The mass of a black hole can dynamically evolve due to various physical processes, such as for instance accretion, Hawking radiation, absorption of gravitational/electromagnetic waves, superradiance, etc. This evolution can have an impact on astrophysical observables, like the ringdown gravitational signal. An effective description of a spherically symmetric black hole with evolving mass is provided by the Vaidya metric. In our investigation, we explore the dynamics of linear perturbations on this background, assuming a constant rate of change for the mass. Despite the time-dependent background, a judicious change of coordinates allows us to treat the perturbations in the frequency domain and to compute explicitly the quasinormal modes and the tidal Love numbers.

The main goal of the CRESST-III experiment is the direct detection of dark matter particles via their scattering off target nuclei in cryogenic detectors. In this work we present the results of a silicon-on-sapphire (SOS) detector with a mass of 0.6 g and an energy threshold of $(6.7\pm 0.2)\mathrm{eV}$ with a baseline energy resolution of $(1.0\pm 0.2)\mathrm{eV}$. This allowed for a calibration via the detection of single luminescence photons in the eV-range, which could be observed in CRESST for the first time. We present new exclusion limits on the spin-independent and spin-dependent dark matter-nucleon cross section that extend to dark matter particle masses of less than $100\mathrm{MeV}/{\mathrm{c}}^2$.

The search for charged-lepton flavor violation in muon capture on nuclei is a powerful probe of heavy new physics. A smoking gun signal for $\mu \to e$ conversion is a monochromatic electron with energy almost equal to the muon mass. We show that light new physics can mimic this signature and that it can also lead to electrons above the $\mu \to e$ signal peak. A concrete example of such light new physics is ${\mu }^{-}$-nucleon annihilation into a light dark sector, which can produce an energetic $e^{-}$ as well as $e^{+}{e}^{-}$ by-products. Due to the size of the muon mass, the exotic muon capture process can be kinematically allowed, while the otherwise stringent constraints, e.g., from proton decay, are kinematically forbidden. We also discuss other relevant constraints, including those from the stability of nuclei and muon capture in the interior of neutron stars.

Highly magnified individual stars such as Icarus and Earendel have recently been observed near critical curves of galaxy clusters with Hubble Space Telescope (HST) observations. These stars are estimated to be magnified with a factor of more than a few thousands. In addition to the smooth mass distribution in the macrolens model, the distribution of microlenses originating from, for instance, intracluster stars affects the event rate and the peak magnification significantly. We propose an analytic model of the high-magnification tail of the probability distribution function (PDF) in which the probability is assumed to be proportional to the number of independent microlens critical curves. Our model can explain the parameter dependence of the PDF on the mass fraction of the microlenses and the background magnification seen in ray-tracing simulations. The effect of a finite source size is also studied to derive a fitting formula for the suppression factor. For an application of our model, we calculate the event rate of the Icarus-like system and the probability distribution of observed positions of such a system, showing good agreement with the HST observations. Our model predicts a complicated dependence of the probability distribution of observed positions of highly magnified events on the magnification threshold.

We investigate nucleosynthesis in the subrelativistic outflows from black hole (BH) accretion disks formed in failed supernovae from rapidly rotating Wolf-Rayet stars. These disks reach the neutrino-cooled regime during a portion of their evolution, undergoing significant neutronization and thus having the potential to support the $r$ process. Here, we analyze the formation of heavy elements in the ejecta from global, axisymmetric, long-term, viscous hydrodynamic simulations of these systems that include neutrino emission and absorption, Newtonian self-gravity, a pseudo-Newtonian potential for the BH gravity, and a 19-isotope nuclear reaction network. Tracer particles are used for postprocessing with a larger reaction network. In addition to analyzing models introduced in a previous paper, we present new models in which we modify the rotation profile of the progenitor star, to maximize neutrino reprocessing of circularized mass shells. All of our models produce several $M_{\odot }$ of oxygen, followed by about a solar mass of carbon, neon, and nickel, with other alpha elements produced in smaller quantities. Only one of our models, with the lowest strength of viscous angular momentum transport, yields significant amounts of first $r$-process peak elements, with negligible yields at higher nuclear masses. The rest of the set, including models with a modified rotation profile, produces very small or negligible quantities of elements beyond the iron group. Models that produce the heaviest elements (up to $A\sim 200$) do so along the proton-rich side of the valley of stability at high entropy ($s/k_B\sim 80$), pointing to the $rp$ process as a mechanism that operates in collapsars. The absence of neutron-rich ejecta proves to be insensitive to changes in the rotation profile of the star, suggesting that heavy $r$-process elements are difficult to produce in collapsars if no large-scale poloidal magnetic field is present in the disk to drive outflows during neutronization.

We derive the quantum effective action and the respective quantum equations of motion from multi-graviton correlation functions in asymptotically safe quantum gravity. The fully momentum-dependent couplings of three- and four-graviton scatterings are computed within the functional renormalization group approach and the effective action is reconstructed from these vertices. The resulting quantum equations of motion are solved numerically for quantum black hole geometries. Importantly, the black hole solutions show signatures of quantum gravity outside the classical horizon, which manifest in the behavior of the temporal and radial components of the metric. Three different types of solutions with distinct causal structures are identified and the phase structure of the solution space is investigated.

We present cosmological constraints from the abundance of galaxy clusters selected via the thermal Sunyaev-Zel’dovich (SZ) effect in South Pole Telescope (SPT) data with a simultaneous mass calibration using weak gravitational lensing data from the Dark Energy Survey (DES) and the Hubble Space Telescope (HST). The cluster sample is constructed from the combined SPT-SZ, SPTpol ECS, and SPTpol 500d surveys, and comprises 1,005 confirmed clusters in the redshift range 0.25–1.78 over a total sky area of $5200{\mathrm{deg}}^2$. We use DES Year 3 weak-lensing data for 688 clusters with redshifts $z<0.95$ and HST weak-lensing data for 39 clusters with $0.6<z<1.7$. The weak-lensing measurements enable robust mass measurements of sample clusters and allow us to empirically constrain the SZ observable-mass relation without having to make strong assumptions about, e.g., the hydrodynamical state of the clusters. For a flat $\mathrm{\Lambda }\mathrm{CDM}$ cosmology, and marginalizing over the sum of massive neutrinos, we measure ${\mathrm{\Omega }}_{\mathrm{m}}=0.286\pm 0.032$, ${\sigma }_8=0.817\pm 0.026$, and the parameter combination ${\sigma }_8({\mathrm{\Omega }}_{\mathrm{m}}/0.3{)}^{0.25}=0.805\pm 0.016$. Our measurement of $S_8\equiv {\sigma }_8\sqrt{{\mathrm{\Omega }}_{\mathrm{m}}/0.3}=0.795\pm 0.029$ and the constraint from Planck CMB anisotropies (2018 TT, TE, $\mathrm{EE}+\mathrm{lowE}$) differ by $1.1\sigma$. In combination with that Planck dataset, we place a 95% upper limit on the sum of neutrino masses $\sum m_{\nu }<0.18\mathrm{eV}$. When additionally allowing the dark energy equation of state parameter $w$ to vary, we obtain $w=-1.45\pm 0.31$ from our cluster-based analysis. In combination with Planck data, we measure $w=-1.34_{-0.15}^{+0.22}$, or a $2.2\sigma$ difference with a cosmological constant. We use the cluster abundance to measure ${\sigma }_8$ in five redshift bins between 0.25 and 1.8, and we find the results to be consistent with structure growth as predicted by the $\mathrm{\Lambda }\mathrm{CDM}$ model fit to Planck primary CMB data.

We present a Bayesian population modeling method to analyze the abundance of galaxy clusters identified by the South Pole Telescope (SPT) with a simultaneous mass calibration using weak gravitational lensing data from the Dark Energy Survey (DES) and the Hubble Space Telescope (HST). We discuss and validate the modeling choices with a particular focus on a robust, weak-lensing-based mass calibration using DES data. For the DES Year 3 data, we report a systematic uncertainty in weak-lensing mass calibration that increases from 1% at $z=0.25$ to 10% at $z=0.95$, to which we add 2% in quadrature to account for uncertainties in the impact of baryonic effects. We implement an analysis pipeline that joins the cluster abundance likelihood with a multiobservable likelihood for the Sunyaev-Zel’dovich effect, optical richness, and weak-lensing measurements for each individual cluster. We validate that our analysis pipeline can recover unbiased cosmological constraints by analyzing mocks that closely resemble the cluster sample extracted from the SPT-SZ, SPTpol ECS, and SPTpol 500d surveys and the DES Year 3 and HST-39 weak-lensing datasets. This work represents a crucial prerequisite for the subsequent cosmological analysis of the real dataset.

We investigate the three-dimensional clustering of sources emitting electromagnetic pulses traveling through cold electron plasma, whose radial distance is inferred from their dispersion measure. As a distance indicator, dispersion measure is systematically affected by inhomogeneities in the electron density along the line of sight and special and general relativistic effects, similar to the case of redshift surveys. We present analytic expressions for the correlation function of fast radio bursts (FRBs) and for the galaxy-FRB cross-correlation function, in the presence of these dispersion measure-space distortions. We find that the even multipoles of these correlations are primarily dominated by nonlocal contributions (e.g., the electron density fluctuations integrated along the line of sight), while the dipole also receives a significant contribution from the Doppler effect, one of the major relativistic effects. A large number of FRBs, $\mathcal{O}({10}^5–{10}^6)$, expected to be observed in the Square Kilometre Array, would be enough to measure the even multipoles at very high significance, $\mathrm{S}/\mathrm{N}\approx 100$, and perhaps to make a first detection of the dipole ($\mathrm{S}/\mathrm{N}\approx 10$) in the FRB correlation function and FRB-galaxy cross correlation function. This measurement could open a new window to study and test cosmological models.

Primordial black holes (PBHs) remain a viable dark matter candidate in the asteroid-mass range. We point out that, in this scenario, the PBH abundance would be large enough for at least one object to cross through the inner Solar System per decade. Since Solar System ephemerides are modeled and measured to extremely high precision, such close encounters could produce detectable perturbations to orbital trajectories with characteristic features. We evaluate this possibility with a suite of simple Solar System simulations, and we argue that the abundance of asteroid-mass PBHs can plausibly be probed by existing and near-future data.

We discuss the possibility that a dominant fraction of the cosmic rays above the ankle (i.e., above 5 EeV) is due to a single nearby source, considering in particular the radio galaxy Centaurus A. We focus on the properties of the source spectrum and composition required to reproduce the observations, showing that the nuclei are strongly suppressed for $E>10Z\mathrm{EeV}$, either by a rigidity dependent source cutoff or by the photodisintegration interactions with the cosmic microwave background at the giant dipole resonance. The very mild attenuation effects at lower energies imply that the secondary nuclei from this source, produced in photodisintegration processes during propagation, only provide a small contribution. Given the moderate anisotropies observed, the deflections in extragalactic and Galactic magnetic fields should play a crucial role in determining the cosmic ray arrival direction distribution. The diffusion in extragalactic fields as well as the finite source lifetime also significantly affect the shape of the observed spectrum. The cosmic ray flux at tens of EeV is dominated by the CNO component, and we show that it is actually better reproduced by a mixture of C and O nuclei rather than by the usual assumption of a N component effectively describing this mass group. The Si and Fe group components become dominant above 70 EeV, in the energy range in which a strong spectral suppression is present. If the localized flux excess appearing above 40 EeV around the Centaurus A direction is attributed to the CNO component, the He nuclei from the source in the energy range from 10 to 20 EeV could lead to a similar anisotropy unless its contribution is suppressed. The cosmic ray flux at a few EeV should mostly result from a more isotropic light component associated to a population of extragalactic sources. The inclusion of the subdominant contribution of heavy nuclei from the Galactic component helps to reproduce the observations around 1 EeV.

Rotating black holes can produce superradiant clouds of ultralight bosons. When the black hole is part of a binary system, its cloud can undergo resonances and ionization. These processes leave a distinct signature on the gravitational waveform that depends on the cloud’s properties. To determine the state of the cloud by the time the system enters the band of future millihertz detectors, we study the chronological sequence of resonances encountered during the inspiral. For the first time, we consistently take into account the nonlinearities induced by the orbital backreaction, and we allow the orbit to have generic eccentricity and inclination. We find that the resonance phenomenology exhibits striking new features. Resonances can “start” or “break” above critical thresholds of the parameters, which we compute analytically, and induce dramatic changes in eccentricity and inclination. Applying these results to realistic systems, we find two possible outcomes. If the binary and the cloud are sufficiently close to counterrotating, then the cloud survives in its original state until the system enters in band; otherwise, the cloud is destroyed during a resonance at large separations, but leaves an imprint on the eccentricity and inclination. In both scenarios, we characterize the observational signatures, with particular focus on future gravitational wave detectors.

Multiple pulsar timing array (PTA) collaborations have recently reported the first detection of gravitational waves (GWs) of nanohertz frequencies. The signal is expected to be primarily sourced by inspiralling supermassive black hole binaries (SMBHBs), and these first results are broadly consistent with the expected GW spectrum from such a population. Curiously, the measured amplitude of the GW background in all announced results is a bit larger than theoretical predictions. In this work, we show that the amplitude of the stochastic gravitational wave background (SGWB) predicted from the present-day abundance of SMBHs derived from local scaling relations is significantly smaller than that measured by the PTAs. We demonstrate that this difference cannot be accounted for through changes in the merger history of SMBHs and that there is an upper limit to the boost to the characteristic strain from multiple merger events, due to the fact that they involve black holes of decreasing masses. If we require the current estimate of the black hole mass density—equal to the integrated quasar luminosity function through the classic Sołtan argument—to be preserved, then the currently measured PTA result would imply that the typical total mass of SMBHs contributing to the background should be at least $\sim 3\times {10}^{10}{M}_{\odot }$, a factor of $\sim 10$ larger than previously predicted. The required space density of such massive black holes corresponds to order 10 $3\times {10}^{10}{M}_{\odot }$ SMBHs within the volume accessible by stellar and gas dynamical SMBH measurements. By virtue of the GW signal being dominated by the massive end of the SMBH distribution, PTA measurements offer a unique window into such rare objects and complement existing electromagnetic observations.

In recent years, the formation and evolution of rapidly accreting supermassive stars has received significant attention in the hope of better understanding the origin of high redshift quasars. It is often taken for granted that, once formed, these supermassive stars will encounter the general relativistic radial instability and collapse to form massive black holes. Here, we present the first ever general relativistic hydrodynamical simulations of the collapse of rapidly accreting supermassive stars. We find that black hole formation is in many cases prevented by nuclear burning due to the long timescales of the collapse of these stars (${10}^6\mathrm{s}$). Consequently, this is a novel astrophysical site for hot CNO burning and hydrogen burning via proton captures. For Pop III accreting supermassive stars, we find that only stars with very high ($100M_{\odot }/\mathrm{yr}$) or low ($0.1M_{\odot }/\mathrm{yr}$) accretion rates can form black holes, with models in between undergoing energetic thermonuclear pulsations. The final fate of these pulsating models may be to undergo subsequent pulsations or explosions or to collapse to black holes. For metal rich accreting supermassive stars ($Z\ge 0.1Z_{\odot }$), we do not find any black hole formation, with some models undergoing extremely energetic explosions (${10}^{55}\mathrm{ergs}$). Our results invite further study on the formation of massive black holes from rapidly accreting supermassive stars which have reached the general relativistic radial instability.

In six dimensions there exists a unique one-parameter family of nonlinear conformal electrodynamics for a chiral 2-form gauge field that includes (in a free-field limit) the linear chiral 2-form theory and is related, by dimensional reduction, to the four-dimensional ModMax electrodynamics. In this work, we present the first exact solutions of this theory in presence of gravity. In particular, we will consider plane wave, Robinson-Trautman, and self-dual dyonic string configurations, generalizing well-known solutions of this type in six-dimensional supergravities with linear chiral 2-form multiplets.

This work aims to review several aspects of the current status of the rare ${\pi }^0\to e^{+}{e}^{-}$ decay. A particular emphasis is made on radiative corrections and detailed interpretation of related quantities, some numbers appearing in the literature are updated, and the connection with the Dalitz decay, ${\pi }^0\to e^{+}{e}^{-}\gamma$, is discussed. This comes timely as it is aligned with an announcement of a preliminary result of a new branching-ratio measurement done by the NA62 Collaboration, which brings new light into an earlier-reported discrepancy between the Standard Model prediction and the (until-recently latest) precise KTeV result.

Photon rings are key targets for near-future space-based very long-baseline interferometry missions. The ratio of flux measured between successive light rings is characterized by the Lyapunov exponents of the corresponding nearly bound null geodesics. Therefore, understanding Lyapunov exponents in this environment is of crucial importance to understanding black hole observations in general, and in particular, they may offer a route for constraining modified theories of gravity. While recent work has made significant progress in describing these geodesics for Kerr, a theory-agnostic description is complicated by the fact that Lyapunov exponents are time-parametrization-dependent, which necessitates care when comparing these exponents in two different theories. In this work, we present a robust numerical framework for computing and comparing the Lyapunov exponents of null geodesics in Kerr with those in an arbitrary modified theory. We then present results obtained from calculating the Lyapunov exponents for null geodesics in two particular effective theories: scalar Gauss-Bonnet gravity and dynamical Chern-Simons gravity. Using this framework, we determine accuracy lower bounds required before a very long-baseline interferometry observation can constrain these theories.

We present details on a new measurement of the muon magnetic anomaly, $a_{\mu }=(g_{\mu }-2)/2$. The result is based on positive muon data taken at Fermilab’s Muon Campus during the 2019 and 2020 accelerator runs. The measurement uses $3.1\mathrm{GeV}/c$ polarized muons stored in a 7.1-m-radius storage ring with a 1.45 T uniform magnetic field. The value of $a_{\mu }$ is determined from the measured difference between the muon spin precession frequency and its cyclotron frequency. This difference is normalized to the strength of the magnetic field, measured using nuclear magnetic resonance. The ratio is then corrected for small contributions from beam motion, beam dispersion, and transient magnetic fields. We measure $a_{\mu }=116592057(25)\times {10}^{-11}$ (0.21 ppm). This is the world’s most precise measurement of this quantity and represents a factor of 2.2 improvement over our previous result based on the 2018 dataset. In combination, the two datasets yield $a_{\mu }(\mathrm{FNAL})=116592055(24)\times {10}^{-11}$ (0.20 ppm). Combining this with the measurements from Brookhaven National Laboratory for both positive and negative muons, the new world average is $a_{\mu }(\exp )=116592059(22)\times {10}^{-11}$ (0.19 ppm).

We discuss numerical aspects of instantons in two- and three-dimensional ${\varphi }^4$ theories with an internal $O(N)$ symmetry group, the so-called $N$-vector model. By combining asymptotic transseries expansions for large arguments with convergence acceleration techniques, we obtain high-precision values for certain integrals of the instanton that naturally occur in loop corrections around instanton configurations. Knowledge of these numerical properties is necessary in order to evaluate corrections to the large-order factorial growth of perturbation theory in ${\varphi }^4$ theories. The results contribute to the understanding of the mathematical structures underlying the instanton configurations.

In-ice radio detection is a promising technique to discover and characterize ultrahigh-energy (UHE) neutrinos, with energies above ${10}^{17}\mathrm{eV}$, adopted by present—ARA, ARIANNA, and RNO-G—and planned—IceCube-Gen2—experiments. So far, their ability to measure neutrino flavor had remained unexplored. We show and quantify how the neutrino flavor can be measured with in-ice radio detectors using two complementary detection channels. The first channel, sensitive to ${\nu }_e$, identifies them via their charged-current interactions, whose radio emission is elongated in time due to the Landau-Pomeranchuk-Migdal effect. The second channel, sensitive to ${\nu }_{\mu }$ and ${\nu }_{\tau }$, identifies events made up of multiple showers generated by the muons and taus they generate. We show this in state-of-the-art forecasts geared at IceCube-Gen2, for representative choices of the UHE neutrino flux. This newfound sensitivity could allow us to infer the UHE neutrino flavor composition at their sources—and thus the neutrino production mechanism—and to probe UHE neutrino physics.