In this paper, we focus on massive Einstein-dilaton gravity including the coupling of dilaton scalar field to massive graviton terms, and then derive static and spherically symmetric solutions of dilatonic black holes in four dimensional spacetime. We find that the dilatonic black hole could possess two horizons (event and cosmological), extreme (Nariai) and naked singularity for the suitably fixed parameters. In addition, we investigate thermodynamic properties of these dilatonic black holes, and check the corresponding first law of black hole thermodynamics. Extending to the massive Einstein-dilaton gravity in high dimensions, we further obtain the dilatonic black hole solutions in ($d+1$) dimensional spacetime.

Loop quantum gravity, as one branch of quantum gravity, holds the potential to explore the fundamental nature of black holes. Recently, according to the quantum Oppenheimer-Snyder model in loop quantum cosmology, a novel loop quantum corrected black hole in de Sitter spacetime has been discovered. Here, we first investigate the corresponding quasinormal modes and late-time behavior of massless neutral scalar field perturbations based on such a quantum-modified black hole in de Sitter spacetime. The frequency and time domain analysis of the lowest-lying quasinormal modes is derived by the Prony method, the matrix method as well as Wentzel-Kramers-Brillouin approximation. The influences of loop quantum correction, the black hole mass ratio, and the cosmological constant on the quasinormal frequencies are studied in detail. The late-time behaviors of quantum-modified black holes possess an exponential decay, which is mainly determined not only by the multipole number but also by the cosmological constant. The impact of loop quantum correction on the late-time tail is negligible, but it has a significant impact on damping oscillation. To explore spacetime singularities, we examine the validity of strong cosmic censorship for a near-extremal quantum-modified black hole in de Sitter spacetime. As a result, it is found that the strong cosmic censorship is destroyed as the black hole approaches the near-extremal limit, but the violation becomes weaker as the cosmological constant and the loop quantum correction increase.

We provide the quantization of a charged black hole. We consider a redefinition of the scalar constraint in order to render the algebra of constraints a Lie algebra. We apply loop quantum gravity techniques adhered to a novel improved dynamics scheme. We show that the model is solvable in closed form. We compute effective geometries, and show that the resulting effective space-times replace the inner horizon with a transition surface that connects trapped and antitrapped regions within the charged black hole interior. Quantum effects therefore stabilize the classical inner Cauchy horizons, as long as the charge is small compared to the mass. We further discuss the properties of these effective geometries by defining an effective stress-energy tensor out of the Einstein tensor, concluding that the null energy condition is violated.

The space-time explorer and quantum equivalence principle space test (STE-QUEST) recently proposed, aims at performing a precision test of the weak equivalence principle (WEP), a fundamental cornerstone of general relativity. Taking advantage of the ideal operation conditions for high-precision quantum sensing on board of a satellite, it aims to detect possible violations of WEP down to the ${10}^{-17}$ level. This level of performance leads to stringent environmental requirements on the control of the spacecraft. We assume an operation of a dual-species atom interferometer of rubidium and potassium isotopes in a double-diffraction configuration and derive the constraints to achieve an Eötvös parameter $\eta ={10}^{-17}$ in statistical and systematic uncertainties. We show that technical heritage of previous satellite missions, such as MICROSCOPE, satisfies the platform requirements to achieve the proposed objectives underlying the technical readiness of the STE-QUEST mission proposal.

We present a classification of Kerr–de Sitter spacetimes based on the presence of horizons, ergospheres, and the characteristics of photon motion. We utilize the concept of local escape cones for isotropically radiating point sources to create shadows of the Kerr–de Sitter naked singularities within a class containing astrophysically relevant parameters. For completeness, we also consider in the construction photons entering the region of negative radii of the naked singularity spacetimes. The shadow construction is associated with two astrophysically significant families of local reference frames (or local observers). The first family represents locally nonrotating frames that, near the so-called static radius in Kerr–de Sitter spacetimes, exhibit characteristics similar to those of static observers at large distances in asymptotically flat spacetimes. The second family involves radially escaping geodesic frames, which are suitable for constructing the shadow near the cosmological horizon of Kerr–de Sitter spacetimes. We explore how the aberration effect, caused by the motion of free observers due to the repulsive influence of the cosmological constant, modifies the shadow in comparison to those related to stationary locally nonrotating observers.

The deep learning technique has been employed in removing foreground contaminants from 21-cm intensity mapping, but its effectiveness is limited by the large dynamic range of the foreground amplitude. In this study, we develop a novel foreground removal technique grounded in U-Net networks. The essence of this technique lies in introducing an innovative data preprocessing step specifically, utilizing the temperature difference between neighboring frequency bands as input. Combining with the frequency difference, we refer to our method as the UNet-fd (UNet frequency-difference), where the U-Net structure is the same as that in deep21. Based on our tests, we demonstrate that this frequency-difference preprocessing technique can substantially reduce the dynamic range of foreground amplitudes by approximately two orders of magnitude. This reduction proves to be highly advantageous for the U-Net foreground removal. We observe that the HI signal can be reliably recovered, as indicated by the cross-correlation power spectra showing unity agreement at the scale of $k\lesssim 0.3h{\mathrm{Mpc}}^{-1}$ in the absence of instrumental effects. Moreover, accounting for the systematic beam effects, our reconstruction displays consistent autocorrelation and cross-correlation power spectrum ratios at the $1\sigma$ level across scales $k\lesssim 0.1h{\mathrm{Mpc}}^{-1}$, with only a 10% reduction observed in the cross-correlation power spectrum at $k\simeq 0.2h{\mathrm{Mpc}}^{-1}$. The effects of redshift-space distortion are also reconstructed successfully, as evidenced by the quadrupole power spectra matching with the target truth. In order to test how thermal noise affects the performance of our method, we simulated various white noise levels in the map. This shows the mean cross-correlation ratio ${\overline{R}}_{\text{cross}}\gtrsim 0.8$ when the level of the thermal noise is smaller than or equal to that of the HI signal. In comparison, our method outperforms the traditional principal component analysis (PCA) method. The PCA-derived cross-correlation ratios are underestimated by around 60%. We conclude that the proposed frequency-difference technique can significantly enhance network performance by reducing the amplitude range of foregrounds and aiding in the prevention of HI loss.

We present a new constraint on the Hubble constant $H_0$ using the latest measurements of the electromagnetic counterpart to the gravitational wave (GW) event GW170817. We use the latest optical, x-ray and radio observations of the afterglow up to $\sim 3.5\mathrm{years}$ after the GW detection, and properly take into account the impact of the host galaxy peculiar velocity. We find ${75.46}_{-5.39}^{+5.34}\mathrm{km}{\mathrm{s}}^{-1}{\mathrm{Mpc}}^{-1}$ (68% credible interval), a $\sim 7\%$ precision measurement, which is a significant improvement compared to the 14% precision of the first standard siren measurement. Our result is consistent within $1\sigma$ with the cepheid-anchored supernova and within $1.5\sigma$ with the cosmic microwave background measurements of the Hubble constant. We also explore the impact of the various assumptions made when fitting for the afterglow on the Hubble constant estimate.

Isocurvature fluctuations, where the relative number density of particle species spatially varies, can be generated from initially adiabatic, or curvature, fluctuations if the various species fall out of or were never in thermal equilibrium. The freezing of the thermal relic dark matter abundance is one such case, but for modes that are still outside the horizon the amplitude is highly suppressed and originates from the small change in the local expansion rate due to the local space curvature produced by the curvature fluctuation. We establish a simple separate-universe method for calculating this generation that applies to both freeze-in and freeze-out models, identify three critical epochs for this process, and give general scaling behaviors for the amplitude in each case: the freezing epoch, the kinetic decoupling epoch and matter-radiation equality. Freeze-out models are typically dominated by spatially modulated annihilation from the latter epochs and can generate much larger isocurvature fluctuations compared with typical freeze-in models, albeit still very small and observationally allowed by cosmic microwave background measurements. We illustrate these results with concrete models where the dark matter interactions are vector or scalar mediated.

Magnetic fields surrounding black holes are responsible for various astrophysical phenomena related to accretion processes and relativistic jets. Depending on the source, the configuration of the field lines may differ significantly, affecting the trajectories of charged particles and the corresponding observables. Usually, the magnetic fields around black holes are modeled within a single source or current generating the field. However, magnetic fields can have more than a single origin, being a combination of different fields, such as, e.g., that of an accretion disk and external large-scale or Galactic ones. In this paper, we propose a combined magnetic field solution given by the superposition of the uniform and Blandford-Znajek split-monopole magnetic fields in a strong gravity regime of the Schwarzschild black hole. We show that when the combined magnetic field components are aligned, the resulting field is of a paraboloidal jetlike shape. Such a configuration is supported by relativistic jet observations and is often utilized in general relativistic magnetohydrodynamical simulations. In the opposite orientation of the two field components, we observe looplike field structures magnetically connecting the black hole with an accretion disk and the magnetic null points, which can be related to the regions of magnetic reconnection. In the combined magnetic field configurations, we analyze the dynamics of charged particles, study their stability conditions, and find the locations of stable off-equatorial structures close to the symmetry axis. Finally, we consider an ionization of Keplerian accretion disk as a particular scenario of particle scattering. From the numerical experiments, we conclude that charged particles in the jetlike combination show a strong tendency to escape from the black hole, which is not observed in the case of individual fields. In contrast, the looplike combination supports accretion of charged particles into the black hole.

Long-period radio transients have unusual properties that challenge their interpretation as pulsars or magnetars. We examine whether they might instead be powered by primordial black holes (PBHs) making repeated passages through a host star, thereby providing a signature of elusive dark-matter candidates. We demonstrate that constraints derived from the transients’ period and period derivative alone already rule out this scenario for most potential host stars. While white dwarfs may satisfy these constraints, they are unlikely to capture PBHs in the required mass range.

In the beyond Standard Model (BSM) scenarios, the possibility of neutrinos decaying into a lighter state is one of the prime quests for the new-generation neutrino experiments. The observation of high-energy astrophysical neutrinos by IceCube opens up a new avenue for studying neutrino decay. In this work, we investigate a novel scenario of invisible neutrino decay to axionlike particles (ALPs). These ALPs propagate unattenuated and reconvert into gamma rays in the magnetic field of the Milky Way. This is complementary and independent of the previously done studies where gamma rays produced at the source are used to investigate the ALP hypothesis. We exploit the Fermi-LAT and IceCube observations of NGC 1068 to set constraints on the ALP parameters. Being a steady source of neutrinos, it offers a better prospect over transient sources. We obtain 95% confidence level (CL) upper limits on the photon-ALP coupling constant $g_{a\gamma }\lesssim 1.37\times {10}^{-11}{\mathrm{GeV}}^{-1}$ for ALP masses $m_a\le 2\times {10}^{-9}\mathrm{eV}$. Our results are comparable to previous upper limits obtained using the GeV to sub-PeV gamma-ray observations. Moreover, we estimate the contribution from NGC 1068-like sources to diffuse gamma-ray flux at GeV energies under the ALP scenario.

Gubser flow provides an analytic model for describing the spacetime dynamics of the quark-gluon plasma produced in heavy-ion collisions. Along with boost and rotation invariance along the beam axis, the model assumes invariance under a combination of translations and special conformal transformations in the transverse plane, leading to a flow profile which evolves not just along the beam axis, but also radially. We argue that Gubser flow and its associated symmetry assumptions arise naturally as a consequence of Carrollian symmetries for a conformal Carroll fluid, thereby providing a dual geometric picture for the flow. Given the inherent ultrarelativistic nature of the flow, this duality with Carroll hydrodynamics which arises in the $c\to 0$ limit of relativistic hydrodynamics, is natural. We provide a precise map between Gubser flow and the conformal Carroll fluid, appropriate to capture the duality between the two, not just at the ideal level, but also with the inclusion of hydrodynamic derivative corrections.

We analyze in detail the effect of varying entropy degrees of freedom on low-scale leptogenesis models. As an archetypal model, we consider the triresonant leptogensis (TRL) scenario introduced recently by the authors, where the neutrino-Yukawa coupling matrix is dictated by an approximate ${\mathbb{Z}}_n$ discrete symmetry (with $n=3$, 6). TRL models exhibit no preferred direction in the leptonic flavor space and have the remarkable feature that leptogenesis can successfully take place even if all light neutrinos are strictly massless up to one-loop order. Most interestingly, for TRL scenarios with heavy Majorana neutrinos lighter than 100 GeV, temperature varying degrees of freedom associated with the entropy of the plasma have a dramatic impact on the predictions of the baryon asymmetry in the Universe (BAU), and may depend on the freeze-out sphaleron temperature $T_{\mathrm{sph}}$. We find that this is a generic feature of most freeze-out low-scale leptogenesis models discussed in the literature. In the same context, we consider heavy-neutrino scenarios realizing dynamics related to critical unstable qudits in the thermal plasma and assess their significance in generating the BAU. The phenomenological implications of TRL scenarios at the intensity and high-energy frontiers are analyzed.

Axion strings are horizon-size topological defects that may be produced in the early Universe. Ultralight axion-like particles may form strings that persist to temperatures below that of big bang nucleosynthesis. Such strings have been considered previously as sources of gravitational waves and cosmic microwave background (CMB) polarization rotation. In this work we show, through analytic arguments and dedicated adaptive mesh refinement cosmological simulations, that axion strings deposit a subdominant fraction of their energy into high-energy Standard Model (SM) final states, for example, by the direct production of heavy radial modes that subsequently decay to SM particles. This high-energy SM radiation is absorbed by the primordial plasma, leading to novel signatures in precision big bang nucleosynthesis, the CMB power spectrum, and gamma-ray surveys. In particular, we show that CMB power spectrum data constrains axion strings with decay constants $f_a\lesssim {10}^{12}\mathrm{GeV}$, up to model dependence on the ultraviolet completion, for axion masses $m_a\lesssim {10}^{-29}\mathrm{eV}$; future CMB surveys could find striking evidence of axion strings with lower decay constants.

We develop a model aimed at understanding the three mass distributions of pairs of mesons in the Cabibbo-suppressed $D_s^{+}\to K^{+}{\pi }^{+}{\pi }^{-}$ decay recently measured with high statistics by the BESIII collaboration. The largest contributions to the process come from the $D_s^{+}\to K^{+}{\rho }^0$ and $D_s^{+}\to K^{*0}{\pi }^{+}$ decay modes, but the $D_s^{+}\to K_0^{*}(1430){\pi }^{+}$ and $D_s^{+}\to K^{+}{f}_0(1370)$ modes also play a moderate role and all of them are introduced empirically. Instead, the contribution of the $f_0(500)$, $f_0(980)$, and $K_0^{*}(700)$ resonances is introduced dynamically by looking at the decay modes at the quark level, hadronizing $q\overline{q}$ pairs to give two mesons, and allowing these mesons to interact, for which we follow the chiral unitary approach, to finally produce the $K^{+}{\pi }^{+}{\pi }^{-}$ final state. While the general features of the mass distributions are fairly obtained, we pay special attention to the specific effects created by the light scalar resonances, which are visible in the low mass region of the ${\pi }^{+}{\pi }^{-}(f_0(500))$ and $K^{+}{\pi }^{-}(K_0^{*}(700))$ mass distributions and a narrow peak for ${\pi }^{+}{\pi }^{-}$ distribution corresponding to $f_0(980)$ excitation. The contribution of these three resonances is generated by only one parameter. We see the agreement found in these regions as further support for the nature of the light scalar states as dynamically generated from the interaction of pseudoscalar mesons.

A simple phenomenological hybrid hadron-quark model with excluded volume effects of baryons and chiral dynamics is investigated. The hybrid equation of state naturally connects the low-density baryonic matter with the high-density quark matter. In the intermediate region, a phase, which cannot be regarded as pure hadron matter or pure quark matter, appears. In this model, there is a possibility that the abrupt first-order-like transition to pure quark matter induces the strong chiral symmetry restoration and the speed of sound has a large peak at considerable large density.

In light of the discovery of the long-period radio pulsar PSR J0901-4046, it is interesting to revisit a question about how the magnetized neutron star slows down its rotation. In the case of a weak or liquid outer crust, the mechanism of spin-down becomes unclear because the braking stress cannot then be transmitted from the surface to the main bulk of the star. We show that even if the outer crust does not withstand the surface electromagnetic forces creating the braking torque, the stellar spin-down does not stop, and the matter rearranges so that the necessary electromagnetic forces form in more deep and rigid layers capable of withstanding these forces. The spin-down rate remains the same and corresponds to the transformation of the rotational energy of the neutron star into the energy of the generated relativistic electron-positron plasma. The solid iron surface of ultrastrongly magnetized PSR J0901-4046 appears not to be yielding and withstands the braking stress without breaking.

The recently released data by pulsar timing array (PTA) collaborations present strong evidence for a stochastic signal consistent with a gravitational-wave background. Assuming this signal originates from scalar-induced gravitational waves, we jointly use the PTA data from the NANOGrav 15-yr dataset, PPTA DR3, and EPTA DR2 to probe the small-scale non-Gaussianity. We put the first-ever constraint on the non-Gaussianity parameter, finding $|F_{\mathrm{NL}}|\lesssim 13.9$ for a lognormal power spectrum of the curvature perturbations. Furthermore, we obtain $-13.9\lesssim F_{\mathrm{NL}}\lesssim -0.1$ to prevent excessive production of primordial black holes. Moreover, the multiband observations with the space-borne gravitational-wave detectors, such as LISA/Taiji/TianQin, will provide a complementary investigation of primordial non-Gaussianity. Our findings pave the way to constrain inflation models with PTAs.

Bondi-Metzner-Sachs (BMS) algebra in three spacetime dimensions can be deformed into a two parameter family of algebra known as $W(a,b)$ algebra. For $a=0$, we show that other than $W(0,-1)$, no other $W(0,b)$ algebra admits a nondegenerate bilinear and thus one cannot have a Chern-Simons gauge theory formulation with them. However, they may appear in a three-dimensional gravity description, where we also need to have a spin 2 generator, that comes from the $(a=0,b=-1)$ sector. In the present work, we have demonstrated that the asymptotic symmetry algebra of a spin-3 gravity theory on flat spacetime has both the $W(0,-1)$ and $W(0,-2)$ algebras as subalgebras. We have also constructed a dual boundary field theory for this higher spin gravity theory by using the Chern-Simons/Wess-Zumino-Witten correspondence.

We review the main ideas underlying the emerging theory of Yangians—the new type of hidden symmetry in string-inspired models. Their classification by quivers is a far-going generalization of simple Lie algebras classification by Dynkin diagrams. However, this is still a kind of project, while a more constructive approach goes through toric Calabi-Yau spaces, related supersymmetric systems, and the Duistermaat-Heckman or equivariant integrals between the fixed points in the Atiyah-Drinfeld-Hitchin-Manin (ADHM)-like moduli spaces. These fixed points are classified by crystals (Young-type diagrams), and Yangian generators describe “instanton” transitions between them. Detailed examples will be presented elsewhere.