General Relativity and Quantum Cosmology
Einstein-aether Elliptic Charges and the First Law of Asymptotically AdS Black Holes
Walter Arata, Moustafa Ismail, Stefano Liberati et al. (+3 more)
We investigate the thermodynamic role of asymptotic aether
alignment for universal horizons in Einstein-aether theory. In the static, spherically symmetric, asymptotically AdS sector with $c_{14}=0$, the known first law for universal horizons contains an additional term whenever the aether is misaligned with the timelike Killing vector at infinity. While this term has recently been interpreted in Hořava–Lifshitz
gravity as the contribution of an
elliptic charge associated with khronon reparameterizations, no corresponding explanation was available in Einstein-aether theory. We show that, in the same sector, Einstein-aether theory possesses a previously unidentified
symmetry of the reduced action, generated by infinitesimal transformations of the form $\delta u^a=f a^a$, where $a^a$ is the aether acceleration and $f$ obeys an
elliptic constraint. We derive the associated current and charge, and show that the aligned limit is naturally interpreted as the ensemble in which this aether-charge contribution vanishes. This provides the Einstein-aether counterpart of the
elliptic-charge mechanism in Hořava–Lifshitz
gravity and clarifies the thermodynamic significance of asymptotic aether
alignment.
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All authors Walter Arata, Moustafa Ismail, Stefano Liberati, Luke Martin, David Mattingly, Giulio Neri
Cosmology and Nongalactic Astrophysics
Three-form dark energy: constraints and multi-probe comparison with $\Lambda$CDM
Mariam Bouhmadi-López, Hsu-Wen Chiang, Carlos G. Boiza et al. (+3 more)
Three-form fields provide a theoretically well-motivated framework for dark energy, arising in higher-dimensional theories and exhibiting a rich cosmological phenomenology. We investigate a minimally coupled three-form dark energy model with a Gaussian potential and constrain it using current cosmological observations, including CMB shift parameters, DESI DR2
baryon acoustic oscillation measurements, Pantheon+
supernovae with and without SH0ES calibration,
cosmic chronometers, and gamma-ray bursts. Parameter estimation is performed within a
Bayesian Markov-chain Monte Carlo framework, while model comparison relies on several information criteria and the
Bayesian evidence, as well as tension statistics. We find that the three-form model provides a viable and competitive description of the expansion history of the Universe. It is mildly preferred over $\Lambda$CDM for the combination of early and late-time
datasets that are heavily tensioned (CMB+BAO and Pantheon+SH0ES). This preference decreases to neutrality for the other, less tensioned combination of early and late-time data, while for individual early-time or late-time
datasets analysed separately, the information criteria are neutral or favour $\Lambda$CDM. This suggests that the additional degrees of freedom of the three-form field may help accommodate cosmological observations of different origins within a common framework. The reconstructed dark energy dynamics exhibit a characteristic phantom phase at intermediate
redshifts while approaching a cosmological-constant-like behaviour at early and late times, providing a distinctive observational signature. Although the model does not significantly alleviate the Hubble tension despite allowing higher values of $H_0$, it remains consistent with current observations and offers a well-motivated alternative to $\Lambda$CDM whose predictions can be tested by future cosmological surveys.
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All authors Mariam Bouhmadi-López, Hsu-Wen Chiang, Carlos G. Boiza, Javier Ortega del Río, Thomas J. Broadhurst, Pisin Chen
High Energy Astrophysical Phenomena
Parsec-scale polarimetry and kinematics of a spine-sheath jet in the neutrino-blazar TXS 0506+056
F. Eppel, P. Benke, C. Degli Agosti et al. (+10 more)
In 2017, the blazar TXS 0506+056 showed a remarkable gamma-ray outburst simultaneously with a high-energy
neutrino detection by IceCube from the same sky region. The significance of this association was found to be on the order of 3 sigma thus providing a strong link between the
neutrino emission and the blazar
flare. The high-energy
flare in TXS 0506+056 was followed by a delayed
radio flare, peaking in $\sim2020$ in the aftermath of the
neutrino event. We investigate the parsec-scale jet structure and dynamics of TXS 0506+056 using 15 GHz full-polarization VLBI observations obtained between 2009 and 2025 with the Very Long Baseline Array. Our kinematic analysis reveals moderate superluminal jet speeds of $\sim(1-2)$c and two quasi-stationary components. A new jet component with comparable speed was ejected contemporaneously with the 2017 IceCube
neutrino event. The stacked polarization map is consistent with a stratified spine-sheath jet structure: an inner spine with EVPA aligned with the jet, surrounded by a sheath layer with perpendicular EVPA. Variability in total intensity and polarization further indicates interaction between these layers, particularly evident in characteristic linear polarization
flares, associated with EVPA rotations of the quasi-stationary components. The multi-layered jet configuration is consistent with previous studies that were able to explain the
neutrino emission in this TXS 0506+056 through a spine-sheath jet structure. We suggest that TXS 0506+056 represents an archetypal case and that similar polarization signatures and
geometric light curve
flares may be present in other
neutrino-emitting sources, potentially offering a solution to the Doppler-crisis phenomenon observed in TeV-emitting blazars.
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All authors F. Eppel, P. Benke, C. Degli Agosti, J. L. Gómez, D. C. Homan, M. Kadler, Y. Y. Kovalev, M. L. Lister, V. A. Makeev, A. V. Plavin, A. B. Pushkarev, E. Ros, T. Savolainen
High Energy Astrophysical Phenomena
Gamma-ray Bursts in the Radio Sky: the Role of the SKA-VLBI
Stefano Giarratana, Om Sharan Salafia, Xue-Feng Wu et al. (+6 more)
Radio observations of $\gamma$-ray bursts (GRBs) employing the very long baseline interferometry (VLBI) technique provide us with fundamental information on the dynamics and the geometry of the GRB blast wave. With its high angular resolution ($\sim$milli-arcsecond), VLBI allows us to measure the apparent superluminal expansion, to characterise the structure of the jet and to constrain the viewing angle and jet opening angle. While this information is crucial to understand these transient events, such studies have been possible only for three GRBs to date, owing to both the poor sensitivity of current
radio facilities and the paucity of close and bright GRBs. In this chapter, we estimate the impact that the SKA-Mid will have on these studies, when included in a VLBI network. We performed a series of dedicated simulations of VLBI observations of GRBs, considering five VLBI networks and the SKA-Mid, both in its AA* and AA4 configurations. We show that including the SKA-Mid in a global-VLBI experiment will: (i) allow us to measure the size and the expansion of a GRB up to a
redshift $z\simeq 0.25$ (at a confidence level of $3\sigma$); (ii) constrain the size $\gtrsim$2 times better than the current global-VLBI array; (iii) improve the localisation precision in Declination from 4 to 30 times; (iv) detect the apparent proper motion of GRBs seen slightly off-axis with a confidence level 3 times better than current VLBI networks. Ultimately, the SKA-Mid will open a new window on a portion of the GRB population that has been inaccessible so far.
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All authors Stefano Giarratana, Om Sharan Salafia, Xue-Feng Wu, Jin-Jun Geng, Tao An, Benito Marcote, Marcello Giroletti, Giancarlo Ghirlanda, Tiziana Venturi
General Relativity and Quantum Cosmology
Tidal Forces in the Presence of Torsion and Nonmetricity
Armin van de Venn, Marcelo Netz-Marzola, David Vasak et al. (+1 more)
This work investigates how torsion and nonmetricity modify
tidal accelerations in metric-affine
gravity. We derive a projected deviation equation that generalizes the standard geodesic deviation equation to metric-affine geometry, and apply it to the relative acceleration of neighboring autoparallels in the weak-field, nonrelativistic limit. In this regime, the
tidal acceleration separates into the usual Newtonian contribution and linear post-Riemannian corrections sourced by torsion and non-metricity. By decomposing torsion and nonmetricity into their irreducible Lorentz components, we identify the corresponding signatures in the
tidal tensor and discuss to what extent these contributions can be distinguished. We then show how future direct
tidal measurements could be translated into
benchmark bounds on post-Riemannian
tidal contributions, assuming probe dynamics sensitive to the affine connection. Our results suggest that the
tidal acceleration may provide a systematic route toward probing post-Riemannian spacetime features in the future.
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All authors Armin van de Venn, Marcelo Netz-Marzola, David Vasak, Jürgen Struckmeier
Instrumentation and Methods for Astrophysics
The Hidden Geometry of Astrophysical Spectra: Path-Signatures of Line Profiles
Rafael S. de Souza and Severin Bunk
The morphology of a spectral-line profile contains information beyond scalar summaries of line strength, centroid, width, global asymmetry, or diagnostic line ratios. Broad wings, shoulders, double peaks, secondary components, and composite emission–absorption structures encode how flux is ordered across wavelength but can remain indistinguishable under conventional summaries. We introduce an interpretable
geometric representation of line profiles inspired by rough path theory. Each wavelength-sampled profile is mapped to a common systemic rest-frame velocity grid and treated as a trajectory in velocity–flux space, traversed from blue to red. From this path, we define a compact set of low-order descriptors measuring signed velocity–flux area, blue–red imbalance localization, higher-order shape complexity, and emission–absorption ordering. Using synthetic profiles, we show that these descriptors separate morphologies with similar full width at half maximum (FWHM), non-parametric velocity width ($W_{80}$), and low-order moment summaries. We then apply the method to MaNGA integral-field spectroscopy by computing H$\alpha$ descriptors in individual spaxels and clustering them in a low-dimensional feature space. The resulting classes form spatially coherent regions of similar ordered line morphology. Although no external velocity field is supplied to the clustering, stacked spectra within these regions recover coherent large-scale centroid-velocity patterns broadly consistent with the MaNGA reference velocity fields. We release a minimalist MIT-licensed package ${\it spectropath}$, available at \href{https://rafaelsdesouza.com.br/spectropath/}{the project website}.
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General Relativity and Quantum Cosmology
Critical collapse of vacuum spacetimes: Nakamura wave initial data
Thomas W. Baumgarte, Carsten Gundlach and David Hilditch
We report on numerical simulations of critical phenomena in the collapse of axisymmetric
vacuum gravitational waves, adopting families of initial data that, to the best of our knowledge, have not been used in this context before. Like Teukolsky waves, the data are based on linear wave solutions to the Einstein equations. We follow Nakamura's construction and encode the wave content in the extrinsic
curvature rather than the spatial
curvature, which leads to several simplifications when the data are "dressed up" so that they satisfy the nonlinear constraint equations. We are able to fine-tune these data to the onset of black hole formation slightly better than in our previous simulations, allowing us to observe and examine one more echo in the approximately self-similar threshold solution. Our findings are consistent with earlier studies: while we find threshold solutions that are approximately discretely self-similar, the self-similarity is not exact, and we find no evidence for a unique critical solution. We discuss common features between the different threshold solutions, including the appearance of alternating maxima in the direction of the poles and the equator.
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High Energy Astrophysical Phenomena
A hidden ultra-relativistic spine in the jet of a neutrino-associated blazar
Y. Y. Kovalev, F. Eppel, D. C. Homan et al. (+16 more)
Supermassive black holes launch powerful jets of
plasma that can accelerate particles to extreme energies, but the physical conditions required to produce high-energy
neutrinos remain unknown. In the blazar TXS 0506+056, the first source individually linked to a high-energy
neutrino,
radio images had seemed to reveal a jet too slow to sustain the extreme conditions required for
neutrino production. Here we resolve this tension using long-term
radio monitoring, particularly Very Long Baseline Interferometry (VLBI) imaging. We uncover a disturbance in emission propagating with an apparent speed of 21+-1 times the speed of light, that is masked by slower,
radio-bright features that dominated earlier analyses. We interpret this as the signature of a stratified jet: an ultra-relativistic spine with Lorentz factor Gamma>20 embedded within a slower outer sheath. As the disturbance travels along the spine, it progressively illuminates the sheath, producing the delayed
radio flare and naturally accounting for the years-long offset between
neutrino and
radio emission. The same pattern recurs in a second
neutrino-associated event, pointing to a repeatable multi-messenger engine. These findings challenge the standard interpretation of VLBI jet speeds and establish a concrete, testable framework connecting structured jets to the sources of the Universe's highest-energy
neutrinos.
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All authors Y. Y. Kovalev, F. Eppel, D. C. Homan, A. V. Plavin, P. Benke, A. K. Erkenov, J. L. Gomez, M. Kadler, K. I. Kellermann, P. I. Kivokurtseva, Yu. A. Kovalev, M. L. Lister, V. A. Makeev, A. V. Popkov, A. B. Pushkarev, E. Ros, T. Savolainen, Yu. V. Sotnikova, S. V. Troitsky
General Relativity and Quantum Cosmology
Massive scalar fields in eccentric regime: Detectability and constraints from LISA observations of extreme mass-ratio inspirals
Tieguang Zi, Shailesh Kumar, Genliang Li et al. (+3 more)
Extreme mass-ratio inspirals (EMRIs) are among the most promising sources for future space-based gravitational wave (GW) observatories and provide sensitive probes of additional fundamental fields in the strong-
gravity regime. In the present work, we investigate eccentric equatorial EMRIs around Kerr black holes in the presence of a massive scalar field. We assume that the inspiralling object carries a scalar charge, therefore, emits scalar radiation in addition to GWs. By solving the massive scalar perturbation equation in the frequency domain, we compute the relativistic scalar energy fluxes at the event horizon and at infinity and incorporate them into an adiabatic inspiral model. We investigate the impact of the scalar charge and scalar field mass on the orbital
evolution and gravitational waveforms by analysing the accumulated phase differences and waveform mismatches relative to both general relativity (GR) and the massless scalar limit. Our results show that the massive scalar radiation can produce significant GW dephasing, with the effect becoming increasingly pronounced for more eccentric orbits. In addition, the scalar flux is suppressed for larger scalar field masses as fewer scalar harmonics satisfy the propagation condition at infinity. Finally, using both Fisher-information-
matrix forecasts and
Bayesian parameter estimation, we assess the capability of the
Laser Interferometer Space
Antenna to constrain the scalar charge and scalar field mass. The two inference approaches gives consistent constraints, demonstrating that eccentric EMRIs provide a promising avenue for probing massive scalar fields and scalar-tensor extensions of
gravity in the strong-field regime.
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All authors Tieguang Zi, Shailesh Kumar, Genliang Li, Jun-Kun Zhao, Bao-Min Gu, Fu-Wen Shu
Quantum Physics
Multi-parameter two-photon polarimetry at the quantum limit
Joseph Niblo, Luca Maggio, Russell M. J. Brooks et al. (+3 more)
Photonic
quantum metrology has demonstrated advantages in precision and resource efficiency for a wide range of applications, with several schemes approaching the fundamental
quantum Cramér-Rao precision bound (QCRB). However, the intrinsic incompatibility of
quantum measurements represents a hurdle in extending these advantages to the simultaneous estimation of multiple parameters. In this paper, we present an experimental protocol approaching the QCRB simultaneously in two polarisation parameters, across a wide range of the parameter space, with as few as $\sim 200$
photon pairs, offering advantages for polarimetric sensing for dim sources such as in X-ray astronomy or photosensitive samples.
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All authors Joseph Niblo, Luca Maggio, Russell M. J. Brooks, Joseph Ho, Vincenzo Tamma, Alessandro Fedrizzi
Astrophysics of Galaxies
SEEDZ: Rapid Galaxy Assembly as a Pathway to Supermassive Stars, Dense Stellar Environments and Massive Black Hole Seeds
Lewis R. Prole, John A. Regan, Daxal Mehta et al. (+14 more)
We investigate the assembly history of early
galaxies in the SEEDZ hydrodynamic simulations, to investigate the high inflow rates believed to be required for the formation of supermassive
stars (SMSs), dense
stellar clusters and subsequently heavy seed black holes. Using a heavy seed formation criteria of $>$1 M$_\odot$ yr$^{-1}$ flowing into 10 pc regions, we find that heavy seeds form in
halos that grow rapidly compared to those
halos that never meet the criteria.
Halos with growth rates of $\gtrsim$1 M$_\odot$ yr$^{-1}$ at their virial radius (scales of a few hundred pc) are able to sustain a flow rate of 0.1 M$_\odot$ yr$^{-1}$ into the inner 1 pc of the
halo, maintaining higher density environments within the central 10 - 100~pc. These
halos continue to grow rapidly after their initial collapse, typically forming heavy seeds $\sim$100 Myr after forming their first
stars and
stellar mass black holes. By $z=10$, most heavy seeds form in regions of near-
solar metallicity, although a minority of heavy seeds do continue to form in low
metallicity (10$^{-2}$ Z$_\odot$) regions. Under the assumption that a SMS forms as the progenitor to a heavy seed if it forms in a region of low (10$^{-2}$ Z$_\odot$)
metallicity, and can sustain high
accretion rates above 0.02 M$_\odot$ yr$^{-1}$ throughout the SMS lifetime of 2 Myr, we find a number density of SMSs of 0.1 cMpc$^{-3}$, meaning that only a fraction of 10$^{-4}$ of these SMSs would need to be visible to JWST to account for the observed population of Little Red Dot
galaxies.
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All authors Lewis R. Prole, John A. Regan, Daxal Mehta, Devesh Nandal, Rüdiger Pakmor, Ricarda S. Beckmann, Michael Tremmel, Martin G. Haehnelt, Simon C.O. Glover, Ralf S. Klessen, John H. Wise, Sophie Koudmani, Martin A. Bourne, Debora Sijacki, John Brennan, Pelle van de Bor, Paul C. Clark
Astrophysics of Galaxies
Too shy to spin? Cosmic wallflowers as proto-globular clusters
Floor van Donkelaar, Lucio Mayer and Pedro R. Capelo
We investigate the rotational properties of
star-forming clusters at $z \sim 7.6$ in the high-resolution simulation MassiveBlackPS, focusing on two formation channels: clusters forming in
galactic discs via gravitational instability and isolated circumgalactic systems, referred to as
cosmic wallflowers, born out of
cosmic filaments. Using
stellar kinematics, we compare their rotational velocities, $v_{\rm rot}$, and rotational support, $v/\sigma$, to study whether formation environment leaves a clear dynamical imprint. We find a clear separation, wherein
cosmic wallflowers systematically have lower rotational velocities and span a wide range in $v/\sigma$, whereas the identified disc clusters are strongly rotation-dominated and extend to higher $v_{\rm rot}$. When combined with
stellar surface densities, a subset of the low-$v_{\rm rot}$
cosmic wallflowers lie surprisingly close to the observed globular cluster population in the Milky Way, whereas disc clusters remain offset. Within the
cosmic wallflower population, we identify two regimes: lower-density, weakly rotating systems that overlap with these globular cluster properties, and denser, more rotationally supported systems that likely follow a different evolutionary pathway, possibly linking them to the origin of massive black hole seeds at high
redshift. We further find that the gas content correlates with this behaviour, with gas-rich
cosmic wallflowers preferentially occupying this low-rotation regime. This all suggests that environment and baryonic content together play a key role in setting the initial dynamical state and possible fate of clusters. In particular, weakly rotating, gas-rich
cosmic wallflowers emerge as natural proto-globular cluster candidates, potentially evolving towards present-day systems through angular momentum loss and dynamical heating.
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High Energy Astrophysical Phenomena
Impact of neutrino-electron scattering and an improved treatment of pair processes on binary neutron star mergers
Francois Foucart, Samantha Rath, Rowan Davidson et al. (+5 more)
Multimessenger observations of
neutron star mergers are unique opportunities to constrain the properties of dense matter and the production site of heavy
nuclei. To leverage these observations, we require reliable models of the electromagnetic signals powered by mergers. An important limitation to our ability to develop such models is the use of approximate
neutrino physics in simulations. Here, we present simulations using an improved version of our Monte Carlo transport
algorithm specifically designed to allow for more advanced on-the-fly calculations of reaction rates that use the simulated energy distribution of
neutrinos, including in blocking factors, while still relying on approximations for the angular distribution of
neutrinos. We use these new methods to include in simulations inelastic scattering of
neutrinos on electrons, and to improve our treatment of
neutrino-antineutrino pair annihilation. We find that, without increasing the cost of simulations, we can marginally get to the point when the addition of a single packet represents a change $\Delta f_\nu<1$ in the angle-integrated distribution function, at the cost of increased shot noise in the coupling to the fluid. With inelastic scattering and a better treatment of pair processes, we find a reduction in the average energy and total luminosity of heavy-
lepton neutrinos, and an increase in the amount of mass ejected – here by $50\%$, although on a relatively low amount of total ejected mass $<0.005M_\odot$. In a separate set of simulations varying the total mass of the binary away from its
prompt collapse threshold, we find rapid variations in the amount of ejected matter and in the geometry and composition of the
outflows with the total mass of the system. Finally, we use the simulations with our more advanced transport scheme to study in more detail the energy spectrum of
neutrinos across the merger remnant.
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All authors Francois Foucart, Samantha Rath, Rowan Davidson, Patrick Chi-Kit Cheong, Matthew D. Duez, Lawrence Kidder, Harald Pfeiffer, Mark Scheel
Quantum Physics
Engineering of non-Hermitian interactions in digital qudit quantum simulators
Matteo M. Wauters, Paolo Boschetto, Edoardo Ballini et al. (+2 more)
Non-Hermitian
Hamiltonians are a fascinating class of many-body models that describe the effective dynamics of
quantum systems interacting with the environment through particle, energy, or information exchange. Although their theoretical framework is well established, the controlled engineering of such
Hamiltonians in the context of
quantum simulations remains challenging, even more so when the non-Hermitian part describes a $k$-body interaction. Qudit
quantum simulators offer a compelling framework to implement such models. We theoretically investigate the dynamics of a one-dimensional chain of qudits undergoing hybrid
unitary-projective
evolution, where suitably designed measurements constrain the dynamics to a Zeno subspace. As we illustrate for the case of qutrits, within the Zeno subspace the dynamics is governed by an effective non-Hermitian
Hamiltonian for an ensemble of pseudo-
spins $1/2$, which can inherit non-Hermitian two-body interactions with the same connectivity as the full qutrit chain. We derive an analytical relation linking the monitored qutrits'
evolution to a desired target non-Hermitian
Hamiltonian and validate the effective description through numerical simulations of a representative model. Our scheme provides a constructive route for the realization of a large class of interacting non-Hermitian many-body
Hamiltonians in experimentally relevant multilevel
quantum platforms, including trapped ions and superconducting
circuits.
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All authors Matteo M. Wauters, Paolo Boschetto, Edoardo Ballini, Alberto Biella, Philipp Hauke
Astrophysics of Galaxies
Analytical and fitting formulae for solutions to Lyman-alpha radiative transfer equations: the effects of geometry, recoil, and velocity gradients
Pengfei Li and Zheng Zheng
Lyman-alpha (Ly$\alpha$) radiative transfer (RT) is important in many astrophysical environments and governed by multiple physical processes. In this paper, we provide analytical formulae/procedures for the solutions to Ly$\alpha$ RT equations under three simple geometrical
symmetries and investigate the effects of atomic
recoil and gas bulk motion. We first study Ly$\alpha$ spectra by solving Ly$\alpha$ RT equations for a static, uniform gas cloud under cylindrical geometry. The solution is verified through Ly$\alpha$ Monte Carlo RT simulations, and compared to those under slab and spherical geometries in literature. Second, to characterise the
recoil effect, we empirically modify
recoil-free Ly$\alpha$ spectra. The method is motivated by Ly$\alpha$ RT equations with
recoil and justified by simulations. Finally, we account for constant velocity gradients in Ly$\alpha$ RT equations and obtain series solutions for Ly$\alpha$ spectra. The solutions demonstrate good agreement to Ly$\alpha$ spectra from simulations for small velocity gradients (i.e. edge velocity $v_{\rm E}$ of a cloud being comparable to the thermal velocity $b$) but become less accurate for large ones. To characterise Ly$\alpha$ spectra under large velocity gradients, we empirically extend the functional form of solutions and constrain them from fitting simulated Ly$\alpha$ spectra. The resulting fitting formulae show significant improvement for large velocity gradients ($v_{\rm E}/b \sim 100$) under large optical depths. The analytical study of Ly$\alpha$ spectra in this work completes the set of solutions under simple geometries, provides physical insights for Ly$\alpha$ RT under
recoil and velocity gradient, and develops analytical tools for theoretical studies that require inputs from Ly$\alpha$ RT.
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Strongly Correlated Electrons
Magnetic long-range order at finite temperature in two-dimensional hyperbolic lattices
Alexander Hickey and Joseph Maciejko
Infrared singularities of gapless Goldstone modes preclude
magnetic long-range order at finite temperature in conventional two-dimensional systems. By studying the
spin-$S$ Heisenberg model on regular tilings of the
hyperbolic plane, we show that this obstruction is absent in negatively curved space. Using
spin-wave theory, we find that the zero-energy collective modes required by
symmetry carry vanishing local spectral weight and are separated from the thermodynamic bulk
magnon continuum by a finite gap in the bulk local spectral density. As a result, local transverse correlations remain short ranged, with a finite correlation length, despite the presence of Goldstone modes associated with the broken SO(3)
spin-rotation
symmetry. Stronger negative
curvature is found to suppress
quantum fluctuations in bulk thermodynamic quantities, pushing the ordered state toward "mean-field-like" behavior. We further estimate the ordering temperature from the thermal
spin-wave correction to the ordered moment. These results establish
hyperbolic geometry as a route to finite-temperature
magnetic order that circumvents the Mermin-Wagner obstruction without breaking or modifying the continuous
symmetry.
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High Energy Physics (Theory)
Observing Massive Scattering from Null Infinity
Walker Melton, Kyrill Michaelsen and Romain Ruzziconi
Because massive particles asymptote to timelike rather than null infinity, current flat space
holographic proposals such as celestial or Carrollian holography struggle to describe scattering processes with massive external states. We take a step toward addressing this limitation by studying how information about massive scattering amplitudes is carried to the late-time limit of null infinity by soft graviton radiation. We show that continuity between the boundaries of timelike and null infinity implies that the late-time limit of the Bondi mass aspect naturally acts as a detector operator for massive outgoing radiation. We further relate in-in correlation functions of the Bondi mass aspect at $\mathscr{I}^+_+$ to weighted sums of scattering cross sections, implying that an observer at $\mathscr{I}$ can extract information about massive scattering processes at late times. Finally, we interpret the Bondi mass aspect as a Carrollian stress-tensor component, and study Ward identities to constrain its two-point functions.
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High Energy Physics (Phenomenology)
Machine learning fully hadronic events with spectral functions
Mohammad Mahdi Altakach, Hadi Hassan, Sabine Kraml et al. (+2 more)
Characterising fully hadronic events is a difficult task at
hadron colliders. Signal jets from the hard process are mingled with an arbitrary number of ISR and FSR jets, leading to a large combinatorial background. This also poses a challenge for machine-learning analyses, where the number of input features is fixed while the jet multiplicity fluctuates from event to event due to QCD radiation. In this work, we explore the use of the two-point correlation spectral function as an input feature for machine-learning analyses of such events. The spectral function maps the transverse-momentum data of an event into a one-dimensional function of the angular distance, encoding the event information modulo
collider isometries and jet permutations, and is defined independently of the jet multiplicity. As a concrete
benchmark we apply the method to discriminate gluino-pair production followed by $\tilde{g} \to t \bar{t} \tilde{\chi}_1^0$ against the fully hadronic $t \bar{t}$ background. With $139~{\rm fb}^{-1}$ of $\sqrt{s} = 13$ TeV $pp$ collision data, a dense neural network supplied with spectral-function features improves the expected reach in gluino-mass by roughly 150 GeV relative to a recent ATLAS analysis, and by roughly 250 GeV relative to the same network trained on jet kinematics alone.
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All authors Mohammad Mahdi Altakach, Hadi Hassan, Sabine Kraml, Kazuki Sakurai, Haitham Zaraket
Earth and Planetary Astrophysics
Revisiting the picture of circumbinary disc truncation
Enrico Ragusa, Elliot Lynch, Guillaume Laibe et al. (+1 more)
Circumbinary discs are observed to develop central cavities carved by the gravitational influence of the binary. Analytical estimates of cavity sizes predict truncation at $\sim 2 \textrm{--} 3$ binary separations, depending on the binary properties. However, numerical studies show only qualitative agreement with these predictions: cavity sizes often evolve on long timescales and can exceed substantially the analytically predicted values. In this work, we revise this paradigm, suggesting that
tidal truncation in circumbinary discs responds to additional dynamical parameters that have so far been neglected. We analyse a suite of 80 numerical simulations of circumbinary discs to re-examine the physical mechanism responsible for cavity truncation and to provide a prescription for the cavity size independent of the state of
evolution of the system. We find that truncation depends not only on the binary parameters $a_{\rm bin}$, $e_{\rm bin}$, and mass ratio $q$, but also on the instantaneous cavity eccentricity $e_{\rm cav}$ and the relative apsidal orientation $\varpi_{\rm bin}-\varpi_{\rm cav}$. These quantities jointly determine the pericentre of the innermost stable disc orbit $R_{\rm p}$, in a way that shares some similarities with orbital stability in the restricted three body problem. Hydrodynamical effects introduce secondary corrections, with the disc scale height $H$ and viscosity $\alpha$ mildly shifting the cavity edge relative to the purely gravitational prediction. We introduce a semi-analytical prescription that captures these dependences for $R_{\rm p}$ and cavity semi-major axis $a_{\rm cav}$. We conclude that cavity truncation for binaries with mass ratios $q>0.05$ is a process where the instantaneous orbital properties of the disc ($e_{\rm cav}$, $\varpi_{\rm cav}$) play a fundamental role and should be taken into account to accurately evaluate the truncation efficiency.
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All authors Enrico Ragusa, Elliot Lynch, Guillaume Laibe, Richard Alexander
Cosmology and Nongalactic Astrophysics
Unveiling the Microhertz Gravitational-Wave Sky with the Square Kilometre Array Observatory
Alexander C. Jenkins, Diego Blas and Joshua W. Foster
The gravitational-wave sky is expected to contain a rich variety of sources across a very broad range of frequencies. Much like in electromagnetic astronomy, exploring new gravitational-wave frequency bands therefore has the potential to unlock powerful new insights into the Universe. In this chapter, we investigate the prospects for using high-precision timing of binary millisecond
pulsars with the Square Kilometre Array Observatory (SKAO) to search for gravitational waves in the microhertz ($\mu$Hz) frequency band by targeting resonant gravitational-wave perturbations to the orbits of these binaries. Using only a handful of known systems, we show that SKAO observations can achieve unprecedented sensitivity to microhertz gravitational waves, with the potential to detect inspiralling massive black hole binaries in this band. These searches are complementary to conventional
pulsar timing array analyses, adding a new dimension to the gravitational-wave science achievable with the SKAO.
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High Energy Astrophysical Phenomena
Discriminating blazar emission models with high-energy polarimetry: Multi-band predictions and detectability
Sara Capecchiacci, Ioannis Liodakis, Haocheng Zhang et al. (+2 more)
Polarimetric properties of blazars provide key constraints on the acceleration mechanisms powering their relativistic jets, the high-energy emission processes involved, and the composition of the jet itself. We present a multi-band polarimetric study spanning from soft X-rays to gamma-ray energies, considering several bands for current and future missions (0.275 keV, 2-8 keV, 0.5-10 keV, 6-35 keV, 0.2-5 MeV, and 1-100 GeV). Our sample is drawn from the RoboPol monitoring programme, a statistically complete gamma-ray sample including low-, intermediate-, and high-synchrotron-peaked blazars. Using spectral energy distribution fitting performed with the Bjet_MCMC tool, we give predictions on the flux expected for each source in the selected energy bands. We model the polarimetric signatures under three competing emission scenarios: leptonic, hadronic, and hybrid. The detectability of each source was assessed by accounting for the instruments' minimum detectable polarisation (MDP) and by computing the probability of the detection in a blind survey. We show that simultaneous multi-wavelength observations can effectively discriminate between competing emission models due to the difference in the expected polarisation degree. Finally, we derive sensitivity requirements for future gamma-ray polarimetric missions aimed at increasing the number of detectable sources.
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All authors Sara Capecchiacci, Ioannis Liodakis, Haocheng Zhang, Michela Negro, Jorge Otero-Santos
Superconductivity
Elimination of Flux Trapping in Superconducting Circuits in Ambient Magnetic Fields
Rohan T. Kapur, Alex Wynn, Sergey K. Tolpygo et al. (+10 more)
Superconductor digital electronics and
quantum computing with superconducting
qubits are promising next-generation computing technologies. When cooled down or operated in the presence of a nonzero background
magnetic field $B_r$, superconducting thin films comprising the
circuits can trap
magnetic vortices that can degrade
circuit or
qubit performance. In this work, we report a practical solution for eliminating flux trapped during cooldown in ambient
magnetic fields, $B_r\leq 60$ $\upmu$T, based on controlled local thermal gradients and moats, etched holes in the superconducting films of the
circuit. Thermal gradients created by integrated on-chip resistive heaters move
vortices towards the moats, where they become trapped away from circuitry regions and pinning sites. Using
magnetic imaging and electrical
circuit readout, we demonstrate that this approach is capable of removing
magnetic flux trapped during field cooling and
magnetic flux nucleated by
circuit operation. If used in an environment with basic
magnetic shielding, this solution is capable of suppressing all
magnetic flux in a large-scale
circuit, overcoming one of the long-standing challenges preventing high-performance scalable computing using
superconductors.
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All authors Rohan T. Kapur, Alex Wynn, Sergey K. Tolpygo, Neel Parmar, Anil Mankame, Adam A. Libson, Rabindra Das, Michele Kelley, Pauli Kehayias, Nathaniel J. O'Connor, Collin N. Muniz, Justin L. Mallek, Jennifer M. Schloss
Instrumentation and Methods for Astrophysics
The Karl G. Jansky Very Large Array Sky Survey (VLASS). Data Products
Amy Kimball, Mark Lacy, Juergen Ott et al. (+5 more)
The VLA Sky Survey (VLASS) is a
radio continuum survey of the entire sky visible to the VLA (dec > -40deg) at ~2.5 arcsecond resolution over 2-4 GHz with full polarization. Data processing and quality assurance have proven challenging due to limited computing and staff resources, and require innovative approaches. Although "Quick Look" images in Stokes I continuum were produced within a few weeks of observation, high accuracy images that utilize the full potential of the
dataset are computationally intensive and take much longer to produce. Half of the sky will need correction for w-terms to account for sky
curvature, increasing the computational cost per image by ~100x. This problem will be tackled using GPUs and High-Throughput Computing (HTC) centers. Quality assurance of the tens of thousands of individual images has used a mix of algorithmic and machine learning techniques to automatically identify common artifacts and anomalies in the data. Archiving and dissemination of VLASS data products also pose a significant challenge.
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All authors Amy Kimball, Mark Lacy, Juergen Ott, John Tobin, Tierra Candelaria, Sergio Garza, Drew Medlin, Steven T. Myers
Quantum Physics
Compression-Driven Anomaly Detection in Brain MRI Using an Interpretable Quantum Autoencoder
Santanu Ganguly, Xing Liang and Dimitrios Makris
We study a
quantum autoencoder (QAE) for compression-driven anomaly detection in
brain MRI data. The approach leverages angle encoding to map image patches into
quantum states, followed by a variational encoder-decoder architecture trained to discard information via auxiliary trash
qubits. Anomaly scores reflect the degree to which inputs resist compression relative to normal data, with higher scores corresponding to deviations from the learned normal
manifold. Evaluated on publicly available
brain MRI DICOM
datasets, the method achieves a slice-level ROC-AUC of approximately 0.95 and a patch-level ROC-AUC of approximately 0.813, outperforming classical autoencoder and PCA baselines. Analysis of the learned parameters reveals a pronounced encoder-decoder asymmetry, where effective anomaly detection arises from structured information compression within the encoder rather than increased parameter magnitude or decoder expressivity. This results in a controlled compression-reconstruction trade-off with a clear operating regime that supports principled threshold selection. Qualitative evaluation further shows that the QAE produces spatially localized anomaly heatmaps aligned with tumorous regions. The results, supported by promising baseline performances, demonstrate that
quantum autoencoders provide an interpretable and controllable mechanism for anomaly detection based on incompressibility with respect to a learned latent representation. This work highlights the potential of
quantum autoencoders as a principled tool for studying compression dynamics in
quantum machine learning, with promising implications for decision support in medical imaging workflows.
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Plasma Physics
Collective modes and screening in an electric-magnetic dual plasma
Hyeong-Chan Kim
We study the linear response of an effective relativistic two-fluid medium carrying separately conserved electric and
magnetic charge currents. The model is defined by the duality-symmetric Maxwell equations with electric and
magnetic sources, together with Lorentz-force dynamics for two fluids with independent inertia and possible Carter-type entrainment. The
magnetic component is treated as an effective charge-carrying constituent, so the analysis uses only the closed two-fluid equations. Around a homogeneous, neutral, and unmagnetized background, the transverse electromagnetic response contains two stable branches whose cutoffs are set by the electric and
magnetic plasma frequencies and are exchanged by electric–
magnetic duality. In the longitudinal sector, entrainment mixes the electric and
magnetic density oscillations, turns their crossing into an avoided crossing, and gives the stability condition $ \kappa^2<1 ,$ equivalent to positive definiteness of the two-fluid momentum
matrix. Resolving the
magnetic component into monopole and antimonopole species gives a neutral branch selected by
magnetic charge conjugation \(C_m\). In this branch the net
magnetic current vanishes, so the long-range monopole field is absent, while the total
magnetic density can still produce screened collective response. The resulting picture is that
magnetic charge can be statically hidden but dynamically visible. A robust observable signature is the density scaling $\omega_{\rm coll}^2\sim\omega_{pm}^2\propto n^0_{(m)},$ which may survive dissipative broadening even when sharp ideal-
plasma poles are not resolved. We briefly comment on possible dyonic interpretations of magnetically neutral composites, but the linear-response results do not rely on that interpretation.
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Quantum Physics
Reservoir-independent lossless charging and protected storage of an open quantum battery
Asad Ali, H.Kuniyil, M.I Hussain et al. (+3 more)
A
quantum battery charged through a lossy intermediate state faces a structural trade-off between charging speed and dissipation. We show that an exact algebraic cancellation removes it in a driven three-level
cell: the radiatively decaying state is fed by a single bright amplitude, and a counterdiabatic field annuls the lone residual source that drives it, holding the lossy state identically empty. Charging is then lossless – not one
photon is emitted through the bridge – at any one-
photon detuning, coupling, linewidth, and speed down to the rotating-wave limit, with no adiabatic elimination, so the charging power is bounded by the drive amplitude (a
quantum speed limit) rather than by dissipation. Crucially, this losslessness is independent of the reservoir: because the dark sector never engages the system-bath coupling, the emission vanishes exactly for an arbitrary spectral density, Markovian or not, as an exact damped-pseudomode treatment confirms to machine precision across all
memory times. The entire non-Hermitian structure – a Markovian second-order exceptional point that reservoir
memory promotes to a third-order one, and the attendant dissipation phase diagram – lives in the bright sector, from which the protocol is by construction exempt. This inverts dissipation-engineered charging, where an exceptional point or reservoir
memory is a resource; here the lossy sector is never populated at all. The same dark-state structure protects the stored charge, converting fast radiative self-discharge into the slow metastable lifetime, with residuals quadratic in the control error. We detail experimental requirements and representative parameters for neutral alkaline-earth atoms, trapped ions, transmons, and defect centers.
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All authors Asad Ali, H.Kuniyil, M.I Hussain, M.T Rahim, Saif Al-Kuwari, James Q.Quach
Mesoscale and Nanoscale Physics
Dirac fermions in non-Hermitian magnetic fields: Zero modes and index theorem
Christopher A. Leong and Bitan Roy
In a Lorentz symmetric non-Hermitian (NH) Dirac theory, containing the canonical relativistic
Hamiltonian accompanied by a masslike anti-Hermitian Dirac operator, when the associated NH parameter becomes spatially modulated it couples massless Dirac
fermions as NH gauge fields. With specific choices of such resulting NH gauge potential, the system experiences NH
magnetic fields. When a planar Dirac system encloses a finite flux of such NH
magnetic fields, a
manifold of spatially localized right or left zero-energy eigenmodes appear in the spectrum, which we numerically anchor from microscopic realizations of NH
magnetic fields on
graphene's honeycomb
lattice. Potential experimental platforms to test these predictions are discussed. Altogether, zero-energy NH flat bands of right or left modes promise fascinating future realizations of NH
magnetic catalysis, strongly-coupled NH fractional topological phases, and NH
chiral anomaly, to name a few.
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Strongly Correlated Electrons
Hidden-ordered Dirac fermions
Bitan Roy
I propose a Hermitian extension of the Lorentz-symmetric Dirac theory by complementing the associated
Hamiltonian with another masslike anticommuting Dirac operator. The resulting theory manifests the iconic linear energy-momentum relationship in any dimension ($d$) and hence the emergent nodal quasiparticle excitations are named hidden-ordered Dirac
fermions, which are
symmetry protected and their responses are analogous to those in original Dirac systems, however, in terms of a renormalized (due to the hidden ordering)
Fermi velocity. Typically, such a hidden ordering pushes any
quantum phase transition into an insulation toward even stronger coupling in any $d>1$. However, depending on the internal
algebra between the candidate insulating order parameter and masslike Dirac operator, the hidden-ordering may survive or disappear near the corresponding itinerant
quantum critical point. I construct
lattice models for such hidden-ordered massless Dirac
fermions and outline promising platforms (numerical and experimental) to test these predictions.
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Optics
Accessing both electrochemical SEIRA and SERS with ultrasensitive metamaterials for enhanced molecular identification
Nicolas Spiesshofer, Tabitha Jones, Sarah May Sibug Torres et al. (+11 more)
Surface-enhanced IR absorption (SEIRA) and surface-enhanced Raman spectroscopy (SERS) are complementary techniques that allow for ultrasensitive chemical fingerprinting. Non-invasive optical sensing would be significantly improved by a robust implementation of a reusable substrate that combines these techniques. Here, we present an electrochemically-cleanable metamaterial that enables combined real-time SEIRA and SERS in flow. This metamaterial facilitates the study of surface-adsorbed species and
diffusion layers, elicits spectral shifts from changes in nanogap refractive index of 1400 nm/RIU, and delivers ultrasensitive analyte detection. Combining SERS and SEIRA clarifies molecular (electro)chemical transformations and tracks changes in selection rules and
symmetry breaking at the analyte-electrode interface. This development in enhanced
multimodal spectro-electrochemistry is suited for multiple domains, including understanding charge transport mechanisms and interfacial dynamics at electrodes, and is capable of real-time flow monitoring for a wide range of molecular processes.
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All authors Nicolas Spiesshofer, Tabitha Jones, Sarah May Sibug Torres, Zoltan Sztranyovszky, Caleb Todd, Shijie Zhu, Yeeun Roh, Rakesh Arul, Alexander Squires, Ivana Qianqi Lin, Angela Demtriadou, David O. Scanlon, Viv Lindo, Jeremy J. Baumberg
Mathematical Physics
Integration against POVMs in von Neumann algebras and Operational Quantum Reference Frames
Jan Głowacki and Yui Kuramochi
We construct integrals of uniformly bounded ultraweakly measurable functions against positive operator-valued measures (POVMs) in von Neumann
algebras, assuming that the integrand
algebra has separable predual. The integral lies in the spatial tensor product and is uniquely characterized by its evaluations on product normal states. Integration is unital and completely positive and descends faithfully to the quotient by POVM-null functions. When both preduals are separable, this quotient is a von Neumann
algebra and integration is normal, agreeing with the amplification of scalar POVM integration. We establish a dilation factorization, a Leibniz rule and a Fubini
theorem, and specify the additional joint-normality hypothesis needed for realization in an ambient
algebra. As an application, under the stated separability and joint-normality assumptions, we extend operational
quantum reference frame relativization to covariant POVMs on arbitrary measurable spaces carrying a group action. Its domain is the fixed-point von Neumann
algebra of system-valued functions modulo null equality. For homogeneous spaces of second countable locally compact Hausdorff groups with closed stabilizers, this domain is identified with the stabilizer-fixed system
algebra. For sharp frames, relativization is a normal unital $*$-homomorphism, faithful when ambient multiplication is injective. For localizable frames on metrizable spaces, restriction recovers continuous integrands at supported configurations. On trivial principal bundles, the domain is identified with system-valued fields on the base. These results provide integration machinery for forthcoming applications to relativistic gauge theories.
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