We calculate the finite-temperature $r$-mode spectrum of a superfluid neutron star accounting for both muons in the core and the entrainment between neutrons and protons. We show that the standard perturbation scheme, considering the rotation rate as an expansion parameter, breaks down in this case. We develop an original perturbation scheme which circumvents this problem by treating both the perturbations due to rotation and (weak) entrainment simultaneously. Applying this scheme, we propose a simple method for calculating the superfluid $r$-mode eigenfrequency in the limit of vanishing rotation rate. We also calculate the $r$-mode spectrum at finite rotation rate for realistic microphysics input (adopting, however, the Newtonian framework and Cowling approximation when considering perturbed oscillation equations) and show that the normal $r$-mode exhibits resonances with superfluid $r$-modes at certain values of temperatures and rotation frequencies in the parameter range relevant to neutron stars in low-mass x-ray binaries (LMXBs). This turns the recently suggested phenomenological model of resonance $r$-mode stabilization into a quantitative theory, capable of explaining observations. A strong dependence of resonance rotation rates and temperatures on the neutron superfluidity model allows us to constrain the latter by confronting our calculations with the observations of neutron stars in LMXBs.

We use density estimation likelihood-free inference, $\mathrm{\Lambda }$ cold dark matter simulations of $\sim 2M$ galaxy pairs, and data from Gaia and the Hubble Space Telescope to infer the sum of the masses of the Milky Way and Andromeda (M31) galaxies, the two main components of the local group. This method overcomes most of the approximations of the traditional timing argument, makes the writing of a theoretical likelihood unnecessary, and allows the nonlinear modeling of observational errors that take into account correlations in the data and non-Gaussian distributions. We obtain an $M_{200}$ mass estimate $M_{\mathrm{MW}+\mathrm{M}31}=4.6_{-1.8}^{+2.3}\times {10}^{12}{M}_{\odot }$ (68% C.L.), in agreement with previous estimates both for the sum of the two masses and for the individual masses. This result is not only one of the most reliable estimates of the sum of the two masses to date, but is also an illustration of likelihood-free inference in a problem with only one parameter and only three data points.

Gravitational waves produced at kilohertz frequencies in the aftermath of a neutron star collision can shed light on the behavior of matter at extreme temperatures and densities that are inaccessible to laboratory experiments. Gravitational-wave interferometers are limited by quantum noise at these frequencies but can be tuned via their optical configuration to maximize the probability of postmerger signal detection. We compare two such tuning strategies to turn Advanced LIGO into a postmerger-focused instrument: first, a wideband tuning that enhances the instrument’s signal-to-noise ratio 40–80% broadly above 1 kHz relative to the baseline, with a modest sensitivity penalty at lower frequencies; second, a “detuned” configuration that provides even more enhancement than the wideband tuning, but over only a narrow frequency band and at the expense of substantially worse quantum noise performance elsewhere. With an optimistic accounting for instrument loss and uncertainty in postmerger parameters, the detuned instrument has a $\lesssim 40\%$ sensitivity improvement compared to the wideband instrument.

We demonstrate how quantum field theory problems can be practically encoded by using a discretization of the field theory problem into a general Ising model, with the continuous field values being encoded into Ising spin chains. To illustrate the method, and as a simple proof of principle, we use a (hybrid) quantum annealer to recover the correct profile of the thin-wall tunnelling solution. This method is applicable to many nonperturbative problems.

There exists a great deal of concrete evidence in favor of the exotic four-quark nature of light scalars. At the same time, the further expansion of the area of the $q^2{\overline{q}}^2$ model validity for light scalars on ever new processes seems extremely interesting and important. We analyze the BESIII data on the decay $J/\psi \to \gamma {\pi }^0{\pi }^0$ and show that the results of this high-statistics experiment can be interpreted in favor of the four-quark nature of light scalar mesons $f_0(980)$ and $f_0(500)$.

We suggest that the uncertain state $f_X(1500)$ observed by Belle and BABAR more than a decade ago, which has been viewed as a single scalar or a combination of several even spin resonances, is the vector ${\rho }^0(1450)$ reported recently by LHCb. Adopting the perturbative QCD approach, we determine the dikaon distribution amplitudes with the ${\rho }^0(1450)$ resonance from the LHCb data for the quasi-two-body decays $B^{\pm }\to {\pi }^{\pm }{\rho }^0(1450)\to {\pi }^{\pm }{K}^{+}{K}^{-}$. It is then shown that the $B^{+}\to K^{+}{K}^{+}{K}^{-}$ decay spectrum around the invariant mass $M(K^{+}{K}^{-})\sim 1.5\mathrm{GeV}$ measured by BABAR can be well described by the resonant contribution from ${\rho }^0(1450)$. The broad structure in the $B^{+}\to K^{+}{K}_S{K}_S$ spectrum around the invariant mass 1.5 GeV of a $K_S{K}_S$ pair, which ${\rho }^0(1450)$ cannot decay into because of Bose-Einstein statistics, can be accounted for by a nonresonant $S$-wave contribution alone. The branching fractions and/or the direct $CP$ asymmetries of the $B^{\pm }\to {\pi }^{\pm }{\rho }^0(1450)\to {\pi }^{\pm }{K}^{+}{K}^{-}$, $B^{+}\to K^{+}{\rho }^0(1450)\to K^{+}{K}^{+}{K}^{-}$ and $B^0\to K^0{\rho }^0(1450)\to K^0{K}^{+}{K}^{-}$ modes are predicted, which can be tested at the ongoing LHCb and Belle-II experiments. We encourage experimental colleagues to scrutinize our postulation by analyzing relevant data with higher precision.

We inspect recently updated neutrino oscillation data—specifically coming from the Tokai to Kamioka and NuMI Off-axis ${\nu }_e$ Appearance experiments—and how they are analyzed to determine whether the neutrino mass ordering is normal ($m_1<m_2<m_3$) or inverted ($m_3<m_1<m_2$). We show that, despite previous results giving a strong preference for the normal ordering, with the newest data from T2K and NOvA, this preference has all but vanished. Additionally, we highlight the importance of this result for nonoscillation probes of neutrinos, including neutrinoless double beta decay and cosmology. Future experiments, including JUNO, DUNE, and T2HK will provide valuable information and determine the mass ordering at a high confidence level.

We calculate the rate of collisional decay of the axial charge in an ultrarelativistic electron-positron plasma, also known as the chirality flipping rate. We find that contrary to the existing estimates, the chirality flipping rate appears already in the first order in the fine-structure constant $\alpha$ and is therefore orders of magnitude greater than previously believed. The main channels for the rapid relaxation of the axial charge are the collinear emission of a weakly damped photon and the Compton scattering. The latter contributes to the $\mathcal{O}(\alpha )$ result because of the infrared divergence in its cross section, which is regularized on the soft scale $\sim eT$ due to the thermal corrections. Our results are important for the description of the early Universe processes (such as leptogenesis or magnetogenesis) that affect differently left- and right-chiral fermions of the Standard Model, as discussed in more details in the companion Letter.

We report a search for a magnetic monopole component of the cosmic-ray flux in a 95-day exposure of the NOvA experiment’s Far Detector, a 14 kt segmented liquid scintillator detector designed primarily to observe GeV-scale electron neutrinos. No events consistent with monopoles were observed, setting an upper limit on the flux of $2\times {10}^{-14}{\mathrm{cm}}^{-2}{\mathrm{s}}^{-1}{\mathrm{sr}}^{-1}$ at 90% C.L. for monopole speed $6\times {10}^{-4}<\beta <5\times {10}^{-3}$ and mass greater than $5\times {10}^8\mathrm{GeV}$. Because of NOvA’s small overburden of 3 meters-water equivalent, this constraint covers a previously unexplored low-mass region.

We investigate the existence of double copy structure, or the lack thereof, in higher derivative operators for Nambu-Goldstone bosons. At the leading $\mathcal{O}(p^2)$, tree amplitudes of Nambu-Goldstone bosons in the adjoint representation can be (trivially) expressed as the double copy of itself and the cubic biadjoint scalar theory, through the Kawai-Lewellen-Tye bilinear kernel. At the next-to-leading $\mathcal{O}(p^4)$ there exist four operators in general, among which we identify one operator whose amplitudes exhibit the flavor-kinematics duality and can be written as the double copy of $\mathcal{O}(p^2)$ Nambu-Goldstone amplitudes and the $\mathrm{Yang}\text{−}\mathrm{Mills}+{\varphi }^3$ theory, involving both gluons and gauged cubic biadjoint scalars. The specific operator turns out to coincide with the scalar $\mathcal{O}(p^4)$ operator in the so-called extended Dirac-Born-Infeld theory, for which the aforementioned double copy relation holds more generally.

In this paper, we derive general conditions for a shadow to occur, without a photon sphere in a spacetime, caused by central nulllike or timelike naked singularities. Using these conditions, we propose classes of spacetimes which have nulllike and timelike naked singularities at the center, and that fulfill these ‘shadow without photon sphere’ conditions. Considering additional asymptotically flat conditions, we show that, for a fixed Schwarzschild mass, the timelike naked singularities can cast a shadow of a size that is equal to, greater or smaller, than the size of a black hole shadow. On the other hand, the size of shadow of a nulllike naked singularity is always less than that of a black hole. Such novel features of shadows of nulllike and timelike naked singularities in the absence of photon spheres may help us to distinguish between black holes and naked singularities observationally.

We introduce TEOBResumSP: an efficient yet accurate hybrid scheme for generating gravitational waveforms from spin-precessing compact binaries. The precessing waveforms are generated via the established technique of Euler rotating aligned-spin (nonprecessing) waveforms from a precessing frame to an inertial frame. We employ the effective-one-body approximant TEOBResumS to generate the aligned-spin waveforms. We obtain the Euler angles by solving the post-Newtonian precession equations expanded to ${(\mathrm{next}\text{−}\mathrm{to})}^4$ leading (second post-Newtonian) order. Current version of TEOBResumSP produces precessing waveforms through the inspiral phase up to the onset of the merger. We compare TEOBResumSP to current state-of-the-art precessing approximants NRSur7dq4, SEOBNRv4PHM, and IMRPhenomPv3HM in terms of frequency-domain matches of the $\ell =2$ gravitational-wave strain for 200 cases of precessing compact binary inspirals with orbital inclinations up to 90 degrees, mass ratios up to four, and the effective precession parameter ${\chi }_p$ up to 0.75. We further provide an extended comparison with SEOBNRv4PHM involving 1030 more inspirals with ${\chi }_p$ ranging up to one and mass ratios up to 10. We find that 91% of the TEOBResumSP-NRSur7dq4 matches, 85% of the TEOBResumSP-SEOBNRv4PHM matches, and 77% of the TEOBResumSP-IMRPhenomPv3HM matches are greater than 0.965. Most of the significant disagreements occur for large mass ratios and ${\chi }_p\gtrsim 0.6$. We identify the mismatch of the non-precessing (2,1) mode as one of the leading causes of disagreements. We also introduce a new parameter, ${\chi }_{\perp ,\max }$, to measure the strength of precession and hint that the strain mismatch between the above waveform approximants shows an exponential dependence on ${\chi }_{\perp ,\max }$ though this requires further study. Our results indicate that TEOBResumSP is on its way to becoming a robust precessing approximant to be employed in the parameter estimation of generic-spin compact binaries.

We demonstrate that there are theories that exhibit spontaneous scalarization in the strong gravity regime while having general relativity with a constant scalar as a cosmological attractor. We identify the minimal model that has this property and discuss its extensions.

We investigate linear and nonlinear dynamics of spherically symmetric perturbations on a static configuration in scalar-tensor theories focusing on the chameleon screening mechanism. We particularly address two questions: how much the perturbations can source the fifth force when the static background is well screened, and whether the resultant fifth force can change the stability and structure of the background configuration. For linear perturbations, we derive a lower bound for the square of the Fourier mode frequency ${\omega }^2$ using the adiabatic approximation. There may be unstable modes if this lower bound is negative, and we find that the condition of the instability can be changed by the fifth force although this effect is suppressed by the screening parameter. For nonlinear perturbations, because we are mainly interested in short wavelength modes for which the fifth force may become stronger, we perform numerical simulations under the planar approximation. For a sufficiently large initial amplitude of the density perturbation, we find that the magnitude of the fifth force can be comparable to that of Newtonian gravity even when the model parameters are chosen so that the static background is well screened. It is also shown that if the screening is effective for the static background, the fluid dynamics is mostly governed by the pressure gradient and is not significantly affected by the fifth force.

We extend the work of Contaldi et al. [J. Cosmol. Astropart. Phys. 07 (2003) 002.] and derive analytical approximations for primordial power spectra arising from models of inflation which include primordial spatial curvature. These analytical templates are independent of any specific inflationary potential and therefore illustrate and provide insight into the generic effects and predictions of primordial curvature, manifesting as cutoffs and oscillations at low multipoles and agreeing with numerical calculations. We identify through our analytical approximation that the effects of curvature can be mathematically attributed to shifts in the wave vectors participating dynamically.

Fast radio bursts (FRBs) are astrophysical transients of currently unknown origin, and so far several events have been detected at extragalactic distances. The dispersion measure (DM) of the radio signal is a probe of the integrated electron density along the line of sight and therefore allows to map the electron distribution within the large-scale structure. Since a fraction of electrons get expelled from galaxies by feedback, they are anticorrelated with halos at large scales and hence the angular DM correlations show a scale-dependent bias caused by primordial non-Gaussianity. Although the signal is weaker than in other probes like galaxy clustering, FRBs can potentially probe considerably larger volumes. We show that while studying the FRB clustering signal requires very large samples, correlations in the DM are cosmic-variance limited on large angular scales with only $\sim 10^{3-4}$ events. A tomographic analysis of the angular DM correlation function can constrain the local primordial bispectrum shape parameter $f_{\mathrm{NL}}$ to a precision down to $f_{\mathrm{NL}}\sim \mathcal{O}(1)$ depending on assumptions about the FRB redshift distribution and the astrophysical feedback on large scales. This makes FRBs a competitive probe to constrain inflationary physics.

Many theories beyond the Standard Model of particle physics predict the existence of axionlike particles (ALPs) that mix with photons in the presence of a magnetic field. One prominent indirect method of searching for ALPs is to look for irregularities in blazar gamma-ray spectra caused by ALP-photon mixing in astrophysical magnetic fields. This requires the modeling of magnetic fields between Earth and the blazar. So far, only very simple models for the magnetic field in the blazar jet have been used. Here, we investigate the effects of more complicated jet magnetic field configurations on these spectral irregularities by imposing a magnetic field structure model onto the jet model proposed by Potter & Cotter. We simulate gamma-ray spectra of Mrk 501 with ALPs and fit them to ALP-less spectra, scanning the ALP and B-field configuration parameter space, and show that the jet can be an important mixing region, able to probe new ALP parameter space around $m_a\sim 1–1000\mathrm{neV}$ and $g_{a\gamma }\gtrsim 5\times {10}^{-12}{\mathrm{GeV}}^{-1}$. However, reasonable (i.e., consistent with observation) changes of the magnetic field structure can have a large effect on the mixing. For jets in highly magnetized clusters, mixing in the cluster can overpower mixing in the jet. This means that the current constraints using mixing in the Perseus cluster are still valid.

Fluctuations in the muon content of extensive air showers are anticorrelated to the fluctuations of the energy taken by the neutral pions which emerge from the first interaction of the cosmic ray in the atmosphere. We show that the high-energy tail of the neutral pion spectrum produced in the first proton-air interaction can be constrained, within the uncertainties of present cosmic ray experiments, through the analysis of the shower-to-shower distribution of the muon content of the air showers, $P(N_{\mu })$.