We consider unified dark sector models in which the fluid can collapse and cluster into halos, allowing for hierarchical structure formation to proceed as in standard cosmology. We show that both background evolution and linear perturbations tend toward those in $\mathrm{\Lambda }$ cold dark matter ($\mathrm{\Lambda }\mathrm{CDM}$) as the clustered fraction $f\to 1$. We confront such models with various observational datasets, with emphasis on the relatively well-motivated standard Chaplygin gas. We show that the strongest constraints come from secondary anisotropies in the cosmic microwave background (CMB) spectrum, which prefer models with $f\to 1$. However, as a larger Hubble constant is allowed for smaller $f$, values of $f\simeq 0.99$ (rather than tending to exact unity) are favored when late universe expansion data is included, with $f\simeq 0.97$ and $H_0\simeq 70\mathrm{km}/\mathrm{s}/\mathrm{Mpc}$ allowed at the $2\text{−}\sigma$ level. Such values of $f$ imply extremely efficient clustering into nonlinear structures. They may nevertheless be compatible with clustered fractions in warm dark matter based cosmologies, which have similar minimal halo mass scales as the models considered here. Tight CMB constraints on $f$ also apply to the generalized Chaplygin gas, except for models that are already quite close to $\mathrm{\Lambda }\mathrm{CDM}$, in which case all values of $0\le f\le 1$ are allowed. In contrast to the CMB, large scale structure data, which were initially used to rule out unclustered unified dark matter models, are far less constraining. Indeed, late universe data, including the large scale galaxy distribution, prefer models that are far from $\mathrm{\Lambda }\mathrm{CDM}$. But these are in tension with the CMB data.

Contemporary cosmic microwave background (CMB) experiments typically have observing bands covering the range 20–800 GHz. Certain science goals, including the detection of $\mu$-type distortions to the CMB spectrum and the characterization of low-frequency foregrounds, benefit from extended low-frequency coverage, but the standard CMB detector technology is not trivially adaptable to radio wavelengths. We propose using the upcoming Square Kilometer Array (SKA) as a CMB experiment, exploiting the immense raw sensitivity of SKA, in particular in single-dish mode, to measure medium-to-large-angular-scale modes of the CMB at radio wavelengths. As a worked example, we forecast the power of SKA combined with the upcoming LiteBIRD CMB space mission to constrain primordial non-Gaussianity through measurements of the correlation between anisotropies in the CMB $\mu$-distortion, temperature, and $E$-mode polarization fields. We find that adding SKA data significantly improves the constraints on $f_{\mathrm{NL}}$, even for spatially varying low-frequency foregrounds.

We present the first general-relativistic resistive magnetohydrodynamics simulations of self-consistent, rotating neutron stars with mixed poloidal and toroidal magnetic fields. Specifically, we investigate the role of resistivity in the dynamical evolution of neutron stars over a period of up to 100 ms and its effects on their quasiequilibrium configurations. Our results demonstrate that resistivity can significantly influence the development of magnetohydrodynamic instabilities, resulting in markedly different magnetic field geometries. Additionally, resistivity suppresses the growth of these instabilities, leading to a reduction in the amplitude of emitted gravitational waves. Despite the variations in magnetic field geometries, the ratio of poloidal to toroidal field energies remains consistently $9:1$ throughout the simulations, for the models we investigated.

We investigate shear and interface modes excited in neutron stars with an elastic crust in the full general relativistic framework and compare them to the results obtained within the relativistic Cowling approximation. We observe that the Cowling approximation has virtually no impact on the frequencies or the eigenfunctions of the shear modes; in contrast, the interface modes that arise due to the discontinuities of the shear modulus experience a considerable shift in frequency when applying the Cowling approximation. Furthermore, we extend a scheme based on the properties of the phase of amplitude ratios, which allows us to estimate the damping times of slowly damped modes; our extension can provide an estimation of the damping time even if the features of the amplitude ratio are incomplete or if some of them violate the underlying linearity assumption. The proposed scheme is also computationally less expensive and numerically more robust and we provide accurate estimates as well as lower bounds for damping times of shear and interface modes. We estimate the damping times also via the quadrupole formula and find that it provides good order-of-magnitude estimates.

Ultralight bosons are a hypothetical class of particles predicted under various extensions of Standard Model physics. As a result of the superradiance mechanism, we expect ultralight bosons, should they exist in certain mass ranges, to form macroscopic clouds around rotating black holes, so that we can probe their existence by looking for the long-transient gravitational wave emission produced by such clouds. In this paper, we propose a statistically robust framework for constraining the existence of ultralight vector bosons in the absence of detecting such a signal from searches targeting merger remnant black holes, effectively marginalizing over the uncertainties present in the properties of the target black holes. We also determine the impact of weak kinetic mixing with the ordinary photon and vector mass generation through a hidden Higgs mechanism on the constraining power of these searches. We find that individual follow-up searches, particularly with the next-generation gravitational wave detectors, can probe regions of parameter space for such models where robust constraints are still lacking.

Neutrino flavor evolution is critical for understanding the physics of dense astrophysical regimes, including core-collapse supernovae (CCSN). Powerful numerical integration codes exist for simulating these environments, yet a complete understanding of the inherent nonlinearity of collective neutrino flavor oscillations and how it fits within the overall framework of these simulations remains an open challenge. For this reason, we continue developing statistical data assimilation (SDA) to infer solutions to the flavor field in a CCSN envelope, given simulated measurements far from the source. SDA is an inference paradigm designed to optimize a model with sparse data. Our model consists of neutrino beams emanating from a CCSN and coherently interacting with each other and with a background of other matter particles in one dimension $r$. One model feature of high interest is the distribution of those matter particles as a function of radius $r$, or the “matter potential” $V(r)$—as it significantly dictates flavor evolution. In this paper, we expand the model beyond previous incarnations, by replacing the monotonically decaying analytic form for $V(r)$ we previously used with a more complex—and more physically plausible—set of profiles derived from a one-dimensional (spherically symmetric) hydrodynamics simulation of a CCSN explosion. We ask whether the SDA procedure can use simulated flavor measurements at physically accessible locations (i.e. in vacuum) to determine the extent to which different matter density profiles through which the neutrinos propagate in the matter-dominated regime are compatible with these measurements. Within the scope of our small-scale model, we find that the neutrino flavor measurements in the vacuum regime are able to discriminate between different matter profiles, and we discuss implications regarding a future galactic CCSN detection.

We study the rotational properties of inverted hybrid stars (IHSs), which have been recently proposed as a possible new class of compact stars characterized by an outer layer of quark matter and a core of hadronic matter, in an inverted structure compared to traditional hybrid stars. We analyze distinct models representing varying depths of quark-hadron phase transitions. Our findings reveal that, while IHSs rotating at their Kepler frequencies typically exhibit a significantly higher mass and larger circumferential radius as anticipated, interestingly, there is a significant increase in potential twin configurations in the case of rapid rotations. We further study sequences of constant baryonic mass, representing potential paths of rotational evolution. Our results indicate that not all stars in these sequences are viable due to the onset of phase transitions during spin-down, leading to possible minicollapses. We also investigate the phenomenon of “back-bending” during spin-down sequences, which is manifested in a rather distinct shape for IHSs due to their inverted structure and the large density discontinuity caused by the strong phase transition. Our study extends to the braking index of IHSs, which could serve as observational hints for the detection of such objects. Furthermore, we also consider sequences of IHSs with constant angular momentum and demonstrate that they exhibit, with relatively high confidence, an approximate universal relation between supramassive configurations and the spherical mass limit. Furthermore, we also show that $\widehat{I}-\widehat{Q}$ relations found in previous studies also hold approximately for IHSs to some extent. Our research enriches existing studies by introducing the significant aspect of rotation, unveiling intriguing phenomena that could serve as observational markers.

The effect of the returning radiation has long been ignored in the analysis of the reflection spectra of Galactic black holes and active galactic nuclei and only recently has been implemented in the relxill package. Here we present a study on the impact of the returning radiation on the estimate of the parameters of Galactic black holes. We consider high-quality NuSTAR spectra of three Galactic black holes (GX 339–4, Swift J1658.2–4242, and MAXI J1535–571) and we fit the data with the lamppost model in the latest version of relxill, first without including the returning radiation and then including the returning radiation. We do not find any significant difference in the estimate of the parameters of these systems between the two cases, even if all three sources are fast-rotating black holes and for two sources the estimate of the height of the corona is very low, two ingredients that should maximize the effect of the returning radiation. We discuss our results and the approximations in relxill.

The Large High Altitude Air Shower Observatory (LHAASO) is located at Haizi Mountain (4410 m a. s. l.), Daocheng, Sichuan province, China. Due to its high-altitude location with frequent thunderstorm activities, the LHAASO is suited for studying the effects of near-Earth thunderstorm electric fields on cosmic ray air showers. In this paper, Monte Carlo simulations are performed with corsika and g4km2a to analyze the flux variations of cosmic ray air showers detected by the kilometer-square array of LHAASO (LHAASO-KM2A) during thunderstorms. The strength, polarity, and layer thickness of the atmospheric electric field (AEF) during thunderstorm are found to be associated with the shower rate variations. The flux of shower events satisfying trigger conditions of the LHAASO-KM2A increases with field intensity, particularly within negative fields, and the enhanced amplitude is more than 5% in $-600\mathrm{V}/\mathrm{cm}$ and 12% in AEF of $-1000\mathrm{V}/\mathrm{cm}$, whereas it increases only by 1% and 7% in equivalent positive fields, respectively. While in positive fields ranging from 0 to $400\mathrm{V}/\mathrm{cm}$, the shower rate decreases with smaller amplitudes. Furthermore, the shower rate increases dramatically with the AEF layer thickness until a certain value, above which the variation trend slows down. The dependence of the trigger rate variation on the primary zenith angle has also been revealed, increasing in lower zenith angle ranges and showing opposite behavior in higher ones. Additionally, we study that the relationship between the trigger rate variations and the primary energies, and find the enhanced amplitude of the shower rate decreases with increasing primary energy. Simultaneously, the shower events with lower primary energy show a significant increase, whereas events with higher primary energy are hardly affected during thunderstorms. These simulation results offer valuable insights into the variation of the trigger rate detected by LHAASO-KM2A during thunderstorms and are beneficial for understanding the acceleration mechanisms of secondary charged particles caused by AEF.

Quantum angular moment transport schemes are an important avenue toward describing neutrino flavor mixing phenomena in dense astrophysical environments such as supernovae and merging neutron stars. Successful implementation will require new closure relations that go beyond those used in classical transport. In this paper, we derive the first analytic expression for a quantum M1 closure, valid in the limit of small flavor coherence, based on the maximum entropy principle. We verify that the resulting closure relation has the appropriate limits and characteristic speeds in the diffusive and free-streaming regimes. We then use this new closure in a moment linear stability analysis to search for fast flavor instabilities in a binary neutron star merger simulation and find better results as compared with previously designed, ad hoc, semiclassical closures.

In the presence of a magnetic field, axions can convert into photons and vice versa. The phenomenology of the conversion is captured by a system of two coupled Klein-Gordon equations, which, assuming that the axion is relativistic, is usually recast into a pair of first-order Schrödinger-like equations. In such a limit, focusing on a constant magnetic field and plasma frequency, the equations admit an exact analytic solution. The relativistic limit significantly simplifies the calculations and, therefore, it is widely used in phenomenological applications. In this work, we discuss how to evaluate the axion-photon system evolution without relying on such relativistic approximation. In particular, we give an exact analytical solution, valid for any axion energy, in the case that both the magnetic field and plasma frequency are constant. Moreover, we devise an analytic perturbative expansion that allows for tracking the conversion probability in a slightly inhomogeneous magnetic field or plasma frequency, whose characteristic scale of variation is much larger than the typical axion-photon oscillation length. Finally, we discuss a case of resonant axion-photon conversion giving useful simplified formulae that might be directly applied to dark matter axions converting in neutron star magnetospheres.

The evolution of quantum states influenced by semiclassical gravity is distinct from that in quantum gravity theory due to the presence of a state-dependent gravitational potential. This state-dependent potential introduces nonlinearity into the state evolution, of which the theory is named the Schrödinger-Newton (SN) theory. The formalism for understanding the continuous quantum measurement process on the quantum state in the context of semiclassical gravity theory has been previously discussed using the Schrödinger picture in Paper I [Semiclassical gravity phenomenology under the causal-conditional quantum measurement prescription, Phys. Rev. D 107, 024004 (2023).]. In this work, an equivalent formalism using the Heisenberg picture is developed and applied to the analysis of two optomechanical experiment protocols that targeted testing the quantum nature of gravity. This Heisenberg picture formalism of the SN theory has the advantage of helping the investigation of the covariance matrices of the outgoing light fields in these protocols and further the entanglement features. We found that the classical gravity between the quantum trajectories of two mirrors under continuous quantum measurement in the SN theory can induce an apparent entanglement of the outgoing light field (though there is no quantum entanglement of the mirrors), which could serve as a false alarm for those experiments designed for probing the quantum gravity induced entanglement.

Gravitational wave detectors like the Einstein Telescope and LISA generate long multivariate time series, which pose significant challenges in spectral density estimation due to the large number of observations as well as the presence of correlated noise. Addressing both issues is crucial for accurately interpreting the signals detected by these instruments. This paper presents an application of a variational inference spectral density estimation method specifically tailored for dealing with correlated noise in the data. It is flexible in that it does not rely on any specific parametric form for the multivariate spectral density. We provide the multivariate Whittle likelihood in a form that is easy to evaluate as it depends on a low-dimensional covariance matrix. To deal with very long time series, the method employs a blocked Whittle likelihood approximation for stationary time series. It utilizes the Cholesky decomposition of the inverse spectral density matrix to ensure a positive definite estimator. A discounted regularized horseshoe prior is applied to the spline coefficients of each Cholesky factor, and the posterior distribution is computed using a stochastic gradient variational Bayes approach. This method is particularly effective in addressing correlated noise, a significant challenge in the analysis of multivariate data from colocated detectors. The method is demonstrated by analyzing 2000 s of simulated Einstein Telescope noise, which shows its ability to produce accurate spectral density estimates and quantify coherence between time series components. This makes it a powerful tool for analyzing correlated noise in gravitational wave data.

Conventional wisdom teaches us that the electrical conductivity in a material is the inverse of its resistivity. In this work, we show that, when both of these transport coefficients are defined in linear response through the Kubo formulas as two-point correlators of conserved currents in quantum field theory, this Ohm’s reciprocity relation is generically violated in theories with dynamical electromagnetism. We then elucidate how in certain special limits (e.g., in the dc limit in the presence of thermal effects, in certain $2+1d$ conformal theories, and in holographic supersymmetric theories) the reciprocity relation is reinstated as an emergent property of conductive and resistive transport. We also show that if the response of a material is measured with respect to the total electric field that includes quantum corrections, then the reciprocity relation is satisfied by definition. However, in that case, the transport coefficients are given by the photon vacuum polarization and not the correlators of conserved currents that dominate the hydrodynamic macroscopic late-time transport.

We study neutrino oscillations in background matter within the quantum field theory formalism where neutrino mass eigenstates are virtual particles. In this case, neutrino mass eigenstates are mixed owing to the interaction with matter. Assuming that neutrinos are Majorana particles, we find the exact propagators for massive neutrinos accounting for the interaction with matter by solving the analog of the Dyson equation. These propagators are used to calculate the transition probability, which coincides with the prediction of the standard quantum-mechanical treatment of neutrino flavor oscillations in uniform matter. Finally, we analyze the approximations made in our analysis.

In the present paper, we investigate the production of a baryon pair in $e^{+}{e}^{-}$ annihilation to study the structure of baryons. To study the basic structure of the Standard Model, it is also necessary to consider the baryon-antibaryon pair production at the electron-positron linear collider. The production of a baryon pair in electron-positron annihilation provides a powerful tool at higher center-of-mass energies. In this work, we present phenomenological results for ${\mathrm{\Sigma }}^{+}{\overline{\mathrm{\Sigma }}}^{-}$ production in $e^{+}{e}^{-}$ collision at the BESIII Collider. We investigate a hyperon pair produced in the reaction $e^{+}{e}^{-}\to {\mathrm{\Sigma }}^{+}{\overline{\mathrm{\Sigma }}}^{-}$. Two different contributions are considered: the $D$ meson loop and the three-gluon charmonium annihilation loop. Taking into account the contributions of the $D$-meson loop and three-gluon loops and the interference of all diagrams, we calculate the total cross section of the process $e^{+}{e}^{-}\to {\mathrm{\Sigma }}^{+}{\overline{\mathrm{\Sigma }}}^{-}$. With respect to a purely electromagnetic mechanism, large relative phases are generated for these contributions. We obtain as a byproduct a fit of the electromagnetic form factor of the $\mathrm{\Sigma }$ hyperon for a large momentum transferred region. In this process, in addition to $\psi (3770)$ charmonium, we also take into account the contributions of other charmonium (like) states, $\psi (4040)$, $\psi (4160)$, $Y(4230)$, $Y(4360)$, $\psi (4415)$, and $Y(4660)$. The obtained results are in good agreement with experimental data.

Recent measurements of the CMS experiment at the LHC show possibly, with about $3\sigma$ significance, a resonance in diphoton events with an invariant mass of 95.4 GeV. If this resonance can be confirmed, this could be a hint for a new elementary particle beyond the Standard Model. An additional Standard-model-like Higgs boson with this mass could be excluded by the CMS experiment. We investigate whether this resonance could fit into a two-Higgs-doublet model highly constrained by $CP$ symmetry, the so-called maximally $CP$-symmetric model (MCPM). In the strict symmetry limit of the MCPM only the fermions of the third generation obtain masses. We discuss a mechanism where the first and second generation fermions get masses through effects from interactions with very high mass particles. The latter can be integrated out at Large Hadron Collider (LHC) energies giving effective Lagrangian terms, among them these mass terms. This procedure also gives us a Cabibbo-Kobayashi-Maskawa (CKM) matrix which automatically satisfies some salient structural features observed in experiments. We call the resulting theory MCPM’. Our finding shows that indeed the enhancement measured by CMS could originate from the pseudoscalar Higgs boson $h^{\prime \prime }$ of this model. According to the model the boson $h^{\prime \prime }$ would mainly be produced in the Drell-Yan reaction by charm-anticharm-quark fusion. The main decay mode of $h^{\prime \prime }$ is predicted to be $h^{\prime \prime }\to c\overline{c}$. We then consider the so called oblique parameters $S$, $T$, $U$ which give us an allowed region for the mass of the scalar Higgs boson $h^{\prime }$ versus that of the charged ones $H^{\pm }$ of the MCPM’. We calculate the effect of these charged bosons $H^{\pm }$ in the leptonic decays of the charm mesons $D^{\pm }$ and the charm-strange mesons $D_s^{\pm }$. Our results indicate that the mass $m_{H^{\pm }}$ of the charged Higgs bosons $H^{\pm }$ of the MCPM’ should be around 300 GeV.

Lorentz symmetry is a cornerstone of both the general relativity and Standard Model and its experimental verification deepens our understanding of nature. This paper focuses on the investigation of Lorentz violations with the context of clock comparison experiments in the framework of Standard Model Extension (SME). Considering the matter-gravity coupling sector, we provide a generic frame to study the sensitivities of Lorentz-violating coefficients for three distinct types of clock redshift tests, including the traditional gravitational redshift test, null-redshift test I, and null-redshift test II. Each of these tests is sensitive to different combinations of Lorentz-violating coefficients. By using the current clock comparison results, we estimate the limits of SME coefficients at level of parts in ${10}^4$ down to parts in ${10}^7$. Better sensitivity may be achieved in the clock comparisons by using the state-of-the-art optical clocks. Additionally considering relativistic factors in null-redshift I, the frequency comparison result of E2 and E3 transitions of ${\mathrm{Yb}}^{+}$ can set the limit $c_{00}^e=(7.4\pm 9.3)\times {10}^{-9}$ in the electron sector. Our analysis demonstrates that clock-comparison redshift experiments may contribute to explore the vast parameters space on searching for the Lorentz violation.

PandaX-4T and XENONnT have recently reported the first measurement of nuclear recoils induced by the ${}^8\mathrm{B}$ solar neutrino flux, through the coherent elastic neutrino-nucleus scattering ($\mathrm{CE}\nu \mathrm{NS}$) channel. As long anticipated, this is an important milestone for dark matter searches as well as for neutrino physics. This measurement means that these detectors have reached exposures such that searches for low mass, $\lesssim 10\mathrm{GeV}$ dark matter cannot be analyzed using the background-free paradigm going forward. It also opens a new era for these detectors to be used as neutrino observatories. In this paper we assess the sensitivity of these new measurements to new physics in the neutrino sector. We focus on neutrino nonstandard interactions (NSI) and show that—despite the still moderately low statistical significance of the signals—these data already provide valuable information. We find that limits on NSI from PandaX-4T and XENONnT measurements are comparable to those derived using combined COHERENT CsI and LAr data. Furthermore, they provide sensitivity to pure $\tau$ flavor parameters that are not accessible using stopped-pion or reactor sources. With larger exposures and consequently improvements of statistical uncertainties, forthcoming data from these experiments will provide important, novel results for $\mathrm{CE}\nu \mathrm{NS}$-related physics.

The formalism developed in the preceding papers that connects integrated correlation function of a trapped two-particle system to infinite volume scattering phase shift is further extended to coupled-channel systems in the present work. Using a trapped nonrelativistic two-channel system as an example, a new relation is derived that retains the same structure as in the single channel, and has explicit dependence on the phase shifts in both channels but not on the inelasticity. The relation is illustrated by a exactly solvable coupled-channel quantum mechanical model with contact interactions. It is further validated by path integral Monte Carlo simulation of a quasi-one-dimensional model that can admit general interaction potentials. In all cases, we found rapid convergence to the infinite volume limit as the trap size is increased, even at short times, making it potentially a good candidate to overcome signal-to-noise issues in Monte Carlo applications.