Results are presented for a semicoherent search for continuous gravitational waves from the millisecond pulsar PSR $\mathrm{J}0437\text{−}4715$, using a hidden Markov model to track spin wandering, in LIGO data from the third LIGO-Virgo observing run. This is the first search for PSR $\mathrm{J}0437\text{−}4715$ to cover a wide frequency range from 60 to 500 Hz and simultaneously accommodate random spin deviations from the secular radio ephemeris. Two searches are performed with plausible coherence times of 10 and 30 days, as the frequency wandering time scale of the gravitational-wave-emitting quadrupole is unknown. The former analysis yields no surviving candidates, while the latter yields five candidates after the veto procedure. The detection statistic of each of the five survivors is mapped as a function of sky position, in preparation for follow-up analyses in the future, e.g., during the LIGO-Virgo-KAGRA fourth observing run.

We present the $\mathcal{E}$-boson star; a novel configuration of a boson star with an exotic matter nucleus with the exotic matter being described by a real massive scalar field with self-interaction term and kinetic term of the opposite sign. The other scalar field is canonical, so that the system is similar to the material component of the quintom cosmological scenario. Considering the static spherical symmetric case, we obtain cases where both fields are distributed as concentric spheres, and others with the remarkable feature that the canonical matter is pushed outwards and obtain a shell-like distribution of the canonical field, with a nucleus of exotic matter at the center. We present global properties of such $\mathcal{E}$-boson stars and stress the differences that these configuration have with respect to the usual boson stars. In particular, we obtain cases where the compactness goes beyond the Buchdahl limit.

We investigate the linear stability of the two known branches of spherically symmetric black holes in quadratic gravity. We extend previous work on the long-wavelength (Gregory-Laflamme) instability of the Schwarzschild branch to a corresponding long-wavelength instability in the non-Schwarzschild branch. In both cases, the instability sets in below a critical horizon radius at which the two black-hole branches intersect. This suggests that classical perturbations enforce a lower bound on the horizon radius of spherically symmetric black holes in quadratic gravity.

In 2007, Pretorius and Khurana [Black hole mergers and unstable circular orbits, Classical Quantum Gravity 24, S83 (2007).] did “speculate that at threshold [at a critical impact parameter], all of the kinetic energy of the system [two ultrarelativistic black holes] is converted to gravitational waves, which can be an arbitrarily large fraction of the total energy.” However, in 2012, Sperhake et al. [Universality, Maximum Radiation and Absorption in High-Energy Collisions of Black Holes with Spin, Phys. Rev. Lett. 111, 041101 (2013).] performed numerical calculations that led them to the contrary conclusion: “An extrapolation of our results to the limit $\gamma \to \infty$ suggests that about half of the center-of-mass energy of the system can be emitted in gravitational radiation, while the rest must be converted into rest-mass and spin energy.” Here I present arguments against this latter conclusion and in support of the earlier speculation that for sufficiently large $\gamma$, all but an arbitrarily small fraction of the total energy can be radiated away as gravitational waves.

Gravitational-wave memory effects arise from nonoscillatory components of gravitational-wave signals, and they are predictions of general relativity in the nonlinear regime that have close connections to the asymptotic properties of isolated gravitating systems. There are many types of memory effects that have been studied in the literature. In this paper we focus on the “displacement” and “spin” memories, which are expected to be the largest of these effects from sources such as the binary black hole mergers which have already been detected by LIGO and Virgo. The displacement memory is a change in the relative separation of two initially comoving observers due to a burst of gravitational waves, whereas the spin memory is a portion of the change in relative separation of observers with initial relative velocity. As both of these effects are small, LIGO, Virgo, and KAGRA can only detect memory effects from individual events that are much louder (and thus rarer) than those that have been detected so far. By combining data from multiple events, however, these effects could be detected in a population of binary mergers. In this paper, we present new forecasts for how long current and future detectors will need to operate in order to measure these effects from populations of binary black hole systems that are consistent with the populations inferred from the detections from LIGO and Virgo’s first three observing runs. We find that a second-generation detector network of LIGO, Virgo, and KAGRA operating at the O4 (“design”) sensitivity for 1.5 years and then operating at the O5 (“plus”) sensitivity for an additional 1.5 years can detect the displacement memory. For Cosmic Explorer, we find that displacement memory could be detected for individual loud events, and that the spin memory could be detected in a population after 5 years of observation time.

We present for smooth nonoscillating backgrounds an analytic formula which calculates the energy density of massive and massless particles created via gravitational particle production, thus giving the corresponding reheating temperature. It can be applied to models of quintessential inflation such as $\alpha$-attractors, and shows that for masses larger than the Hubble rate at the end of inflation, namely $H_{\mathrm{END}}$, the reheating temperature is exponentially suppressed. On the contrary, for masses of the order of $H_{\mathrm{END}}$ one obtains a maximum reheating temperature of the order of ${10}^7\mathrm{GeV}$. Finally, to overcome the constraints coming from the overproduction of gravitational waves in quintessential inflation, we have shown that the viable masses which ensure the big bang nucleosynthesis success are in the range between $2\times {10}^{10}\mathrm{GeV}$ and $4\times {10}^{13}\mathrm{GeV}$, leading to a maximum reheating temperature of the order ${10}^5–{10}^7\mathrm{GeV}$.

We show that dense neural networks can be used to accurately model the cooling of high-energy particles in the early universe, in the context of the public code package darkhistory. darkhistory self-consistently computes the temperature and ionization history of the early universe in the presence of exotic energy injections, such as might arise from the annihilation or decay of dark matter. The original version of darkhistory uses large precomputed transfer function tables to evolve photon and electron spectra in redshift steps, which require a significant amount of memory and storage space. We present a light version of darkhistory that makes use of simple dense neural networks to store and interpolate the transfer functions, reducing their total size by a factor of $\sim 400$, from $\sim 17\mathrm{Gb}$ to $\sim 45\mathrm{Mb}$, which performs well on small computers with limited memory and storage. This method anticipates future expansion with additional parametric dependence in the transfer functions without requiring exponentially larger data tables.

The presence of delayed GeV emission after a strong transient, such as a gamma-ray burst (GRB), in the very-high energy (VHE) $E>100\mathrm{GeV}$ band can be the signature of a nonzero magnetic field in the intergalactic medium. We used a synchrotron self-Compton multiwavelength model to infer an analytical description of the intrinsic VHE spectrum (corrected for absorption by the extragalactic background light) of GRB 190114C to predict the light curves and spectral energy distributions of the delayed emission with Monte Carlo simulations for different intergalactic magnetic field (IGMF) configurations (strengths $B=8\times {10}^{-21}\mathrm{G}$, ${10}^{-20}\mathrm{G}$, $3\times {10}^{-20}\mathrm{G}$ and correlation length $\lambda >1\mathrm{Mpc}$), and compared them with the Fermi Large Area Telescope (Fermi LAT) limits computed for several exposure times. We found that the Fermi LAT is not sensitive enough to constrain any IGMF strengths using GRB 190114C.

In recent years, artificial intelligence technology for gravitational wave data analysis has developed rapidly. In this paper, we put forward a new artificial intelligence model for gravitational wave search. The framework of such a model includes a detection stage and a testing stage. We first use the deep learning technology to extract the envelope information of the gravitational wave candidate and use the coalescence time obtained from the envelope to further confirm the detection results. Within the detection stage, we use wavelet denoising and a special training strategy to improve the performance of the gravitational wave detection model. The lowest false alarm rate of the detection model is about 1.7 per month without the testing stage. When the testing stage is added, the lowest false alarm rate decreases to 0.046 per year. The efficiency of our model is demonstrated by the data obtained from the first, second, and third observing runs of the LIGO-VIRGO-KAGRA collaboration. The search results of confident events on the three observing runs indicate that the efficiency of our deep learning algorithm can achieve 80% of the traditional algorithm based on matched filtering.

We show how to use the worldline-instanton formalism to calculate the momentum spectrum of the electron-positron pairs produced by an electric field that depends on both space and time. Using the Lehmann-Symanzik-Zimmermann (LSZ) reduction formula with a worldline representation for the propagator in a spacetime field, we make use of the saddle-point method to obtain a semiclassical approximation of the pair-production spectrum. To check the final result, we integrate the spectrum and compare with the results obtained using a previous instanton method for the imaginary part of the effective action.

We constrain the parameters of a representative new physics model with a possible dark matter (DM) signature from a global Cabibbo-Kobayashi-Maskawa (CKM) fit analysis. The model has neutral quark current interactions mediated by a scalar, impacting the semileptonic and purely leptonic meson decays at one loop. We take this opportunity to update the fit results for the Wolfenstein parameters and the CKM elements with and without a contribution from the new model using several other updated inputs. In addition, we analyze and include the $B\to D^{*}\ell {\nu }_{\ell }$ decay in the CKM fit. The newly available inputs on the relevant form factors from lattice calculations are included, and the possibility of new physics effects in $B\to D^{*}\ell {\nu }_{\ell }$ is considered. We obtain tight constraints on the relevant new physics parameters. We study the possible implications of this constraint on DM phenomenology. Apart from DM, the bounds are also applicable in other relevant phenomenological studies.

It is possible that there is another scalar hiding behind the known 125 GeV Higgs boson. If the hidden scalar exhibits a $CP$ property different from the Higgs boson, then it can be exposed in the di-Higgs production at the high-luminosity large hadron collider and future colliders.

Neutrino-nucleus coherent scattering measurements by the COHERENT collaboration provide us with a unique capability to test various beyond the standard model scenarios. In this work, we constrain scalar leptoquarks (LQs) using the COHERENT data. LQs arise in many extensions of the Standard Model (SM). Generally, the mass of the LQs is assumed to be very high to avoid the bounds from proton decay. However, there are low-scale LQ models which prohibit proton decay by construction. We consider two electroweak doublet scalar LQ models with hypercharge $\mathrm{Y}=1/6$, and $\mathrm{Y}=7/6$ and provide the bounds in the plane of the Yukawa coupling and the mass of LQ. We also compare the bounds on LQs coming from various other experiments and find that the COHERENT one covers a wide range of LQ masses from MeV to TeV and in certain regions the constraints are competitive with the others.

We investigate several aspects of chiral symmetry in QCD at a temperature of $T=128\mathrm{MeV}$. The study is based on a $24\times 96^3$ lattice-QCD ensemble with $\mathrm{O}(a)$-improved Wilson quarks and physical up, down and strange quark masses. The pion quasiparticle turns out to be significantly lighter than the zero-temperature pion mass, even though the corresponding static correlation length is shorter. We perform a quantitative comparison of our findings to predictions of chiral perturbation theory. Among several order parameters for chiral symmetry restoration, we compute the difference of the vector- and axial-vector time-dependent correlators and find it to be reduced by a factor $\sim 2/3$ as compared to its vacuum counterpart.

We calculate the next-to-leading order corrections to dihadron production in deep inelastic scattering (DIS) at small $x$ using the color glass condensate formalism for the case when the virtual photon is transverse polarized. Similar to the case of longitudinal photon exchange all UV and soft singularities cancel while the collinear divergences are absorbed into quark and antiquark-hadron fragmentation functions. Rapidity divergences lead to Jalilian-Marian, Iancu, McLerran, Wiegert, Leonidov, Kovner (JIMWLK) evolution of dipoles and quadrupoles which describe multiple scatterings of the quark antiquark dipole on the target proton/nucleus and contain all the QCD dynamics of the target leading to a finite final result for the dihadron production cross section.

We make a systematical diffusion Monte Carlo (DMC) calculation for all ground state baryons in two confinement scenarios, the pairwise confinement and the three-body flux-tube confinement. With the baryons as an example, we illustrate a feasible procedure to investigate the few-quark states with possible few-body confinement mechanisms, which can be extended to the multiquark states easily. For each baryon, we extract the mass, mean square radius, charge radius, and the quark distributions. We use the jackknife resampling method to estimate the statistical uncertainties of masses to be less than 1 MeV. To determine the baryon charge radii, we include the constituent quark size effect, which is fixed by the experimental and lattice QCD results. Our results show that both two-body and three-body confinement mechanisms can give a good description of the experimental data if the parameters are chosen properly. In the flux-tube confinement, introducing different tension parameters for the baryons and mesons are necessary, specifically, ${\sigma }_Y=0.9204{\sigma }_{Q\overline{Q}}$. The lesson from the calculation of the nucleon mass with the DMC method is that the improper preassignment of the channels may prevent us from obtaining the real ground state. With this experience, we obtain the real ground state (the ${\eta }_c{\eta }_c$ threshold with the dimeson configuration) of the $cc\overline{c}\overline{c}$ system with $J^{PC}=0^{++}$ starting from the diquark-antidiquark spin-color channels alone, which is difficult to achieve in the variational method and was not obtained in the previous DMC calculations.

The decay rates of the XYZ exotics discovered in the heavy quarkonium sector are crucial observables for identifying the nature of these states. Based on the framework of nonrelativistic effective field theories, we calculate the rates of semi-inclusive decays of heavy quarkonium hybrids into conventional heavy quarkonia. We compute them at leading and subleading power in the inverse of the heavy-quark mass, extending and updating previous results. We compare our predictions with experimental data of inclusive decay rates for candidates of heavy quarkonium hybrids.

Considering a fixed-flavor number scheme and based on Laplace transformation, we perform leading-order and next-to-leading-order QCD analyses that include world data on polarized structure functions $g_1$ and $g_2$. During our analysis, taking the DGLAP evolution equations, we employ the Jacobi polynomials expansion technique. In our recent analysis we utilize the recent available data and consequently include more data than what we did in our previous analysis. We obtain good agreements between our results for the polarized parton densities and nucleon structure functions with all available experimental data and some common parametrization models.

We report cross-section measurements of the final-state muon kinematics for ${\nu }_{\mu }$ charged-current interactions in the NOvA near detector using an accumulated $8.09\times {10}^{20}$ protons on target in the NuMI beam. We present the results as a double-differential cross section in the observed outgoing muon energy and angle, as well as single-differential cross sections in the derived neutrino energy, $E_{\nu }$, and square of the four-momentum transfer, $Q^2$. We compare the results to inclusive cross-section predictions from various neutrino event generators via ${\chi }^2$ calculations using a covariance matrix that accounts for bin-to-bin correlations of systematic uncertainties. These comparisons show a clear discrepancy between the data and each of the tested predictions at forward muon angle and low $Q^2$, indicating a missing suppression of the cross section in current neutrino-nucleus scattering models.

Using $7.33{\mathrm{fb}}^{-1}$ of $e^{+}{e}^{-}$ collision data collected by the BESIII detector at c.m. energies between 4.128 GeV and 4.226 GeV, we observe for the first time the decay $D_s^{\pm }\to \omega {\pi }^{\pm }\eta$ with a statistical significance of $7.6\sigma$. The measured branching fraction of this decay is $(0.54\pm 0.12\pm 0.04)\%$, where the first uncertainty is statistical and the second is systematic.