Using the constraints from astrophysical observations and heavy-ion experiments, we investigate the equation of state (EOS) of hybrid star matter and the properties of quark-matter cores in hybrid stars. The quark matter interactions in hybrid stars are described based on 3-flavor Nambu-Jona-Lasinio model with various vector and vector-isovector coupling constants. In this work, we find that the hybrid star matter EOS is more sensitive to the strength of the vector interaction, and the EOS becomes stiffer with increasing vector strength $R_V$. The vector-isovector interaction characterized by the coupling constant $R_{\mathrm{IV}}$ make main contributions to the hadron-quark mixed phase. Meanwhile, we note that a step change of both the sound velocity and the polytropic index $\gamma$ occurs in the hadron-quark phase transition, and it is restored with the decrease of nucleon and lepton degrees of freedom in the high density quark phase. The approximate rule that the polytropic index $\gamma \le 1.75$ can also be used as a criterion for separating hadronic matter from quark matter in our work. Using the hybrid star matter EOS, we predict the radius and mass information of quark-matter cores inside hybrid stars. Although the coupling constants increase the hybrid star maximum mass up to $2.08M_{\odot }$, they also decrease the mass and radius of the quark core and the mixed core. With different quark coupling constants, we also find that the maximum mass and radius of the quark matter core in a stable hybrid star can reach $0.80M_{\odot }$ and 6.95 km, which are close to half of the maximum mass and radius of the complete star. However, properties of quark matter have no effect on the $M=1.4M_{\odot }$ hybrid star as a result of no quark matter inner core, which can also be confirmed by the criterion of the polytropic index, and thus our results also indicate that the quark interactions have no effect on the tidal deformability ${\mathrm{\Lambda }}_{1.4}$ of hybrid stars.

We determine complex saddles of three-dimensional gravity with a positive cosmological constant by applying the recently proposed holography. It is sometimes useful to consider a complexified metric to study quantum gravity as in the case of the no-boundary proposal by Hartle and Hawking. However, there would be too many saddles for complexified gravity, and we should determine which saddles to take. We describe the gravity theory by three-dimensional $\mathrm{SL}(2,\mathbb{C})$ Chern-Simons theory. At the leading order in the Newton constant, its holographic dual is given by Liouville theory with a large imaginary central charge. We examine geometry with a conical defect, called a de Sitter black hole, from a Liouville two-point function. We also consider geometry with two conical defects, whose saddles are determined by the monodromy matrix of Liouville four-point function. Utilizing Chern-Simons description, we extend the similar analysis to the case with higher-spin gravity.

Pulsar timing arrays (PTA) are a promising probe to the cosmologically novel nanohertz gravitational wave (GW) regime through the stochastic GW background. In this work, we consider subluminal GW modes as a possible source of correlations in a PTA, utilizing the public code ptafast and the 12.5 years correlations data by NANOGrav, which we hypothesize are sourced by GWs. Our results show no evidence in support of tensor- or vector-induced GW correlations in the data, and that vector correlations are disfavored. This places an upper bound to the graviton mass, $m_{\mathrm{g}}\lesssim {10}^{-22}\mathrm{eV}$, characteristic of the PTA GW energy scale.

We investigate the problem of scattering and conversion of monochromatic planar gravitational and electromagnetic waves impinging upon a Reissner-Nordström black hole using a Regge pole description, i.e., a complex angular momentum approach. For this purpose, we first compute numerically the Regge pole spectrum for various charge-to-mass ratio configurations. We then derive an asymptotic expressions for the lowest Regge poles, and by considering Bohr-Sommerfeld-type quantization conditions, obtain the spectrum of weakly damped quasinormal frequencies from the Regge trajectories. Next, we construct the scattering and conversion amplitudes as well as the total differential cross sections for different processes using both a complex angular momentum representation and a partial wave expansion method. Finally, we provide an analytical approximation of the scattering and conversion cross sections of different processes from asymptotic expressions for the lowest Regge poles and the associated residues based on the correspondence Regge poles, “surface waves” propagating close to the photon (graviton) sphere. This allows us to extract the physical interpretation encoded in the partial wave expansions in the high-frequency regime (i.e., in the short-wavelength regime), and to describe semiclassically with very good agreement both black hole glory and a large part of the orbiting oscillations, thus unifying these two phenomena from a purely wave point of view.

We find accurate quasinormal frequencies of a quantum corrected black hole constructed in the renormalization group theory via the coordinate-independent iterative procedure, leading to the Dymnikova regular black hole. We show that while the fundamental mode is only slightly affected by the quantum correction, the overtones change at a much stronger rate. This outburst of overtones occurs because of the deformation of the geometry of the Schwarzschild black hole solely near the event horizon. For finding accurate values of overtones we developed a general procedure allowing one to use the Leaver method to metrics which, initially, are not expressed in terms of rational functions.

By adding a matter-coupled dark energy field to Einstein’s general relativity, this paper proves that the dynamical dark energy field can change the frequency of photons from distant galaxies as well as from background radiation of remote Universe. Therefore, when the observed frequency shift of the photons is entirely attributed to the temporal variation of the cosmic scale factor, the calculated expansion rate of the Universe will be slightly greater than its actual value. The predicted values of the temperature of the cosmic blackbody radiation in the past (future) of the Universe are slightly larger (gradually smaller and smaller) than those in the standard cosmology. Since the blackbody radiation becomes the present cosmic microwave background and its present-day temperature is directly estimated according to the Planck’s law of blackbody radiation, the measured value of the cosmic microwave background temperature is independent of whether to consider the scalar field or not.

In this companion to our Letter, we elaborate on the full details of the predicted corrections to the primordial scalar and tensor power spectra that arise from quantum gravity-motivated, natural, covariant ultraviolet cutoffs. We implement these cutoffs by covariantly restricting the fields which are summed over in the path integrals for the primordial correlators, and we discuss in detail the functional analytic techniques necessary for evaluating such path integrals. Our prediction, which is given in terms of measured cosmological parameters and without assuming any particular inflationary potential, is that the corrections take the form of small oscillations which are superimposed on the conventional power spectra. The frequency of these oscillations only depends on the location of the cutoff scale and the first inflationary slow-roll parameter, while the amplitude and phase are also moderately sensitive to how smoothly the cutoff turns on. The specificity of the new predictions offers an opportunity to significantly enhance experimental sensitivity in observations of the cosmic microwave background and large-scale structure. This may be used to place ever higher bounds on the scale at which quantum gravity becomes important in quantum field theory or may even provide positive evidence for quantum gravity effects.

The flux of high-energy astrophysical $\gamma$ rays is attenuated by the production of electron-positron pairs from scattering off of extragalactic background light (EBL). We use the most up-to-date information on galaxy populations to compute their contributions to the pair-production optical depth. We find that the optical depth inferred from $\gamma$-ray measurements exceeds that expected from galaxies at the $\sim 2\sigma$ level. If the excess is modeled as a frequency-independent re-scaling of the standard contribution to the EBL from galaxies, then an excess (an overall 14–30% increase of the EBL) is favored over the null hypothesis of no excess at the $2.7\sigma$ level. If the frequency dependence of the excess is instead modeled as a two-photon decay of a dark-matter axion, then the excess is favored over the null hypothesis at the $2.1\sigma$ confidence level. While we find no evidence for a dark-matter signal, the analysis sets the strongest current bounds on the photon-axion coupling over the 8–25 eV mass range. This work highlights the sensitivity of $\gamma$-ray optical depth measurements to ALPs, which is expected to improve with new observatories and better EBL determinations from future observations.

The possibility of forming gravitational-wave sources with high center-of-mass (c.m.) velocities in the vicinity of supermassive black holes requires us to develop a method of deriving the waveform in the observer’s frame. Here we show that in the limit where the c.m. velocity is high but the relative velocities of the components of the source are small, we can solve the problem by directly integrating the relaxed Einstein field equation. In particular, we expand the result into multipole components which can be conveniently calculated given the orbit of the source in the observer’s frame. Our numerical calculations using arbitrary c.m. velocities show that the result is consistent with the Lorentz transformation of gravitational waves (GWs) to the leading order of the radiation field. Moreover, we show an example of using this method to calculate the waveform of a scattering event between the high-speed ($\sim 0.1c$) stellar objects embedded in the accretion disk of an active galactic nucleus. Our multipole-expansion method not only has advantages in analyzing the results from stellar-dynamical models but also provides new insight into the multipole properties of the GWs emitted from a high-speed source.

The effects of magnetic fields on accretion disks around compact objects are of high importance in the study of their general properties and dynamics. Here we analyze the influence of magnetic fields on thick accretion disks around rotating boson stars. We assume a uniform constant specific angular momentum distribution and a polytropic equation of state. The purely hydrodynamical thick disk solutions are extended to magnetized solutions by adding a toroidal magnetic field and then analyzed in terms of a magnetization parameter ${\beta }_{mc}$. We consider one-centered solutions as well as two-centered solutions and focus on retrograde tori, since they are more distinctive due to their unique properties. Our computed solutions indicate that strong magnetic fields influence the characteristics of thick disks around rotating boson stars and possibly affect their unique features.

We study compact stars with hybrid equations of state consisting of a nuclear outer region and two nested quark phases, each separated from the lower density phase by a strong first-order phase transition. The stability of these models is determined by calculating their radial oscillation modes with different conversion rates between adjacent phases and hence junction conditions for the modes at the phase separation interface between them. In the case when the timescale of transition is faster than the period of oscillations, we recover the traditional stability criterion implying that $\partial M/\partial {\rho }_c>0$ on the stable branch(es), where $M$ is the mass and ${\rho }_c$ is the central density. In the opposite limit of slow conversion, we find stable stellar multiplets beyond triplets consisting of stars that are stable by the usual criterion plus slow-conversion (denoted by $s$) hybrid stars with $\partial M/\partial {\rho }_c<0$ that are stabilized due to an alternative junction condition on the fluid displacement field at the interface reflecting the slow rate of conversion. We also study the properties of the reaction mode, the radial mode that only exists for stars with rapid (abbreviated by $r$) phase transitions, in stars with either two rapid phase transitions or alternating rapid and slow phase transitions for the first time. The implications of alternative junction conditions are also examined, with these conditions generally being found to provide stability properties similar to those for a slow conversion rate.

We present the first numerical simulations of the symmetric-hyperbolic theory for conformal dissipative relativistic fluids developed in Lehner et al. [Hyperbolic theory of relativistic conformal dissipative fluids, Phys. Rev. D 97, 024013 (2018)]. In this theory, the information of the fluid dynamics is encoded in a scalar generating function which depends on three free parameters. By adapting the WENO-Z high-resolution shock-capturing central scheme, we present numerical solutions restricted to planar symmetry in Minkowski spacetime, from two qualitatively different initial data: a smooth bump and a discontinuous step. We perform a detailed exploration of the effect of the different parameters of the theory, and numerically assess the constitutive relations associated with the shear viscosity by analyzing the entropy production rate when shocks are produced.

In the framework of a nonrelativistic potential quark model, we investigate the mass spectrum of the $1S$-wave charmed-strange tetraquark states of $cn\overline{s}\overline{n}$ and $cs\overline{n}\overline{n}$ ($n=u$ or $d$) systems. The tetraquark system is solved by a correlated Gaussian method. With the same parameters fixed by the meson spectra, we obtained the mass spectra for the $1S$-wave tetraquark states. Furthermore, based on the predicted tetraquark spectra we estimate their rearrangement decays in a quark-exchange model. We find that the rearrangement decays of the tetraquarks may be mainly driven by the spin-spin interactions. The resonances $X_0(2900{)}^0$ and $T_{c\overline{s}0}^a(2900{)}^{++/0}$ reported from LHCb may be assigned to be the lowest $1S$-wave tetraquark states ${\overline{T}}_{cs0}^f(2818)$ and $T_{c\overline{s}0}^a(2828)$ classified in the quark model, respectively. It also allows us to extract the couplings for the initial tetraquark states to their nearby $S$-wave interaction channels. We find that some of these couplings turn out to be sizeable. Following the picture of the wave function renormalization for the near-threshold strong $S$-wave interactions, the sizeable coupling strengths can be regarded as an indication of their dynamic origins as candidates for hadronic molecules. Furthermore, our predictions suggest that signals for the $1S$-wave charmed-strange tetraquark states can also be searched in the other channels, such as $D^0{K}^{+}$, $D^{+}{K}^{+}$, $D^{*+}{K}^{-}$, $D^{*+}{K}^{+}$, $D^{*0}{K}^{+}$, $D^0{\overline{K}}^{*0}$, $D_s^{+}{\rho }^0$, etc.

We show results from the Coherent CAPTAIN Mills (CCM) 2019 engineering run which begin to constrain regions of parameter space for axionlike particles (ALPs) produced in electromagnetic particle showers in an 800 MeV proton beam dump, and further investigate the sensitivity of ongoing data-taking campaigns for the CCM200 upgraded detector. Based on beam-on background estimates from the engineering run, we make realistic extrapolations for background reduction based on expected shielding improvements, reduced beam width, and analysis-based techniques for background rejection. We obtain reach projections for two classes of signatures; ALPs coupled primarily to photons can be produced in the tungsten target via the Primakoff process, and then produce a gamma-ray signal in the liquid argon CCM detector either via inverse Primakoff scattering or decay to a photon pair. ALPs with significant electron couplings have several additional production mechanisms (Compton scattering, $e^{+}{e}^{-}$ annihilation, ALP-bremsstrahlung) and detection modes (inverse Compton scattering, external $e^{+}{e}^{-}$ pair conversion, and decay to $e^{+}{e}^{-}$). In some regions, the constraint is marginally better than both astrophysical and terrestrial constraints. With the beginning of a three year run, CCM will be more sensitive to this parameter space by up to an order of magnitude for both ALP-photon and ALP-electron couplings. The CCM experiment will also have sensitivity to well-motivated parameter space of QCD axion models. It is only a recent realization that accelerator-based large volume liquid argon detectors designed for low-energy coherent neutrino and dark matter scattering searches are also ideal for probing ALPs in the unexplored $\sim \mathrm{MeV}$ mass scale.

We propose using quantum dots as novel targets to probe sub-GeV dark matter-electron interactions. Quantum dots are nanocrystals of semiconducting material, which are commercially available, with gram-scale quantities suspended in liter-scale volumes of solvent. Quantum dots can be efficient scintillators, with near unity single-photon quantum yields, and their band-edge electronic properties are determined by their characteristic size, which can be precisely tuned. Examples include lead sulfide and lead selenide quantum dots, which can be tuned to have sub-eV optical gaps. A dark-matter interaction can generate one or more electron-hole pairs (excitons), with the multiexciton state decaying via the emission of two photons with an efficiency of about 10% of the single-photon quantum yield. An experimental setup using commercially available quantum dots and two photomultiplier-tubes for detecting the coincident two-photon signal can already improve on existing dark-matter bounds, while using photodetectors with lower dark-count rates can improve on current constraints by orders of magnitude.

The high temperature electroweak symmetry nonrestoration (SNR) opens a window to realize baryogenesis at high energy scales, which can alleviate the tight phenomenological constraints. An effective way to realize the electroweak SNR is to extend the Standard Model (SM) by adding a second Higgs doublet and a few new singlet fermions which interact with the second Higgs through a five-dimension operator. In this scenario, the second Higgs has a nonvanishing vacuum expectation value above the electroweak scale and thus breaks the electroweak symmetry. As the temperature decreases, the SM electroweak phase transition occurs and the Universe is located at SM electroweak vacuum. We show that the electroweak phase transition is the first order and the gravitational waves (GWs) generated during this process can be detected by the future GW experiments such as LISA, TianQin, DECIGO, and BBO.

It is well known that the fraction of energy in a hadron collision going into electromagnetic particles (electrons and photons, including those from decays) has a large impact on the number of muons produced in air shower cascades. Recent measurements at the LHC confirm features that can be linked to a mixture of different underlying particle production mechanisms such as a collective statistical hadronization (core) in addition to the expected string fragmentation (corona). Since the two mechanisms have a different electromagnetic energy fraction, we present a possible connection between statistical hadronization in hadron collisions and muon production in air showers. Using a novel approach, we demonstrate that the core-corona effect as observed at the LHC can have a significant impact and should be properly taken into account before trying to find a more exotic solution for the lack of muon production in simulations of high energy cosmic rays.

In the paper we suggest the homotopy method for solving of the nonlinear evolution equation. This method consists of two steps. First is the analytical solution for the linearized version of the nonlinear evolution deep in the saturation region. Second, the perturbative procedure is suggested to take into account the remaining parts of the nonlinear corrections. It turns out that these corrections are rather small and can be estimated in the regular iterative procedure.