We treat prospects for multimessenger astronomy with giant flares (GFs), a rare transient event featured by magnetars that can be as luminous as a hundred of the brightest supernovae ever observed. The beamed photons could correlate with an axion counterpart via resonant conversion in the magnetosphere. In a realistic parameter space, we find that the sensitivity limit to Galactic GFs for currently viable experiments is ${\mathrm{g}}_{\varphi \gamma }\gtrsim \text{several}\times {10}^{-13}{\mathrm{GeV}}^{-1}$ and ${\mathrm{g}}_{\varphi e}\gtrsim \mathrm{few}\times {10}^{-12}$. We rule out the compatibility of axion flares with the recent XENON1T excess only due to the time persistence of the signal.

We investigate the finite-size effects on the transition temperature associated with the quark-gluon plasma (QGP) formation. From a percolation perspective, the onset of the QGP in high-energy collisions occurs when the spanning cluster of color strings emerges. The principal result presented here is the finite-size effects on the transition temperature expressed as a power law in terms of the nucleon number. We found that the transition temperature is higher for small systems than for large ones. It means that minimal triggering conditions events in pp collisions require about 20 times higher energies than AuAu-PbPb collisions. We also estimate the center-of-mass energy required for the QGP formation as a function of the nucleon number. Our results are consistent with the minimal center-of-mass energies at which the QGP has been observed.

In this article we introduce a new operator representing the three-dimensional scalar curvature in loop quantum gravity. Our construction does not apply to the entire kinematical Hilbert space of loop quantum gravity; instead, the operator is defined on the Hilbert space of a fixed cubical graph. The starting point of our work is to write the spatial Ricci scalar classically as a function of the densitized triad and its $SU(2)$-covariant derivatives. We pass from the classical expression to a quantum operator through a regularization procedure, in which covariant derivatives of the triad are discretized as finite differences of gauge covariant flux variables on the cubical lattice provided by the graph. While more work is needed in order to extend our construction to encompass states based on all possible graphs, the operator presented here can be applied in models such as quantum-reduced loop gravity and effective dynamics, which are derived from the kinematical framework of full loop quantum gravity, and are formulated in terms of states defined on cubical graphs.

It is widely accepted that curvature singularity resolution should be a feature of quantum gravity. We present a class of time-dependent asymptotically flat spherically symmetric metrics that model gravitational collapse in quantum gravity. The metrics capture intuitions associated with the dynamics of singularity resolution, and horizon formation and evaporation following a matter bounce. A parameter in the metric associated with the speed of the bounce determines black hole lifetime as a power of its mass; this includes the Hawking evaporation time $M^3$.

We study the Hayden-Preskill thought experiment at finite temperature and obtain the decoupling condition that the information thrown into an old black hole can be extracted by decoding the Hawking radiation. We then consider the decoding Hayden-Preskill protocol at finite temperature assuming the observer outside the black hole who has the access to the full radiation and the unitary dynamics of the black hole. We also consider the cases when the Hawking radiation has noise and decoherence in the storage. The decoding probabilities and the corresponding fidelities are calculated. It is shown that for all the three cases we have considered, the decoding fidelities are less than unity in general. This result indicates that at finite temperature, the decoding strategy and the recovery algorithm are harder to realize than that at infinite temperature.

We calculate the eccentricity dependence of the high-order post-Newtonian (PN) expansion of the spin-precession invariant $\psi$ for eccentric-orbit extreme-mass-ratio inspirals with a Schwarzschild primary. The series is calculated in first-order black hole perturbation theory through direct analytic expansion of solutions in the Regge-Wheeler-Zerilli formalism, using a code written in Mathematica. Modes with small values of $l$ are found via the Mano-Suzuki-Takasugi analytic function expansion formalism for solutions to the Regge-Wheeler equation. Large-$l$ solutions are found by applying a PN expansion ansatz to the Regge-Wheeler equation. Previous work has given $\psi$ to 9.5PN order and to order $e^2$ (i.e., the near circular orbit limit). We calculate the expansion to 9PN but to $e^{16}$ in eccentricity. It proves possible to find a few terms that have closed-form expressions, all of which are associated with logarithmic terms in the PN expansion. We also compare the numerical evaluation of our PN expansion to prior numerical calculations of $\psi$ in close orbits to assess its radius of convergence. We find that the series is not as rapidly convergent as the one for the redshift invariant at $r\simeq 10M$ but still yielding $\sim 1\%$ accuracy for eccentricities $e\lesssim 0.25$.

Building upon the Noether charge formalism of Iyer and Wald, we derive a variational formula for spacetimes admitting a Killing vector field for a generic energy-momentum distribution with compact support. Applying this general result to the particular case of a binary system of spinning compact objects moving along an exactly circular orbit, modeled using the multipolar gravitational skeleton formalism, we derive a first law of compact binary mechanics at dipolar order. We prove the equivalence of this new result with the canonical Hamiltonian first law previously derived for binary systems of spinning compact objects, for spins collinear with the orbital angular momentum. This paper paves the way to an extension of the first law of binary mechanics to the next quadrupolar order, thereby accounting for the spin- and tidally induced deformability of the compact bodies.

We present a new method designed to avoid numerical challenges that have impeded calculation of the Lorenz gauge self-force acting on a compact object inspiraling into a Kerr black hole. This type of calculation is valuable in creating waveform templates for extreme mass-ratio inspirals, which are an important source of gravitational waves for the upcoming Laser Interferometer Space Antenna mission. Prior hyperbolic partial differential equation (PDE) formulations encountered numerical instabilities involving unchecked growth in time; our new method is based on elliptic PDEs, which do not exhibit instabilities of that kind. For proof of concept, we calculate the self-force acting on a scalar charge in a circular orbit around a Kerr black hole. We anticipate this method will subsequently facilitate calculation of first-order Lorenz gauge Kerr metric perturbations and self-force, which could serve as a foundation for second-order Kerr self-force investigations.

We perform an analysis of the ultraviolet divergences of the quantum nonprojectable Hořava gravity. We work the quantum-field theory directly in the Hamiltonian formalism provided by the Batalin-Fradkin-Vilkovisky quantization. In this way the second-class constraints can be incorporated into the quantization. A known local gauge-fixing condition leads to a local canonical Lagrangian. Although the canonical fields acquire regular propagators, irregular propagators persist dangerous subdivergences. We show that all these loops cancel exactly between them due to a perfect matching between the propagators and vertices of the fields and ghosts forming the loops. The rest of the divergences behave similarly to the projectable theory, they can be removed by local counterterms. This result points to the renormalization of the nonprojectable Hořava theory.

LISA will detect gravitational waves (GWs) in the milli-Hz frequency band in space. Time-delay interferometry (TDI) is developed to suppress laser frequency noise beneath the acceleration noise and optical metrology noise. To identify stochastic GW signals, we need to characterize these noise components entangled in TDI data streams. In this work, we investigate noises characterization by combining the first-generation TDI channels from Michelson and Relay configurations. The Michelson channels are helpful to characterize acceleration noises in the lower frequency band, and the Relay configuration could effectively resolve optical path noises in the higher frequencies. Synergy could be achieved from their combination to determine these instrumental noises. Based on the characterized noises, we further reconstruct the power spectrum of noise in the selected TDI channel. Two cases are performed to characterize the spectrum shape of a stochastic GW signal. For a modeled signal, its parameter(s) could be directly estimated from the TDI data, and its spectrum could be recovered from the inferred values. And for an unexpected signal, its spectrum may be recognized and retrieved from noise-subtracted residual in which its power spectral density surpasses the noise level.

We discuss gravitational waves (GWs) induced by a heavy spectator field that starts to oscillate during inflation. During the oscillation of the spectator field, its effective mass can also oscillate in some potentials. This mass oscillation can resonantly amplify the spectator field fluctuations. We show that these amplified fluctuations can induce large GWs, which could be investigated by future gravitational wave observations. This kind of induced GW can be produced even if the spectator field does not have any interaction with other fields except for the gravitational interaction.

Multimessenger astronomy with gravitational waves is a blooming area whose limits are not clear. After the first detection of binary black hole merger and the famous event GW170817 and its electromagnetic counterpart, the compact-object astrophysical community is starting to grasp the physical implications of such an event and trying to improve numerical models to compare with future observations. Moreover, recent detections made by the NICER collaboration increased the tension between several theoretical models used to describe matter in the inner core of compact objects. In this paper, we focus on quadrupolar purely spacetime $wI$ modes of oscillating compact objects described using a wide range of hybrid equations of state able to include several theoretical possibilities of exotic matter in the inner core of such stars. We study the case in which a sharp first order hadron-quark phase transition occurs and explore the scenarios of rapid and slow phase conversions at the interface. We put special attention on the validity of universal relationships for the oscillation frequency and damping time that might help unravel the mysteries hidden at the inner cores of compact objects. We show that, within the slow conversion regime where extended branches of hybrid stars appear, universal relationships for $wI$ modes proposed in the literature do not hold.

In this paper we present a study of some relevant steps of the hierarchical frequency-Hough (FH) pipeline, used within the LIGO and Virgo Collaborations for wide-parameter space searches of continuous gravitational waves (CWs) emitted, for instance, by spinning neutron stars (NSs). Because of their weak expected amplitudes, CWs have not been still detected so far. These steps, namely the spectral estimation, the peakmap construction and the procedure to select candidates in the FH plane, are critical as they contribute to determine the final search sensitivity. Here, we are interested in investigating their behavior in the (presently quite) extreme case of signal clusters, due to many and strong CW sources, emitting gravitational waves (GWs) within a small (i.e., $<1\mathrm{Hz}$ wide) frequency range. This could happen for some kinds of CW sources detectable by next generation detectors, like LISA, Einstein Telescope, and Cosmic Explorer. Moreover, this possibility has been recently raised even for current Earth-based detectors, in some scenarios of CW emission from ultralight boson clouds around stellar mass black holes (BHs). We quantitatively evaluate the robustness of the FH analysis procedure, designed to minimize the loss of single CW signals, under the unusual situation of signal clusters. Results depend mainly on how strong in amplitude and dense in frequency the signals are, and on the range of frequency they cover. We show that indeed a small sensitivity loss may happen in presence of a very high mean signal density affecting a frequency range of the order of one Hertz, while when the signal cluster covers a frequency range of one tenth of Hertz, or less, we may actually have a sensitivity gain. Overall, we demonstrate the FH to be robust even in presence of moderate-to-large signal clusters.

The new strange pentaquarks observed by LHCb are very likely hadronic molecules consisting of ${\mathrm{\Xi }}_c\overline{D}$ and ${\mathrm{\Xi }}_c{\overline{D}}^{*}$. We discuss the experimental evidence supporting this conclusion, pointing out the similarities and differences with the $P_c(4312)$, $P_c(4440)$ and $P_c(4457)$ pentaquarks in the nonstrange sector. The latter clearly are hadronic molecules consisting of ${\mathrm{\Sigma }}_c\overline{D}$ and ${\mathrm{\Sigma }}_c{\overline{D}}^{*}$. Following this line of thought, we predict three additional strange pentaquarks consisting of ${\mathrm{\Xi }}_c^{\prime }\overline{D}$ and ${\mathrm{\Xi }}_c^{\prime }{\overline{D}}^{*}$. The masses of these states are expected to be shifted upward by $M({\mathrm{\Xi }}_c^{\prime })-M({\mathrm{\Xi }}_c)\approx 110\mathrm{MeV}$ with respect to the corresponding known strange pentaquarks.

Millicharged particles (MCPs) arise in many well-motivated extensions of the Standard Model and are a popular subject for experimental searches. We investigate the attenuation of the MCP flux produced at accelerator experiments due to their interactions in the media and demonstrate that it can significantly affect the final sensitivity to the MCP parameter space, leaving its essential part still unexplored. Applying our analysis to the SLACmQ experiment [A. A. Prinz et al., Phys. Rev. Lett. 81, 1175 (1998)], we correct their published exclusion bounds; the obtained results are numerically in a good accordance with A. A. Prinz [Report No. SLAC-R-569]. We also show that this newly reopened area with the MCP masses in the range ${10}^{-4}\mathrm{eV}–1\mathrm{GeV}$ and charges $\gtrsim {10}^{-5}e$ can be effectively probed by the $\mathrm{NA}64e$ experiment at the CERN SPS. Light MCPs are mostly produced by a virtual photon in electron scattering off nuclei. The main source of heavy MCP is decays of vector mesons, produced by the electrons on nuclei.

We study the feebly-interacting massive particle dark matter whose production processes are significantly affected by the phase evolution and the complicated thermal corrections to the vector boson. We calculate the freeze-in processes to obtain the correct dark matter relic density by enumerating all the possible $1\leftrightarrow 2$ and $2\leftrightarrow 2$ processes. The predicted gravitational waves emitted by the first-order phase transitions and the cosmic strings are evaluated.

The existence of large extra dimensions can be probed in various neutrino experiments. We analyze several neutrino datasets in a model with a dominant large extra dimension. We show that the gallium anomaly can be explained with neutrino oscillations induced by the large extra dimension, but the region of parameter space that is preferred by the gallium anomaly is in tension with the bounds from reactor rate data, as well as the data of Daya Bay and MINOS. We also present bounds obtained from the analysis of the KATRIN data. We show that current experiments can put strong bounds on the size $R_{\mathrm{ED}}$ of the extra dimension: $R_{\mathrm{ED}}<0.20\mu \mathrm{m}$ and $R_{\mathrm{ED}}<0.10\mu \mathrm{m}$ at 90% C.L. for normal and inverted ordering of the standard neutrino masses, respectively.

In this work we demonstrate that the mixed gravitational and scalar sectors of the five-dimensional Goldberger-Wise (GW) model, in which the size of a warped extra dimension is dynamically determined, has a “hidden” dual $N=2$ supersymmetric structure. This symmetry structure, a generalization of one found in the unstabilized Randall-Sundrum model, is a result of the spontaneously broken five-dimensional diffeomorphism invariance of the underlying gravitational theory. The supersymmetries relate the properties of the spin-1 and spin-0 modes “eaten” by the massive spin-2 Kaluza-Klein states of the theory to the mode functions of the spin-2 modes. Because the symmetries relate the couplings and masses of the massive spin-2 states to those of the tower of physical spin-0 states of the GW model, they enable us to analytically prove the sum rule relations which ensure the tree-level scattering amplitudes of the massive spin-2 states will grow no faster than $\mathcal{O}(s)$. The analysis given here also explains the unconventional forms of the spin-0 mode equation, boundary condition(s), and normalization found in the GW model.

The extension of Standard Model made by inclusion of additional $U(1)$ gauge $L_{\mu }-L_{\tau }$ symmetry can explain the difference between the measured and the predicted value of the muon magnetic moment and solve the tension in $B$ meson decays. This model predicts the existence of a new, light $Z^{\prime }$ vector boson, predominantly coupled to second and third generation leptons, whose interaction with electrons is due to a loop mechanism involving muons and taus. In this work, we present a rigorous evaluation of the upper limits in the $Z^{\prime }$ parameter space, obtained from the analysis of the data collected by the NA64-$e$ experiment at CERN SPS, that performed a search for light dark matter with $2.84\times {10}^{11}$ electrons impinging with 100 GeV on an active thick target. The resulting limits touch the muon $g-2$ preferred band for values of the $Z^{\prime }$ mass of order of 1 MeV, while the sensitivity projections for the future high-statistics NA64-$e$ runs demonstrate the power of the electrons/positron beam approach in this theoretical scenario.