Dark photons (DPs) produced in the early Universe are well-motivated dark matter (DM) candidates. We show that the recently proposed tunable plasma haloscopes are particularly advantageous for DP searches. While in-medium effects suppress the DP signal in conventional searches, plasma haloscopes make use of metamaterials that enable resonant absorption of the DP by matching its mass to a tunable plasma frequency and thus enable efficient plasmon production. Using thermal field theory, we confirm the in-medium DP absorption rate within the detector. This scheme allows us to competitively explore a significant part of the DP DM parameter space in the DP mass range of $6–400\mu \mathrm{eV}$. If a signal is observed, the observation of a daily or annual modulation of the signal would be crucial to clearly identify the signal as due to DP DM and could shed light on the production mechanism.

We present a minimal left-right symmetric flavor model and analyze the predictions for the neutrino sector. In this scenario, the Yukawa sector is shaped by the dihedral $D_4$ symmetry which leads to correlations for the neutrino mixing parameters. We end up with the four possible solutions within this model. We further analyzed the impact of the upcoming long-baseline neutrino oscillation experiment, DUNE. Due to its high sensitivity, it has been observed that the DUNE will be able to rule out two of the solutions. Finally, the predictions for the neutrinoless double beta decay and the lepton flavor violating process $\mu \to e\gamma$ for the model have also been examined.

Lorentz- and $CPT$-violating models of electrodynamics with Chern-Simons terms are typically plagued by various sorts of instabilities. However, when the Chern-Simons term arises from a slow time variation in a pseudoscalar field with an axionlike electromagnetic coupling, the total energy of the theory is bounded below. We examine the behavior of such a theory, finding that in a systematic power series expansion of the magnetic and pseudoscalar fields, singularities appear in the field profiles. Some of the questionable behavior can be cured by taking a fully nonperturbative approach, but other problematic terms remain. This may be an indication that Cerenkov-like radiation will automatically carry away energy from a moving charge, preventing a charge from moving with uniform velocity over extended distances.

If new physics contains new, heavy strongly interacting particles belonging to irreducible representations of SU(3) different from the adjoint or the (anti)fundamental, it is a nontrivial question to calculate what is the minimum number of quarks/antiquarks/gluons needed to form a color-singlet bound state (“hadron”), or, perturbatively, to form a gauge-invariant operator, with the new particle. Here, I prove that for an SU(3) irreducible representation with Dynkin label $(p,q)$, the minimal number of quarks needed to form a product that includes the (0,0) representation is $2p+q$. I generalize this result to $\mathrm{SU}(N)$, with $N>3$. I also calculate the minimal total number of quarks/antiquarks/gluons that, bound to a new particle in the $(p,q)$ representation, gives a color-singlet state, or, equivalently, the smallest-dimensional gauge-invariant operator that includes quark/antiquark/gluon fields and the new strongly interacting matter field. Finally, I list all possible values of the electric charge of the smallest hadrons containing the new exotic particles and discuss constraints from asymptotic freedom both for QCD and for grand unification embeddings thereof.

We survey the sensitivity of past and present neutrino experiments to MeV-GeV scale vector portal dark matter and find that these experiments possess novel sensitivity that has not yet fully explored. Taking ${\alpha }_D=0.1$ and a dark photon to dark matter mass ratio of three, the combined recast of previous analyses of Big European Bubble Chamber and a projection of $\mathrm{NO}\nu \mathrm{A}$’s sensitivity are found to rule out the scalar thermal target for dark matter masses between 10 and 100 MeV with existing data, while CHARM-II and $\mathrm{MINER}\nu \mathrm{A}$ place somewhat weaker limits. These limits can be improved by off-axis searches using the NuMI beam line and the MicroBooNE, MiniBooNE, or ICARUS detectors and can even begin to probe the Majorana thermal target. We conclude that past and present neutrino facilities can search for light dark matter concurrently with their neutrino program and reach a competitive sensitivity to proposed future experiments.

In this article, we construct the color-singlet-color-singlet type currents to study the scalar and axialvector ${\mathrm{\Xi }}_{cc}{\mathrm{\Sigma }}_c$ dibaryon states with QCD sum rules in details by taking into account both the dibaryon states and two-baryon scattering sates at the hadron side, and examine the existence of the ${\mathrm{\Xi }}_{cc}{\mathrm{\Sigma }}_c$ dibaryon states. Our calculations indicate that the two-baryon scattering states cannot saturate the QCD sum rules, it is necessary to introduce the dibaryon states, the color-singlet-color-singlet type currents couple potentially to the molecular states, not to the two-particle scattering states, the molecular states begin to receive contributions at the order $\mathcal{O}({\alpha }_s^0)$, not at the order $\mathcal{O}({\alpha }_s^2)$.

As a result of continuous developments, the recent experimental searches lead to the observations of new particles at different hadronic channels. Among these hadrons are the excited states of the heavy baryons containing single bottom or charmed quark in their valance quark content. The recently observed ${\mathrm{\Lambda }}_b(6072{)}^0$ state is one of these baryons and possibly $2S$ radial excitation of the ${\mathrm{\Lambda }}_b$ state. Considering this information from the experiment, we conduct a QCD sum rule analysis on this state and calculate its mass and current coupling constant considering it as a $2S$ radially excited ${\mathrm{\Lambda }}_b$ resonance. For completeness, in the analyses, we also compute the mass and current coupling constant for the ground state ${\mathrm{\Lambda }}_b^0$ and its first orbital excitation. We also consider the ${\mathrm{\Lambda }}_c^{+}$ counterpart of each state and attain their mass, as well. The obtained results are consistent with the experimental data as well as existing theoretical predictions.

We discuss the physics of a restricted Weyl symmetry in a curved space-time where a gauge parameter $\mathrm{\Omega }(x)$ of Weyl transformation satisfies a constraint $\square \mathrm{\Omega }=0$. First, we present a model of QED where we have a restricted gauge symmetry in the sense that a $U(1)$ gauge parameter $\theta (x)$ obeys a similar constraint $\square \theta =0$ in a flat Minkowski space-time. Next, it is precisely shown that a global scale symmetry must be spontaneously broken at the quantum level. Finally, we discuss the origin of the restricted Weyl symmetry and show that its symmetry can be derived from a full Weyl symmetry by taking a gauge condition $R=0$ in the BRST formalism.

We study $U(1)$ gauged gravitating compact $Q$-ball, $Q$-shell solutions in a nonlinear sigma model with the target space $\mathbb{C}{P}^N$. The models with odd integer $N$ and a special potential can be parameterized by $N$th complex scalar fields and they support compact solutions. By implementing the $U(1)$ gauge field in the model, the behavior of the solutions becomes complicated than the global model. Especially, they have branches, i.e., two independent solutions with the same shooting parameter. The energy of the solutions in the first branch behaves as $E\sim Q^{5/6}$ for small $Q$, where $Q$ stands for the $U(1)$ Noether charge. For the large $Q$, it gradually deviates from the scaling $E\sim Q^{5/6}$ and, for the $Q$-shells it is $E\sim Q^{7/6}$, which forms the second branch. A coupling with gravity allows for harboring of the Schwarzschild black holes for the $Q$-shell solutions, forming the charged boson shells. The space-time then consists of a charged black hole in the interior of the shell, surrounded by a $Q$-shell, and the outside becomes a Reissner-Nordström space-time. These solutions inherit the scaling behavior of the flat space-time.

A Lorentz symmetry violation aether-type theoretical model is considered to investigate the Casimir effect and the generation of topological mass associated with self-interacting massive scalar fields obeying Dirichlet, Newman, and mixed boundary conditions on two large and parallel plates. By adopting the path integral approach, we find the effective potential at one- and two-loop corrections, which provides both the energy density and the topological mass when taken in the ground state of the scalar field. We then analyze how these quantities are affected by the Lorentz symmetry violation and compare the results with previous ones found in literature.

We extend recent work of Hatsuda on the computation of quasinormal mode frequencies via analytic continuation of bound state energies and Borel-Padé resummation of the Bender-Wu perturbation series to the case of charged fields in the background of Reissner-Nordström black holes. We compare the quasinormal mode frequencies obtained in this manner to calculations using Leaver’s method of continued fractions, and find good agreement for damped modes with the imaginary part remaining finite in the extremal limit. We also present numerical evidence that the frequencies of certain zero-damped modes with the imaginary part tending to zero in the extremal limit can be computed when constructing the Bender-Wu expansion about a peak of the potential inside the outer horizon of the black hole.

We study the dynamics of unstable Reissner-Nordström anti–de Sitter black holes under charged scalar field perturbations in spherical symmetry. We unravel their general behavior and approach to the final equilibrium state. In the first part of this work, we present a numerical analysis of massive charged scalar field quasinormal modes. We identify the known mode families—superradiant modes, zero-damped modes, AdS modes, and the near-horizon mode—and we track their migration under variation of the black hole and field parameters. We show that the zero-damped modes become superradiantly unstable for large RNAdS with large gauge coupling; the leading unstable mode is identified with the near-horizon condensation instability. In the second part, we present results of numerical simulations of perturbed large RNAdS, showing the nonlinear development of these unstable modes. For generic initial conditions, charge and mass are transferred from the black hole to the scalar field, until an equilibrium solution with a scalar condensate is reached. We use results from the linear analysis, however, to select special initial data corresponding to an unstable overtone mode. We find that these data evolve to produce a new equilibrium state—an excited hairy black hole with the scalar condensate in an overtone configuration. This state is, however, unstable, and the black hole eventually decays to the generic end state. Nevertheless, this demonstrates the potential relevance of overtone modes as transients in black hole dynamics.

We study the motion of electrically charged particles, magnetic monopoles, and magnetic dipoles around electrically and magnetically charged stringy black holes. From the analysis of the radius of the innermost stable circular orbit of electrically charged particles, we show that the electric charge $Q$ of stringy black holes can mimic well the spin of Kerr black holes; the black hole magnetic charge $Q_m$ can mimic spins up to $a_{*}\simeq 0.85$ for magnetic dipoles; the magnetic charge parameter $g$ of a magnetic monopole can mimic spins up to $a_{*}\simeq 0.8$. This is due to the destructive character of the magnetic field, and such a result excludes the existence of an appreciable black hole magnetic charge in astrophysical black holes from the observation of rapidly rotating objects with dimensionless spin up to $a_{*}\simeq 0.99$. We then consider the magnetar SGR (PSR) J1745-2900 as a magnetic dipole orbiting the supermassive black hole Sagittarius A* (Sgr A*). We show that Sgr A* may be interpreted as a stringy black hole with magnetic charge $Q_m/M\le 0.4118$.

In a recent work on rotating black hole shadows [Z. Chang and Q.-H. Zhu, Phys. Rev. D 101, 084029 (2020)], we proposed a new approach for calculating size and shape of the shadows in terms of astrometrical observables with respect to finite-distance observers. In this paper, we introduce a distortion parameter for the shadow shapes and discuss the appearance of the shadows of static spherical black holes and Kerr black holes in a uniform framework. We show that the shape of the shadow of a spherical black hole is circular in the view of arbitrary observers, and the size of the shadows tends to be shrunk in the view of a moving observer. The diameter of the shadows is contracted even in the direction perpendicular to the observers’ motion. This seems not to be understood as length contraction effect in special relativity. The shape of Kerr black holes is dependent on motional status of the observers located at finite distance. In spite of this, it is found that there is not a surrounding observer who could view the shape of the Kerr black hole shadows as circularity. These results could be helpful for observation of the Sagittarius A* in the center of the Milky Way, as our Solar System is moving around the center of the black hole.

The so-called black hole shadow is not a silhouette of a black hole but an image of a collapsing object or a white hole. Hence it is nontrivial whether black hole shadows merge with each other when black holes coalesce with each other. In this paper, by analyzing the null geodesic generators of the event horizon in Kastor-Traschen spacetime which describes a coalescence of black boles, we see that observers who will never see a merger of black hole shadows exist.

This paper provides an extended exploration of the inverse-chirp gravitational-wave signals from stellar collapse in massive scalar-tensor gravity reported in [Phys. Rev. Lett. 119, 201103]. We systematically explore the parameter space that characterizes the progenitor stars, the equation of state, and the scalar-tensor theory of the core collapse events. We identify a remarkably simple and straightforward classification scheme of the resulting collapse events. For any given set of parameters, the collapse leads to one of three end states: a weakly scalarized neutron star, a strongly scalarized neutron star, or a black hole, possibly formed in multiple stages. The latter two end states can lead to strong gravitational-wave signals that may be detectable in present continuous-wave searches with ground-based detectors. We identify a very sharp boundary in the parameter space that separates events with strong gravitational-wave emission from those with negligible radiation.

Two of the dominant channels to produce the black-hole binary mergers observed by LIGO and Virgo are believed to be the isolated evolution of stellar binaries in the field and dynamical formation in star clusters. Their relative efficiency can be characterized by a “mixing fraction.” Pair instabilities prevent stellar collapse from generating black holes more massive than about $45{\mathrm{M}}_{\odot }$. This “mass gap” only applies to the field formation scenario, and it can be filled by repeated mergers in clusters. A similar reasoning applies to the binary’s effective spin. If black holes are born slowly rotating, the high-spin portion of the parameter space (the “spin gap”) can only be populated by black-hole binaries that were assembled dynamically. Using a semianalytical cluster model, we show that future gravitational-wave events in either the mass gap, the spin gap, or both can be leveraged to infer the mixing fraction between the field and cluster formation channels.

Electrostatic charge control of isolated free-falling test masses is a key enabling technology for space-based gravitational missions. Contact-free electrostatic charge control can be achieved using photoelectron emission from metal surfaces under illumination with deep UV light. A contact-free method minimizes force disturbances that can perturb measurements or interrupt science operations. In this paper, we present charge control experiments using a gravitational reference sensor geometry relevant to the Laser Interferometer Space Antenna (LISA) gravitational wave observatory in a torsion pendulum apparatus. We use a UV light-emitting diode light source to control the test-mass potential, taking advantage of their high bandwidth to phase lock the light output to 100 kHz electric fields used for capacitive position sensing of the test mass. We demonstrate charge-rate and test-mass potential control by adjustment of the phase of the light with respect to the electric field. We present a simple physics-based model of the discharging process which explains our experimental results in terms of the UV light distribution in the sensor, surface work functions, and quantum yields. A robust fitting method is used to determine the best-fit physical parameters of the model that describe the system.

We explore the link between the chiral symmetry of QCD and the numerical results of the light-front quark model, analyzing both the two-point and three-point functions of the pion. Including the axial-vector coupling as well as the pseudoscalar coupling in the light-front quark model, we discuss the implication of the chiral anomaly in describing the pion decay constant, the pion-photon transition form factor and the electromagnetic form factor of the pion. In constraining the model parameters, we find that the chiral anomaly plays a critical role and the analysis of $F_{\pi \gamma }(Q^2)$ in timelike region is important. Our results indicate that the constituent quark picture is effective for the low and high $Q^2$ ranges implementing the quark mass evolution effect as $Q^2$ grows.

Propagation of photons (or of any spin-1 boson) is of interest in different kinds of nontrivial background, including a thermal bath, or a background magnetic field, or both. We give a unified treatment of all such cases, casting the problem as a matrix eigenvalue problem. The matrix in question is not a normal matrix, and therefore care should be given to distinguish the right eigenvectors from the left eigenvectors. The polarization vectors are shown to be right eigenvectors of this matrix, and the polarization sum formula is seen as the completeness relation of the eigenvectors. We show how this method is successfully applied to different nontrivial backgrounds.