By studying a simple model of relativistic particles propagating through a background medium with an energy-dependent relaxation time that is unbounded from above, we investigate how long-term memory obstructs the emergence of local hydrodynamics in systems with a gapless nonhydrodynamic sector. In the relaxation-time approximation matching frame, we show that the full gradient expansion is generically divergent in most flows, even for Fourier modes, and that any resummation necessarily retains an infinite set of slow nonhydrodynamic degrees of freedom. The divergence of the gradient expansion therefore reflects a more fundamental breakdown of hydrodynamic locality caused by persistent nonhydrodynamic memory. We finally show that sufficiently singular relaxation spectra can invalidate ordinary diffusion itself. In these regimes, the diffusivity diverges, and the late-time dynamics become superdiffusive, governed by intrinsically nonlocal constitutive relations.

We present a charged-current quasielastic neutrino-nucleus scattering model based on an unfactorized representation of the spectral function, employing relativistic momentum distributions for bound nucleons and the relativistic distorted-wave impulse approximation with an energy-dependent relativistic potential to describe the scattered nucleon. The model incorporates two-body meson-exchange currents contributing to one-particle-one-hole final states and tests several axial form factor parametrizations, including recent LQCD and MINERvA fits. It is implemented in the NEUT event generator and benchmarked against T2K and MINERvA ${\nu }_{\mu }\text{−}{}^{12}\mathrm{C}$ $\mathrm{CC}0\pi$ measurements. We find that two-body meson-exchange currents lead to a sizeable increase of the total cross section, arising from an enhancement of the transverse response, which is the dominant component in charged-current neutrino scattering. On the other hand, recent fits of the axial form factor predict larger values than the standard dipole form, yielding a systematic enhancement of the cross section. The $\mathrm{LQCD}+\mathrm{MINERvA}$ parametrization tends to overestimate the data, while the MINERvA-only fit provides a more moderate increase. Overall, no single configuration consistently provides the best agreement with the different datasets.

The flux of Hidden Sector particles from the Galactic halo reaching an underground detector can be significantly attenuated by interactions within the Earth for sufficiently large scattering cross- sections. This attenuation gives rise to a characteristic daily modulation in the detection rate, due to Earth’s rotation. We present results from a search for such a modulation using a 1.257 kg-day dataset collected with the DAMIC-M Low Background Chamber. A model-independent analysis reveals no significant modulation in the $1e^{-}$ event rate over periods from 1 to 48 h, highlighting the excellent temporal stability of the detector. In a complementary model-dependent analysis, we target the expected daily modulation signature of Hidden Sector particles, with masses in the range $[0.53,2]\mathrm{MeV}/{\mathrm{c}}^2$, interacting with electrons via a dark photon mediator. By leveraging the expected temporal evolution of the signal, we set improved constraints on Dark Matter masses below $1.2\mathrm{MeV}/{\mathrm{c}}^2$, surpassing our previous limits.

We investigate the thermodynamic properties of the Kerr-Bertotti-Robinson black hole, an exact Petrov type-D solution of Einstein-Maxwell theory describing a rotating black hole immersed in an external electromagnetic field. While the conserved angular momentum and electric charge can be computed straightforwardly, the conserved mass cannot be obtained through standard integrability methods due to the nontrivial asymptotically uniform external electromagnetic field. To overcome this difficulty, we adopt the Christodoulou-Ruffini mass relation as a thermodynamic definition of the conserved mass and identify the associated generator, thereby fixing the ambiguity in defining this conserved mass and constructing the thermodynamic potentials. These thermodynamic quantities naturally satisfy the first law of black-hole thermodynamics as well as the Smarr formula.

In this work, we study the classical phase space for the gravitational degrees of freedom along a null ray. We construct gauge-invariant observables localized on a null ray segment that commute with those localized on the complement; thus, the phase space describes a genuine gravitational subsystem compatible with both locality and diffeomorphism invariance. Our construction employs “dressing time” (a null time coordinate built from spin 0 gravitational degrees of freedom) as a dynamical reference frame. The existence of such a frame depends on the use of edge mode variables, which we argue are generally required to upgrade a local gauge-fixing condition to a global “frame fixing.” To analyze the effects of quantum diffeomorphism anomalies on these structures, we then establish an “effective” classical description in which the Raychaudhuri equation, symplectic form, and edge mode variables all acquire Virasoro-type deformations. Within this framework, we identify three distinct diffeomorphism actions: reparametrizations (gauge transformations), reorientations (physical symmetries of the reference frame), and dressed reparametrizations. Each acquires its own central extension and plays a different crucial role in the effective theory. The resulting structures provide a foundation for quantizing gravitational null ray segments, including promoting dressing time to a genuine quantum reference frame.

We study the complexity of Hawking radiation for an evaporating black hole from the perspective of the stabilizer theory of quantum computation. Specifically, we calculate Wigner negativity—a magic monotone that can be interpreted as a measure of the stabilizer complexity, or equivalently, the complexity of classical simulation—in various toy models for evaporating black holes. We first calculate the Wigner negativity of Hawking radiation in the Penington-Shenker-Stanford-Yang (PSSY) model directly using the gravitational path integral, and show that the negativity is $O(1)$ before the Page transition, but becomes exponentially large past the Page transition. We also derive a universal, information theoretic formula for the negativity that interpolates between the two extremes. We then study the Wigner negativity of radiation in a dynamical model of black hole evaporation. In this case, the negativity shows a sharp spike at early times resulting from the coupling between the black hole and the radiation system, but at late times when the system settles down, we find that the negativity satisfies the same universal formula as in the PSSY model. Finally, we also propose a geometric formula for Wigner negativity in general holographic states using intuition from fixed area states and random tensor networks, and argue that a python’s lunch in the entanglement wedge implies a stabilizer complexity that is exponentially large in $\frac{1}{8G_N}$ times the difference between the areas corresponding to the outermost and minimal extremal surfaces.

Charged massive spin-$3/2$ fields have long been regarded as problematic, because their coupling to electromagnetism generically leads to loss of hyperbolicity, acausal propagation and loss of unitarity. At the same time, fractionally charged supermassive gravitinos play a central role in a recent proposal of two of the present authors, where they are the only fermionic degrees of freedom beyond the Standard Model and provide novel dark matter candidates. We address this apparent tension by revisiting the result of Deser and Waldron, who showed that the inclusion of gravity can compensate the electromagnetic source of the inconsistency. For a minimally coupled Rarita-Schwinger field in an Einstein-Maxwell background, consistency requires a lower bound on the mass in terms of the charge and the cosmological constant. What is usually a severe obstruction to low-energy charged spin-$3/2$ phenomenology becomes an independent indication that such particles must lie close to the Planck scale, as argued by two of the present authors on other grounds. We rederive the inequality from the solvability of the Rarita-Schwinger constraints and from the characteristic determinant, emphasizing how the Einstein-Maxwell stress tensor compensates the purely electromagnetic pathology. We then reformulate the system using a Stückelberg spinor, showing that the helicity-$1/2$ sector reproduces the same condition. This formulation is also essential for obtaining a renormalizable propagator. We discuss this propagator and the corresponding ghost system.

We establish a deformation framework for highly symmetric solutions to the Einstein equations. In this framework, four-dimensional metrics are constructed from three-dimensional $\eta$-Einstein metrics admitting a deformation locally determined by a single function. Under this deformation, the resulting spacetime solves the Einstein equations with a string-cloud source. Within this framework, a wide range of symmetric spacetimes can be treated in a unified manner. These include FLRW, Kantowski-Sachs, and LRS Bianchi cosmological models [including Taub-NUT-(A)dS solutions], as well as Reissner-Nordström-(A)dS black holes admitting spherical, planar, or hyperbolic symmetry. In the cosmological setting, the deformation leaves the evolution equations for the scale factors unchanged, and hence the expansion history coincides with that of the corresponding undeformed models. For the deformed Reissner-Nordström-(A)dS black holes, the structure of Killing horizons is insensitive to the deformation.

We propose an idea to build a bridge between reheating and late-time observations in quintessential inflation by backtracking the evolution of the inflaton field from the present time to the end of reheating. This idea is implemented first in the freezing case when the potential gradient is negligible compared to the Hubble friction, rendering the inflaton field frozen, till the present time. We find a simple analytic relation between the reheating temperature and the current values of observational parameters for dark energy and numerically confirm its validity for explicit models. This relation implies that any quintessential inflation model with a successful reheating with the reheating temperature $1\mathrm{MeV}\lesssim T_{\mathrm{re}}\lesssim {10}^9\mathrm{GeV}$ predicts the current value of the equation of state of dark energy to be within an extremely narrow range very close to $-1$, i.e., $-1+{10}^{-48}\lesssim w_0\lesssim -1+{10}^{-24}$. All of the results are universal and can apply to all quintessential inflation models with any reheating mechanism, unless the inflaton field unfreezes before the present time. Motivated by the results that the imprint of reheating on $w_0$ is not observationally measurable in the freezing case, we extend the analysis to the unfreezing case in which the inflaton field unfreezes before the present time. In particular, we derive the general conditions to have the measurable imprint of reheating on $w_0$ and determine the parameter ranges to be compatible with these conditions for the typical models of quintessential inflation.

Big bang nucleosynthesis (BBN) predictions of primordial light-element abundances offer a powerful probe of early-Universe physics. However, high-accuracy numerical BBN calculations have become a major computational bottleneck for large-scale cosmological inferences due to the complex nuclear network. Here we present bbnet, a fast and accurate deep learning emulator for primordial abundances. The training data are generated by full numerical calculations using two public BBN codes, parthenope and alterbbn, modified to accommodate extended cosmologies that include dark radiation and a stiff equation of state. The network employs a residual multihead architecture to capture convoluted physical relationships. bbnet produces primordial helium-4 and deuterium abundances with negligible errors in milliseconds per sample, achieving a speed-up of up to ${10}^4$ times relative to first-principles solvers while remaining unbiased over wide parameter ranges. Therefore, our emulator can supersede traditional simplified numerical prescriptions that compromise accuracy for speed. Based on extensive assessments of its performance, we conclude that bbnet is an optimal solution to the theoretical prediction of primordial element abundances. It will serve as a reliable tool for precision cosmology and new physics searches.

We investigate the prospects for probing large-scale power asymmetry through galaxy clustering and intrinsic alignments (IA) in stage IV galaxy surveys. Specifically, we consider a dipolar modulation in the primordial power spectrum and evaluate the Fisher information matrix using the two-point statistics of both the galaxy clustering and IA. Our analysis reveals that while IA alone provides limited improvement in constraining the modulation amplitude, the cross-spectrum between galaxy density and IA can contribute up to half the constraining power of galaxy clustering, especially for surveys with low galaxy bias and high number density of galaxies, such as Euclid. This demonstrates the potential of IA-clustering cross-correlations as a robust consistency check against systematics, and highlights the complementary roles of galaxy clustering and IA in constraining the asymmetry. We also show that marginalizing over galaxy bias and IA bias parameters has a negligible impact on the final constraint on the modulation amplitude.

The generation of white noise on large scales is a generic property of the dynamics of physical systems described by local nonlinear partial differential equations. Nonlinearities prevent the small-scale dynamics from being erased by smoothing. Unresolved small-scale dynamics act as an uncorrelated (white or Poissonian) noise (seemingly stochastic but actually deterministic) contribution to large-scale dynamics. This white noise exists even when the dynamics is very nearly linear. In cases where the power spectrum is sub-Poissonian on large scales, this noise will dominate on the largest scale power no matter the amplitude of the inhomogeneities. Such is the case in the standard model of cosmology, where the primordial density power spectrum is expected to have an almost Harrison-Zel’dovich, $P[k]\sim k$, spectrum on a much broader range of scales than can be observed. Even though linear gravitational evolution dominates nonlinear corrections by a factor of $\sim {10}^5$, the nonobservation of white noise on the Hubble scale precludes the extrapolation of this power law below the comoving 1 pc scale. More generally, observation or nonobservation of large-scale white noise provides a powerful probe of the Universe on very small scales in the early Universe. Gravitational radiation, phase transitions, vorticity, and running of the spectral index are all phenomena that can be probed with large-scale white noise. Large-scale white noise is a nonoptional feature of all cosmological models but one which has not heretofore been appreciated.

Ultrahigh energy cosmic rays (UHECR) can produce relativistic cascades that emit radio-frequency (RF) pulses in the 0.1–1 GHz bandwidth via two distinct effects: the geomagnetic effect, and the Askaryan effect. The geomagnetic effect occurs when the magnetic field of the Earth causes cascade charges to form a transverse current that radiates linearly polarized radiation aligned with the Lorentz force direction. The Askaryan effect is caused by the net negative charge excess in the cascade that radiates linearly polarized radiation along the Cherenkov cone. When UHECR cascades enter solid, RF transparent matter at altitudes where the cascade develops, Askaryan radiation created in the solid medium can propagate to RF detectors. The Askaryan Radio Array (ARA) at the South Pole has observed 13 UHECR candidates in precisely this fashion. We present an analytical model that confirms the events are UHECRs. The model includes Askaryan radiation created within the ice sheet and the ARA RF channel response. The coherently summed waveforms (CSWs) from the UHECR candidates match our model with correlation coefficients between 0.69 and 0.86, and with minimal fractional power differences. Finally, we demonstrate how to obtain the Askaryan $\overrightarrow{E}$-field from our model, and that it matches the results from the ARA collaboration.

We study the production of ultra-high-energy particles via the Bañados-Silk-West mechanism in the premerger phase of binary systems detected by LIGO-Virgo-KAGRA. By solving the geodesic equations for charged particles in magnetized Kerr spacetime with fields of $B\sim {10}^{12}–{10}^{14}\mathrm{G}$, we demonstrate that collisions near the horizon can achieve center-of-mass energies $E_{\mathrm{cm}}\sim {10}^{18}–{10}^{20}\mathrm{eV}$, placing them firmly in the ultra-high-energy cosmic-ray (UHECR) range. We systematically explore the parameter space of merger remnants, varying black hole mass ($M\sim 20–150M_{\odot }$, characteristic of the binary black hole population), dimensionless spin (${\chi }_f\sim 0.7–0.9$), magnetic field strength, and particle angular momenta. Our analysis reveals three distinct acceleration regimes: a gravity-dominated regime ($B<{10}^{12}\mathrm{G}$) with negligible magnetic enhancement, a transition regime (${10}^{12}\mathrm{G}\lesssim B\lesssim {10}^{13}\mathrm{G}$) where gravitational and magnetic effects compete, and a magnetic-dominated regime ($B>{10}^{13}\mathrm{G}$) where fields amplify collision energies by nearly an order of magnitude. For the 34 gravitational-wave events with high remnant spins (${\chi }_f>0.7$), we compute the maximum achievable energies, finding that systems with ${\chi }_f\gtrsim 0.85$ and $M\gtrsim 100M_{\odot }$ can reach $E_{\max }\sim {10}^{20}\mathrm{eV}$. Our results establish magnetized binary mergers, particularly black hole–neutron star systems and postmerger black hole remnants formed in binary neutron star coalescences, as promising sources of UHECRs and provide quantitative predictions linking gravitational-wave observables to particle acceleration efficiency.

We present a measurement of the free-streaming length of dark matter (DM) and subhalo abundance around 28 quadruple image strong lenses using observations from James webb space telescope mid-infrared instrument presented in Paper III of this series. We improve on previous inferences on DM properties from lensed quasars by simultaneously reconstructing extended lensed arcs with image positions and relative magnifications (flux ratios). Our forward modeling framework generates full populations of subhalos, line-of-sight halos, and globular clusters, uses an accurate model for subhalo tidal evolution, and accounts for free-streaming effects on halo abundance and concentration. Modeling lensed arcs leads to more-precise model-predicted flux ratios, breaking covariance between subhalo abundance and the free-streaming scale parametrized by the half-mode mass $m_{\mathrm{hm}}$. Assuming subhalo abundance predicted by the semianalytic model galacticus ($N$-body simulations), we infer (Bayes factor of $10:1$) $m_{\mathrm{hm}}<{10}^{7.4}{M}_{\odot }$ ($m_{\mathrm{hm}}<{10}^{7.2}{M}_{\odot }$), a 0.4 dex improvement relative to omitting lensed arcs. These bounds correspond to lower limits on thermal relic DM particle masses of 6.5 and 7.4 keV, respectively. Conversely, assuming DM is cold, we infer a projected mass in subhalos (${10}^6<m/M_{\odot }<{10}^{10.7}$) of ${1.7}_{-1.2}^{+2.6}\times {10}^7{M}_{\odot }{\mathrm{kpc}}^{-2}$ at 95% confidence. This is consistent with galacticus predictions ($0.9\times {10}^7{M}_{\odot }{\mathrm{kpc}}^{-2}$), but in mild tension with recent $N$-body simulations ($0.6\times {10}^7{M}_{\odot }{\mathrm{kpc}}^{-2}$). Our results are among the strongest bounds on warm dark matter, and the most precise measurement of subhalo abundance around strong lenses. Further improvements will follow from the large sample of lenses to be discovered by Euclid, Rubin, and Roman.

We present the full sample of measurements of the warm dust emission of 31 strongly-lensed, multiply imaged quasars, observed with JWST MIRI multiband imaging, which we use to constrain the particle properties of dark matter. The strongly lensed warm dust region of quasars is compact and statistically sensitive to a population of dark matter halos down to masses of ${10}^6{M}_{\odot }$. The high spatial resolution and infrared sensitivity of MIRI make it uniquely suited to measure multiply imaged warm dust emission from quasars and thus to infer the properties of low-mass dark halos. In this work, we present image fluxes as well as dark matter sensitive warm dust flux ratios inferred from spectral energy distribution fitting. We then use these flux ratios to test for the presence of a warm dark matter turnover in the halo mass function. We use a forward modeling pipeline which explores dark matter parameters while also accounting for tidal stripping effects on subhalos, globular clusters, and complex deflector macromodels with $m=1,m=3$, and $m=4$ elliptical multipole moments. Adopting a comparable prior on the projected density of substructure to previous analyses, the data presented here provide a factor of 2 improvement in sensitivity to a turnover in the halo mass function. Assuming subhalo abundance predicted by the semianalytic model galacticus, we infer with a Bayes factor of $10:1$, a half-mode mass $m_{\mathrm{hm}}<{10}^{7.8}{M}_{\odot }$. If instead we use a prior from $N$-body simulations, we infer $m_{\mathrm{hm}}<{10}^{7.6}{M}_{\odot }$. This corresponds to a thermally produced dark matter mass of 5.6 (6.4) keV for the galacticus and $N$-body priors, respectively. This is one of the strongest constraints to date on a turnover on the halo mass function, and the flux ratios and inference methodology presented here can be used to test a broad range of dark matter physics.

This work investigates the allowed parameter spaces of a simplified dark matter (DM) model characterized by a spin-0 mediator with masses in the low to intermediate range ($<10\mathrm{GeV}$). We systematically divide the parameter space into various mass regions of the mediator and constrain the model parameters using a diverse set of observables, including flavor-changing charged and neutral current processes such as rare and semileptonic decays of pseudoscalar mesons (B and K), electroweak precision observables, alongside data from fixed-target experiments. Additionally, we explore the model’s capability to explain recent Belle II data on invisible B meson decays. Our study includes a detailed examination of DM properties and the constraints from big bang nucleosynthesis. We present bounds on model parameters through individual and simultaneous analyses of the available inputs and highlight their implications for understanding DM phenomenology. Furthermore, we obtain bounds on the couplings of the possible gauge-invariant dimension-5 operators, leading to the possible interactions between the spin-0 mediator and the SM gauge bosons and fermions. This study comprehensively investigates the constraints and theoretical implications associated with low-mass spin-0 mediator DM models.

We consider a quenched $\mathrm{SU}(2)\times \mathrm{U}(1)$ gauge Higgs theory on the lattice, coupled to a static vectorlike fermion which, in this case, is in the same gauge group representation as the Higgs field. Physical (i.e., locally gauge invariant) electrically charged and electrically neutral states of matter particles in the electroweak theory were described decades ago, but those constructions do not exhaust all the possibilities, and new types of electrically charged/neutral states, orthogonal to former constructions, are described here. The difference has to do with how the static source, which by itself does not create a physical state, is dressed by dynamical fields. We find that, unsurprisingly, the neutral static fermion is much lighter than any of the charged fermion states. But a lattice study of the propagation of the charged fermion states indicates the existence of (at least) two particle states with different masses in charged particle spectrum.

Global QCD analyses of nuclear parton distribution functions (nPDFs) have traditionally relied on the Hessian method for uncertainty estimation. However, the inherent Gaussian approximation and reliance on local curvature often prove insufficient for nPDF fits, which are frequently characterized by limited data constraints and non-Gaussian likelihoods. In this paper, we present the first nPDF determination based on Markov Chain Monte Carlo (MCMC) techniques, implemented within the nCTEQ framework using an adaptive Metropolis-Hastings algorithm. The MCMC approach enables a direct mapping of the posterior distribution and reveals a highly nontrivial parameter-space structure, including multiple modes and pronounced non-Gaussian behavior, particularly for the valence PDFs. We perform the first single-nucleus global analysis of lead PDFs using exclusively lead data and compare it to a multi-nuclei fit employing a standard analytic $A$ dependence. The inclusion of lighter nuclei reduces quark uncertainties and modifies the shape of the lead PDFs, while leaving the gluon distribution largely unaffected. A complementary Hessian analysis exposes systematic limitations of the Gaussian approximation. Our results demonstrate that MCMC methods provide a more reliable framework for uncertainty quantification in nPDF determinations.