We report a measurement of the $e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}{\pi }^0$ cross section in the energy range from 0.62 to 3.50 GeV using an initial-state radiation technique. We use an $e^{+}{e}^{-}$ data sample corresponding to $191{\mathrm{fb}}^{-1}$ of integrated luminosity, collected at a center-of-mass energy at or near the $\mathrm{\Upsilon }(4S)$ resonance with the Belle II detector at the SuperKEKB collider. Signal yields are extracted by fitting the two-photon mass distribution in $e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}{\pi }^0\gamma$ events, which involve a ${\pi }^0\to \gamma \gamma$ decay and an energetic photon radiated from the initial state. Signal efficiency corrections with an accuracy of 1.6% are obtained from several control data samples. The uncertainty on the cross section at the $\omega$ and $\varphi$ resonances is dominated by the systematic uncertainty of 2.2%. The resulting cross sections in the 0.62–1.80 GeV energy range yield $a_{\mu }^{3\pi }=[48.91\pm 0.23(\mathrm{stat})\pm 1.07(\mathrm{syst})]\times {10}^{-10}$ for the leading-order hadronic vacuum polarization contribution to the muon anomalous magnetic moment. This result differs by 2.5 standard deviations from the most precise current determination.

The gravitational asymptotic safety program envisions the high-energy completion of gravity through an interacting renormalization group fixed point, the Reuter fixed point. The predictive power of the construction is encoded in the spectrum of the stability matrix which is obtained from linearizing the renormalization group flow around this fixed point. A key result of the asymptotic safety program is that parts of this spectrum exhibit an almost-Gaussian scaling behavior, entailing that operators which are classically highly UV irrelevant do not induce new free parameters. In this article, we track down the origin of this property by contrasting the structure of the stability matrix computed from the Wetterich equation and the composite-operator equation within the realm of $f(R)$ truncations. We show that the almost-Gaussian scaling is not linked to the classical part of the beta functions. It is a quantum-induced almost-Gaussian scaling originating from the quantum corrections in the flow equation. It relies on a subtle interplay among the analytic structure of the theory’s two-point function and the way the Wetterich equation integrates out fluctuation modes. As a byproduct we determine the parts of the eigenmode spectrum that is robust with respect to changing the regularization procedure.

The vacuum and electrovacuum Einstein equations for spacetimes with two commuting Killing vectors can be solved by indirect methods of integrable systems. But if, in addition, the spacetime admits an irreducible Killing tensor and the corresponding Klein-Gordon equation is separable, they can be integrated directly by separation of variables, as shown by Carter in 1968. We generalize this approach to supergravity and derive a metric ansatz that ensures the above properties for Petrov-type $I$. Our derivation is based on the Benenti-Francavilla ansatz for metrics admitting two commuting Killing vectors and an irreducible Killing tensor. We find additional constraints that guarantee the existence of two shear-free null geodesic congruences and the separability of the Klein-Gordon equation. The resulting class of metrics belongs to a certain sector of Petrov type $I$, called $I_B$, whose algebraically special subsector contains only type $D$. For this class, a direct integration of the supergravity equations seems possible. We also show that these spacetimes admit a general description of the generalized photon and massive particle surfaces recently introduced in connection with black hole shadows.

The detection of quasinormal modes during the ringdown phase is a crucial method for testing the no-hair theorem. In this paper, the detectabilities and resolvabilities of multiple quasinormal modes using space-based gravitational wave detectors have been analyzed. The results indicate that TianQin and LISA have the potential to detect and resolve a series of modes, including six fundamental modes, one overtone, and two nonlinear second-order modes. Furthermore, the analysis of systematic errors in the waveform suggests that even modes such as $(l,m,n)=(3,3,1)$ and (4, 3, 0), which are unlikely to be directly detected and resolved, need to be taken into account in the ringdown waveform templates.

We study the exterior solution for a static, spherically symmetric source in Weyl conformal gravity in terms of the Newman-Penrose formalism. We first show that both the static, uncharged black hole solution of Mannheim and Kazanas and the static, charged Reissner-Nordström-like solution can be found more easily in this formalism than in the traditional coordinate-basis approach, where the metric tensor components are taken as the basic variables. Second, we show that the Newman-Penrose formalism offers a particularly convenient framework that is well suited for the discussion of conformal gravity solutions corresponding to Petrov “type-D” spacetimes. This is illustrated with a two-parameter class of wormhole solutions that includes the Ellis-Bronnikov wormhole solution of Einstein’s gravity as a limiting case. Other salient issues, such as the gauge equivalence of solutions and the inclusion of the electromagnetic field are also discussed.

Accurate modeling of compact binaries is essential for gravitational-wave detection and parameter estimation, with spin being an important effect to include in waveform models. In this paper, we derive new post-Newtonian (PN) results for the conservative aligned-spin dynamics at next-to-next-to-leading order for the ${\mathrm{spin}}^3$ and ${\mathrm{spin}}^4$ contributions, in addition to the next-to-leading order (NLO) ${\mathrm{spin}}^5$ and ${\mathrm{spin}}^6$ contributions. One approach we follow is the Tutti Frutti method, which relates PN and gravitational self-force results through the redshift and spin-precession invariants, by making use of the simple dependence of the scattering angle on the symmetric mass ratio. However, an ambiguity arises at the NLO ${\mathrm{spin}}^5$ contribution, due to transcendental functions of the Kerr spin in the redshift; this is also the order at which Compton amplitudes calculations are affected by spurious poles. Therefore, we follow an additional approach to determine the NLO ${\mathrm{spin}}^5$ and ${\mathrm{spin}}^6$ dynamics: using on-shell Compton amplitudes obtained from black hole perturbation theory. The Compton amplitude used in this work is composed of the unambiguous tree-level far-zone part reported in [Phys. Rev. D 109, 084071 (2024)], as well as the full, noninterfering with the far-zone, $\ell =2$ partial wave contributions from the near zone, which are responsible for capturing Kerr finite-size effects. Other results in this paper include deriving the scattering angle of a spinning test body in a Kerr background from a parametrized worldline action and computing the redshift and spin-precession invariants for eccentric orbits without an eccentricity expansion.

Gravitational radiation reaction has been one of the fundamental issues in general relativity. Over a span of decades, this process has been analyzed in the adiabatic limit in order to comprehend how it drives extreme-mass-ratio binaries that are prime targets for spaceborne detectors. It has been shown that spherical orbits around Schwarzschild and Kerr black holes remain spherical (zero eccentricity) under the influence of gravitational radiation reaction. Here, we show that spherical orbits in non-Kerr black holes that still preserve most of the good qualities and symmetries of Kerr spacetime can access certain resonances in such a way that an initially spherical inspiral acquires nonzero eccentricity and becomes nonspherical. Therefore, the crossing of resonances under radiation reaction interrupts and even inverts, up to some small radius close to plunge, the process of circularization of orbits. The strength of resonant excitation of eccentricity depends on the initial position and inclination of the integrable extreme-mass-ratio system, as well as the integrability-breaking parameter introduced in the background spacetime that amplifies further the excitation. We find that the harmonics of gravitational waves emitted from these inspirals undergo a frequency modulation as the orbit “metamorphoses” from spherical to nonspherical, due to the effect of resonant eccentricity excitation. The gain that low-amplitude harmonics experience in these oligochromatic extreme-mass-ratio inspirals, due to resonances, may be detectable with future spaceborne detectors and serves as an indicator of non-Kerrness of the background spacetime.

We evaluate the quantum backreaction due to a gauge field coupled to a pseudoscalar field driving a slow-roll inflationary stage, the so-called axion inflation. The backreaction is evaluated for the first time using a gauge invariant approach, going to second order in perturbation theory, and taking into consideration inflaton fluctuations as well as scalar perturbations of the metric. Within our gauge-invariant, but observer-dependent approach, we naturally consider as physical observers the ones comoving with the inflaton field. Considering the effective expansion rate consequent to the gauge field’s backreaction, we observe that the backreaction effect becomes significant quite rapidly, moving the system out of the perturbative regime and into what is often referred to as the strong backreaction regime. This behavior also applies to the parameter that dictates the production of the gauge fields. The spacetime backreaction is mainly due to the helicity contribution within the region of validity of the perturbative regime. As a final result, we see that the evaluated backreaction goes in the direction of prolonging the inflationary period more compared to the scenarios previously studied.

What if the dark matter sector is truly dark, self-interacting, and unreachable by terrestrial experiments? How could we find hints of such dark sector if it is experimentally unreachable by any terrestrial experiment? In this work we study a low-scale mirror standard model that can act as a model for dark matter, which interacts only gravitationally with the standard model particles. The mirror standard model sector particles are stable particles that can comprise a measurable part of the dark matter of the Universe. These mirror standard model particles acquire mass through a low-temperature dark first order phase transition. We examine in detail this dark phase transition and we indicate how stochastic gravitational waves can be generated through this transition. Such a phase transition can generate stochastic gravitational waves that can be detected by the future gravitational wave experiments. For the model we use, the produced energy spectrum of the gravitational waves can be detected by the Square Kilometer Array. Moreover, we propose a possible way to detect effects of the particle nature of dark matter, using observational data coming from the Guitar Nebula, which can work if dark matter is collisional, so interacting dark matter. Without specifying a model for interacting dark matter, thus choosing an agnostic approach for interacting dark matter, we assume that the Guitar Nebula bow shock is generated by the interaction of the high-speed neutron star that passes through the interstellar medium, which is assumed to be composed of interacting dark matter and hydrogen. Our main proposal is that the opening angle of the bow shock can be directly related to the speed of sound of the dark matter particles, and a large angle of the bow shock could be a strong indicator that the interstellar medium is comprised by collisional dark matter and hydrogen gas. This is motivated by the Bosma effect, which indicates that hydrogen is always in correlation with dark matter, and hydrogen gas is strongly present in the Guitar Nebula.

In recent years, cosmic microwave background (CMB) observations, weak lensing surveys, and $f{\sigma }_8(z)$ measurements from redshift-space distortions (RSD) have revealed a significant ($\sim 3–5\sigma$) discrepancy in the inferred value of the matter clustering parameter $S_8$. In this work, we investigate the implications of RSD for a cosmological framework postulating an interaction between dark energy (DE) and dark matter (DM). We explore scenarios where DM can transfer energy momentum to DE or vice versa. The energy-momentum flow is characterized by the strength and the sign of the coupling parameter $\xi$. Our baseline analysis combines RSD measurements with the latest data from baryon acoustic oscillations (BAO) observed by DESI, type Ia supernovae from the PantheonPlus sample, and CMB data from Planck. We demonstrate that RSD measurements provide significant additional information imposing new and strong upper bounds on possible interaction in the dark sector. Models with $\xi >0$ can effectively alleviate the tension in $S_8$, presenting them as compelling alternatives.

Pulsar timing arrays (PTAs) hunt for gravitational waves (GWs) by searching for the correlations that GWs induce in the time-of-arrival residuals from different pulsars. If the GW sources are of astrophysical origin, then they are located at discrete points on the sky. However, PTA data are often modeled, and subsequently analyzed, via a “standard Gaussian ensemble.” That ensemble is obtained in the limit of an infinite density of vanishingly weak, Poisson-distributed sources. In this paper, we move away from that ensemble, to study the effects of two types of “source anisotropy.” The first (a), which is often called “shot noise,” arises because there are $N$ discrete GW sources at specific sky locations. The second (b) arises because the GW source positions are not a Poisson process, for example, because galaxy locations are clustered. Here, we quantify the impact of (a) and (b) on the mean and variance of the pulsar-averaged Hellings and Downs correlation. For conventional PTA sources, we show that the effects of shot noise (a) are much larger than the effects of clustering (b).

The cryogenic scintillating calorimeter technology devoted to rare event searches is reaching the sensitivity level required for the hunt of dark matter-electron scatterings. Dark matter-electron interactions in scintillating targets are expected to stimulate the emission of single photons, each of energy equal to the target electronic band gap. The electronic band gap in scintillators like $\mathrm{NaI}/\mathrm{GaAs}$ is of $\mathcal{O}(\mathrm{eV})$. The search for this signal can be done by an array of cryogenic light detectors with $\mathrm{eV}/\mathrm{sub}\text{−}\mathrm{eV}$ energy resolution. In this work, we describe the detection principle, the detector response, and the envisioned detector design to search for dark matter interacting with electrons via the measurement of the scintillation light at millikelvin. First sensitivity projections are provided, which show the potential of this research.

We investigate f-mode oscillations of anisotropic, nonrotating, neutron stars within the framework of full general relativity, considering linear order perturbations in both the metric and the fluid. First, we present the equations governing unperturbed stellar structures as well as oscillations under a phenomenological Ansatz to account for local anisotropy. Then, we solve those equations for two different equations of states, namely BSk21 and BSk19, the former being stiffer than the latter. For both of the cases, we consider only stable neutron stars. We see that moderately anisotropic neutron stars with the tangential pressure larger than the radial pressure can give more massive stable neutron stars than the isotropic or highly anisotropic ones. We find that the frequency of the f-mode exhibits a linear relationship with the square root of the average density of neutron stars and the slope of the linear fit depends on the anisotropic strength. We also see that, for any given value of the anisotropic strength, neutron stars of higher masses have higher values of the frequency. For lower values of the mass, the increase of the frequency with the mass is linear, but for higher values of the mass, the frequency increases rapidly with the increase in the value of the mass. However, this nonlinear rise in the frequency with the mass is not prominent when the radial pressure is larger than the tangential pressure. We also see that for a fixed value of a small mass, higher anisotropy leads to a larger value of the frequency, but when the fixed mass is above a threshold value, higher anisotropy leads to a smaller value of the frequency. Moreover, for a fixed mass of the neutron star and for the same amount of the anisotropy, the value of the frequency is higher for the softer equation of state, but the nature of the variation in the frequency with the change in the anisotropic strength is similar for the two equations of state. We also find that the damping time of the f-mode oscillation decreases as the mass of the neutron star increases for all values of the anisotropic strength. However, for mildly anisotropic neutron stars, a slight increase in the damping time occurs near the stable maximum mass. Moreover, for a fixed mass of the neutron star and for the same amount of the anisotropy, the value of the damping time is lower for the softer equation of state, but the nature of the variation in the damping time with the change in the anisotropic strength is similar for the two equations of state.

Magnetic reconnection provides a new avenue to extract energy from a rotating black hole in astrophysical scenarios. There have been many works studying the feasibility of extracting energy via magnetic reconnection in the scheme of magnetohydrodynamics. However, most of them focused on circularly flowing bulk plasma only, and the influence of orientation angle, the angle between flowing direction of bulk plasma and ejection direction of plasmoids, was never carefully considered. In this work, we would like to study the energy extraction via magnetic reconnection, via the so-called Comisso-Asenjo process specifically, in the plunging plasma. More importantly, we analyze the influence of orientation angle in depth. Actually, we consider the magnetic reconnection occurring in bulk plasma with two kinds of streamlines, one being the circular flow and the other being the plunging flow from the innermost stable circular orbit. We find that the plunging plasma has higher energy-extraction efficiency. Moreover, we notice that it is favorable for energy extraction when the orientation angle is suitably increased if the bulk plasma plunges. We further define the covering factor. We further define the covering factor. Under the assumption that the magnetic reconnection occurs equally probably along any direction on any position within ergosphere, this value helps us to primitively judge the probability of energy extraction via magnetic reconnection, through which we conclude that the plunging bulk plasma is much more capable in energy extraction than the circularly flowing one.

Measurements of neutron star masses, radii, and tidal deformability have direct connections to nuclear physics via the equation of state (EoS), which for the cold, catalyzed matter in neutron star cores is commonly represented as the pressure as a function of energy density. Microscopic models with exotic degrees of freedom display nontrivial structure in the speed of sound ($c_s$) in the form of first-order phase transitions and bumps, oscillations, and plateaus in the case of crossovers and higher-order phase transitions. We present a procedure based on Gaussian processes to generate an ensemble of EoS that include nontrivial features. Using a Bayesian analysis incorporating measurements from x-ray sources, gravitational wave observations, and perturbative QCD results, we show that these features are compatible with current constraints. We investigate the possibility of a global maximum in $c_s$ that occurs within the densities realized in neutron stars—implying a softening of the EoS and possibly an exotic phase in the core of massive stars—and find that such a global maximum is consistent with, but not required by, current constraints.

We report new Lyman-$\alpha$ and 21-cm constraints on freeze-in dark matter (FIDM) which injects energy into the intergalactic medium either through annihilation or decay to photon(s) or electron-positron pair. With respect to Lyman-$\alpha$ we fix the baseline ionization history using low redshift data about astrophysical reionization, whereas for 21-cm signal we adopt the baseline values of 21-cm power spectrum through a standard modeling of star formation developed so far. Using the latest numerical tools, we show that (i) for sterile neutrino FIDM, current Lyman-$\alpha$ data and future sensitivity of SKA-low (1000 hrs) on the 21-cm power spectra excludes the FIDM mass up to $1.8\times {10}^{-3}\mathrm{GeV}$ at 95% CL and $5.46\times {10}^{-4}\mathrm{GeV}$, respectively, and (ii) for millicharged FIDM, current Lyman-$\alpha$ data only excludes the millicharge down to ${10}^{-8}$ within the FIDM mass range of ${10}^{-3}–1\mathrm{GeV}$ at 95% CL, suggesting that the surviving parameter space of millicharged FIDM is still intact.

We propose a gauge singlet scalar with mass around 1–100 TeV as a thermal heavy dark matter candidate along with a dilaton as a Higgs portal mediator in a dimensionless scalar extension of the Standard Model. We demonstrate analytically that such a model gives rise to very strong first-order electroweak phase transition through supercooling. We calculate the corresponding gravitational wave signals due to bubble collisions during the phase transition. The produced gravitational waves can be detected by future space-based gravitational wave detectors in the frequency range from ${10}^{-4}$ to 0.1 Hz.

We reinvestigate the interactions between static color sources in a finite temperature gluonic medium using both high resolution isotropic and anisotropic quenched lattice QCD ensembles. The underlying ill-posed inverse problem, related to the extraction of spectral functions, is attacked with a range of different methods, including Bayesian inference, Padé interpolation and model fits. Among the latter we include a tail amended Gaussian ansatz and a HTL-inspired fit ansatz. We reconfirm the presence of a dominant low lying spectral feature that supports the existence of a potential picture for the in-medium evolution of the static charges at late real times. Using the raw unmodified lattice data, all applicable methods show clear signs of screening of the real part of the potential. After applying a subtraction procedure featured in a previous study, we find however that screening disappears from the extracted potential. Paths toward the resolution of this puzzle are discussed.

A novel approach for describing the evolution of nucleon structure from low-$Q^2$ regime to high-$Q^2$ asymptotic region is proposed. This infrared-safe scheme modifies the parton distribution evolution equations to incorporate the corrections from emergent hadron mass mechanisms and parton-parton recombination at low $Q^2$. The effective quark mass, generated by dynamical chiral symmetry breaking, slows the evolution of parton distributions in the infrared region, causing the Dokshitzer-Gribov-Lipatov-Altarelli-Parisi evolution to freeze when $Q^2\ll M_{\mathrm{q}/\mathrm{g}}$. Notably, this scheme renders the high-$Q^2$ parton distributions insensitive to the choice of input hadronic scale. The parton-parton recombination effect is crucial in suppressing the rapid growth of parton distributions at small $x$, consistent with experimental data. When applied to three valence quark distributions derived from a quark model, our scheme yields parton distributions that agree well with deep-inelastic scattering data in both large-$x$ and small-$x$ regions, providing a unified description of nucleon structure across the entire $Q^2$ range.

In this paper, we compute the total and differential cross sections for $e^{+}{e}^{-}\to J/\psi +c+\overline{c}$ at the $B$ factories up to next-to-leading order (NLO) corrections within the framework of nonrelativistic quantum chromodynamics (QCD) factorization theory. We then obtain improved perturbative QCD (pQCD) series of those cross sections by using the principle of maximum conformality (PMC). We show that the PMC can be applied for any pQCD calculable observable at the total and differential levels via a self-consistent way in perturbation theory. We observe that a more precise prompt total cross section at the NLO level can be achieved after applying the PMC, e.g., $\sigma {|}_{\text{prompt}}^{\mathrm{PMC}}=0.565_{-0.125}^{+0.144}\mathrm{pb}$. Here the uncertainty is the squared average of those from the ${\alpha }_s$ fixed-point uncertainty $\mathrm{\Delta }{\alpha }_s(M_Z)$, the uncertainty of charm quark mass $\mathrm{\Delta }{m}_c$, and an estimated contribution of the uncalculated NNLO-terms as predicted by the Padé approximation approach. The differential cross sections $d\sigma /d{P}_{J/\psi }$, $d\sigma /d|\cos \theta |$, and $d\sigma /dz$ for $e^{+}{e}^{-}\to J/\psi +c+\overline{c}$ are further examined. Those results show that by further considering the feed-down contributions, the PMC predictions show better agreement with the Belle measurements.