watts, Sudhanshu Barway, Mousumi Das, Ewa L. Lokas
Earth and Planetary Astrophysics
Hidden worlds: A non-transiting candidate planet in the Neptunian desert around the solar-type pulsator KIC 9139163
Sylvain N. Breton, Achrène Dyrek, Carlos Allende Prieto et al. (+16 more)
Close-in substellar companions experience strong
tidal and
magnetic interactions with their host
stars and are therefore subject to fast orbital
evolution. The
solar-type pulsator KIC 9139163 exhibits in its light curve a stable 0.6-day modulation for which the best explanation is the presence of a close-in non-transiting companion that we therefore attempt to characterise. We combine Kepler and TESS photometric data with spectroscopic observations obtained with HARPS-N. The analysis of the radial velocities obtained with HARPS-N provides a companion mass $M_p \sin i = 7.3 \pm 1.4 \, \mathrm{M}_{\oplus}$. We infer a planetary radius of $2.43 \pm 0.14 \, \mathrm{R}_\oplus$, which, combined with the measured mass and retrieved inclination, implies a bulk density consistent with a hot water-rich world. This places the non-transiting companion candidate of KIC 9139163 within the Neptunian desert, a regime where
planets are expected either to have lost their
primordial hydrogen/helium envelopes or to harbour metal-enriched atmospheres. We further detect significant variations in amplitude between the Kepler and TESS phase curves, obtained six years apart, as well as a secular increase in amplitude over the Kepler baseline. Our fit favours a model with two distinct longitudinal cloud offsets over a single-offset scenario. Both
datasets indicate a moderate-to-high
geometric albedo and low-to-moderate heat redistribution. The opposite phase offsets observed in the Kepler and TESS
datasets suggest a time-variable longitudinal brightness distribution. While making KIC 9139163 an interesting candidate for future ground follow-ups, it also suggests that searching for other non-transiting
planets around fast
stellar rotators in space-borne photometric surveys might provide new insights into the physics of the Neptunian
planets located in the desert. [shortened]
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All authors Sylvain N. Breton, Achrène Dyrek, Carlos Allende Prieto, Andrea Bonfanti, Hans J. Deeg, Rafael A. García, Enric Pallé, Fernando Pérez Hernández, Othman Benomar, Lina Borg, Ilaria Carleo, Clémence Gourvès, Antonino F. Lanza, Kento Masuda, Stéphane Mathis, Savita Mathur, Dinil B. Palakkatharappil, Angela R.G. Santos, Franck Selsis
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-th
Inflation with vector fields revisited: non-Gaussianities
Chong-Bin Chen
{We revisit the resulting bispectrum of inflation with kinetic-coupled vector fields by organizing the dynamics in terms of $h$, which measures the vector kinetic contribution relative to that of the scalar field. We derive a low-energy effective field theory (EFT) and evaluate the bispectrum of the
curvature perturbation for the large-$h$ regime. For $h\gg1$, the entropic perturbation becomes heavy and can be integrated out; the remaining
curvature mode has an imaginary sound speed and undergoes transient growth before horizon crossing. In contrast to the $h\ll1$ regime, where transfer from the vector sector persists outside the horizon and produces a local-type contribution enhanced as $h^2N_K^3$, we find that the bispectrum signals are controlled by the matching parameter $x\simeq1.63Ah$, where $A<1$ is a numerical factor remaining dependent on the UV-to-EFT matching prescription. As a result, in addition to the known flattened-enhanced signals scaling as $x^3$, a flattened-enhanced signal scaling as $x^2$ and a pronounced local projection scaling as $x$ are present. The bispectrum therefore distinguishes vector-supported inflationary dynamics even for an exactly isotropic background.
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Astrophysics of Galaxies
MIGHTEE-HI: HI catalogue of 293 sources for the COSMOS field and comparative study of 3-dimensional source finding methods
Michalina Maksymowicz-Maciata, Natasha Maddox, Catherine Hale et al. (+12 more)
We present a catalogue of HI sources extracted from the MIGHTEE survey data cubes covering the COSMOS field. The catalogue contains 293 sources in the
redshift range of 0.004 < z < 0.093. In addition to HI masses and velocity widths, the catalogue includes optical through near-infrared photometry and inferred
stellar masses and
star-formation rates. The quantity of sources in the HI catalogue acquired through untargeted source finding is greatly influenced by the source finding methods used. This study therefore also provides a well-characterised expected completeness of the detected sample of
galaxies based on their properties, informing of any detection biases, inferred through a comparative study of different source finding
algorithms. We have tested the performance of widely-used source finders: PyBDSF, ProFound and SoFiA, along with new source finder LESHI, focusing exclusively on HI source detection rather than source characterisation in the first instance. The source finders were tested by injecting a sample of simulated
galaxies divided into narrow bins of mass, inclination and distance into a MeerKAT data cube. The results inform the source finding strategies for the MeerKAT International GigaHertz Tiered Extragalactic Exploration (MIGHTEE) survey, as well as upcoming SKAO surveys.
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All authors Michalina Maksymowicz-Maciata, Natasha Maddox, Catherine Hale, Ben Maughan, Matt J. Jarvis, Anastasia A. Ponomareva, Ian Heywood, Hengxing Pan, Sushma Kurapati, Tom G. Hardy, Marcin Glowacki, Tobias Westmeier, Maarten Baes, Seoyoung Lyla Jung, Andreea A. Vărăşteanu
High Energy Astrophysical Phenomena · Cross-listed from nucl-th
Impact of hyperon mixing on neutron star structure based on Skyrme-type equations of state: Systematic analysis of $\Lambda NN$ and $\Lambda\Lambda N$ three-body forces with Bayesisan inference
Taeho Lee, Yoonhak Nam and Kazuyuki Sekizawa
We study hyperonic density-dependent three-body effects in cold
neutron-
star matter using a Skyrme energy-density-functional framework. In beta-equilibrated $npe\mu\Lambda$ matter, the effective $\Lambda NN$ and $\Lambda\Lambda N$ terms are varied separately in the $(\beta,A_3)$ and $(\gamma,C_3)$ planes, and each tabulated equation of state is used in Tolman–Oppenheimer–Volkoff calculations. The calculated $P$–$\varepsilon$ branches are classified by monotonicity and extremum structure. The $\Lambda\Lambda N$ term does not affect the $\Lambda$-onset condition, but modifies the finite-$\Lambda$ post-onset EOS: increasing $C_3$ generally stiffens the post-onset branch and raises $M_{\max}$ in mechanically admissible regions, whereas increasing $\gamma$ reduces this enhancement at fixed $C_3$. In contrast, the $\Lambda NN$ term shifts the $\Lambda$-onset density and modifies the post-onset EOS simultaneously, producing organized branch-limited and Maxwell-candidate regions for some reference interactions. Representative two-extrema cases are examined with Maxwell constructions. We also perform an exploratory
Bayesian analysis using
neutron-
star mass–radius information alone and apply XGBoost–SHAP surrogate diagnostics to summarize parameter sensitivities. Within the adopted likelihood and prior ranges, the posterior weight tends to favor sizable hyperonic three-body repulsion, and the SHAP analysis identifies $A_3$ and $C_3$ as important controls of $M_\text{max}$ and $R_{2.0}$. These results show that maximum-mass recovery in hyperonic
neutron stars is not a single mechanism: $M_\text{max}$ maps must be interpreted together with onset behavior, branch admissibility, and extremum-count diagnostics. *shortened due to the arXiv's word limit.
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Earth and Planetary Astrophysics
A Homogeneous Catalog of Rossiter-McLaughlin Systems: Distinct $e$-$\lambda$ Trends in Three Gas-Giant Mass Regimes
Xian-Yu Wang, Songhu Wang and Konstantin Batygin
Stellar obliquity ($\lambda$) and orbital eccentricity ($e$) trace the dynamical histories of close-in
giant planets, but the current observational picture is assembled from heterogeneous analyses that have obscured population-level trends. In this work, we homogeneously refit systems with Rossiter-McLaughlin (RM) measurements by performing a joint global fit to spectral energy distributions, transit light curves, mid-transit times, out-of-transit and in-transit radial velocities, yielding self-consistent posterior distributions for the physical and orbital parameters of both
stars and
planets across 256 systems. Restricting to 146 single-
star systems with reliable
planet-mass measurements, we uncover pronounced structure in the $e-\lambda$ plane that depends on
planet mass: (i) sub-Saturns ($M_{\rm p} \leq \sim0.3M_{\rm J}$) can be both eccentric and misaligned; (ii) Jupiters ($\sim0.3M_{\rm J}<M_{\rm p} \leq \sim3 M_{\rm J}$) are misaligned only on circular orbits; and (iii) super Jupiters and brown
dwarfs ($M_{\rm p}>\sim3M_{\rm J}$) are aligned across the full eccentricity range. A two-dimensional Kolmogorov-Smirnov test shows that the joint $(e,\lambda)$ distributions differ significantly among these three mass regimes. These trends demonstrate that $\lambda$ depends jointly on eccentricity and
planet mass, implying that obliquity alone is not a unique tracer of evolutionary history and underscoring the need for a unified framework for the origins of
spin-orbit misalignment. The full catalog from this work is publicly available at https://www.stellarobliquity.com .
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