We reanalyze the problems in the assignment of $3{}^3{S}_1$ and $4{}^3{S}_1$ light mesons, which have not yet been well established with the $q\overline{q}$ quark model. Regge trajectories and the ${}^3{P}_0$ decay model are used, respectively, to study the mass and width of the observed states and predict the missing ones. By comparing our calculations with the latest experiments, we suggest that the inconsistent data of $\rho (2150)$ may include two similar structures, $\rho (4{{}^{3}S}_1)$ and $\omega (4{{}^{3}S}_1)$. In addition, the problem of the $K^{*}(2{{}^{3}S}_1)$ assignment, with two observed states $K^{*}(1410)$ and $K^{*}(1680)$, is investigated, with several possible explanations.

We discuss the recent results on the muon anomalous magnetic moment in the context of new physics models with light scalars. We propose a model of one-loop contributions to $g-2$ of a scalar and a pseudoscalar which naturally cancel in the massless limit by symmetry. This model allows us to interpolate between two possible interpretations while keeping new physics light. In the first interpretation, the results provide a strong evidence of the existence of new physics, dominated by the (positive) contribution of a $CP$-even scalar. In the second one, supported by the recent lattice result, the data provides a strong upper bound on new physics, specifically in the case of (negative) pseudoscalar contributions. We emphasize that tree-level signatures of the new scalars are enhanced relative to conventional explanations of the discrepancy. As a result, this model can be tested in the near future with accelerator-based experiments and possibly also at the precision frontier.

Semileptonic flavor-changing neutral-current transitions with a pair of neutrinos in the final state are very accurately determined in the Standard Model (SM) and thus provide an accurate and sensitive probe for physics beyond the SM. Until recently, the poor tagging efficiency for the $B\to K^{(*)}\nu \overline{\nu }$ modes made them less advantageous as a probe of new physics (NP) compared to the charged lepton counterparts. The most recent Belle II result on $B\to K\nu \overline{\nu }$ uses an innovative inclusive tagging technique, resulting in a higher tagging efficiency; this together with previous BABAR and Belle results indicates a possible enhancement in the branching fraction of $B^{+}\to K^{+}\nu \overline{\nu }$. A reanalysis of the full Belle dataset together with the upcoming Belle II dataset is expected to result in a much more precise measurement of this mode. If the branching ratio is indeed found to be enhanced with improved measurements, this would provide an unambiguous signal of NP without uncertainties due to long-distance nonfactorizable effects or power corrections (in contrast to $B\to K^{(*)}\ell \ell$). We have explored the possibilities of such an enhancement as a signal of NP within several scenarios, which can also explain some of the other tensions observed in neutral- as well as charged-current $B$ decays. In an effective field theory approach, with the most general dimension-6 Hamiltonian including light right-handed neutrinos, we explore the viability of all scalar and vector leptoquarks, as well as the parameter space possible with a generic vector gauge boson $Z^{\prime }$ model, assuming minimal new particle content. While being consistent with all data, correlations between the observed intriguing discrepancies in $B$ decays are also obtained, which will discriminate between the various NP scenarios.

We reformulate the Palatini action for general relativity in terms of moving frames that exhibit local Galilean covariance in a large speed of light expansion. For this, we express the action in terms of variables that are adapted to a Galilean subgroup of the $\mathrm{GL}(n,\mathbb{R})$ structure group of a general frame bundle. This leads to a novel Palatini-type formulation of general relativity that provides a natural starting point for a first-order nonrelativistic expansion. In doing so, we show how a comparison of Lorentzian and Newton-Cartan metric compatibility explains the appearance of torsion in the nonrelativistic expansion.

We use holography in order to study the entropy of thermal conformal field theory (CFT) on ($1+1$)-dimensional curved backgrounds that contain horizons. Starting from the metric of the Bañados-Teitelboim-Zanelli (BTZ) black hole, we perform explicit coordinate transformations that set the boundary metric in de Sitter or black hole form. The dual picture describes a CFT at a temperature different from that of the horizon. We determine minimal surfaces that allow us to compute the entanglement entropy of a boundary region, as well as the temperature affecting the energy associated with a probe quark on the boundary. For an entangling surface that coincides with the horizon, we study the relation between entanglement and gravitational entropy through an appropriate definition of the effective Newton constant. We find that the leading contribution to the entropy is proportional to the horizon area, with a coefficient that exceeds the standard value for the Bekenstein-Hawking entropy. The difference is attributed to the divergence of the stress-energy tensor of the thermal CFT on the horizon. We demonstrate the universality of these findings by considering the most general metric in a ($2+1$)-dimensional anti–de Sitter bulk containing a nonrotating black hole and a static boundary with horizons.

Complete set of modes and the Hadamard function are constructed for a scalar field inside and outside a sphere in ($D+1$)-dimensional de Sitter spacetime foliated by negative constant curvature spaces. We assume that the field obeys Robin boundary condition on the sphere. The contributions in the Hadamard function induced by the sphere are explicitly separated and the vacuum expectation values (VEVs) of the field squared and energy-momentum tensor are investigated for the hyperbolic vacuum. In the flat spacetime limit the latter is reduced to the conformal vacuum in the Milne universe and is different from the maximally symmetric Bunch-Davies vacuum state. The vacuum energy-momentum tensor has a nonzero off-diagonal component that describes the energy flux in the radial direction. The latter is a purely sphere-induced effect and is absent in the boundary-free geometry. Depending on the constant in Robin boundary condition and also on the radial coordinate, the energy flux can be directed either from the sphere or towards the sphere. At early stages of the cosmological expansion the effects of the spacetime curvature on the sphere-induced VEVs are weak and the leading terms in the corresponding expansions coincide with those for a sphere in the Milne universe. The influence of the gravitational field is essential at late stages of the expansion. Depending on the field mass and the curvature coupling parameter, the decay of the sphere-induced VEVs, as functions of the time coordinate, is monotonic or damping oscillatory. At large distances from the sphere the falloff of the sphere-induced VEVs, as functions of the geodesic distance, is exponential for both massless and massive fields.

In this work, we provide consistent compactifications of Einstein-Maxwell and Einstein-Maxwell-Lovelock theories on direct product spacetimes of the form ${\mathcal{M}}_D={\mathcal{M}}_d\times {\mathcal{K}}^p$, where ${\mathcal{K}}^p$ is a Euclidean internal manifold of constant curvature. For these compactifications to take place, the distribution of a precise flux of $p$-forms over the internal manifold is required. The dynamics of the $p$-forms are demanded to be controlled by two types of interactions: first, by specific couplings with the curvature tensor and, second, by a suitable interaction with the electromagnetic field of the $d$-dimensional brane, the latter being dictated by a modification of the recently proposed theory of quasitopological electromagnetism. The field equations of the corresponding compactified theories, which are of second order, are solved, and general homogenously charged black $p$-branes are constructed. We explicitly provide homogenous Reissner-Nordström black strings and black $p$-branes in Einstein-Maxwell theory and homogenously charged Boulware-Deser black $p$-branes for quadratic and cubic Maxwell-Lovelock gravities.

In this work, we reanalyze the possibility of finding bound states (scalar clouds) of a test, charged and complex-valued scalar field with mass $\mu$ and charge $q$ in the background of a Reissner-Nordstrom black hole (RNBH). In order to determine the existence of such scalar clouds, we impose suitable regularity conditions for the scalar field at the event horizon. We find numerical evidence for the absence of such clouds in the subextremal and extremal RNBH when the field is massive but not self-interacting. More importantly, we put forward a theorem that proves that such clouds cannot exist. On the other hand, when a suitable self-interacting potential is included, the theorem no longer applies, providing a heuristic justification behind the existence of charged clouds (dubbed Q-clouds) that were reported recently.

In this paper, we study the influence of the axion-plasmon, as proposed in [Phys. Rev. Lett. 120, 181803 (2018)] on the optical properties of the Schwarzschild black hole. Our aim is to provide a test to detect the effects of a fixed axion background using black holes. To accomplish our goal, we explore the effect of the axion-plasmon coupling on the motion of photons around the Schwarzschild black hole and check the possibility of observing those effects upon the black hole shadow, the gravitational deflection angle, Einstein rings and shadow images obtained by radially infalling gas on a black hole within a plasma medium. We find that these quantities are indeed affected by the axion-plasmon coupling parameters which consequently generalize some of the well-known results in the literature. It is shown that the size of the black hole shadow decreases with increasing axion-plasmon if observed from a sufficiently large distance.

We study observational constraints on the nonmetricity $f(Q)$-gravity which reproduces an exact $\mathrm{\Lambda }\mathrm{CDM}$ background expansion history while modifying the evolution of linear perturbations. To this purpose we use cosmic microwave background (CMB) radiation, baryonic acoustic oscillations (BAO), redshift-space distortions (RSD), supernovae type Ia (SNIa), galaxy clustering (GC) and weak gravitational lensing (WL) measurements. We set stringent constraints on the parameter of the model controlling the modifications to the gravitational interaction at linear perturbation level. We find the model to be statistically preferred by data over the $\mathrm{\Lambda }\mathrm{CDM}$ according to the ${\chi }^2$ and deviance information criterion statistics for the combination with CMB, BAO, RSD and SNIa. This is mostly associated to a better fit to the low-$\ell$ tail of CMB temperature anisotropies.

We present a novel machine learning (ML) based strategy to search for binary black hole (BBH) mergers in data from ground-based gravitational wave (GW) observatories. This is the first ML-based search that not only recovers all the compact binary coalescences (CBCs) in the first GW transients catalog (GWTC-1), but also makes a clean detection of GW151216, which was not significant enough to be included in the catalog. Moreover, we achieve this by only adding a new coincident ranking statistic (MLStat) to a standard analysis that was used for GWTC-1. In CBC searches, reducing contamination by terrestrial and instrumental transients, which create a loud noise background by triggering numerous false alarms, is crucial to improving the sensitivity for detecting true events. The sheer volume of data and a large number of expected detections also prompts the use of ML techniques. We perform transfer learning to train “InceptionV3,” a pretrained deep neural network, along with curriculum learning to distinguish GW signals from noisy events by analyzing their continuous wavelet transform (CWT) maps. MLStat incorporates information from this ML classifier into the coincident search likelihood used by the standard pycbc search. This leads to at least an order of magnitude improvement in the inverse false-alarm-rate (IFAR) for the previously “low significance” events GW151012, GW170729, and GW151216. We also perform the parameter estimation of GW151216 using seobnrv4hm_rom. We carry out an injection study to show that MLStat brings substantial improvement to the detection sensitivity of Advanced LIGO for all compact binary coalescences. The average improvement in the sensitive volume is $\sim 10\%$ for low chirp masses ($0.8–5{\mathrm{M}}_{\odot }$) and $\sim 30\%$ for higher masses ($5–50{\mathrm{M}}_{\odot }$). Performance in the lower masses may become even better if the training set for the ML classifier, currently restricted to black hole binaries with component masses in the range $2–98{\mathrm{M}}_{\odot }$ only, is expanded to include binaries with neutron stars. Considering the impressive ability of the statistic to distinguish signals from glitches, the list of marginal events from MLStat could be quite reliable for astrophysical population studies and further follow-up. This work demonstrates the immense potential and readiness of MLStat for finding new sources in current data and the possibility of its adaptation in similar searches.

In models of minicharged dark matter associated with a hidden $U(1)$ symmetry, astrophysical black holes may acquire a “dark” charge, in such a way that the inspiral dynamics of binary black holes can be formally described by an Einstein-Maxwell theory. Charges enter the gravitational wave signal predominantly through a dipole term, but their effect is known to effectively first post-Newtonian order in the phase, which enables measuring the size of the charge-to-mass ratios $|q_i/m_i|$, $i=1$, 2, of the individual black holes in a binary. We set up a Bayesian analysis to discover, or constrain, dark charges on binary black holes. After testing our framework in simulations, we apply it to selected binary black hole signals from the second gravitational wave transient catalog, namely, those with low masses so that most of the signal-to-noise ratio is in the inspiral regime. We find no evidence for charges on the black holes and place typical $1\sigma$ bounds on the charge-to-mass ratios of $|q_i/m_i|\lesssim 0.2–0.3$.

We show that photon spheres of supermassive black holes generate high-frequency stochastic gravitational waves through photon-graviton conversion. Remarkably, the frequency is universally determined as $m_e\sqrt{m_e/m_p}\simeq {10}^{20}\mathrm{Hz}$ in terms of the proton mass $m_p$ and the electron mass $m_e$. It turns out that the density parameter of the stochastic gravitational waves ${\mathrm{\Omega }}_{\mathrm{gw}}$ could be ${10}^{-12}$. Since the existence of the gravitational waves from photon spheres is robust, it is worth seeking methods of detecting high-frequency gravitational waves around ${10}^{20}\mathrm{Hz}$.

The first-order phase transitions in the early Universe are one of the well-known sources which release the stochastic background of gravitational waves (GWs). In this paper, we study the contribution of an external static and strong magnetic field on the stochastic background of gravitational waves expected during QCD phase transition. In the light of the strongly magnetized hot QCD equation of state which deviated from the ideal gas up to the one-loop approximation, we estimate two phenomenologically important quantities: peak frequency redshifted to today ($f_{\mathrm{peak}}$) and GW strain amplitude ($h^2{\mathrm{\Omega }}_{\mathrm{gw}}$). The trace anomaly induced by the magnetized hot QCD matter around the phase transition generates the stochastic background of GW with peak frequencies lower than the ideal gas-based signal (around nHz). Instead, the strain amplitudes corresponding to the peak frequencies are of the same order of magnitude of the expected signal from ideal gas. This may be promising in the sense that although the strong magnetic field could mask the expected stochastic background of GWs by upgrading the frequency sensitivity of detectors in the future, the magnetized GW is expected to be identified. Faced with the projected reach of detectors EPTA, IPTA, and SKA, we find that for the tail of the magnetized GW signals there remains a mild possibility of detection as it can reach the projected sensitivity of SKA.

We computed the kinematics of $Z$-boson decay into a heavy–light neutrino pair when the $Z$-boson is produced at rest in $e^{+}{e}^{-}$ collisions, including the subsequent decay of the heavy neutrino into a visible final state containing a charged-lepton. We concentrated on heavy-neutrino masses of order dozens of GeV and the issue of addressing the nature of the neutrinos—Dirac fermions or Majorana fermions. We find that while it is not possible to tell the nature of the heavy and light neutrinos on an event-by-event basis, the nature of the neutrinos can nonetheless be inferred given a large-enough sample of heavy–light neutrino pairs. We identify two observables sensitive to the nature of neutrinos. One is the forward-backward asymmetry of the daughter-charged-leptons. This asymmetry is exactly zero if the neutrinos are Majorana fermions and is nonzero (and opposite) for positively- and negatively-charged daughter-leptons if the neutrinos are Dirac fermions. The other observable is the polarization of the heavy neutrino, imprinted in the laboratory-frame energy distribution of the daughter-charged-leptons. Dirac neutrinos and antineutrinos produced in $e^{+}{e}^{-}$ collisions at the $Z$-pole are strongly polarized while Majorana neutrinos are at most as polarized as the $Z$-bosons.

In this paper, we adopt an extended relativized quark model to investigate the triply-heavy tetraquarks systematically. The mass spectra are obtained by solving the four-body relativized Hamiltonian including the Coulomb potential, confining potential, spin-spin interactions, and relativistic corrections. We find that all of the triply-heavy tetraquarks lie above the corresponding meson-meson thresholds, and thus no stable one exists. In particular, besides the spin-spin interactions, the Coulomb and confining potentials also contribute to the mass splittings in the $cb\overline{c}\overline{q}$ and $cb\overline{b}\overline{q}$ systems. Moreover, the whole mass spectra for triply heavy tetraquarks show quite similar patterns, which preserve the light flavor SU(3) symmetry and heavy quark symmetry well. Through the fall-apart mechanism, the triply-heavy tetraquarks may easily decay into the heavy quarkonium plus heavy-light mesons, which are good candidates for investigation in future experiments.

We investigate radial excitation of the quark-antiquark pair in the ${\pi }^0$ meson and its effects on the $\gamma {\gamma }^{*}\to {\pi }^0$ transition form factor in the framework of light cone perturbative QCD. The existing constraints on the light cone wave function of the lowest Fock state $|q\overline{q}⟩$ in the ${\pi }^0$ meson allow a sizeable radial excitation of the quark-antiquark pair. We construct the light cone wave function for the quark-antiquark pair in the first radially excited state (the 2S state) using a simple harmonic oscillator potential. The distribution amplitude obtained for the 2S state has two nodes in $x$ at low scale of $Q$ and thereby has a much strong scale dependence than the 1S state. Contributions from this radial excitation to the $\gamma {\gamma }^{*}\to {\pi }^0$ transition form factor exhibit different $Q^2$-dependence behavior from the ground state and thus can modify the prediction for the transition form factor in the medium-large region of $Q^2$.

The recent measurement of the muon $g-2$ anomaly continues to defy a Standard Model explanation but can be accommodated within the framework of two-Higgs doublet models, although the pseudoscalar mass must be fairly light. If one further includes extra fermion content in the form of a generation of vectorlike leptons, the allowed parameter range that explains the anomaly is even further extended, and clashes with $B$-decay constraints may be avoided. We show how the muon magnetic moment anomaly can be fit within these models, under the assumption that the vectorlike leptons do not mix with the muon. We update previous analyses and include all theoretical and experimental constraints, including searches for extra scalars. It is shown that the inclusion of vectorlike fermions allows the lepton-specific and muon-specific models to perform much better in fitting the muon’s $g-2$. However, these fits do require the Yukawa coupling between the Higgs and the vectorlike leptons to be large, causing potential problems with perturbativity and unitarity, and thus, models in which the vectorlike leptons mix with the muon may be preferred.

We show that gravitons with energy $E<\mathrm{\Omega }$, where $\mathrm{\Omega }$ is the energy gap a localized nonrelativistic system, can be detected by finite-time interactions with a detector. Our detector is based on a quadrupole moment interaction between the hydrogen atom and the gravitational field in the linearized approximation. In this model, the external agent responsible for switching the interaction on an off inputs energy into the system, which creates a nonzero excitation probability even when the field is in the vacuum state. However, when the gravitational field is in a one-particle state with angular momentum, we obtain excitations due to the field’s particle content. These detector excitations are then associated with the detection of gravitons. We also discuss a possible physical realization of our model where the electromagnetic field plays the role of the external agent.