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Physics Astrophysics

astro-ph Watch Astrophysics

Wednesday 25 March

High Energy Astrophysical Phenomena

Distance estimate to NGC 6951 from supernova siblings Type IIP SN 2020dpw and Type Ib SN 2021sjt

Réka Könyves-Tóth, Zsófia Bodola, Tamás Szalai et al. (+24 more)

{Supernova (SN) siblings are powerful tools used to calibrate and improve distance measurement methods, and to make the systematic uncertainty to distances to their host galaxies considerably lower compared to other techniques.} {In this paper we present distance estimates to NGC6951, a galaxy that hosted the Type IIP SN~2020dpw, the Type Ib SN~2021sjt, and three other SNe.} {Photometric observations of the two objects were carried out using two 80cm RC telescopes located in Hungary, while spectra were obtained from the LCO and the WiseRep database. For the distance estimates, we applied the expanding photosphere method (EPM), which connects the observed angular radius ($\theta$) of a SN to its physical radius and is related to the velocity of the photosphere ($v_{\rm ph}$). Although the EPM is mostly applied to derive the distance of Type IIP SNe, in the literature there are several examples of this technique being used for Type IIn and stripped-envelope SNe as well. Therefore, we made another attempt to infer the distance of the Type Ib SN~2021sjt by applying the EPM together with its Type IIP sibling SN~2020dpw. } {Our analysis resulted in a distance of $25.76 \pm 0.34 (\rm random) \pm 5.51$ (systematic) Mpc and $24.57 \pm 1.27 (\rm random) \pm 4.64$ (systematic) Mpc for SN~2020dpw and SN~2021sjt, respectively. Systematic errors were estimated with respect to the used dilution factor, the interstellar reddening, and the date of the explosion (which was fixed to a value between the last non-detection and the first detection for each object).} {The obtained distance values agree with each other and with the literature, which shows the validity of the methods used. In this way, new and perhaps improved distance estimates to NGC 6951 were obtained, and the applicability of the EPM for Type Ib SNe was tested.}
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All authors Réka Könyves-Tóth, Zsófia Bodola, Tamás Szalai, Moira Andrews, Iair Arcavi, Dominik Bánhidi, Imre Barna Bíró, Federica Bianco, Jamison Burke, István Csányi, Benjamin Dilday, Joseph R. Farah, Estefania Padilla Gonzalez, Daichi Hiramatsu, D. Andrew Howell, Levente Kriskovics, Megan Newsome, Yuan Qi Ni, Curtis McCully, András Ordasi, András Pál, Craig Pellegrino, Róbert Szakáts, Giacomo Terreran, Stefano Valenti, Krisztián Vida, Kathryn Wynn

Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Primordial black hole formation from transient $f(T)$ cosmology

Gerasimos Kouniatalis, Theodoros Papanikolaou, Spyros Basilakos et al. (+1 more)

We study primordial black hole (PBH) formation in a minimally coupled $f(T)$ teleparallel cosmology that generates a transient departure from standard radiation domination. The model is constructed so that modified-gravity effects are negligible at early and late times, but become dynamically relevant over a finite epoch, during which an effective torsion component reduces the total equation-of-state parameter below 1/3.We show that this transient softening lowers the collapse threshold for overdensities at horizon re-entry, leading to an exponential enhancement of PBH formation. In addition, the modified background alters the relation between temperature and horizon mass, producing a localized feature in the PBH mass function. For representative parameters, PBHs with asteroid-scale masses can account for a significant fraction, or even the entirety, of dark matter for perturbation amplitudes $\sigma^2 \sim \mathcal{O}(10^{-3})$, while remaining consistent with current constraints. Our results demonstrate that modified gravity alone can efficiently generate PBHs, without requiring ad hoc modifications of the radiation sector.
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All authors Gerasimos Kouniatalis, Theodoros Papanikolaou, Spyros Basilakos, Emmanuel N. Saridakis

High Energy Astrophysical Phenomena

Production of heavy $\alpha$-elements and $^{44}$Ti in Cas A: comparison to abundances from 1D core-collapse supernova models and evidence for Carbon-Oxygen shell mergers

Luca Boccioli, Lorenzo Roberti, Chris L Fryer et al. (+3 more)

The merger between the carbon (C) and oxygen (O) shells hours to days before the collapse of a massive star significantly changes its nucleosynthesis, which is reflected in the elemental ratios observed in supernova remnants (SNRs). We present a nucleosynthesis study of $^{44}$Ti production in core-collapse supernovae (CCSNe), highlighting large silicon (Si), sulfur (S), calcium (Ca), and, most importantly, argon (Ar) to neon (Ne) ratios as diagnostics for carbon-oxygen (C–O) shell mergers. We compare yields from eight different sets of CCSNe models to observations of Cassiopeia A (Cas A), and show that C–O shell mergers are consistently the models that best match X-ray and infrared observations. These models produce high Ar/Ne ratios ($\gtrsim 0.1$), due to $^{20}$Ne depletion and production of $^{36}$Ar and $^{38}$Ar, while lower ratios are obtained from non-merger cases. Based on the Ar/Ne diagnostic, we compare the range of expected $^{44}$Ti produced by C–O shell mergers, which is up to $\sim 20 - 30 \%$ of the overall $^{44}$Ti, but expected to be located outside the reverse shock. Based on the sets of models considered, the photon flux expected from the $^{44}$Ti synthesized in the C–O shell merger in Cas A is below the $NuSTAR$ and $COSI$ detection limits, compatible with current limits locating most of the $^{44}$Ti interior to the reverse shock, but might be detectable from proposed missions like $ASCENT$. Finally, for the SNR of 1987A, a dominant C–O merger origin of the observed $^{44}$Ti is unlikely based on the observed redshift in its $^{44}$Ti line.
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All authors Luca Boccioli, Lorenzo Roberti, Chris L Fryer, Samar Safi-Harb, Samuel Jones, Marco Pignatari

High Energy Astrophysical Phenomena

The diffuse gamma-ray sky of a Milky Way analogue: Local diversity and global constraints

Karin Kjellgren, Philipp Girichidis, Maria Werhahn et al. (+8 more)

Diffuse gamma-ray emission is a key tracer of cosmic rays (CRs) in galaxies, encoding information about their transport, energetics, and interactions with the interstellar medium. Interpreting the Milky Way gamma-ray sky is challenging because the observed emission depends on the three-dimensional distributions of CRs and gas, as well as the observer location within the Galaxy. Using the Rhea suite of CR-MHD simulations of a Milky Way analogue, we study how pion-decay gamma-ray emission varies with galactic environment, local conditions, and CR transport physics. Emission is computed in post-processing under steady-state assumptions, enabling analysis of luminosities, spectra, full-sky maps, and angular power spectra (APS) for multiple observer positions, including those inside Local-Bubble-like cavities. The simulated galaxy reproduces Milky Way-like gamma-ray luminosities and spectral slopes without parameter tuning. While total luminosity is relatively stable, the morphology of the gamma-ray sky varies strongly with observer location due to the complex local gas distribution, consistent with observations. For all observers, the APS traces gas column density rather than the smoother CR energy density, in agreement with previous studies. Comparisons with Fermi-LAT data show good agreement in both the all-sky spectrum and APS, with a diffusion coefficient scaling proportional to E^0.5 providing the best match. These results show that key features of Galactic gamma-ray emission arise naturally in self-consistent CR-MHD simulations. Gas density fluctuations primarily shape emission morphology, while CR transport governs spectral and structural properties. The Rhea simulations provide a physically grounded framework for interpreting diffuse gamma-ray observations and highlight the importance of local environment in tracing Galactic CR physics.
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All authors Karin Kjellgren, Philipp Girichidis, Maria Werhahn, Ralf S. Klessen, Christoph Pfrommer, Juan Soler, Brian Reville, Jim Hinton, Patrick Hennebelle, Noé Brucy, Simon C. O. Glover

Solar and Stellar Astrophysics

The Coldest Known Y Dwarfs: Estimates of their Effective Temperatures

S. K. Leggett

For a decade there has been a factor of 2.5 gap in luminosity between the 275K WISE J085510.83-071442.5 (Luhman 2014) and all other Y dwarfs, with Teff >= 350K. Recently three objects were found which may fall in this gap. Two are companions to Y dwarfs: WISE J033605.05-014350.4B (Calissendorff et al. 2023) and CWISEP J193518.58-154620.3B (De Furio et al. 2025); the third is MEAD 62B, a candidate companion to a white dwarf (Albert et al. 2025). Evolutionary models calculate a tight relationship between luminosity and Teff for Y dwarfs. I determine luminosities and hence Teff for three Y dwarfs (WISE J085510.83-071442.5, WISE J173835.53+273259.0, WISE J182831.08+265037.7). I derive relationships between Teff and mid-infrared colors using these together with 22 T and Y dwarfs from Beiler et al. (2024) with luminosity-based Teff values. These relationships are used to explore the Teff distribution for Y dwarfs. A sample of 31 Y dwarfs within ~20 pc is presented with 275 < Teff K < 425. The JWST colors for WISE J053516.80-750024.9 and WISE J182831.08+265037.7 support previous suggestions that they are unresolved binaries, the former a 480K and 340K dwarf pair and the latter a pair of 387K dwarfs. Five other dwarfs have unusual colors; two are likely high gravity and/or metal-poor (WISE J024714.52+372523.5, WISEA J215949.54-480855.2), two low gravity and/or metal-rich (CWISEP J104756.81+545741.6, WISE J150115.92-400418.4), and the fifth cannot be interpreted (WISE J043052.92+463331.6). An Appendix provides colors which can be used as a reference for searches for brown dwarfs in JWST data.
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Astrophysics of Galaxies

A striking excess of red quasars with steep radio spectral slopes: a dusty blow-out phase revealed through AGN-driven shocks?

Ciera L. Sargent, David M. Alexander, Claire L. Greenwell et al. (+5 more)

Red quasars exhibit a higher incidence of compact (galaxy-scale or smaller) radio emission than blue quasars, arising from systems near the radio-loud/radio-quiet threshold. In this paper we select quasars from SDSS ($0.2 <z <2.4$), and use archival radio data (FIRST, VLASS, LoTSS) to visually determine the radio morphologies of 573 red quasars compared to a control sample of 1278 typical blue quasars. We find an excess of steep-slope radio emission ($\alpha_{1.4-3\text{ GHz}}\sim-1$, where $S_\nu \propto \nu^\alpha$) from red quasars with compact ($<6''$) radio morphologies over 144 MHz, 1.4 GHz, and 3 GHz. This excess steep radio emission signature is not seen in normal blue quasars (radio compact or extended) or red quasars with extended low-frequency radio emission, which instead show a broad range of radio spectral slopes consistent with a range of different physical processes. We show that the strength of the excess steep spectral slope component increases with dust extinction, along with an overall increase in the radio-detection fraction. We argue that this excess steep-slope radio emission is due to shocks between quasar-driven winds/jets and the dusty nuclear-host galaxy environment. The majority ($86^{+5}_{-21}\%$) of the dustiest quasars ($E(B-V)>0.4$ mag) with steep slopes have radio luminosities consistent with the prediction from a wind-shock model with wind efficiencies of up to 7%. This agrees with the scenario where these compact red quasars are undergoing a "dusty blow-out" phase, where compact jets and/or AGN-driven winds interact with a dusty ISM, causing shocks, leading to steep spectral slopes and enhanced radio detection rates.
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All authors Ciera L. Sargent, David M. Alexander, Claire L. Greenwell, Victoria A. Fawcett, Leah K. Morabito, Chris M. Harrison, Moun Meenakshi, Ryan C. Hickox

High Energy Astrophysical Phenomena

Photon Ring Astrometry I: A Simple Spin Measurement Technique for High-Resolution Images of M87*

Delilah E. A. Gates, Dominic O. Chang, Aaron Held et al. (+1 more)

The supermassive black hole M87* is a target for future horizon-scale imaging that will resolve the first lensed (${n}~{=}~{1}$) sub-image of the photon ring. In this work, we identify a concrete observable—the displacement between the centers of the ${n}~{=}~{1}$ photon-ring sub-image and the direct image. Assuming that the observed large-scale jet of M87 is aligned with the black-hole spin axis, we separate the relative position of the photon ring into components parallel and transverse to the projected spin axis. We show that the parallel shift is primarily determined by inclination and emission radius, while the transverse shift is tightly correlated with inclination and spin. We demonstrate these effects both in a simple geometric model (to explain the underlying physics) and in {general-relativistic magnetohydrodynamics} simulations with magnetically arrested disks (to provide realistic instantiations). We find that a relative astrometric resolution of ${\lesssim}~{0.1\;\mu\rm{as}}$, achievable by the proposed Black Hole Explorer mission, is sufficient to constrain the spin to better than 9% if the accretion flow is prograde, 25% if the flow is retrograde, or 24% if the direction of the flow is undetermined. More generally, this identifies photon-ring astrometry as a promising method to constrain the underlying spacetime geometry without relying on geometric modeling of the observed emission.
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All authors Delilah E. A. Gates, Dominic O. Chang, Aaron Held, Daniel C. M. Palumbo

Instrumentation and Methods for Astrophysics

A scalable Bayesian framework for galaxy emission line detection and redshift estimation

Alexander Kuhn, Bonnabelle Zabelle, Sara Algeri et al. (+2 more)

Estimating galaxy redshifts is crucial for constraining key physical quantities like those in the equation of state of dark energy. Modern telescopes such as the James Webb Space Telescope, the Euclid Space Telescope, and the NASA Nancy Grace Roman Space Telescope are producing massive amounts of spectroscopic data that enable precise redshift estimation. However, a galaxy's redshift can be estimated only when emission lines are present in the observed spectrum, which is unknown a priori. A novel Bayesian approach to estimating redshift and simultaneously testing for the presence of emission lines is developed. Although modern spectroscopic surveys involve millions of spectra and give rise to highly multimodal posterior distributions, the proposed framework remains computationally efficient, admitting a parallelizable implementation suitable for large-scale inference.
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All authors Alexander Kuhn, Bonnabelle Zabelle, Sara Algeri, Galin L. Jones, Claudia Scarlata

Earth and Planetary Astrophysics

From dust to planets – II. Effects of wide binary companions and external photoevaporation on planetesimal and embryo formation

Gavin A. L. Coleman

More than half of Solar-type stars are found in binary systems. The numbers of exoplanets within binary systems in s-type orbits now numbers over 700. However, whilst the numbers have increased, there still does not exist a global model of planet formation for wide binary systems, where there does for single stars and circumbinary systems. As a precursor to such a model, that includes the necessary physical planet formation processes, it is important to understand how an outer binary companion affects the evolution of circumstellar discs, and the formation of planetesimals and planetary embryos. The main mechanism for which these processes are affected, is through truncation of the protoplanetary disc outer edges. In this paper, we determine these effects, whilst also comparing them to the effects of external photoevaporation that competes to truncate protoplanetary discs. We find that disc truncation by both a binary companion and external photoevaporation significantly reduces the efficiency to which planetary embryos are able to accrete pebbles and grow into terrestrial mass planets. This is due to the pebble supply being cut off as the pebble production front reaches the disc outer edge before planets are able to significantly increase in mass. This hindrance to planet formation occurs when the truncation radius due to the binary companion is below $\sim 30$ au, corresponding to binary separations of $\sim90$ au for equal mass, circular binary stars. For separations greater than 300 au, planet formation operates similar to that around single stars. Our results highlight the detrimental effects of a binary companion for intermediate binaries, that can provide possible explanations for the dearth of multiple planets within binary systems of separations $<100$ au
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Astrophysics of Galaxies

A PANORAMIC of UV-optical morphologies of "Little Red Dots": Two groups of LRDs distinguished by UV half-light radius

Aidan P. Cloonan, Katherine E. Whitaker, Sinclaire M. Manning et al. (+13 more)

Among the most remarkable results from JWST is the discovery of abundant, compact, and very red sources in the early Universe known as "Little Red Dots" (LRDs). The relative degree to which starlight and active galactic nuclei (AGN) drive the rest-frame UV and optical emission from LRDs remains unclear. With a large sample of LRDs selected photometrically from the pure-parallel PANORAMIC survey, we study their morphology as a function of rest-wavelength and find that the rest-UV light is typically more extended than the rest-optical. This result holds both when measuring LRD sizes with a single Sérsic profile and when comparing the fraction of light from a point source via joint PSF+Sérsic modeling. A shift occurs at the Balmer break, with LRDs becoming highly compact and unresolved ($R_{50,\rm{opt}}\lesssim100\;\rm{pc}$) in the rest-optical relative to the rest-UV. When splitting the sample at the Balmer break into those that are resolved and unresolved, a stacking analysis demonstrates that the latter are compact ($R_{50}\lesssim100\;\rm{pc}$) on average across the full rest-UV-optical spectrum. Conversely, those LRDs resolved at the break show extended UV emission ($R_{50,\rm{UV}}>200\;\rm{pc}$) on average. We find a similar dichotomy when repeating with a spectroscopic sample. Altogether, these results are consistent with the rest-UV emission driven by a combination of emission from starlight and a dense, dust-poor cloud of hydrogen gas enveloping an AGN. Differences between LRDs in the relative contribution from the AGN and starlight could reflect an ensemble of black hole seed masses, where a heavier seed produces an LRD of smaller $R_{50,\rm{UV}}$.
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All authors Aidan P. Cloonan, Katherine E. Whitaker, Sinclaire M. Manning, Christina C. Williams, Jenny E. Greene, Pascal A. Oesch, Andrea Weibel, Gabriel Brammer, Anna de Graaff, Raphael E. Hviding, Pratika Dayal, Christian Kragh Jespersen, Zhiyuan Ji, Ivo Labbe, Mengyuan Xiao, Yunchong Zhang

Astrophysics of Galaxies

The mmax-Mecl relation in the LEGUS clusters

Marie Zinnkann, Tereza Jerabkova, Zhiqiang Yan et al. (+6 more)

The relation between the maximum stellar mass in a very young cluster (mmax) and the total stellar mass of the cluster (Mecl), known as the mmax-Mecl relation, remains debated in the literature. To test the validity of this relation, we modelled young star clusters with masses between 102.5 and 105.0 M_sun and ages of 1-4 Myr using the galIMF code, in which stellar masses are optimally sampled from a varying initial stellar mass function. We compared the results with literature observations of extragalactic young star clusters. We incorporated stellar evolution via PARSEC and COLIBRI tracks and computed Halpha luminosities using the Pegase code. To account for dynamical ejections, we stochastically removed stars based on their spectral type, following previous N-body simulations. Additional sources of scatter, including uncertainties in age determination and contamination by field stars, were considered. Our results indicate that, under the assumptions explored here, optimal sampling is consistent with the extragalactic star cluster observations considered, whereas purely random sampling produces distributions that are not in agreement. These findings support a highly self-regulated interpretation of cluster formation in which stellar masses align optimally with the initial mass function rather than being drawn independently at random.
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All authors Marie Zinnkann, Tereza Jerabkova, Zhiqiang Yan, Pavel Kroupa, Yannik Ostermann, Eda Gjergo, Akram Hasani Zonoozi, Hosein Haghi, Jan Pflamm-Altenburg

Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Cogenesis of visible and dark matter in type-I Dirac seesaw

Debasish Borah, Partha Kumar Paul and Narendra Sahu

We propose a novel cogenesis framework based on the type-I Dirac seesaw mechanism. The minimal type-I Dirac seesaw with three heavy vector-like fermions $(N)$, one singlet scalar $(\eta)$, and the right-handed counterparts $(\nu_R)$ of the Standard Model (SM) neutrinos is extended to include a Dirac fermion dark matter (DM) $(\chi)$ and its heavier scalar companion ($\phi$). The out-of-equilibrium decays of the vector-like fermion generate asymmetries simultaneously in the visible sector, through decay channels involving $(\nu_R,\eta)$ or lepton, Higgs doublets in the SM, and in the dark sector via decaying into $(\chi,\phi)$. The resulting lepton asymmetry is partially converted into the observed baryon asymmetry by electroweak sphaleron processes, while the dark-sector asymmetry survives to constitute the present-day asymmetric DM relic. The generation of asymmetries in multiple sectors and their mutual washouts provide rich dynamics while also keeping the model testable at different observations involving DM, neutrinos, cosmic microwave background (CMB), as well as gravitational waves (GW). We find that successful cogenesis can be realized for DM masses in the range $100~\mathrm{MeV} \lesssim m_\chi \lesssim 39~\mathrm{TeV}$. The lower bound arises from the requirement that the symmetric component of DM annihilates efficiently before the big bang nucleosynthesis (BBN) epoch, while the upper bound is set by unitarity constraints on the asymmetric DM.
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Cosmology and Nongalactic Astrophysics

A New Method to Simulate Dark Matter-Baryon Interactions and Application to an Isolated Disk Galaxy

Connor Hainje and Glennys R. Farrar

We report on a new method for incorporating interactions between dark matter (DM) and baryons in cosmological simulations, capable of handling the challenging regime in which the dark matter particle mass is comparable to or lighter than the baryon mass. The method hybridizes two distinct approaches: gas particles receive momentum and energy transfer according to a mean-field calculation while DM particles undergo Monte Carlo scatterings. These approaches are derived from the Boltzmann equation and shown to be statistically equivalent. We present an open-source implementation of this method in the simulation code GIZMO. As a first application, we investigate the effects of DM-baryon interactions on an isolated Milky Way-like disk galaxy for dark matter having twice the proton mass, which roughly maximizes the average energy transfer per collision. For cross sections of order 1 barn ($10^{-24}$ cm$^2$), these interactions cause strong changes to the mass distribution in the center of the galaxy in less than 1 Gyr, even when bar formation is suppressed by hand. For cross sections typical of hadronic interactions ($\lesssim 30$ mb), high-fidelity galaxy formation simulations will be needed to assess the effects on observable features of galaxies.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

UV-complete and stable Quintom Dark Energy models in the light of DESI DR2

Fotis Koutroulis

We propose that Quintom dark energy, the simplest framework allowing crossing of the cosmological-constant boundary, admits a natural UV completion in a 5D anisotropic orbifold lattice: the Non-Perturbative Gauge-Higgs Unification (NPGHU) model. In this setup, a bulk 5D SU(2) gauge field projects on the 4D boundary to a complex scalar and a U(1) gauge field, identified with the dynamical dark-energy sector, while the Standard Model and dark matter remain localized in four dimensions. At late times, bulk-induced dimension-6 higher-derivative operators generate both physical and phantom scalar and gauge degrees of freedom. We show that the resulting 4D effective action is a modified Quintom model whose background equation of state can naturally realize Quintom-B behavior. A crucial contribution arises from the massive gauge ghost, allowing an excellent fit to DESI data with negligible fine-tuning, unlike standard Quintom scenarios. We further show that the inherited properties of the NPGHU construction e.g. absence of fundamental ghost instabilities, absence of potential terms and a finite low-energy cutoff $\Lambda$ associated with approximate Lorentz invariance, play a central role in the consistency of the effective theory under linear perturbations and vacuum decay. For the most natural regime, $\Lambda \approx {\cal O}(10)H_0$, the model remains robust despite the presence of IR phantom modes. Our results provide a natural and predictive framework in which Quintom dark energy can be consistently embedded in a fundamental theory.
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High Energy Astrophysical Phenomena

The rise of the black hole X-ray binary AT2019wey observed with TESS

Alyana Jusino, Kishalay De and Andrea Antoni

Black hole X-ray binaries (BHXRBs) have traditionally been discovered by X-ray surveys with cadences of hours to days. However, large optical time-domain surveys now provide novel avenues for early detection and insights into their elusive outburst triggering mechanisms. We present early-time light curves of the BHXRB AT 2019wey serendipitously observed by the Transiting Exoplanet Survey Satellite (TESS). The TESS images are sampled at 30 minute cadence from $\approx2$ d prior to $\approx25$ d after outburst, providing the highest time resolution optical rising phase observations of any known BHXRB. We fit a piece-wise power law to the rising light curve, finding an outburst onset time of MJD $58817.86\pm0.09$ and power-law rise index $n=0.74\pm0.04$. The onset time precedes all ground-based optical detections, and suggests that the optical rise began after the start of the faint X-ray brightening in MAXI data. We search for periodic high frequency modulation and detect none exceeding amplitude $\approx0.48$ mJy at periods of $\gtrsim1$ h at 90% confidence.
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Earth and Planetary Astrophysics

GJ 523b is a Massive, 170 Myr-old Mega-Earth, Likely on a Polar Orbit

Maxwell A. Kroft, Thomas G. Beatty, Joseph M. Salzer et al. (+18 more)

We use WIYN/NEID radial velocity measurements to confirm the planetary nature and measure the mass of the TESS transiting exoplanet candidate around the mid-K dwarf GJ 523 ($V=9.23$, $K=6.525$). We find that GJ 523b is on a 17.75 day orbit and has a radius of $2.55\pm0.15\,R_\oplus$, a mass of $23.5\pm3.3\,M_\oplus$, and a zero-albedo equilibrium temperature of 538 K. GJ 523b's high bulk density of $7.8\pm1.8$ g cm$^{-3}$ and position on a mass-radius diagram implies a surprising low atmospheric mass fraction despite its relatively large mass. Additionally, we determine that the system has an age of $169^{+100}_{-48}$ Myr through a gyrochronological analysis of GJ 523 and its comoving companions. We also use the SED-derived stellar radius, the photometric rotation period, and the spectroscopic $v\sin i_\star$ to derive a stellar inclination of $17.6\pm5.0$ degrees, implying that GJ 523b has a minimum orbital obliquity of $71.4_{-5.0}^{+4.7}$ degrees. GJ 523b's high mass, apparent lack of a gas envelope, young age, and high orbital obliquity present a challenge to typical planet formation pathways, and at the moment there is not enough data on the system to definitively determine how GJ 523b formed. Finally, we present a new observational classification for ultra-dense, sub-Neptune-sized exoplanets similar to GJ 523b: the mega-Earths, planets with $R_p \geq2.1\,R_\oplus$ and $\rho_p \geq 5.5$ g cm$^{-3}$.
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All authors Maxwell A. Kroft, Thomas G. Beatty, Joseph M. Salzer, Claire Zwicker, Anastasia Triantafillides, Juliette Becker, Melinda Soares-Furtado, Jessi Cisewski-Kehe, Jack J. Lissauer, Tayt S. Armitage, Joseph R. Livesey, Ritvik Sai Narayan, Susanna Widicus Weaver, Ke Zhang, Allyson Bieryla, David R. Ciardi, Catherine A. Clark, Miranda Felsmann, Rachel B. Fernandes, Steve B. Howell, Michael B. Lund

High Energy Astrophysical Phenomena

The background gas humming and multi-messenger transients of stalled supermassive black hole binaries

Pau Amaro Seoane, Alessandra Mastrobuono Battisti, Chingis Omarov et al. (+5 more)

We establish the multi-messenger mechanics of episodic mass transfer in supermassive black hole binaries stalled within circumbinary discs. Utilizing continuous wavelet transforms, we isolate localized gas clumps at the cavity edge and track their evolution. By regularizing the forced fluid equations at Lindblad resonances via the inhomogeneous Airy differential equation, we bypass linear singularities to extract the finite wave amplitudes that trigger non-linear shock formation. These shocks produce bounded accretion bursts. We model the time-domain thermal luminosity, deriving an analytical power spectral density that forms a harmonic cascade. The superposition of the accretion streams generates a spectral beat frequency, providing an exact mathematical extraction of the binary mass ratio. The radiative cooling of shock-accelerated electrons produces a multi-wavelength spectral energy distribution from a synchrotron radio continuum to an inverse-Compton gamma-ray tail. We identify a relativistic signature: a discontinuous, high-frequency gravitational wave sideband termed the “background gas humming”. This emission arises from the highly asymmetric, transient fluid geometry of the accretion shocks. Evaluating the asymptotic properties of the Airy regularization, we show that this humming manifests as a sequence of discrete high-frequency bursts with temporal quiescence gaps that systematically compress as the cavity shrinks. We show that the instantaneous mass of the gas actively trapped within the cavity violently amplifies prior to decoupling, culminating in a terminal burst near 4.0 mHz that serves as a multi-messenger precursor to the final vacuum inspiral.
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All authors Pau Amaro Seoane, Alessandra Mastrobuono Battisti, Chingis Omarov, Denis Yurin, Maxim Makukov, Dana Kuvatova, Gulnara Omarova, Anton Gluchshenko

Earth and Planetary Astrophysics

Beyond the Largest Lyapunov Exponent: Entropy-Based Diagnostics of Chaos in Henon-Heiles and N-Body Dynamics

Alessandro Alberto Trani, Pierfrancesco Di Cintio and Michele Ginolfi

The largest Lyapunov exponent is widely used to diagnose chaos in gravitational dynamics, but in mixed phase spaces and finite-N systems it does not always provide a complete description of orbital complexity and phase-space transport. Entropy-based diagnostics may offer a complementary perspective. We investigate whether trajectory-based information entropy can provide a useful diagnostic of chaos in gravitational systems and how it relates to the largest Lyapunov exponent as a function of orbital energy and of the number of degrees of freedom. We computed the largest Lyapunov exponent and a coarse-grained Shannon entropy for ensembles of trajectories in the Henon-Heiles potential and for test-particle orbits in live N-body realizations of a Plummer model. We then compared the dependence of both quantities on orbital energy and, for the N-body case, on particle number. In the Henon-Heiles system, the Shannon entropy follows the transition from weak to widespread chaos and exhibits an energy dependence that closely mirrors that of the largest Lyapunov exponent. For test-particle orbits in live N-body potentials, both diagnostics indicate stronger chaos for more tightly bound trajectories. However, their dependence on N differs: the largest Lyapunov exponent remains nearly constant over the explored range of particle numbers, whereas the Shannon entropy decreases monotonically as N increases. These results show that the information entropy can complement the largest Lyapunov exponent and may better capture changes in global phase-space mixing, especially in systems where the leading Lyapunov exponent alone is not sufficiently informative. It therefore provides a promising alternative for diagnosing chaos when tangent-space dynamics is unavailable or computationally expensive, and it is naturally suited to systems with densely sampled trajectories, such as minor bodies in the Solar System.
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Astrophysics of Galaxies

A Fast, Hot Wind from a Nuclear Starburst

XRISM Collaboration: Marc Audard, Hisamitsu Awaki, Ralf Ballhausen et al. (+136 more)

Galaxies with intense star formation often host multiphase, galaxy-scale winds powered by supernovae and fast stellar winds. These are strong enough to disrupt the star-forming interstellar medium, and they chemically enrich the surrounding circumgalactic medium. However, their launching mechanism remains unknown. Here we show that thermal gas pressure is sufficient to drive the multiphase wind in the prototypical starburst galaxy M82. Using a high energy-resolution ($\Delta E = 4.5$ eV) XRISM Resolve spectrum, including detections of FeXXV 6.7 keV, ArXVII 3.1 keV, and SXVI 2.6 keV, we measure the temperature ($T = 2.3^{+0.5}_{-0.2} \times 10^7$ K) and mass ($M \approx 6 \pm 2 \times 10^5$ M$_\odot$) of the hot gas in the starburst and provide the first direct measurement of its line-of-sight velocity dispersion ($\sigma = 595^{+464}_{-128}$ km s$^{-1}$). These values are consistent with a freely-expanding wind exceeding the galactic escape velocity. The size of the FeXXV-emitting region suggests a hot gas outflow rate of $\dot{M} \approx 4$ M$_\odot$ yr$^{-1}$, carrying a total energy of $\dot{E} \approx 2 \times 10^{42}$ erg s$^{-1}$. This is sufficient to drive the molecular, atomic, and ionized outflows while transporting up to $\approx 2$ M$_\odot$ yr$^{-1}$ of hot gas to the intergalactic medium. The estimated supernova rate implies that $\approx$ 60% of the supernova energy must be thermalized in hot gas. Our results suggest that additional driving mechanisms, such as cosmic-ray pressure, are not required to launch the wind.
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All authors XRISM Collaboration: Marc Audard, Hisamitsu Awaki, Ralf Ballhausen, Aya Bamba, Ehud Behar, Rozenn Boissay-Malaquin, Laura Brenneman, Gregory V. Brown, Lia Corrales, Elisa Costantini, Renata Cumbee, María Díaz Trigo, Chris Done, Tadayasu Dotani, Ken Ebisawa, Megan E. Eckart, Dominique Eckert, Satoshi Eguchi, Teruaki Enoto, Yuichiro Ezoe, Adam Foster, Ryuichi Fujimoto, Yutaka Fujita, Yasushi Fukazawa, Kotaro Fukushima, Akihiro Furuzawa, Luigi Gallo, Javier A. García, Liyi Gu, Matteo Guainazzi, Kouichi Hagino, Kenji Hamaguchi, Isamu Hatsukade, Katsuhiro Hayashi, Takayuki Hayashi, Natalie Hell, Edmund Hodges-Kluck, Ann Hornschemeier, Yuto Ichinohe, Daiki Ishi, Manabu Ishida, Kumi Ishikawa, Yoshitaka Ishisaki, Jelle Kaastra, Timothy Kallman, Erin Kara, Satoru Katsuda, Yoshiaki Kanemaru, Richard Kelley, Caroline Kilbourne, Shunji Kitamoto, Shogo Kobayashi, Takayoshi Kohmura, Aya Kubota, Maurice Leutenegger, Michael Loewenstein, Yoshitomo Maeda, Maxim Markevitch, Hironori Matsumoto, Kyoko Matsushita, Dan McCammon, Brian McNamara, François Mernier, Eric D. Miller, Jon M. Miller, Ikuyuki Mitsuishi, Misaki Mizumoto, Tsunefumi Mizuno, Koji Mori, Koji Mukai, Hiroshi Murakami, Richard Mushotzky, Hiroshi Nakajima, Kazuhiro Nakazawa, Jan-Uwe Ness, Kumiko Nobukawa, Masayoshi Nobukawa, Hirofumi Noda, Hirokazu Odaka, Shoji Ogawa, Anna Ogorzalek, Takashi Okajima, Naomi Ota, Stephane Paltani, Robert Petre, Paul Plucinsky, Frederick S. Porter, Katja Pottschmidt, Kosuke Sato, Toshiki Sato, Makoto Sawada, Hiromi Seta, Megumi Shidatsu, Aurora Simionescu, Randall Smith, Hiromasa Suzuki, Andrew Szymkowiak, Hiromitsu Takahashi, Mai Takeo, Toru Tamagawa, Keisuke Tamura, Takaaki Tanaka, Atsushi Tanimoto, Makoto Tashiro, Yukikatsu Terada, Yuichi Terashima, Yohko Tsuboi, Masahiro Tsujimoto, Hiroshi Tsunemi, Takeshi Tsuru, Ayşegül Tümer, Hiroyuki Uchida, Nagomi Uchida, Yuusuke Uchida, Hideki Uchiyama, Yoshihiro Ueda, Shinichiro Uno, Jacco Vink, Shin Watanabe, Brian J. Williams, Satoshi Yamada, Shinya Yamada, Hiroya Yamaguchi, Kazutaka Yamaoka, Noriko Yamasaki, Makoto Yamauchi, Shigeo Yamauchi, Tahir Yaqoob, Tomokage Yoneyama, Tessei Yoshida, Mihoko Yukita, Irina Zhuravleva, Kazuki Ampuku, Erin Boettcher, Skylar Grayson, Gabriel Grell, Peter Kosec, Seiya Sasamata, Evan Scannapieco

High Energy Astrophysical Phenomena

Systematic Monitoring of Extreme X-ray Variability from Weak-line Quasars

Madison Reich, W. N. Brandt, Bin Luo et al. (+5 more)

We present the results of a multi-cycle Chandra program to systematically monitor the X-ray variability of 10 weak-line quasars (WLQs) that previously had limited multi-epoch X-ray observations. Three new Chandra 2.8 to 8.2 ks observations were obtained for each WLQ with C$\,$IV rest-frame equivalent widths (REWs) $\lesssim 10$ Å, substantially improving the monitoring data quality of WLQs and our ability to characterize their long-term X-ray variability behavior. We observe recurrent extreme X-ray variability in the historically variable WLQ SDSS J1539+3954, with an X-ray flux rise of a factor of $\gtrsim 6$ between 2023 and 2024 ($\gtrsim 21$ relative to 2013). Another previously X-ray weak WLQ in the sample, SDSS J0825+1155, underwent a significant X-ray flux variation by a factor of $\gtrsim 14$ between 2019 and 2023. We find the fraction of WLQs exhibiting evidence of extreme X-ray variability to be $0.20^{+0.17}_{-0.07}$. In the context of the thick disk and outflow (TDO) model, the substantial fraction of WLQs displaying extreme X-ray variability may suggest that the variability is more likely driven by the intrinsic motion of the TDO wind rather than changes in the height of the TDO disk. We performed a statistical comparison between the distribution of variability amplitudes of WLQs and general radio-quiet quasars. We find that these underlying distributions are statistically different, with WLQs having $\approx 6.8$ times higher odds of exhibiting an extreme X-ray variability event than the general radio-quiet quasar population.
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All authors Madison Reich, W. N. Brandt, Bin Luo, Qingling Ni, Richard Plotkin, Ohad Shemmer, Fabio Vito, Weimin Yi

Cosmology and Nongalactic Astrophysics · Cross-listed from hep-th

The Universe Originating from an Empty Planck-Size Torus

Bartosz Fornal

We consider a Universe with a three-torus topology which before inflation is devoid of any matter or radiation. Its pre-inflationary evolution is driven solely by Casimir energies of the existing fields, with a radiation-like equation of state. We show that, under natural assumptions and with the appropriate number of fermions and bosons in the theory, such a Universe can start its evolution from a Planck size at the Planck time. Moreover, assuming typical parameters for inflation and reheating, the three-torus Universe can be several Hubble radii across at present time, which is precisely the size hinted by the anomaly in the cosmic microwave background observed at low multipole moments. We derive a relation between the size of the Universe, the number of e-folds of inflation, and the energy density decrease during reheating, which we then use to determine the parameter values consistent with the anomaly and the lower bound on the size of the Universe from the Planck satellite.
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Instrumentation and Methods for Astrophysics

A Probabilistic Autoencoder for Galaxy SED Reconstruction and Redshift Estimation: Application to Mock SPHEREx Spectrophotometry

Richard M. Feder, Liam Parker and Uroš Seljak

We present a probabilistic autoencoder (PAE) framework for galaxy spectral energy distribution (SED) modeling and redshift estimation, applied to synthetic SPHEREx 102-band spectrophotometry. Our PAE learns a compact latent representation of rest-frame galaxy SEDs transformed to a simple Gaussian base density using a normalizing flow, combined with an explicit forward model enabling joint Bayesian inference over intrinsic SED parameters and redshift with well-defined priors. In controlled tests on simulated SPHEREx spectra, our PAE improves on template fitting (TF) in source recovery, outlier rate, and posterior calibration, with trade-offs in redshift performance that depend on the assumed priors. A simple cut on the ratio of PAE and TF uncertainties identifies sources that are overwhelmingly TF outliers, which can be used to clean existing TF samples while retaining the vast majority of well-recovered sources. By directly profiling over PAE latent variables, we show these cases correspond to shallow likelihood surfaces where the PAE's continuous SED manifold produces broader likelihoods that more faithfully reflect the lack of constraining power in the data, whereas the TF discrete model grid yields artificially confident but incorrect redshift estimates. Lastly, we present an alternative, simulation-based inference approach using a Transformer encoder and conditional normalizing flow, which provides similar redshift performance to the PAE but with $\sim200\times$ faster inference throughput. Our implementation, PAESpec, is publicly available and provides a foundation for principled redshift estimation in modern photometric surveys.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

ACT-Planck data and phase transitions from a viable no-scale Standard Model completion

Filippo Cutrona, Francesco Rescigno and Alberto Salvio

Classically scale-invariant (and perturbative) theories provide a way to understand large hierarchies, as scales are generated through dimensional transmutation. They always lead to first-order phase transitions, since symmetries are radiatively broken, and they generically feature quasi-flat potentials, which are suitable for inflation. We construct a simple but fully realistic model of this kind that accounts for all observational evidence of new physics and is remarkably compatible with the most recent constraints on inflationary observables from both the Planck/BICEP/Keck and the Atacama Cosmology Telescope (ACT) collaborations. This model illustrates how classical scale invariance generically leads to a non-standard cosmology in which inflation occurs in two stages: a slow-roll stage and a thermal stage, separated by a radiation-dominated era.
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Earth and Planetary Astrophysics

Disentangling auroral, cloud and magnetic spot driven variability in three early L-dwarfs with HST/WFC3

C. O'Toole, J. M. Vos, E. N. Nasedkin et al. (+5 more)

Variability monitoring provides an unparalleled insight into the atmospheric processes of brown dwarfs and directly imaged exo-planets. Inhomogeneous clouds, aurorae and magnetic spots have all been postulated as potential drivers of variability. While objects at the L/T transition have had their variability studied extensively, the variability of early L-dwarfs remains an understudied region of the parameter space. We use observations from the Hubble Space Telescope in the near-infrared, using WFC3/G141 to disentangle the drivers of variability in three known variable early L-dwarfs: 2MASS J1721039+334415, 2MASS J00361617+1821104 and 2MASS J19064801+4011089. We find that all three objects exhibit significant variability at all wavelengths, with white-light amplitudes of 0.53-1.41 %. We find that their colour variations are brighter and bluer compared to later spectral types, except for 2MASSJ19064801+4011089 which exhibits largely grey variations. We report a new period for 2MASS J1721039+334415, of 4.9^{+0.4}_{-0.2} hours. We find evidence of long term light curve stability in each object, which may indicate the presence of long lived features on their surfaces. We create a flexible modelling framework to model three potential drivers of variability: clouds, aurorae and magnetic spots. We fit our models to the spectral variability amplitude from 1.1-1.67 {\mu}m of each object. We find that changing cloud properties or magnetic spots are the most likely drivers of variability in each object. Auroral models do not reproduce the variability within the HST wavelengths, however future observations at longer wavelengths that probe higher in the atmosphere may be more sensitive to auroral effects. This work provides a foundation for future variability studies of early L-dwarfs and directly imaged exoplanets to disentangle auroral, cloud and magnetic spot driven variability.
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All authors C. O'Toole, J. M. Vos, E. N. Nasedkin, J. S. Pineda, M. M Kao, Y. Zhou, M. Schrader, A. M. McCarthy

Solar and Stellar Astrophysics

Clouds with a silicate lining: Using JWST spectra to probe atmospheric diversity in young AB Dor L dwarfs

M. B. Lam, J. M. Vos, G. Suárez et al. (+13 more)

We present the first full JWST NIRSpec Prism and MIRI LRS 0.6 - 14 $\mu$m (R ~ 100) spectra and analysis of five ~ 133 Myr L dwarf members of the AB Doradus moving group and one probable $\sim 500$ Myr T dwarf of the Oceanus moving group with known inclination angles between ~ $23 - 90^{\circ}$: W0047+68, 2M0355+11, 2M0642+41, W1741-46, 2M2206-42, and 2M2244+20. We construct near-complete spectral energy distributions of each of our objects to measure their bolometric luminosities, and estimate their fundamental parameters ($T_{\text{eff}}$, radius, $M$ and $\log g$). We use cross-sections of relevant gases to identify the species that are present in each atmosphere. Of particular interest is the silicate absorption feature at 8 - 11 $\mu$m, which provides insight into the complex cloud structure of brown dwarfs. We examine this silicate absorption feature in detail and also test whether there exists a latitudinal dependence in the silicate absorption feature within a coeval sample of brown dwarfs. Various molecular absorption bands are visible in our spectra, including H$_2$O, CH$_4$, CO and CO$_2$. The shape of the silicate absorption feature varies within our sample, and we find that 4/5 of our L type objects agree with previously observed trends stating that objects viewed equator-on have deeper silicate absorption. We highlight W1741-46 as an outlier in our sample with an unusually strong silicate absorption given its near pole-on orientation. We also present a tentative correlation between the wavelength of peak silicate absorption and inclination, which may suggest variations in cloud chemical composition or physical properties. We find an unexpected spectral diversity within our sample, which motivates future studies on these objects through atmospheric retrievals, which will determine the silicate cloud composition and reveal whether there exists a trend with inclination.
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All authors M. B. Lam, J. M. Vos, G. Suárez, C.-C. Hsu, T. P. Bickle, J. Faherty, J. Gagné, D. Bardalez Gagliuffi, B. Biller, B. Burningham, K. L. Cruz, C. V. Morley, S. Luszcz-Cook, S. Lawsky, C. L. Phillips, A. Rothermich

High Energy Astrophysical Phenomena · Cross-listed from gr-qc

Fixing the center-of-mass frame of numerical relativity waveforms using the post-Newtonian center-of-mass charge

Aniket Khairnar, Leo C. Stein, Michael Boyle et al. (+7 more)

The Bondi–van der Burg–Metzner–Sachs (BMS) frame of gravitational waves produced by numerical relativity (NR) simulations is crucial for building accurate waveform models. A proper comparison of NR waveforms with other models requires fixing the arbitrary BMS frame. In this work we improve the center-of-mass (CoM) frame fixing for quasicircular, nonprecessing binary systems. Past work approximated the CoM motion with just a linear fit. We compute a post-Newtonian result of the boosted CoM charge to also capture its physical out-spiraling oscillations. We show that using the analytical results improves the robustness of the fit parameters – translation and boost vectors – to the choice of duration and time of the fitting window. Our analysis demonstrates a maximum improvement in robustness when the window is placed at the center of the inspiral. We quantified this improvement by computing the ratio of variances of fit parameters when the fit window size is varied. The largest improvement in robustness of parameters is by a factor of $\sim 25$ for the boost vector and $\sim 20$ for the translation vector. Finally, we incorporate this method into the BMS frame-fixing routine of the python package $\texttt{scri}$ for waveforms produced with Cauchy-characteristic evolution.
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All authors Aniket Khairnar, Leo C. Stein, Michael Boyle, Nils Deppe, Lawrence E. Kidder, Keefe Mitman, Jordan Moxon, Kyle C. Nelli, William Throwe, Nils L. Vu

High Energy Astrophysical Phenomena

BLAZ4R and the eROSITA view of z>4 blazars

Tullia Sbarrato, Silvia Belladitta, Julien Wolf et al. (+8 more)

We present BLAZ4R, the first living catalog of confirmed $z>4$ blazars, with a focus on the contribution of eROSITA, on board of the Spectrum Roentgen Gamma (SRG) spacecraft. Blazars at $z>4$ are rare but powerful probes of how active supermassive black holes evolve in connection to relativistic jets, in the first 2 billion years of cosmic history. At these redshifts, X-ray observations are essential for constraining blazars jet power and orientation, enabling effective trace of their parent population. The all-sky surveys provided by eROSITA ensure X-ray detection for BLAZ4R sources and, in some cases, allow spectral and temporal studies of their jetted emission. BLAZ4R includes 54 confirmed blazars, characterized through their X-ray properties, radio spectra and morphology, and multiwavelength profiles. We confirm that jetted sources are significantly more numerous relative to non-jetted counterparts at high-$z$, and that blazars (and therefore the overall jetted population) do not exhibit significantly different features compared to the total active galactic nuclei population in the early Universe. Fast accretion processes that involve relativistic jets are clearly required to justify the existence of fully formed jetted AGN at $z>4$. However, the diverse multiwavelength properties characterizing BLAZ4R do not yet allow us to identify the specific signatures of these processes. We will continue updating BLAZ4R to search for such signatures and ultimately understand the early formation of jetted AGN.
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All authors Tullia Sbarrato, Silvia Belladitta, Julien Wolf, Pietro Baldini, Dusan Tubín-Arenas, Mara Salvato, Emmanuel Momjian, Steven Hämmerich, Andrea Merloni, Werner Collmar, Joern Wilms

High Energy Astrophysical Phenomena

Neutrino and electromagnetic signatures from Superluminous Supernovae: a case study for SN 2017egm

Mainak Mukhopadhyay, Shigeo S. Kimura, Indrek Vurm et al. (+1 more)

Superluminous supernovae (SLSNe) are rare transients that are $\sim 10 - 100$ times more luminous than ordinary stellar explosions, reaching peak optical luminosities $\sim 10^{44} - 10^{45}$ erg s$^{-1}$. The energy source powering SLSNe remains uncertain. In this work, we explore the multi-wavelength and multi-messenger signatures of the scenario in which SLSNe are powered by a newly born millisecond magnetar. We model the dynamical evolution and emission from the coupled system comprised of the magnetar, wind, nebula, and supernova ejecta, consistently evaluating the pair multiplicity of the wind and nebula regions, and the bulk wind Lorentz factor governing the $e^+ - e^-$ injection spectra in the nebula. We compute the thermal and non-thermal electromagnetic signatures, neutrino signatures, and investigate their detection prospects. For SN 2017egm, the nearest observed SLSNe, our prediction for high-energy gamma rays matches the recent detection by Fermi LAT. For neutrinos, using SN 2017egm a canonical SLSNe, we find that in the era of the Vera C. Rubin Observatory, a stacking analysis with upcoming neutrino observatories can lead to $3\sigma$ detection significance of neutrino events from a population of SLSNe within a decade of operation.
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All authors Mainak Mukhopadhyay, Shigeo S. Kimura, Indrek Vurm, Brian D. Metzger

Instrumentation and Methods for Astrophysics

Global detector network to search for high-frequency gravitational waves (GravNet): conceptual design

Dorian Amaral, Diego Blas, Yuliia Borysenkova et al. (+30 more)

We propose GravNet (Global detector network to search for high-frequency gravitational waves), a novel experimental scheme enabling the search for gravitational waves in the MHz to GHz frequency range. Such high-frequency gravitational waves could arise from a variety of phenomena connected to some of the most pressing and fundamental questions in modern cosmology. The GravNet concept is based on synchronous measurements of signals from multiple experimental measurement devices operating at geographically separated locations. While gravitational-wave-induced signatures may be present in the signal of a single detector, distinguishing them from instrumental or environmental noise is highly challenging. By analyzing correlations between signals from several distant detectors, the detection significance is substantially enhanced, while simultaneously enabling studies of the nature and origin of the gravitational-wave signal. In this work, we discuss the GravNet concept specifically in the context of cavities operated in strong magnetic fields, as these currently represent the most technically mature and experimentally advanced realization of the scheme. As part of this proposal, a first demonstration experiment using a non-superconducting cavity has been performed, providing the basis for the data-analysis strategies discussed in this work. Finally, we outline the prospects and future development of GravNet as a global network for high-frequency gravitational-wave searches.
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All authors Dorian Amaral, Diego Blas, Yuliia Borysenkova, Dmitry Budker, Alessandro D'Elia, Giorgio Dho, Alejandro Díaz-Morcillo, Daniele Di Gioacchino, Sebastian Ellis, Claudio Gatti, Benito Gimeno, Jordan Gué, Stefan Horodenski, Saarik Kalia, Younggeun Kim, Tom Krokotsch, Tomas Kvietkauskas, Adrián Lambíes-Asensio, Carlo Ligi, Giovanni Maccarrone, Giovanni Mazzitelli, Juan Monzó-Cabrera, José R. Navarro-Madrid, José Reina-Valero, Alessio Rettaroli, Kristof Schmieden, Tim Schneemann, Matthias Schott, Simone Tocci, Sandro Tomassini, Oleg Tretiak, Luca Visinelli, Changhao Xu

Cosmology and Nongalactic Astrophysics · Cross-listed from hep-th

Cosmological correlators from the Inflation end to CMB sky via reheating

Chandra Prakash and Debaprasad Maity

We investigate the imprint of post-inflationary evolution on primordial cosmological correlators by relaxing the standard assumption of instantaneous reheating. We compute the power spectrum and bispectrum for a conformally coupled and non-minimally coupled ($\xi \neq \frac{1}{6},0$) scalar field with cubic self-interaction, across a finite reheating epoch characterized by an effective equation of state $w$, and reheating temperature $T_{\rm reh}$. We find that for a conformally coupled scalar field, the signatures of reheating, such as the modification to oscillatory features, are strictly confined to the subhorizon regime. On superhorizon scales, the correlators receive negligible corrections at leading order. In sharp contrast, for a non-minimally coupled field, we identify a distinct phenomenology where non-trivial values of $\xi$ and reheating equation of state $w$, can induce a tachyonic enhancement of the field modes on superhorizon scales. This enhancement modifies both the power spectrum and bispectrum, marking a sharp deviation from the instantaneous transition limit. Our results demonstrate that to the leading order while conformal coupling shields large-scale correlations from the expansion history, non-minimal coupling breaks this degeneracy and opens an observable window into the physics of reheating.
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