Solar and Stellar Astrophysics
Variable X-ray Emission of the Planet Hosting T Tauri Star CI Tau
Stephen L. Skinner and Manuel Guedel
We report results of Chandra X-ray observations of CI Tau, a young magnetically active classical T Tauri
star for which previous studies have reported periodic variability attributed to a massive
planet in a short-period orbit. CI Tau was clearly detected by Chandra in four separate observations acquired in late 2023. The X-ray emission was steady in the first two observations with a characteristic
plasma temperature kT ~ 2 keV (~23 MK) and X-ray luminosity log Lx = 29.74 erg/s. During each of the last two observations obtained two weeks later the count rate increased slowly and the X-ray
plasma temperature was much higher but remained nearly steady at kT ~ 4 - 5 keV (~46 - 58 MK) and peak luminosity log Lx = 30.5 erg/s. Such variable X-ray emission in T Tauri
stars accompanied by high
plasma temperatures is a signature of
magnetic activity, consistent with the known presence of a strong
magnetic field in CI Tau. We summarize the variable X-ray emission properties of CI Tau within the framework of T Tauri
stars of similar mid-K spectral type, identify possible variability mechanisms, and assess the effects of
stellar X-ray irradiation on the claimed
planet.
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Astrophysics of Galaxies
Recoiling Black Hole Candidates from Spatially Offset Broad Emission Lines in MaNGA
R. Scott Barrows, Julia M. Comerford, James Negus et al. (+1 more)
From the Mapping Nearby
Galaxies at Apache Point Observatory (MaNGA) survey, we identify 14 off-
nuclear broad (FWHM>1000 km/s) Halpha and/or Hbeta emission line sources that indicate spatially offset active
galactic nuclei (AGN) candidates. In addition to massive black holes (MBHs) in on-going
galaxy mergers, this selection can also find MBHs that have been ejected from the host
galaxy nucleus due to MBH binary coalescence and asymmetric gravitational wave emission or the dynamical `slingshot' mechanism. Recoiling/slingshot MBHs are predicted to affect co-
evolution between MBHs and their host
galaxies, and they are observational tracers of past binary MBH mergers and gravitational wave emission. This is the first systematic search through an integral field spectroscopy survey for ejected MBHs to enable uniform constraints on their surface densities. We find that 42% (6/14) have optical image counterparts consistent with
galaxy stellar cores from infalling MBHs before the close binary MBH stage. The remaining 58% (8/14) have large broad line luminosities relative to their
stellar core mass upper limits (~2 times larger than for central AGN), suggesting merger-driven MBH
accretion enhancements or potentially ejected MBHs. The signatures of AGN-ionized narrow emission lines for
recoil/slingshot candidates are weaker by 68%, which is consistent with the ejected MBH scenario. The broad line projected velocity offsets range from ~10-600 km/s and suggest motion within the host
galaxy potentials. Finally, the implied recoiling MBH surface density upper limit is consistent with predictions that assume random
spin orientations in MBH binaries.
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All authors R. Scott Barrows, Julia M. Comerford, James Negus, Francisco Muller-Sanchez
Cosmology and Nongalactic Astrophysics
Dynamical Heating from Dark Compact Objects and Axion Minihalos: Implications for the 21-cm Signal
Badal Bhalla, Aurora Ireland, Hongwan Liu et al. (+2 more)
The temperature of
baryons at the end of the
cosmic dark ages can be inferred from observations of the 21-cm hyperfine transition in neutral hydrogen. Any energy injection from the dark sector can therefore be detected through these measurements. Dark compact objects and dark-matter substructures can modify the
baryon temperature by transferring heat via dynamical friction. In this work, we evaluate the prospects for detecting dynamical friction-induced heating from dark compact objects with a mass in the range $10^2 M_{\odot}$ to $10^5 M_{\odot}$, as well as from
axion minihalos, using upcoming 21-cm experiments. We find that both the 21-cm global signal and power-spectrum measurements will be sensitive to dark compact objects that constitute about 10% of the dark matter, and will substantially improve our sensitivity to
axion-like particles with masses in the range $10^{-18}$ eV to $10^{-9}$ eV.
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All authors Badal Bhalla, Aurora Ireland, Hongwan Liu, Huangyu Xiao, Tao Xu
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Widen the Resonance at Ultra-High Energies: Novel Probes of Neutrino Self-interactions in the High-Mass Regime
Pedro A. N. Machado, Isaac R. Wang, Xun-Jie Xu et al. (+1 more)
Neutrino self-interaction beyond the Standard Model is well motivated by the nonzero masses of
neutrinos, which are the only known particles guaranteed to have new physics.
Cosmic messengers, especially
neutrinos, play a central role in probing new physics, as they provide experimental conditions far beyond the reach of laboratories and serve as the link between laboratory fundamental-physics discoveries and their roles in the Universe, where many new physics motivations originate. In this work, we propose a novel probe of
neutrino self-interactions through ultra-high-energy
neutrinos scattering off the
cosmic neutrino background when the lightest
neutrino species remains relativistic today. This allows us to “Widen the Resonance” of such scattering. Meanwhile, we also provide a semi-analytic framework for cosmogenic UHE
neutrino production, avoiding computationally intensive simulations and yielding results precise enough for BSM studies. The widened resonance enables future ultrahigh-energy
neutrino telescopes, in particular GRAND, to probe mediator masses from MeV to GeV, reaching couplings down to $g \sim 10^{-3}$ – up to two orders of magnitude beyond current bounds. Our results enhance the discovery potential of $\nu$SI in the high-mass regime, potentially offering crucial insights into the connections between the
neutrino sector and dark sector.
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All authors Pedro A. N. Machado, Isaac R. Wang, Xun-Jie Xu, Bei Zhou
Astrophysics of Galaxies
Menelaos Raptis, Gwen C. Rudie, Ryan F. Trainor et al. (+9 more)
A
galaxy's
metallicity and its relation to
stellar mass encode the history of gas
accretion,
star formation, and
outflows within
cosmic ecosystems. We present new constraints on the low-mass end of the mass-
metallicity relation (MZR) at $z\sim2-3$ from ultra-deep JWST/NIRSpec spectroscopy of seven continuum-faint
galaxies in the Chemical
Evolution Constrained using Ionized Lines in Interstellar Aurorae (CECILIA) Faint sample (Raptis et al. 2025). Our sample includes Ly$\alpha$-selected and other low-luminosity
star-forming
galaxies with
stellar masses $\log(M_\star / M_\odot)\sim7.2-9.7$ and moderately faint rest-UV magnitudes ($-20.7 \lesssim M_{\rm UV} \lesssim -17.3$). Gas-phase oxygen abundances, calculated using empirical calibrations of [O III]/H$\beta$ together with [N II]/H$\alpha$ constraints, span $\sim0.04-0.5$ $Z_\odot$. We measure a steep MZR slope of $\gamma = 0.48 \pm 0.11$, suggesting a rapid increase in metal retention efficiency with mass, consistent with energy-driven
outflows. Comparison with lower- and higher-
redshift studies indicates an
evolution in normalization from $z\sim0$ to $z\sim2$, reflecting less metal enrichment in early
galaxies. We find no significant
evolution in the MZR between $z\sim2$ and the Epoch of Reionization, suggesting that our
galaxies may serve as useful analogs of reionization-era systems. Expanded samples and direct $T_e$-based abundance measurements will be crucial to fully trace the build-up of metals in low-mass
galaxies during the peak epoch of
cosmic star formation and to test the reliability of strong-line calibrations in these
galaxies.
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All authors Menelaos Raptis, Gwen C. Rudie, Ryan F. Trainor, Noah S. J. Rogers, Allison L. Strom, Nathalie A. Korhonen Cuestas, Caroline von Raesfeld, Ye Lin, Ojima Ojodomo Abraham, Christopher Chapman, Charles C. Steidel, Michael V. Maseda
Earth and Planetary Astrophysics
First Astrometric Limits on Binary Planets and Exomoons orbiting $\beta$ Pictoris b
Isabella Macias, Sydney Jenkins and Andrew Vanderburg
The search for exomoons, or moons in other
star systems, has attracted significant interest in recent years, driven both by advancements in detection sensitivity and by the expanding population of known
exoplanets. The $\beta$ Pictoris system is a particularly favorable target, as its proximity and directly imaged
planets allow for precise astrometric monitoring. We present astrometric constraints on the presence of binary
planets and exomoons in the $\beta$ Pictoris system using archival observations from the
GRAVITY interferometer and SPHERE instruments. We calculate these limits by modeling the motion of the two orbiting
planets and introducing an additional perturbation to the model that simulates the astrometric motion caused by an exomoon orbiting the
planet $\beta$ Pictoris b. We find that for short orbital periods ($\approx50$ days), a lunar companion is only allowed if its mass remains below $\approx 180~M_{\oplus}$ ($0.6~M_{\text{Jup}}$) at $3\sigma$ confidence. At intermediate periods near 300 days, we exclude moons more massive than $\approx 65~M_{\oplus}$ ($0.2~M_{\text{Jup}}$) at $3\sigma$ confidence. At longer orbital periods, we place the tightest constraints, ruling out any potential exomoon above $\approx 50~M_{\oplus}$ ($0.15~M_{\text{Jup}}$) at $700$ days and $\approx 30~M_{\oplus}$ ($0.1~M_{\text{Jup}}$) at $1,100$ days (both at $3\sigma$ confidence). These results place the first astrometric constraints on moons and binary
planets in the $\beta$ Pictoris system and demonstrate the sensitivity of interferometric observations for exomoon studies.
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Earth and Planetary Astrophysics
Astrometric view of companions in the inner dust cavities of protoplanetary disks
Miguel Vioque, Richard A. Booth, Enrico Ragusa et al. (+16 more)
Protoplanetary disks with inner
dust cavities (often referred to as "transition disks") are potential signposts of
planet formation. We use
Gaia astrometry to search for planetary and
stellar companions in a sample of 98 transition disks, assessing the occurrence rate of such companions and their potential influence on cavity formation. For the 98 Young
Stellar Objects (YSOs), we compute
Gaia proper motion anomalies which, together with the RUWE, identify companions with mass ratios $q \gtrsim 0.01$ at $\sim$0.1-30 au. We assess the impact of disk
gravity,
accretion, disk-scattered light, dippers, starspots, jets, and
outflows on the measured proper motion anomalies, concluding that astrometric techniques such as the one of this work can be robustly applied to YSOs. Significant proper motion anomalies are found in 31 transition disks (32% of the sample), indicative of companions. We recover 85% of known companions within our sensitivity range. We model the semi-major axis and mass required for a companion to reproduce the observed astrometric signals. Most inferred companions have $M > 30$ M$\rm{_{J}}$, placing many within or near the
stellar mass regime. Seven sources host companions compatible with a planetary mass ($M < 13$ M$\rm{_{J}}$, HD 100453, J04343128+1722201, J16102955-3922144, MHO6, MP Mus, PDS 70, and Sz 76). For the non-detections, we provide the companion masses and semi-major axes that can be excluded in future searches. About half (53%) of detected companions cannot be reconciled with having carved the observed
dust cavities. We find that transition disks host as many companions within our sensitivity range as do randomly sampled groups of YSOs and main-sequence
stars. If
dust cavities are shaped by companions, such companions must reside at larger orbital separations than those of the companions detected here, and we predict them to be of planetary mass. [abridged]
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All authors Miguel Vioque, Richard A. Booth, Enrico Ragusa, Álvaro Ribas, Nicolás T. Kurtovic, Giovanni P. Rosotti, Zephyr Penoyre, Stefano Facchini, Antonio Garufi, Carlo F. Manara, Nuria Huélamo, Andrew Winter, Sebastián Pérez, Myriam Benisty, Ignacio Mendigutía, Nicolás Cuello, Anna B. T. Penzlin, Alfred Castro-Ginard, Richard Teague
High Energy Astrophysical Phenomena
Magnetized Shocks Mediated by Radiation from Leptonic and Hadronic Processes
Shunke Ai and Irene Tamborra
Shocks in astrophysical transients are key sites of particle acceleration. If the shock upstream is optically thick, radiation smoothens the velocity discontinuity at the shock (radiation-mediated shocks). However, in mildly magnetized
outflows, a collisionless subshock can form, enhancing the efficiency of particle acceleration. We solve the hydrodynamic equations of a steady-state, radiation-mediated shock together with the radiative transfer equations accounting for electron and
proton acceleration. Our goal is to explore the impact of the
magnetic field and non-thermal radiation on the shock structure and the resulting spectral distribution of
photons. To this purpose, we assume a relativistic upstream fluid velocity ($\Gamma_u = 10$) and investigate shock configurations with variable upstream magnetization ($\sigma_u = 0$, $10^{-8}$, $10^{-4}$, $0.1$, and $0.3$). We find that synchrotron self-absorption alters the shock profile for $\sigma_u \gtrsim 10^{-8}$, with resulting changes up to $100\%$ in the bulk Lorentz factor at the shock; for $\sigma_u \gtrsim 0.1$, a prominent subshock forms. The spectral energy distributions of upstream- and downstream-going
photons are also altered. Radiative processes linked to accelerated
protons are responsible for a high-energy ($\gtrsim 10$ GeV) tail in the
photon spectrum; however, the radiation flux and pressure are negligibly affected with consequent minor impact on the shock structure. Our work highlights the importance of coupling the shock hydrodynamics to the transport of
photons, electrons,
protons, and intermediate particles to forecast the multi-messenger emission from astrophysical transients.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Cosmology of Gravi-Axions
Stephon Alexander, Gregory Gabadadze, Leah Jenks et al. (+1 more)
We show how a mass term for gravitational
axions (”gravi-
axions”) with a Chern-Simons coupling to
gravity can naturally arise due to non-perturbative contributions from Euclidean wormholes, breaking the continuous shift
symmetry of the standard theory. The induced mass can be generated in a cosmologically relevant range to be the dark matter or dark energy of the universe for a reasonable and well-motivated range of the
symmetry breaking scale. Upon generating the gravi-
axion mass term, we discuss the cosmology of the theory. We find that the gravi-
axion can be produced to be the dominant dark matter component via misalignment or gravitational particle production, and that in a different regime, the gravi-
axion can act as dynamical dark energy. We discuss gravi-
axion decay into gravitons as a potential observational window for this theory. Finally, we find that, for late-time, astrophysical compact objects, cosmologically relevant gravi-
axions behave as minimally-coupled, massive scalar fields.
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All authors Stephon Alexander, Gregory Gabadadze, Leah Jenks, Nicolás Yunes
Astrophysics of Galaxies
Episodic Star Formation – I. Overview and Scatter of the Star-Forming Main Sequence
Yuqian Gui, Dandan Xu, Haoyi Wang et al. (+4 more)
Episodic
star formation cycles in both high- and low-
redshift galaxies have gained more and more evidence. This paper aims to understand the detailed physical processes behind such behaviors and investigate how such an episodic
star-forming scenario can explain the scatter in
star-formation rate (SFR) of
star-forming main-sequence
galaxies. This is achieved through tracing back in time the history of z=0
star-forming central
galaxies in the TNG100 simulation over the past 7-8 Gyrs. As the first paper in this series, we provide an overview of the episodic
star formation history. We find that two branches of
star formation typically develop during each episode: while one branch happens in heavily metal-enriched gas in the centers of
galaxies, a secondary branch starts in lower-
metallicity regions at
galaxy outskirts where fresh gas first arrives, and gradually progresses to inner regions of
galaxies. Additionally, the temporal variation in the SFR at
galaxy outskirts is more significant than that at centers. As a consequence, the
metallicities in both gas and young
stars exhibit remarkably different distributions between SFR peaks and valleys. The resulting temporal SFR fluctuation within individual
galaxies has an average of ~ 0.2 dex, while the intrinsic differentiation between (the historical mean of)
galaxies is ~ 0.15 dex. These two together can well account for the scatter in SFR of ~ 0.25 dex as observed for z=0
star-forming main-sequence
galaxies.
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All authors Yuqian Gui, Dandan Xu, Haoyi Wang, Xuelun Mei, Enci Wang, Cheng Li, Stijn Wuyts
Astrophysics of Galaxies
The DREAMS Project: A New Suite of 1,024 Simulations to Contextualize the Milky Way and Assess Physics Uncertainties
Jonah C. Rose, Mariangela Lisanti, Paul Torrey et al. (+17 more)
We introduce a new suite of 1,024 cosmological and hydrodynamical zoom-in simulations of Milky Way-mass
halos, run with Cold Dark Matter, as part of the DREAMS Project. Each simulation in the suite has a unique set of initial conditions and combination of cosmological and astrophysical parameters. The suite is designed to quantify theoretical uncertainties from
halo-to-
halo variance, as well as
stellar and black hole feedback. We develop a novel weighting scheme that prioritizes regions of the input parameter space, yielding
galaxies consistent with the observed present-day
stellar mass–
halo mass relation. The resulting
galaxy population exhibits a wide diversity in structural properties that encompasses those of the actual Milky Way, providing a powerful statistical sample for
galactic archaeology. To demonstrate the suite's scientific utility, we investigate the connection between a
galaxy's merger history, focusing on
Gaia-Sausage-Enceladus~(GSE) analogs, and its present-day properties. We find that
galaxies with a GSE analog have lower
star formation rates, more compact disks, and more spherical
stellar halos. Crucially, significant
halo-to-
halo scatter remains, demonstrating that matching more than the most significant events in the Milky Way's past is necessary to recover its present-day properties. Our results highlight the necessity for large statistical samples to disentangle the
stochastic nature of
galaxy formation and robustly model the Milky Way's unique history.
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All authors Jonah C. Rose, Mariangela Lisanti, Paul Torrey, Francisco Villaescusa-Navarro, Alex M. Garcia, Arya Farahi, Carrie Filion, Alyson M. Brooks, Nitya Kallivayalil, Kassidy E. Kollmann, Ethan Lilie, Bonny Y. Wang, Akaxia Cruz, Sandip Roy, Andrew B. Pace, Niusha Ahvazi, Stephanie O'Neil, Cian Roche, Xuejian Shen, Mark Vogelsberger
Astrophysics of Galaxies
The ALMA Survey of 70 \mu m Dark High-mass Clumps in Early Stages (ASHES). XIII. Core Mass Function, Lifetime, and Growth of Prestellar Cores
Kaho Morii, Patricio Sanhueza, Qizhou Zhang et al. (+10 more)
The core mass function (CMF) of prestellar cores is essential for understanding the initial conditions of
star and cluster formation. However, the universality of the CMF and its relationship to the initial mass function (IMF) remain unclear. We study the CMF in the earliest stage of high-mass
star formation using 461 prestellar core candidates and 254 protostellar cores as a part of the ALMA Survey of 70 \mu m Dark High-mass Clumps in Early Stages (ASHES). We find that prestellar core candidates tend to have lower masses than protostellar cores. We also find that the lifetime of prestellar cores is several times longer than the freefall time, although it approaches the freefall time as the core mass increases. The CMF, including both protostellar and prestellar cores, has a power-law slope of $-2.05\pm0.04$, shallower than Salpeter's IMF slope of -2.35. Conversely, the CMF of gravitationally bound, prestellar cores has a steeper slope ($-2.32\pm0.30$), indistinguishable from Salpeter's slope. This finding is consistent with observations in both low-mass
star-forming regions and high-mass protoclusters, implying a universal core formation mechanism. The protostellar CMF with a larger maximum core mass can be reproduced by the prestellar CMF when an external gas infall is considered. The inferred mass infall rate is higher than the Bondi-Hoyle-Lyttleton
accretion rate and follows a shallower mass dependence (smaller power-law index), more consistent with the
tidal-lobe
accretion. This may contribute to the
evolution of CMFs seen in later stages.
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All authors Kaho Morii, Patricio Sanhueza, Qizhou Zhang, Giovanni Sabatini, Shanghuo Li, Fabien Louvet, Henrik Beuther, Fernando A. Olguin, Shuting Lin, Daniel Tafoya, Takeshi Sakai, Xing Lu, Fumitaka Nakamura
Astrophysics of Galaxies
Role of prompt cusps in driving the core collapse of SIDM halos
Vinh Tran, Daniel Gilman, M. Sten Delos et al. (+4 more)
Prompt cusps (PCs) form from the direct collapse of overdensities in the early Universe, reside at the center of every dark matter
halo, and have density profiles steeper than $r^{-1}$ NFW cusps. Using a suite of high-resolution N-body simulations, we study the
evolution of isolated
halos in self-interacting dark matter (SIDM) with massive PCs embedded at their centers, a scenario that could be realized in certain SIDM models with light mediators that predict a small-scale suppression of the linear matter power spectrum. We track the
evolution of three equally concentrated $10^7\,{\rm{M}}_\odot$
halos, hosting PCs of various total masses, and quantify how the presence of a PC affects the processes of core formation and collapse. Early in the core-formation phase,
halos with more prominent PCs exhibit a delayed
evolution by a factor of $\sim 2$ due to smaller velocity dispersion gradients in the inner region. During most of the core-collapse phase, the
halo evolution becomes closely aligned in physical time, with appropriate rescaling of densities, radii, and velocity dispersions. The scale densities and radii preserve the virial mass of the original
halos, but with increased concentration. Deviations occur at the late phase of core-collapse at the level of $\sim 5\%$ relative to the reference collapse track of an NFW
halo. These deviations depend non-trivially on both the increased concentration incurred by the PCs, as well as the velocity dispersion (temperature) of the outer
halo regions, which can inhibit or enhance the heat transfer process. Our simulations illustrate the complex interplay between the inner and outer
halo profiles in determining the onset of core collapse and motivate future studies in the full cosmological context.
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All authors Vinh Tran, Daniel Gilman, M. Sten Delos, Xuejian Shen, Oliver Zier, Mark Vogelsberger, David Xu
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-th
Bayesian inference on Calabi–Yau moduli spaces and the axiverse: experimental data meets string theory
Mudit Jain, Elijah Sheridan, David J. E. Marsh et al. (+3 more)
We develop tools of
Bayesian inference on the
moduli space of Calabi–Yau (CY)
manifolds. We sample from the invariant Weil–Petersson (WP) measure using Markov Chain Monte Carlo and normalising flows on \Kahler
moduli space with dimension up to $h^{1,1}=30$, and present results on the spectrum of the CY volume and properties of divisors when the measure is restricted in physically meaningful ways. We furthermore present a theory-informed prior on
axion masses and decay constants $(m_a,f_a)$ marginalised over the WP measure for all inequivalent CYs constructable from the Kreuzer–Skarke database with $h^{1,1}\leq 5$. We then impose likelihoods based on
axion physics. We demonstrate how detection of a relatively heavy QCD
axion at small $h^{1,1}$, e.g. by ADMX, provides detailed information about CY geometry and
topology. Finally, we compute a full forward model incorporating likelihoods from the
cosmic microwave background and Lyman-alpha forest and find the maximum posterior probability region on the
moduli space of a given CY favoured by a resolution of the tension in these data by an ultralight
axion composing $\mathcal{O}(1\%)$ of the dark matter. This demonstration serves as a blueprint for future statistical analyses within string phenomenology.
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All authors Mudit Jain, Elijah Sheridan, David J. E. Marsh, Elli Heyes, Keir K. Rogers, Andreas Schachner
Cosmology and Nongalactic Astrophysics
Kinetic Mixing and the Phantom Illusion: Axion-Dilaton Quintessence in Light of DESI DR2
Michael W. Toomey, Ellie Hughes, Mikhail M. Ivanov et al. (+1 more)
Recent results from DESI BAO analyses suggest that dark energy may not be a cosmological constant and is in fact dynamical. Furthermore, the data suggest that the equation of state may have been in the phantom regime in the distant past, recently undergoing a phantom crossing. In this work, we investigate whether this preference can be realized within a kinetically mixed
axion-dilaton (KMIX) quintessence model, a string-motivated system in which an
axion-like field couples exponentially to a dilaton-like (
moduli) field. Crucially, KMIX can appear phantom in a standard Chevallier-Polarski-Linder (CPL) based analysis. To confront the model with data, we develop a fast pipeline based on normalizing flows that (i) learns a theory-informed prior on $(w_0,w_a)$ from KMIX realizations and (ii) provides an inverse mapping from CPL parameters back to the physical KMIX parameters. By importance-sampling pre-computed CPL chains using this framework, we effectively transform generic phenomenological constraints into direct, computationally efficient constraints on the underlying KMIX theory, avoiding the prohibitive cost of full parameter space exploration. Applied to Planck+DESI DR2 BAO measurements, our framework finds support for KMIX at $2.5\sigma$ compared to the base CPL fit at $3.1\sigma$, demonstrating that KMIX may account for the DESI preference without invoking true phantom behavior. When additionally including Type Ia
supernovae data, we find that the preference remains above $3\sigma$ for Union3 and DES Y5, but drops to $2.1\sigma$ with Pantheon+. The latter, combined with the DESI full-shape power spectrum and bispectrum data, further reduces the preference to $1.7\sigma$. Ultimately, should the DESI deviation persist with future data, KMIX may offer a theoretically well-motivated explanation for the phantom-like signatures inferred from phenomenological fits.
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All authors Michael W. Toomey, Ellie Hughes, Mikhail M. Ivanov, James M. Sullivan
Cosmology and Nongalactic Astrophysics
Baryon fraction from the BAO amplitude: a consistent approach to parameterizing perturbation growth
Andrea Crespi, Will J. Percival, Alex Krolewski et al. (+51 more)
Galaxy clustering constrains the
baryon fraction Omega_b/Omega_m through the amplitude of
baryon acoustic oscillations and the suppression of perturbations entering the horizon before recombination. This produces a different pre-recombination distribution of
baryons and dark matter. After recombination, the gravitational potential responds to both components in proportion to their mass, allowing robust measurement of the
baryon fraction. This is independent of new-physics scenarios altering the recombination background (e.g. Early Dark Energy). The accuracy of such measurements does, however, depend on how
baryons and CDM are modeled in the power spectrum. Previous template-based splitting relied on approximate transfer functions that neglected part of information. We present a new method that embeds an extra parameter controlling the balance between
baryons and dark matter in the growth terms of the perturbation equations in the CAMB Boltzmann solver. This approach captures the baryonic suppression of CDM prior to recombination, avoids inconsistencies, and yields a clean parametrization of the
baryon fraction in the linear power spectrum, separating out the simple physics of growth due to the combined matter potential. We implement this framework in an analysis pipeline using Effective Field Theory of Large-Scale Structure with HOD-informed priors and validate it against noiseless LCDM and EDE cosmologies with DESI-like errors. The new scheme achieves comparable precision to previous splitting while reducing systematic biases, providing a more robust way to
baryon-fraction measurements. In combination with BBN constraints on the
baryon density and Alcock-Paczynski estimates of the matter density, these results strengthen the use of
baryon fraction measurements to derive a Hubble constant from energy densities, with future DESI and Euclid data expected to deliver competitive constraints.
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All authors Andrea Crespi, Will J. Percival, Alex Krolewski, Marco Bonici, Hanyu Zhang, Jessica Nicole Aguilar, Steven Ahlen, Abhijeet Anand, Davide Bianchi, David Brooks, Edmond Chaussidon, Todd Claybaugh, Todd Cuceu, Axel de la Macorra, Peter Doel, Simone Ferraro, Andreu Font-Ribera, Jaime E. Forero-Romero, Enrique Gaztañaga, Gaston Gutierrez, Julien Guy, Hiram K. Herrera-Alcantar, Dragan Huterer, Mustapha Ishak, Dick Joyce, David Kirkby, Theodore Kisner, Anthony Kremin, Ofer Lahav, Claire Lamman, Martin Landriau, Laurent Le Guillou, Michael E. Levi, Marc Manera, Paul Martini, Aaron Meisner, Ramon Miquel, Seshadri Nadathur, Nathalie Palanque-Delabrouille, Claire Poppett, Francisco Prada, Ignasi Pérez-Ràfols, Graziano Rossi, Lado Samushia, Eusebio Sanchez, David Schlegel, Michael Schubnell, Hee-Jong Seo, Joseph H. Silber, David Sprayberry, Gregory Tarlé, Benjamin A. Weaver, Rongpu Zhou, Hu Zou
Astrophysics of Galaxies
From metallicity distributions to mutual information: A new perspective on stellar halo assembly
Amit Mondal and Biswajit Pandey
The
metallicity structure of
stellar halos encodes the fossil record of
galaxy assembly, tracing the chemical
evolution and dynamical imprint of past mergers. Using five Milky Way-mass
halos from the Aquarius simulations, we introduce an information-theoretic framework to quantify spatial-chemical correlations through the mutual information (MI) between angular position and
metallicity. We divide
stars in each
halo into high- and low-
metallicity populations based on their median
metallicity and examine their
metallicity distribution functions (MDFs), spatial anisotropies, and angular-
metallicity couplings as a function of galactocentric radius. The MDFs exhibit remarkable diversity, ranging from single-peaked distributions dominated by one or two massive progenitors to broad or bimodal forms shaped by multiple
accretion events, revealing the
stochastic nature of
halo assembly. The low-
metallicity stars, primarily contributed by disrupted satellites, display higher spatial anisotropy and stronger angular clustering than their metal-rich counterparts. After removing bound satellites, anisotropy decreases significantly, yet high-
metallicity stars remain marginally more anisotropic, reflecting the lingering debris of massive, centrally deposited progenitors. The mutual information between angular position and
metallicity increases with radius before saturating in the outskirts, with the difference between the data and randomized controls confined mainly to the inner
halo signifying residual spatial-chemical coupling driven by incomplete phase mixing. Our results demonstrate that information-theoretic diagnostics provide a powerful and intuitive way to quantify the chemical complexity of
stellar halos and offer a promising route to compare simulations with forthcoming high-dimensional
Galactic survey data.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-th
Klein Bottle Cosmology
Brian Greene, Daniel Kabat, Janna Levin et al. (+1 more)
We explore a higher-dimensional universe that is a product of Minkowski space and the nonorientable Klein bottle. The
topology explicitly breaks important
symmetries, such as translational invariance and (5+1)-dimensional CP invariance. Somewhat surprisingly, the (3+1)-dimensional cp of the Minkowski space can also be broken by the Klein bottle, both explicitly and in the presence of a brane. The
topology enforces a background of
fermion correlations that amounts to a condensate wall localized in the Klein bottle. The wall acts as an order parameter for the broken
symmetries. If a brane passes through the wall, brane
fermions that couple to the condensate are produced as quantified by the Bogoliubov coefficients for a time-dependent mass. The scenario meets the conditions, including cp violation, to potentially generate the matter-antimatter asymmetry of the universe.
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All authors Brian Greene, Daniel Kabat, Janna Levin, Massimo Porrati
Cosmology and Nongalactic Astrophysics
A measurement of $H_0$ from DESI DR1 using energy densities
Alex Krolewski, Andrea Crespi, Will J. Percival et al. (+57 more)
We present a new measurement of the Hubble constant, independent of standard rulers and robust to pre-recombination modifications such as Early Dark Energy (EDE), obtained by calibrating the total energy density of the Universe. We start using the present-day
photon density as an anchor, and use the
baryon-to-
photon ratio from Big Bang Nucleosynthesis based measurements and the
baryon-to-matter ratio from the
baryons' imprint on
galaxy clustering to translate to a physical matter density at present day. We then compare this to measurements of the ratio of the matter density to the critical density ($\Omega_{\mathrm{m}}$), calculated using the relative positions of the
baryon acoustic oscillations, to measure the critical density of the universe and hence $H_0$. The important measurements of the
evolution of the energy density all happen at low
redshift, so we consider this a low-
redshift measurement. We validate our method both on a suite of $N$-body mocks and on noiseless theory vectors generated across a wide range of Hubble parameters in both $\Lambda$CDM and EDE cosmologies. Using DESI DR1 data combined with the angular CMB acoustic scale and the latest BBN constraints, we find $H_0 = 69.0 \pm 2.5$ km s$^{-1}$ Mpc$^{-1}$, consistent with existing early and late-time determinations of the Hubble constant. We consider the impact of non-standard dark energy
evolution on our measurement. Future data, including that from further iterations of DESI and from Euclid, will add to these results providing a powerful test of the Hubble tension.
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All authors Alex Krolewski, Andrea Crespi, Will J. Percival, Marco Bonici, Hanyu Zhang, J. Aguilar, S. Ahlen, D. Bianchi, D. Brooks, R. Canning, E. Chaussidon, T. Claybaugh, A. Cuceu, S. Cole, A. de la Macorra, J. Della Costa, P. Doel, J. Edelstein, S. Ferraro, A. Font-Ribera, J. Forero-Romero, E. Gaztañaga, S. Gontcho a Gontcho, G. Gutierrez, J. Guy, H. Herrera-Alcantar, K. Honscheid, D. Huterer, M. Ishak, D. Joyce, R. Kehoe, D. Kirkby, T. Kisner, A. Kremin, O. Lahav, C. Lamman, M. Landriau, L. Le Guillou, M. Levi, M. Manera, A. Meisner, R. Miquel, J. Moustakas, A. Muñoz-Gutiérrez, S. Nadathur, G. Niz, N. Palanque-Delabrouille, C. Poppett, F. Prada, I. Pérez-Ràfols, G. Rossi, L. Samushia, E. Sanchez, D. Schlegel, M. Schubnell, J. H. Silber, D. Sprayberry, G. Tarlé, B. A. Weaver, H. Zou
Solar and Stellar Astrophysics
The EBLM Project XVIII. 3D Obliquities of Five Low-Mass Eclipsing Binaries
Becca Spejcher, David V. Martin, Jake Pandina et al. (+17 more)
The formation of tight
stellar binaries remains an unsolved problem. There is too much angular momentum in a collapsing and fragmenting protostellar cloud to form a
stellar binary in situ with a separation less than an AU, yet thousands of these short-period binaries have been discovered. One indication of a binary's formation is the angle between the
stellar spin and orbital axes — its obliquity. The classical method for determining projected
stellar obliquities is the Rossiter-McLaughlin effect. This has been applied to 132 hot Jupiters, but only a handful of
stellar binaries. Of the binary systems with measured projected obliquities, even fewer have measured 3D obliquities. In this paper, we add five more short-period binary 3D obliquity measurements to the sample previously consisting of one system. We present Rossiter-McLaughlin measurements for EBLM J0239-20, EBLM J0941-31, EBLM J1037-25, EBLM J1141-37, and EBLM J2025-45. These systems consist of an M-
dwarf eclipsing an F/G type primary. We combine CORALIE and HARPS spectroscopy with TESS photometry of primary and secondary eclipses. We show that even though the sky-projected obliquities seem to be aligned, there is modest but non-zero
spin-orbit misalignment ($\psi$ between 5 and 20$^{\circ}$). Our primary
stars straddle the Kraft break at $\sim 6250K$. We derive the M-
dwarf masses and radii to precisions better than 3%. With the exception of EBLM J0941-31, each system has an inflated radius, exceeding
stellar model predictions by more than 5$\sigma$.
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All authors Becca Spejcher, David V. Martin, Jake Pandina, Andy Zhang, Max Ammons, Wata Tubthong, Amaury Triaud, Ritika Sethi, Noah Vowell, Adrian Barker, Pierre Maxted, Alison Duck, Shelby Summers, François Bouchy, Monika Lendl, Maxime Marmier, Vincent Megevand, Francesco Pepe, Malte Tewes, Stéphane Udry
High Energy Astrophysical Phenomena
Variation of Microphysical Parameters in Reverse-shock Scenario
Nissim Fraija, Boris Betancourt-Kamenetskaia, Antonio Galván et al. (+1 more)
Gamma-ray bursts (GRBs), among the most compelling astrophysical phenomena, are potential candidates for exploring the
evolution of energy distribution among
magnetic fields and particles through multiwavelength observations. The fraction of energy transferred between particles and the
magnetic field is governed by microphysical parameters, typically assumed to be constant during relativistic shocks but may in fact vary with time. In this work, we derive the light curves and closure relations (CRs) of the synchrotron-self Compton (SSC) process from the external reverse shock (RS) with variations of microphysical parameters in a homogeneous and
stellar-wind medium. We consider the
evolution of the RS in the thick- and thin-shell regimes. We demonstrate that, depending on the microphysical parameters, this process can mimic plateau phases and produce temporal decay indices steeper than those predicted by high-latitude emission alone. The current model is employed to examine the
evolution of the spectral and temporal indices of GRBs reported in the Second
Fermi-LAT Gamma-ray Burst Catalog (2FLGC) and bursts detected at very high energies, using Markov Chain Monte Carlo (MCMC) simulations.
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All authors Nissim Fraija, Boris Betancourt-Kamenetskaia, Antonio Galván, Maria Dainotti
Cosmology and Nongalactic Astrophysics
Inflation Driven by Scalar-Neutrino Coupling in a Mass-Varying Neutrino Framework
Hemanshi Bundeliya, Gaurav Bhandari, S. D. Pathak et al. (+1 more)
We propose a cosmological framework in which
neutrino masses evolve dynamically through coupling with a scalar field that simultaneously drives inflation. The
neutrino mass is modeled as a power-law, exponential, or hybrid function of the scalar field, yielding an effective potential that includes
neutrino backreaction. Starting from the Einstein-
Hilbert action in a flat FLRW background, we derive the modified Friedmann and Klein Gordon equations incorporating this coupling. Using the
Fermi-Dirac integrals, we account for the continuous transition of
neutrinos from relativistic to non-relativistic regimes. The inflationary dynamics are analyzed via the slow roll parameters derived from the effective potential. Our results show that the scalar
neutrino coupling alters the potential slope and
curvature, thereby influencing the duration of inflation. The hybrid coupling form provides the most flexible realization, unifying
neutrino mass generation with early universe inflation within a single scalar field framework.
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All authors Hemanshi Bundeliya, Gaurav Bhandari, S. D. Pathak, V. K. Sharma
Cosmology and Nongalactic Astrophysics
Detection of the Pairwise Kinematic Sunyaev-Zel'dovich Effect and Pairwise Velocity with DESI DR1 Galaxies and ACT DR6 and Planck CMB Data
Yulin Gong, Patricio A. Gallardo, Rachel Bean et al. (+50 more)
We present a 9.3-sigma detection of the pairwise kinematic Sunyaev-Zeldovich (kSZ) effect by combining a sample of 913,286 Luminous Red
Galaxies (LRGs) from the Dark Energy Spectroscopic Instrument Data Release 1 (DESI DR1) catalog and co-added Atacama Cosmology
Telescope (ACT DR6) and Planck
cosmic microwave background (CMB) temperature maps. This represents the highest-significance pairwise kSZ measurement to date. The analysis uses three ACT CMB temperature maps: co-added 150 GHz, total frequency maps, and a component-separated Internal Linear Combination (ILC) map, all of which cover 19,000 square degrees of the sky from Advanced ACTPol observations conducted between 2017 and 2022. Comparison of the results of these three maps serves as a consistency check for potential foreground contamination that may depend on the observation frequency. An estimate of the best-fit mass-averaged optical depth is obtained by comparing the pairwise kSZ curve with the linear-theory prediction of the pairwise velocity under the best-fit Planck cosmology, and is compared with predictions from simulations. This estimate serves as a reference point for future comparisons with thermal SZ-derived optical depth measurements for the same DESI cluster samples, which will be presented in a companion paper. Finally, we employ a machine-learning approach trained on simulations to estimate the optical depth for 456,803 DESI LRG-identified clusters within the simulated mass range (greater than about 1e13
solar masses). These are combined with the measured kSZ signal to infer the individual cluster peculiar velocities, providing the opportunity to constrain the behavior of
gravity and the dark sector over a range of
cosmic scales and epochs.
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All authors Yulin Gong, Patricio A. Gallardo, Rachel Bean, Jenna Moore, Eve M. Vavagiakis, Nicholas Battaglia, Boryana Hadzhiyska, Yun-Hsin Hsu, Jessica Nicole Aguilar, Steven Ahlen, Davide Bianchi, David Brooks, Todd Claybaugh, Rebecca Canning, Mark Devlin, Peter Doel, Axel de la Macorra, Simone Ferraro, Andreu Font-Ribera, Jaime E. Forero-Romero, Enrique Gaztañaga, Gaston Gutierrez, Satya Gontcho A Gontcho, Julien Guy, Klaus Honscheid, Cullan Howlett, R. Henry Liu, Mustapha Ishak, Dick Joyce, Anthony Kremin, Claire Lamman, Michael Levi, Martin Landriau, Marc Manera, Aaron Meisner, Ramon Miquel, Michael D. Niemack, Seshadri Nadathur, Will Percival, Francisco Prada, Graziano Rossi, Bernardita Ried Guachalla, Eusebio Sanchez, Hee-Jong Seo, David Sprayberry, David Schlegel, Cristóbal Sifón, Michael Schubnell, Joseph Harry Silber, Gregory Tarlé, Benjamin Alan Weaver, Rongpu Zhou, Hu Zou
Astrophysics of Galaxies
Consensus based Algorithm for Nonparametric Detection of Star Clusters (CANDiSC)
C O Obasi, J G Fernandez Trincado, M Gomez et al. (+14 more)
Context: The VISTA Variables in the Via Lactea (VVV) and its extension (VVVX) are near-infrared surveys mapping the
Galactic bulge and adjacent disk. These data have enabled the discovery of numerous
star clusters obscured by high and spatially variable extinction. Most previous searches relied on visual inspection of individual tiles, which is inefficient and biased against faint or low-density systems. Aims: We aim to develop an automated, homogeneous
algorithm for systematic cluster detection across different surveys. Here, we apply our method to VVVX data covering low-latitude regions of the
Galactic bulge and disk, affected by extinction and crowding. Methods: We introduce the Consensus-based
Algorithm for Nonparametric Detection of
Star Clusters (CANDiSC), which integrates kernel density estimation, the Density-Based Spatial Clustering of Applications with Noise (DBSCAN), and nearest-neighbour density estimation within a consensus framework. A
stellar overdensity is classified as a candidate if identified by at least two of these methods. We apply CANDiSC to 680 tiles in the VVVX PSF photometric catalogue, covering approximately 1100 square degrees. Results: We detect 163
stellar overdensities, of which 118 are known clusters. Cross-matching with recent catalogues yields five additional matches, leaving 40 likely new candidates absent from existing compilations. The estimated false-positive rate is below 5 percent. Conclusions: CANDiSC offers a robust and scalable approach for detecting
stellar clusters in deep near-infrared surveys, successfully recovering known systems and revealing new candidates in the obscured and crowded regions of the
Galactic plane.
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All authors C O Obasi, J G Fernandez Trincado, M Gomez, D Minniti, J Alonso Garcia, B P L Ferreira, E R Garro, B Dias, R K Saito, B Barbuy, M C Parisi, T Palma, B Tang, M Ortigoza Urdaneta, L D Baravalle, M V Alonso, F Mauro
Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
Alessio Belfiglio, Roberto Franzosi and Orlando Luongo
We discuss some
entanglement features associated with cubic non-Gaussian perturbations in single-field inflationary scenarios. We adopt standard momentum-space techniques to show how multipartite
entanglement arises for inflationary perturbation modes, focusing on the dynamics of the comoving
curvature perturbation. In particular, we quantify
entanglement generation via the recently proposed
Entanglement Distance, which introduces a
geometric interpretation of
quantum correlations in terms of the Fubini-Study metric. In the continuum limit, we show that the
Entanglement Distance arising from displacement transformations is proportional to the total number of excitations in the
quantum state for cubic perturbations, thus providing an upper bound on the von Neumann
entanglement entropy of any reduced state compatible with such excitations. Within the interaction picture, we further observe that the
quantum correlations arising from cubic gravitational interactions are typically much larger than the standard squeezing contribution, in agreement with previous studies focusing on von Neumann
entropy generation across the Hubble horizon. We further show how the inflationary parameters affect the total amount of such correlations, highlighting in particular their dependence on the inflationary energy scales and the number of e-foldings during slow-roll.
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