Instrumentation and Methods for Astrophysics
Exoplanets in reflected starlight with dual-field interferometry and a fifth Unit Telescope at VLTI
Óscar Carrión-González, Sylvestre Lacour and Mathias Nowak
In this white paper, we propose an upgrade to the Very Large
Telescope Interferometer (VLTI) consisting of the addition of a new 8m Unit
Telescope (UT5). The primary goal of this upgrade is to optimise the VLTI for
exoplanet detection by creating four additional baselines of approximately 200m oriented toward the north-west. The inclusion of this
telescope would reduce the inner working angle and improve the achievable contrast of the VLTI, thereby enabling the detection of mature
exoplanets in reflected light.
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Cosmology and Nongalactic Astrophysics
The contribution from small scales on two-point shear analysis: comparison between power spectrum and correlation function
João Ferri, Elisa G. M. Ferreira and Ryo Terasawa
A known problem in
cosmic shear two-point statistics is the apparent inconsistency between analyses performed in harmonic space (power spectrum) and real space (angular correlation). This arises mainly from two factors: first, scale cuts in one space correspond to soft cuts in the other, as the relationship between the two spaces is mediated by Bessel functions. For the same reason, astrophysical effects that are compact in one space may not be in the other, which can lead to biased parameter estimates. In this paper, we argue that these two statistics are complementary: we expect a robust theory to provide consistent constraints regardless of the chosen scale cuts. We present the consequences of pushing our analysis to smaller scales in both spaces, accounting for different models of Intrinsic
Alignment and Baryonic Feedback in HSC Y3 data: we find that the harmonic-space analysis is significantly less sensitive to the specific modeling of small-scale physics, with model-choice-driven biases in $S_8$ being 2-3 times smaller than in real space. We show that using a flexible, simulation-based emulator for baryonic feedback (BACCO) in combination with the TATT model for intrinsic
alignments provides the most consistent cosmological constraints between the two spaces when pushing to the smallest scales. In contrast, the standard HMCode-2016 model results in a $\sim 1.1\sigma$ tension between the two statistics. While harmonic space appears more robust for cosmological inference given current model uncertainties, real-space analyses offer a clearer separation of baryonic effects and will play a crucial role in distinguishing between baryonic feedback models in upcoming surveys.
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Instrumentation and Methods for Astrophysics
SatTrack: Software for Evaluating Satellite Interference and Rim-Based Interference Mitigation Using a Reconfigurable Parabolic Antenna
J. M. Santana, L. Heller and R. M. Buehrer
Large Low Earth Orbit (LEO) constellations (e.g., Starlink and Iridium) significantly increase the likelihood of transient, high-power interference events at ground receivers. This report presents SatTrack, a GUI-driven simulation framework that (i) tracks satellite motion relative to a fixed
antenna boresight, (ii) predicts reflector gain patterns of a
parabolic reflector
antenna with a reconfigurable rim of specified size using a physical optics (PO) surface-current model decomposed into fixed and reconfigurable rim regions, and (iii) synthesizes deep, directional nulls using fast rim-weight optimization
algorithms. Beyond baseline serial greedy and greedy bit-flip methods, additional files support advanced weight optimization
algorithms including simulated annealing and majorization-minimization operating over higher-order complex weight alphabets, enabling deeper null formation. Interference power from satellites is estimated using free-space path loss and an FCC-derived Starlink EIRP versus steering-angle model, and event-level throughput for each satellite is computed using Shannon capacity. Results show simple binary rim control achieves about 40-55 dB of average interference suppression, while advanced optimization methods can exceed 65-70 dB under favorable geometries, with best-case received interference below -220 dBm. We compare no mitigation, satellite muting, and rim-based spatial nulling, showing rim-based nulling approaches muting-level suppression while preserving throughput close to the no-mitigation case. These results highlight both the scalability of rim-based reflector reconfiguration and the fundamental limitation when satellites cross the main lobe.
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Earth and Planetary Astrophysics
On the Divergent Evolution of Io and Europa as Primordial Ocean Worlds
Yannis Bennacer, Olivier Mousis and Vincent Hue
The Galilean moons exhibit a decrease in bulk density with distance from Jupiter, which may reflect differences in evolutionary paths and water loss. Early in its history, Jupiter was more luminous and may have driven substantial atmospheric escape on Io and Europa. We investigate whether Io could have lost its water inventory while Europa retained its volatiles, assuming both moons initially accreted hydrous silicates. The formation and early thermal
evolution of the protosatellites are modeled using an interior
evolution model coupled with an atmospheric escape framework. Dehydration timescales and volatile losses for Io and Europa are computed during their early
evolution, accounting for accretional heating from both satellitesimal and pebble
accretion, as well as irradiation from Jupiter's
primordial luminosity. Europa likely retained most of its volatiles under nearly all plausible formation and
evolution scenarios, as large-scale dehydration would have taken place only after the first 10 Myr of its
evolution. In contrast, Io was unlikely to lose a substantial amount of water through atmospheric escape and therefore probably accreted predominantly anhydrous silicates. If Europa initially accreted hydrous minerals, the present-day volatile contrast between Io and Europa could be explained by their relative locations with respect to the phyllosilicate dehydration line in the Jovian subnebula. Distinct evolutionary pathways or atmospheric escape processes alone appear insufficient to reproduce the observed differences.
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Astrophysics of Galaxies
Archaeological investigation of galaxies' evolutionary history in the cosmic middle ages
Anna R. Gallazzi, Stefano Zibetti, Mark Sargent et al. (+14 more)
The
cosmic Middle Ages, spanning the last 8-10 Gyr of the Universe, is a critical period in which massive early-formed systems coexist with global
star formation quenching in less massive
galaxies, yet
galaxies experience further dynamical, morphological and chemical
evolution. Understanding the relative role of internal drivers and of interaction with the evolving large-scale structures remains a highly complex and unsettled issue. To make transformative progress on these questions we must characterize the physical and kinematic properties (integrated and spatially resolved) of
stellar populations in
galaxies, fossil record of their past
star formation and assembly histories, together with gas properties, across a wide range of masses and environmental scales, over this critical
cosmic epoch. Volume-representative samples of 10^6
galaxies down to 10^9
solar masses are essential to fully trace the complex interplay between physical processes and to physically connect progenitor and descendant
galaxy populations. This demands a deep and extensive survey with high signal-to-noise, medium-resolution, rest-frame optical spectroscopy. Current and planned facilities in the 2020-2030s cannot simultaneously achieve the required sample size, spectral quality, mass limit, and spatial coverage. A dedicated large-aperture spectroscopic facility with wide-area high-multiplex MOS and large field-of-view IFU is needed to provide transformative insights into the physical mechanisms regulating
star formation and
galaxy evolution.
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All authors Anna R. Gallazzi, Stefano Zibetti, Mark Sargent, Nicolas Bouche', Luke Davies, Marcella Longhetti, Annagrazia Puglisi, Laura Scholz-Diaz, Fabio Ditrani, Daniele Mattolini, Sabine Thater, Crescenzo Tortora, Bodo Ziegler, Mirko Curti, Lucia Pozzetti, Mojtaba Raouf, Umberto Rescigno
Solar and Stellar Astrophysics
Empirical instability strip for classical Cepheids II. The Small Magellanic Cloud galaxy
Felipe Espinoza-Arancibia, Bogumił Pilecki and Matylda Łukaszewicz
Aims. This study aims to determine empirical intrinsic edges of the classical Cepheids instability strip (IS) in the Small Magellanic Cloud (SMC)
galaxy, considering various effects that alter its shape, and compare them with theoretical models and other
galaxies. Methods. We used the data of classical fundamental-mode (F) and first-overtone mode (1O) SMC Cepheids from the OGLE-IV variable
star catalog, with the final cleaned sample including 2388 F and 1560 1O Cepheids. The IS borders are determined by tracing the edges of the color distribution along the strip. Based on that, and using evolutionary tracks, the IS crossing times are computed. Results. We obtained the blue and red edges of the IS in V- and I-photometric bands and in the HR diagram, and detected breaks at periods between 1.4 and 3 days. A comparison with existing theoretical models showed good agreement for the blue edge and significant differences for the red edge. We also found that the IS of the SMC is wider than that of the Large Magellanic Cloud (LMC), with its red edge being redder despite its lower
metallicity. The analysis of crossing times showed that the expected number of Cepheids as a function of period agrees with the observed distribution for P > 1 days but differs for P < 1 days. Conclusions. Slope changes along the SMC IS borders are most likely explained by the distribution of
metallicity. The behavior of the blue loops at the SMC
metallicity is not consistent with observations, and at the LMC
metallicity, the blue loops are too short for lower-mass
stars. A comparison of theoretical edges with our empirical ISs imposes constraints on the models and enables the identification of valid ones. Based on the positions of the breaks, our study also suggests that fundamental-mode Cepheids with periods longer than 3 days should be used for distance determination.
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Earth and Planetary Astrophysics
Towards an agnostic algorithm for sampling empirical structure models: The case of Uranus and Neptune
Stefano Wirth, Luca Morf and Ravit Helled
We present an
algorithm to efficiently sample the full space of planetary interior density profiles. Our approach uses as few assumptions as possible to pursue an agnostic
algorithm. The
algorithm avoids the common Markov Chain Monte Carlo method and instead uses an optimisation-based gradient-descent approach designed for computational efficiency. In this work, we use Uranus and Neptune as test cases and obtain empirical models that provide density and pressure profiles consistent with the observed physical properties (total mass, radius, and gravitational moments). We compare our findings to other work and find that while other studies are generally in line with our findings, they do not cover the entire space of solutions faithfully. Furthermore, we present guidance for modellers that construct Uranus or Neptune interior models with a fixed number of layers. We provide a statistical relation between the steepness classifying a density discontinuity and the resulting number of discontinuities to be expected. For example, if one classifies a discontinuity as a density gradient larger than 0.02 kg$\,$m$^{-4}$, then most solutions should have at most one such discontinuity. Finally, we find that discontinuities, if present, are concentrated around a planetary normalised radius of 0.65 for Uranus and 0.7 for Neptune. Our
algorithm to efficiently and faithfully investigate the full space of possible interior density profiles can be used to study all planetary objects with gravitational field data.
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High Energy Astrophysical Phenomena · Cross-listed from hep-ph
Fermion Thermal Field Theory for a Rotating Plasma (with Applications to Neutron Stars)
Alberto Salvio
This paper provides a systematic and complete study of thermal field theory with
fermion fields of any kind for generic
equilibrium density
matrices, which feature arbitrary values not only of temperature and chemical potentials, but also average angular momentum. This extends a previous study that focused on scalar fields, to all
fermion-scalar theories. Both Dirac and Majorana
fermions and both Dirac and Majorana masses are covered. A general technique to compute ensemble averages is provided. Path-integral methods are developed to study thermal Green's functions (with an arbitrary number of points) in generic interacting
fermion-scalar theories, which cover both the real-time and imaginary-time formalism. These general results are applied to physical situations typical of
neutron stars, which are often quickly rotating: the
Fermi surface and
Fermi momentum, the average energy, number density and angular momentum for degenerate
fermions and particle production (such as
neutrino production from rotating
neutron stars, e.g.
pulsars). In particular, it is shown that the
neutrino production rate due to the direct URCA (DU) processes grows indefinitely as the angular velocity approaches the inverse linear size of the
plasma and, therefore, rotation can significantly increase this rate.
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Cosmology and Nongalactic Astrophysics
The imprints of massive neutrinos on the three-point correlation function of large-scale structures
Andrea Labate, Massimo Guidi, Michele Moresco et al. (+1 more)
Free-streaming of
cosmic neutrinos affects the distribution and growth of
cosmic structures on small scales. This enables the sum of
neutrino masses $M_\nu$ to be constrained from clustering studies. We investigate the possibility of disentangling massive
neutrino cosmologies with the three-point correlation function (3PCF) for the first time. We measured the isotropic connected 3PCF $\zeta$ and the reduced 3PCF $Q$ of
halo catalogs from the Quijote suite of $N$-body simulations, considering $M_\nu =0.0, 0.1, 0.2,$ and $0.4 \, \mathrm{eV}$ in different
redshift bins. We developed a framework to quantify the detectability of massive
neutrinos for different triangle configurations and shapes, and applied it to a case compatible with a stage-IV spectroscopic survey. We also compared our results with the analysis of simulations without
neutrinos, but with different $\sigma_8$ values, to test whether the 3PCF can break the well-known degeneracy between the two parameters. We found that as a result of free-streaming, the strongest signal is found for quasi-isosceles and squeezed triangles; this signal increases for decreasing
redshifts. Among these configurations, elongated triangles, tracing the filamentary structure of the
cosmic web, are the most affected by massive
neutrinos, with a 3PCF signal increasing with $M_\nu$. A complementary source of signal comes from right-angled triangles in $Q$. Importantly, we found that the signatures of a $\sigma_8$ variation appear to be significantly different on elongated triangles in $\zeta$ and right-angled triangles in $Q$, suggesting that the 3PCF can be used to effectively break the $M_\nu - \sigma_8$ degeneracy. These results open the possibility to use the 3PCF as a powerful complementary tool for constraining
neutrino masses in current and future spectroscopic surveys such as DESI, Euclid, 4MOST, and the Nancy Grace Roman Space
Telescope.
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All authors Andrea Labate, Massimo Guidi, Michele Moresco, Alfonso Veropalumbo
Instrumentation and Methods for Astrophysics
The supernova Ia progenitor problem in the 2040s
Thomas Kupfer, Simone Scaringi, Ingrid Pelisoli et al. (+8 more)
Type Ia
supernovae (SNe Ia) are fundamental to cosmology and
galactic chemical
evolution, yet the nature of their progenitor systems remains unresolved. Multiple evolutionary pathways, including single-degenerate, double-degenerate, and helium-donor systems, are thought to contribute to the SN Ia population, but direct observational constraints are limited. This uncertainty hampers our understanding of SN Ia diversity and introduces systematic uncertainties in their use as precision cosmological probes. By the 2040s, surveys such as
Gaia, LSST, SDSS-V, 4MOST, and the gravitational-wave mission LISA will identify thousands of compact binaries in the Milky Way that are potential SN Ia progenitors. However, survey discoveries alone are insufficient. Robust identification and characterization require high-time-resolution, phase-resolved spectroscopy to determine fundamental parameters such as component masses, orbital inclinations, chemical compositions, and
accretion states. Addressing these challenges demands new observational capabilities. The most compact binaries require continuous, dead-time-free spectroscopy with negligible readout noise, while the progenitor population spans a wide range of brightness and orbital periods. A modular, multi-aperture
telescope array equipped with fast, low-noise spectrographs can flexibly combine collecting area for faint targets, observe bright systems efficiently, and deliver uninterrupted time series through staggered exposures. Such observations are difficult for single-aperture facilities.
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All authors Thomas Kupfer, Simone Scaringi, Ingrid Pelisoli, Anna F. Pala, Silvia Toonen, Domitilla de Martino, Christa Gall, Kunal Deshmukh, Valerie Van Grootel, Stéphane Blondin, Samaya Nissanke
Astrophysics of Galaxies
The AURORA Survey: The Mass – Metallicity and Fundamental Metallicity Relations at $z \sim 2.3$ Based Purely on Direct $T_e$ Metallicities
Ali Ahmad Khostovan, Ryan L. Sanders, Alice E. Shapley et al. (+14 more)
We present new constraints on the Mass –
Metallicity (MZR) and Fundamental
Metallicity Relations (FMR) using a sample of 34
galaxies at $1.38\leq~z\leq~3.5$ (median $z=2.28$). These
galaxies have direct $T_e$ measurements from [O\sc{iii}]4363Å~and/or [O\sc{ii}]7320,7331Å~auroral emission lines detected with JWST/NIRSpec as part of the AURORA survey. The detection of both oxygen auroral lines allows for dual-zone direct $T_e$ measurements and expands the dynamic range in $12+\log\mathrm{(O/H)}$ (7.68 to 8.65 dex),
stellar mass ($10^{8}$ to $10^{10.4}$ M$_\odot$), and
star-formation rate ($1$ to $100$ M$_\odot$ yr$^{-1}$) compared to previous direct $T_e$ studies of the high-
redshift MZR and FMR. We characterize the $z\sim2$ MZR and find a slope of $0.27\pm0.04$ and normalization of $12+\log\mathrm{(O/H)} = 8.44\pm0.04$ at $10^{10}$ M$_\odot$ with an intrinsic scatter of 0.10 dex, consistent with past strong-line MZR measurements. Comparisons with $z\sim2$ predictions from six simulations reveal that none reproduce our observed MZR normalization
evolution between $z\sim0$ and $z\sim2$. This discrepancy suggests current models do not fully capture the chemical enrichment and feedback processes occurring at
cosmic noon. However, all 34
galaxies are on or above the
star-forming main sequence such that our sample may be biased towards lower $12+\log\mathrm{(O/H)}$ if the FMR persists at $z\sim2$. Correcting for this selection effect would increase O/H by $\approx0.1$ dex at 10$^{9.3}$ M$_\odot$ (the median mass of our sample) bringing our MZR into better agreement with that of TNG. Lastly, we find our $z\sim2.3$ sample is consistent with the $z\sim0$ FMR within 0.1 dex in O/H, indicating that the smooth secular mechanisms regulating chemical enrichment,
star formation,
stellar mass, and
outflows were in place at
cosmic noon.
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All authors Ali Ahmad Khostovan, Ryan L. Sanders, Alice E. Shapley, Michael W. Topping, Naveen A. Reddy, Alex M. Garcia, Danielle A. Berg, Leonardo Clarke, Fergus Cullen, Richard S. Ellis, N. M. Förster Schreiber, Karl Glazebrook, Tucker Jones, Derek J. McLeod, Anthony J. Pahl, Max Pettini, Paul Torrey
Instrumentation and Methods for Astrophysics
The final stages of binary evolution using multi-messenger studies
Thomas Kupfer, Simone Scaringi, Paul Groot et al. (+11 more)
Ultracompact
Galactic binaries with orbital periods below an hour are among the strongest persistent gravitational-wave (GW) sources in the mHz band and will constitute the dominant population detected by the
Laser Interferometer Space
Antenna (LISA). Tens of thousands are predicted to be individually resolved, with a substantial fraction bright enough for electromagnetic (EM) follow-up. This opens an unprecedented multi-messenger window on compact binary
evolution,
tidal interactions, mass transfer, and the progenitors of Type Ia
supernovae. We highlight key science enabled by joint GW + EM constraints and emphasize the critical need for rapid, high-cadence spectroscopic capabilities in the 2040s. In particular, the most compact (<10 min) binaries detected by LISA will require read-noise-free, zero-dead-time spectroscopic facilities, potentially realized through coordinated arrays of
telescopes with time-staggered exposures, to measure radial velocities,
tidal heating signatures, and orbital
evolution with the precision needed for transformative multi-messenger studies.
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All authors Thomas Kupfer, Simone Scaringi, Paul Groot, Boris Gänsicke, Ingrid Pelisoli, Anna F. Pala, Jan van Roestel, Silvia Toonen, Domitilla de Martino, Noel Castro Segura, David Buckley, Valerie Van Grootel, Kieran O'Brien, Samaya Nissanke
Cosmology and Nongalactic Astrophysics
Reviving sub-keV warm dark matter: a UVLF-based analysis
Raymond T. Co, Siu Cheung Lam, Sai Chaitanya Tadepalli et al. (+1 more)
Thermal warm dark matter (WDM) particles with $m_{\rm WDM} \leq 1~\mathrm{keV}$ are ruled out at more than $4\sigma$ by multiple observational probes, owing to the strong suppression of small-scale structure induced by early-time free-streaming. Recently, it was highlighted that a small admixture of $\sim1\%$ ($f_{\rm CDM} \sim\!0.01$) cold dark matter (CDM) endowed with a blue-tilted isocurvature spectrum could offset the WDM-induced suppression and relax the WDM mass bound by a factor of $\mathcal{O}(10)$. If viable, this ”warm + cold-isocurvature” scenario would allow sub-keV WDM particles to constitute nearly the full dark matter abundance while potentially alleviating some small-scale tensions. In this work, we test this mechanism by constraining the WDM mass $m_{\rm WDM}$ while marginalizing over CDM isocurvature parameters. We combine ultraviolet luminosity function measurements from the Hubble Space
Telescope and James Webb Space
Telescope over
redshift $4 \leq z \leq 11$ with CMB, BAO, and SNe data. For a pure WDM model, our joint analysis yields a lower bound $m_{\rm WDM} > 1.8~\mathrm{keV}$ (95% credible intervals). When CDM isocurvature is introduced at $f_{\rm CDM} = 0.01$, the limit relaxes to $m_{\rm WDM} > 0.27~\mathrm{keV}$ (95% credible intervals), reflecting a shallow degeneracy in which blue-tilted isocurvature fluctuations partially compensate for WDM suppression. These results provide new constraints on thermal WDM in the presence of CDM isocurvature fluctuations and quantify the extent to which such fluctuations can mask the small-scale signatures of light relics.
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All authors Raymond T. Co, Siu Cheung Lam, Sai Chaitanya Tadepalli, Tomo Takahashi
Astrophysics of Galaxies
The accretion of quasars at the epoch of reionisation: $JWST$ catches the primeval monsters slowly feasting
B. Trefoloni, E. Nardini, S. Carniani et al. (+8 more)
Quasars (QSOs) emit an enormous amount of light as a result of the
accretion of gas onto supermassive black holes (SMBHs). Thanks to their luminosity, the most distant known QSOs allow us to trace the growth of SMBHs deep into the epoch of reionisation. In this work, we employed $JWST$/NIRSpec observations of eight luminous (log$(L_{3000\,A^{\circ}}/(erg \, s^{-1}))>$45.7) QSOs at $z\geq$5.9 to constrain their
accretion properties, namely black hole mass,
accretion disc (AD) luminosity, and Eddington ratio ($M_{BH}$, $L_{AD}$, $\lambda_{Edd}$), by fitting the rest-frame UV and optical emission with different AD models. This method provided self-consistent measurements of both $M_{BH}$ and $L_{AD}$. The uncertainties on $M_{BH}$ and $L_{AD}$, obtained within the AD-modelling framework ($\sigma^{AD}_{M_{BH}}\sim$0.2 dex; $\sigma^{AD}_{L_{AD}}\sim$0.1 dex), are significantly smaller than the systematic uncertainties associated with single-epoch $M_{BH}$ ($\sim$0.4 dex) and $L_{AD}$ derived via bolometric corrections ($\sim$0.2 dex). Based on these results, in our sample we found an average Eddington ratio of $\langle \log(\lambda_{Edd}) \rangle=-0.9$, with a dispersion of $\sim$0.2 dex. Assuming that our high-z QSOs are representative of optically-selected bright blue QSOs, we derive a fraction of systems accreting above the Eddington limit of $\sim$0.2%. In conclusion, this work i) demonstrates the suitability of $JWST$ to test AD models on high-
redshift ($z\gtrsim$4) QSOs, thanks to the large NIRSpec spectral coverage; ii) shows that AD modelling can yield robust $M_{\rm BH}$ and $L_{\rm AD}$ measurements, with smaller uncertainties than the typical calibrations; and iii) provides compelling evidence for sub-Eddington
accretion in bright high-$z$ QSOs, challenging the widespread paradigm of near- or super-Eddington
accretion occurring in these sources.
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All authors B. Trefoloni, E. Nardini, S. Carniani, E. Lusso, A. Marconi, E. Parlanti, A. Sacchi, A. Shlentsova, M. Signorini, G. Risaliti, S. Zamora
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Creation of spin-3/2 dark matter via cosmological gravitational particle production
Edward W. Kolb, Andrew J. Long, Evan McDonough et al. (+1 more)
We study the cosmological gravitational particle production (CGPP) of
spin-3/2 particles during and after
cosmic inflation, and map the parameter space that can realize the observed dark matter density in stable
spin-3/2 particles. Originally formulated by Rarita and Schwinger, the relativistic theory of a massive
spin-3/2 field later found a home in supergravity as the superpartner of the graviton, and in
nuclear physics as baryonic resonances and
nuclear isotopes. We study a minimal model realization, namely a free massive
spin-3/2 field minimally coupled to
gravity, and adopt the name raritron for this field. We demonstrate that CGPP of raritrons crucially depends on the hierarchy between the raritron mass $m_{3/2}$ and the Hubble parameter at the end of inflation $H_e$, with high-mass and low-mass cases distinguished by the
evolution of the sound speed $c_s$ of the longitudinal (helicity-1/2) mode, which is approximately unity at all times for heavy (relative to Hubble) raritrons and can become small or vanish for lighter raritrons, leading to a dramatic enhancement of production of high momentum particles in the latter case. Assuming the raritrons are stable, this leads to a wide parameter space to produce the observed dark matter density. Finally, we consider a time-dependent raritron mass, which can be chosen to remove the vanishing sound speed of the longitudinal mode, but which nonetheless enhances the production relative to the constant high-mass case, and in particular does not necessarily tame the high momentum tail of the spectrum. We perform our calculations using the Bogoliubov formalism and compare, when applicable, to the Boltzmann formalism.
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All authors Edward W. Kolb, Andrew J. Long, Evan McDonough, Jingyuan Wang
Instrumentation and Methods for Astrophysics
ESO Expanding Horizon White Paper: Revealing the properties of matter at supranuclear densities with gravitational waves
Tim Dietrich, Tanja Hinderer, Micaela Oertel et al. (+40 more)
Understanding dense matter under extreme conditions is one of the most fundamental puzzles in modern physics. Complex interactions give rise to emergent, collective phenomena. While
nuclear experiments and Earth - based
colliders provide valuable insights, much of the
quantum chromodynamics phase diagram at high density and low temperature remains accessible only through astrophysical observations of
neutron stars,
neutron star mergers, and
stellar collapse. Astronomical observations thus offer a direct window to the physics on subatomic scales with gravitational waves presenting an especially clean channel. Next-generation gravitational - wave observatories, such as the Einstein
Telescope, would serve as unparalleled instruments to transform our understanding of
neutron star matter. They will enable the detection of up to tens of thousands of binary
neutron star and
neutron star - black hole mergers per year, a dramatic increase over the few events accessible with current detectors. They will provide an unprecedented precision in probing cold, dense matter during the binary inspiral, exceeding by at least an order of magnitude what current facilities can achieve. Moreover, these observatories will allow us to explore uncharted regimes of dense matter at finite temperatures produced in a subset of
neutron star mergers, areas that remain entirely inaccessible to current instruments. Together with multimessenger observations, these measurements will significantly deepen our knowledge of dense
nuclear matter.
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All authors Tim Dietrich, Tanja Hinderer, Micaela Oertel, Conrado A. Torres, Nils Andersson, Dániel Barta, Andreas Bauswein, Béatrice Bonga, Marica Branchesi, G. Fiorella Burgio, Stefano Burrello, Prasanta Char, Sylvain Chaty, Maria Colonna, Daniela Doneva, Anthea F. Fantina, Tobias Fischer, Juan Garcia-Bellido, Archisman Ghosh, Bruno Giacomazzo, Fabian Gittins, Vanessa Graber, Francesca Gulminelli, Jan Harms, Kostas Kokkotas, Felipe J. Llanes-Estrada, Michele Maggiore, Gabriel Martinez-Pinedo, Andrea Maselli, Chiranjib Mondal, Samaya Nissanke, M Angeles Perez Garcia, Cristiano Palomba, Pantelis Pnigouras, Anna Puecher, Michele Punturo, Adriana R. Raduta, Violetta Sagun, Armen Sedrakian, Nikolaos Stergioulas, Laura Tolos, Kadri Yakut, Stoytcho Yazadjiev
Instrumentation and Methods for Astrophysics
The Nature of Galactic Spiral Arms
Robert J. J. Grand and Martin Roth
Spiral arms are the defining features of broad morphological classes of disc
galaxies, but their nature and influence on
galaxy evolution is still under debate. A key diagnostic for their nature is the spiral arm pattern speed: the radial profile of the angular rotation rate of spiral features. This profile determines the location and number of dynamical resonances where peculiar motions and azimuthal
metallicity fluctuations in
stars and gas can manifest; their precise patterns have the potential to support or reject theories of spiral structure. However, limited observations of this type have been carried out so far, despite an increasing number of theoretical predictions emerging from realistic and detailed cosmological simulations. A systematic observational programme focussed on the resolved kinematics and
metallicities of
stellar populations around
galaxy spiral arms is required to confront these predictions. This calls for wide-area multi-object spectrographs on 12m-class
telescopes capable of accurately capturing such data across the full coverage of spiral arms in nearby
galaxies.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
Discovering gravitational waveform distortions from lensing: A deep dive into GW231123
Juno C. L. Chan, Jose María Ezquiaga, Rico K. L. Lo et al. (+3 more)
Gravitational waves (GWs) are unique messengers as they travel through the Universe without alteration except for gravitational
lensing. Their long wavelengths make them susceptible to diffraction by
cosmic structures, providing an unprecedented opportunity to map dark matter substructures. Identifying lensed events requires the analysis of thousands to millions of simulated events to reach high statistical significances. This is computationally prohibitive with standard GW parameter estimation methods. We exploit DINGO-
lensing, a deep-learning
algorithm that accelerates the inference from CPU days to minutes to thoroughly reanalyze GW231123, the most promising
lensing candidate to date. By performing more than 200,000 simulations with 3 different waveform models, we find that its statistical significance is below 4$\sigma$ and the event cannot be claimed as lensed. We observe that 8% of GW231123-like nonlensed simulations favor
lensing, which could be explained by the self-similarity of short-duration signals. Still, 58% of GW231123-like lensed simulations have larger support for
lensing, showing that higher detection statistics are possible. We show that analyzing simulations with different waveform models only lowers the significance, highlighting the relevance of waveform systematics. Although GW231123 exposes the challenges of claiming the first GW
lensing detection, our deep-learning methods have demonstrated to be powerful enough to enable the upcoming discovery of lensed GWs.
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All authors Juno C. L. Chan, Jose María Ezquiaga, Rico K. L. Lo, Joey Bowman, Lorena Magaña Zertuche, Luka Vujeva
Cosmology and Nongalactic Astrophysics
Robust CMB B-mode analysis with Needlet-ILC and simulation-based inference
Adriaan J. Duivenvoorden, Kristen Surrao, Adrian E. Bayer et al. (+4 more)
We explore a novel analysis framework for parameter inference with large-scale CMB polarization data. Our method uses simulation-based inference combined with the needlet internal linear combination (NILC)
algorithm and cross-correlation-based statistics to compress the data into a vector that is robust to model misspecification and small enough to be amenable to neural posterior estimation with normalizing flows. By leveraging this compressed data representation, our method enables the robust use of the anisotropic and non-Gaussian information in the foreground fields to more accurately separate the CMB polarization signal from these contaminants. Using an idealized ground-based experimental setup inspired by the Simons Observatory Small Aperture
Telescopes, we demonstrate improved statistical constraining power for the tensor-to-scalar ratio $r$ compared to the (constrained) NILC
algorithm and improved robustness to complex foregrounds compared to other techniques in the literature. Trained on a relatively simple semi-analytical foreground model, the method yields unbiased $r$ results across a range of PySM
Galactic foreground simulations, including the high-complexity d12 model, for which we obtain $r=(1.09 \pm 0.27)\cdot 10^{-2}$ for input $r=0.01$ and sky fraction $f_{\mathrm{sky}} = 0.21$. We thus demonstrate the feasibility and advantages of a complete, maps-to-parameters, simulation-based analysis of large-scale CMB polarization for current ground-based observatories.
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All authors Adriaan J. Duivenvoorden, Kristen Surrao, Adrian E. Bayer, Alexandre E. Adler, Nadia Dachlythra, Susanna Azzoni, J. Colin Hill
Earth and Planetary Astrophysics
A Radio Search for Star-Planet Interaction in TOI-540 and SPECULOOS-3
Kevin N. Ortiz Ceballos, Yvette Cendes and Edo Berger
We present the first targeted centimeter-band
radio observations of two recently-discovered
exoplanet systems that are
prime candidates for
magnetic star-
planet interaction (SPI): TOI-540 and SPECULOOS-3. The targets were selected due to the small orbital separation of their known
planets, as well as for indications of
stellar magnetic activity, given that for SPI
radio emission may be strongest when a sufficiently magnetized
star hosts a close-in
planet. The deep, multi-epoch Very Large Array (SPECULOOS-3) and MeerKAT (TOI-540) observations yield non-detections, with $3\sigma$ limits of $\lesssim 7.5$ $\mu$Jy ($4-8$ GHz) and $\lesssim 30-80$ $\mu$Jy ($0.8-1.7$ GHz), respectively. For SPECULOOS-3 b we rule out observable SPI for most of its orbit, while for TOI-540 b we sample a narrower range, around planetary transit. We model possible planetary
magnetic field strength constraints for both systems, and conclude that our observations are sensitive enough to sample SPI emission in these systems if present and directed at us, even for a planetary field of only $\sim 1$ G.
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High Energy Astrophysical Phenomena
BeppoSAX-WFC catalog of fast X-ray transients
J.J.M. in 't Zand, C. Guidorzi, J. Heise et al. (+5 more)
We performed a search for fast X-ray transients (FXTs), with durations longer than one second and less than one day, through data of the Wide Field Camera (WFC) instrument onboard the BeppoSAX X-ray observatory collected between June 1996 and April 2002. (..) We focused our search on gamma-ray bursts (GRBs), X-ray flashes (XRFs), X-ray
flares from high-mass X-ray binaries and
stellar flares, while Type-I and II X-ray bursts from
Galactic neutron stars were excluded. 149 such fast transient events were detected. 63 of these are new to the literature. 38
flares are identified with 22 nearby
stars. Three
stars have never been seen flaring before in X-rays or optical (NLTT 51688, GR Dra and UCAC4 255-003783). We find that the MeV transient GRO J1753+57 is most likely the same object as GR Dra rather than an AGN as previously thought. Eleven
flares were detected from known high-mass X-ray binaries with irregular wind
accretion (four of which are of the subclass of supergiant fast X-ray transients). 100 GRBs were identified of which 24 have not been published before. We classify 37% of the X-ray detected GRBs as XRFs with relatively large X-ray to gamma-ray flux ratio, gamma-rays being measured with the BeppoSAX Gamma Ray Burst Monitor. The duration/spectral hardness distribution of all FXTs is bimodal, separating the group roughly in transients shorter and longer than 1 ksec and with relatively hard and soft spectra, respectively. We identify the 'short' FXTs as GRBs and XRFs and the `long' FXTs as
flares from nearby late-type
stars and X-ray binaries. The BeppoSAX-WFC FXT sample is found to be consistent with the one observed by Einstein Probe, when the sensitivity of the two instruments is taken into account.
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All authors J.J.M. in 't Zand, C. Guidorzi, J. Heise, L. Amati, E. Kuulkers, F. Frontera, G. Gianfagna, L. Piro
Astrophysics of Galaxies
Connecting current and future dual AGN searches to LISA and PTA gravitational wave detections
Nianyi Chen, Yihao Zhou, Ekaterine Dadiani et al. (+10 more)
Dual active
galactic nuclei (DAGN) mark an observable stage of massive black hole (MBH) pairing in
galaxy mergers and are precursors to the MBH binaries that generate low-frequency gravitational waves. Using the large-volume ASTRID cosmological simulation, we construct DAGN catalogs matched to current (COSMOS-Web, DESI) and forthcoming (AXIS, Roman) searches. With realistic selection functions applied, ASTRID reproduces observed dual fractions, separations, and host-
galaxy properties across
redshifts. We predict a substantial population of small-separation (<5 kpc) duals that current surveys fail to capture, indicating that the apparent paucity of sub-kpc systems in COSMOS-Web is driven primarily by selection effects rather than a physical deficit. By following each simulated dual forward in time, we show that dual AGN are robust tracers of MBH mergers: ~30-70% coalesce within $\lesssim 1$ Gyr, and 20-60% of these mergers produce gravitational-wave signals detectable by LISA. Duals accessible to AXIS and Roman are the progenitors of ~10% of low-
redshift LISA events and ~30% of the PTA-band
stochastic background. Massive green-valley
galaxies with moderate-luminosity AGN, together with massive
star-forming hosts containing bright
quasars at $z>1$, emerge as the most likely environments for imminent MBH binaries. These results provide a unified cosmological framework linking dual AGN demographics, MBH binary formation, and gravitational-wave emission, and they identify concrete, high-priority targets for coordinated electromagnetic and GW searches in upcoming multi-messenger surveys.
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All authors Nianyi Chen, Yihao Zhou, Ekaterine Dadiani, Tiziana Di Matteo, Cici Wang, Antonella Palmese, Yue Shen, Junyao Li, Adi Foord, Simeon Bird, Yueying Ni, Yanhui Yang, Rupert Croft
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Multiple Axions in Laboratory Experiments
Arturo de Giorgi, Joerg Jaeckel, Sebastian Monath et al. (+1 more)
Axions and
axion-like particles generically appear in extensions of the Standard Model. While many searches assume only a single
axion species, there may exist a whole spectrum of multiple such fields. We develop general formulas for
axion-
photon oscillations in the presence of multiple
axions and analyze the implications for experimental searches, including light-shining-through-a-wall experiments, helioscopes and haloscopes. We demonstrate that
axion multiplicity can qualitatively alter observational signatures, particularly through coherence and interference effects. Multiple
axions can not only enhance signals compared to single
axion scenarios, but also suppress them. We show that variations of experimental parameters and searches allow identifying contributions of multiple
axions and obtaining information about their properties.
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All authors Arturo de Giorgi, Joerg Jaeckel, Sebastian Monath, Volodymyr Takhistov
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Delayed Scaling of Multi-Type Cosmic F- and D-strings in VOS Models
Kazuto Nakamura and Masaki Yamada
We investigate the velocity-dependent one-scale (VOS) model to the case of one
cosmic F-string and two D-strings as color flux tubes in pure
Spin($4N$) gauge theory. We analytically calculate the scaling string density as a function of the reconnection probabilities, and confirm our results with numerical calculations. We also determine the timescale at which the string density reaches the scaling regime, and find that for certain values of the reconnection probability, the scaling time can become extremely large, by many orders of magnitude. This leads to a characteristic suppression signature of the gravitational-wave signal at high frequencies, which may become observable in the frequency range of future interferometric gravitational-wave observations.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
Quasi-pole inflation in metric-affine gravity
Antonio Racioppi
We propose a new mechanism for inflationary model building in the framework of metric-affine
gravity. Such a mechanism involves an inflaton non-minimally coupled with the Holst invariant. If the non-minimal coupling function has a zero point and it is very steep at that same point, the corresponding inflaton kinetic function will feature a quasi-pole behaviour, implying a canonically normalized potential featuring an exponential plateau, regardless of the shape of the original inflaton potential. The inflationary predictions in such a region are equivalent to the ones of Starobinsky inflation.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Impact of Supercooling on Direct Searches for Dark Matter and Gravitational Wave Backgrounds
Davide Racco and Alfredo Stanzione
An interesting feature of a cosmological phase transition can be a stage of exponential expansion (supercooling). The modified expansion history and the
entropy injection at reheating, can affect the final energy fraction of dark matter. In this paper, we revisit the calculation of the freeze-out and freeze-in dynamics, showing additional effects on top of the standard dilution factor if the dark matter production is completed during the supercooling stage. We show for the first time how these effects can be particularly interesting for direct detection, as the parameter space for WIMP-like candidates shifts from excluded to allowed regions, and freeze-in candidates get closer to experimental reach. A phenomenological motivation to consider supercooling is the associated gravitational wave background. The implications of a finite-duration reheating stage, when the equation of state is close to matter-domination, are a peculiar low-frequency spectrum, and its shift to lower frequencies. These effects are a complementary test of the dynamics that we study for dark matter production, and remarkably can link direct detection of dark matter and gravitational wave astronomy.
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Cosmology and Nongalactic Astrophysics
Future Dark Energy Constraints from Atomic Clocks
Oem Trivedi
We show that atomic clock measurements provides an exceptionally sensitive
Solar System probe of scalar tensor dark energy. By connecting variations in Newton's constant and differential clock drifts to the dynamics of a single dark energy scalar, we derive a direct constraint on the present day equation of state and our results force any locally coupled scalar dark energy into a very slowly rolling regime, giving the strongest bounds on the equation of state parameter. This is independent of potential shape or kinetic structure and rules out broad classes of canonical and non canonical models, leaving only near Lambda CDM behavior or fully decoupled fields as viable late time scalar dark energy, thereby leaving cosmological constant and minimally coupled scalar field models as the most consistent dark energy regimes. We also use results from Lunar
Laser Ranging and
photon trajectories to further strengthen our the depth of our constraints.
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Solar and Stellar Astrophysics
SNR 1987A : Spitzer data from days 6000 to 8000 revisited
Patrice Bouchet, René Gastaud, Alain Coulais et al. (+1 more)
An excess emission has been observed by Spitzer in the [3, 5] micron range of the SNR 1987A spectrum. It is generally argued that this excess could be due to the presence of warm amorphous carbon
dust in the equatorial ring (ER) around the
supernova, but the proposed models all have problems. This prompted us to present an alternative view on the interpretation of the Spectral Energy Distribution (SED) of SNR 1987A from the near-IR wavelengths to the
radio frequencies (from 3 micron up to 1.4 GHz), between 6000 and 8000 days after outburst. We argue that the origin of that excess could be attributed instead to a free-free emission. We show that under very specific conditions (the free-free is self-absorbed at a cut-off frequency imposed by the mass of the emitting region), it could be produced by collisional heating of the gas. We then discuss the time
evolution of the various components of the SED. We establish a linear relationship between the growth of the warm carbon
dust mass and that of the silicates
dust during the analyzed period. Finally, we build the Spitzer light curves and we show that our models reproduce the observations pretty well, although our study clearly favors the free-free case. In conclusion, we argue that the free-free model provides a formally very good description of the data, however the model does require some very specific parameter choices, and results in an unusually low temperature for the ionized gas.
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All authors Patrice Bouchet, René Gastaud, Alain Coulais, Richard G. Arendt
Cosmology and Nongalactic Astrophysics
Dark energy and neutrinos along the cosmic expansion history
Pietro Ghedini, Rasmi Hajjar and Olga Mena
Recent cosmological measurements are hinting that dark energy may evolve, with its equation of state, $w_\mathrm{DE}$, even showing oscillatory patterns. In this work, we employ a model-independent approach to jointly reconstruct $w_\mathrm{DE}$ and the sum of
neutrino masses, $\sum m_\nu$, adopting the PCHIP method with seven fixed nodes in which we allow the two parameters to vary. We employ CMB,
Baryon Acoustic Oscillations and
Supernovae Ia data to constrain the values of $w_\mathrm{DE}$ and $\sum m_\nu$ at each node. We conduct three different analyses in which we reconstruct $w_\mathrm{DE}$: one with fixed $\sum m_\nu=0.06~\mathrm{eV}$; one in which we allow $\sum m_\nu$ to vary, and one in which we also reconstruct $\sum m_\nu$ using the PCHIP method. We find the dark energy equation of state to be consistent with the cosmological constant scenario, except when including DESI data and allowing for phantom crossing, where we find a $95\%$ CL deviation from $w_\mathrm{DE}=-1$ around $z\sim1.2$. For
neutrino masses, we obtain looser constraints when focusing on phantom dark energy, that show further early and late relaxation when reconstructing the mass via the PCHIP method.
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Instrumentation and Methods for Astrophysics
Strategies for Accurate Effective Point Spread Function (ePSF) Modelling on Undersampled Images
Emma Godden and Katherine M. Blundell
Accurate modelling of the effective point spread function (ePSF) is essential for high-precision photometry and astrometry, particularly in undersampled imaging regimes. In this work, we build on a well-established ePSF modelling framework and its commonly used open-source Python implementation and demonstrate that several simple but effective modifications to existing ePSF modelling routines can significantly improve model accuracy. We use synthetic ePSFs to generate simulated
datasets of
stellar images, allowing us to evaluate the accuracy of ePSF models and determine the scale of the pixel-phase errors in resulting flux and position measurements. We systematically investigate how specific modelling choices affect ePSF accuracy, and evaluate the influence of oversampling, interpolation, gridpoint estimation, smoothing,
star-sample distribution, and dithering on photometric precision. We apply our refined ePSF modelling routine to images from the Global Jet Watch observatories, demonstrating its improved ability to recover an accurate ePSF for real astronomical images. Our findings highlight the importance of tailoring the modelling approach to the specific characteristics of the instrument and detector, as well as to the nature of the available imaging data used to construct the ePSF model. These results provide practical guidance for optimising ePSF construction, thereby improving the reliability of photometric and astrometric measurements.
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