<p>We present the first general relativistic, neutrino-radiation hydrodynamics simulations of accretion-induced collapse (AIC) extending to seconds after core bounce, using realistic hadron–quark hybrid equations of state (EOSs). A first-order QCD phase transition (PT) triggers a second dynamical collapse and the formation of a quasistable protohybrid star (PHS) with a deconfined quark core and a distinctive second neutrino burst. We find that the thermally suppressed onset of the mixed phase allows low-mass protoneutron stars to enter the hadron-quark mixed phase during long-term evolution, even for hybrid EOSs with high onset densities. In contrast to core-collapse supernovae (CCSNe), AIC models exhibit a tightly constrained onset mass with minimal EOS dependence, owing to the absence of a massive envelope and thus the reduced postbounce accretion. This enhances the sensitivity of neutrino observables in AIC to hybrid EOS properties. We establish empirical relations between PT onset density and neutrino signatures, revealing a distinct behavior in AIC not seen in CCSNe. Our results suggest that a single Galactic AIC neutrino detection could place strong constraints on QCD PT thresholds, hybrid EOS characteristics, and the existence of PHSs. PT in AIC may also produce gravitational waves, gamma-ray bursts, and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>r</mi></math>-process elements, motivating multidimensional simulations with rotation, magnetic fields, and improved microphysics for realistic multimessenger predictions.</p>

Denmark

Juno C.L. Chan

Germany

Harry Ho-Yin Ng

United States

Patrick Chi-Kit Cheong

Distinct neutrino signatures and onset condition of quark deconfinement in accretion-induced collapse of white dwarfs

We describe an electromagnetic system which is related to black hole production with Hawking radiation through the double copy. We consider the scattering of a massless scalar particle through a collapsing electromagnetic background — the single copy of Vaidya — and identify the Feynman diagrams that exponentiate in the geometric-optics limit. The Bogoliubov coefficients obtained from the diagrammatic approach are reproduced by a semiclassical ray-tracing computation of null rays in this same background. We discuss the thermodynamic interpretation of the resulting number distribution in light of the double copy.

United Kingdom

Rafael Aoude

Donal O’Connell

France

Matteo Sergola

Chris White

Hawking radiation meets the double copy

We investigate the structure of strange dwarfs, modeled as hybrid compact stars composed of a self bound strange quark matter core surrounded by a white dwarf like crust, within a fully relativistic framework. Static configurations are constructed by solving the Tolman Oppenheimer Volkoff equations, and uniformly rotating configurations are modeled within the Hartle-Thorne slow rotation expansion (to $$\mathcal{O}(\Omega ^2)$$ ). We therefore interpret results at large fractional spins conservatively, and use the Kepler frequency mainly as a reference scale for comparing different masses and models. The stellar matter is described using a hybrid equation of state, in which the crust is modeled by a degenerate electron-ion system and the core by the MIT Bag Model. By comparing strange dwarfs with conventional white dwarfs across a range of rotation rates, we show that rotation inflates the radius and can reduce (in a quantifiable way) the separation between the two families in the ($\textit{M}$, $\textit{R}$) plane, potentially masking structural signatures associated with the presence of a quark core. Our results highlight the importance of accounting for rotational effects when interpreting mass radius measurements and other global observables in the context of searches for exotic compact objects in current and future high precision surveys.

Brazil

Edson da Silva

Peru

José Arbañil

Geanderson Carvalho

Fridolin Weber

Rotating strange dwarfs and their indistinguishability from white dwarfs

We study ultralight scalar fields with quadratic couplings to Standard-Model fermions and derive strong constraints from white-dwarf mass-radius data. Such couplings source scalar profiles inside compact stars, shift fermion masses, and can produce a new ground state of matter. We analyze couplings to electrons and to nucleons, incorporating composition and finite-temperature effects in white dwarf structure and equations of state. We identify two robust observables: (i) $\textit{forbidden gaps}$-ranges of radii with no stable configurations — and (ii) characteristic $\textit{shape}$ distortions that drive white dwarf masses toward the Chandrasekhar limit (electron couplings) or shift the maximum mass (nucleon couplings). Confronting these predictions with precise measurements for Sirius B and Procyon B, together with the global white dwarf population, excludes large regions of unexplored parameter space and extends earlier QCD-axion-specific bounds to a broader class of scalar theories. Our stellar constraints rely only on sourcing and do not assume the scalar constitutes dark matter; where mass reductions are small, precision laboratory searches remain competitive. White-dwarf astrophysics thus provides a powerful, largely assumption-minimal probe of ultralight, quadratically coupled scalars.

Kai Bartnick

Israel

Konstantin Springmann

Switzerland

Stefan Stelzl

Andreas Weiler

$\textit{ϕ}$-dwarfs: white dwarfs probe quadratically coupled scalars

<p>Using magnetic white dwarfs as a case study, we show that the emission of sub-MeV bosons from stellar plasmas can be substantially modified in the presence of a magnetic field. In particular, the magnetic field-induced anisotropy and cyclotron resonance both significantly affect the in-medium dispersion relations of the Standard Model photon. As a result, resonant level crossing between photons and other light bosons occurs under environmental conditions that differ from the resonance criteria in unmagnetized environments. We find that the magnetic field opens additional regions within magnetic white dwarfs where resonance can occur. These findings motivate revisiting astrophysical constraints on light bosons in systems where the cyclotron frequency is comparable to or larger than the plasma frequency.</p>

Canada

Nirmalya Brahma

Ella Iles

Hugo Schérer

Katelin Schutz

Resonant axion and dark photon production in magnetic white dwarfs

The double copy relates scattering amplitudes and classical solutions in non-abelian gauge theories and gravity. As such, it is usually expressed in the conventional second-order formalisms in both theories corresponding to standard Yang-Mills theory, and the Einstein-Hilbert action in General Relativity. In this paper, we instead consider alternative formulations of gravity, which are known to terminate at finite order in the coupling at Lagrangian level. We focus in particular on the Chern-Simons-Witten (CSW) formulation in 2+1 dimensions, and argue that the double copy then becomes a doppelgänger relationship between gauge theory and gravity, allowing straightforward replacement of generators and structure constants in both theories. We show how explicit (multiple) static point-source solutions can be mapped in the two approaches, and use the CSW formalism to examine when double copies are expected to be possible, and when not. In addition, we present an explicit double copy between the Wong equations for colour charges, and the Mathisson-Papapetrou-Dixon equations for spinning particles, that extends also to higher dimensions.

Nathan Moynihan

Michael Reichenberg Ashby

The double copy as a doppelgänger

In this work, we investigate the relativistic structure of white dwarfs (WDs) within the framework of modified gravity theory <math altimg='si3.svg'><mrow><mi>f</mi><mrow><mo>(</mo><mi>R</mi><mo>,</mo><mi>T</mi><mo>,</mo><msub><mi>L</mi><mi>m</mi></msub><mo>)</mo></mrow><mo linebreak='goodbreak'>=</mo><mi>R</mi><mo linebreak='goodbreak'>+</mo><mi>&#945;</mi><mi>T</mi><msub><mi>L</mi><mi>m</mi></msub></mrow></math>, which introduces a non-minimal coupling between matter and curvature. Using a realistic equation of state (EoS) that includes contributions from a relativistic degenerate electron gas and ionic lattice effects, we solve the modified Tolman-Oppenheimer-Volkoff (TOV) equations for two standard choices of the matter Lagrangian density: <math altimg='si9.svg'><mrow><msub><mi>L</mi><mi>m</mi></msub><mo linebreak='goodbreak'>=</mo><mi>p</mi></mrow></math> and <math altimg='si6.svg'><mrow><msub><mi>L</mi><mi>m</mi></msub><mo linebreak='goodbreak'>=</mo><mo>&#8722;</mo><mi>&#961;</mi></mrow></math>. We show that the extra <italic>&#945;TL<inf>m</inf></italic> term significantly alters the mass-radius relation of WDs, especially at high central densities <math altimg='si11.svg'><mrow><mo>(</mo><msub><mi>&#961;</mi><mi>c</mi></msub><mo>&#8819;</mo><msup><mn>10</mn><mn>8</mn></msup><mo linebreak='goodbreak'>&#8722;</mo><msup><mn>10</mn><mn>9</mn></msup><mspace width='0.16em' /><mrow><mi mathvariant='normal'>g</mi></mrow><mo linebreak='goodbreak'>/</mo><mi>c</mi><msup><mi>m</mi><mn>3</mn></msup><mo>)</mo></mrow></math>, allowing for stable super-Chandrasekhar configurations. In particular, depending on the sign and magnitude of the parameter <italic>&#945;</italic>, the maximum mass can increase or decrease, and in some regimes, the usual critical point indicating the transition from stability to instability disappears. Our findings suggest that <italic>f</italic>( <italic>R, T, L<inf>m</inf></italic>) gravity provides a viable framework to explain the existence of massive WDs beyond the classical Chandrasekhar limit. Using Bayesian inference with WD observational data, we further constrain the coupling parameter <italic>&#945;</italic> for the two choices of the Lagrangian density <italic>L<inf>m</inf></italic>.

Edson Otoniel

Juan M.Z. Pretel

Clésio E. Mota

César O.V. Flores

Victor B.T. Alves

Franciele M. da Silva

White dwarf structure in <italic>f</italic>( <italic>R, T, L<inf>m</inf></italic>) gravity: Beyond the Chandrasekhar mass limit

The description of low-energy (“soft”) gravitons using universal theorems continues to attract attention. In this paper, we consider the emission of two soft gravitons, using a previously developed formalism that describes (next-to) soft graviton emission in terms of generalised Wilson lines (GWLs). Based on Schwinger’s proper time methods, the GWL allows for a systematic accounting of graviton emission from external hard particles in the amplitude, as well as from three-graviton vertices located off the individual worldlines. By combining these effects, previously derived results for the leading double soft graviton theorem are recovered. Still, the formalism allows us to go further in deriving new universal double soft graviton terms at subleading order in the momentum expansion. We further demonstrate how gauge invariance can be utilized to account for double soft graviton emissions within the non-radiative amplitude, including the effects of non-zero initial positions of the hard particles. Our results can be packaged into an exponential dressing operator, and we comment on possible applications to the effective field theory for binary scattering processes.

Taiwan

Karan Fernandes

Feng-Li Lin

Double soft graviton factors from the gravitational Wilson line

In this work, we present an exact solution describing a static, spherically symmetric black hole immersed in a cored Navarro–Frenk–White (NFW) dark matter halo. We examine the energy conditions and find that the null, weak, strong and dominant energy conditions are all satisfied, confirming the physical plausibility of our solution. Furthermore, we examine its optical and scalar perturbation properties, highlighting their connections to the Lyapunov exponent and black hole thermodynamics. By applying the principle of least action, we derive the null geodesics to study gravitational lensing and light ring phenomena in the presence of the dark matter halo. The stability of photon orbits is analyzed using the Lyapunov exponent, which we relate to the imaginary part of the massless quasinormal modes in the eikonal limit. We also investigate the thermodynamic behavior of the black hole–dark matter system by evaluating the mass function, entropy, temperature, heat capacity, Gibbs free energy and the entropy to assess both local and global stability. Overall, our results demonstrate that the surrounding dark matter halo significantly influences the black hole’s properties, enhancing its thermodynamic stability and allowing the possibility of phase transitions.

Thailand

David Senjaya

Cored Navarro-Frenk-White dark matter halo: novel black hole solution, energy condition, optical properties, quasinormal modes and thermodynamics

Upcoming space-based gravitational-wave detectors will be sensitive to millions and resolve tens of thousands of stellar-mass binary systems at mHz frequencies. The vast majority of these will be double white dwarfs in our Galaxy. The greatest part will remain unresolved, forming an incoherent stochastic foreground signal. Using state-of-the-art galactic models for the formation and evolution of binary white dwarfs and accurate LISA simulated signals, we introduce a test for foreground Gaussianity and stationarity, building on methods available for ground-based detectors. We explain the observed non-stationarity with a new analytical modulation induced by the LISA constellation motion and the intrinsic anisotropy of the source distribution. By demodulating the foreground signal, we reveal a deviation from Gaussianity in the 2–10 mHz frequency band. Our finding is crucial to design faithful data models: the proposed method serves as a diagnostic and estimation tool to flag and model deviations, respectively. Neglecting them would introduce systematic biases on individual sources and astrophysical foregrounds parameter estimation, ultimately leading to inaccurate interpretation of the LISA data.

Italy

Riccardo Buscicchio

Antoine Klein

Valeriya Korol

Francesco Renzo

Christopher Moore

Davide Gerosa

Alessandro Carzaniga

Test for LISA foreground Gaussianity and stationarity: galactic white-dwarf binaries