A hypothetical pseudoscalar particle axion, which is an immediate result of the Peccei-Quinn solution to the strong $CP$ problem, may couple to gluons and lead to an oscillating electric dipole moment (EDM) of fundamental particles. This paper proposes a novel method of probing the axion-induced oscillating EDM in storage rings, using a radio frequency (rf) Wien filter. The Wien filter at the frequency of the sidebands of the axion and $g-2$ frequency, $f_{\text{axion}}\pm f_{g-2}$, generates a spin resonance in the presence of an oscillating EDM, as confirmed both by an analytical estimation of the spin equations and independently by simulation. A brief systematic study also shows that this method is unlikely to be limited by Wien filter misalignment issues.

We show that massless Kähler-Dirac fermions exhibit a mixed gravitational anomaly involving an exact $U(1)$ symmetry which is unique to Kähler-Dirac fields. Under this $U(1)$ symmetry the partition function transforms by a phase depending only on the Euler character of the background space. Compactifying flat space to a sphere we learn that the anomaly vanishes in odd dimensions but breaks the symmetry down to $Z_4$ in even dimensions. This $Z_4$ is sufficient to prohibit bilinear terms from arising in the fermionic effective action. Four fermion terms are allowed but require multiples of two flavors of Kähler-Dirac field. In four dimensional flat space each Kähler-Dirac field can be decomposed into four Dirac spinors and hence these anomaly constraints ensure that eight Dirac fermions or, for real representations, sixteen Majorana fermions are needed for a consistent interacting theory. These constraints on fermion number agree with known results for topological insulators and recent work on discrete anomalies rooted in the Dai-Freed theorem. Our work suggests that Kähler-Dirac fermions may offer an independent path to understanding these constraints. Finally we point out that this anomaly survives intact under discretization and hence is relevant in understanding recent numerical results on lattice models possessing massive symmetric phases.

We calculate the nucleon isovector scalar charge in lattice QCD using overlap fermions on five ensembles of gauge configurations generated by the RBC/UKQCD collaboration using the domain-wall quark action with $2+1$ dynamical flavors. The five ensembles cover five pion masses, $m_{\pi }\approx 139$, 171, 302, 337 and 371 MeV, and four lattice spacings, $a\approx 0.06$, 0.08, 0.11 and 0.14 fm. Three to six valence quark masses are computed on each ensemble to investigate the pion mass dependence. The extrapolation to the physical pion mass, continuum and infinite volume limits is obtained by a global fit of all data to a formula originated from partially quenched chiral perturbation theory. The excited-states contamination is carefully analyzed with 3–5 sink-source separations and multi-state fits. Our final result, in the $\overline{\mathrm{MS}}$ scheme at 2 GeV, is $g_S^{u-d}=0.94(10{)}_{\text{stat}}(8{)}_{\mathrm{sys}}$, where the first error is the statistical error and the second is the systematic error.

We calculate masses of light and heavy mesons as well as baryons of negative parity containing $u$, $d$, $s$, $c$, and $b$ quarks. It is an extension of our previous work where we had studied the positive parity baryons. We adopt a quark-diquark picture of baryons where the diquarks are nonpointlike with a finite spatial extension. The mathematical foundation for this analysis is implemented through a symmetry-preserving Schwinger-Dyson equations treatment of a vector-vector contact interaction, which preserves key features of quantum chromodynamics, such as confinement, chiral symmetry breaking, axial vector Ward-Takahashi identity, and low-energy Goldberger-Treiman relations. This treatment simultaneously describes mesons and provides attractive correlations for diquarks in the $\overline{3}$ representation. Employing this model, we compute the spectrum and masses of all spin-$1/2$ and spin-$3/2$ baryons of negative parity, supplementing our earlier evaluation of positive parity baryons, containing one, two, or three heavy quarks. In the process, we calculate the masses of a multitude of mesons and corresponding diquarks. Wherever possible, we make comparisons of our results with known experimental observations as well as theoretical predictions of several models and approaches including lattice quantum chromodynamics, finding satisfactory agreement. We also make predictions for heavier states not yet observed in the experiment.

In this work, we systematically investigate the heavy-strange meson systems, $D^{(*)}{K}^{(*)}/{\overline{B}}^{(*)}{K}^{(*)}$ and ${\overline{D}}^{(*)}{K}^{(*)}/B^{(*)}{K}^{(*)}$, to study possible molecules in a quasipotenial Bethe-Salpter equation approach together with the one-boson exchange model. The potential is achieved with the help of the hidden-gauge Lagrangians. Molecular states are found from all six $S$-wave isoscalar interactions of $D^{(*)}{K}^{(*)}$ or ${\overline{B}}^{(*)}{K}^{(*)}$. The charmed-strange mesons $D_{s0}^{*}(2317)$ and $D_{s1}(2460)$ can be related to the $DK$ and $D^{*}K$ states with spin parities $0^{+}$ and $1^{+}$, respectively. In the current model, the $\overline{B}{K}^{*}$ molecular state with $1^{+}$ is the best candidate of the recent observed $B_{sJ}(6158)$. Four molecular states are produced from the interactions of ${\overline{D}}^{(*)}{K}^{(*)}$ or $B^{(*)}{K}^{(*)}$. The relation between the ${\overline{D}}^{*}{K}^{*}$ molecular state with $0^{+}$ and the $X_0(2900)$ is also discussed. No isovector molecular states are found from the interactions considered. The current results are helpful to understand the internal structure of $D_{s0}^{*}(2317)$, $D_{s1}(2460)$, $X_0(2900)$, and new $B_{sJ}$ states. The experimental research for more heavy-strange meson molecules is suggested.

In this paper we explore practicable ways for self-consistent calculations of spectral functions from analytically continued functional renormalization group (aFRG) flow equations. As a particularly straightforward one we propose to include parametrizations of self-energies based on explicit analytic one-loop expressions. To exemplify this scheme we calculate the spectral functions of pion and sigma meson of the $O(4)$ model at vanishing temperature in the broken phase. Comparing the results with those from previous aFRG calculations, we explicitly demonstrate how self-consistency at all momenta fixes the tight relation between particle masses and decay thresholds. In addition, the two-point functions from our new semianalytic FRG scheme have the desired domain of holomorphy built in and can readily be studied in the entire cut-complex frequency plane, on physical as well as other Riemann sheets. This is very illustrative and allows, for example, to trace the flow of the resonance pole of the sigma meson across an unphysical sheet. In order to assess the limitations due to the underlying one-loop structure, we also introduce a fully self-consistent numerical scheme based on spectral representations with scale-dependent spectral functions. The most notable improvement of this numerically involved calculation is that it describes the three-particle resonance decay of an off-shell pion, ${\pi }^{*}\to \sigma \pi \to 3\pi$. Apart from this further conceptual improvement, overall agreement with the results from the considerably simpler semianalytic one-loop scheme is very encouraging, however. The latter can therefore provide a sound and practicable basis for self-consistent calculations of spectral functions in more realistic effective theories for warm and dense matter.

Measuring longitudinally polarized vector boson scattering in, e.g., the $ZZ$ channel is a promising way to investigate the unitarization scheme from the Higgs and possible new physics beyond the Standard Model. However, at the LHC, it demands the end of the high-luminosity-LHC lifetime luminosity, $3000{\mathrm{fb}}^{-1}$, and advanced data analysis technique to reach the discovery threshold due to its small production rates. Instead, there could be great potential at future colliders. In this paper, we perform a Monte Carlo study and examine the projected sensitivity of longitudinally polarized $ZZ$ scattering at a TeV scale muon collider. We conduct studies at 14 and 6 TeV muon colliders respectively and find that a 5 standard deviation discovery can be achieved at a 14 TeV muon collider, with $3000{\mathrm{fb}}^{-1}$ of data collected. While a 6 TeV muon collider can already surpass high-luminosity LHC, reaching 2 standard deviations with around $4{\mathrm{ab}}^{-1}$ of data. The effect from lepton isolation and detector granularity is also discussed, which may be more obvious at higher energy muon colliders, as the leptons from longitudinally polarized $Z$ decays tend to be closer.

At the Fermilab Tevatron proton-antiproton ($p\overline{p}$) collider, high-mass electron-neutrino ($e\nu$) pairs are produced predominantly in the process $p\overline{p}\to W(\to e\nu )+X$. The asymmetry of the electron and positron yield as a function of their pseudorapidity constrain the slope of the ratio of the $u$- to $d$-quark parton distributions versus the fraction of the proton momentum carried by the quarks. This paper reports on the measurement of the electron-charge asymmetry using the full data set recorded by the Collider Detector at Fermilab in 2001–2011 and corresponding to $9.1{\mathrm{fb}}^{-1}$ of integrated luminosity. The measurement significantly improves the precision of the Tevatron constraints on the parton-distribution functions of the proton. Numerical tables of the measurement are provided.

In this paper, we study the ’t Hooft type instantons in eight dimensions, which satisfy the (anti)self-dual equations $F\wedge F=\pm *{}_{8}F\wedge F$. Using various designs of such instantons, we find new soliton solutions to the low-energy effective theory of the heterotic fivebrane. We investigate conditions under which these instanton configurations can be identified with the $D$-instantons embedded in the $D7$-brane world volume. Finally, we discuss the relationship between eight-dimensional periodic instantons and monopoles.

Gravitational wave echoes can be used as a significant observable to understand the properties of black holes horizon. In addition, echoes would also closely relate to the unique properties of compact objects. In this work, we study the evolution of electromagnetic field and scalar field under the background of novel black-bounce spacetimes. Our results show an obvious echoes signal that can characterize the properties of novel black-bounce spacetimes, and a detailed analysis about the characteristics of the echoes signal is given. By studying the quasinormal ringdown of the three states of novel black-bounce spacetimes, including black holes in $0<a<2M$, the one-way wormhole in $a=2M$ and the traversable wormhole in $a>2M$, we find that the echoes signal only appears when $a>2M$ in this spacetime, but when the parameter $a$ increases to a threshold, the echoes signal will be transformed into a quasinormal ringdown of the two-way traversable wormhole.

The need for more and more accurate gravitational-wave templates requires taking into account all possible contributions to the emission of gravitational radiation from a binary system. Therefore, working within a multipolar-post-Minkowskian framework to describe the gravitational-wave field in terms of the source multipole moments, the dominant instantaneous effects should be supplemented by hereditary contributions arising from nonlinear interactions between the multipoles. The latter effects include tails and memories and are described in terms of integrals depending on the past history of the source. We compute higher-order tail (i.e., tail-of-tail, tail-squared, and memory) contributions to both energy and angular momentum fluxes and their averaged values along hyperboliclike orbits at the leading post-Newtonian approximation, using harmonic coordinates and working in the Fourier domain. Because of the increasing level of accuracy recently achieved in the determination of the scattering angle in a two-body system by several complementary approaches, the knowledge of these terms will provide useful information to compare results from different formalisms.

Gravitational-wave (GW) memory effects produce permanent shifts in the GW strain and its time integrals after the passage of a burst of GWs. Their presence is closely tied to the symmetries of asymptotically flat spacetimes and the corresponding fluxes of conserved charges conjugate to these symmetries. While the phenomenology of GW memory effects (particularly for compact-binary mergers) is now well understood in general relativity, it is less well understood in the many modifications to general relativity. We recently, however, computed asymptotically flat solutions, symmetries, conserved quantities, and GW memory effects in one such modified theory with an additional scalar degree of freedom, Brans-Dicke theory. In this paper, we apply our results from this earlier work to compute the GW memory effects from compact binaries in the post-Newtonian approximation. In addition to taking the post-Newtonian limit of these effects, we work in the approximation that the energy and angular momentum losses through scalar radiation are small compared to the energy and angular momentum losses through (tensor) gravitational radiation. We focus on the tensor (as opposed to scalar) GW memory effect, which we compute through Newtonian order, and the small differences induced by the radiation of scalar waves at this order. Specifically, we compute the nonlinear parts of the tensor displacement and spin GW memory effects produced during the inspiral of quasicircular, nonprecessing binaries in Brans-Dicke theory. Because the energy radiated through the scalar dipole moment appears as a negative post-Newtonian order-effect, then in this approximation, the displacement memory has a logarithmic dependence on the post-Newtonian parameter and the spin memory has a relative minus-one-post-Newtonian-order correction; these corrections, however, are ultimately small because they are related to the total energy and angular momentum radiated in the scalar field, respectively. At Newtonian order, the scalar radiation also gives rise to a sky pattern of the memory effect around an isolated source that differs from that of the memory effect in general relativity.

In this paper, we investigate gravitational waves (GWs) from the axionlike particle inflation by applying the multinature inflation model. The model parameter $n$ determines the exit way of inflation, the number of phase transitions (PTs), and the number of multiples of inflation. In the inflation exit with PTs, there is a lower bound for parameter $n$ to reach the corresponding multiples of inflation, but the magnitude of $n$ is negligible for the physical observations, such as $n_s$, $r$, and ${\mathrm{\Omega }}_{\mathrm{GW}}{h}^2$. GWs can be generated in two ways for the inflation exit with PTs, one derives from quantum fluctuations, which dominate the low-frequency regions, and these GWs can be detected by the Ultimate-Decigo detector at around ${10}^{-1}\mathrm{Hz}$. However, the other one derives from PTs, which dominate the high-frequency regions, and it is expected to be detected by the future higher-sensitivity 3DSR GW detector.

Stellar-mass binary black holes (BBHs) may merge in the vicinity of a supermassive black hole (SMBH). It is suggested that the gravitational wave (GW) emitted by a BBH has a high probability to be lensed by the SMBH if the BBH’s orbit around the SMBH (i.e., the outer orbit) has a period of less than a year and is less than the duration of observation of the BBH by a space-borne GW observatory. For such a “$\mathrm{BBH}+\mathrm{SMBH}$” triple system, the de Sitter precession of the BBH’s orbital plane is also significant. In this work, we thus study GW waveforms emitted by the BBH and then modulated by the SMBH due to effects including Doppler shift, de Sitter precession, and gravitational lensing. We show specifically that for an outer orbital period of 0.1 yr and an SMBH mass of ${10}^7{M}_{\odot }$, there is a 3–10% chance for the standard, strong lensing signatures to be detectable by space-borne GW detectors such as LISA and/or TianGO. For more massive lenses ($\gtrsim {10}^8{M}_{\odot }$) and more compact outer orbits with periods $\lesssim 0.1\mathrm{yr}$, retrolensing of the SMBH (which is closely related to the glory scattering) might also have a 1%-level chance of detection. Furthermore, by combining the lensing effects and the dynamics of the outer orbit, we find that the mass of the central SMBH can be accurately determined with a fraction error of $\sim {10}^{-4}$. This is much better than the case of static lensing because the degeneracy between the lens’ mass and the source’s angular position is lifted by the outer orbital motion. Including lensing effects also allows the de Sitter precession to be detectable at a precession period 3 times longer than the case without lensing. Finally, we demonstrate that one can check the consistency between the SMBH’s mass determined from the orbital dynamics and the one inferred from gravitational lensing, which serves as a test on theories behind both phenomena. The statistical error on the deviation between two masses can be constrained to a 1% level.

The recently discovered very massive stellar black holes (BHs), i.e., the binary BH (BBH) merger for the gravitational-wave (GW) event GW190521 by LIGO-Virgo O3a with the component masses of ${85}_{-14}^{+21}{M}_{\odot }$ and ${66}_{-18}^{+17}{M}_{\odot }$, have aroused much attention. Our statistical knowledge of the mass distributions of the BBHs observed in LIGO-Virgo GW detections is helpful to understanding the origin of GW190521. Hence, in order to determine whether GW190521 is consistent with the same population as the other LIGO-Virgo BBHs, we analyze the BBH total masses in the GWTC-2 catalog with the classical Gaussian mixture models (GMMs). Based on the model selection results in this analysis, we cannot confidently conclude that GW190521 is a new population of BBHs distinct from the other LIGO-Virgo BBHs due to the limitation of the current small sample size of GW-observed BBHs. Moreover, our results suggest that there is a clear preference for a two-component GMM for the sample of BBHs in GWTC-2 without GW190521, implying that two (or more) distinct underlying populations of these BBHs may exist because of the differing astrophysical origins. After a consideration for the detailed features of the above two-component GMM, we find statistical evidence that tends to support a mixture model for LIGO-Virgo BBH formation, which is in line with previous studies that also supported a multicomponent model (for example, one consisting of isolated binary evolution and dynamical channels).

The axion objects such as axion miniclusters and axion clouds around spinning black holes induce parametric resonances of electromagnetic waves through the axion-photon interaction. In particular, it has been known that the resonances from the axion with the mass around ${10}^{-6}\mathrm{eV}$ may explain the observed fast radio bursts (FRBs). Here we argue that similar bursts of high frequency gravitational waves, which we call fast gravitational wave bursts (FGBs), are generated from axion clumps with the presence of gravitational Chern-Simons (CS) coupling. The typical frequency is half of the axion mass, which in general can range from kHz to GHz. We also discuss the secondary gravitational wave production associated with FRB, as well as the possible host objects of the axion clouds, such as primordial black holes with typical masses around ${10}^{-5}{M}_{\odot }$. Future detections of FGBs together with the observed FRBs are expected to provide more evidence for the axion.

Axionlike particles (ALPs) coupled with electrons would be produced in a supernova (SN) via electron-proton bremsstrahlung and electron-positron fusion. We evaluate the ALP emissivity from these processes by taking into account the ALP mass and thermal effects on electrons in the strongly degenerate and relativistic SN plasma. Using a state-of-the-art SN simulation, we evaluate the SN 1987A cooling bound on ALPs for masses in the range 1–200 MeV, which excludes currently unprobed regions down to $g_{ae}\sim 2.5\times {10}^{-10}$ at $m_a\sim 120\mathrm{MeV}$.

We compute the dispersion relations for scalar, vector and tensor modes of a viscous relativistic fluid, linearized around an equilibrium solution, for a divergence type theory (which, in the linearized theory, includes Israel-Stewart theory and anisotropic hydrodynamics as particular cases) and contrast them to the corresponding results derived from kinetic theory under the relaxation time approximation, and from causal first order theories. We conclude that all approaches give similar dynamics for the scalar and vector modes, while the particular divergence type theory presented here also contains propagating damped tensor waves, in agreement with kinetic theory. Nonhydrodynamic tensor modes are also a feature of holographic fluids. These results support the application of hydrodynamics in problems involving the interaction between fluids and gravitational waves.

The electronlike excess observed by the MiniBooNE experiment is explained with a model comprising a new low mass state ($\mathcal{O}(1)\mathrm{eV}$) participating in neutrino oscillations and a new high mass state ($\mathcal{O}(100)\mathrm{MeV}$) that decays to $\nu +\gamma$. Short-baseline oscillation datasets are used to predict the oscillation parameters. Fitting the MiniBooNE energy and scattering angle data, there is a narrow joint allowed region for the decay contribution at 95% CL. The result is a substantial improvement over the single sterile neutrino oscillation model, with $\mathrm{\Delta }{\chi }^2/\mathrm{dof}=19.3/2$ for a decay coupling of $2.8\times {10}^{-7}{\mathrm{GeV}}^{-1}$, high mass state of 376 MeV, oscillation mixing angle of $7\times {10}^{-4}$ and mass splitting of $1.3{\mathrm{eV}}^2$. This model predicts that no clear oscillation signature will be observed in the FNAL short baseline program due to the low signal-level.

The molecular assignments to the three $P_c$ states and the similar production mechanism between the ${\mathrm{\Lambda }}_b\to P_c+K$ and $B\to XYZ+K$ convince us the $B$ decaying to a charmonium state plus light mesons could be the appropriate production process to search for the charmoniumlike molecular tetraquarks. In this work, we systematically study the interactions between a charmed (charmed-strange) meson and an anticharmed (anticharm-strange) meson, which include the $D^{(*)}{\overline{D}}^{(*)}$, ${\overline{D}}^{(*)}{\overline{D}}_1$, $D^{(*)}{\overline{D}}_2^{*}$, $D_s^{(*)}{\overline{D}}_s^{(*)}$, $D_s^{(*)}{\overline{D}}_{s0}^{*}$, $D_s^{(*)}{\overline{D}}_{s1}^{\prime }$, $D_s^{(*)}{\overline{D}}_{s1}$, $D_s^{(*)}{\overline{D}}_{s2}^{*}$ systems. After adopting the one-boson-exchange effective potentials, our numerical results indicate that, on one hand, there can exist a serial of isoscalar charmoniumlike $\mathcal{D}\overline{\mathcal{D}}$ and ${\mathcal{D}}_s{\overline{\mathcal{D}}}_s$ molecular states, on the other hand, we can fully exclude the charged charmoniumlike states as the isovector charmoniumlike molecules. Meanwhile, we discuss the two-body hidden-charm decay channels for the obtained $\mathcal{D}\overline{\mathcal{D}}$ and ${\mathcal{D}}_s{\overline{\mathcal{D}}}_s$ molecules, especially the $D^{*}{\overline{D}}^{*}$ molecular tetraquarks. By analyzing the experimental data collected from the $B\to XYZ+K$ and the mass spectrum and two-body hidden-charm decay channels for the obtained $\mathcal{D}\overline{\mathcal{D}}$ and ${\mathcal{D}}_s{\overline{\mathcal{D}}}_s$ molecules, we find several possible hints of the existence of the charmoniumlike molecular tetraquarks, i.e., a peculiar characteristic mass spectrum of the isoscalar $D^{*}{\overline{D}}^{*}$ molecular systems can be applied to identify the charmoniumlike molecule. We look forward to the future experiments like the LHCb, Belle II, and BESIII Collaborations can test our results with more precise experimental data.