We present the vacuum of a two-dimensional conformal field theory as a network of Wilson lines in $SL(2,\mathbb{R})\times SL(2,\mathbb{R})$ Chern-Simons theory, which is conventionally used to study gravity in three-dimensional anti–de Sitter space. The position and shape of the network encode the cutoff scale at which the ground state density operator is defined. In the framework of query complexity, a general argument relates the “density of complexity” of the network to the extrinsic curvature of the cutoff surface in ${\mathrm{AdS}}_3$, which accords with the holographic $\mathrm{complexity}=\text{volume proposal}$.

The Rivlin-Ericksen model is one of the oldest models in fluid dynamics to describe non-Newtonian properties. The model comes with two independent transports at second order. In this paper, we study the relativistic origin of the Rivlin-Ericksen fluid. Starting from a relativistic Weyl invariant uncharged fluid in $3+1$ dimensions, we reduce it over light-cone directions and obtain a generic nonrelativistic uncharged fluid in one lower dimension with all possible second-order terms in the constitutive relations. We observe that the Rivlin-Ericksen fluid is a subclass of our generalized nonrelativistic system. We also compute the holographic values of all the nonrelativistic second-order transports and find that three of them satisfy a universal constraint relation.

We derive an exact, axially symmetric solution representing stationary accretion of the relativistic, collisionless Vlasov gas onto a moving Schwarzschild black hole. The gas is assumed to be in thermal equilibrium at infinity, where it obeys the Maxwell-Jüttner distribution. The Vlasov equation is solved analytically in terms of suitable action-angle variables. We provide explicit expressions for the particle current density and accretion rates. In the limit of infinite asymptotic temperature of the gas, we recover the qualitative picture known from the relativistic Bondi-Hoyle-Lyttleton accretion of the perfect gas with the ultrahard equation of state, in which the mass accretion is proportional to the Lorentz factor associated with the black hole velocity. For a finite asymptotic temperature, the mass accretion rate is not in general a monotonic function of the velocity of the black hole.

We find new effects for gravitational waves and memory in asymptotically flat spacetimes of slow decay. In particular, we find growing magnetic memory for these general systems. These effects do not arise in spacetimes resulting from data with fast decay towards infinity, including data that is stationary outside a compact set. The new results are derived for the Einstein vacuum as well as for the Einstein-null-fluid equations describing neutrino radiation, where the neutrino distribution falls off slowly towards infinity. Moreover, they hold for other matter and energy fields coupled to the Einstein equations as long as the data obey corresponding decay laws and other conditions are fulfilled. The magnetic memory occurs naturally in the Einstein vacuum regime of pure gravitation, and in the Einstein-matter systems satisfying the aforementioned conditions. As a main new effect, we find that there is diverging magnetic memory sourced by the magnetic part of the curvature. In the most extreme case, the magnetic memory, in addition, features a curl term from the neutrino cloud, growing at the same rate. Electric memory is diverging as well, sourced by the electric part of the curvature tensor and the corresponding energy-momentum component. Shear (news) adds to the electric memory. Moreover, a multitude of lower order terms contribute to both electric and magnetic memory. It has been known that for stronger decay of the data, including data that is stationary outside a compact set, gravitational wave memory is finite and of electric parity only. The more general scenarios in this article exhibit richer structures displaying the physics of these more general systems. We lay open these new structures. Further, we identify a range of decay rates for asymptotically flat spacetimes for which the new effects occur but with different leading order behavior. The new effects are expected to be seen in current and future gravitational wave detectors. They have an abundance of applications of which we mention a few in this paper. Applications include exploring gravitational wave sources of the above types, detecting dark matter via gravitational waves and other areas of physics.

We investigate the observability of higher harmonics in gravitational wave signals emitted during the coalescence of binary black holes. We decompose each harmonic into an overall amplitude, dependent upon the masses and spins of the system, and an orientation-dependent term, dependent upon the inclination and polarization of the source. Using this decomposition, we investigate the significance of higher multipole moments over the parameter space and show that the $\ell =|m|=3$ harmonic is most significant across much of the sensitive band of ground-based interferometric detectors, with the $\ell =|m|=4$ harmonic having a significant contribution at high masses. We introduce the higher harmonic signal-to-noise ratio (SNR), and show that a simple threshold on this SNR can be used as a criterion for observation of higher harmonics. Finally, we investigate observability in a population of binaries and show that higher harmonics will be observable in a few percent of binaries, typically those with unequal masses and viewed close to edge-on. We find that he majority of binaries with mass ratio greater than $4:1$ will have an observable $\ell =|m|=3$ harmonic.

The “no-hair” theorem states that astrophysical black holes are fully characterized by just two numbers: their mass and spin. The gravitational-wave emission from a perturbed black-hole consists of a superposition of damped sinusoids, known as quasinormal modes. Quasinormal modes are specified by three integers $(\ell ,m,n)$: the $(\ell ,m)$ integers describe the angular properties and ($n$) specifies the (over)tone. If the no-hair theorem holds, the frequencies and damping times of quasinormal modes are determined uniquely by the mass and spin of the black hole, while phases and amplitudes depend on the particular perturbation. Current tests of the no-hair theorem attempt to identify these modes in a semiagnostic way, without imposing priors on the source of the perturbation. This is usually known as black-hole spectroscopy. Applying this framework to GW150914, the measurement of the first overtone led to the confirmation of the theorem to 20% level. We show, however, that such semiagnostic tests cannot provide strong evidence in favor of the no-hair theorem, even for extremely loud signals, given the increasing number of overtones (and free parameters) needed to fit the data. This can be solved by imposing prior assumptions on the origin of the perturbed black hole that can further constrain the explored parameters: in particular, our knowledge that the ringdown is sourced by a binary black-hole merger. Applying this strategy to GW150914, we find a natural log Bayes factor of $\sim 6.5$ in favor of the Kerr nature of its remnant, indicating that the hairy object hypothesis is disfavored with $<1:600$ with respect to the Kerr black-hole one.

In recent years, convolutional neural network (CNN) and other deep learning models have been gradually introduced into the area of gravitational-wave (GW) data processing. Compared with the traditional matched-filtering techniques, CNN has significant advantages in efficiency in GW signal detection tasks. In addition, matched-filtering techniques are based on the template bank of the existing theoretical waveform, which makes it difficult to find GW signals beyond theoretical expectation. In this paper, based on the task of GW detection of binary black holes, we introduce the optimization techniques of deep learning, such as batch normalization and dropout, to CNN models. Detailed studies of model performance are carried out. Through this study, we recommend to use batch normalization and dropout techniques in CNN models in GW signal detection tasks. Furthermore, we investigate the generalization ability of CNN models on different parameter ranges of GW signals. We point out that CNN models are robust to the variation of the parameter range of the GW waveform. This is a major advantage of deep learning models over matched-filtering techniques.

We analyze Dark Energy Survey (DES) data to constrain a cosmological model where a subset of parameters—focusing on ${\mathrm{\Omega }}_m$—are split into versions associated with structure growth (e.g., ${\mathrm{\Omega }}_m^{\mathrm{grow}}$) and expansion history (e.g., ${\mathrm{\Omega }}_m^{\mathrm{geo}}$). Once the parameters have been specified for the $\mathrm{\Lambda }\mathrm{CDM}$ cosmological model, which includes general relativity as a theory of gravity, it uniquely predicts the evolution of both geometry (distances) and the growth of structure over cosmic time. Any inconsistency between measurements of geometry and growth could therefore indicate a breakdown of that model. Our growth-geometry split approach therefore serves both as a (largely) model-independent test for beyond-$\mathrm{\Lambda }\mathrm{CDM}$ physics, and as a means to characterize how DES observables provide cosmological information. We analyze the same multiprobe DES data as [Phys. Rev. Lett. 122, 171301 (2019)] : DES Year 1 (Y1) galaxy clustering and weak lensing, which are sensitive to both growth and geometry, as well as Y1 BAO and Y3 supernovae, which probe geometry. We additionally include external geometric information from BOSS DR12 BAO and a compressed Planck 2015 likelihood, and external growth information from BOSS DR12 RSD. We find no significant disagreement with ${\mathrm{\Omega }}_m^{\mathrm{grow}}={\mathrm{\Omega }}_m^{\mathrm{geo}}$. When DES and external data are analyzed separately, degeneracies with neutrino mass and intrinsic alignments limit our ability to measure ${\mathrm{\Omega }}_m^{\mathrm{grow}}$, but combining DES with external data allows us to constrain both growth and geometric quantities. We also consider a parametrization where we split both ${\mathrm{\Omega }}_m$ and $w$, but find that even our most constraining data combination is unable to separately constrain ${\mathrm{\Omega }}_m^{\mathrm{grow}}$ and $w^{\mathrm{grow}}$. Relative to $\mathrm{\Lambda }\mathrm{CDM}$, splitting growth and geometry weakens bounds on ${\sigma }_8$ but does not alter constraints on $h$.

If neutrinos have self-interactions, these will induce scatterings between astrophysical and cosmic neutrinos. Prior work proposed looking for possible resulting resonance features in astrophysical neutrino spectra in order to seek a neutrino self-interaction which can be either diagonal in the neutrino flavor space or couple different neutrino flavors. The calculation of the astrophysical spectra involves either a Monte Carlo simulation or a computationally intensive numerical integration of an integro-partial-differential equation. As a result, only limited regions of the neutrino self-interaction parameter space have been explored, and only flavor-diagonal self-interactions have been considered. Here, we present a fully analytic form for the astrophysical neutrino spectra for arbitrary neutrino number and arbitrary self-coupling matrix that accurately obtains the resonance features in the observable neutrino spectra. The results can be applied to calculations of the diffuse supernova neutrino background and of the spectrum from high-energy astrophysical neutrino sources. We illustrate with a few examples.

A large-scale neutrino observatory based on water-based liquid scintillator (WbLS) will be excellently suited for a measurement of the diffuse supernova neutrino background (DSNB). The WbLS technique offers high signal efficiency and effective suppression of the otherwise overwhelming background from neutral-current interactions of atmospheric neutrinos. To illustrate this, we investigate the DSNB sensitivity for two configurations of the future Theia detector by developing the expected signal and background rejection efficiencies along a full analysis chain. Based on a statistical analysis of the remaining signal and background rates, we find that a rather moderate exposure of $190\mathrm{kt}·\mathrm{yrs}$ will be sufficient to claim a ($5\sigma$) discovery of the faint DSNB signal for standard model assumptions. We conclude that, in comparison with other experimental techniques, WbLS offers the highest signal efficiency of more than 80% and best signal significance over background.

Results are presented from a semicoherent search for continuous gravitational waves from a nearby neutron star candidate, Fomalhaut b, using data collected in the second observing run of Advanced LIGO. The search is based on a hidden Markov model scheme, capable of tracking signal frequency evolution from the star’s secular spin-down and stochastic timing noise simultaneously. The scheme is combined with a frequency domain matched filter ($\mathcal{F}$-statistic), calculated coherently over five-day time stretches. The frequency band 100–1000 Hz is searched. After passing the above-threshold candidates through a hierarchy of vetoes, one candidate slightly above the 1% false alarm probability threshold remains for further scrutiny. No strong evidence of continuous waves is found. We present the strain upper limits in the full frequency band searched at 90% confidence level.

Certain strongly interacting dark matter candidates could have evaded detection, and much work has been done on constraining their parameter space. Recently, it was shown theoretically that the scattering cross section for $m_{\chi }\gtrsim 1\mathrm{GeV}$ pointlike dark matter with a nucleus cannot be significantly larger than the geometric cross section of the nucleus. This realization closes the parameter space for pointlike strongly interacting dark matter. However, strongly interacting dark matter is still theoretically possible for composite particles, with much parameter space open. We set new, wide-ranging limits based on data from a novel detector at the University of Chicago. Backgrounds are greatly suppressed by requiring coincidence detection between two spatially separated liquid-scintillator modules. For dark matter ($v\sim {10}^{-3}\mathrm{c}$), the time of flight would be $\sim 2\mu \mathrm{s}$, whereas for cosmic rays, it would be $\sim 2\mathrm{ns}$. We outline ways to greatly increase sensitivity at modest costs.

In this work, the triangle singularity mechanism is investigated in the $\psi (2S)\to p\overline{p}\eta /p\overline{p}{\pi }^0$ process. The triangle loop composed by $J/\psi$, $\eta$, and $p$ has a singularity in the physical kinematic range for the $\psi (2S)\to p\overline{p}\eta /p\overline{p}{\pi }^0$ process, and it would generate a very narrow peak in the invariant mass spectrum of $p\eta (\pi )$ around 1.56387 GeV, which is far away from both the threshold and relative resonances. In these processes, all the involved vertices are constrained by the experimental data. Thus, we can make a precise model independent prediction here. It turns out that the peak in the $p\eta$ invariant mass spectrum is visible, while it is very small in the $p{\pi }^0$ invariant mass spectrum. We expect this effect shown in $p\overline{p}\eta$ final state can be observed by the Beijing Spectrometer and Super Tau-Charm Facility in the future.

The $\mathrm{SU}(3)$ pure gauge theory exhibits a first-order thermal deconfinement transition due to spontaneous breaking of its global $Z_3$ center symmetry. When heavy dynamical quarks are added, this symmetry is broken explicitly and the transition weakens with decreasing quark mass until it disappears at a critical point. We compute the critical hopping parameter and the associated pion mass for lattice QCD with $N_{\mathrm{f}}=2$ degenerate standard Wilson fermions on $N_{\tau }\in \{6,8,10\}$ lattices, corresponding to lattice spacings $a=0.12\mathrm{fm}$, $a=0.09\mathrm{fm}$, $a=0.07\mathrm{fm}$, respectively. Significant cutoff effects are observed, with the first-order region growing as the lattice gets finer. While current lattices are still too coarse for a continuum extrapolation, we estimate $m_{\pi }^c\approx 4\mathrm{GeV}$ with a remaining systematic error of $\sim 20\%$. Our results allow us to assess the accuracy of the leading-order and next-to-leading-order hopping expanded fermion determinant used in the literature for various purposes. We also provide a detailed investigation of the statistics required for this type of calculation, which is useful for similar investigations of the chiral transition.

The LHCb pentaquarks—the $P_c(4312)$, $P_c(4440)$, and $P_c(4457)$—have been theorized to be ${\mathrm{\Sigma }}_c\overline{D}$ and ${\mathrm{\Sigma }}_c{\overline{D}}^{*}$ S-wave molecules. Here, we explore the possibility that two of these pentaquarks—the $P_c(4440)$ and $P_c(4457)$—contain in addition a ${\mathrm{\Lambda }}_c(2595)\overline{D}$ component in the P-wave. We will analyze the effects of this extra channel within two effective field theories: the first one will be a standard contact-range effective field theory, and the second one will include the nondiagonal pion dynamics connecting the ${\mathrm{\Sigma }}_c{\overline{D}}^{*}$ and ${\mathrm{\Lambda }}_c(2595)\overline{D}$ channels, which happens to be unusually long ranged. The impact of the coupled-channel dynamics between the ${\mathrm{\Sigma }}_c{\overline{D}}^{*}$ and ${\mathrm{\Lambda }}_c(2595)\overline{D}$ components is modest at best for the $P_c(4440)$ and $P_c(4457)$, which will remain predominantly ${\mathrm{\Sigma }}_c{\overline{D}}^{*}$ molecules. However, if the quantum numbers of the $P_c(4457)$ are $J^P={\frac{1}{2}}^{-}$, the coupled-channel dynamics is likely to induce the binding of a $\mathrm{\Lambda }(2595)\overline{D}$ S-wave molecule (coupled to ${\mathrm{\Sigma }}_c{\overline{D}}^{*}$ in the P-wave) with $J^P={\frac{1}{2}}^{+}$ and a mass similar to the $P_c(4457)$. If this is the case, the $P_c(4457)$ could actually be a double peak containing two different pentaquark states.

We investigate the prospects of the diffractive production of $J/\psi$ mesons at a large momentum transfer $|t|$ at the future Electron Ion Collider (EIC) in electron-proton collisions. In particular, we focus on the measurements of the rapidity gap size. The model used for the calculations is based on the diffractive exchange of the Balitsky-Fadin-Kuraev-Lipatov perturbative Pomeron. Calculations for the cross section and the estimates for the rates assuming integrated luminosity of $10{\mathrm{fb}}^{-1}$ are provided. Two experimental strategies were considered. First, measuring the rapidity gap size directly, by observing the activity in the forward part of the central detector, and second by putting a lower limit on the rapidity gap size in the case when the detector cannot measure forward activity. We find that it is possible to measure at the EIC the dependence of the cross section on rapidity gap interval up to four units in rapidity. This should allow us to measure the change of the cross section by a factor of 1.6 expected due to the BFKL exchange. This is possible with the present setup of the detector which projects the coverage up to 3.5 units of rapidity. We conclude however, that the extension of the detector up to higher rapidity, for example to 4.5 would be desirable and provide even better lever arm for testing rapidity gap physics at the EIC.

We present an exact computation of effective Hamiltonians for an elementary model obtained from the Yukawa theory by going to the limit of bare fermions being infinitely heavy and bare bosons being at rest with respect to the fermions that emit or absorb them. The coupling constant can be arbitrarily large. The Hamiltonians are computed by solving the differential equation of the renormalization group procedure for effective particles (RGPEP). Physical fermions, defined in the model as eigenstates of the effective Hamiltonians, are obtained in the form of an effective fermion dressed with a coherent state of effective bosons. The model computation illustrates the method that can be used in perturbative computations of effective Hamiltonians for realistic theories. It shows the mechanism by which the perturbative expansion and Tamm-Dancoff approximation increase in accuracy along the RGPEP evolution.

As a baryon number violating process with $\mathrm{\Delta }B=2$, neutron-antineutron oscillation ($n\to \overline{n}$) provides a unique test of baryon number conservation. We have performed a search for $n\to \overline{n}$ oscillation with bound neutrons in Super-Kamiokande, with the full dataset from its first four run periods, representing an exposure of $0.37\mathrm{Mton}\text{−}\mathrm{years}$. The search used a multivariate analysis trained on simulated $n\to \overline{n}$ events and atmospheric neutrino backgrounds and resulted in 11 candidate events with an expected background of 9.3 events. In the absence of statistically significant excess, we derived a lower limit on $\overline{n}$ appearance lifetime in ${}^{16}\mathrm{O}$ nuclei of $3.6\times {10}^{32}\mathrm{years}$ and on the neutron-antineutron oscillation time of ${\tau }_{n\to \overline{n}}>4.7\times {10}^8\mathrm{s}$ at 90% C.L.

We consider a nonlocal theory of a scalar massive field in a flat spacetime background in the presence of an external potential and construct WKB solutions for this theory. We use a model in which the kinetic part of the scalar field action is modified by changing $\square$ to $\square f(\square )$ operator. We discuss conditions when the corresponding form factor $f$ is chosen so that the theory does not contain new unphysical degrees of freedom. We applied the obtained WKB solutions for study energy levels of the field trapped by a one-dimensional potential and the probability of the barrier penetration. This allows us to illustrate how the effects of the nonlocality change the known results obtained for the local field theory.