Fast radio bursts (FRBs) have emerged as powerful probes in cosmology. An optimized method was recently proposed to extract the cosmic baryon density from localized FRBs by maximizing the joint likelihood function of the extragalactic dispersion measure (${\mathrm{DM}}_{\mathrm{ext}}$). In this paper, we identify a crucial factor that was omitted in the probability density function (PDF) for ${\mathrm{DM}}_{\mathrm{ext}}$ in that method. Using simulated FRB data, we demonstrate that neglecting this factor leads to a systematic bias in the inferred cosmic baryon density, with deviations exceeding the $1\sigma$ confidence level. This highlights the necessity of including the missing factor for reliable cosmological applications of FRBs. Furthermore, applying our corrected PDF to a sample of 88 real localized FRBs, we find that the baryon density inferred with the original PDF is inconsistent with the Planck 2018 CMB results, whereas our corrected PDF yields excellent agreement.

Recently, the Alpha Magnetic Spectrometer (AMS-02) Collaboration presented tentative evidence for the detection of cosmic antihelion-3 ($\overline{{}^3\mathrm{He}}$) events, alongside a comparable number of antideuterons ($\overline{\mathrm{D}}$). If confirmed, these observations could revolutionize our understanding of cosmic-ray production and propagation and/or serve as compelling indirect evidence for dark matter. Given that the detection of cosmic $\overline{\mathrm{D}}$ is already at the limit of AMS-02 sensitivity, explaining the observation of $\overline{{}^3\mathrm{He}}$ even within the standard coalescence framework poses a significant challenge. It has recently been shown that a previously overlooked mechanism within the Standard Model of particle physics—namely, the production of antihelion via the displaced-vertex decay of ${\overline{\mathrm{\Lambda }}}_b^0$ baryons—could substantially enhance the $\overline{{}^3\mathrm{He}}$ flux arising from dark matter-induced processes. In light of these challenges, we present a tuning of pythia that is consistent with LEP data on the fragmentation function of $b$ quarks into $b$ hadrons—a critical factor for determining the ${\overline{\mathrm{\Lambda }}}_b^0$ multiplicity—and with ALICE and ALEPH data for the $\overline{\mathrm{D}}$ and $\overline{{}^3\mathrm{He}}$ spectra, which we employ to determine our coalescence model. Our refined pythia tuning, in conjunction with our coalescence model, results in a predicted branching ratio for the production of $\overline{{}^3\mathrm{He}}$ from ${\overline{\mathrm{\Lambda }}}_b^0$ decays that is consistent with the recent upper limit measured by LHCb. Furthermore, our prediction indicates that the contribution of $\overline{\mathrm{D}}$ and $\overline{{}^3\mathrm{He}}$ from beauty-hadron decays is negligible relative to the direct production from hadronization.

The blazar TXS $0506+056$ has been suggested to be a potential high-energy neutrino source thanks to the observations of IceCube, which found outburstlike neutrino emissions during 2014–2015 and 2017 in the transient emission search, and a $3.5\sigma$ local significance in a ten-year time-integrated search. The conventional one-zone jet model cannot explain the observed neutrino flux during outbursts due to the constraint from the x-ray flux, leading to proposals of multizone models (e.g., two-zone model) with multiple radiation zones. In literature, it has been shown that multizone models may consistently explain the high-state neutrino emission and the multiwavelength emission of TXS $0506+056$, while the quasi-steady-state long-term emission has not been well studied. In this work, we investigate a physically based model for the quasi-steady-state neutrino and electromagnetic radiation under the same framework, and successfully reproduce the multimessenger emission of TXS $0506+056$.

We study the transverse energy-energy correlator (TEEC) observable in photon-hadron and photon-jet production in $\mathrm{p}+\mathrm{p}$ and $\mathrm{p}+\mathrm{A}$ collisions at small $x$. We derive the relevant expressions in the high-energy limit of the scattering where the dipole picture is applicable and show how the dependence on the fragmentation function of the hadron cancels due to the momentum-sum rule. The nonperturbative scattering with the target nucleus is expressed in terms of the dipole amplitude, which also describes nonlinear gluon saturation effects. The TEEC observable is computed in the Relativistic Heavy Ion Collider (RHIC) and Large Hadron Collider (LHC) kinematics, and we show that it can be sensitive to the dipole amplitude, making it a potentially good observable for studying saturation effects.

We show, in the framework of a space-time resolved relativistic quantum field theory approach to tunneling, that microcausality precludes superluminal tunneling dynamics. More specifically in this work dealing with Dirac and Klein-Gordon fields, we first prove that microcausality holds for such fields in the presence of a background potential. We then use this result to show that an intervention performed on a localized region of an initial wave packet subsequently scattering on a potential barrier does not result in any effect outside the light cone emanating from that region. We illustrate these results with numerical computations for Dirac fermions and Klein-Gordon bosons.

Neural control variates (NCVs) have emerged as a powerful tool for variance reduction in Monte Carlo (MC) simulations, particularly in high-dimensional problems where traditional control variates are difficult to construct analytically. By training neural networks to learn auxiliary functions correlated with the target observable, NCVs can significantly reduce estimator variance while preserving unbiasedness. However, a critical but often overlooked aspect of NCV training is the role of autocorrelated samples generated by Markov chain Monte Carlo (MCMC). While such samples are typically discarded for error estimation due to their statistical redundancy, they may contain useful information about the structure of the underlying probability distribution that can benefit the training process. In this work, we systematically examine the effect of using correlated configurations in training neural control variates. We demonstrate, both conceptually and numerically, that training on correlated data can improve control variate performance, especially in settings with limited computational resources. Our analysis includes empirical results from $U(1)$ gauge theory and scalar field theory, illustrating when and how autocorrelated samples enhance NCV construction. These findings provide practical guidance for the efficient use of MCMC data in training neural networks.

Dark matter candidates with masses around the Planck scale are theoretically well-motivated, and it has been suggested that it might be possible to search for dark matter solely via gravitational interactions in this mass range. In this work, we explore the pathway towards searching for dark matter candidates with masses around the Planck scale using mechanical sensors while considering realistic experimental constraints, and develop analysis techniques needed to conduct such searches. These dark matter particles are expected to leave tracks as their signature in mechanical sensor arrays, and we show that we can effectively search for such tracks using statistical approaches to track-finding. We analyze a range of possible experimental setups and compute sensitivity projections for searches for ultraheavy dark matter coupling to the Standard Model via long-range forces. We find that while a search for Planck-scale dark matter purely via gravitational couplings would be exceedingly difficult, requiring $\sim 80\mathrm{dB}$ of quantum noise reduction with a ${100}^3$ array of devices, there is a wide range of currently unexplored dark matter candidates which can be searched for with already existing or near-term experimental platforms.

We present a manifestly diffeomorphism-invariant simple model of galaxy dynamics obtained by applying the dressing field method (DFM) to a general relativistic system comprising the metric and four scalar fields, phenomenologically representing the four-velocity of a cosmological fluid or dust field. The DFM, a systematic tool for extracting the gauge-invariant content in general relativistic theories, provides a physical coordinatization that yields corrective terms to the rotational velocity profile. These corrections produce galaxy rotation curves that combine Keplerian and constant velocity terms, effectively emulating a dark matter contribution. We compare DFM-derived rotation curves to observed data for spiral galaxies, from the Spitzer Photometry and Accurate Rotation Curves database, showing that the DFM allows one to fit them well.

We derive a compact analytical expression for the growth factor $\mathrm{\Upsilon }$, which characterizes how the gravitational wave spectrum sourced by sound waves evolves in a universe with a generic expansion history. Assuming the dominant energy density scales as $\rho \propto a^{-3(1+w)}$, we obtain $\mathrm{\Upsilon }=\frac{2[1-y^{3(w-1)/2}]}{3(1-w)}$, where $y=a(t)/a(t_s)$ is the ratio of the scale factor at a later time $t$ to that at $t_s$ when gravitational wave production from sound waves starts. This general result reduces to known forms in radiation- and matter-dominated eras, thereby extending previous formulas to a broader class of cosmological backgrounds. The derivation assumes only that the source is stationary, making $\mathrm{\Upsilon }$ a universal factor that captures gravitational wave growth in various scenarios—not limited to phase transitions.

The Lie algebra of symmetries generated by the left-moving current $j={\partial }_{-}\varphi$ in the two-dimensional (2D) single scalar conformal field theory is infinite dimensional, exhibiting mutually commuting subalgebras. The infinite-dimensional mutually commuting subalgebras define integrable deformations of the 2D single scalar conformal field theory that preserve the Poisson bracket structure. We study these mutually commuting subalgebras, finding general properties that the generators of such a subalgebra must satisfy. Along the way, we derive constraints on integrable equations of the Korteweg–de Vries type. We also confirm that the recently found $[j]=0,-1,-2$ mutually commuting subalgebras are infinite dimensional.

We develop a technique to construct solutions of the Dirac equation employing the underlying group symmetries and the classical-quantum relationship within the Clifford algebra formalism. In particular, we construct a novel solution of the Dirac equation in the form of an electron vortex beam in a gravitational plane wave and show its relationship to the solution of the classical analog of the Dirac equation—rotor equation—for a particle in a gravitational wave. Our approach put forward a new paradigm in treating dynamical problems based on the underlying group symmetries.

A new perspective on the inverse string theory Kawai-Lewellen-Tye (KLT) kernel is provided which establishes the universality of scattering amplitudes in the biadjoint scalar theory, pions in the nonlinear sigma model (NLSM), and mixed amplitudes (NLSM+${\varphi }^3$) recently studied in the literature. We show that all these amplitudes can be viewed as equivalent, arising from a single function, the inverse string theory KLT kernel, evaluated at different kinematic points. In this way cubic colored scalars and pions become interchangeable through a procedure we call the ${\alpha }^{\prime }$ shift. The latter complements the $\delta$ shift proposed by Arkani-Hamed et al., and demonstrates an inherent equivalence of scattering amplitudes in different quantum field theories by embedding them in a common stringy framework.

Ultracold fermionic atoms in an optical lattice, with a sudden position-dependent change (a quench) in the effective dispersion relation, have been proposed by Rodríguez-Laguna et al. as an analog spacetime test of the Unruh effect. We provide new support for this analog by analyzing the entanglement of a scalar field in a ($1+1$)-dimensional continuum spacetime with a similar quench, and the harvesting of this entanglement by a pair of Unruh-DeWitt detectors. We present numerical evidence that the concurrence and mutual information harvested by the detectors are qualitatively similar to those in Rindler spacetime, but they exhibit a small yet noticeable variation when the energy pulse created by the quench crosses the detectors. These findings provide further motivation to implement the experimental proposal of Rodríguez-Laguna et al.

In the framework of the beyond Horndeski action, we consider three subtheories that support scalarized black-hole solutions, and look for modified characteristics compared to GR. We first study the propagation of massless scalar and vector test fields in the fixed background of an analytical spherically symmetric black hole derived in the context of a parity-symmetric beyond Horndeski theory, and show that the profiles of the effective gravitational potentials, greybody factors, absorption cross sections, and quasinormal frequencies exhibit distinct modifications as we move away from the GR limit. We then turn our attention to the perturbations of the gravitational field itself and adopt a full-theory analysis that takes into account the backreaction of the scalar field on the metric. Employing as background solutions scalarized black holes arising in the shift-symmetric Horndeski theory and in the quadratic-quartic-scalar-Gauss-Bonnet theory, we compute the greybody factors and quasinormal modes of the axial sector. In both theories, in direct correspondence to the form of the gravitational potential, which features multiple extremal points, we find modified (suppressed or nonmonotonic) greybody curves and altered quasinormal frequencies (smaller oscillating frequencies and larger damping times), especially as the hair-sourcing parameter increases.

Extreme mass-ratio inspirals (EMRIs) are binary systems where a compact object slowly inspirals into its much larger compact partner (i.e., a galactic center supermassive black hole [SMBH]). Since we anticipate such systems to exist within and be dynamically influenced by the galactic center environment, we expect them to be instrumental in studying these environments and testing our theories of gravity in the strong field regime. The gravitational waves associated with the EMRI motion fall within the mHz regime, making them target sources for future space-based detectors. However, because of the crowded nature of these galactic centers, these EMRIs could be perturbed by other nearby orbiting bodies. This paper focuses on cataloging potential perturbations in EMRIs due to a third-body perturber near resonance. We use the formalism and code tools developed in the previous paper in this series [Silva and Hirata, Phys. Rev. D 106, 084508 (2022)] and expand them to account for a general outer body orbit, allowing for multiple resonant interactions within an orbit and across a variety of SMBH spins. We find that, after investigating nearly 142,000 resonant interactions across a restricted set of 180 different simulated orbit systems, none cause changes to the EMRI dynamics beyond a perturbative correction ($\lesssim 1\%$ to the action variables), but could lead to potentially large changes in the phase of the waveform of order 0.1 radian. Detectable phase changes in the waveform induced by third-body perturbers could therefore be a common occurrence and will require careful consideration for developing accurate EMRI waveform models. This analysis suggests that our formalism and pipeline are robust enough to handle a wide variety of resonances from various perturbing orbit configurations around the EMRI, which will aid in developing more accurate waveform models to better probe galactic center environments and test theories of gravity using gravitational wave observations of EMRIs.

We investigate how screening mechanisms, reconciling light scalar fields driving cosmic acceleration with local fifth force constraints, can be probed via their impact on nonlocal quantum correlations between entangled spin pairs, whose evolution on a curved background is affected by general relativity (GR) and screened modified gravity effects. We consider a gedanken experiment featuring a pair of massive, spin-$1/2$ particles orbiting the Earth, evaluating their nonlocal correlations through spin observables associated to the Clauser-Horne-Shimony-Holt (CHSH) inequality. Using a general formalism developed earlier for curved spacetime spin evolution, we compute the effects of screening on the CHSH inequality, finding its degree of violation to be suppressed relative to the flat spacetime case. Applying this formalism to the chameleon, symmetron, and dilaton mechanisms, we identify currently unconstrained regions of parameter space where the screening contribution is comparable to that of GR. While detecting these effects will be challenging, our work provides a proof of principle for testing screened dark energy through quantum nonlocality.

In this work, we find a new branch of hairy black hole solutions in the Einstein-Maxwell-scalar theory in four-dimensional asymptotically flat spacetimes. Different from spontaneous scalarization induced by tachyonic instabilities in Reissner-Nordström (RN) black holes with a negative coupling parameter, these scalar-hairy black hole solutions arise when the coupling parameter is positive, where nonlinear coupling plays the dominant role, meaning that the coupling is positively correlated with the degree of deviation from the trivial state. Our numerical analysis reveals that the scalar field grows monotonically with the radial coordinate and asymptotically approaches a finite constant, exhibiting behavior that is qualitatively similar to that of the Maxwell potential. In these solutions, an increase in the charge $q$ causes the scalar-hairy solutions to deviate further from the RN state, while excessive charging drives the system back toward hairless solutions. Strengthening the coupling parameter compresses the existence domain of the scalar-hairy state, which lies entirely within the parameter region of RN black holes. Moreover, by evaluating the quasinormal modes, we show that the obtained scalar-hairy solutions are stable against linearized scalar perturbations.

We study the gravitational waveforms generated by critical, equatorial plunging geodesics of the Kerr metric that start from an unstable-circular-orbit, which describe the test-mass limit of spin-aligned eccentric black hole mergers. The waveforms are generated employing a time-domain teukolsky code. We span different values of the Kerr spin $-0.99\le a\le 0.99$ and of the critical eccentricity $e_c$, for bound ($0\le e_c<1$) and unbound plunges ($e_c\ge 1$). We find that, contrary to expectations, the waveform modes $h_{\ell m}$ do not always manifest a peak for high eccentricities or spins. In case of the dominant $h_{22}$ mode, we determine the precise region of the parameter space in which its peak exists. In this region, we provide a characterization of the merger quantities of the $h_{22}$ mode and of the higher-order modes, providing the merger structure of the equatorial-eccentric plunges of the Kerr spacetime in the test-mass limit.

We report the performance of a newly implemented fourth-order accurate finite-volume Harten-Lax-van Leer-contact Riemann solver in the adaptive-mesh-refinement numerical relativity code sacra-mpi. First, we validate our implementation in one-dimensional special relativistic hydrodynamics tests, i.e., a simple wave and shock tube test, which have analytic solutions. We demonstrate that the fourth-order convergence is achieved for the smooth flow, which cannot be achieved in our original second-order accurate finite-volume Riemann solver. We also show that our new solver is robust for the strong shock wave emergence problem. Second, we validate the implementation in a dynamical spacetime by demonstrating that sacra-mpi perfectly preserves the $\pi$ symmetry without imposing the $\pi$ symmetry in a short-term ($\sim 20\mathrm{ms}$ in the inspiral and subsequent postmerger phase) nonspinning equal-mass binary neutron star merger simulations. Finally, we quantify the accuracy of $\approx 28$ cycle inspiral gravitational waveforms from binary neutron star mergers by conducting a resolution study with $\approx 78$, 94, 118, and 135 m. We find that the fourth-order accurate Riemann solver achieves the convergence order $\approx 2.1\pm 0.05–2.4\pm 0.27$, i.e., slightly evolving with time, in the inspiral gravitational wave phase, while the second-order accurate Riemann solver achieves the convergence order $\approx 2.0\pm 0.5$. The residual phase error towards the continuum limit at the merger is $0.27\pm 0.07\mathrm{rad}$ and $0.58\pm 0.22\mathrm{rad}$ out of a total phase of $\approx 176\mathrm{rad}$, respectively, for the fourth- and second-order accurate Riemann solver.