We establish the general conditions under which evolution in the laws of physics leads to violations of the conservation of the energy-momentum tensor for matter, resulting in matter creation or destruction. They make use of global time variables canonically dual to the constants of nature. Such times flow at a rate determined by what can be interpret as the chemical potential of the fundamental constants (in analogy with phenomenological clocks based on isentropic fluids). The general condition for violations of energy conservation is then that a matter parameter evolves as a function of a gravity clock or vice versa. This framework can be envisaged as the environment within which a natural selection scenario operates, powered by random mutations in the values of the constants of nature (or indeed any other variability in the laws in terms of the times defined above). The prize function is the creation of matter, followed by its preservation. This can be accomplished in an environment where diffeomorphism invariance is among the possible theories, with mutations modeled, for example, on the absorbing Markov chain. In such a setup, the diffeormorphism invariant state with fixed constants (or any nearby state) should be the absorbing state. John Wheeler’s “higgledy-piggledy” chaotic cosmic start therefore finds a realization in this model, where its own demise and the establishment of order and seemingly immutable laws is also a prediction of the model.

Accurately inferring black hole spin is crucial for understanding black hole dynamics and their astrophysical environments. In this work, we outline a geometric method for spin estimation by using the interferometric shape of the first photon ring ($n=1$) as an approximation to the critical curve, which, given an assumed value of the black hole inclination, is then mapped to a spin value. While future space-based missions will capture a wealth of data on the first photon ring—including the full angle-dependent diameter, angular brightness profile, and astrometric offset from the $n=0$ ring—our analysis is restricted to using only two angle-dependent diameters to compute its shape asymmetry and infer spin. Focusing on low inclinations and moderate-to-high spins, we test the method across various emission models, baselines, and noise sources, including a mock space-based observation. Although the size of the $n=1$ ring depends on the emission model, its interferometric shape remains a robust spin probe at low inclinations. We find that the inferred asymmetry of the $n=1$ image may be biased by the critical curve morphology, and it can be heavily skewed by the presence of noise, whether astrophysical or instrumental. In low-noise limits at low viewing inclination, significant contributions from the $n=0$ image at short baselines may lead to a downward bias in asymmetry estimates. While our method can estimate high spins in noise-free time-averaged images, increasing the noise and astrophysical variability degrades the resulting constraints, providing only lower bounds on the spin when applied to synthetic observed data. Remarkably, even using only the ring’s asymmetry, we can establish lower bounds on the spin, underscoring the promise of photon ring-based spin inference in future space-based very long baseline interferometry missions, such as the proposed Black Hole Explorer.

Variations in the instrumental noise of the Laser Interferometer Space Antenna (LISA) over time are expected as a result of, e.g., scheduled satellite operations or unscheduled glitches. We demonstrate that these fluctuations can be leveraged to improve the sensitivity to stochastic gravitational wave backgrounds (SGWBs) compared to the stationary noise scenario. This requires optimal use of data segments with downward noise fluctuations, and thus a data analysis pipeline capable of analyzing and combining shorter time segments of mission data. We propose that simulation based inference is well suited for this challenge. In an approximate, but state-of-the-art, modeling setup, we show by comparison with Fisher information matrix estimates that the optimal information gain can be achieved in practice.

Spectral densities connect correlation functions computed in quantum field theory to observables measured in experiments. For strongly interacting theories, their nonperturbative determinations from lattice simulations are therefore of primary importance. They entail the inverse Laplace transform of correlation functions calculated in Euclidean time. By making use of the Mellin transform, we derive explicit analytic formulas to define spectral densities from the time dependence of correlation functions, both in the continuum and on the lattice. The generalization to smeared spectral densities turns out to be straightforward. The formulas obtained here within the context of lattice field theory can easily be applied or extended to other areas of research.

Quantum electrodynamics in $1+1\mathrm{D}$ (QED2) shares intriguing properties with quantum chromodynamics (QCD), including confinement, string breaking, and interesting phase diagram when the nontrivial topological $\theta$-term is considered. Its lattice regularization is a commonly used toy model for quantum simulations of gauge theories on near-term quantum devices. In this work, we address algorithms for adiabatic state preparation in digital quantum simulations of QED2. We demonstrate that, for specific choices of parameters, the existing adiabatic procedure leads to level crossing between states of different charge sectors, preventing the correct preparation of the ground state. We further propose a new adiabatic Hamiltonian and verify its efficiency in targeting systems with a nonzero topological $\theta$-term and in studying string breaking phenomena.

We give a new perspective on the Lorentzian operator product expansion inversion formula [S. Caron-Huot, Analyticity in spin in conformal theories, J. High Energy Phys. 09 (2017) 078.; D. Simmons-Duffin, D. Stanford, and E. Witten, A spacetime derivation of the Lorentzian OPE inversion formula, J. High Energy Phys. 07 (2018) 085.], building on [P. Agarwal et al., companion paper, Embedding space approach to Lorentzian CFT amplitudes and causal spherical functions, Phys. Rev. D 110, 086019 (2024).]. We introduce an “auxiliary” fourpoint function that can be related to the traditionally defined ones via a Radon transform. The Mellin amplitudes associated with this auxiliary function can be shown to be equivalent to the conventional partial wave amplitudes. This has the intuitive geometrical meaning of a generalization of the projection-slice theorem.

Marino’s Conjecture remains underexplored within the framework of $SO(N)$ string dualities. In this article, we investigated the reformulated invariants of one-parameter families of knots ${[\mathcal{K}]}_p$ derived from tangle surgery on Manolescu’s quasialternating knot diagrams [C. Manolescu, Math. Res. Lett. 14, 839 (2007)]. Within topological string dualities, we have verified Marino’s integrality conjecture for these families of knots up to the Young diagram representation $\mathbf{R}$, with $|\mathbf{R}|\le 2$. Furthermore, through our analysis, we have conjectured a closed structure for the extremal refined Bogomol’nyi–Prasad–Sommerfeld (BPS) integers for the torus knots ${[{\mathbf{3}}_{\mathbf{1}}]}_{2p+1}$ and ${[{\mathbf{8}}_{\mathbf{20}}]}_{2p+1}$, $p\in {\mathbb{Z}}_{\ge 0}$. As the parameter $p$ of the knot diagram increases, the total crossing number of a knot exceeds 16, which we describe as a complex knot. Interestingly, we discovered the maximum number of gaps in the BPS spectra associated with complex knot families. Moreover, our observations indicated that as $p$ increases, the size of these gaps also expands.

We investigate $\beta$-functions of quantum gravity using dimensional regularization. In contrast to minimal subtraction, a nonminimal renormalization scheme is employed which is sensitive to power-law divergences from mass terms or dimensionful couplings. By construction, this setup respects global and gauge symmetries, including diffeomorphisms, and allows for systematic extensions to higher loop orders. We exemplify this approach in the context of four-dimensional quantum gravity. By computing one-loop $\beta$-functions, we find a nontrivial fixed point. It shows two real critical exponents and is compatible with Weinberg’s asymptotic safety scenario. Moreover, the underlying structure of divergences suggests that gravity becomes, effectively, two-dimensional in the ultraviolet. We discuss the significance of our results as well as further applications and extensions to higher loop orders.

We provide the first example of interacting quantized Carrollian Dirac fermions in four dimensions and investigate their discrete symmetries, including charge conjugation ($C$), parity ($P$), and time reversal ($T$) transformations. As a toy model, we couple these fermions to a Carrollian scalar field using Carrollian Yukawa theory and compute the tree-level diagram, revealing an ultralocal interaction between the Carrollian fermions and the scalar field. This interaction, widely known as a Dirac delta interaction with time-dependent factor, frequently appears in quantum physics. We then address the renormalization of the theory by employing the Wilsonian procedure at one-loop order. Furthermore, we analyze the fixed points and stability properties of Carrollian Yukawa theory, comparing them with their relativistic counterparts. Beyond the specific Yukawa model studied here, we expect that our framework will have broader applications in Carrollian physics, particularly in understanding ultralocal interactions and their role in condensed matter systems, where similar phenomena arise in strongly correlated and nonrelativistic regimes.

Considering (Euclidean) quantum gravity in the Einstein-Hilbert truncation, we calculate the one-loop effective action ${\mathrm{\Gamma }}_{\mathrm{grav}}^{1l}$ using a spherical background. Usually, this calculation is performed resorting to proper-time regularization within the heat kernel expansion and gives rise to quartically and quadratically UV-sensitive contributions to the vacuum energy ${\rho }_{\mathrm{vac}}=\frac{{\mathrm{\Lambda }}_{\mathrm{cc}}}{8\pi G}$, with ${\mathrm{\Lambda }}_{\mathrm{cc}}$ and $G$ cosmological and Newton constant, respectively. We show that, if the measure in the path integral that defines ${\mathrm{\Gamma }}_{\mathrm{grav}}^{1l}$ is correctly taken into account, and the physical UV cutoff ${\mathrm{\Lambda }}_{\mathrm{cut}}$ properly introduced, ${\rho }_{\mathrm{vac}}$ presents only a (mild) logarithmic sensitivity to ${\mathrm{\Lambda }}_{\mathrm{cut}}$. We also consider a free scalar field and a free Dirac field on a spherical gravitational background and find that the same holds true even in the presence of matter. These results are found without resorting to any supersymmetric embedding of the theory and shed new light on the cosmological constant problem.

We consider $N$ clones of the quantized world, interacting with each other via quantum gravity, coupled by the downscaled Newton constant $G/N$. In the limit $N\to \infty$, we obtain the semiclassical Einstein equation for every single cloneworld. In the nonrelativistic limit, De Filippo had already obtained the semiclassical Schrödinger-Newton equation; we present an alternative elementary proof. In the general-relativistic case, we complete the semifinished derivation of Hartle and Horowitz. We compare our simple correlated cloneworlds with Stamp’s more complicated proposal of correlated worldlines and show why the two constructions differ despite the conceptual similarity.

Analyzing the stability of quasinormal modes (QNM) is essential for understanding black hole dynamics, particularly in the context of gravitational wave emissions and black hole spectroscopy. In this study, we employ the hyperboloidal approach to reformulate the quasinormal mode problem of a rotating analog black hole, effectively transforming it into an eigenvalue problem associated with a nonself-adjoint operator. Using this method, we examine the influence of rotation on the stability of the QNM spectrum, relying on the associated pseudospectrum for qualitative assessment. Our findings indicate that the prograde overtones become more stable as rotation increases. This work enhances our understanding of spectrum stability in rotating systems and expands the study of pseudospectra in nonspherically symmetric spacetimes, with potential for empirical testing in terrestrial laboratories.

Most distinguishing features of black holes and their mimickers are concentrated near the horizon. In contrast, astrophysical observations and theoretical considerations primarily constrain the far-field geometry. In this work we develop tools to effectively describe both, using the two-point Padé approximation to construct interpolating metrics connecting the near and far field. We extend our previous work by computing the quasinormal modes of gravitational perturbations for static, spherically symmetric metrics that deviate from Schwarzschild spacetime. Even at the lowest order, this approach compares well with existing methods in both accuracy and applicability. Additionally, we show that the lowest-order interpolating metric reliably predicts light ring locations. It closely matches exact results, even when unsuitable for quasinormal frequency calculations.

The future space-borne gravitational wave detector, Laser Interferometer Space Antenna (LISA), has the potential of detecting fundamental fields, such as the charge and mass of the ultralight scalar field. In this paper, we study the effect of lighter vector fields on the gravitational waveforms from the extreme-mass-ratio inspirals (EMRI) system, consisting of a stellar-mass object and the massive black hole in the Einstein-Proca theory of a massive vector field coupling to gravity. Using the perturbation theory, we compute the energy fluxes, including the contributions of the Proca field and the gravitational field, then obtain the adiabatic inspiraling orbits and corresponding waveforms. Our results demonstrate that the vector charge and mass carried by the secondary body lead to detectable effects on the EMRI waveform, and LISA has the potential to measure the mass of the Proca field with greater precision.

We compute the semiclassical current and stress-energy fluxes both at the event and Cauchy horizon of a near-extremal Reissner-Nordström black hole. We consider a minimally coupled, massless, weakly charged scalar field in the Unruh state, describing an evaporating black hole. The near-extremal domain allows for an analytical treatment of the scattering problem of the Boulware modes both in the interior and exterior regions. We present this and explicit analytical expressions for $⟨j_v⟩$ and $⟨T_{vv}⟩$ at the horizons, as well as estimates for $⟨j_u⟩$ and $⟨T_{uu}⟩$. We cross-check the analytical results numerically by bringing the radial Klein-Gordon equation into the form of the confluent Heun equation. Inserting these expectation values as sources to the Einstein-Maxwell equations, we find that at least in the near-extremal regime of small field charge, quantum effects drive the black hole interior away from extremality. Our work generalizes the known results for the real scalar field [Noa Zilberman and Amos Ori, Quantum fluxes at the inner horizon of a near-extremal spherical charged black hole, Phys. Rev. D 104, 024066 (2021).] and is in agreement with recent work on charged fields in expanding Reissner–Nordström–de Sitter universes [Christiane Klein et al., Quantum (dis)charge of black hole interiors, Phys. Rev. Lett. 127, 231301 (2021)., Christiane Klein and Jochen Zahn, Renormalized charged scalar current in the Reissner–Nordström–de Sitter spacetime, Phys. Rev. D 104, 025009 (2021).].

Following the recently proposed stable and causal first order relativistic hydrodynamics by Bemfica, Disconzi, and Noronha, we find the heat flow equation in the presence of gravity for a nonviscous fluid, which suffers heat dissipation. The derivation is confined to static and stationary backgrounds. We find that in the presence of gravity, the heat flux times a redshift factor is conserved. Then for radial heat flow, the temperature profiles are obtained from the heat equation when the gravity is sourced by Schwarzschild, Schwarzschild-de Sitter, Kerr, and Kerr-de Sitter, respectively. Consequently, the chemical potential profile is also discussed.

Primordial isocurvature perturbations, which can arise from various sources in the early Universe, have the potential to leave observable imprints on the gravitational-wave background and provide insights into the nature of primordial fluctuations. In this study, we investigate the gauge dependence of induced gravitational waves (IGWs) sourced by these isocurvature perturbations during radiation dominated era and the kination period in the early Universe. We analyze the energy density spectra of IGWs in three different gauges: synchronous, Newtonian, and uniform curvature gauges. To facilitate this analysis, we derive analytical solutions for the perturbations that contribute to the IGW spectra and a general gauge transformation from Newtonian gauge to an arbitrary gauge. Our results reveal significant differences in the energy spectra across these gauges. We find that the energy density of IGWs during radiation domination increases with conformal time as ${\eta }^8$ and ${\eta }^4$ for synchronous and uniform curvature gauges, respectively, while it converges in the Newtonian gauge. These findings highlight the importance of gauge choice in calculating IGWs and have implications for the interpretation of future observations of the gravitational-wave background.

The dynamics of ultralight dark matter with non-negligible self-interactions are determined by a nonlinear Schrödinger equation rather than by the Vlasov equation of collisionless particles. This leads to wavelike effects, such as interferences, the formation of solitons, and a velocity field that is locally curl-free, implying that vorticity is carried by singularities associated with vortices. Using analytical derivations and numerical simulations in 2D, we study the evolution of such a system from stochastic initial conditions with nonzero angular momentum. Focusing on the Thomas-Fermi regime, where the de Broglie wavelength of the system is smaller than its size, we show that a rotating soliton forms in a few dynamical times. The rotation is not associated with a large orbital quantum number of the wave function. Instead, it is generated by a regular lattice of vortices that gives rise to a solid-body rotation in the continuum limit. Such rotating solitons have a maximal radius and rotation rate for a given central density, while the vortices follow the matter flow on circular orbits. We show that this configuration is a stable minimum of the energy at fixed angular momentum and we check that the numerical results agree with the analytical derivations. We expect most of these properties to extend to the 3D case where point vortices would be replaced by vortex rings.

The rotation curves of spiral galaxies exhibit a great diversity that challenges our understanding of galaxy formation and the nature of dark matter. Previous studies showed that in self-interacting dark matter (SIDM) models with a cross section per unit mass of $\sigma /m\approx \mathcal{O}(1){\mathrm{cm}}^2/\mathrm{g}$, the predicted dark matter central densities are a good match to the observed densities in galaxies. In this work, we explore a regime with a larger cross section of $\sigma /m\approx 20-40{\mathrm{cm}}^2/\mathrm{g}$ in dwarf galactic halos. We will show that such strong dark matter self-interactions can further amplify the diversity of halo densities inherited from their assembly history. High concentration halos can enter the gravothermal collapse phase within 10 Gyr, resulting in a high density, while low concentration ones remain in the expansion phase and have a low density. We fit the rotation curves of 14 representative low surface brightness galaxies and demonstrate how the large range of observed central densities is naturally accommodated in the strong SIDM regime of $\sigma /m\approx 20–40{\mathrm{cm}}^2/\mathrm{g}$. Galaxies that are outliers in the previous studies, due to their high halo central densities, are no longer outliers in this SIDM regime as their halos would be in the collapse phase. For galaxies with a low density, the SIDM fits are robust to the variation of the cross section. Our findings open up a new window for testing gravothermal collapse, the unique signature of strong dark matter self-interactions, and exploring a broader SIDM model space. As an example, we illustrate how the larger cross sections favored by our fits, together with upper limits from strong lensing observations in clusters, pick out the preferred SIDM model space for a dark matter particle coupled to a light gauge boson in the Born regime.