Papers for Friday, Nov 11 2022

Active Galactic Nuclei (AGN) are known to show flux variability over all observable timescales and across the entire electromagnetic spectrum. Over the past decade, a growing number of sources have been observed to show dramatic flux and spectral changes, both in the X-rays and in the optical/UV. Such events, commonly described as "changing-look AGN", can be divided into two well-defined classes. Changing-obscuration objects show strong variability of the line-of-sight column density, mostly associated with clouds or outflows eclipsing the central engine of the AGN. Changing-state AGN are instead objects in which the continuum emission and broad emission lines appear or disappear, and are typically triggered by strong changes in the accretion rate of the supermassive black hole. Here we review our current understanding of these two classes of changing-look AGN, and discuss open questions and future prospects.

We present optical and near-infrared (NIR) observations of the Type Icn supernova (SN Icn) 2022ann, the fifth member of its newly identified class of SNe. Its early optical spectra are dominated by narrow carbon and oxygen P-Cygni features with absorption velocities of 800 km/s; slower than other SNe Icn and indicative of interaction with a dense, H/He-poor circumstellar medium (CSM) that is outflowing slower than a typical Wolf-Rayet wind velocity of $>$1000 km/s. We identify helium in NIR spectra obtained two weeks after maximum and in optical spectra at three weeks, demonstrating that the CSM is not fully devoid of helium. We never detect broad spectral features from SN ejecta, including in spectra extending to the nebular phase, a unique characteristic among SNe~Icn. Compared to other SNe Icn, SN 2022ann has a low luminosity, with a peak o-band absolute magnitude of -17.7, and evolves slowly. We model the bolometric light curve and find it is well-described by 1.7 M_Sun of SN ejecta interacting with 0.2 M_sun of CSM. We place an upper limit of 0.04 M_Sun of Ni56 synthesized in the explosion. The host galaxy is a dwarf galaxy with a stellar mass of 10^7.34 M_Sun (implied metallicity of log(Z/Z_Sun) $\approx$ 0.10) and integrated star-formation rate of log(SFR) = -2.20 M_sun/yr; both lower than 97\% of the galaxies observed to produce core-collapse supernovae, although consistent with star-forming galaxies on the galaxy Main Sequence. The low CSM velocity, nickel and ejecta masses, and likely low-metallicity environment disfavour a single Wolf-Rayet progenitor star. Instead, a binary companion star is likely required to adequately strip the progenitor before explosion and produce a low-velocity outflow. The low CSM velocity may be indicative of the outer Lagrangian points in the stellar binary progenitor, rather than from the escape velocity of a single Wolf-Rayet-like massive star.

Axion-Like Particles (ALPs) are well-motivated extensions of the Standard Model of Particle Physics and a generic prediction of some string theories. X-ray observations of bright Active Galactic Nuclei (AGN) hosted by rich clusters of galaxies are excellent probes of very-light ALPs, with masses $\mathrm{log}(m_\mathrm{a}/\mathrm{eV})<-12.0$. We evaluate the potential of future X-ray observatories, particularly $Athena$ and the proposed $AXIS$, to constrain ALPs via observations of cluster-hosted AGN, taking NGC1275 in the Perseus cluster as our exemplar. Assuming perfect knowledge of instrument calibration, we show that a modest exposure (200-ks) of NGC1275 by $Athena$ permits us to exclude all photon-ALP couplings $g_\mathrm{a\gamma}>6.3 \times 10^{-14} \ {\mathrm{GeV}}^{-1}$ at the 95% level, as previously shown by $Conlon$ et al. (2017), representing a factor of 10 improvement over current limits. We proceed by assessing the impact of realistic calibration uncertainties on the $Athena$ projection via a standard $Cash$ likelihood procedure, showing the projected constraints on $g_\mathrm{a\gamma}$ weaken by a factor of 10 (back to the current most sensitive constraints). However, we show how the use of a deep neural network can disentangle the energy-dependent features induced by instrumental miscalibration and those induced by photon-ALP mixing, allowing us to recover most of the sensitivity to the ALP physics. In our explicit demonstration, the machine learning applied allows us to exclude $g_\mathrm{a\gamma}>1.25 \times 10^{-13} \ {\mathrm{GeV}}^{-1}$, complementing the projected constraints of next-generation ALP dark matter birefringent cavity searches for very-light ALPs. Finally, we show that a 200-ks $AXIS$/on-axis observation of NGC1275 will tighten the current best constraints on very-light ALPs by a factor of 3.

Luminous red novae (LRNe) are transients characterized by low luminosities and expansion velocities, and are associated with mergers or common envelope ejections in stellar binaries. Intermediate-luminosity red transients (ILRTs) are an observationally similar class with unknown origins, but generally believed to either be electron capture supernovae (ECSN) in super-AGB stars, or outbursts in dusty luminous blue variables (LBVs). In this paper, we present a systematic sample of 8 LRNe and 8 ILRTs detected as part of the Census of the Local Universe (CLU) experiment on the Zwicky Transient Facility (ZTF). The CLU experiment spectroscopically classifies ZTF transients associated with nearby ($<150$ Mpc) galaxies, achieving 80% completeness for m$_{r}<20$\,mag. Using the ZTF-CLU sample, we derive the first systematic LRNe volumetric-rate of 7.8$^{+6.5}_{-3.7}\times10^{-5}$ Mpc$^{-3}$ yr$^{-1}$ in the luminosity range $-16\leq$M$_{\rm{r}}$$\leq -11$ mag. We find that in this luminosity range, the LRN rate scales as dN/dL $\propto L^{-2.5\pm0.3}$ - significantly steeper than the previously derived scaling of $L^{-1.4\pm0.3}$ for lower luminosity LRNe (M$_{V}\geq-10$). The steeper power law for LRNe at high luminosities is consistent with the massive merger rates predicted by binary population synthesis models. We find that the rates of the brightest LRNe (M$_{r}\leq-13$ mag) are consistent with a significant fraction of them being progenitors of double compact objects (DCOs) that merge within a Hubble time. For ILRTs, we derive a volumetric rate of $2.6^{+1.8}_{-1.4}\times10^{-6}$ Mpc$^{-3}$yr$^{-1}$ for M$_{\rm{r}}\leq-13.5$, that scales as dN/dL $\propto L^{-2.5\pm0.5}$. This rate is $\approx1-5\%$ of the local core-collapse supernova rate, and is consistent with theoretical ECSN rate estimates.

The fine structure constant, $\alpha$, sets the strength of the electromagnetic force. The Standard Model of particle physics provides no explanation for its value, which could potentially vary. The wavelengths of stellar absorption lines depend on $\alpha$, but are subject to systematic effects owing to astrophysical processes in stellar atmospheres. We measured precise line wavelengths using 17 stars, selected to have almost identical atmospheric properties to those of the Sun (solar twins), which reduces those systematic effects. We found that $\alpha$ varies by $\lesssim$50 parts-per-billion (ppb) within 50 parsecs from Earth. Combining the results from all 17 stars provides an empirical, local reference for stellar measurements of $\alpha$ with an ensemble precision of 12 ppb.

The magnetosphere of an exoplanet has yet to be unambiguously detected. Investigations of star-planet interaction and neutral atomic hydrogen absorption during transit to detect magnetic fields in hot Jupiters have been inconclusive, and interpretations of the transit absorption non-unique. In contrast, ionized species escaping a magnetized exoplanet, particularly from the polar caps, should populate the magnetosphere, allowing detection of different regions from the plasmasphere to the extended magnetotail, and characterization of the magnetic field producing them. Here, we report ultraviolet observations of HAT-P-11b, a low-mass (0.08 MJ) exoplanet showing strong, phase-extended transit absorption of neutral hydrogen (maximum and tail transit depths of 32 \pm 4%, 27 \pm 4%) and singly ionized carbon (15 \pm 4%, 12.5 \pm 4%). We show that the atmosphere should have less than six times the solar metallicity (at 200 bars), and the exoplanet must also have an extended magnetotail (1.8-3.1 AU). The HAT-P-11b equatorial magnetic field strength should be about 1-5 Gauss. Our panchromatic approach using ionized species to simultaneously derive metallicity and magnetic field strength can now constrain interior and dynamo models of exoplanets, with implications for formation and evolution scenarios.

Radial velocity (RV) measurements of transiting multiplanet systems allow us to understand the densities and compositions of planets unlike those in the Solar System. Kepler-102, which consists of 5 tightly packed transiting planets, is a particularly interesting system since it includes a super-Earth (Kepler-102d) and a sub-Neptune-sized planet (Kepler-102e) for which masses can be measured using radial velocities. Previous work found a high density for Kepler-102d, suggesting a composition similar to that of Mercury, while Kepler-102e was found to have a density typical of sub-Neptune size planets; however, Kepler-102 is an active star, which can interfere with RV mass measurements. To better measure the mass of these two planets, we obtained 111 new RVs using Keck/HIRES and TNG/HARPS-N and modeled Kepler-102's activity using quasi-periodic Gaussian Process Regression. For Kepler-102d, we report a mass upper limit of M$_{d} < $5.3 M$_{\oplus}$ [95\% confidence], a best-fit mass of M$_{d}$=2.5 $\pm$ 1.4 M$_{\oplus}$, and a density of $\rho_{d}$=5.6 $\pm$ 3.2 g/cm$^{3}$ which is consistent with a rocky composition similar in density to the Earth. For Kepler-102e we report a mass of M$_{e}$=4.7 $\pm$ 1.7 M$_{\oplus}$ and a density of $\rho_{e}$=1.8 $\pm$ 0.7 g/cm$^{3}$. These measurements suggest that Kepler-102e has a rocky core with a thick gaseous envelope comprising 2-4% of the planet mass and 16-50% of its radius. Our study is yet another demonstration that accounting for stellar activity in stars with clear rotation signals can yield more accurate planet masses, enabling a more realistic interpretation of planet interiors.

The Crab Pulsar is the prime example of an emitter of giant pulses. These short, very bright pulses are thought to originate near the light cylinder, at $\sim\!1600{\rm\;km}$ from the pulsar. The pulsar's location inside the Crab Nebula offers an unusual opportunity to resolve the emission regions, using the nebula, which scatters radio waves, as a lens. We attempt to do this using a sample of 61998 giant pulses found in coherently combined European VLBI network observations at $18{\rm\;cm}$. These were taken at times of relatively strong scattering and hence good effective resolution, and from correlations between pulse spectra, we show that the giant pulse emission regions are indeed resolved. We infer apparent diameters of $\sim\!2000$ and $\sim\!2400{\rm\;km}$ for the main and interpulse components, respectively, and show that with these sizes the correlation amplitudes and decorrelation timescales and bandwidths can be understood quantitatively, both in our observations and in previous ones. Using pulse-spectra statistics and correlations between polarizations, we also show that the nebula resolves the nanoshots that comprise individual giant pulses. The implied diameters of $\sim\!1100{\rm\;km}$ far exceed light travel-time estimates, suggesting the emitting plasma is moving relativistically, with $\gamma\simeq10^{4}$, as inferred previously from drifting bands during the scattering tail of a giant pulse. If so, the emission happens over a region extended along the line of sight by $\sim\!10^{7}{\rm\;km}$. We conclude that relativistic motion likely is important for producing giant pulses, and may be similarly for other sources of short, bright radio emission, such as fast radio bursts.

Instrumental aberrations strongly limit high-contrast imaging of exoplanets, especially when they produce quasi-static speckles in the science images. With the help of recent advances in deep learning, we have developed in previous works an approach that applies convolutional neural networks (CNN) to estimate pupil-plane phase aberrations from point spread functions (PSF). In this work we take a step further by incorporating into the deep learning architecture the physical simulation of the optical propagation occurring inside the instrument. This is achieved with an autoencoder architecture, which uses a differentiable optical simulator as the decoder. Because this unsupervised learning approach reconstructs the PSFs, knowing the true phase is not needed to train the models, making it particularly promising for on-sky applications. We show that the performance of our method is almost identical to a standard CNN approach, and that the models are sufficiently stable in terms of training and robustness. We notably illustrate how we can benefit from the simulator-based autoencoder architecture by quickly fine-tuning the models on a single test image, achieving much better performance when the PSFs contain more noise and aberrations. These early results are very promising and future steps have been identified to apply the method on real data.

The theme of tensions in cosmology has become increasingly important in the cosmological community, proving capable of attracting new generations of scientists who want to be there and contribute to the next paradigm shift.

Binary neutron star (BNS) post-merger gravitational-wave emission can occur in the aftermath of a BNS merger -- provided the system avoids prompt collapse to a black hole -- as a quasistable hypermassive remnant experiences quadrupolar oscillations and non-axisymmetric deformations. The post-merger gravitational-wave spectrum possesses a characteristic peak frequency that has been shown to be dependent on the binary chirp mass and the neutron star equation of state (EoS), rendering post-merger gravitational waves a powerful tool for constraining neutron star composition. Unfortunately, the BNS post-merger signal is emitted at high ($\gtrsim 1.5$ kHz) frequencies, where ground-based gravitational wave detectors suffer from reduced sensitivity. It is therefore unlikely that post-merger signals will be detected with sufficient signal-to-noise ratio (SNR) until the advent of next-generation detectors. However, by employing empirical relations derived from numerical relativity simulations, we can combine information across an ensemble of BNS mergers, allowing us to obtain EoS constraints with many low-SNR signals. We present a hierarchical Bayesian method for deriving constraints on $R_{1.6}$, the radius of a 1.6$\mathrm{M_{\odot}}$ neutron star, through an ensemble analysis of binary neutron star mergers. We apply this method to simulations of the next two LIGO-Virgo-KAGRA observing runs, O4 and O5, as well as an extended 4-year run at A+ sensitivity, demonstrating the potential of our approach to yield EoS information from the post-merger signal with current-generation detectors. The A+ 4-year scenario is predicted to improve the constraint on $R_{1.6}$ from the currently available multimessenger-based 95% C.I. uncertainty of $R_{1.6}=12.07^{+0.98}_{-0.77}$ km to $R_{1.6}=11.91^{+0.80}_{-0.56}$ km, a 22% reduction of the 95% C.I. width.

During the Grand Finale stage of the Cassini mission, organic-rich ring material was discovered to be flowing into Saturn's equatorial upper atmosphere at a surprisingly large rate. Through a series of photochemical models, we have examined the consequences of this ring material on the chemistry of Saturn's neutral and ionized atmosphere. We find that if a substantial fraction of this material enters the atmosphere as vapor or becomes vaporized as the solid ring particles ablate upon atmospheric entry, then the ring-derived vapor would strongly affect the composition of Saturn's ionosphere and neutral stratosphere. Our surveys of Cassini infrared and ultraviolet remote-sensing data from the final few years of the mission, however, reveal none of these predicted chemical consequences. We therefore conclude that either (1) the inferred ring influx represents an anomalous, transient situation that was triggered by some recent dynamical event in the ring system that occurred a few months to a few tens of years before the 2017 end of the Cassini mission, or (2) a large fraction of the incoming material must have been entering the atmosphere as small dust particles less than ~100 nm in radius, rather than as vapor or as large particles that are likely to ablate. Future observations or upper limits for stratospheric neutral species such as HC$_3$N, HCN, and CO$_2$ at infrared wavelengths could shed light on the origin, timing, magnitude, and nature of a possible vapor-rich ring-inflow event.

The Tucana-Horologium Association (Tuc-Hor) is a 40 Myr old moving group in the southern sky. In this work, we measure the rotation periods of 313 Tuc-Hor objects with TESS light curves derived from TESS full frame images and membership lists driven by Gaia EDR3 kinematics and known youth indicators. We recover a period for 81.4% of the sample and report 255 rotaion periods for Tuc-Hor objects. From these objects we identify 11 candidate binaries based on multiple periodic signals or outlier Gaia DR2 and EDR3 re-normalised unit weight error (RUWE) values. We also identify three new complex rotators (rapidly rotating M dwarf objects with intricate light curve morphology) within our sample. Along with the six previously known complex rotators that belong to Tuc-Hor, we compare their light curve morphology between TESS Cycle 1 and Cycle 3 and find they change substantially. Furthermore, we provide context for the entire Tuc-Hor rotation sample by describing the rotation period distributions alongside other youth indicators such as H{\alpha} and Li equivalent width, as well as near ultra-violet and X ray flux. We find that measuring rotation periods with TESS to be a fast and effective means to confirm members in young moving groups.

This Special Topic focuses on magnetohydrodynamic (MHD) processes in deep interiors of planets, in which their fluid dynamos are in operation. The dynamo-generated, global, magnetic fields provide a background for our solar-terrestrial environment. Probing the processes within the dynamos is a significant theoretical and computational challenge and any window into interior dynamics greatly increases our understanding. Such a window is provided by exploring rapid dynamics, particularly MHD waves about the dynamo-defined basic state. This field is the subject of current attention as geophysical observations and numerical modellings advance. We give here particular attention to torsional Alfv\'{e}n waves/oscillations and magnetic Rossby waves, which may be regarded as typical axisymmetric and nonaxisymmetric modes, respectively, amongst a wide variety of wave classes of the rapidly-rotating MHD fluids. The excitation of those waves is being evidenced for the geodynamo, whilst also being suggested for Jupiter. We shall overview their dynamics, summarise our current understanding, and give open questions for future perspectives.

We examine the quenching characteristics of $328$ isolated dwarf galaxies $\left(10^{8} < M_{\rm star}/M_\odot < 10^{10} \right)$ within the \Rom{} cosmological hydrodynamic simulation. Using mock observation methods, we identify isolated dwarf galaxies with quenched star formation and make direct comparisons to the quenched fraction in the NASA Sloan Atlas (NSA). Similar to other cosmological simulations, we find a population of quenched, isolated dwarf galaxies below $M_{\rm star} < 10^{9} M_\odot$ not detected within the NSA. We find that the presence of massive black holes (MBHs) in \Rom{} is largely responsible for the quenched, isolated dwarfs, while isolated dwarfs without an MBH are consistent with quiescent fractions observed in the field. Quenching occurs between $z=0.5-1$, during which the available supply of star-forming gas is heated or evacuated by MBH feedback. Mergers or interactions seem to play little to no role in triggering the MBH feedback. At low stellar masses, $M_{\rm star} \lesssim 10^{9.3} M_\odot$, quenching proceeds across several Gyr as the MBH slowly heats up gas in the central regions. At higher stellar masses, $M_{\rm star} \gtrsim 10^{9.3} M_\odot$, quenching occurs rapidly within $1$ Gyr, with the MBH evacuating gas from the central few kpc of the galaxy and driving it to the outskirts of the halo. Our results indicate the possibility of substantial star formation suppression via MBH feedback within dwarf galaxies in the field. On the other hand, the apparent over-quenching of dwarf galaxies due to MBH suggests higher resolution and/or better modeling is required for MBHs in dwarfs, and quenched fractions offer the opportunity to constrain current models.

Based on 2-minute cadence TESS data from sectors 1-50, we report the results of the systematic extraction of $\delta$ Scuti-type pulsations in the 6431 eclipsing binaries with orbital periods shorter than 13 days. A total number of 242 pulsators were found in those systems, including 143 new discoveries. We examined their pulsation properties based on the H-R diagram and the relationships between the dominant pulsation period $P_{\rm dom}$, orbital period $P_{\rm orb}$, and effective temperature $T_{\rm eff}$. As a consequence, 216 targets are likely $\delta$ Scuti stars (123 new), 11 likely $\gamma$ Doradus-$\delta$ Scuti hybrid stars (8 new), 5 likely $\beta$ Cephei stars (4 new), 4 likely $\delta$ Scuti-$\gamma$ Doradus hybrid stars (3 new), 3 likely Maia stars (3 new), 2 likely pulsating red giants (1 new), and a new unclassified star. As for the 6 new $\delta$ Scuti pulsators in eclipsing binaries with $P_{\rm orb}$ $<$ 0.65 days, we found that 3 of them significantly exceed the upper limits of the $P_{\rm dom}$/$P_{\rm orb}$ ratio. This may indicate that $P_{\rm dom}$ and $P_{\rm orb}$ are uncorrelated for them. Finally, we statistically analyzed the dominant pulsation periods of the 216 $\delta$ Scuti stars in eclipsing binaries. Those stars concentrate around 225 $\mu$Hz and the proportion of stars in the high-frequency region is significantly higher than that of single stars, which could be ascribed to the mass transfer process.

The effects of an accretion disk are crucial to understanding the evolution of young stars. During the combined evolution, stellar and disk parameters influence each other, motivating a combined stellar and disk model. This makes a combined numerical model, evolving the disk alongside the star, the next logical step in the progress of studying early stellar evolution. We aim to understand the effects of metallicity on the accretion disk and the stellar spin evolution during the T~Tauri phase. We combine the numerical treatment of a hydrodynamic disk with stellar evolution, including a stellar spin model, allowing a self-consistent calculation of the back-reactions between the individual components. We present the self-consistent theoretical evolution of T-Tauri stars coupled to a stellar disk. We find that disks in low metallicity environments are heated differently and have shorter lifetimes, compared to their solar metallicity counterparts. Differences in stellar radii, the contraction rate of the stellar radius, and the shorter disk lifetimes result in faster rotation of low metallicity stars. We present an additional explanation for the observed short disk lifetimes in low metallicity clusters. A combination of our model with previous studies (e.g., a metallicity-based photo-evaporation) could help to understand disk evolution and dispersal at different metallicities. Furthermore, the stellar spin evolution model includes several important effects, previously ignored (e.g., the stellar magnetic field strength and a realistic calculation of the disk lifetime) and we motivate to include our results as initial or input parameters for further spin evolution models, covering the stellar evolution towards and during the main sequence.

Lower atmospheric lines show peculiar profiles at the leading edge of ribbons during solar flares. In particular, increased absorption of the BBSO/GST \hei~10830~\AA\ line \citep[e.g.][]{Xu2016}, as well as broad and centrally reversed profiles in the spectra of the \mgii~and \cii~lines observed by the \iris~satellite \citep[e.g.][]{Panos2018,Panos2021a} have been reported. In this work, we aim to understand the physical origin of the \iris\ ribbon front line profiles, which seem to be common of many, if not all, flares. To achieve this, we quantify the spectral properties of the \iris~\mgii~ribbon front profiles during four large flares and perform a detailed comparison with a grid of radiative hydrodynamic models using the \radynfp~code. We also studied their transition region counterparts, finding that these ribbon front locations are regions where transition region emission and chromospheric evaporation are considerably weaker compared to other parts of the ribbons. Based on our comparison between the \iris~observations and modelling, our interpretation is that there are different heating regimes at play in the leading and trailing regions of the ribbons. More specifically, we suggest that bombardment of the chromosphere by more gradual and modest non-thermal electron energy fluxes can qualitatively explain the \iris~observations at the ribbon front, while stronger and more impulsive energy fluxes are required to drive chromospheric evaporation and more intense TR emission. Our results provide a possible physical origin for the peculiar behaviour of the \iris~chromospheric lines in the ribbon leading edge and new constraints for the flare models.

We present a 2D kinematic model to study the acceleration of solar energetic particles (SEPs) at a shock driven by a coronal mass ejection. The shock is assumed to be spherical about an origin that is offset from the center of the Sun. This leads to a spatial and temporal evolution of the angle between the magnetic field and shock normal direction ($\theta_{Bn}$) as it propagates through the Parker spiral magnetic field from the lower corona to 1 AU. We find that the high-energy SEP intensity varies significantly along the shock front due to the evolution of $\theta_{Bn}$. Generally, the west flank of the shock preferentially accelerates particles to high energies compared to the east flank and shock nose. This can be understood in terms of the rate of acceleration, which is higher at the west flank. Double power-law energy spectra are reproduced in our model as a consequence of the local acceleration and transport effects. These results will help better understand the evolution of SEP acceleration and provide new insights into large SEP events observed by multi-spacecraft, especially those close to the Sun, such as Parker Solar Probe and Solar Orbiter.

The cosmic microwave background temperature is a cornerstone astrophysical observable. Its present value is tightly constrained, but its redshift dependence, which can now be determined until redshift $z\sim6.34$, is also an important probe of fundamental cosmology. We show that its constraining power is now comparable to that of other background cosmology probes, including Type Ia supernovae and Hubble parameter measurements. We illustrate this with three models, each based on a different conceptual paradigm, which aim to explain the recent acceleration of the universe. We find that for parametric extension of $\Lambda$CDM the combination of temperature and cosmological data significantly improves constraints on the model parameters, while for alternative models without a $\Lambda$CDM limit this data combination rules them out.

The nonattractor evolution in ultra-slow-roll (USR) inflation results in the amplification of superhorizon curvature perturbations and then induces a strong and detectable stochastic gravitational wave background. In this letter, we search for such a stochastic gravitational wave background in data from the third LIGO-Virgo observing run and place constraints on the USR inflationary models. The $e$-folding number of the USR phase are constrained to be $\Delta N \lesssim 2.9$ at the 95% confidence level and the power spectrum of curvature perturbations amplified during the USR phase is constrained to be $\log_{10}P_{R\mathrm{p}}<-1.7$ at the scales $2.9\times10^5 ~\mathrm{pc^{-1}} \lesssim k \lesssim 1.7\times10^{11}~\mathrm{pc^{-1}}$. Besides, we forecast the ability of future experiments to constrain USR inflation, and find $P_{R\mathrm{p}}\lesssim 10^{-3.6}$ for LISA and Taiji, $P_{R\mathrm{p}}\lesssim 10^{-3.3}$ for Cosmic Explore and Einstein Telescope, $P_{R\mathrm{p}}\lesssim 10^{-5.5}$ for DECIGO and Big Bang Observer and $P_{R\mathrm{p}}\lesssim 10^{-5.2}$ for Square Kilometre Array.

From the main sequence to their late evolutionary stages, massive stars spend most of their life as hot stars. Due to their high effective temperatures, the maximum of their emitted flux falls into the ultraviolet (UV) regime. Consequently, these stars emit a significant number of photons with energies sufficiently high enough to ionize hydrogen and other elements. As simple as these fundamental considerations are, as complex is a realistic estimate of the resulting ionizing fluxes, in particular for energies above 54 eV. Estimating the ionizing flux budget of hot stars requires accurate models of their spectral energy distributions (SEDs), covering in particular the far and extreme UV region. Modern atmosphere models that incorporate the so-called line-blanketing effect, i.e. taking into account the millions of lines from iron and other elements, yield a complex picture, illustrating that the SED of a hot, massive star usually deviates significantly from a blackbody.

The flare activity of the Sun has been studied for decades, using both space- and ground-based telescopes. In particular, the Interface Region Imaging Spectrograph (IRIS) provides unique diagnostics to investigate the thermodynamics of flares in the solar atmosphere. The Mg II h&k and Mg II UV triple lines provide key information about the thermodynamics of low to upper chromosphere, while the C II 1334 & 1335 AA lines cover the upper-chromosphere and low transition region. The Mg II h&k and Mg II UV triplet lines show a peculiar, pointy shape before and during the flare activity. The physical interpretation that can explain these profiles has remained elusive. In this paper, we show the results of a non-LTE inversion of such peculiar profiles. To better constrain the atmospheric conditions, the Mg II h&k and Mg II UV triple lines are simultaneously inverted with the C II 1334 & 1335 AA lines. This combined inversion leads to more accurate derived thermodynamic parameters, especially the temperature and the turbulent motions (micro-turbulence velocity). We use the inversion code STiC to look for the best fit between the observed profile and a synthetic profile obtained by solving the radiative transfer problem considering non-local thermodynamic equilibrium and partial frequency redistribution of the radiation due to scattered photons. We are able to conclude that these unique, pointy profiles are associated with a simultaneous increase of the temperature and the electron density in the chromosphere, while the micro-turbulence velocity has values between 5-15 km/s, which seem to be more realistic values than the ones suggested in previous work. More importantly, the line-of-sight velocity shows a large gradient along the optical depth in the high chromosphere. This seems to be the parameter that gives the pointy aspect to these profiles.

Determining the composition of giant exoplanets is crucial for understanding their origin and evolution. However, the planetary bulk composition is not measured directly but must be deduced from a combination of mass-radius measurements, knowledge of the planetary age and evolution simulations. Accurate determinations of stellar ages, mass-radius, and atmospheric compositions from upcoming missions can significantly improve the determination of the heavy-element mass in giant planets. In this paper, we first demonstrate the importance of an accurate age measurement, as expected from Plato, in constraining the planetary properties. Well-determined stellar ages can reduce the bulk-metallicity uncertainty up to about a factor of two. We next infer the bulk metallicity of warm giants from the Ariel mission reference sample and identify the Ariel high-priority targets for which a measured atmospheric metallicity can clearly break the degeneracy in the inferred composition. We show that knowledge of the atmospheric metallicity can broadly reduce the bulk-metallicity uncertainty by a factor of four to eight. We conclude that the accurate age determination from Plato and atmospheric measurements by Ariel and the James Webb Space Telescope will play a key role in revealing the composition of giant exoplanets.

We look at dark energy from a biology inspired viewpoint by means of the Approximate Bayesian Computation (ABC) and late time cosmological observations. We find that dynamical dark energy comes out on top, or in the ABC language naturally selected, over the standard $\Lambda$CDM cosmological scenario. We confirm this conclusion is robust to whether baryon acoustic oscillations and Hubble constant priors are considered. Our results show that the algorithm prefers low values of the Hubble constant, consistent or at least a few standard deviation away from the cosmic microwave background estimate, regardless of the priors taken initially in each model. This supports the result of the traditional MCMC analysis and could be viewed as strengthening evidence for dynamical dark energy being a more favorable model of late time cosmology.

In this paper we present a numerical study of the dynamics of partially ionized coronal rain blobs. We use a two-fluid model to perform a high-resolution 2D simulation that takes into account the collisional interaction between the charged and neutral particles contained in the plasma. We follow the evolution of a cold plasma condensation as it falls through an isothermal vertically stratified atmosphere that represents the much hotter and lighter solar corona. We study the consequences of the different degrees of collisional coupling that are present in the system. On the one hand, we find that at the dense core of the blob there is a very strong coupling and the charged and neutral components of the plasma behave as a single fluid, with negligible drift velocities (of a few cm s^-1). On the other hand, at the edges of the blob the coupling is much weaker and larger drift velocities (of the order of 1 km s^-1) appear. In addition, frictional heating causes large increases of temperature at the transition layers between the blob and the corona. For the first time we show that such large drift velocities and temperature enhancements can develop as a consequence of ion-neutral decoupling associated to coronal rain dynamics. This can lead to enhanced emission coming from the plasma at the coronal rain-corona boundary, which possesses transition region temperature.

Star formation models predict that the metal-poor initial mass function (IMF) can be substantially different from that observed in the metal-rich Milky Way. This changeover occurs because metal-poor gas clouds cool inefficiently due to their lower abundance of metals and dust. However, predictions for the metal-poor IMF to date rely on assuming Solar-scaled abundances, that is, [X/O] = 0 at all [O/H]. There is now growing evidence that elements such as C and O that dominate metal line cooling in the ISM do not follow Solar scaling at low metallicities. In this work, we extend models that predict the variation in the characteristic (or, the peak) IMF mass as a function of metallicity using [C/O] ratios derived from observations of metal-poor Galactic stars and of H II regions in dwarf galaxies. These data show [C/O] < 0 at sub-Solar [O/H], which leads to a substantially different metal-poor IMF in the metallicity range where C I and C II cooling dominate ISM thermodynamics, resulting in an increase in the characteristic mass by a factor as large as 7. An important consequence of this difference is a shift in the location of the transition from a top- to a bottom-heavy IMF upwards by 0.5 $-$ 1 dex in metallicity. Our findings indicate that the IMF is very sensitive to the assumptions around Solar-scaled ISM compositions in metal-poor systems (e.g., dwarf galaxies, the Galactic halo and metal-poor stars) that are a key focus of JWST.

Solar flares are often accompanied by filament/prominence eruptions, sometimes leading to coronal mass ejections (CMEs). By analogy, we expect that stellar flares are also associated with stellar CMEs whose properties are essential to know the impact on exoplanet habitability. Probable detections of stellar CMEs are still rare, but in this decade, there are several reports that (super-)flares on M/K-dwarfs and evolved stars sometimes show blue-shifted optical/UV/X-ray emissions lines, XUV/FUV dimming, and radio bursts. Some of them are interpreted as indirect evidence of stellar prominence eruptions/CMEs on cool stars. More recently, evidence of stellar filament eruption, probably leading to a CME, is reported even on a young solar-type star (G-dwarf) as a blue-shifted absorption of H$\alpha$ line associated with a superflare. Notably, the erupted masses for superflares are larger than those of the largest solar CMEs, indicating severe influence on exoplanet environments. The ratio of the kinetic energy of stellar CMEs to flare energy is significantly smaller than expected from the solar scaling relation and this discrepancy is still in debate. We will review the recent updates of stellar CME studies and discuss the future direction in this paper.

The redshifted 21-cm radiation from the atomic hydrogen (HI) provides an excellent direct probe to study the evolution of HI in IGM and thus reveal the nature of the first luminous objects, their evolution and role during Cosmic Dawn (CD) and Epoch of Reionization (EoR), and formation and evolution of the structures thereafter. Direct mapping of the HI density during the CD-EoR is rather difficult with the current and future instruments due to large foreground and other observational contamination. The first detection of this redshifted HI signal is planned through statistical estimators. Given the utmost importance of the detection and analysis of the redshifted 21-cm signal, physics of CD-EoR is one of the objectives of the upcoming SKA-Low telescope. This paper summarizes the collective effort of Indian astronomers to understand the origin of the redshifted 21-cm signal, sources of first ionizing photons, their propagation through the IGM, various cosmological effects on the expected 21-cm signal, various statistical measures of the signal like power spectrum, bispectrum, etc. A collective effort on detection of the signal by developing estimators of the statistical measures with rigorous assessment of their expected uncertainties, various challenges like that of the large foreground emission and calibration issues are also discussed. Various versions of the detection methods discussed here have also been used in practice with the GMRT with successful assessment of the foreground contamination and upper limits on the matter density in EoR and post-EoR. The collective efforts compiled here has been a large part of the global effort to prepare proper observational technique and analysis procedure for the first light of the CD-EoR through the SKA-Low.

A trade-off between speed and information controls our understanding of astronomical objects. Fast-to-acquire photometric observations provide global properties, while costly and time-consuming spectroscopic measurements enable a better understanding of the physics governing their evolution. Here, we tackle this problem by generating spectra directly from photometry, through which we obtain an estimate of their intricacies from easily acquired images. This is done by using multi-modal conditional diffusion models, where the best out of the generated spectra is selected with a contrastive network. Initial experiments on minimally processed SDSS galaxy data show promising results.

We present a new derivation of the Milky Way's current star formation rate (SFR) based on the data of the Hi-GAL Galactic plane survey. We estimate the distribution of the SFR across the Galactic plane from the star-forming clumps identified in the Hi-GAL survey and calculate the total SFR from the sum of their contributions. The estimate of the global SFR amounts to $2.0 \pm 0.7$~M$_{\odot}$~yr$^{-1}$, of which $1.7 \pm 0.6$~M$_{\odot}$~yr$^{-1}$ coming from clumps with reliable heliocentric distance assignment. This value is in general agreement with estimates found in the literature of last decades. The profile of SFR density averaged in Galactocentric rings is found to be qualitatively similar to others previously computed, with a peak corresponding to the Central Molecular Zone and another one around Galactocentric radius $R_\mathrm{gal} \sim 5$~kpc, followed by an exponential decrease as $\log(\Sigma_\mathrm{SFR}/[\mathrm{M}_\odot~\mathrm{yr}^{-1}~\mathrm{kpc}^{-2}])=a\,R_\mathrm{gal}/[\mathrm{kpc}]+b $, with $a=-0.28 \pm 0.01$. In this regard, the fraction of SFR produced within and outside the Solar circle is 84\% and 16\%, respectively; the fraction corresponding to the far outer Galaxy ($R_\mathrm{gal} > 13.5$~kpc) is only 1\%. We also find that, for $R_\mathrm{gal}>3$~kpc, our data follow a power law as a function of density, similarly to the Kennicutt-Schmidt relation. Finally, we compare the distribution of the SFR density across the face-on Galactic plane and those of median parameters, such as temperature, luminosity/mass ratio and bolometric temperature, describing the evolutionary stage of Hi-GAL clumps. We found no clear correlation between the SFR and the clump evolutionary stage.

The intensity of radiation at millimeter wavelengths from the solar atmosphere is closely related to the plasma temperature and the height of formation of the radiation is wavelength dependent. From that follows that the slope of the brightness temperature (T$_\mathrm{b}$) continuum, samples the local gradient of the gas temperature of the sampled layers in the solar atmosphere. We use solar observations from the Atacama Large Millimeter/sub-millimeter Array (ALMA) and perform estimations and prediction of the slope of the T$_\mathrm{b}$ continuum based on differences between synthetic observables at different ALMA receiver sub-bands (2.8-3.2 mm; band 3) and (1.20-1.31 mm; band 6) from a state-of-the-art 3D rMHD simulation. The slope of the continuum is coupled to the small-scale dynamics and a positive sign indicates an increase in temperature with height while a negative sign implies a decrease. Network patches are dominated by large positive slopes while quiet Sun region show a mixture of positive and negative slopes, much in connection to propagating shock waves and the temporal evolution of the slopes can therefore be used to identify shocks. The observability of the slope of brightness temperatures is estimated for angular resolutions corresponding to ALMA observations. The simulations also show that the radiation of both bands 3 and 6 can origin from several components at different heights simultaneously and that the delay of shock signatures between two wavelengths does not necessarily reflect the propagation speed, but could be caused by different rate of change of opacity of above-lying layers. The slope of the T$_\mathrm{b}$ continuum sampled at different ALMA receiver sub-bands serves as indicator of the slope of the local plasma temperature at the sampled heights in the atmosphere, which offers new diagnostic possibilities to measure the underlying physical properties.

Tidal orbital decay is suspected to occur especially for hot Jupiters, with the only observationally confirmed case of this being WASP-12 b. By examining this effect, information on the properties of the host star can be obtained using the so-called stellar modified tidal quality factor $Q_*'$, which describes the efficiency with which kinetic energy of the planet is dissipated within the star. This can help to get information about the interior of the star. In this study, we aim to improve constraints on the tidal decay of the KELT-9, KELT-16 and WASP-4 systems, to find evidence for or against the presence of this particular effect. With this, we want to constrain each star's respective $Q_*'$ value. In addition to that, we also aim to test the existence of the transit timing variations (TTVs) in the HD 97658 system, which previously favoured a quadratic trend with increasing orbital period. Making use of newly acquired photometric observations from CHEOPS and TESS, combined with archival transit and occultation data, we use Markov chain Monte Carlo (MCMC) algorithms to fit three models, a constant period model, an orbital decay model, and an apsidal precession model, to the data. We find that the KELT-9 system is best described by an apsidal precession model for now, with an orbital decay trend at over 2 $\sigma$ being a possible solution as well. A Keplerian orbit model with a constant orbital period fits the transit timings of KELT-16 b the best due to the scatter and scale of their error bars. The WASP-4 system is represented the best by an orbital decay model at a 5 $\sigma$ significance, although apsidal precession cannot be ruled out with the present data. For HD 97658 b, using recently acquired transit observations, we find no conclusive evidence for a previously suspected strong quadratic trend in the data.

We apply a statistical deconvolution of the parallax errors based on the Lucy's inversion method (LIM) to the Gaia-DR3 sources to measure their three dimensional velocity components in the range of Galactocentric distances $R$ between 8 kpc and 30 kpc with their corresponding errors and root mean square values. We find results that are consistent with those obtained by applying the LIM to the Gaia-DR2 sources, and we conclude that the method gives convergent and more accurate results by improving the statistics of the data-set and lowering observational errors. The kinematic maps reconstructed with the LIM up to $R \approx 30$ kpc show that the Milky Way is characterized by asymmetrical motions with significant gradients in all velocity components. Furthermore, we determine the Galaxy rotation curve $V_C(R)$ up to $\approx 27.5$ kpc with the cylindrical Jeans equation assuming an axisymmetric gravitational potential. We find that $V_C(R)$ is significantly declining up to the largest radius investigated. Finally, we also measure $V_C(R)$ at different vertical heights, showing that, for $R <15$ kpc, there is a marked dependence on $Z$, whereas at larger $R$ the dependence on $Z$ is negligible.

Hundreds of black holes with massive main-sequence companions (OB+BHs) might be identified from Gaia astrometry with the Astrometric Mass-Ratio Function (AMRF). We investigate the impact of blue supergiant companions (BSG) instead of dwarfs and the presence of additional companions in the system that are unresolved by Gaia on the astrometric identification of OB+BHs. We also explore how accurate the primary mass needs to be constrained. Moreover, we assess how the high-precision publishing constraints of astrometric binary orbits in the latest Gaia data release DR3 impact the detection of OB+BHs. We establish a BSG mass-magnitude relation and compute BSG AMRF curves. From a mock population of non- and single-degenerate massive binaries and triples with OB or BSG primaries, we asses the false-positive identification fraction and the effect of the BSG AMRF curves. We compare the number of stars with astrometric DR3 orbits in the second Alma Luminous Star catalogue (ALSII) with new predictions on the OB+BH detection using the conservative DR3 publishing criteria. BSG primaries and triples are not expected to impact the false-positive identification fractions significantly. However, if the evolutionary stage of the primary star is unknown, the usage of the BSG curves is still recommended. This also reduces the OB+BH identification fraction significantly. The primary mass does not need to be known to benefit from the high identification fraction of OB+BHs, while keeping the fraction of false-positives low. We find no OB+BH candidates in the ALS II among the DR3 orbits. This null-detection cannot be attributed to the underlying BH-formation scenario, but rather to the stringent DR3 selection criteria. To infer the BH-formation scenario with Gaia, we propose that the constraint on the relative parallax precision in DR4 should be 95% less conservative than the DR3 criterion.(Abridged)

Polarization of the cosmic microwave background (CMB) can probe new parity-violating physics such as cosmic birefringence (CB), which requires exquisite control over instrumental systematics. The non-idealities of the half-wave plate (HWP) represent a source of systematics when used as a polarization modulator. We study their impact on the CMB angular power spectra, which is partially degenerate with CB and miscalibration of the polarization angle. We use full-sky beam convolution simulations including HWP to generate mock noiseless time-ordered data, process them through a bin averaging map-maker, and calculate the power spectra including $TB$ and $EB$ correlations. We also derive analytical formulae which accurately model the observed spectra. For our choice of HWP parameters, the HWP-induced angle amounts to a few degrees, which could be misinterpreted as CB. Accurate knowledge of the HWP is required to mitigate this. Our simulation and analytical formulae will be useful for deriving requirements for the accuracy of HWP calibration.

We quantify the cosmological constraining power of the `lensing PDF' - the one-point probability density of weak lensing convergence maps - by modelling this statistic numerically with an emulator trained on $w$CDM cosmic shear simulations. After validating our methods on Gaussian and lognormal fields, we show that `multi-scale' PDFs - measured from maps with multiple levels of smoothing - offer considerable gains over two-point statistics, owing to their ability to extract non-Gaussian information: for a mock Stage-III survey, lensing PDFs yield 33\% tighter constraints on the clustering parameter $S_8=\sigma_8\sqrt{\Omega_{\rm m}/0.3}$ than the two-point shear correlation functions. For Stage-IV surveys, we achieve $>$90\% tighter constraints on $S_8$, but also on the Hubble and dark energy equation of state parameters. Interestingly, we find improvements when combining these two probes only in our Stage-III setup; in the Stage-IV scenario the lensing PDFs contain all information from the standard two-point statistics and more. This suggests that while these two probes are currently complementary, the lower noise levels of upcoming surveys will unleash the constraining power of the PDF.

We present deep 1.4 GHz source counts from $\sim$5 deg$^2$ of the continuum Early Science data release of the MeerKAT International Gigahertz Tiered Extragalactic Exploration (MIGHTEE) survey down to $S_{1.4\textrm{GHz}}\sim$15 $\mu$Jy. Using observations over two extragalactic fields (COSMOS and XMM-LSS), we provide a comprehensive investigation into correcting the incompleteness of the raw source counts within the survey to understand the true underlying source count population. We use a variety of simulations that account for: errors in source detection and characterisation, clustering, and variations in the assumed source model used to simulate sources within the field and characterise source count incompleteness. We present these deep source count distributions and use them to investigate the contribution of extragalactic sources to the sky background temperature at 1.4 GHz using a relatively large sky area. We then use the wealth of ancillary data covering{a subset of the COSMOS field to investigate the specific contributions from both active galactic nuclei (AGN) and star forming galaxies (SFGs) to the source counts and sky background temperature. We find, similar to previous deep studies, that we are unable to reconcile the sky temperature observed by the ARCADE 2 experiment. We show that AGN provide the majority contribution to the sky temperature contribution from radio sources, but the relative contribution of SFGs rises sharply below 1 mJy, reaching an approximate 15-25% contribution to the total sky background temperature ($T_b\sim$100 mK) at $\sim$15 $\mu$Jy.

We present a further observational analysis of the $\Lambda_{\rm s}$CDM model proposed in Akarsu et al. [Phys. Rev. D 104, 123512 (2021)]. This model is based on the the recent conjecture suggesting the universe has transitioned from anti-de Sitter vacua to de Sitter vacua (viz., the cosmological constant switches sign from negative to positive), at redshift ${z_\dagger\sim2}$, inspired by the graduated dark energy (gDE) model proposed in Akarsu et al. [Phys. Rev. D 101, 063528 (2020)]. $\Lambda_{\rm s}$CDM was previously claimed to simultaneously relax five cosmological discrepancies, namely, the $H_0$, $S_8$, and $M_B$ tensions along with the Ly-$\alpha$ and $\omega_{\rm b}$ anomalies, which prevail within the standard $\Lambda$CDM model as well as its canonical/simple extensions. In the present work, we extend the previous analysis by constraining the model using the Pantheon data (with and without the SH0ES $M_B$ prior) and/or the completed BAO data along with the full Planck CMB data. We find that $\Lambda_{\rm s}$CDM exhibits a better fit to the data compared to $\Lambda$CDM, and relaxes the six discrepancies of $\Lambda$CDM, namely, the $H_0$, $M_B$, $S_8$, Ly-$\alpha$, $t_0$, and $\omega_{\rm b}$ discrepancies, each one discussed in detail. When the $M_B$ prior is included in the analyses, $\Lambda_{\rm s}$CDM performs significantly better in relaxing the $H_0$, $M_B$, and $S_8$ tensions with the constraint ${z_\dagger\sim1.8}$ even when the Ly-$\alpha$ data (which imposed the $z_\dagger\sim2$ constraint in the previous studies) are excluded. In contrast, the presence of the $M_B$ prior causes only negligible improvements for $\Lambda$CDM. Thus, the $\Lambda_{\rm s}$CDM model provides remedy to various cosmological tensions simultaneously, only that the galaxy BAO data hinder its success to some extent.

Infrared (IR), sub-millimetre (sub-mm) and millimetre (mm) databases contain a huge quantity of high quality data. However, a large part of these data are photometric, and are thought not to be useful to derive a quantitative information on the nebular emission of galaxies. The aim of this project is first to identify galaxies at z > 4-6, and in the epoch of reionization from their sub-mm colours. We also aim at showing that the colours can be used to try and derive physical constraints from photometric bands, when accounting for the contribution from the IR fine structure lines to these photometric bands. We model the flux of IR fine structure lines with CLOUDY, and add them to the dust continuum emission with CIGALE. Including or not emission lines in the simulated spectral energy distribution (SED) modifies the broad band emission and colours. The introduction of the lines allows to identify strong star forming galaxies at z > 4 - 6 from the log10 (PSW_250um/PMW_350um) versus log10 (LABOCA_870um/PLW_500um) colour-colour diagramme. By comparing the relevant models to each observed galaxy colour, we are able to roughly estimate the fluxes of the lines, and the associated nebular parameters. This method allows to identify a double sequence in a plot built from the ionization parameter and the gas metallicity. The HII and photodissociation region (PDR) fine structure lines are an essential part of the SEDs. It is important to add them when modelling the spectra, especially at z > 4 - 6 where their equivalent widths can be large. Conversely, we show that we can extract some information on strong IR fine structure lines and on the physical parameters related to the nebular emission from IR colour-colour diagrams.

The detection of the hyper-bright gamma-ray burst (GRB) 221009A enables us to explore the nature of GRB emission and the origin of very-high-energy (VHE) gamma-rays. We analyze the ${\it Fermi}$-LAT data and investigate GeV-TeV emission in the framework of the external reverse shock model. We show that early $\sim1-10$ GeV emission can be explained by the external inverse-Compton mechanism via upscattering MeV gamma-rays by electrons accelerated at the reverse shock, in addition to the synchrotron self-Compton component. The predicted early optical flux could have been brighter than the naked-eye GRB 080319B. We also show that proton synchrotron emission from accelerated ultra-high-energy cosmic rays (UHECRs) is detectable, and could potentially explain $\gtrsim \rm TeV$ photons detected by LHAASO or UHECR acceleration can be constrained. Our model suggests that the detection of $\mathcal{O}(10\rm~TeV)$ photons with energy up to $\sim18$ TeV is possible for reasonable models of the extragalactic background light without invoking new physics, and predicts anti-correlations between MeV photons and TeV photons, which can be tested with the LHAASO data

Spiral density waves generated by an embedded planet are understood to cause ``kinks'' in observed velocity channel maps of CO surface emission, by perturbing the gas motion within the spiral arms. If velocity kinks are a reliable probe of embedded planets, we should expect to see the planet-driven spiral arms in other observational tracers. We test this prediction by searching the dust continuum for the midplane counterparts of the spirals responsible for all of the velocity kink planet candidates reported to date, whose orbits lie inside the dust continuum disk. We find no clear detection of any spiral structure in current continuum observations for 6 of the 10 velocity kink planet candidates in our sample (DoAr 25, GW Lup, Sz 129, HD 163296 #2, P94, and HD 143006), despite the high planet masses inferred from the kink amplitude. The remaining 4 cases include 3 clear detections of two-armed dust spirals (Elias 27, IM Lup and WaOph 6) wherein neither spiral arm aligns with a wake originating from reported planet location, suggesting that under the planetary-origin hypothesis, an accurate method for inferring the location of the planet in the midplane may need to encompass vertical effects. The 10th case, HD 97048, is inconclusive with current knowledge of the disk geometry.

We review aspect of primordial black holes, i.e., black holes which have been formed in the early Universe. Special emphasis is put on their formation, their r\^ole as dark matter candidates and their manifold signatures, particularly through gravitational waves.

We present MGLenS, a large series of modified gravity lensing simulations tailored for cosmic shear data analyses and forecasts in which cosmological and modified gravity parameters are varied simultaneously. Based on the FORGE and BRIDGE $N$-body simulation suites presented in companion papers, we construct 500,000 deg$^2$ of mock Stage-IV lensing data, sampling a pair of 4-dimensional volumes designed for the training of emulators. We validate the accuracy of MGLenS with inference analyses based on the lensing power spectrum exploiting our implementation of $f(R)$ and nDGP theoretical predictions within the cosmoSIS cosmological inference package. A Fisher analysis reveals that the vast majority of the constraining power from such a survey comes from the highest redshift galaxies alone. We further find from a full likelihood sampling that cosmic shear can achieve 95% CL constraints on the modified gravity parameters of log$_{10}\left[ f_{R_0}\right] < -5.24$ and log$_{10}\left[ H_0 r_c\right] > -0.05$, after marginalising over intrinsic alignments of galaxies and including scales up to $\ell=5000$. Such a survey setup could in fact detect with more than $3\sigma$ confidence $f(R)$ values larger than $3 \times 10^{-6}$ and $H_0 r_c$ smaller than 1.0. Scale cuts at $\ell=3000$ reduce the degeneracy breaking between $S_8$ and the modified gravity parameters, while photometric redshift uncertainty seem to play a subdominant role in our error budget. We finally explore the consequences of analysing data with the wrong gravity model, and report the catastrophic biases for a number of possible scenarios. The Stage-IV MGLenS simulations, the FORGE and BRIDGE emulators and the cosmoSIS interface modules will be made publicly available upon journal acceptance.

Using the TNG50 cosmological simulation and observations from the Kilo-Degree Survey (KiDS), we investigate the connection between galaxy mergers and optical morphology in the local Universe over a wide range of galaxy stellar masses ($8.5\leqslant\log(M_\ast/\text{M}_\odot)\leqslant11$). To this end, we have generated over 16,000 synthetic images of TNG50 galaxies designed to match KiDS observations, including the effects of dust attenuation and scattering, and used the $\mathrm{\mathtt{statmorph}}$ code to measure various image-based morphological diagnostics in the $r$-band for both data sets. Such measurements include the Gini-$M_{20}$ and concentration-asymmetry-smoothness statistics. Overall, we find good agreement between the optical morphologies of TNG50 and KiDS galaxies, although the former are slightly more concentrated and asymmetric than their observational counterparts. Afterwards, we trained a random forest classifier to identify merging galaxies in the simulation (including major and minor mergers) using the morphological diagnostics as the model features, along with merger statistics from the merger trees as the ground truth. We find that the asymmetry statistic exhibits the highest feature importance of all the morphological parameters considered. Thus, the performance of our algorithm is comparable to that of the more traditional method of selecting highly asymmetric galaxies. Finally, using our trained model, we estimate the galaxy merger fraction in both our synthetic and observational galaxy samples, finding in both cases that the galaxy merger fraction increases steadily as a function of stellar mass.

We study the dynamics of gauge-invariant scalar perturbations in cosmological scenarios with a modified Friedmann equation, such as quantum gravity bouncing cosmologies. We work within a separate universe approximation which captures wavelengths larger than the cosmological horizon; this approximation has been successfully applied to loop quantum cosmology and group field theory. We consider two variables commonly used to characterise scalar perturbations: the curvature perturbation on uniform-density hypersurfaces $\zeta$ and the comoving curvature perturbation $\mathcal{R}$. For standard cosmological models in general relativity as well as in loop quantum cosmology, these quantities are conserved and equal on super-horizon scales for adiabatic perturbations. Here we show that while these statements can be extended to a more general form of modified Friedmann equations similar to that of loop quantum cosmology, in other cases, such as the simplest group field theory bounce scenario, $\zeta$ is conserved across the bounce whereas $\mathcal{R}$ is not. We relate our results to approaches based on a second order equation for a single perturbation variable, such as the Mukhanov-Sasaki equation.

AEROS is a 3U CubeSat pathfinder toward a future ocean-observing constellation, targeting the Portuguese Atlantic region. AEROS features a miniaturized, high-resolution Hyperspectral Imager (HSI), a 5MP RGB camera, and a Software Defined Radio (SDR). The sensor generated data will be processed and aggregated for end-users in a new web-based Data Analysis Center (DAC). The HSI has 150 spectrally contiguous bands covering visible to near-infrared with 10 nm bandwidth. The HSI collects ocean color data to support studies of oceanographic characteristics known to influence the spatio-temporal distribution and movement behavior of marine organisms. Usage of an SDR expands AEROS's operational and communication range and allows for remote reconfiguration. The SDR receives, demodulates, and retransmits short duration messages, from sources including tagged marine organisms, autonomous vehicles, subsurface floats, and buoys. The future DAC will collect, store, process, and analyze acquired data, taking advantage of its ability to disseminate data across the stakeholders and the scientific network. Correlation of animal-borne Argos platform locations and oceanographic data will advance fisheries management, ecosystem-based management, monitoring of marine protected areas, and bio-oceanographic research in the face of a rapidly changing environment. For example, correlation of oceanographic data collected by the HSI, geolocated with supplementary images from the RGB camera and fish locations, will provide researchers with near real-time estimates of essential oceanographic variables within areas selected by species of interest.

The detection of massless kinetically-mixed dark photons is notoriously difficult, as the effect of this mixing can be removed by a field redefinition in vacuum. In this work, we study the prospect of detecting massless dark photons in the presence of a cosmic relic directly charged under this dark electromagnetism. Such millicharged particles, in the form of dark matter or dark radiation, generate an effective dark photon mass that drives photon-to-dark photon oscillations in the early universe. We also study the prospect for such models to alleviate existing cosmological constraints on massive dark photons, enlarging the motivation for direct tests of this parameter space using precision terrestrial probes.

Intermediate Mass Ratio Inspirals (IMRIs) will be observable with space-based gravitational wave detectors such as the Laser Interferometer Space Antenna (LISA). To this end, the environmental effects in such systems have to be modeled and understood. These effects can include (baryonic) accretion disks and dark matter (DM) overdensities, so called spikes. For the first time, we model an IMRI system with both an accretion disk and a DM spike present and compare their effects on the inspiral and the emitted gravitational wave signal. We study the eccentricity evolution, employ the braking index and derive the dephasing index, which turn out to be complementary observational signatures. They allow us to disentangle the accretion disk and DM spike effects in the IMRI system.

Pulsar timing arrays will be a window into the gravitational wave background

In minisuperspace quantum cosmology, the Lorentzian path integral formulations of the no-boundary and tunneling proposals have recently been analyzed. But it has been pointed out that the wave function of linearized perturbations around a homogeneous and isotropic background is of an inverse Gaussian form and thus that their correlation functions are divergent. In this paper, we revisit this issue and consider the problem of perturbations in Lorentzian quantum cosmology by modifying the dispersion relation based on trans-Planckian physics. We consider two modified dispersion relations, the generalized Corley-Jacobson dispersion relation with higher momentum terms and the Unruh dispersion relation with a trans-Planckian mode cut-off, as examples. We show that the inverse Gaussian problem of perturbations in Lorentzian quantum cosmology is hard to overcome with the trans-Planckian physics modifying the dispersion relation at short distances.

Thermalization and heating of plasma flows at shocks result in unstable charged-particle distributions which generate a wide range of electromagnetic waves. These waves, in turn, can further accelerate and scatter energetic particles. Thus, the properties of the waves and their implication for wave-particle interactions are critically important for modeling energetic particle dynamics in shock environments. Whistler-mode waves, excited by the electron heat flux or a temperature anisotropy, arise naturally near shocks and foreshock transients. As a result, they can often interact with supra-thermal electrons. The low background magnetic field typical at the core of such transients and the large wave amplitudes may cause such interactions to enter the nonlinear regime. In this study, we present a statistical characterization of whistler-mode waves at foreshock transients around Earth bow shock, as they are observed under a wide range of upstream conditions. We find that a significant portion of them are sufficiently intense and coherent to warrant nonlinear treatment. Copious observations of background magnetic field gradients and intense whistler wave amplitudes suggest that phase trapping, a very effective mechanism for electron acceleration in inhomogeneous plasmas, may be the cause. We discuss the implications of our findings for electron acceleration in planetary and astrophysical shock environments.

The forbidden dark matter cannot annihilate into heavier partner or SM particles by definition at the late stage of the cosmological evolution. We point out the possibility of reactivating the annihilation channel of forbidden dark matter around supermassive black holes. Being attracted towards black hole, the forbidden dark matter is significantly accelerated to overcome the annihilation threshold. The subsequent decay of the annihilation products to photon leaves unique signal around the black hole, which can serve as smoking gun of the forbidden dark matter.

We consider an evolution of anisotropic cosmological model on the example of the Bianchi type I homogeneous universe. It is filled by the mixture of matter and dark energy with an arbitrary barotropic equation of state (EoS). The general solution for this case is found and analyzed. A complete list of possible future singularities for this model is given. Some new solution were obtained for a particular EoSs, e.g. for the Bianchi type I {\Lambda}CDM homogeneous model. It is shown that all special cases corresponding to different EoSs have common properties, provided that now or at another moment of time the Universe is expanding, and the density of the mixture is positive. Then the evolution always begins with an anisotropic "Big Bang" which happened a finite time ago. After that the universe is constantly expanding and, in all cases, with rare exceptions, becomes more isotropic. A particularly strong isotropization is associated with the epoch of inflation. After its completion, the expansion of the universe becomes almost isotropic, and this case cannot be distinguished from isotropic by astronomical observations. This fact allows us to consider an anisotropic cosmological model as a possible candidate for the description of the observed Universe despite the isotropic pattern of expansion.

Dark energy can be modeled as an effective energy-momentum tensor (EMT) in the Einstein's equations, responsible for the acceleration of the Universe. Using this effective approach, we derive a model independent equation for the propagation of gravitation waves (GW) in terms of an effective GW speed $c_T$, showing that it can depend on polarization, time and space, and is related to the anisotropy of the dark energy EMT. A similar result is derived in moment space, in terms of an appropriately defined momentum effective sound speed $\tilde{c}_T$. The friction term depends on $\tilde{c}'_T/\tilde{c}_T$, and can be expressed in terms of an effective frequency dependent scale factor. The modification of the friction term induces a frequency dependent difference between GW and electromagnetic luminosity distance, given by the relation $d_L^{GW}(z)=\tilde{c}_T(z)\, d_L^{EM}(z)$. We discuss the implications for constraining dark energy models and modified gravity theories with GW luminosity distance observations, using bright and dark sirens.

This report summarizes the recent progress and promising future directions in theoretical high-energy physics (HEP) identified within the Theory Frontier of the 2021 Snowmass Process.