We study analytically the superradiant instability properties of the hydrodynamic vortex model, an asymptotically flat acoustic geometry which, like the spinning Kerr black-hole spacetime, possesses an effective ergoregion. In particular, we derive a compact analytical formula for the complex resonant frequencies that characterize the long-wavelength dynamics of sound modes in this physically interesting acoustic spacetime.

We compute the spectrum of linearized gravitational excitations of black holes with substantial angular momentum in the presence of higher-derivative corrections to general relativity. We do so perturbatively to leading order in the higher-derivative couplings and up to order fourteen in the black hole angular momentum. This allows us to accurately predict quasinormal mode frequencies of black holes with spins up to about 70% of the extremal value. For some higher-derivative corrections, we find that sizable rotation enhances the frequency shifts by almost an order of magnitude relative to the static case.

Identifying a general quasilocal notion of energy-momentum and angular momentum would be an important advance in general relativity with potentially important consequences for mathematical and astrophysical studies in general relativity. In this paper, we study a promising approach to this problem first proposed by Wang and Yau in 2009 based on isometric embeddings of closed surfaces in Minkowski space. We study the properties of the Wang-Yau quasilocal mass in high-accuracy numerical simulations of the head-on collisions of two nonspinning black holes within full general relativity. We discuss the behavior of the Wang-Yau quasilocal mass on constant expansion surfaces, and we compare its behavior with the irreducible mass. We investigate the time evolution of the Wang-Yau quasilocal mass in numerical examples. In addition, we discuss mathematical subtleties in defining the Wang-Yau mass for marginally trapped surfaces.

Joint observations of gravitational waves and electromagnetic counterparts will answer questions about cosmology, gamma-ray bursts, and the behavior of matter at supranuclear densities. The addition of a Southern-hemisphere gravitational-wave observatory to proposed global networks creates a longer baseline, which is beneficial for sky localization. We analyze how an observatory in Australia can enhance the multimessenger astronomy capabilities of future networks. We estimate the number of binary neutron star mergers with joint observations of gravitational waves and kilonova counterparts detectable by the Vera C. Rubin Observatory. First, we consider a network of upgrades to current observatories. Adding an Australian observatory to a three-observatory network (comprising two observatories in the USA and one in Europe) boosts the rate of joint observations from ${2.5}_{-2.0}^{+4.5}{\mathrm{yr}}^{-1}$ to ${5.6}_{-4.5}^{+10}{\mathrm{yr}}^{-1}$ (a factor of two improvement). Then, we consider a network of next-generation observatories. Adding a 20 km Australian observatory to a global network of a Cosmic Explorer 40 km in the USA and an Einstein Telescope in Europe only marginally increases the rate from ${40}_{-32}^{+71}{\mathrm{yr}}^{-1}$ to ${44}_{-35}^{+79}{\mathrm{yr}}^{-1}$ (a factor of 1.1 improvement). The addition of an Australian observatory, however, ensures that at least two observatories are online far more often. When the Cosmic Explorer 40 km is offline for a major upgrade, the Australian observatory increases the joint observation rate from ${0.5}_{-0.4}^{+0.8}{\mathrm{yr}}^{-1}$ to ${38}_{-30}^{+68}{\mathrm{yr}}^{-1}$ (a factor of 82 improvement). When the Einstein Telescope is offline, the joint observation rate increases from ${0.2}_{-0.1}^{+0.3}{\mathrm{yr}}^{-1}$ to ${19}_{-15}^{+34}{\mathrm{yr}}^{-1}$ (a factor of 113 improvement). We sketch out the broader science case for a Southern-hemisphere gravitational-wave observatory.

Reduced order quadrature (ROQ) methods can greatly reduce the computational cost of gravitational wave (GW) likelihood evaluations and therefore greatly speed up parameter estimation analyses, which is a vital part to maximize the science output of advanced GW detectors. In this paper, we do an in-depth study of ROQ techniques applied to GW data analysis and present novel algorithms to enhance different aspects of the ROQ bases’ construction. We improve upon previous ROQ construction algorithms, allowing for more efficient bases in regions of parameter space that were previously challenging. In particular, we use singular value decomposition methods to characterize the waveform space and choose a reduced order basis close to optimal and also propose improved methods for empirical interpolation node selection, greatly reducing the error added by the empirical interpolation model. To demonstrate the effectiveness of our algorithms, we construct multiple ROQ bases ranging in duration from 4 to 256 s for compact binary coalescence waveforms, including precession and higher order modes. We validate these bases by performing likelihood error tests and percent-percent tests and explore the speedup they induce both theoretically and empirically with positive results. Furthermore, we conduct end-to-end parameter estimation analyses on several confirmed GW events, showing the validity of our approach in real GW data.

Neutrinos are known to undergo flavor conversion processes among the three flavors. The fast flavor conversion (FFC) has been the central piece of flavor conversions taking place in core-collapse supernovae (CCSNe) due to its shorter timescale to the completion of flavor conversion compared to other types of flavor conversion. Although the ordinary collisions between neutrinos and matter were once thought to decohere neutrinos and thus damp flavor conversions, it was recently realized that they can also induce the flavor conversion. The linear analysis showed that the so-called collisional flavor instability or CFI occurs in the absence of FFC. In this paper, we investigate if CFI takes place in of the postbounce core of CCSNe, using the results of spherically symmetric Boltzmann simulations of CCSNe for four progenitor models with different masses. We also provide an empirical correlation between matter properties and the occurrence of CFI in optically thick and semitransparent regions; baryon mass density ($\rho$), electron fraction ($Y_e$), and the degeneracy of electron-type neutrinos (${\eta }_{{\nu }_e}$) need to be ${10}^{10}{\mathrm{g}/\mathrm{cm}}^3\lesssim \rho \lesssim {10}^{12}{\mathrm{g}/\mathrm{cm}}^3$, $Y_e\lesssim 0.4$, and ${\eta }_{{\nu }_e}\lesssim 0.5$, respectively. This condition allows us to easily locate the place of possible CFI occurence without detailed stability analyses, which is useful for analyzing CFI in CCSN models phenomenologically.

Due to their cosmological distances high-energy astrophysical sources allow for unprecedented tests of fundamental physics. Gamma-ray bursts (GRBs) comprise among the most sensitive laboratories for exploring the violation of the central physics principle of Lorentz invariance (LIV), by exploiting the spectral time lag of arriving photons. It has been believed that GRB spectral lags are inherently related with their luminosities, and intrinsic source contributions, which remain poorly understood, could significantly impact the LIV results. Using a combined sample of 49 long and short GRBs observed by the Swift telescope, we perform a stacked spectral lag search for LIV effects. We set novel limits on LIV, including limits on quadratic effects, and systematically explore for the first time the impacts of the intrinsic GRB lag-luminosity relation. We find that source contributions can strongly impact resulting LIV tests, modifying their limits by up to a factor of a few. We discuss constraints coming from GRB 221009A.

We consider the effects of a noisy magnetic field background over the fermion propagator in QED, as an approximation to the spatial inhomogeneities and time fluctuations that would naturally arise in certain physical scenarios, such as heavy-ion collisions or the quark-gluon plasma in the early stages of the evolution of the Universe. We considered a classical, finite and uniform average magnetic field background $⟨\mathbf{B}(\mathbf{x}){⟩}_{\mathrm{\Delta }}=\mathbf{B}$, subject to white-noise fluctuations with autocorrelation of magnitude ${\mathrm{\Delta }}_B$. By means of the Schwinger representation of the propagator in the average magnetic field as a reference system, we used the replica formalism to study the effects of the magnetic noise at the mean-field level, in terms of a vector order parameter $Q_j=\mathrm{i}e{\mathrm{\Delta }}_B⟪\overline{\psi }{\gamma }_j\psi {⟫}_{\mathrm{\Delta }}$ whose magnitude represents the ensemble average (over magnetic noise) of the fermion currents. We identified the region where this order parameter acquires a finite value, thus breaking the $U(1)$ symmetry of the model due to the presence of the magnetic noise.

Cascaded Compton scattering and Breit-Wheeler (BW) processes play fundamental roles in high-energy astrophysical sources and laser-driven quantum electrodynamics (QED) plasmas. A thorough comprehension of the polarization transfer in these cascaded processes is essential for elucidating the polarization mechanism of high-energy cosmic gamma rays and laser-driven QED plasmas. In this study, we employ analytical cross-sectional calculations and Monte Carlo (MC) numerical simulations to investigate the polarization transfer in the cascade of electron-seeded inverse Compton scattering (ICS) and BW process. Theoretical analysis indicates that the polarization of background photons can effectively transfer to final-state particles in the first-generation cascade due to helicity transfer. Through MC simulations involving polarized background photons and nonpolarized seed electrons, we reveal the characteristic polarization curves as a function of particle energy produced by the cascaded processes of ICS and BW pair production. Our results demonstrate that the first-generation photons from ICS exhibit the nondecayed stair-shape polarization curves, in contrast to the linearly decayed ones of the first-generation electrons. Interestingly, this polarization curve trend can be reversed in the second-generation cascade, facilitated by the presence of polarized first-generation BW pairs with fluctuant polarization curves. The cascade culminates with the production of second-generation BW pairs, due to diminished energy of second-generation photons below the threshold of the BW process. Our findings provide crucial insights into the cascaded processes of Compton scattering and BW process, significantly contributing to the understanding and further exploration of laser-driven QED plasma creation in laboratory settings and high-energy astrophysics research.

A fluid-dynamic approach to charm-quark diffusion in the quark-gluon plasma (QGP) is developed for the first time. Results for integrated yields and momentum distributions of charmed hadrons obtained with a fluid-dynamic description for the dynamics of the QGP coupled to an additional heavy-quark-antiquark current are shown. In addition to the thermodynamic equation of state, this description uses a heavy-quark diffusion constant which we take from lattice QCD calculations. The results describe the experimental data measured at the LHC at the center-of-mass energy of $\sqrt{s_{\mathrm{NN}}}=5.02\mathrm{TeV}$ up to $p_{\mathrm{T}}\sim 4–5\mathrm{GeV}/c$, showing that charm quarks undergo a very fast hydrodynamization in the medium created by ultrarelativistic heavy-ion collisions.

The Casimir friction phenomenon involves the excitation of microscopic degrees of freedom in a medium, as a result of the relative motion of another object. When we consider a planar medium in the presence of a moving atom, excitations are expected to have a nontrivial spatial dependence, given the preferential direction set up by the atom’s trajectory. Here, for a medium consisting of planar graphene, we evaluate the spatial (angular) dependence of such an effect. Using the Dirac field description, that phenomenon appears as the creation of electron-hole pairs, namely, in quantum electrodynamics terms, to pair creation. We present explicit results on the angular dependence of the fermion emission probability, as a function of the atom’s velocity, and the distance of the trajectory to the sheet. This microscopic, i.e., local aspect, complements previous work on global features, like the total frictional force, which we also evaluate.

Several pulsar timing arrays including NANOGrav, EPTA, PPTA, and CPTA have recently reported the observation of a stochastic background of gravitational wave spectrum in the nanohertz frequencies. An inflationary interpretation of this observation is challenging from various aspects. We report that such a signal can arise from the Chern-Simons coupling in axion inflation, where a pseudoscalar inflaton couples to a (massive) $U(1)$ gauge field, leading to efficient production of a transverse gauge mode. Such tachyonic particle production during inflation exponentially enhances the primordial perturbations and leads to a unique parity-violating gravitational wave spectrum, that remains flat near the CMB scales but becomes blue-tilted at smaller scales. We identify the parameter space consistent with various cosmological constraints and show that the resultant gravitational wave signals can provide extra contribution on top of the standard astrophysical contribution from inspiraling supermassive black hole binaries towards explaining the observed excess at NANOGrav. The parity-violating nature of the signal can be probed in future interferometers, distinguishing it from most other new physics signals attempting to explain the NANOGrav result.

It is shown that the solution for $B-L$ gauge symmetry with $B-L=-4,-4,+5$ assigned for three right-handed neutrinos, respectively, reveals a novel scotogenic mechanism with implied matter parity for neutrino mass generation and dark matter stability. Additionally, the world with two-component dark matter is hinted.

The seesaw mechanism is the most attractive mechanism to explain the small neutrino masses, which predicts the neutrinoless double beta decay ($0\nu \beta \beta$) of the nucleus. Thus the discovery of $0\nu \beta \beta$ is extremely important for future particle physics. However, the present data on the neutrino oscillation is not sufficient to predict the value of $m_{ee}$ as well as the neutrino mass $m_{\nu }^i$. In this short article, by adopting a simple and consistent Froggatt-Nielsen model, which can well explain the observed masses and mixing angles of quark and lepton sectors, we calculate the distribution of $m_{ee}$ and $m_{\nu }^i$. Interestingly, a relatively large part of the preferred parameter space can be detected in the near future.

Recently, pulsar timing array experiments reported the observation of a stochastic gravitational wave background in the nanohertz range frequency band. We show that such a signal can be originated from a cosmological first-order phase transition (PT) within a well-motivated heavy (visible) QCD axion model. Considering the Peccei-Quinn symmetry breaking at the TeV scale in the scenario, we find a supercooled PT, in the parameter space of the model, prolonging the PT with the reheating temperature at the GeV scale.

The two gravitational form factors of the pion, $A^{\pi }(t)$ and $D^{\pi }(t)$, are computed as functions of the momentum transfer squared $t$ in the kinematic region $0\le -t<2{\mathrm{GeV}}^2$ on a lattice QCD ensemble with quark masses corresponding to a close-to-physical pion mass $m_{\pi }\approx 170\mathrm{MeV}$ and $N_f=2+1$ quark flavors. The flavor decomposition of these form factors into gluon, up/down light-quark, and strange-quark contributions is presented in the $\overline{\mathrm{MS}}$ scheme at energy scale $\mu =2\mathrm{GeV}$, with renormalization factors computed nonperturbatively via the RI-MOM scheme. Using monopole and $z$-expansion fits to the gravitational form factors, we obtain estimates for the pion momentum fraction and $D$ term that are consistent with the momentum fraction sum rule and the next-to-leading order chiral perturbation theory prediction for $D^{\pi }(0)$.

We study the molecular probability of the $X(3872)$ in the $D^0{\overline{D}}^{*0}$ and $D^{+}{D}^{*-}$ channels in several scenarios. One of them assumes that the state is purely due to a genuine nonmolecular component. However, it gets unavoidably dressed by the meson components to the point that in the limit of zero binding of the $D^0{\overline{D}}^{*0}$ component becomes purely molecular. Yet, the small but finite binding allows for a nonmolecular state when the bare mass of the genuine state approaches the $D^0{\overline{D}}^{*0}$ threshold, but, in this case the system develops a small scattering length and a huge effective range for this channel in flagrant disagreement with present values of these magnitudes. Next we discuss the possibility to have hybrid states stemming from the combined effect of a genuine state and a reasonable direct interaction between the meson components, where we find cases in which the scattering length and effective range are still compatible with data, but even then the molecular probability is as big as 95%. Finally, we perform the calculations when the binding stems purely from the direct interaction between the meson-meson components. In summary we conclude, that while present data definitely rule out the possibility of a dominant nonmolecular component, the precise value of the molecular probability requires a more precise determination of the scattering length and effective range of the $D^0{\overline{D}}^{*0}$ channel, as well as the measurement of these magnitudes for the $D^{+}{D}^{*-}$ channel which have not been determined experimentally so far.

We investigate the tetraquark bound states that are manifestly exotic using three distinct few-body methods; Gaussian expansion method (GEM), resonating group method (RGM), and diffusion Monte Carlo (DMC). We refer to manifestly exotic states that do not involve a mixture with the conventional mesons through the creation and annihilation of $n\overline{n}$, where $n=u$, $d$. Our calculations are conducted with two types of quark models; the pure constituent quark model featuring one-gluon-exchange interactions and confinement interactions, and the chiral constituent quark model, supplemented by extra one-boson-exchange interactions. This study represents a comprehensive benchmark test of various few-body methods and quark models. Our findings reveal the superiority of GEM over RGM and DMC methods based on present implements for the tetraquark bound states. Additionally, we observe a tendency for the chiral quark model to overestimate the binding energies. We systematically explore the fully, triply, doubly, and singly heavy tetraquark states with $J^P=0^{+},1^{+},2^{+}$, encompassing over 150 states in total. We successfully identify several bound states, including $[cc\overline{n}\overline{n}{]}_{J^P=1^{+}}^{I=0}$, $[bb\overline{n}\overline{n}{]}_{J^P=1^{+}}^{I=0}$, $[bc\overline{n}\overline{n}{]}_{J^P=0^{+},1^{+},2^{+}}^{I=0}$, $[bs\overline{n}\overline{n}{]}_{J^P=0^{+},1^{+}}^{I=0}$, $[cs\overline{n}\overline{n}{]}_{J^P=0^{+}}^{I=0}$, and $[bb\overline{n}\overline{s}{]}_{J^P=1^{+}}$, all found to be bound states below the dimeson thresholds.

Collective modes within a hot quantum chromodynamics (QCD) medium are obtained from the polarization tensor, considering both constant and time-varying electromagnetic fields. In both scenarios, five complex modes emerge, reliant on the wave vector ($k$), with electrical conductivity exerting significant influence. The impact of the modes on the energy loss of heavy quarks in the hot QCD medium with a background electromagnetic field has been studied by obtaining the induced electric field in terms of the polarization tensor while invoking Wong’s equations. The findings are seen to be consistent with analogous approaches, reinforcing the significance of the results.

A new approach to partial widths is proposed through the analytical extension of the wave function in momentum space. By including the residue of the wave function, the Schrödinger equation is extended to the second Riemann sheet. As a result, the partial width is associated with the pole of the wave function. The resonance wave function is convergent in momentum space and can be used to evaluate other observables. This approach is applied to a coupled-channel analysis for $P_c$ states, involving the contact interactions and one-pion-exchange potential with the three-body effects. Under the reasonable assumption that the off-diagonal contact interactions are small, the $J^P$ quantum numbers of the $P_c(4440)$ and the $P_c(4457)$ are ${\frac{1}{2}}^{-}$ and ${\frac{3}{2}}^{-}$ respectively. The low energy constants are fitted using the experimental masses and widths as input. The $P_c(4312)$ is found to decay mainly to ${\mathrm{\Lambda }}_c{\overline{D}}^{*}$, while the branching ratios of the $P_c(4440)$ and $P_c(4457)$ in different channels are comparable. Three additional $P_c$ states at 4380 MeV, 4504 MeV and 4516 MeV, together with their branching ratios, are predicted. Additionally, a deduction for the revised one-pion-exchange potential involving the on-shell three-body intermediate states is provided.