Cosmology and Nongalactic Astrophysics · Cross-listed from physics.ins-det
Cryogenic sub-Hz cROss torsion bar detector with quantum NOn-demolition Speed meter (CHRONOS) for gravitational wave detection
Yuki Inoue, Daiki Tanabe, M.Afif Ismail et al. (+3 more)
We present the optical design and sensitivity modeling of the Cryogenic sub-Hz cROss torsion-bar detector with
quantum NOn-demolition Speed meter (CHRONOS), a triangular Sagnac speed-meter interferometer incorporating power and signal recycling. Using ABCD-
matrix analysis and Finesse3 simulations, we obtain stable optical eigenmodes with mode-matching efficiencies above 99.5%. The optimized configuration achieves a
quantum-noise-limited strain sensitivity of $h \simeq 3\times10^{-18},\mathrm{Hz^{-1/2}}$ at 1 Hz, with a ring-cavity finesse of $\mathcal{F}\simeq3.1\times10^{4}$ and a round-trip Gouy phase of $\psi\approx153^{\circ}$. The low-frequency
quantum noise is primarily governed by the power-recycling cavity detuning, while the signal-recycling cavity produces an approximately uniform quadrature rotation. An optimal homodyne angle of $\zeta\simeq46^{\circ}$ provides the best sensitivity near 1 Hz. Assuming an end-mirror reflectivity of $R_{\mathrm{ETM}}=99.9999%$ at 10 K, CHRONOS can achieve
quantum-noise-limited performance on a laboratory scale. Its projected science reach includes intermediate-mass black-hole binaries out to approximately $271,\mathrm{Mpc}$, a 10-year
stochastic-background sensitivity of $\Omega_{\mathrm{GW}}\simeq4.7\times10^{-4}$ at $2.15,\mathrm{Hz}$, constraints on Yukawa-type deviations from Newtonian
gravity, and
prompt gravity-gradient signals from nearby earthquakes.
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All authors Yuki Inoue, Daiki Tanabe, M.Afif Ismail, Vivek Kumar, Mario Juvenal S Onglao III, Ta-Chun Yu
Cosmology and Nongalactic Astrophysics · Cross-listed from physics.ins-det
Torque cancellation effect of Intensity noise for Cryogenic sub-Hz cROss torsion bar detector with quantum NOn-demolition Speed meter (CHRONOS)
Daiki Tanabe, Yuki Inoue, Vivek Kumar et al. (+2 more)
Detection of sub-Hz gravitational waves is of significant importance for astrophysics. It enables the observation of intermediate-mass black hole mergers, the issuance of early alerts for gravitational-wave events, and the exploration of the
stochastic gravitational-wave background. The Cryogenic sub-Hz cROss torsion-bar detector with
quantum NOn-demolition Speed meter (CHRONOS) is a proposed gravitational-wave detector based on a Sagnac speed-meter
topology that uses torsion bars as test masses. Its prototype design aims to achieve a strain sensitivity of $3 \times 10^{-18}~\mathrm{Hz}^{-1/2}$ at 1~Hz and thus enable the detection of $\mathcal{O}(10^4),M_\odot$ intermediate-mass black hole mergers at 100~Mpc with a signal-to-noise ratio of 3. We show that the torsion-bar-based speed meter can suppress noise originating from
laser intensity fluctuations by canceling the net torque on the bar and by using a balanced homodyne readout. We further present, for the first time, an analytic intensity-noise model for a gravitational-wave detector employing a torsion-bar Sagnac speed-meter configuration. Using this model, we evaluate the expected performance of a 2.5~m arm-length CHRONOS prototype. The projected
laser-intensity noise is $2.9 \times 10^{-20}~\mathrm{Hz}^{-1/2}$ at 1~Hz, which is sufficiently low to allow the detection of binary intermediate-mass black hole mergers.
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All authors Daiki Tanabe, Yuki Inoue, Vivek Kumar, Miftahul Ma'arif, Ta-Chun Yu
Earth and Planetary Astrophysics
Implications for the formation of Oort cloud-like structures and interstellar comets in dense environments
Santiago Torres
Most
stars form in dense
stellar environments, where frequent close encounters can strongly perturb and reshape the early architecture of planetary systems. The
solar system, with its rich population of distant comets, provides a natural laboratory to study these processes. We perform detailed numerical simulations using the LonelyPlanets framework that combines NBODY6++GPU and REBOUND, to explore the
evolution of debris disks around
solar system analogues embedded in
stellar clusters. Two initial configurations are considered, an $Extended$ and a $Compact$ model, each containing four
giant planets and either an extended or compact debris disk. We find that compact disks primarily form Kuiper belt and scattered disk-like populations through
planet-disk interactions, while extended disks are more strongly shaped by
stellar encounters, producing Oort cloud-like structures and interstellar comets with ejection velocities of 1-3 km/s.
Stellar perturbations are most effective for encounter inclinations between $0^{\circ}$ and $30^{\circ}$, giving rise to distinct dynamical populations, like Sednoids, and inner Oort cloud analogues, and a characteristic tail in semi-major axis-eccentricity space. In coplanar encounters, the disk remains largely flattened, whereas polar flybys redistribute angular momentum vertically, producing nearly isotropic outer populations that resemble an emerging Oort cloud. Our results suggest that cometary reservoirs and interstellar objects are natural byproducts of
planet-disk interactions and
stellar flybys in dense clusters, linking the architecture of outer planetary systems to their birth environments.
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High Energy Astrophysical Phenomena
Probing AGN-ISM Feedback through Extended X-ray Emission in ESO 137-G034
D.Ł. Król, G. Fabbiano, M. Elvis et al. (+6 more)
We present a detailed analysis of the X-ray emission of the Compton-thick (CT) AGN ESO\,137-G034 based on deep ($\sim230$\,ks) Chandra observations. As in other CT AGNs, the morphology of the emission is elongated, approximately following the [O III] ionization bicone. With spatially resolved spectral modeling, we show that the extended emission within the bi-cone regions { is most readily explained} as from a mixture of photo-ionized gas and shock-heated
plasma, reflecting the combined effects of radiative and kinematic AGN feedback. By comparing the morphology of the { X-ray emission in narrow spectral bands and that of the 3\,cm
radio jet, we find suggestive evidence of thermal, possibly shocked emission associated with the SE termination of the
radio jet. This interpretation is also supported by the lack of [O~III] relative to the $0.3-3.0$ keV flux in the inner $3^{\prime\prime}$ ($\sim600$\,pc) of the SE cone, which would be consistent with an additional thermal X-ray component on top of the photonized emission of an outflowing wind. A similar effect is only seen within the inner $1^{\prime\prime}$ ($200$\,pc) of the NW cone. In the radial profile of the [OIII]/X-ray flux ratio and the X-ray hardness ratio within the inner $\sim3^{\prime\prime}$ ($\sim600$\,pc) of the SE cone we see an asymmetry, with no counterpart in the NW cone. We detect soft extended X-ray emission in the cross-cones which may originate from the interaction of an embedded
radio jet with a clumpy interstellar medium (ISM). }These results highlight the { importance of both} radiative and mechanical feedback in shaping the circumnuclear environment of ESO\,137-G034.
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All authors D.Ł. Król, G. Fabbiano, M. Elvis, A. Trindade Falcão, R. Middei, D. Rosario, R. Davies, T. Shimizu, D. Hill
Astrophysics of Galaxies
High Resolution (<100pc) Ionization Structures in the ISM of AGN ESO~137-G34
D.Ł. Król, G. Fabbiano, M. Elvis et al. (+8 more)
We present a detailed, spatially resolved { Veilleux & Osterbrock (VO) diagram} analysis of ESO\,137-G034, a Compton-thick Active
Galactic Nucleus (AGN), based on narrowband HST imaging in [O~III], [S~II], H$\alpha$, and H$\beta$ emission lines. The narrowband optical emission exhibits a bi-conical morphology and traces the diffuse X-ray emission observed with Chandra. We dissect the Interstellar Medium (ISM) into Seyfert-, LINER-, and H~II-dominated regions with a resolution of $\sim0.1^{\prime\prime}$ ($\sim20$\,pc at $z=0.009$). To { visualize} the fine spatial structure of the { ISM excitation}, we introduce a new parameter: the Seyfert/LINER Index (SLI), defined as the perpendicular distance of each point in the { VO} diagram from the Seyfert/LINER division line. { SLI mapping reveals fine spatial structures in the ISM excitation especially in the Seyfert ionization bi-cones where the statistical significance of our data is higher.} Most of the emission within the bi-cones is Seyfert-like, with SLI values consistent with regions of the { VO} diagram that can be modeled with AGN photoionization. In the North-West Seyfert cone three radial SLI peaks suggest episodic
nuclear outbursts, with estimated timescales of a few $10^3$\,yrs and $<100$\,yrs duration. The South-East cone shows inhomogeneous excitation, with a higher SLI region in its inner part, coinciding with a wider region of enhanced soft X-ray emission at the
radio lobe inner edge. This region is characterized by line ratios consistent with fast shocks ($>1000$\,km\,s$^{-1}$) induced excitation. The North-West cone is surrounded by a smooth LINER “cocoon”. The LINER region in the SE cone appears more irregular, with inter-cone LINER points likely shaped by both local ISM structure and shocks. Our findings highlight the complex interplay of different AGN feedback mechanisms in the ISM.
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All authors D.Ł. Król, G. Fabbiano, M. Elvis, A. Trindade Falcão, P.Zhu, L.J.Kewley, R. Middei, D. Rosario, R. Davies, T. Shimizu, D. Hill
High Energy Astrophysical Phenomena
Multivariate Time Series Classification of Fermi-Detected Gamma-Ray Transients Using Convolutional-Recurrent Neural Networks
Arpan Aryam John, Krushna Govind Shete, Shabnam Iyyani et al. (+1 more)
Fermi Gamma-ray Space
Telescope has detected a diverse range of gamma-ray transients since its launch in 2008. Over the years,
Fermi has accumulated an extensive public archive of transient events. Traditional classification methods for these events typically rely on fixed thresholds, localisation accuracy, and characteristic light curve features. However, in the current era of time-critical, multi-wavelength, and multi-messenger astronomy, rapid and reliable classification is essential to enable timely follow-up and coordinated observations. In this work, we develop and present two deep learning-based classifiers that integrate convolutional and recurrent neural network architectures. Using multivariate time-series inputs derived from
Fermi-GBM data, our models are trained to distinguish among four classes of gamma-ray transients: Gamma-Ray Bursts (GRBs), Terrestrial Gamma-ray Flashes (TGFs),
Solar Flares (SFLAREs), and Soft Gamma Repeaters (SGRs). Furthermore, the models are designed to flag events that do not conform to any of these categories, providing a pathway for identifying potentially new or rare transient types. Training was conducted using a carefully curated subset of high-confidence
Fermi events. The resulting models achieve an overall classification accuracy of 93%, and identify approximately 2.5% of the triggers as outliers of unknown origin. When applied to
Fermi events with uncertain classifications, our models assign 60% of them to the TGF category with over 60% confidence. These results demonstrate that incorporating deep learning-based classification into onboard or automated data pipelines can significantly enhance transient identification, minimize misclassification, and improve the discovery potential of new phenomena in future high-energy astrophysics missions.
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All authors Arpan Aryam John, Krushna Govind Shete, Shabnam Iyyani, Saptarshi Bej
Astrophysics of Galaxies
SHELLQs-JWST: Revealing the Spectra of Extended Emission in 12 z > 6 Quasar Host Galaxies using the JWST NIRSpec Fixed Slit
Camryn L. Phillips, Michael A. Strauss, Masafusa Onoue et al. (+15 more)
We present an analysis of the rest frame optical JWST NIRSpec Fixed Slit spectra of extended host
galaxy emission in 12
quasars from the Subaru High-z Exploration of Low-Luminosity
Quasars (SHELLQs) sample at
redshifts 6.0 < z < 6.4. The spatial point spread function is modeled primarily by a sum of two Gaussians as a function of wavelength and is used to fit and subtract the
quasar from the 2D spectra, leaving only extended
galaxy emission which we analyze. Ten of 12 systems show spatially extended line emission and five of 12 systems show an extended
stellar continuum. From the extended [OIII]5008 emission line, we measure a 132 ${\pm}$ 19 km/s ionized
outflow in one system and 52 ${\pm}$ 12 km/s rotation, suggesting a coherent disk, in another. From the extended narrow H${\alpha}$ emission, which we hypothesize is ionized by
star-forming regions rather than the
quasar, we measure
star formation rates ranging from ${\sim}$ 7 to 111 M${_\odot}$/yr, the majority of which are consistent with the
star-forming main sequence at z ${\approx}$ 6. The positions of our host
galaxies on the log10[OIII]5008/H${\beta}$ vs. log10[NII]6584/H${\alpha}$ (R3N2) Baldwin-Phillips-Terlevich (BPT) diagram indicate ionization rates typical of AGN activity in the low-
redshift universe, but are consistent with the placement of similar z ${\approx}$ 6
quasar host
galaxies, suggesting that the R3N2 line ratios cannot distinguish AGN and
star-formation powered line emission at high
redshifts. We conclude from the consistency between our
quasar host sample with z ${\sim}$ 6
galaxies that the presence of a low-luminosity AGN causes little significant change in the properties of
galaxies at z ${\approx}$ 6 on 10 Myr timescales.
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All authors Camryn L. Phillips, Michael A. Strauss, Masafusa Onoue, Xuheng Ding, John D. Silverman, Yoshiki Matsuoka, Takuma Izumi, Junya Arita, Kentaro Aoki, Shunsuke Baba, Masatoshi Imanishi, Nobunari Kashikawa, Toshihiro Kawaguchi, Chien-Hsiu Lee, Mahoshi Sawamura, Yoshiki Toba, Feige Wang, Jinyi Yang
High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Thermodynamic Geodesics in Bardeen Regular Black Hole: Conventional vs. Modified Geometrothermodynamics Metrics
Gunindra Krishna Mahanta
Thermodynamic geometry allow us to study the microscopic behavior of black hole system by defining a metric structure in thermodynamic phase space. Among the various thermodynamic metric structures, metrics defined by geometrothermodynamics (GTD) are extensively used to study the various thermodynamic system due to its Legendre invariant nature. In this work we investigate the behavior of thermodynamic geodesic of Bardeen regular black hole in thermodynamic space defined by three different GTD metrics. Based on the behavior of thermodynamic geodesic as well as thermodynamic
curvature we argued that conventional GTD metric need some modifications to reflect all the thermodynamical properties of a system. We also modified the conventional GTD metrics and explore the behavior of thermodynamic geodesic defined by the modified metrics. Our study shows that the modified GTD metrics contain most of the information about the thermodynamical boundaries such as temperature vanishing line, spinodal line etc. of a black hole system. Based on the property of geodesic and
Ricci scalar defined by the modified metrics we argued that the modified version of GTD metric are most suitable metric structures for studying the underlying thermodynamic behavior of a black hole system.
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Solar and Stellar Astrophysics
Instability and vertical eccentricity variation in global hydrodynamic disk simulations
Janosz W. Dewberry, Henrik N. Latter, Gordon I. Ogilvie et al. (+1 more)
Many dynamical interactions can induce eccentricities in astrophysical
accretion disks. Disk eccentricities in turn seed a variety of instabilities, even in ideal hydrodynamics. We use 3D nonlinear simulations and 2+1D linear calculations to characterize local and global instabilities in strongly distorted disks. On local scales, our simulations show the growth of parametrically excited inertial waves, which drive wave
turbulence. The inertial waves' growth rates and localizations agree with the predictions of local theory. On global scales, we observe the growth of a separate family of low-frequency, vertically structured modes that compare favorably with eigenmodes computed from the linear theory of an eccentric background state. These low-frequency modes interact nonlinearly with the inertial wave
turbulence driven by parametric instability, and they induce variation in eccentricity profiles that are initially uniform in the vertical direction. Extrapolating from our vertically local framework, we postulate that these secondary distortions may correspond to the corrugation of an initially planar eccentric disk. Our simulations demonstrate that strong disk eccentricities drive numerous dynamical phenomena even in a purely hydrodynamic, Newtonian framework.
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All authors Janosz W. Dewberry, Henrik N. Latter, Gordon I. Ogilvie, Sebastien Fromang
Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
Collective Properties of Gravitational Perturbations in Thermal Environments on a Dynamical Background
Atsuhisa Ota
A thermal
plasma dresses soft gauge fields, turning them into collective modes with a plasmon gap and Landau damping. In this paper, we ask whether a thermal radiation
plasma does the same to gravitational perturbations. For
gravity, the thermal soft scale coincides with the Hubble rate. Any such gap therefore lies at the horizon scale, where the expansion of the background cannot be neglected. We model radiation by a conformal scalar and compute its linear response to metric perturbations directly on a flat FLRW background. We test this response against the diffeomorphism Ward identities. The adiabatic dispersion relation yields a gapped collective mode with $\omega_p^2 = 8\mathcal{H}^2/5$, where $\mathcal{H}$ is the conformal Hubble rate. The imaginary part of its frequency, however, is dominated by the background expansion and does not represent Landau damping. In the radiation background, the tensor modes obey a real-time integro-differential equation that reproduces Weinberg's damping of gravitational waves. The initial-time boundary of the retarded response keeps superhorizon modes frozen until horizon reentry despite the gap. The superhorizon growth found in earlier analyses arises from discarding the
memory of the retarded response and from a local-
equilibrium state prescription that violates the Ward identities. More generally, the Ward identities forbid any local state response beyond the collisionless kernel.
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Astrophysics of Galaxies
SWIFTGalaxy: a Python package to work with particle groups from SWIFT simulations
Kyle A. Oman
SWIFTGalaxy is an open-source astrophysics module that extends SWIFTSimIO to analyses of particles belonging to individual
galaxies simulated with SWIFT. It inherits from and extends the functionality of SWIFTSimIO's SWIFTDataset class. It understands the content of
halo catalogues and therefore which particles belong to a
galaxy or other group of particles, and its integrated properties. The particles occupy a coordinate frame that is enforced to be consistent, such that particles loaded on-the-fly will match e.g.~rotations and translations of particles already in
memory. Intuitive masking of particle
datasets is also enabled. Utilities to make working in cylindrical and spherical coordinate systems more convenient are also provided. Finally, tools to iterate efficiently over multiple
galaxies are provided.
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High Energy Astrophysical Phenomena
Analyzing GW231109_235456 and understanding its potential implications for population studies, nuclear physics, and multi-messenger astronomy
Thibeau Wouters, Anna Puecher, Peter T. H. Pang et al. (+1 more)
We study the gravitational-wave trigger GW231109_235456, a sub-threshold binary
neutron star merger candidate observed in the first part of the fourth observing run of the LIGO-Virgo-KAGRA collaboration. Assuming the trigger is of astrophysical origin, we analyze it using state-of-the-art waveform models and investigate the robustness of the inferred source parameters under different prior choices in
Bayesian inference. We assess the implications for population studies,
nuclear physics, and multi-messenger astronomy. Analyzing the component masses, we find that GW231109_235456, if astrophysical, supports the proposed double Gaussian mass distribution of
neutron stars. Moreover, we find that the remnant most likely collapsed promptly to a black hole and that, because of the large distance, a possible kilonova connected to the merger was noticeably dimmer than AT2017gfo but within reach of observatories such as LSST and Roman. In addition, we provide constraints on the equation of state from the candidate GW231109_235456 alone, as well as combined with GW170817 and GW190425. In our projections for the future, we simulate a similar event using the planned next generation of ground-based gravitational-wave detectors. Our findings indicate that we can constrain the
tidal deformability of a $1.4 \ M_\odot$
neutron star to about $10\%$, depending on the specific designs and network considered.
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All authors Thibeau Wouters, Anna Puecher, Peter T. H. Pang, Tim Dietrich
Solar and Stellar Astrophysics
Photometric and Spectroscopic Studies of Four Low Mass-ratio Contact Binaries with Period Longer than 0.7 days
Yi-Fan Wang, Kai Li, Fei Liu et al. (+7 more)
Photometric and spectroscopic studies of four long-period low mass-ratio contact binaries, V0508 And, V0844 Aur, V0699 Cep, and NSVS 6259046, are performed. V0508 And, V0844 Aur, and V0699 Cep are found to be A-type low-mass-ratio medium-contact binaries, while NSVS 6259046 is found to be an A-type deep-contact binary. O - C analysis indicates no long-term variation in V0844 Aur. However, the orbital periods of the other three targets are increasing. We conclude that V0844 Aur, V0699 Cep and NSVS 6259046 are magnetically active, as evidenced by the presence and variable nature of the O'Connell effect in these systems. By analyzing the LAMOST spectroscopic data, we find out that NSVS 6259046 and V0508 And exhibit no chromospheric activity on the dates the LAMOST spectra were taken, while the low signal-to-noise ratio in LAMOST data for V0844 Aur prevents us from obtaining reliable results. We discover that V0699 Cep is an early-type contact binary with chromospheric activity. Their initial masses and ages are calculated. All four systems are determined to be currently stable. We collect 217 contact binaries with both spectroscopic and photometric observations, and compare the differences between short-period and long-period systems in terms of mass-luminosity relation and mass-radius relation, using 0.7 days as the period boundary.
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All authors Yi-Fan Wang, Kai Li, Fei Liu, Xin Xu, Mu-Zi-Mei Li, Cheng-Yu Wu, Yu-Tong Li, Yan-Ke Tang, Xing Gao, Guo-You Sun
Astrophysics of Galaxies
K-DRIFT: Unveiling New Imagery of the Hidden Universe
Jongwan Ko, Woowon Byun, Kwang-Il Seon et al. (+31 more)
Low-surface-brightness (LSB) structures play a crucial role in understanding
galaxy evolution by providing significant insights into
galaxy interactions, the histories of mass assembly, and the distribution of dark matter. Nevertheless, their inherently faint nature, coupled with observational difficulties such as stray light interference and variations in the sky background, has significantly impeded comprehensive studies of LSB features. The KASI Deep Rolling Imaging Fast
Telescope (K-DRIFT) project aims to address these observational challenges by developing off-axis freeform three-mirror
telescopes and observational strategies specifically designed for LSB imaging surveys. The first generation of the K-DRIFT (K-DRIFT G1) has been successfully completed, and the forthcoming survey, scheduled to commence shortly, is expected to yield novel insights into the LSB universe. This paper outlines the scientific motivations of the project, discusses the technical challenges encountered, highlights the innovative solutions devised, and describes the future trajectory of the K-DRIFT.
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All authors Jongwan Ko, Woowon Byun, Kwang-Il Seon, Jihun Kim, Yunjong Kim, Daewook Kim, Seunghyuk Chang, Dohoon Kim, Il Kweon Moon, Hyuksun Kwon, Yeonsik Kim, Kyohoon Ahn, Gayoung Lee, Yongseok Lee, Sangmin Lee, Sang-Mok Cha, Dong-Jin Kim, Kyusu Park, Jaewon Yoo, Jae-Woo Kim, Jihye Shin, Sang-Hyun Chun, Yongmin Yoon, Jaehyun Lee, Kyungwon Chun, Jinsu Rhee, Sungryong Hong, Jongyeob Park, Young-Beom Jeon, Eon-Chang Sung, Hong Soo Park, Seonwoo Kim, GyeongGon Bahk, Seri Yeon
Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
The Ultra Slow-Roll Phase Of Warm Inflation In Braneworld Cosmology
Aarav Shah
Slow-roll of the inflaton (inflationary field) defines the standard dynamics of the inflationary epoch. However, the inflaton deviates from slow-roll when it encounters an extremely flat region in the inflationary potential, and enters a phase dubbed Ultra Slow Roll (USR). In previous studies, there have been various theories which modify the theory of general relativity, all of them having different motivations based on different paradigms. Among these, braneworld
gravity, motivated from string theory; is one of the most prominent theories as it provides a geometrical explanation for the weakness of
gravity. In this article, we explore two possible braneworld background theories, the Randall-Sundrum (RS-II) model and the Dvali-Gabadadze-Porratai (DGP) model, and then realize an USR phase in a particularly interesting inflationary scenario, called warm inflation. In the warm inflationary scenario, a thermal radiation bath coexists with the inflationary energy density as an effect of the dissipative dynamics. We then derive inflationary slow roll parameters and the
primordial power spectrum of scalar
curvature perturbations in such a setup. We then numerically investigate the
evolution of the inflaton and the
primordial power spectrum of scalar
curvature perturbations. Our analysis shows that the braneworld contributions become progressively suppressed as the USR conditions are made more stringent, indicating that the USR phase effectively diminishes brane-induced corrections to standard inflationary dynamics.
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Cosmology and Nongalactic Astrophysics
Avoiding PBH overproduction in inflation model with modified dispersion relation
Chengrui Yang, Weixin Cai and Taotao Qiu
The
Pulsar Timing Array (PTA) data of nano-Hertz gravitational waves released in 2023 implies that if such gravitational waves comes from the scalar perturbation induction at the end of inflation, the accompanied
primordial black holes (PBHs) will be over-produced, with the fraction exceed the upper bound of unity. This is recognized as the “overproduction problem", which calls for nontrivial features in the early universe. In this paper, we try to check out whether a modified dispersion relation (MDR) of the
primordial perturbations can be helpful for solving the problem. From the constraint on PTA data, we obtain a posterior distribution of the parameters of
primordial perturbation, and find that the MDR model, where the $k^4$ term becomes important at later time, can give rise to a broken-power-law (BPL) power spectrum which can alleviate the overproduction problem to nearly $2\sigma$ level. However, to improve furtherly into $1\sigma$ still needs small negative non-Gaussianity, e.g. $f_{\rm nl}\simeq -1$. The mass distribution of the PBHs generated is also discussed.
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High Energy Astrophysical Phenomena
Ultraviolet Spectral Evidence for Ansky as a Slowly Evolving Featureless Tidal Disruption Event with Quasiperiodic Eruptions
Jiazheng Zhu, Ning Jiang, Yibo Wang et al. (+13 more)
X-ray quasi-periodic eruptions (QPEs) are rare and enigmatic phenomena that increasingly show a connection to
tidal disruption events (TDEs). However, the recently discovered QPEs in ZTF19acnskyy ("Ansky") appear to be linked to an active
galactic nucleus (AGN) rather than a TDE, as their slow decay and AGN-like variability differ markedly from that of typical TDEs. This finding may imply broader formation channels for QPEs. To further investigate Ansky's nature, we obtained a timely ultraviolet (UV) spectrum, which reveals a featureless, TDE-like spectrum devoid of broad optical or UV emission lines. Additionally, the steep UV continuum, fitted by a power law with an index of -2.6, aligns more closely with TDEs than with AGNs. Compared to other featureless TDEs, Ansky exhibits a significantly lower blackbody luminosity (10^43 erg s^-1) and much longer rise and decay timescales, suggesting a distinct TDE subclass. An offset TDE involving an intermediate-mass black hole is unlikely, given its position consistent with the
galactic center with a 3 sigma upper limit of 54 pc. Instead, we propose that Ansky may result from the
tidal disruption of a post-main-sequence
star by a typical supermassive black hole. Our findings strengthen the growing evidence for TDE-QPE associations, although other formation channels for QPEs remain plausible and await future observational efforts.
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All authors Jiazheng Zhu, Ning Jiang, Yibo Wang, Tinggui Wang, Luming Sun, Shiyan Zhong, Yuhan Yao, Ryan Chornock, Lixin Dai, Jianwei Lyu, Xinwen Shu, Christoffer Fremling, Erica Hammerstein, Shifeng Huang, Wenkai Li, Bei You
Instrumentation and Methods for Astrophysics
RGC: a radio AGN classifier based on deep learning. I. A semi-supervised multiclass model for VLA images
M.S. Hossain, M.S.H. Shahal, K.M.B. Asad et al. (+10 more)
Bent
radio active
galactic nuclei (RAGNs) – wide-angle tails (WATs) and narrow-angle tails (NATs) – trace dense environments in
galaxy groups and clusters, yet no multiclass classifier simultaneously separates them from straight Fanaroff–Riley types (sFRI, sFRII) using visually inspected labels and unlabelled data. We release FIRST-2060, a four-class labelled
dataset of 2060 RAGNs (sFRI, sFRII, WAT, NAT) constructed from three publicly available catalogues through multi-tier visual inspection, together with the semi-supervised RGC 1.0 model that leverages 20,000 unlabelled sources. We
benchmark RGC against five supervised baselines. FIRST-2060 is provided in two preprocessing variants: $\mathbf{R}_{L1}$, which retains spurious sources, and $\mathbf{R}_{L2}$, from which they are removed. The RGC model integrates the self-supervised framework BYOL (Bootstrap Your Own Latent) with an $E(2)$-equivariant steerable CNN (E2CNN) encoder, pre-trained on the unlabelled data and fine-tuned on the labelled sets. All six models are evaluated with 5-fold cross-validation, Grad-CAM
attention analysis, and controlled class-imbalance experiments. ConvNeXT ($M_1$) and RGC ($M_2$) form a top tier at macro-$F_1$ $0.80\pm0.02$ and $0.79\pm0.02$ respectively, a difference within one standard deviation. $M_2$ is the only model whose Grad-CAM contours consistently trace the morphological structure of RAGNs – lobes, jets, and bends – rather than defaulting to compact blobs or diffuse patterns. The four-class scheme introduced here enables WAT/NAT-resolved catalogues that can serve as environment probes and progenitor classifications for diffuse cluster
radio emission. The complementary strengths of $M_1$ and $M_2$ – in cross-type and within-type discrimination respectively – suggest that an ensemble approach may offer a practical framework for survey-scale morphological catalogues.
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All authors M.S. Hossain, M.S.H. Shahal, K.M.B. Asad, P. Saikia, A. Khan, F. Akter, A. Ali, M.A. Amin, D.P. Guha, M. O. B. Jihad, A. Momen, S. Sen, A.K.M.M. Rahman
Cosmology and Nongalactic Astrophysics
Constraining the Hubble Constant using Cross-Correlation of Gravitational Wave Events with Flux-Limited Galaxy Catalog
Tathagata Ghosh and Surhud More
Gravitational waves (GWs) from the compact binary coalescence provide direct measurement of the luminosity distance to the event. However, unlike binary
neutron stars,
redshift information is not available from GW observations of binary black holes. Consequently, independent
redshift measurements of such GW events are necessary to measure $H_0$. In this study, we demonstrate a novel
Bayesian formalism to infer $H_0$ utilizing the $3$D cross-correlation of GW events with
galaxies from flux-limited catalog in configuration space. We demonstrate the efficacy of our method with $300$ simulated GW events distributed within $1$ Gpc in colored Gaussian noise of Advanced LIGO and Advanced Virgo detectors operating at O4 sensitivity. We show that such measurements can constrain the Hubble constant with a precision of $\sim 9 \%$ ($90\%$ highest density interval). We highlight the potential improvements that need to be accounted for in further studies before the method can be applied to real data.
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