We describe a model that generates first order adiabatic extreme mass ratio inspiral waveforms for quasi-circular equatorial inspirals of compact objects into rapidly rotating (near-extremal) black holes. Using our model, we show that LISA could measure the spin parameter of near-extremal black holes (for $a\gtrsim 0.9999$) with extraordinary precision, $\sim 3-4$ orders of magnitude better than for moderate spins, $a\sim 0.9$. Such spin measurements would be one of the tightest measurements of an astrophysical parameter within a gravitational wave context. Our results are primarily based off a Fisher matrix analysis, but are verified using both frequentist and Bayesian techniques. We present analytical arguments that explain these high spin precision measurements. The high precision arises from the spin dependence of the radial inspiral evolution, which is dominated by geodesic properties of the secondary orbit, rather than radiation reaction. High precision measurements are only possible if we observe the exponential damping of the signal that is characteristic of the near-horizon regime of near-extremal inspirals. Our results demonstrate that, if such black holes exist, LISA would be able to successfully identify rapidly rotating black holes up to $a=1-{10}^{-9}$, far past the Thorne limit of $a=0.998$.

Using exclusively the 777 full numerical waveforms of the third binary black hole RIT catalog, we reanalyze the ten black hole merger signals reported in LIGO/Virgo’s O1/O2 observation runs. We obtain binary parameters, extrinsic parameters, and the remnant properties of these gravitational waves events which are consistent with, but not identical to, previously presented results. We have also analyzed three additional events (GW170121, GW170304, GW170727) reported by Venumadhav, Zackay, Roulet, Dai, and Zaldarriaga [Phys. Rev. D 101, 083030 (2020)] and found closely matching parameters. We finally assess the accuracy of our waveforms with convergence studies applied to O1/O2 events and found them adequate for current estimation of parameters.

In this note, we investigate outcomes of a symplectic formula for the gravitational wave charges in general relativity linearized around the de Sitter spacetime. We derive their explicit form at ${\mathcal{I}}^{+}$ in the Bondi frame, compare with the connected Noether expression, and analyze their gauge dependence, which allows us to fix unambiguously the boundary terms. We also discuss the minimal requirements needed to be imposed on the initial data in order to have finite values of charges. Furthermore, we analyze the transformation laws of the energy upon the action of the de Sitter group and discuss their physical interpretation. Finally, we calculate their flux through a cosmological horizon instead of ${\mathcal{I}}^{+}$. We show that in the limit $\mathrm{\Lambda }\to 0$, one recovers the Trautman-Bondi formula, strengthening a recent proposal that one should choose a null surface as a more natural boundary for the astrophysical systems in the presence of the cosmological constant.

Though the cosmic censorship conjecture states that spacetime singularities must be hidden from an asymptotic observer by an event horizon, naked singularities can form as the end product of a gravitational collapse under suitable initial conditions, so the question of how to observationally distinguish such naked singularities from standard black hole spacetimes becomes important. In the present paper, we try to address this question by studying the ringdown profile of the Janis-Newman-Winicour (JNW) naked singularity under axial gravitational perturbation. The JNW spacetime has a surfacelike naked singularity that is sourced by a massless scalar field and reduces to the Schwarzschild solution in absence of the scalar field. We show that for low strength of the scalar field, the ringdown profile is dominated by echoes which mellows down as the strength of the field increases to yield characteristic quasinormal mode frequency of the JNW spacetime.

Space-based gravitational-wave detectors consist of a triangle of three spacecraft, which makes it possible to detect polarization modes of gravitational waves due to the motion of the detectors in space. In this paper we explore the ability of Taiji to detect the polarization modes in the parametrized post-Einsteinian framework. Assuming massive black hole binaries with the total mass of $M=4\times {10}^5{M}_{\odot }$ at redshift of $z=1$, we find that Taiji can measure the dipole and quadruple emission ($\mathrm{\Delta }{\alpha }_D/{\alpha }_D$ and $\mathrm{\Delta }{\alpha }_Q/{\alpha }_Q$) with the accuracy of up to $\sim 0.04\%$, with the fiducial value of ${\alpha }_D=0.001$, the scalar transverse and longitudinal modes ($\mathrm{\Delta }{\alpha }_B$ and $\mathrm{\Delta }{\alpha }_L$) up to $\sim 0.01$, and the vector modes ($\mathrm{\Delta }{\alpha }_V$) up to $\sim 0.0005$.

It has been shown that the observed dark matter (DM) abundance can be produced by amplification of quantum fluctuations of an energetically subdominant scalar field during inflation. In this paper, we study the robustness of this “spectator dark matter” scenario to changes in the expansion rate of the early Universe. Compared to the standard radiation-dominated (RD) scenario, two aspects will change: the DM energy density evolves differently as a function of time, and also the DM isocurvature perturbation spectrum will be different from the result in the RD case. These can impose sizeable changes to the values of model parameters which allow the field to constitute all DM while simultaneously satisfying all observational constraints. We study both free and self-interacting DM in scenarios with nonstandard expansion and quantify the changes to the cases with a standard cosmological history. We also discuss testability of the scenario through primordial DM isocurvature and non-Gaussianity.

We study the possible occurrence of the hadron-quark phase transition (PT) during the merging of neutron star binaries by hydrodynamical simulations employing a set of temperature-dependent hybrid equations of state (EOSs). Following previous work, we describe an unambiguous and measurable signature of deconfined quark matter in the gravitational-wave (GW) signal of neutron star binary mergers including equal-mass and unequal-mass systems of different total binary mass. The softening of the EOS by the PT at higher densities, i.e., after merging, leads to a characteristic increase of the dominant postmerger GW frequency $f_{\mathrm{peak}}$ relative to the tidal deformability $\mathrm{\Lambda }$ inferred during the premerger inspiral phase. Hence, measuring such an increase of the postmerger frequency provides evidence for the presence of a strong PT. If the postmerger frequency and the tidal deformability are compatible with results from purely baryonic EOS models yielding very tight relations between $f_{\mathrm{peak}}$ and $\mathrm{\Lambda }$, a strong PT can be excluded up to a certain density. We find tight correlations of $f_{\mathrm{peak}}$ and $\mathrm{\Lambda }$ with the maximum density during the early postmerger remnant evolution. These GW observables thus inform about the density regime which is probed by the remnant and its GW emission. Exploiting such relations, we devise a directly applicable, concrete procedure to constrain the onset density of the QCD PT from future GW measurements. We point out two interesting scenarios: if no indications for a PT are inferred from a GW detection, our procedure yields a lower limit on the onset density of the hadron-quark PT. On the contrary, if a merger event reveals evidence for the occurrence of deconfined quark matter, the inferred GW parameters set an upper limit on the PT onset density. Both scenarios would thus have strong implications for high-density matter physics, e.g., determining the range of validity of nuclear physics and constraining the properties for quark deconfinement. These prospects demonstrate the importance of simultaneously measuring pre- and postmerger GW signals to exploit the complementarity of the information encoded in both phases. Hence, our work stresses the value added by dedicated high-frequency GW instruments.

Here, we calculate the effects of astrophysical gravitational waves (GWs) on the travel times of proton bunch test masses in circular particle accelerators. We show that a high-precision proton bunch time-tagging detector could turn a circular particle accelerator facility into a GW observatory sensitive to millihertz GWs. We comment on sources of noise and the technological feasibility of ultrafast single-photon detectors by conducting a case study of the Large Hadron Collider at CERN.

Pulsar timing arrays (PTAs) are currently the only experiments directly sensitive to gravitational waves with decade-long periods. Within the next five to ten years, PTAs are expected to detect the stochastic gravitational-wave background (SGWB) collectively sourced by inspiraling supermassive black hole binaries. It is expected that this background is mostly isotropic, and current searches focus on the monopole part of the SGWB. Looking ahead, anisotropies in the SGWB may provide a trove of additional information on both known and unknown astrophysical and cosmological sources. In this paper, we build a simple yet realistic Fisher formalism for anisotropic SGWB searches with PTAs. Our formalism is able to accommodate realistic properties of PTAs and allows simple and accurate forecasts. We illustrate our approach with an idealized PTA consisting of identical, isotropically distributed pulsars. In a companion paper, we apply our formalism to current PTAs and show that it can be a powerful tool to guide and optimize real data analysis.

Very recently, the XENON1T Collaboration has reported an intriguing electron recoil excess, which may imply light dark matter. To interpret this anomaly, we propose the atmospheric dark matter (ADM) from the inelastic collision of cosmic rays (CRs) with the atmosphere. Because of the boost effect of high-energy CRs, we show that the light ADM can be fast moving and successfully fit the observed electron recoil spectrum through the ADM-electron scattering process. Meanwhile, our ADM predicts the scattering cross section ${\sigma }_e\sim \mathcal{O}({10}^{-38}-{10}^{-39}{\mathrm{cm}}^2$) and thus can evade other direct detection constraints. The search for light meson rare decays, such as $\eta \to \pi +{\cancel{E}}_T$, would provide a complementary probe of our ADM in the future.

We propose a fully nonperturbative method to compute inelastic lepton-nucleon ($\ell N$) scattering cross sections using lattice quantum chromodynamics (QCD). The method is applicable even at low energies, such as the energy region relevant for the recent and future neutrino-nucleon scattering experiments, for which perturbative analysis is invalidated. The basic building block is the forward Compton-scattering amplitude, or the hadronic tensor, computed on a Euclidean lattice. A total cross section is constructed from the hadronic tensor by multiplying a phase space factor and integrating over the energy and momentum of final hadronic states. The energy integral that induces a sum over all possible final states is performed implicitly by promoting the phase space factor to an operator written in terms of the transfer matrix on the lattice. The formalism is imported from that of the inclusive semileptonic $B$ meson decay [P. Gambino and S. Hashimoto, Phys. Rev. Lett. 125, 032001 (2020)] and generalized to compute the $\ell N$ scattering cross sections and their moments, as well as the virtual correction to the nuclear $\beta$ decay.

The $D$-wave admixture in quarkonium wave functions is acquired from the photonlike structure of $V\to Q\overline{Q}$ transition in the light-front frame widely used in the literature. Such a $D$-wave ballast is not justified by any nonrelativistic model for $Q-\overline{Q}$ interaction potential and leads to falsified predictions for the cross sections in heavy quarkonium production in ultraperipheral nuclear collisions. We analyze this negative role of $D$-wave contribution by comparing with our previous studies based on a simple non-photon-like “$S$-wave-only” $V\to Q\overline{Q}$ transition in the $Q\overline{Q}$ rest frame.

We present a new computation in a field-theoretical model of Coulomb-gauge QCD of the first radial and angular excitations of a $qqq$ system in an $SU(3)$ flavor-singlet state, ${\mathrm{\Lambda }}_{\mathrm{S}}$. The traditional motivation for the study is that the absence of flavor singlets in the lowest-lying spectrum is a direct consequence of the color degree of freedom. [The calculation is tested with decuplet baryons $\mathrm{\Delta }(1232)$ and $\mathrm{\Omega }(1672)$.] We also analyze decay branching fractions of the flavor-singlet baryon for various masses with the simplest effective Lagrangians.

The cross sections and polarization components of the $\tau$ leptons produced in the charged current induced quasielastic ${\nu }_{\tau }({\overline{\nu }}_{\tau })-N$ scattering have been studied. The theoretical uncertainties arising due to the use of different vector form factors and the axial dipole mass in the axial vector form factor have been investigated. Due to the high mass of $\tau$ lepton, the contributions from the term containing pseudoscalar and second class current form factors are non-negligible and contribute to the uncertainty in the cross section and polarization observables as these form factors are not well known. In view of the currently proposed experiments by DUNE, SHiP, and DsTau collaborations to study the production of $\tau$ lepton, an updated calculation of the cross sections and polarizations of tau leptons in the case of quasielastic production have been done and the numerical results have been presented along with a discussion of the theoretical uncertainties.

The anomalous magnetic moment of the tau lepton $a_{\tau }=(g_{\tau }-2)/2$ strikingly evades measurement but is highly sensitive to new physics such as compositeness or supersymmetry. We propose using ultraperipheral heavy ion collisions at the LHC to probe modified magnetic $\delta a_{\tau }$ and electric dipole moments $\delta d_{\tau }$. We design a suite of analyses with signatures comprising one electron/muon plus track(s), leveraging the exceptionally clean photon fusion $\gamma \gamma \to \tau \tau$ events to reconstruct both leptonic and hadronic tau decays sensitive to $\delta a_{\tau },\delta d_{\tau }$. Assuming 10% systematic uncertainties, the current $2{\mathrm{nb}}^{-1}$ lead-lead dataset could already provide constraints of $-0.0080<a_{\tau }<0.0046$ at 68% C.L. This surpasses 15-year-old lepton collider precision by a factor of 3 while opening novel avenues to new physics.

We present an analysis of MicroBooNE data with a signature of one muon, no pions, and at least one proton above a momentum threshold of $300\mathrm{MeV}/\mathrm{c}$ ($\mathrm{CC}0\pi Np$). This is the first differential cross-section measurement of this topology in neutrino-argon interactions. We achieve a significantly lower proton momentum threshold than previous carbon and scintillator-based experiments. Using data collected from a total of approximately $1.6\times {10}^{20}$ protons on target, we measure the muon neutrino cross section for the $\mathrm{CC}0\pi Np$ interaction channel in argon at MicroBooNE in the Booster Neutrino Beam which has a mean energy of around 800 MeV. We present the results from a data sample with estimated efficiency of 29% and purity of 76% as differential cross sections in five reconstructed variables: the muon momentum and polar angle, the leading proton momentum and polar angle, and the muon-proton opening angle. We include smearing matrices that can be used to “forward fold” theoretical predictions for comparison with these data. We compare the measured differential cross sections to a number of recent theory predictions demonstrating largely good agreement with this first-ever dataset on argon.

The decay ${\mathrm{\Lambda }}_b^0\to {\eta }_c(1S)p{K}^{-}$ is observed for the first time using a data sample of proton-proton collisions, corresponding to an integrated luminosity of $5.5{\mathrm{fb}}^{-1}$, collected with the LHCb experiment at a center-of-mass energy of 13 TeV. The branching fraction of the decay is measured, using the ${\mathrm{\Lambda }}_b^0\to J/\psi p{K}^{-}$ decay as a normalization mode, to be $\mathcal{B}({\mathrm{\Lambda }}_b^0\to {\eta }_c(1S)p{K}^{-})=(1.06\pm 0.16\pm 0.06_{-0.19}^{+0.22})\times {10}^{-4}$, where the quoted uncertainties are statistical, systematic and due to external inputs, respectively. A study of the ${\eta }_c(1S)p$ mass spectrum is performed to search for the $P_c(4312{)}^{+}$ pentaquark state. No evidence is observed and an upper limit of $\frac{\mathcal{B}({\mathrm{\Lambda }}_b^0\to P_c(4312{)}^{+}{K}^{-})\times \mathcal{B}(P_c(4312{)}^{+}\to {\eta }_c(1S)p)}{\mathcal{B}({\mathrm{\Lambda }}_b^0\to {\eta }_c(1S)p{K}^{-})}<0.24$ is obtained at the 95% confidence level.

We have searched for proton decay via $p\to e^{+}{\pi }^0$ and $p\to {\mu }^{+}{\pi }^0$ modes with the enlarged fiducial volume data of Super-Kamiokande from April 1996 to May 2018, which corresponds to $450\mathrm{kton}·\mathrm{years}$ exposure. We have accumulated about 25% more livetime and enlarged the fiducial volume of the Super-Kamiokande detector from 22.5 kton to 27.2 kton for this analysis, so that $144\mathrm{kton}·\mathrm{years}$ of data, including $78\mathrm{kton}·\mathrm{years}$ of additional fiducial volume data, has been newly analyzed. No candidates have been found for $p\to e^{+}{\pi }^0$ and one candidate remains for $p\to {\mu }^{+}{\pi }^0$ in the conventional 22.5 kton fiducial volume and it is consistent with the atmospheric neutrino background prediction. We set lower limits on the partial lifetime for each of these modes: $\tau /B(p\to e^{+}{\pi }^0)>2.4\times {10}^{34}\mathrm{years}$ and $\tau /B(p\to {\mu }^{+}{\pi }^0)>1.6\times {10}^{34}\mathrm{years}$ at 90% confidence level.

The presence of a massless spin-2 field in an effective field theory results in a $t$-channel pole in the scattering amplitudes that precludes the application of standard positivity bounds. Despite this, recent arguments based on compactification to three dimensions have suggested that positivity bounds may be applied to the $t$-channel pole subtracted amplitude. If correct, this would have deep implications for UV physics and the weak gravity conjecture. Within the context of a simple renormalizable field theory coupled to gravity we find that applying these arguments would constrain the low-energy coupling constants in a way which is incompatible with their actual values. This contradiction persists on deforming the theory. Further enforcing the $t$-channel pole subtracted positivity bounds on such generic renormalizable effective theories coupled to gravity would imply new physics at a scale parametrically smaller than expected, with far-reaching implications. This suggests that generically the standard positivity bounds are inapplicable with gravity, and we highlight a number of issues that impinge on the formulation of a three-dimensional amplitude which simultaneously satisfies the required properties of analyticity, positivity, and crossing symmetry. We conjecture instead a modified bound that ought to be satisfied independently of the precise details of the high energy completion.