Solar and Stellar Astrophysics
Chromosphere of the quiet sun – I. Shock and current-sheet dynamics and heating
Quentin Noraz, Mats Carlsson and Guillaume Aulanier
The
solar chromosphere is a crucial interface between the
solar interior and its interplanetary environment, regulating how energy is locally deposited into heat and transported into the upper atmospheric layers. Despite significant progress, the dominant processes responsible for chromospheric heating remain debated, particularly under quiet-Sun (QS) conditions. We aim to disentangle and quantify the respective roles of shocks and current sheets (CS) in QS chromospheric modeling. We use a simulation performed with the radiation-magnetohydrodynamics code Bifrost. In order to identify shocks and CS events across space and time, we develop and apply physics-based criteria, allowing us to describe their dynamics and evaluate their contributions to both dissipative (viscous and ohmic) and mechanical (including compressive work) heating. Shocks are found to dominate the energy deposition in the lower chromosphere (up to $59\%$ of the mechanical heating), while CS become the primary contributor in the upper chromosphere, as both
plasma $\beta$ and Mach number $Ma$ drop. Overall, $66\%$ of the mechanical chromospheric heating is powered by the combined action of shocks and CS. These results support a multi-process view of the chromospheric heating in the QS, dominated by shocks, CS, and non-steep gradient dynamics. In addition to viscous and ohmic dissipation, compressive heating can play a major role locally in the model, particularly in chromospheric shock structures, where it offsets non-reversibly cooling from expansion and radiation, and therefore constitutes a key heating contribution to consider in the energy budget. This study further highlights the need for next-generation observations to resolve the intermittent and small-scale nature of chromospheric dynamics, in order to bring new constraints on the coupling between the different layers of the
solar atmosphere.
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Earth and Planetary Astrophysics
Origins of Mercury's Big Heart of Iron: Exploring Pathways to Form High Core Mass Fraction (CMF) Planets via N-body Simulations
Haniyeh Tajer, Ji Wang, Anna C. Childs et al. (+3 more)
Mercury's core mass fraction (CMF) is ~0.7, more than double that of the other rocky
planets in the
solar system, which have CMFs of ~0.3. The origin of Mercury's large, iron-rich core remains unknown. Adding to this mystery, an elusive population of "Exo-Mercuries" with high densities is emerging. Therefore, understanding the formation of Mercury and its exoplanetary analogs is essential to developing a comprehensive
planet formation theory. Two hypotheses have been proposed to explain the high CMF of Mercury: (1)
giant impacts during the latest stages of
planet formation strip away mantle layers, leaving Mercury with a large core; and (2) earlier-stage iron enrichment of planetesimals closer to the Sun leads to the formation of an iron-rich
planet. In this work, we conduct N-body simulations to test these two possibilities. Our simulations are focused on the
solar system, however, we aim to provide a framework that can later be applied to the formation of high-CMF
exoplanets. To investigate the
giant impact scenario, we employ uniform initial CMF distributions. To address the other hypothesis, we use a step function with higher CMFs in the inner region. For a uniform initial CMF distribution, our results indicate that although erosive impacts produce iron-rich particles, without mechanisms that deplete stripped mantle material, these particles merge with lower-CMF objects and do not lead to Mercury's elevated CMF. However, a step function initial CMF distribution leads to the formation of a high-CMF
planet alongside Earth-like
planets, resembling the architecture of the terrestrial
solar system.
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All authors Haniyeh Tajer, Ji Wang, Anna C. Childs, Noah Ferich, Tiger Lu, Hanno Rein
High Energy Astrophysical Phenomena
Towards a unified hadron-quark equation of state for neutron stars within the relativistic mean-field model
Marcos O. Celi, Mauro Mariani, Milva G. Orsaria et al. (+2 more)
The equation of state of dense matter remains a central challenge in astrophysics and high-energy physics, particularly at supra-
nuclear densities where exotic degrees of freedom like hyperons or deconfined
quarks are expected to appear.
Neutron stars provide a unique natural laboratory to probe this regime. In this work, we present EVA–01, a novel equation of state that provides a unified description of dense matter by incorporating both
hadron and
quark degrees of freedom within a single relativistic mean-field Lagrangian, from which the equation of state is derived at finite temperature. The model extends the density-dependent formalism by introducing a Polyakov-loop-inspired scalar field to dynamically govern the
hadron-
quark phase transition, following the approach of
chiral mean-field models. The resulting model is consistent with a wide range of theoretical and observational constraints, including those from
chiral effective field theory, massive
pulsars, gravitational-wave events, and NICER data. We analyze its thermodynamic properties by constructing the QCD phase diagram, identifying the deconfinement,
chiral, and
nuclear liquid-gas transitions. As a first application, we model the
evolution of proto-
neutron stars using isentropic snapshots and explore the implications of the slow stable hybrid
star hypothesis. Our findings establish EVA–01 as a robust and versatile framework for exploring dense matter, bridging the gap between microphysical models and multimessenger astrophysical observations.
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All authors Marcos O. Celi, Mauro Mariani, Milva G. Orsaria, Ignacio F. Ranea-Sandoval, Germán Lugones
Cosmology and Nongalactic Astrophysics
$\Lambda$CDM: The path forward
Michael S. Turner
The current cosmological paradigm, $\Lambda$CDM, is characterized its expansive description of the history of the Universe, its deep connections to particle physics and the large amounts of data that support it. Nonetheless, $\Lambda$CDM's critics and boosters alike agree on one thing: it is the not the final cosmological theory and they are anxious to see it replaced by something better! After reviewing some of the impactful events in cosmology since the last \Le Workshop, I focus on the role that the recent evidence for evolving dark energy may play in getting cosmology that better theory.
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Astrophysics of Galaxies
Modeling Stellar Collisions in Galactic Nuclei Using Hydrodynamic Simulations and Machine Learning
Sanaea C. Rose, James C. Lombardi, Jr. et al. (+3 more)
Nuclear star clusters represent some of the most extreme collisional environments in the Universe. A
nuclear star cluster like that of the Milky Way harbors a supermassive black hole at its center, which accelerates
stars to high speeds ($\gtrsim 100$-$1000$ km/s) in a region where millions of other
stars reside. Direct collisions occur in such high-density environments, where they can shape the
stellar populations and influence the
evolution of the cluster. We present a suite of a couple hundred high-resolution smoothed-particle hydrodynamics (SPH) simulations of collisions between $1$ M$_\odot$
stars, at impact speeds representative of
galactic nuclei. We use our SPH
dataset to develop physically-motivated fitting formulae for predicting collision outcomes. While collision-driven mass loss has been examined in detail in the literature, we present a new framework for understanding the effects of “hit-and-run” collisions on a
star's trajectory. We demonstrate that the change in
stellar velocity follows the
tidal-dissipation limit for grazing encounters, while the deflection angle is well-approximated by point-particle dynamics for periapses $\gtrsim 0.3$ times the
stellar radii. We use our SPH
dataset to test two machine learning (ML)
algorithms, k-Nearest Neighbors and neural networks, for predicting collision outcomes. We find that the neural network out-performs k-Nearest Neighbors and delivers results on par with and in some cases exceeding the accuracy of our fitting formulae. We conclude that both fitting formulae and ML have merits for modeling collisions in dense
stellar environments, however ML may prove more effective as the parameter space of initial conditions expands.
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All authors Sanaea C. Rose, James C. Lombardi, Jr., Elena González Prieto, Fulya K{\i}roğlu, Frederic A. Rasio
Astrophysics of Galaxies
DESI DR2 Galaxy Luminosity Functions
Samuel G. Moore, Shaun Cole, Michael Wilson et al. (+54 more)
We present
galaxy luminosity functions (LFs) for the Dark Energy Spectroscopic Instrument (DESI) DR2 Bright
Galaxy Survey (BGS) in the g,r,z, and w1 bands over 0.002<z<0.6. Our analysis uses updated k-corrections and evolutionary corrections, including new
polynomial k-correction fits derived from BGS Year1 data that supersede earlier GAMA-based prescriptions. Exploiting the statistical power of DESI, we measure LFs to very faint magnitudes, reaching M_r-5log h = -10. Independent measurements from the North and South survey regions show excellent agreement around the LF knee, but the very small statistical uncertainties reveal that simple analytic forms fail to capture the full LF shape. The bright end departs from a pure exponential decline, while the faint end exhibits complex, non-power-law behaviour, including a pronounced upturn at M_r-5log h > -15, which is stronger for red
galaxies than for blue. We show that our LFs are largely complete for
galaxies with surface brightness mu_50<25, and that an apparent steepening fainter than -13 is driven primarily by local overdensity and fragmentation of large
galaxies. A systematic North-South offset at the brightest magnitudes is traced to red
galaxies and may reflect shallower North photometry underestimating extended early-type profiles, although this remains inconclusive. We therefore also provide LFs based on model-Petrosian magnitudes.
Redshift-splitting reveals small but significant residuals, indicating limitations of a simple global evolutionary model. Using the
redshift limits of Loveday (2011) we find excellent agreement with GAMA, with substantially reduced statistical errors. These measurements provide a precise reference for studies of environmental and population-dependent LFs and for testing
galaxy formation models.
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All authors Samuel G. Moore, Shaun Cole, Michael Wilson, Peder Norberg, John Moustakas, J. Aguilar, S. Ahlen, A. Anand, D. Bianchi, D. Brooks, F. J. Castander, T. Claybaugh, A. Cuceu, A. de la Macorra, Arjun Dey, Biprateep Dey, S. Ferraro, A. Font-Ribera, J. E. Forero-Romero, E. Gaztanaga, S. Gontcho A Gontcho, G. Gutierrez, H. K. Herrera-Alcantar, K. Honscheid, M. Ishak, R. Joyce, S. Juneau, R. Kehoe, T. Kisner, S. E. Koposov, A. Kremin, O. Lahav, C. Lamman, M. Landriau, L. Le Guillou, M. E. Levi, M. Lucey, J. R. Manera, A. Meisner, R. Miquel, S. Nadathur, W. J. Percival, C. Poppett, F. Prada, A. J. Ross, G. Rossi, E. Sanchez, D. Schlegel, M. Schubnell, H. Seo, J. Silber, D. Sprayberry, G. Tarlé, B. A. Weaver, R. H. Wechsler, R. Zhou, H. Zou
Cosmology and Nongalactic Astrophysics
Gravitational Wave Spectral Shapes as a probe of Long Lived Right-handed Neutrinos, Leptogenesis and Dark Matter: Global versus Local B-L Cosmic Strings
Satyabrata Datta, Anish Ghoshal, Angus Spalding et al. (+1 more)
The scale of the seesaw mechanism is typically much larger than the electroweak scale. This hierarchy can be naturally explained by $U(1)_{B-L}$
symmetry, which after spontaneous
symmetry breaking, simultaneously generates Majorana masses for
neutrinos and produces a network of
cosmic strings. Such strings generate a gravitational wave (GW) spectrum which is expected to be almost uniform in frequency unless there is a departure from the usual early radiation domination. We explore this possibility in Type I, II and III seesaw frameworks, finding that only for Type-I, long-lived right-handed
neutrinos (RHN) may provide a period of early matter domination for parts of the parameter space, even if they are thermally produced. Such a period leaves distinctive imprints in the GW spectrum in the form of characteristic breaks and a knee feature, arising due to the end and start of the periods of RHN domination. These features, if detected, directly determine the mass $M$, and effective
neutrino mass $\tilde m$ of the dominating RHN. We find that GW detectors like LISA and ET could probe RHN masses in the range $M\in[0.1,10^{9}]$ GeV and effective
neutrino masses in the $\tilde m\in[10^{-10},10^{-8}]$ eV range. We investigate the phenomenological implications of long-lived right-handed
neutrinos for both local and global $U(1)_{B-L}$ strings, focusing on dark matter production and leptogenesis. We map the viable and detectable parameter space for successful baryogenesis and asymmetric dark matter production from right-handed
neutrino decays. We derive analytical and semi-analytical relations correlating the characteristic gravitational-wave frequencies to the
neutrino parameters $\tilde m$ and $M$, as well as to the relic abundances of dark matter and
baryons.
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All authors Satyabrata Datta, Anish Ghoshal, Angus Spalding, Graham White
Astrophysics of Galaxies
PRUSSIC III – ALMA and NOEMA survey of dense gas in high-redshift star-forming galaxies
Matus Rybak, G. Sallaberry, J. A. Hodge et al. (+7 more)
Characterising the relationship between dense gas and
star formation is critical for understanding the assembly of
galaxies throughout
cosmic history. However, due to the faintness of standard dense-gas tracers - HCN, HCO+, and HNC - dense gas in high-
redshift galaxies remains largely unexplored. We present ALMA and NOEMA observations targeting HCN/HCO+/HNC (3-2) and (4-3) emission lines in eleven (mostly) gravitationally lensed dusty
star-forming
galaxies (DSFGs) at
redshift z = 1.6–3.2. We detect at least one line in 10 out of 11
galaxies. Altogether, we detect 34 dense-gas transitions, more than quadrupling the number of extant high-
redshift detections. Additionally, in two targets, we detect lower-abundance CO isotopologues 13^CO and C^18O, as well as CN emission. We derive excitation coefficients for HCN, HCO+ and HNC in DSFGs, finding them to be systematically higher than those in nearby luminous infrared
galaxies. Assuming a canonical dense-mass conversion factor (alpha_HCN = 10), we find that DSFGs have shorter dense- gas depletion times (median 23 Myr) than nearby
galaxies (~60 Myr), with a
star-forming efficiency per free-fall time of 1-2%, a factor of a few higher than in local
galaxies. We find a wide range of dense-gas fractions, with HCN/CO ratios ranging between 0.01 and 0.15. Finally, we put the first constraints on the
redshift evolution of the
cosmic dense-gas density, which increases by a factor of 7+/-4 between z = 0 and z = 2.5, consistent with the
evolution of the
cosmic molecular-gas density.
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All authors Matus Rybak, G. Sallaberry, J. A. Hodge, D. Riechers, N. N. Geesink, T. R. Greve, S. Viti, F. Walter, P. P. van der Werf, C. Yang
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Light scalars in light of UV/IR mixing: classicalization via synergy between Vainshtein and chameleon screenings
Florian Nortier
Effective field theories featuring light scalar fields play a pivotal role in addressing fundamental questions in (astro)particle physics and cosmology. However, such theories often confront hierarchy problems in the absence of a
symmetry. Self-completion via classicalization offers a non-Wilsonian approach to ultraviolet (UV) completion, wherein new scalar self-interactions involving derivatives give rise to Vainshtein-like screening around energy-momentum sources. Rather than introducing new UV degrees of freedom to restore unitarity at high energies, these theories reshuffle their infrared (IR) degrees of freedom by generating extended semi-classical objects – referred to as classicalons – which decay into a multitude of soft particles. This mechanism incorporates non-localizable fields, thereby realizing a form of UV/IR mixing that is analogous to the dynamics of black holes in gravitational theories. In this article, having reviewed the fundamental principles of classicalization with a simple k-essence model, we then argue the necessity of maintaining a little hierarchy between the scalar mass and the scale of the first new resonances, thereby illustrating the impact of UV/IR mixing on hierarchy problems. Additionally, we investigate the effects of a scalar potential and couplings to
fermions on the Vainshtein screening mechanism. We discuss that a chameleon-like screening mechanism must accompany the Vainshtein screening to preserve the integrity of classicalon solutions.
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Astrophysics of Galaxies
A Possible "Too-Many-Satellites" Problem in the Isolated Dwarf Galaxy DDO 161
Jiaxuan Li, Jenny E. Greene, Shany Danieli et al. (+2 more)
The abundance of satellite
galaxies provides a direct test of $\Lambda$CDM and
galaxy formation physics on small scales. While satellites of Milky Way-mass
galaxies are well studied, those of
dwarf galaxies remain largely unexplored. We present a systematic search for satellites around the isolated
dwarf galaxy DDO~161 ($M_\star \approx 10^{8.4}\, M_\odot$) at a distance of 6 Mpc. We identify eight satellite candidates within the projected virial radius and confirm three new satellites through surface brightness fluctuation distance measurements from deep Magellan imaging data. Together with its confirmed satellite UGCA~319, DDO~161 has four confirmed satellites above $M_{\star}^{\rm sat} > 10^{5.4}\, M_\odot$, making it the most satellite-rich
dwarf galaxy known to date. We compare this system with predictions from the TNG50 cosmological simulation, combined with currently established
galaxy-
halo connection models calibrated on Milky Way satellites, and find that DDO~161 has a satellite abundance far exceeding all current expectations. The rich satellite system of DDO~161 offers new insight into how low-mass
galaxies occupy dark matter
halos in low-density environments and may provide new constraints on the nature of dark matter.
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All authors Jiaxuan Li, Jenny E. Greene, Shany Danieli, Scott Carlsten, Marla Geha
High Energy Astrophysical Phenomena
Jet-red giant interactions as a source of extragalactic neutrinos: Insights from KM3-230213A
G. Fichet de Clairfontaine, M. Perucho and J.M. Martí
The production sites of high-energy astrophysical
neutrinos remain uncertain, though growing evidence suggests a connection to relativistic jets in active
galactic nuclei (AGN). We present a detailed analysis of the recent PeV
neutrino event KM3-230213A reported by the KM3NeT collaboration, aiming to constrain the physical conditions of its source. Assuming
proton acceleration at shocks, we derive the properties of the
proton distribution and the energetics required to explain the
neutrino emission. Using contemporaneous multiwavelength observations of three AGN flaring candidates within the error region, we examine the plausibility of each of them as the possible counterpart. Our results favor PMN J0606-0724, which exhibits a prominent
radio flare coincident with the
neutrino arrival. In this framework, the red-
giant interaction remains the key driver of
baryon injection and shock acceleration, while the dominant external
photon field sets the
neutrino energy scale: photospheric
photons from the red
giant yield ~1-10 PeV
neutrinos, whereas the ~220 PeV event KM3-230213A is more naturally produced through interactions with colder infrared
photons from the dusty
torus.
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Solar and Stellar Astrophysics
Disk Evolution Study Through Imaging of Nearby Young Stars (DESTINYS): V721 CrA and BN CrA have wide and structured disks in polarised IR
Gabriele Columba, Elisabetta Rigliaco, Raffaele Gratton et al. (+8 more)
We present near-infrared scattered-light observations of the disks around two
stars of the Corona Australis
star-forming region, V721 CrA, and BN CrA, obtained with VLT/SPHERE, in the H band, as part of the DESTINYS large programme. Our objective is to analyse the morphology of these disks, and highlight their main properties. We adopt an analytical axisymmetric disk model to fit the observations and perform a regression on key disk parameters, namely the
dust mass, the height profile, and the inclination. We use RADMC-3D code to produce synthetic observations of the analytical models, with full polarised scattering treatment. Both
stars show resolved and extended disks with substructures in the near-IR. The disk of V721 CrA is vertically thicker, radially smaller (120 au), and brighter than BN CrA (190 au). It also shows spiral arms in the inner regions. The disk of BN CrA shows a dark circular lane, which could be either an intrinsic
dust gap or a self-cast shadow. Both disks are compatible with the evolutionary stage of their parent subgroup within the CrA region: V721 CrA belongs to the "on-cloud" part of CrA, which is dustier, denser and younger, whereas BN CrA is found on the outskirts of the older "off-cloud" group.
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All authors Gabriele Columba, Elisabetta Rigliaco, Raffaele Gratton, Christian Ginski, Antonio Garufi, Myriam Benisty, Stefano Facchini, Rob G. van Holstein, Alvaro Ribas, Jonathan Williams, Alice Zurlo
Astrophysics of Galaxies
Neutral Atomic Hydrogen in a Star-forming Galaxy 7 Billion Years Ago
Graham Lawrie, Roger Deane, Tariq Blecher et al. (+3 more)
Neutral atomic hydrogen (HI) constitutes a key phase of the
cosmic baryon cycle, bridging the ionised circumgalactic medium and the
star-forming molecular gas. Yet, nearly 75 years after its discovery, direct views of HI through its 21cm emission line remain largely confined to the nearby Universe. Indirect measurements and statistical analyses indicate little
evolution in the comoving HI density over the past 10 billion years, in stark contrast to the order-of-magnitude decline in the
cosmic star-formation rate density over the same epoch. Resolving this tension requires direct HI measurements in individual, representative
galaxies at earlier times. Here we report a detection of HI 21cm emission from the Dragon Arc, a gravitationally lensed main-sequence
star-forming
galaxy at $z=0.725$, observed 6.6 billion years in the past with the MeerKAT
radio telescope. The inferred intrinsic HI mass, $M_{\rm HI}=10^{9.66^{+0.16}_{-0.19}}\,\mathrm{M}_\odot$, and velocity width of $205^{+66}_{-48}\,\mathrm{km\,s^{-1}}$ are consistent with expectations from scaling relations for local
star-forming
galaxies. The resulting HI depletion time of $1.2^{+1.0}_{-0.6}\,\mathrm{Gyr}$ is significantly shorter than the $\sim5-10$ Gyr, measured locally for comparable
galaxies. This indicates that the
galaxy must rapidly replenish its atomic gas reservoir to remain on the
star-forming main sequence. This detection demonstrates that strong gravitational
lensing, combined with modern cm-wave facilities, can now reveal the HI reservoirs of typical
galaxies well beyond the local Universe, opening a new path toward statistical samples that will directly trace the
evolution of the
cosmic atomic gas supply.
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All authors Graham Lawrie, Roger Deane, Tariq Blecher, Danail Obreschkow, Ian Heywood, Shilpa Ranchod
Earth and Planetary Astrophysics
High CO/H2 ratios supports an exocometary origin for a CO-rich debris disk
Kevin D. Smith, Luca Matrà, Ke Zhang et al. (+9 more)
Over 20 exocometary belts host detectable circumstellar gas, mostly in the form of CO. Two competing theories for its origin have emerged, positing the gas to be
primordial or secondary.
Primordial gas survives from the belt's parent protoplanetary disk and is therefore H$_2$-rich. Secondary gas is outgassed in-situ by exocomets and is relatively H$_2$-poor. Discriminating between these scenarios has not been possible for belts hosting unexpectedly large quantities of CO. We aim to break this gas origin dichotomy via direct measurement of H$_2$ column densities in two edge-on CO-rich exocometary belts around $\sim$15 Myr-old A-type
stars, constraining the $\frac{\text{CO}}{\text{H}_2}$ ratio and CO gas lifetimes. Observing edge-on belts enables rovibrational absorption spectroscopy against the
stellar background. We present near-IR CRIRES+ spectra of HD 110058 and HD 131488 which provide the first direct probe of H$_2$ gas in CO-rich exocometary belts. We target the H$_2$ (v=1-0 S(0)) line at 2223.3 nm and and the $^{12}$CO $v=2\rightarrow0$ rovibrational lines in the range 2333.8-2335.5 nm and derive constraints on column densities along the line-of-sight to the
stars. We strongly detect $^{12}$CO but not H$_2$ in the CRIRES+ spectra. This allows us to place $3\sigma$ lower limits on the $\frac{\text{CO}}{\text{H}_2}$ ratios of $> 1.35 \times 10^{-3}$ and $> 3.09 \times 10^{-5}$ for HD 110058 and HD 131488 respectively. These constraints demonstrate that at least for HD 110058, the exocometary gas is compositionally distinct and significantly H$_2$-poor, compared to the $<10^{-4}$ $\frac{\text{CO}}{\text{H}_2}$ ratios typical of protoplanetary disks. We also find H$_2$ alone is unlikely to shield CO over the lifetime of the systems. Overall this suggests that the gas in CO-rich belts is most likely not
primordial in origin, supporting the presence of exocometary gas.
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All authors Kevin D. Smith, Luca Matrà, Ke Zhang, Aoife Brennan, Merdith Hughes, Christine Chen, Isa Rebollido, David Wilner, Aki Roberge, Seth Redfield, Antonio Hales, Karin Öberg
Instrumentation and Methods for Astrophysics
Extending to the Submillimeter Universe with the CCAT Observatory
Eve M. Vavagiakis
The CCAT Observatory's Fred Young Submillimeter
Telescope, a novel, high-throughput, 6-meter aperture
telescope, is scheduled for first light in 2026. Located at 5600 m on Cerro Chajnantor in the Chilean Atacama Desert, the CCAT site enables unprecedented submillimeter measurement capabilities, fully overlapping with millimeter-wave surveys like the Simons Observatory. CCAT will address a suite of science goals, from Big Bang cosmology,
star formation, and line-intensity mapping of
cosmic reionization, to
galactic magnetic fields, transients, and
galaxy evolution over
cosmic time. We highlight CCAT's science goals with
Prime-Cam, a first generation science instrument for the Fred Young Submillimeter
Telescope.
Prime-Cam will field over 100,000 kinetic inductance detectors across seven instrument modules to enable over ten times faster mapping speed than previous submillimeter observatories in windows between 1.4 - 0.3 mm (220 - 850 GHz). We give an instrument summary, discuss the project status, and outline preliminary plans for early science.
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Cosmology and Nongalactic Astrophysics
Dynamical Dark Energy from a Massive Vector Field in Generalized Proca Theory
Abhi Savaliya
In this paper, we emphasise the recent observational findings from the Dark Energy Spectroscopic Instrument Data Release 2 (DESI DR2), which provide compelling evidence for a possible deviation from the standard $\Lambda$CDM (Cold Dark Matter) cosmology, suggesting the presence of a dynamically evolving effective dark energy component. Motivated by this, we construct a theoretical framework in which a massive cosmological vector field, $B^{\mu}$, couples non-minimally to the background
curvature through marginal interactions, offering a controlled mechanism to realise the deviation from the $\Lambda$CDM model. A detailed analysis of the effective Equation of State (EoS) parameter $w(\tilde H)$ reveals a narrow region of parameter space consistent with current cosmological observations presented by DESI. The analysis yields a stringent upper bound for the coupling constant $\lambda$ to be $\lambda<2.98\times10^{-11}$, a very strong bound on mass $3.1356\times10^{-66}~\text{g} \leq m \leq 3.3627\times10^{-66}~\text{g},$ and the admissible range $-0.405 \leq \log_{10}\tilde\gamma \leq -0.38$ for which present-day value $w_0 = w(\tilde H = 1)$ corresponding to a deviation $\delta = w_0 + 1$ that lies within the region $0.107 \leq \delta \leq 0.217$. This interval reproduces the deviation inferred from the combined DESI,
Cosmic Microwave Background (CMB), and Pantheon+ data, reflecting a controlled departure from the $\Lambda$CDM behaviour. In summary, the results suggest that the proposed framework of a massive vector field can account for the departure from $\Lambda$CDM behaviour highlighted by DESI in the current
cosmic acceleration. Furthermore, the framework approaches the $\Lambda$CDM behaviour in late-time $t\gtrsim28$ Gyr, establishing a direct phenomenological link between the underlying parameters and the observed dynamical nature of dark energy.
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High Energy Astrophysical Phenomena
ANTARES Collaboration, Pedro De la Torre Luque, Daniele Gaggero et al. (+4 more)
The diffuse emission of gamma-rays and
neutrinos, produced by interactions of
cosmic rays with interstellar matter in the Milky Way, provides valuable insights into
cosmic ray propagation and
Galactic processes. Emission models incorporating different assumptions about
cosmic ray
diffusion, source distribution, and target gas density are tested using data from
neutrino telescopes. In this study, the final all-
flavor neutrino dataset, collected over 15 years (2007–2022) by the ANTARES
neutrino telescope, is analyzed. A maximum likelihood ratio method built to handle templates of
Galactic emission models is employed to evaluate the compatibility of these models with the observed spatial and energy distributions of
neutrino events. The results do not yield stringent constraints on the tested models and upper limits on the diffuse
neutrino flux are derived, which are compatible with the results obtained by other experiments.
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All authors ANTARES Collaboration, Pedro De la Torre Luque, Daniele Gaggero, Dario Grasso, Giulia Pagliaroli, Vittoria Vecchiotti, Francesco Lorenzo Villante
Solar and Stellar Astrophysics
Observing the solar corona from a formation-flying mission. First results of Proba-3/ASPIICS
A. N. Zhukov, L. Dolla, M. Mierla et al. (+32 more)
We report the first results from observations of the
solar corona by the ASPIICS coronagraph aboard the Proba-3 mission. ASPIICS (Association of Spacecraft for Polarimetric and Imaging Investigation of the Corona of the Sun) is a
giant coronagraph consisting of the
telescope mounted aboard one of the mission's spacecraft and the external occulter placed on the second spacecraft. The two spacecraft separated by around 144 m fly in a precise formation up to 5.5 hours at a time, which allows coronal observations in eclipse-like conditions, i.e. close to the limb (typically down to 1.099 Rs, occasionally down to 1.05 Rs) and with very low straylight. ASPIICS observes quasi-stationary structures, such as coronal loops, streamers, quiescent prominences, and a variety of dynamic phenomena: erupting prominences, coronal mass ejections, jets, slow
solar wind
outflows, coronal inflows. In particular, weak, widespread and persistent small-scale
outflows and inflows between 1.3 and 3 Rs are observed at a high spatial (5.6 arcsec) and temporal (30 s) resolution for the first time, expanding the range of scales at which the variable slow
solar wind is observed to form.
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All authors A. N. Zhukov, L. Dolla, M. Mierla, B. D. Patel, S. Shestov, B. Bourgoignie, A. Debrabandere, C. Jean, B. Nicula, D.-C. Talpeanu, Z. Zontou, S. Fineschi, S. Gunár, P. Lamy, H. Peter, P. Rudawy, K. Tsinganos, L. Abbo, C. Aime, F. Auchère, D. Berghmans, D. Besliu-Ionescu, S. E. Gibson, S. Giordano, P. Heinzel, B. Inhester, J. Magdalenic, C. Marqué, L. Rodriguez, M. Steslicki, L. Zangrilli, D. Galano, R. Rougeot, J. Versluys, C. Thizy
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Direct detection of solar chameleons with electron recoil data from XENONnT
Guan-Wen Yuan, Anne-Christine Davis, Maurizio Giannotti et al. (+3 more)
We reassess prospects for direct detection of
solar chameleons, in light of recent progress in modeling their production, and the availability of new XENONnT data. We show that the contribution from Primakoff production in the electric fields of electrons and ions dominates the electron
recoil event rate, which is enhanced compared to earlier estimates based on
magnetic conversion in the tachocline alone. We argue that the signal is governed by the effective coupling $\beta_{\text{eff}} \equiv \beta_{\gamma}M_e^{-4}$, which encodes the combined effects of production and detection, where $\beta_{\gamma}$ and $M_e$ are the chameleon-
photon (conformal) coupling and chameleon-electron disformal coupling scale, respectively. Setting the height of the chameleon potential to the dark energy (DE) scale $\Lambda \simeq 2.4\,{\text{meV}}$, we show that XENONnT electron
recoil data set the upper limit $\log_{10}\beta_{\text{eff}}<-6.9$. This limit is independent of the conformal matter coupling $\beta_m$ and index $n$, and applies to the whole class of inverse power-law chameleons, well beyond the $n=1$ case usually studied. We comment on how future multi-target experiments and lower-threshold analyses could distinguish
solar chameleons from other light (pseudo)scalar particles such as
axions. Our work demonstrates that existing dark matter direct detection experiments can probe regions of parameter space relevant to screened DE models, providing complementary tests to astrophysical and fifth-force searches at no additional experimental cost.
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All authors Guan-Wen Yuan, Anne-Christine Davis, Maurizio Giannotti, Sunny Vagnozzi, Luca Visinelli, Julia K. Vogel
High Energy Astrophysical Phenomena
Double white dwarf ZTF J0538+1953 as the brightest verification binary for space laser interferometers
Serguey Antipin, Alexander Belinski, Leonid Berdnikov et al. (+4 more)
A decrease in the orbital period of the ultrashort-period binary white
dwarf \ZTF, which is one of the
Galactic verification binaries in the millihertz frequency range for planned space
laser interferometers, has been measured. Based on photometric observations carried out on the 2.5-m
telescope of the Caucasian Mountain Observatory of the Sternberg Astronomical Institute of Moscow State University (CMO SAI MSU), a diagram O-C is constructed. It can be described by quadratic elements of the brightness variation, which correspond to a decrease rate of the orbital period of the system of $dP/dt=-(1.16\pm 0.22)\times 10^{-11}$ s/s. The decrease rate of the orbital period in the quadrupole approximation for the emission of gravitational waves by a binary system corresponds to its chirp mass $\mathcal{M}=0.434\pm 0.05 M_\odot$, which turned out to be $\sim 30\%$ higher than the value obtained earlier from spectroscopic mass determination. The chirp mass of \ZTF inferred from the measured orbital decay rate makes this system the brightest
Galactic verification binary for LISA and TianQin space interferometers with a signal-to-noise ratio of $\approx 119$ and $\approx 30$ over 5 years and 2.5 years of observations, respectively.
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All authors Serguey Antipin, Alexander Belinski, Leonid Berdnikov, Alexandra Zubareva, Natalia Maslennikova, Konstantin Postnov, Ivan Strakhov
High Energy Astrophysical Phenomena
Spectral curvature and breaks from Fermi acceleration at oblique shocks
Asma Shirin T, Brian Reville, Nils W. Schween et al. (+2 more)
A major attraction of diffusive shock acceleration is the prediction of power-law spectra for energetic particle distributions. However, this property is not fundamental to the theory. We demonstrate that for planar shocks with an oblique
magnetic field the generation of power-law spectra critically requires the particles' scattering rate to be both directly proportional to their gyro radius (Bohm scaling) and spatially uniform. Non-Bohm scaling results in curved spectra at oblique shocks, while abrupt changes in the spatial profile of the scattering upstream introduces spectral breaks. Using the publicly available code Sapphire++, we numerically explore the magnitude of these effects, which are particularly pronounced at fast shocks, as expected in active
galactic nuclei and microquasar jets, or young
supernova remnants.
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All authors Asma Shirin T, Brian Reville, Nils W. Schween, Florian Schulze, John G. Kirk
High Energy Astrophysical Phenomena
X-rays Emission: a novel tool to detect Extensive Air Showers
Rodrigo Alberto Torres Saavedra, Caterina Trimarelli, Roberto Aloisio et al. (+3 more)
We investigate the feasibility of detecting extensive air showers via their geo-synchrotron X-ray emission from high-altitude platforms. Starting from first principles, we derive a differential expression for the number of emitted
photons per unit grammage and
photon energy for an ensemble of gyrating shower electrons. The calculation uses noted parameterizations of the electron state variable distributions in the shower to establish a scale for the
photon footprint and, further, takes into account the propagation of emitted
photons in the atmosphere. The computed fluxes at the position of the detector are used to estimate the detector acceptance and event rate using a bootstrap Monte Carlo procedure. For a 1 m radius and 70{\deg} half-aperture circular detector at an altitude between 20 to 30 km viewing the Earth's limb, we find acceptances at the 1 $\mathrm{m^2 sr}$ level and integral event rates of roughly 10 per month. These results indicate that X-ray geo-synchrotron emission is a promising, complimentary channel for high-altitude indirect
cosmic ray detection in the PeV regime.
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All authors Rodrigo Alberto Torres Saavedra, Caterina Trimarelli, Roberto Aloisio, John F. Krizmanic, Johannes Eser, Austin Cummings
Cosmology and Nongalactic Astrophysics
Running of the spectral index: Reconciling the CMB with the Lyman-$\alpha$ Forest
Malcolm Fairbairn, Lucien Heurtier and María Olalla Olea-Romacho
We investigate the scale dependence of the
primordial power spectrum by combining \Planck, ACT DR6, SPT-3G, and eBOSS Lyman-$\alpha$ forest data, extending sensitivity to smaller comoving scales than those probed by the CMB alone. Within a parametrisation based on a Taylor expansion around the pivot scale, we constrain the running of the spectral index $\alpha_s$ and its running $\beta_s$. By using eBOSS likelihoods exhibiting a suppression of small-scale power either in amplitude or spectral index, we show that the latter can be accommodated by correlated variations of $(\alpha_s,\beta_s)$, leading to a preference for non-zero running. We show that inflationary potentials with localised features – such as Gaussian dips, bumps, or
axion-monodromy modulations – can reproduce the inferred scale dependence while remaining compatible with current CMB constraints. We release the public PIPE code to enable systematic tests of inflationary potentials against current CMB
datasets.
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Solar and Stellar Astrophysics
Solar cycle evolution of ICME sheath regions at 1 AU
C. Larrodera, M. Temmer and M. Owens
We investigate the
evolution of interplanetary coronal mass ejection (ICME) sheath regions at 1 AU across
solar cycles 23, 24, and the rising phase of 25, focusing on their variability and
turbulence in relation to upstream
solar wind conditions and the global heliospheric state. Using a
dataset of over 900 ICME sheath events, we apply statistical metrics such as the interquartile range (IQR) and the
Turbulence Index (TI) to quantify variability and
turbulence. The analysis compares full and rising phases of
solar cycles and examines both local ICME parameters (e.g., sheath total pressure, non-radial flows) and global interplanetary indicators such as open
solar flux (OSF). From SC23 to SC24, sheath total pressure and
magnetic field strength decreased by over 40% and 25%, respectively, accompanied by reduced
turbulence and variability. In contrast, the rising phase of SC25 shows increased
magnetic complexity, particularly in non-radial field components, despite stable bulk parameters. Non-radial flow patterns also shift from tangentially dominated in SC23-SC24 to normal-dominated in SC25, suggesting changes in ICME orientation and sheath formation mechanisms. No significant correlation is found between OSF and sheath properties, indicating that local
solar wind and ICME specific factors are the primary drivers of sheath
evolution. The study reinforces the importance of upstream
solar wind dynamics in relation to variations in
plasma and
magnetic field measured components of ICME sheaths. The derived trends in
turbulence,
magnetic orientation, and flow geometry suggest that sheath regions are sensitive indicators of
solar cycle phase and should be considered as distinct, structured components in ICME modeling.
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Earth and Planetary Astrophysics
Detailed spectroscopic and photometric analysis of the remarkable planet-hosting wide binary system HD 202772A/B
Emiliano Jofré, Yilen Gómez Maqueo Chew, Romina Petrucci et al. (+15 more)
We conducted a detailed spectroscopic and photometric characterization of the
planet-hosting wide binary HD 202772A/B. No
planet has been detected around HD 202772B, whereas HD 202772A, more evolved than its companion and near the end of its main-sequence (MS) phase, hosts a transiting hot Jupiter. The system has one of the hottest components ($T_{\mathrm{eff}; A} \sim 6440$ K) and one of the largest surface
gravity differences between components ($\Delta\log g_{A-B} \sim 0.4$ dex) among MS
planet-hosting wide binaries. Using a global fit including our
stellar parameters, radial velocities, and new TESS data, we derive refined properties of the
planet orbiting HD 202772A, finding it to be the most irradiated hot Jupiter known in a wide binary. We also constrain the presence of additional transiting
planets around HD 202772A and new transiting
planets around HD 202772B using TESS photometry. We derive high-precision, strictly differential abundances for 27 species based on Gemini-GRACES spectra. HD 202772A shows lower lithium abundance (by 0.45 dex) relative to B, consistent with their
stellar parameter differences. We also detect a small but significant enhancement in refractory elements in HD 202772A, particularly those with condensation temperatures above 1400 K (+0.018 $\pm$ 0.004 dex). We explored several scenarios to explain the observed chemical anomalies. Our analysis suggests that rocky
planet engulfment,
primordial inhomogeneities, and $\delta$ Scuti-related effects are unlikely to fully account for the chemical pattern. Instead, the differences observed in certain refractory elements might support atomic
diffusion as the most plausible explanation.
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All authors Emiliano Jofré, Yilen Gómez Maqueo Chew, Romina Petrucci, Carlos Saffe, Jhon Yana Galarza, Paula Miquelarena, María Paula Ronco, Matías Cerioni, Camila Zuloaga, Eder Martioli, Francesca Faedi, Cintia Martínez, Leila Saker, Jorge Meléndez, Matías Flores Trivigno, Leslie Hebb, Rodrigo Díaz, Luciano García
Earth and Planetary Astrophysics
Planets Across Space and Time (PAST). VIII : Kinematic Characterization and Identification of Radial Velocity Variables for the LAMOST-Gaia-TESS Stars
Di Wu, Di-Chang Chen, Ji-Wei Xie et al. (+6 more)
The Transiting
Exoplanet Survey Satellite (TESS) has discovered over 6700 nearby
exoplanets candidates using the transit method through its all-sky survey. Characterizing the kinematic properties and identifying variable
stars for the TESS
stellar sample is crucial for revealing the correlations between the properties of planetary systems and the properties of
stars (e.g.,
Galactic components, age, chemistry, dynamics, radiation). Based on data from TESS,
Gaia DR3, and LAMOST DR10, we present a catalog of kinematic properties (i.e.,
Galactic positions, velocities, orbits,
Galactic components, and kinematic age) as well as other basic
stellar parameters for $\sim 660,000$ TESS
stars. Our analysis of the kinematic catalog reveals that
stars belonging to different
Galactic components (i.e., thin disk, thick disk,
halo and 12 streams in the disk) display distinctive kinematic and chemical properties. We also find that hot
planets with period less then 10 days in the TESS sample favor thin disk
stars compared to thick disk
stars, consistent with previous studies. Furthermore, using the LAMOST multiple-epoch observations, we identify 41,445
stars exhibiting significant radial velocity variations, among which 7,846 are classified as binary
stars. By fitting the radial velocity curves, we further derive orbital parameters (e.g., mass ratio, orbital period and eccentricity) for 297 binaries. The observed decreasing orbital eccentricity with shorting period reveals evidence of
tidal circularization. The catalogs constructed in this work have laid a solid foundation for future work on the formation and
evolution of
stellar and planetary systems in different
Galactic environments.
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All authors Di Wu, Di-Chang Chen, Ji-Wei Xie, Ji-Lin Zhou, Hai-Feng Wang, Weikai Zong, Subo Dong, Maosheng Xiang, A-Li Luo
Instrumentation and Methods for Astrophysics
Keck Observatory as an HWO Testbed: validating wavefront sensing and control schemes on a large segmented aperture in parallel with high-contrast science
Maïssa Salama, Rebecca Jensen-Clem, Mahawa Cissé et al. (+6 more)
Exoplanet direct imaging allows us to directly probe and characterize an
exoplanet's atmosphere, searching for signs of life in its atmospheric signatures. Directly imaging an Earth-like
planet around a Sun-like
star requires reaching 10$^{-10}$ contrast levels and will be the goal of the Habitable Worlds Observatory (HWO). A key technical barrier to reaching such deep contrasts is maintaining wavefront stability on the order of tens of picometers, in particular in the presence of a segmented primary mirror. Keck Observatory is the only facility with all of the hardware components necessary for validating HWO segment phasing strategies: a large segmented primary mirror, capacitive edge sensors, deformable mirror, Zernike wavefront sensor (ZWFS), and high contrast science instruments. Taking advantage of these parallels, we are using Keck as a testbed for developing and validating HWO wavefront sensing and control loop strategies, as well as demonstrating the full system-level segment control architecture for HWO, using existing infrastructure. Recently, we set the stage for this work by using the ZWFS installed on the Keck II
telescope to sense and correct the primary mirror segment pistons in closed-loop in parallel with science observations. This resulted in improved Strehl ratios on the NIRC2 science camera (Salama et al. 2024a). We now aim to directly address concerns related to control authority, actuator offload, and loop stability - tasks which require Keck's existing infrastructure, but which do not require picometer wavefront stability. Moreover, successful comparisons of observed and predicted performances will validate, on a real operating observatory, the HWO error budget methodology and in particular its approach to nested loops operating at multiple timescales.
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All authors Maïssa Salama, Rebecca Jensen-Clem, Mahawa Cissé, J. Kent Wallace, Mitchell Troy, Laurent Pueyo, Charlotte Guthery, Antonin Bouchez, Vincent Chambouleyron
Astrophysics of Galaxies
$\mbox{H}$ $\mbox{I}$ 21-cm Absorption Spectra Classification using Machine Learning
Debasish Mondal, Anirudh S. Nemmani and Arunima Banerjee
$\mbox{H}$ $\mbox{I}$ 21-cm absorption, an extremely useful tool to study the cold atomic hydrogen gas, can arise either from the intervening
galaxies along the line-of-sight towards the background
radio source or from the
radio source itself. Determining whether $\mbox{H}$ $\mbox{I}$ 21-cm absorption lines detected as part of large, blind surveys are `intervening' or `associated' using optical spectroscopy would be unfeasible. We therefore investigate a more efficient, machine learning (ML)-based method to classify $\mbox{H}$ $\mbox{I}$ 21-cm absorption lines. Using a sample of 118 known $\mbox{H}$ $\mbox{I}$ 21-cm absorption lines from the literature, we train six ML models (Gaussian naive Bayes, logistic regression, decision tree, random forest, SVM and XGBoost) on the spectral parameters obtained by fitting the Busy function to the absorption spectra. We found that a random forest model trained on these spectral parameters gives the most reliable classification results, with an accuracy of 89%, a $F_1$-score of 0.9 and an AUC score of 0.94. We note that the linewidth parameter $w_{20}$ is the most significant spectral parameter that regulates the classification performance of this model. Retraining this random forest model only with this linewidth and the integrated optical depth parameters yields an accuracy of 88%, a $F_1$-score of 0.88 and an AUC score of 0.91. We have applied this retrained random forest model to predict the type of 30 new $\mbox{H}$ $\mbox{I}$ 21-cm absorption lines detected in recent blind surveys, viz. FLASH, illustrating the potential of the techniques developed in this work for future large $\mbox{H}$ $\mbox{I}$ surveys with the Square Kilometre Array.
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Solar and Stellar Astrophysics
Swaying oscillations in Rayleigh-Bénard convection cast new light on solar convection
F. Kupka, D. Fabbian, F. Zaussinger et al. (+2 more)
Horizontally-periodic Boussinesq Rayleigh-Bénard Convection (RBC) is a simple model system to study the formation of large-scale structures in turbulent convective flows. We performed a suite of 2D numerical simulations of RBC between no-slip boundaries at different Prandtl (Pr) and Rayleigh (Ra) numbers, such that their product is representative of the Sun's upper convection zone. When the fluid viscosity is sufficiently low (Pr $\lesssim 0.1$) and
turbulence is strong (Ra $> 10^6$) we find that large structures begin to couple in time and space. For Pr = 0.01 we observe long-lived swaying oscillations of the upflows and downflows, which synchronize over multiple convection
cells. This new regime of oscillatory convection may offer an interpretation for the wave-like properties of the dominant scale of convection on the Sun (supergranulation).
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All authors F. Kupka, D. Fabbian, F. Zaussinger, D. Krüger, L. Gizon
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Stochastic gravitational wave from graviton bremsstrahlung in inflaton decay into massive spin 3/2 particles
Diganta Das, Mihika Sanghi and Sourav
The detection of
primordial gravitational waves would offer a direct evidence of inflation and valuable insights into the dynamics of the early universe. During post-inflation reheating period, when the inflaton coherently oscillates at the bottom of its potential,
primordial stochastic gravitational waves may be sourced by its perturbative decay into particles of different
spins. Assuming the behavior of the potential near the minimum as a
polynomial $V(\phi)\sim \phi^k$, where $k\ge 2$, and treating the inflaton as coherently oscillating classical field, we calculate the decay of inflaton into a pair of
spin $3/2$ particles accompanied by graviton emission. We numerically study the reheating dynamics and calculate the
stochastic gravitational wave spectra. Our analysis shows that the gravitational wave spectra can offer insights into the microscopic physics during inflation.
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