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Physics

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Wednesday 2 September

Cosmology and Nongalactic Astrophysics

Beyond isolated curvature peaks: collective collapse and multiple Primordial Black Hole formation

Albert Escrivà

Primordial black hole (PBH) calculations usually treat rare curvature peaks as isolated collapsing regions. Using fully nonlinear $3+1$ numerical-relativity simulations in a radiation-dominated Universe, we demonstrate that neighbouring primordial curvature perturbations need not map one-to-one onto PBHs: they may ultimately disperse, collapse collectively into a single PBH, or undergo distinct local collapses and form more than one PBH. In the family of two-component profiles studied here, the latter outcome is a pair of PBHs, identified by the coexistence of two disconnected apparent horizons on at least one time slice. We introduce a nonspherical quasi-local compaction diagnostic based on the Hawking mass and referenced to a round flat-FLRW sphere of equal area. It retains the angular structure of the curvature field and reduces to the standard Misner-Sharp compaction function in spherical symmetry. The global maximum of this diagnostic, $\mathcal K_{\rm form}$, provides an empirical indicator of whether at least one PBH forms, with a transition near $\mathcal K_{\rm form,c}\approx0.56$ and modest profile-dependent scatter. For forming bimodal profiles, we supplement the nonlinear compactness with a signed linear surface strength evaluated on the same probing spheres. The viability of the weaker local branch and the competition between the local and common-enclosing branches improve the empirical discrimination between single- and double-PBH outcomes. Our results therefore show that the maximum curvature amplitude alone does not determine the collapse outcome, which also depends on the spatial extent, characteristic scales, and geometry of the surrounding curvature environment.
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Quantum Physics

Resource-adaptive distributed fault tolerance with very noisy Bell pairs

Moritz Schmidt, Martin Moureau, Benjamin Rodatz et al. (+3 more)

Distributed architectures have been proposed as a pathway to large-scale quantum computers. Combined with the need for fault-tolerance, such architectures require distributed quantum error correction (DQEC) and distributed logical gates. An important challenge is how to realize DQEC primitives in the setting where interaction between modules is restricted to shared Bell pairs that are significantly noisier than on-chip operations. We extend the framework known as fault tolerance by construction to this setting, deriving different strategies for handling the additional noise. Through fault-improvement we recover conventional entanglement distillation, and also find more dynamical protocols that enable space-time trade-offs. We show that integrated decoding halves the required distillation code distance compared to entanglement distillation implemented using separate decoding, thus requiring significantly fewer Bell pairs. As a main focus of the work, we synthesize efficient circuits for an important primitive in distributed fault tolerance: distributed stabilizer measurements. These circuits can be adapted to resource constraints, e.g. on the Bell pair generation rate or the space available for on-chip auxiliary qubits. Noting that full local fault-tolerance is not always needed to preserve the correct scaling of logical error rates, we further optimize the circuits depending on the surrounding context. We consider in particular the surface code and the color code, both as distributed memories and in the case of lattice surgery across separate modules. Here, robustness to certain hook and readout errors reduces the number of required Bell pairs even further, compared to the context-free setting. We numerically benchmark the resulting implementations under circuit level noise with additional interconnect noise.
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All authors Moritz Schmidt, Martin Moureau, Benjamin Rodatz, Boldizsár Poór, Elie Mounzer, Linnea Grans-Samuelsson

Quantum Physics

Robust Hamiltonian engineering with subensemble control

Wenjie Gong, Matteo Votto and Soonwon Choi

We present a robust protocol to reshape interactions in a spin ensemble based on global control pulse sequences applied to multiple subensembles in parallel. This setting arises naturally from ensembles of solid-state defects or multi-species atomic arrays. We show that it is provably computationally hard to find pulse sequences that simultaneously engineer interactions both within and between subensembles. Despite its formal hardness, we identify a set of necessary or sufficient conditions under which one can synthesize a target Hamiltonian from the native one. Moreover, we introduce efficient numerical strategies for designing pulse sequences that engineer target Hamiltonians robust against common control imperfections. As a specific application, we discuss the robust generation of two-mode spin squeezing in dual-species atomic ensembles, which is a challenging task without subensemble control. Our results provide a practical toolbox to design novel quantum simulation and sensing experiments with minimal control overhead.
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Chemical Physics

Reactive calcium carbonate precipitation from an atomic cluster expansion potential and enhanced sampling

Eslam Ibrahim, Yury Lysogorskiy, Ralf Drautz et al. (+1 more)

Calcium carbonate formation from aqueous solution is central to biomineralization and to carbon sequestration through mineral carbonation. At near-neutral pH, the process is highly reactive, with proton transfer mediating the interconversion between carbonate species. Most atomistic simulations to date either treat carbonate speciation as fixed or consider proton transfer only in small clusters. Here, we combine an ab initio trained atomic cluster expansion (ACE) machine-learning potential for molecular dynamics with enhanced sampling to enable reactive simulations of the early stages of calcium carbonate precipitation at previously inaccessible length and time scales. We study proton transfer and carbonate speciation in ion pairs and triplets, as well as in the collective aggregation of many ions. Our simulations with few ions show that ion association provides a favorable pathway for proton transfer, facilitating interconversion between carbonate, bicarbonate, and carbonic acid. In many-ion systems, proton transfer occurs spontaneously alongside aggregation, and we observe significant changes in the coordination environments as species evolve during the simulations. These results show that ion aggregation and chemical reactivity can be strongly coupled during the early stages of nucleation from solution.
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All authors Eslam Ibrahim, Yury Lysogorskiy, Ralf Drautz, Pablo M. Piaggi

High Energy Physics (Theory)

Monstrous parafermionic defects and other non-invertible symmetries in chiral CFTs

Roberto Volpato

The structure of non-invertible symmetries in 2D CFT is closely tied to the algebra of preserved holomorphic fields, its representation theory, and its embedding in the full chiral algebra of the CFT. Unfortunately, finding new embeddings of a chiral algebra into another is a difficult mathematical problem, and one of the major obstacles in the pursue of new and exotic categories of non-invertible symmetries. In this work, we describe a simple general technique that leads to a number of new non-trivial results in this direction: (1) For the holomorphic Monster CFT $V^\natural$, we show that for every `Fricke' non-anomalous Monster element of order $N$, there is an embedding of the parafermion algebra $\frac{su(2)_N}{u(1)}$ in $V^\natural$, we compute the characters of its commutant, and describe the topological defects preserving these subalgebras. (2) We provide an easy-to-check sufficient condition for a holomorphic VOA $V$ to be self-orbifold under a cyclic group of (invertible) symmetries, and determine the associated duality defect. (3) We find several new topological defects in CFTs arising from heterotic strings on $T^4$. (4) We prove a number of VOA embeddings and topological defects in the Leech lattice CFT, in Schellekens theories, and other CFTs of various central charges, and suggest several generalizations of our methods.
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Materials Science

Interplay between Isomerization and Spin Crossover in 1D Fe-Indigo Coordination Polymers on Ag substrates

Ritam Chakraborty, Hongxiang Xu, Biao Yang et al. (+5 more)

Spin-crossover (SCO) compounds offer a route to switchable molecular functionality in reduced dimensions. However, one-dimensional (1D) SCO chains, which offer the possibility to study ligand fields other than the paradigmatic octahedral field, remain comparatively little studied. Here, we use first-principles density functional theory (DFT+$U$) to investigate Fe-indigo coordination-polymer chains synthesized experimentally on Ag(111) and Ag(100) substrates. These display a rich interplay between changes in ligand field (isomerization) and spin crossover. On-surface isomerization on Ag(111) interconverts (N,O)-chelated trans configuration and (N,N)-/(O,O)-chelated cis configurations at the Fe centers. The lowest-energy trans and cis solutions on Ag(111) have different spin configurations over the interval $0.66<U<3.00$~eV. At the reference value $U=1$~eV, the preferred trans solution is the mixed LS–LS–HS configuration, whereas the preferred cis solution is LS–LS–LS. The experimentally observed preference for cis chains on Ag(111) and trans chains on Ag(100) is reproduced for the range $0.88<U<3.75$~eV. To interpret these results, toy models and spin-resolved Fe $3d$ projected densities of states are used, while freestanding-chain calculations reveal a strain-sensitive LS–HS competition. These results provide a microscopic explanation for isomerization-controlled spin-state switching in a 1D coordination polymer.
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All authors Ritam Chakraborty, Hongxiang Xu, Biao Yang, Harshdeep Singh Chhabra, Joachim Reichert, Johannes V. Barth, Anthoula C. Papageorgiou, Shobhana Narasimhan

Quantum Physics

Stabilization of dark states in emitter arrays coupled to a half-waveguide

Oriol Rubies-Bigorda, Susanne F. Yelin, Ana Asenjo-Garcia et al. (+1 more)

The radiative properties of quantum emitters are profoundly influenced by their electromagnetic environment. When coupled to a waveguide terminated at one end by a mirror, distant emitters interact strongly via virtual photon exchange, leading to collective superradiant and subradiant states with enhanced or suppressed decay rates. We demonstrate that applying optimal frequency shifts to each emitter enables the formation of perfect single-excitation dark states (i.e. states with zero decay rate) and near-perfect multi-excitation dark states in small ensembles. These collective states can be deterministically prepared with high fidelity using classical driving fields or few-photon pulses propagating along the waveguide. These results, readily implementable in superconducting qubit platforms, open new avenues for quantum information storage, networking and control of light.
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All authors Oriol Rubies-Bigorda, Susanne F. Yelin, Ana Asenjo-Garcia, Stuart J. Masson

Quantum Physics

Nanoscale magnetometry via collective many-body dynamics in diamond

Haoyang Gao, Piotr Put, Nathaniel T. Leitao et al. (+9 more)

Many-body dynamics constitutes a promising approach for creating correlations between quantum particles which can be used for applications in sensing and metrology. However, utilizing this potential for substantial gains in practical settings is a challenging task with only a very few applications realized to date. Here, we demonstrate an approach to nanoscale magnetic sensing enabled by strongly interacting electronic spins in a room temperature solid. By coherently controlling collective many-body dynamics of a dipolar ensemble of $\sim 10^4$ nitrogen-vacancy (NV) centres in diamond with pulsed magnetic field gradients, we demonstrate practical metrological gain up to $7.9(2)\,\mathrm{dB}$ for magnetic signal detection and $8.8(3)\,\mathrm{dB}$ for magnetic noise sensing, fully accounting for experimental overheads. Finally, we combine these methods to demonstrate a momentum-space-resolved sensing modality that enables detection of spatially correlated magnetic noise at continuously tunable length scales down to 50 nanometers. These observations open the door toward practical applications of interaction-enhanced quantum sensors for nanoscale biological imaging and material characterization.
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All authors Haoyang Gao, Piotr Put, Nathaniel T. Leitao, Nazl{\i} U. Köylüoğlu, Andrew Maccabe, Mathew Mammen, Siddharth Dandavate, Lillian B. Hughes Wyatt, Leigh S. Martin, Ania C. Bleszynski Jayich, Hongkun Park, Mikhail D. Lukin

General Relativity and Quantum Cosmology

Scalar quasinormal modes of Kerr–AdS$_{\bf 7}$ via accessory parameter expansions

Julián Barragán Amado

We study scalar perturbations of a seven-dimensional Kerr–AdS black hole with three independent rotation parameters. In this geometry, the Klein–Gordon equation separates into one radial and two angular second-order linear ordinary differential equations, each with five regular singular points. We apply the Hill determinant method to compute analytic expansions of the accessory parameters in two different parameter regimes. The resulting accessory parameter expansions coincide with those obtained from the instanton part of the Nekrasov–Shatashvili function of four-dimensional $\mathcal{N}=2$ quiver gauge theories. These expansions are then used to derive perturbative expressions for the angular eigenvalues in the slowly rotating limit and for the quasinormal mode frequencies in the small black hole limit.
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Mathematical Physics

Estimating the asymptotics of integer partitions in intermediate dimensions ($d = 3,4,5,6$)

Avinandan Mondal

It was recently shown by Yeliussizov \cite{Yeliussizov} that integer partitions in dimensions $d \geq 7$ asymptotically grow strictly faster than MacMahon numbers. As MacMahon numbers match with integer partitions in dimensions $d = 1,2$, the comparison of asymptotics of integer partitions with MacMahon numbers in intermediate dimensions ($d = 3,4,5,6$) is an open question. In this work, we perform Markov chain Monte Carlo (MCMC) simulations till $N=15000$ by using adaptive weight learning followed by conventional MCMC steps to numerically estimate the asymptotics of integer partitions in these intermediate dimensions. We numerically establish that in these intermediate dimensions, partitions asymptotically grow faster than MacMahon numbers. More specifically, assuming that the limits exist, we show: $\lim_{n\to\infty}n^{-3/4}\log p_3(n) = 1.8196 \pm 0.0019$, $\lim_{n\to\infty}n^{-4/5}\log p_4(n) = 1.7215 \pm 0.0045$, $\lim_{n\to\infty}n^{-5/6}\log p_5(n) = 1.6521 \pm 0.0059$, and $\lim_{n\to\infty}\log n^{-6/7}p_6(n) = 1.652 \pm 0.021$ for partitions in dimensions $d=3,4,5,$ and $6$ respectively. These numbers are all larger than MacMahon leading order asymptotic coefficients of $1.7898, 1.6614, 1.5737,$ and $1.509$ respectively. Additionally, we also find estimates for some of the sub-leading asymptotic terms in $\log p_d(n)$ in each of the dimensions.
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Quantum Physics

Approximate cubic phase states in a trapped ion

C. Ventura-Velázquez and Juan Mauricio Torres

Universal quantum computation with continuous variables cannot be attained solely with a set of Gaussian operations, it requires the addition of a non-Gaussian element, at least of third order in the quadrature operators, such as the cubic phase state. In this work, we present a method to generate a quantum state in the vibrational mode of a trapped ion that exhibits characteristics compatible with the cubic phase state, such as the distinctive oscillating pattern in its Wigner function. This state emerges from the nonlinear Jaynes-Cummings interaction native to the trapped-ion model, and under the assumption of an initial coherent vibrational state with a large occupation number. Consequently, the evolved vibrational state approximates the cubic phase state with high fidelity, and we use the variance of a nonlinear combination of the quadratures to characterize it. Finally, we provide an analytical expression for its cubicity that shows the high performance of the approximate vibrational cubic phase state.
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Earth and Planetary Astrophysics

New and Updated Rossiter-McLaughlin Measurements for Three Hot Jupiter-Hosting M Dwarfs

Drew Weisserman, Ryan Cloutier, Alexandra Rochon et al. (+12 more)

Evidence suggests that Kozai-Lidov high-eccentricity migration (HEM) is the dominant migration channel for short-period Giant Exoplanets around M dwarf Stars (GEMS). However, it is unlikely that all short-period GEMS form via HEM, given that most systems lack known massive companions capable of driving HEM. Characterizing the stellar obliquities of GEMS via the Rossiter-McLaughlin (RM) effect can help shed light on the dynamical histories of GEMS. We present RM effect detections for the GEMS TOI-5205 b, TIC 46432937 b, and TOI-3714 b using the Gemini-North/MAROON-X spectrograph, bringing the total number of GEMS with RM detections to five. Our systems are well-aligned, with sky-projected obliquities of $\lambda = 0 \pm 6^\circ$, $3_{-3}^{+4}$$^\circ$, and $15_{-8}^{+12}$$^\circ$, respectively, and we measure a deprojected obliquity of $\psi = 24_{-8}^{+7}$ $^\circ$ for TOI-3714. We analyze archival radial velocities, astrometry, and speckle imaging data to search for additional companions around all five known GEMS with RM detections. We find tentative evidence for a new massive companion around one of these GEMS, TOI-5293 A, in Gaia DR2+DR3 data, though further follow-up is needed for confirmation. We rule out massive companions between $\sim 1-10\textrm{ AU}$ in the remaining systems, but cannot rule out all companions capable of driving HEM. Our findings present further evidence that short-period GEMS are preferentially aligned. While current results remain consistent with both primordial alignment and HEM plus tidal damping, we offer future directions for studies to further constrain the dominant migration channel for GEMS.
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All authors Drew Weisserman, Ryan Cloutier, Alexandra Rochon, Ze'ev Vladimir, Bertram Bitsch, Ritvik Basant, Jacob L. Bean, Tanya Das, Emily Deibert, Thomas M. Evans-Soma, Michael Line, Ralph Pudritz, Andreas Seifahrt, Evgenya L. Shkolnik, Luis Welbanks

Earth and Planetary Astrophysics

JWST MIRI reveals a potential atmosphere on the ultra-hot rocky planet TOI-431b

Cole Smith, Brandon Park Coy, Megan Weiner Mansfield et al. (+13 more)

An open question in exoplanet science is whether rocky exoplanets extremely close in to their host stars, `lava worlds', can retain significant atmospheres. Thermal emission observations via secondary eclipse can be used to determine whether a rocky exoplanet possesses an atmosphere. It is expected that an atmosphere could increase the planet's albedo and/or redistribute heat away from the dayside, reducing the secondary eclipse depth measured. Recent eclipse observations of lava planets, rocky planets hot enough to have liquid magma surfaces, have suggested the presence of atmospheres. Here, we present a single JWST MIRI/LRS partial secondary eclipse of the lava planet TOI-431b. We measure an eclipse depth of 81 $\pm$ 16 ppm, which corresponds to a brightness temperature of $1967^{+237}_{-253}$ K and a brightness temperature ratio R = $0.81\pm0.10$, being 1.2 $\sigma$ higher than the value reported by Spitzer. The observed brightness temperature ratio is 1.8$\sigma$ below that of a zero-albedo, zero heat redistribution bare rock (R=1). Given that magma pools are expected to have low albedos, we find that our results are best explained by the presence of an atmosphere. Future work to measure the exact composition of TOI-431b's atmosphere and improve models of lava planet atmospheres would better constrain the nature and evolution of lava planets.
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All authors Cole Smith, Brandon Park Coy, Megan Weiner Mansfield, Rafael Luque, Anjali A. A. Piette, Qiao Xue, Michael Zhang, Jacob L. Bean, Madison Brady, Peter Gao, Jegug Ih, Eliza M.-R. Kempton, Edwin Kite, Daniel Koll, Jaume Orell, Enric Palle

Instrumentation and Methods for Astrophysics

A fast, wide-field, and real-time imaging prototype for large aperture arrays

Nithyanandan Thyagarajan, Jishnu Thekkeppattu and David Humphrey

Real-time processing on sub-millisecond timescales is essential for detecting fast astrophysical transients such as fast radio bursts (FRBs) and prompt electromagnetic counterparts to gravitational-wave mergers. Immediate localisation enables rapid multi-wavelength follow-up and maximises scientific return. As a result, real-time capability has become a key requirement for modern wide-field aperture arrays, which are increasingly being deployed at scales of thousands to tens of thousands of antenna elements. However, traditional correlator architectures scale as $\mathcal{O}(N^2)$, creating significant computational, bandwidth, and power challenges for large-$N$ arrays. These constraints often limit field of view, angular resolution, or observing duty cycle, ultimately reducing transient discovery potential. Direct imaging of the full field of view using E-field Parallel Imaging “Correlator” (EPIC) offers a promising alternative by avoiding the explicit formation of pairwise correlations. EPIC can achieve $\mathcal{O}(N \log N)$ computational scaling for dense aperture arrays and has been demonstrated on the Long Wavelength Array (LWA) station in Sevilleta (USA) using Graphics Processing Unit (GPU). However, GPU implementations can be limited by memory bandwidth in low-bitwidth gridding and Fast Fourier Transform (FFT) workloads. We, therefore, are developing a prototype implementation of EPIC using Field Programmable Gate Arrays (FPGA) that exploits highly parallel FFT pipelines to improve computational efficiency and reduce power consumption. Using preliminary results, we evaluate its performance particularly from the viewpoint of scalability, and discuss its suitability for next-generation instruments including SKA-Low and mid-frequency aperture arrays.
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General Relativity and Quantum Cosmology

DANSur_HM: Modularly incorporating higher modes in a deep learning based gravitational-wave surrogate

Osvaldo Gramaxo Freitas, Anastasios Theodoropoulos, Nino Villanueva et al. (+4 more)

Numerical relativity (NR) simulations provide the most faithful representation of the gravitational waves (GWs) emitted by binary black hole (BBH) systems during merger. In the context of GW astronomy, tasks such as parameter estimation can require vast numbers of waveform evaluations per second across the entire parameter space. Since performing full NR simulations for each evaluation is not computationally feasible, interpolating methods for existing NR waveforms, known as surrogate models, have been developed with marked success. In this paper, we build on our previous work to introduce methods to train a fast surrogate model based on neural networks in order to generate BBH merger waveforms, including the fundamental (2,2) mode, as well as the (3,3), (2,1), (4,4), (3,2), (4,3) and (5,5) higher-order modes. Applying a pretraining step on approximant data before fine-tuning on NR data allows us to smooth out the parameter space, and making use of the parallelization ability of GPUs to project the NR waveforms in the inclination-phase $(\iota, \phi)$ sphere during training allows the fitting of all the explored modes simultaneously. The developed surrogate model, DANSur\_HM, achieves average mismatches of the order of $10^{-4}$, with the worst mismatch at $2.5\times10^{-3}$, and achieves throughput above $6\times10^5$ waveforms/second on an NVIDIA V100 GPU. Parameter estimation tests confirm the usefulness of the inclusion of higher modes.
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All authors Osvaldo Gramaxo Freitas, Anastasios Theodoropoulos, Nino Villanueva, José A. Font, Antonio Onofre, Alejandro Torres-Forné, José D. Martin-Guerrero

High Energy Physics (Theory)

Holographic zeros and poles from apparent singularities

Edwan Préau

We study general holographic fluctuation equations with apparent singularities, and the associated spectral functions. We consider the regime where an apparent singularity approaches the boundary, for which the near-boundary behavior of solutions can be determined via an inner/outer matching type of calculation. Depending on properties of the equation, we find that the merging of an apparent singularity with the boundary may generate either a zero or a pole for the corresponding spectral function. Our results also indicate that the recently introduced holographic product formula still applies in the presence of apparent singularities.
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Astrophysics of Galaxies

Evolution of bar-induced dark gaps in galaxy discs: evidence of strong bar-driven effects already at $z > 2$

Susnata Chattopadhyay, Soumavo Ghosh, Dimitri A. Gadotti et al. (+5 more)

The properties of stellar bars play a crucial role in determining the bar-driven secular evolution in disc galaxies. However, a systematic observational study of the evolution of several bar properties (such as strength and length) across cosmic time is largely missing. In this paper, using a sample of $625$ barred galaxies, taken from SDSS, HST COSMOS, and JWST CEERS surveys, we systematically investigate the evolution of bar properties over redshifts ($0.02 \lesssim z < 3$) by making a novel usage of dark gap (preferential light deficit along the bar minor axis) properties as a proxy for bar properties. We show that the dark gap strength ($\Delta \mu_{\rm max}$) exhibits a weak evolution, increasing from higher redshifts ($z \sim 2.5$) and slightly declining towards lower redshifts ($z < 0.05$). Conversely, the extent of dark gaps ($R_{\rm DG}, R_{\rm dark}$; normalised by bar length) decreases moderately from $z \geq 1.4$ and remains constant thereafter. Our results suggest that bar formation and the initial rapid growth phase occur before $z \sim 3$, followed by mild growth towards lower redshifts. We also find $R_{\rm dark}$ to be a better proxy (as compared to $R_{\rm DG}$) for estimating bar length, supporting earlier theoretical studies. Furthermore, the $\Delta \mu_{\rm max}$ shows a weak but statistically significant correlation with bar-to-total light ratio (Bar/T) and bar ellipticity ($\epsilon_{\rm bar}$). Studies of the redshift evolution of bar properties over such an extensive redshift range as done here are instrumental in constraining the bar-driven evolution at early cosmic times.
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All authors Susnata Chattopadhyay, Soumavo Ghosh, Dimitri A. Gadotti, Zoe A. Le Conte, Taehyun Kim, Virginia Cuomo, Camila de Sá-Freitas, E. Athanassoula

Quantum Physics

Quantum low-density lattice codes

Timo Hillmann, Jens Eisert and Francesco Arzani

Gottesman-Kitaev-Preskill (GKP) codes provide a family of promising schemes for encoding discrete quantum information (qudits) into infinite-dimensional bosonic modes based on mathematical lattices. While such codes, when concatenated with discrete-variable codes, are relatively well studied, the construction and decoding of native GKP codes has largely remained open due to the computationally hard problems encountered. To address this challenge, we advocate a strategy of co-designing the decoder and the quantum error-correcting code itself by constructing lattices for which decoding is feasible: The requirement of efficient decoding effectively determines the quantum error-correcting code. This construction is built on classical low-density lattice codes (LDLCs), a lattice analogue of low-density parity-check codes, here lifted to families of GKP codes. Concretely, we introduce quantum versions of classical, randomly constructed LDLCs. We show that after suitable dimensionality reduction these codes have code properties comparable to or better than concatenated GKP-surface codes of equal number of modes. However, the GKP-LDLCs constructed here do not have a strictly sparse parity check matrix, which motivates our study of the performance of natively analog message-passing decoders originally developed for LDLCs when applied to concatenated GKP-LDPC codes. We show that the fully analog, linear-time decoder achieves performances close to state-of-the-art hybrid qubit-analog decoders. To facilitate future research on the structure and performance of general GKP codes, the relevant source code will be released in open-source Julia packages LatticeDecoder.jl and SymplecticGKP.jl.
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Mesoscale and Nanoscale Physics

Tuning Andreev reflection and conductance in proximitized nanowires through the spin-orbit field direction

Leonardo Musca and Fabrizio Dolcini

We investigate the Andreev reflection (AR) and the nonlinear conductance in a normal-superconductor junction realized with a proximitized semiconductor nanowire exposed to a magnetic field along its axis. We show that, while at zero energy the AR coefficient is determined by the topological phase of the superconducting side of the junction, at finite energy the AR is strongly affected by the directions of the Rashba spin-orbit field characterizing the normal and the proximitized sides. The tunability of the AR and the nonlinear conductance as a function of the spin-orbit misalignment angle is particularly pronounced when the proximitized side is in the topologically trivial phase. The spin-orbit field direction is revealed to be an efficient knob to control the electron transport through the hybrid junction, realizing an electrically widely tunable device. The implementation in realistic setups is discussed.
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High Energy Astrophysical Phenomena

Multi-epoch Detection of an Ultra-fast Inflow in ESP 39607: Evidence for an Accretion Cascade

Alessandro Peca, Michael J. Koss, Roberto Serafinelli et al. (+10 more)

We present simultaneous XRISM, XMM-Newton, and NuSTAR observations of ESP 39607, a Seyfert 2 galaxy at $z = 0.201$. XRISM/Resolve reveals two absorption features near 4.7 and 4.9 keV in the observed frame, consistent with redshifted Fe XXV He-$\alpha$/Fe XXVI Ly-$\alpha$ absorption from gas inflowing at $v_{\rm in} \simeq 0.16c$. The high velocity identifies the absorber as an ultra-fast inflow (UFI), which is detected at $\sim 3$-$3.7\sigma$ across different methods and continuum models. Photoionization modeling yields $\log \xi/{\rm erg\,s^{-1}\,cm} \simeq 3.7$-$3.8$ and a column density $\log N_{\rm H,abs}/{\rm cm^{-2}} \simeq 23.2$-$23.8$, the latter depending on the assumed metallicity. The inflow velocity and line properties are consistent with those reported from two earlier NuSTAR epochs, indicating that similar inflowing material was present over a baseline of at least 2.2 yr in the source rest frame. Across all three epochs, the combined detection significance of the UFI is $5.3\sigma$. Given the dynamical timescale of a few days at the inferred radius, $R \simeq 49$-$77\,R_{\rm g}$, the multi-year evidence favors a scenario in which the inflow is continuously replenished, forming an accretion "cascade", rather than a single long-lived cloud. With an estimated mass inflow rate of $\dot{M}_{\rm in} \simeq 0.3$-$1.4\,M_\odot$ yr$^{-1}$, depending on metallicity, and a ratio $\dot{M}_{\rm in}/\dot{M}_{\rm acc} \simeq 0.2$-$1.0$, the inflow could supply a substantial fraction of the accretion needed to power the central active galactic nucleus.
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All authors Alessandro Peca, Michael J. Koss, Roberto Serafinelli, C. Megan Urry, Claudio Ricci, Keigo Fukumura, Massimo Gaspari, Elias Kammoun, Alessia Tortosa, Giulia Cerini, Peter G. Boorman, Richard Mushotzky, Quirino D'Amato

Solar and Stellar Astrophysics

The scarcity of white dwarf-brown dwarf binaries in the solar neighbourhood: A population synthesis study

Alejandro Santos-García, Santiago Torres, Alberto Rebassa-Mansergas et al. (+3 more)

White dwarf–brown dwarf (WD–BD) binaries are intrinsically rare systems that provide a unique opportunity to study binary evolution and the formation of substellar companions. Despite recent observational progress, only a small number are known in the solar neighbourhood. We investigate whether their scarcity can be explained by binary formation and evolution together with observational selection effects. We extend the MRBIN binary population synthesis code into the substellar regime by incorporating brown dwarf evolutionary models and an extended initial mass function. We simulate the stellar population within 100 pc of the Sun and compare the predicted WD–BD population with the observed sample. Our simulations predict 13+-5 WD–BD systems within 100 pc, consistent with observations. These systems represent only 0.1% of the local white dwarf population, confirming their rarity. The models reproduce the overall distributions of white dwarf masses, temperatures, and orbital periods, although the simulated brown dwarfs are systematically hotter than observed. Close WD–BD binaries are underproduced with the standard common-envelope efficiency 0.3, suggesting that higher efficiencies may be required to reproduce the observed short-period systems. The simulations also reproduce the observed deficit of systems at intermediate orbital periods between post-common-envelope binaries and wide non-interacting systems, as well as a weakened brown dwarf desert in main-sequence–brown dwarf binaries.
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All authors Alejandro Santos-García, Santiago Torres, Alberto Rebassa-Mansergas, Sarah L. Casewell, Zhangliang Chen, Hongwei Ge

High Energy Physics (Phenomenology)

Strong Constraints on Line Signals from Dark Matter Annihilation in a Nearby Subhalo

Asier Salces Pérez, Thong T.Q. Nguyen, Pedro De la Torre Luque et al. (+1 more)

We present a dedicated search for monochromatic gamma-ray emission from a recently proposed nearby dark matter subhalo candidate. Using nearly 15 years of Fermi-LAT Pass 8 data, we perform a sliding-window search for gamma-ray lines between 10 and 300 GeV. We do not find any statistically significant evidence for a line signal. The largest excess occurs at $E_\gamma \simeq 28 \, {\rm GeV}$ with a local significance of $2.5\sigma$. We therefore derive 95% confidence level upper limits on the annihilation cross section for $\chi\chi \rightarrow \gamma\gamma$. Under the assumed NFW subhalo model, the resulting constraints are stronger than existing Galactic Center line limits over much of the explored mass range. We further translate these line constraints into bounds on well-motivated WIMP models, such as Higgs-portal and Wino dark matter scenarios, restricting previously open parameter regions consistent with thermal freeze-out as well as models associated with dark matter interpretations of the Galactic Center Excess.
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All authors Asier Salces Pérez, Thong T.Q. Nguyen, Pedro De la Torre Luque, Tim Linden

Astrophysics of Galaxies

Classical Cepheids in the Nuclear Stellar Disk: membership via dynamical analysis

M. De Leo, M. Zoccali, R. Albarracin et al. (+2 more)

(abridged) Four classical Cepheids have been associated to the Nuclear Stellar Disk (NSD), suggesting a burst of star formation 20 Myrs ago. In this work, we analyse all available data for these four Cepheids in order to gauge if they are bona fide members of the NSD or interlopers in the region. This allows to confirm or rule out the star formation burst hypothesised in the literature. Our dynamical analysis is based on an updated MWpotential that includes all components of the inner Galaxy. We conduct a thorough study of possible systematics, taking into account both observational errors and model dependencies. Our results suggest that only one Cepheid likely belongs to the NSD, while the orbits of other two extend well beyond it. Accounting for observational uncertainties, only 23-28 percent of the realisations sourced from the error distributions for the latter two are compatible with the NSD. For the fourth there are no proper motion measurements available and the light curve analysis puts into question its classification as a classical Cepheid. Through a comprehensive dynamical analysis of available data on the Cepheids attributed to the NSD, we gauged their membership to this structure. Out of the three Cepheids analysed in unprecedented depth, GCC-a is likely a member of the NSD while both GCC-b and GCC-c do not seem dynamically linked to it. Factoring in the observational uncertainties, a non-negligible percentage of the realisations for GCC-b and GCC-c are still compatible with the NSD, thus membership cannot be completely excluded for either with current data. The robust association of only one Cepheid casts doubt on the occurrence of a star formation episode in the NSD, about 20 Myrs ago.
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All authors M. De Leo, M. Zoccali, R. Albarracin, B. Acosta-Tripailao, J. Minniti

Quantum Physics

Shuttling-aware dynamical decoupling for quantum charge-coupled devices

Linus Schulte, Aaron Sander and Robert Wille

Dynamical decoupling (DD) helps maintain high-fidelity quantum computations by suppressing dephasing noise through carefully timed refocusing pulses. In quantum charge-coupled device (QCCD) architectures, however, where ions are shuttled throughout the device, transport constrains when pulses can be applied and affects the phase accumulated by an ion. Conventional DD methods do not account for shuttling and may therefore schedule pulses that must be omitted or shifted after transport scheduling, weakening the protection from dephasing. We therefore introduce shuttling-aware dynamical decoupling (SADD), an offline compiler pass that jointly selects refocusing pulses and local ion rerouting while preserving logical-gate timings and the total schedule length. In benchmark simulations, SADD improves average final-state fidelity over both the original schedules and a simple nearest-feasible Hahn-echo baseline when dephasing dominates control and transport errors and varies slowly enough for DD. Rerouting enables otherwise infeasible pulse timings, while spatial information about the noise can provide further gains. These benefits disappear, however, when the added transport introduces too much error. Overall, our results show that coordinating DD with ion transport is an effective compiler strategy for reducing dephasing in QCCD processors.
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High Energy Physics (Theory)

From $Z$ to $a$: High-temperature relations, subleading semi-universality, and conformal anomalies

Arnav Advant, Harsh Anand, Nathan Benjamin et al. (+6 more)

The free energy of any CFT, $ \ln Z(\beta; \omega_i)$, admits two expansions: high temperature ($\beta \rightarrow 0$) and fast rotation ($\omega_i \rightarrow 1$). We demonstrate that in $4d$, locality of the thermal effective action forces $\ln Z$ to take a simple analytic form at all orders in the high temperature expansion, and further imposes an infinite number of sharp relations on the coefficients in this expansion. All are homogeneous, except at order $\beta^1$ due to the Weyl anomaly. From this, the $a$-anomaly can be extracted from the partition function. The relations resum in the fast-spinning expansion into differential equations in $\beta$ obeyed by the semi-universal limit and its corrections. We verify the relations in a variety of CFTs. We generalize to any even $d$, but find no similar relations at odd $d$.
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All authors Arnav Advant, Harsh Anand, Nathan Benjamin, Vipul Kumar, Shiraz Minwalla, Jyotirmoy Mukherjee, Sridip Pal, Asikur Rahaman, Pabitra Ray

Cosmology and Nongalactic Astrophysics

Universal CMB Phase Coherence from Single-Field Inflation

Siméon Vareilles, Thomas Colas, Julien Grain et al. (+2 more)

The phase coherence of primordial perturbations shapes the acoustic peaks of the CMB and is regarded as a key signature of inflation. Inflationary scenarios at different energy scales, thus with different durations, are commonly expected to leave different levels of coherence. We show this expectation fails: because the curvature perturbation is conserved on super-Hubble scales, the coherence at recombination inherits a value fixed by the observed primordial spectrum alone. This holds irrespective of the inflationary energy scale and the subsequent expansion history.
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All authors Siméon Vareilles, Thomas Colas, Julien Grain, Federico Piazza, Vincent Vennin

High Energy Astrophysical Phenomena

Unlocking the QPE Mystery: Star-Disk Collisions in Realistic AGN Disks

Zhaohuan Zhu, Xiaoshan Huang, Yan-Fei Jiang et al. (+1 more)

Quasi-periodic eruptions (QPEs) are luminous, recurring soft X-ray outbursts observed in the nuclei of low-mass galaxies. They display two remarkable trends: outburst durations are $\sim$10-20% of the recurrence timescale, and longer bursts are more luminous. A promising theory that naturally explains the quasi-periodicity invokes collisions between a star on an extreme mass-ratio inspiral (EMRI) orbit and the accretion disk around the supermassive black hole. However, it remains unclear how this model reproduces the observed trends. We therefore carry out two-dimensional, multi-frequency radiation hydrodynamic (RH) simulations of star–disk collisions. Crucially, we adopt a more realistic circumnuclear disk structure from previous Radiation MHD simulations of sub-Eddington accretion disks. We find that the thick, puffed-up disk atmosphere, extending to $z/r\sim1$, causes different portions of the bow shock to break out at different times, producing prolonged thermal emission as the shock emerges through the breakout surface at $z/r\sim0.7$. The X-ray flare duration is set by the shock propagation time through the optically thick disk–a $\sim$10% of the orbital timescale, reproducing the observed duty cycle. A more oblique star-disk interaction yields a longer, more luminous flare. The realistic AGN disk models also exhibit a surface density $\Sigma\propto r^2$, giving a collisional energy $E\propto P^{2/3}$ that may explain the luminosity–period trend, especially for the weaker QPEs. Overall, we suggest that a more realistic circumnuclear disk structure can explain several observed QPE trends-and QPEs may, in turn, constrain the disk structure.
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All authors Zhaohuan Zhu, Xiaoshan Huang, Yan-Fei Jiang, Shunquan Huang

Astrophysics of Galaxies

Bridging integrated-light and resolved-star studies of Local Group dwarf spheroidals. A novel use of deep imaging based on amateur telescopes

Sergio Guerra Arencibia, Ignacio Trujillo, Mireia Montes et al. (+4 more)

Low-mass galaxies beyond the Local Group can only be studied through their integrated light, yet it remains unclear whether structural parameters inferred from integrated light are directly comparable to those obtained from resolved-star studies. Using new deep imaging obtained with small-aperture amateur telescopes, we analyse the classical dwarf spheroidals Leo II, Sculptor, and Fornax, whose stellar distributions have been extensively characterised through resolved-star studies. We find that the radial light distributions and effective radii inferred from integrated light are in excellent agreement with those derived from resolved stars, showing that resolved-star and integrated-light analyses can be placed within a common observational framework applicable across a broad range of distances. The two approaches are highly complementary: resolved-star analyses trace galaxies to very large radii but are limited by stellar crowding in their central regions, whereas integrated-light observations are insensitive to crowding and allow the inner stellar distribution to be traced to substantially smaller radii. The integrated-light analysis extends the structural analysis to radii up to an order of magnitude smaller than previous star-counting studies while significantly reducing the scatter in the measured profiles.
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All authors Sergio Guerra Arencibia, Ignacio Trujillo, Mireia Montes, Ignacio Ruiz Cejudo, Carlos Marrero-de la Rosa, Vicente Fontana, Aleix Roig

General Relativity and Quantum Cosmology

Excitation factors and exceptional points of Kerr-de Sitter quasinormal modes

Dario Rossi, Naritaka Oshita, Leonardo Gualtieri et al. (+1 more)

We compute the excitation factors of Kerr-de Sitter black hole quasinormal modes using two different techniques: a Heun function representation and an expansion of the solution in terms of hypergeometric functions. Exceptional points at which the complex frequencies of different overtones coincide are a generic feature of the Kerr-de Sitter quasinormal mode spectrum. Near exceptional points, the modes exhibit a "hysteresis phenomenon" that was previously found for Kerr black holes perturbed by massive fields and the absolute value of the excitation factors of the individual modes is significantly enhanced, while they acquire nearly opposite phases. We extrapolate the excitation factors to small values of the cosmological constant and find good agreement with previous calculations in the Kerr limit.
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All authors Dario Rossi, Naritaka Oshita, Leonardo Gualtieri, Emanuele Berti