We demonstrate that Cherenkov radiation can be interpreted as ghost instability of a certain type. Solutions of modified gravity theories often contain ghost instabilities. One type of such instability is associated with existence of different types of species with causal cones that do not share common time, which leads to vacuum decay via creation of particles with positive and negative energies. We show that this ghost instability can be seen as Cherenkov radiation and vice versa.

Non-Gaussian noise in gravitational-wave detectors, known as “glitches,” can bias the inferred parameters of transient signals when they occur nearby in time and frequency. These biases are addressed with a variety of methods that remove or otherwise mitigate the impact of the glitch. Given the computational cost and human effort required for glitch mitigation, we study the conditions under which it is strictly necessary. We consider simulated glitches and gravitational-wave signals in various configurations that probe their proximity both in time and in frequency. We determine that glitches located outside the time-frequency space spanned by the gravitational-wave model prior and with a signal-to-noise ratio, conservatively, below 50 do not impact estimation of the signal parameters.

Asymptotically Weyl-invariant gravity (AWIG) is further developed within the Palatini formalism as a power-counting renormalizable alternative to general relativity (GR). An expression for the dimensionless exponent $n(\mathcal{R})$ is derived based on dynamical dimensional reduction. We show that this version of AWIG naturally resolves several theoretical issues normally associated with the Palatini formalism. A falsifiable prediction regarding the frequency of gravitational waves from binary black hole mergers is made. A preliminary analysis of gravitational wave GW150914 yields a maximum tension of $0.9\sigma$ with GR and marginally favors AWIG. A similar analysis of gravitational wave GW151226 yields a maximum tension of $2.7\sigma$ with GR and favors AWIG more significantly.

Recent advances in cosmological observations have provided an unprecedented opportunity to investigate the distribution of baryons relative to the underlying matter. In this work, we show that the gas is more extended than the dark matter, and the amount of baryonic feedback at $z\lesssim 1$ disfavors low-feedback models such as that of state-of-the-art hydrodynamical simulation IllustrisTNG compared with high-feedback models such as that of the original Illustris simulation. This has important implications for bridging the gap between theory and observations and understanding galaxy formation and evolution. Furthermore, a better grasp of the baryon-dark matter link is critical to future cosmological analyses, which are currently impeded by our limited knowledge of baryonic feedback. Here, we measure the kinematic Sunyaev-Zel’dovich (kSZ) effect from the Atacama Cosmology Telescope, stacked on the luminous red galaxy sample of the Dark Energy Spectroscopic Instrument (DESI) imaging survey. This is the first analysis to use photometric redshifts for reconstructing galaxy velocities. Due to the large number of galaxies comprising the DESI imaging survey, this is the highest signal-to-noise stacked kSZ measurement to date; we detect the signal at $13\sigma$, finding strong evidence that the gas is more spread out than the dark matter, as well as a preference for larger feedback compared to some commonly used state-of-the-art hydrodynamical simulations. Our work opens up the possibility of recalibrating large hydrodynamical simulations using the kSZ effect. In addition, our findings highlight the importance of properly accounting for baryonic feedback with future surveys such as LSST through direct probes such as the kSZ, and shed light on long-standing enigmas in astrophysics, such as the “missing baryon” problem.

Building on the recent lattice simulations of ultraslow-roll dynamics presented in [A. Caravano et al., Phys. Rev. D 111, 063518 (2025).], we investigate the role of the nonlinear relation between the inflaton field configuration and the curvature perturbation $\zeta$, the key observable after inflation. Using a nonperturbative $\delta N$ approach applied to the lattice output, we generate fully nonlinear three-dimensional maps of $\zeta$. This calculation captures both the non-Gaussianity arising from the nonlinear mapping between $\varphi$ and $\zeta$, and the intrinsic non-Gaussianity generated around Hubble crossing by the nonlinear field dynamics, which is neglected in stochastic approaches. We find that the nonlinear mapping has a profound impact on the statistics, significantly enhancing the positive tail of the $\zeta$ probability distribution, with important implications for observable quantities. A central part of this work is the comparison with the standard perturbative treatment based on a gauge transformation, which allows us to quantify when and how the perturbative picture breaks down as fluctuations grow large. Together with the above article, this work sets the basis for robust, nonperturbative predictions of primordial black hole production and scalar-induced gravitational wave emission from inflation using lattice simulations.

We present the first $\mathrm{\Lambda }\mathrm{CDM}$ cosmological analysis performed on a galaxy survey using marked power spectra. The marked power spectrum is the two-point function of a marked field, where galaxies are weighted by a function that depends on their local density. The presence of the mark leads these statistics to contain higher-order information of the original galaxy field, making them a good candidate to exploit the non-Gaussian information of a galaxy catalog. In this work we make use of SimBIG, a forward modeling framework for galaxy clustering analyses, and perform simulation-based inference using normalizing flows to infer the posterior distribution of the $\mathrm{\Lambda }\mathrm{CDM}$ cosmological parameters. We consider different mark configurations (ways to weight the galaxy field) and deploy them in the SimBIG pipeline to analyze the corresponding marked power spectra measured from a subset of the BOSS galaxy sample. We analyze the redshift-space mark power spectra decomposed in $\ell =0$, 2, 4 multipoles and include scales up to the nonlinear regime. Among the various mark configurations considered, the ones that give the most stringent cosmological constraints produce posterior median and 68% confidence limits on the growth of structure parameters equal to ${\mathrm{\Omega }}_m=0.273_{-0.030}^{+0.040}$ and ${\sigma }_8=0.777_{-0.071}^{+0.077}$. Compared to a perturbation theory analysis using the power spectrum of the same dataset, the SimBIG marked power spectra constraints on ${\sigma }_8$ are up to $1.2\times$ tighter, while no improvement is seen for the other cosmological parameters.

We investigate scale-dependent modifications to the primordial scalar power spectrum as potential solutions to the Hubble tension. We use the Fisher-bias formalism, recently adapted to examine perturbed recombination solutions to the Hubble tension, and extend its range of validity with an iterative method. We first analyze the Planck cosmic microwave background (CMB) anisotropy data, demonstrating the existence of modifications to the primordial power spectrum capable of fully resolving the tension between Planck and SH0ES (Supernovae and $H_0$ for the Equation of State of dark energy). As a proof of concept, we interpret these solutions in terms of small, time-dependent variations in the first slow-roll parameter or in the sound speed of curvature perturbations during a stage of primordial inflation. However, these solutions are associated with a low total matter density ${\mathrm{\Omega }}_m$, which makes them inconsistent with baryon acoustic oscillations (BAO) and uncalibrated supernovae (SNIa) data. When incorporating additional BOSS and PantheonPlus data, the solutions that reduce the Hubble tension tend to overfit Planck CMB data to compensate for the worsened fit to BAO and SNIa data, making them less compelling. These findings suggest that modifying the primordial power spectrum alone is unlikely to provide a robust resolution to the tension and highlight how the viability of such data-driven solutions depends on the specific datasets considered, emphasizing the role of future high-precision observations in further constraining possible resolutions to the tension.

Measuring the distribution of spin tilts—the angles between the spin vectors and the binary orbital angular momentum—in stellar-mass binary black holes detected by LIGO-Virgo-KAGRA would provide valuable insight into their astrophysical origins. Analyses of the 69 binary black holes detected through LIGO-Virgo-KAGRA’s third observing run yielded model-dependent conclusions, particularly regarding whether the spin tilt distribution exhibits a peak near alignment, as expected for binaries formed in galactic fields. In this work, we simulate populations of up to 1500 binary black hole systems with parameters consistent with the default GWTC-3 analysis, while introducing a correlation that favors small spin tilts for binaries with mass ratios near unity. We find that: (a) spurious peaks away from perfect alignment are possible even with catalogs of up to 300 sources; (b) establishing a definitive peak at alignment remains difficult even with 1500 detections; (c) integrated measurements—such as the fraction of events with tilt angles smaller than 10° or greater than 90°—are more robust and should be preferred, achieving relative 90% credible uncertainties of $\sim 20\%-80\%$ with 1500 sources; and (d) even with the largest simulated catalogs, evidence for a mass ratio-tilt correlation remains inconclusive. Our results suggest that identifying the formation channels of merging black holes using spin tilts will remain challenging, but that model-independent measurements may yield more informative insights over model parameters themselves.

Assuming a sufficiently general form for the matter distribution function of a galactic halo, we have derived solutions to the Einstein-Maxwell equations describing a charged black hole embedded in such a halo, while also allowing for a nonzero cosmological constant. These solutions generalize our earlier results for neutral black holes in asymptotically flat spacetime. As specific realizations of the general distribution, we consider the Hernquist, Navarro-Frenk-White, Burkert, Taylor-Silk, and Moore halo profiles, thereby capturing a broad range of astrophysically motivated scenarios.

Although it is commonly assumed that relativistic particles dominate the energy density of the Universe quickly after inflation, a variety of well-motivated scenarios predict an early matter-dominated era (EMDE) before the onset of big bang nucleosynthesis. Subhorizon dark matter density perturbations grow faster during an EMDE than during a radiation-dominated era, leading to the formation of “microhalos” far earlier than in standard models of structure formation. This enhancement of small-scale structure boosts the dark matter annihilation rate, which contributes to the heating of the intergalactic medium (IGM). We compute how the dark matter annihilation rate evolves after an EMDE and forecast how well measurements of the 21-cm background can detect dark matter annihilation in cosmologies with EMDEs. We find that future measurements of the global 21-cm signal at a redshift of $z\sim 17$ are unlikely to improve on bounds derived from observations of the isotropic gamma-ray background, but measurements of the 21-cm power spectrum have the potential to detect dark matter annihilation following an EMDE. Moreover, dark matter annihilation and astrophysical x rays produce distinct heating signatures in the 21-cm power spectrum at redshifts around 14, potentially allowing differentiation between these two IGM heating mechanisms.

The impact of energy exchange among the three relevant fluid components—baryonic matter, fermionic dark matter (DM), and dark energy (DE)—on the internal structure of neutron stars is investigated. Working with a representative DM mass $m_{\chi }=10\mathrm{GeV}$ and a barotropic DE relation $p_{\mathrm{de}}=\omega {\epsilon }_{\mathrm{de}}$, we embed one or two phenomenological source terms $Q_i$ in the Tolman-Oppenheimer-Volkoff equations and analyze three hierarchical scenarios: (i) coexisting but noninteracting fluids (Model I); (ii) fully interacting fluids with independent baryon–DM and DM–DE exchanges and optional DM self-repulsion (Model II); and (iii) a unified dark sector that couples to baryons through a single exchange term while retaining an internal DM/DE partition (Model III). Across all models two complementary mechanisms dominate; softening by massive, pressure-poor DM, and vacuum softening/binding by the negative pressure of DE. Model I exhibits these effects in their purest form, yielding either softened or self-bound stars depending on the dark composition. In Model II the exchange terms self-regulate, cancelling the explicit dependence on the fluid coupling strength $\alpha$, so that mass-radius curves are nearly invariant when $\alpha$ varies from 0.05 to 1000. Model III breaks this $\alpha$-degeneracy; when the dark sector retains a substantial vacuum fraction, the baryonic pressure gradient is strongly suppressed and both the maximum mass and radii decrease appreciably, whereas a pure-DM core remains almost insensitive to the exchange strength. The study delineates the conditions under which dark interactions can (or cannot) imprint macroscopic signatures, thereby providing a theoretical baseline for future, more strongly constrained, microphysical models.

Self-interacting dark matter (SIDM), through gravothermal evolution driven by elastic self-scatterings, offers a compelling explanation for the observed diversity of inner halo densities. In this work, we investigate SIDM dynamics in a two-component dark matter model with mass ratios of order unity, motivated by an asymmetric dark matter framework that naturally evades constraints from relic abundance and mediator decay, while enabling strong, velocity-dependent self-interactions. We show that cross-component scatterings significantly enhance mass segregation, driving the formation of dense, core collapsedlike halos. This effect couples naturally to SIDM-induced diversity, introducing a new mechanism for generating structural variations beyond those arising from gravothermal evolution alone. Our results reveal a novel mechanism for reconciling SIDM with small-scale observational tensions by enabling shifts in central densities while preserving the flexibility to generate diverse halo structures. We further highlight that halo structural diversity may serve as a diagnostic of dark sector composition, opening a new observational window into the particle nature of SIDM.

Current gravitational wave detectors and other high precision instrumentation are limited by the optical quality and thermal noise properties of highly reflective dielectric optical coatings. This study characterizes a custom designed high reflectivity optical coating using silica and tantalum pentoxide (${\mathrm{SiO}}_2$ and ${\text{Ta}}_2{\mathrm{O}}_5$) on an ultralow-expansion glass substrate. This coating has been designed to have high thermal noise properties for a future experiment that aims to reduce the effect of Brownian coating noise. This paper presents, to our knowledge, the first measurement of thermo-optic noise for a ${\mathrm{SiO}}_2:{\text{Ta}}_2{\mathrm{O}}_5$ coating. We also present the coating design process of the unique coating and verify modeled coating properties, including transmission, absorption, Brownian coating noise, and thermo-optic noise. With a better understanding of thermo-optic noise and Brownian noise of unique coatings, the design process for optimizing optical coating for lower thermal noise can be better informed, such that the sensitivity of gravitational wave detectors and other precision instrumentation using highly reflective optical coatings is increased.

As gravitational-wave observations expand in scope and detection rate, the data analysis infrastructure must be modernized to accommodate rising computational demands and ensure sustainability. We present a scalable gravitational-wave search pipeline that modernizes the gstlal pipeline by adapting the core filtering engine to the pytorch framework, enabling flexible execution on both central processing units (CPUs) and graphics processing units (GPUs). Offline search results on the same 8.8 day stretch of public gravitational-wave data indicate that the gstlal and the pytorch adaptation demonstrate comparable search performance, even with float16 precision. Lastly, computational benchmarking results show that the pytorch adaptation executed on an A100 GPU achieves speedups of up to 169 times in the GPU float16 configuration and 123 times in the GPU float32 configuration, compared to gstlal’s performance on a single CPU core.