The analytic structures of scattering amplitudes in gauge theory and gravity are examined on the celestial sphere. The celestial amplitudes in the two theories—computed by employing a regulated Mellin transform—can be compared at low multiplicity. It is established by direct computation that up to five external particles, the double copy relations of Kawai, Lewellen, and Tye continue to hold identically, modulo certain multiplicative factors which are explicitly determined. Supersymmetric representations of the amplitudes are utilized throughout, manifesting the double copy structure between $\mathcal{N}=4$ super Yang-Mills and $\mathcal{N}=8$ supergravity on the celestial sphere.

We theoretically propose an experimentally viable scheme to use an impurity atom in a dipolar Bose-Einstein condensate, in order to probe analogue low-energy Lorentz violation from the modified dispersion at high energies as suggested by quantum theories of gravity. We show that the density fluctuations in the dipolar Bose-Einstein condensate possess a Lorentz-violating Bogoliubov spectrum ${\omega }_{\mathbf{k}}=c_0|\mathbf{k}|f(c_0|\mathbf{k}|/M_{\star })$, with recovery of approximate Lorentz invariance at energy scales well below $M_{\star }$. When $f$ is adjusted to dip below unity somewhere, the impurity, analogously dipole coupled to the density fluctuations, experiences analogous drastic Lorentz violation at arbitrarily low energies, reproducing the same response of the Unruh-DeWitt detector to Lorentz-violating quantum fields. Being a fundamentally quantum mechanical device, our quantum fluid platform provides an experimentally realizable test field to verify whether the effective low-energy theory can reveal unexpected imprints of the theory’s high-energy structure, in quantum field theory.

We present a recursive procedure, which is based on the small time expansion of the propagator, in order to generate a semiclassical expansion of the quantum action for a quantum mechanical potential in arbitrary dimensions. In the method, we use the spectral information emerges from the singularities of the propagator on the complex $t$ plane, which are handled by the $iϵ$ prescription and basic complex analysis. This feature allows for generalization to higher dimensions. We illustrate the procedure by providing simple examples in nonrelativistic quantum mechanics.

The signal of continuous gravitational waves has a longer duration than the observation period. Even if the waveform in the source frame is monochromatic, we will observe the waveform with modulated frequencies due to the motion of the detector. If the source location is unknown, a lot of templates having different sky positions are required to demodulate the frequency, and the required huge computational cost restricts the applicable parameter region of coherent search. In this work, we propose and examine a new method to select candidates, which reduces the cost of coherent search by following up only the selected candidates. As a first step, we consider an idealized situation in which only a single-detector having 100% duty cycle is available and its detector noise is approximated by the stationary Gaussian noise. Also, we assume that the signal has no spin-down, that the polarization angle, the inclination angle, and the initial phase are fixed to be $\psi =0$, $\cos \iota =1$, and ${\varphi }_0=0$, and that they are treated as known parameters. We combine several methods: (1) the short-time Fourier transform with the resampled data such that the Earth motion for the source is canceled in some reference direction, (2) the excess power search in the Fourier transform of the time series obtained by picking up the amplitude in a particular frequency bin from the short-time Fourier transform data, and (3) the deep learning method to further constrain the source sky position. The computational cost and the detection probability are estimated. The injection test is carried out to check the validity of the detection probability. We find that our method is worthy of further study for analyzing $O({10}^7)\sec$ strain data.

Modeling the endpoint of binary black hole mergers is a cornerstone of modern gravitational-wave astronomy. Extracting multiple quasinormal mode frequencies from the ringdown signal allows the remnant black hole to be studied in unprecedented detail. Previous studies on numerical relativity simulations of aligned-spin binaries have found that it is possible to start the ringdown analysis much earlier than previously thought if overtones (and possibly mirror modes) are included. This increases the signal-to-noise ratio in the ringdown making identification of subdominant modes easier. In this paper we study, for the first time, black hole binaries with misaligned spins and find a much greater variation in the performance of ringdown fits than in the aligned-spin case. The inclusion of mirror modes and higher harmonics, along with overtones, improves the reliability of ringdown fits with an early start time; however, there remain cases with poor performing fits. While using overtones in conjunction with an early ringdown start time is an enticing possibility, it is necessary to proceed with caution. We also consider for the first time the use of numerical relativity surrogate models in this type of quasinormal mode study and address important questions of accuracy in the underlying numerical waveforms used for the fit.

We describe the methods used to construct the aligned-spin template bank of gravitational waveforms used by the Gstreamer and Ligo Algorithm Library (GstLAL)-based pipeline to analyze data from the second observing run of Advanced Laser Interferometer Gravitational Wave Observatory (LIGO) and the first observing run of Advanced Virgo. The bank expands upon the parameter space covered during Advanced LIGO’s first observing run, including coverage for merging compact binary systems with total mass between $2{\mathrm{M}}_{\odot }$ and $400{\mathrm{M}}_{\odot }$ and mass ratios between 1 and 97.988. Thus the systems targeted include merging neutron star-neutron star systems, neutron star-black hole binaries, and black hole-black hole binaries expanding into the intermediate-mass range. Component masses less than $2{\mathrm{M}}_{\odot }$ have allowed (anti-)aligned spins between $\pm 0.05$, while component masses greater than $2{\mathrm{M}}_{\odot }$ have allowed (anti-)aligned between $\pm 0.999$. The bank placement technique combines a stochastic method with a new grid-bank method to better isolate noisy templates, resulting in a total of 677,000 templates.

Quasars have recently been used as an absolute distance indicator, extending the Hubble diagram to high redshift to reveal a deviation from the expansion history predicted for the standard, $\mathrm{\Lambda }\mathrm{CDM}$ cosmology. Here we show that the Laser Interferometer Space Antenna (LISA) will efficiently test this claim with standard sirens at high redshift, defined by the coincident gravitational wave (GW) and electromagnetic (EM) observations of the merger of massive black hole binaries (MBHBs). Assuming a fiducial $\mathrm{\Lambda }\mathrm{CDM}$ cosmology for generating mock standard siren data sets, the evidence for the $\mathrm{\Lambda }\mathrm{CDM}$ model with respect to an alternative model inferred from quasar data is investigated. By simulating many realizations of possible future LISA observations, we find that for 50% of these realizations (median result) four MBHB standard siren measurements will suffice to strongly differentiate between the two models, while 14 standard sirens will yield a similar result in 95% of the realizations. In addition, we investigate the measurement precision of cosmological parameters as a function of the number of observed LISA MBHB standard sirens, finding that 15 events will on average achieve a relative precision of 5% for $H_0$, reducing to 3% and 2% with 25 and 40 events, respectively. Our investigation clearly highlights the potential of LISA as a cosmological probe able to accurately map the expansion of the Universe at $z\gtrsim 2$, and as a tool to cross-check and cross-validate cosmological EM measurements with complementary GW observations.

We analyze about 12 years of Fermi-LAT data in the direction of the Andromeda galaxy (M31). We robustly characterize its spectral and morphological properties against systematic uncertainties related to the modeling of the Galactic diffuse emission. We perform this work by adapting and exploiting the potential of the skyfact adaptive template fitting algorithm. We reconstruct the $\gamma$-ray image of M31 in a template-independent way, and we show that flat spatial models are preferred by data, indicating an extension of the $\gamma$-ray emission of about 0.3–0.4° for the bulge of M31. This study also suggests that a second component, extending to at least 1°, contributes to the observed total emission. We quantify systematic uncertainties related to mismodeling of Galactic foreground emission at the level of 2.9%.

Accurately modeling the complete gravitational-wave signal from precessing binary black holes through the late inspiral, merger, and ringdown remains a challenging problem. The lack of analytic solutions for the precession dynamics of generic double-spin systems, and the high dimensionality of the problem, obfuscate the incorporation of strong-field spin-precession information into semianalytic waveform models used in gravitational-wave data analysis. Previously, an effective precession spin ${\chi }_p$ was introduced to reduce the number of spin degrees of freedom. Here, we show that ${\chi }_p$ alone does not accurately reproduce higher-order multipolar modes, in particular the ones that carry strong imprints due to precession such as the (2,1)-mode. To improve the higher-mode content, and in particular to facilitate an accurate incorporation of precession effects in the strong-field regime into waveform models, we introduce a new dimensional reduction through an effective precession spin vector, ${\overrightarrow{\chi }}_{\perp }$, which takes into account precessing spin information from both black holes. We show that this adapted effective precession spin (i) mimics the precession dynamics of the fully precessing configuration remarkably well, (ii) captures the signature features of precession in higher-order modes, and (iii) reproduces the final state of the remnant black hole with high accuracy for the overwhelming majority of configurations. We demonstrate the efficacy of this two-dimensional precession spin in the strong-field regime, paving the path for meaningful calibration of the precessing sector of semianalytic waveform models with a faithful representation of higher-order modes through merger and the remnant black hole spin.

The interpretation of measurements of high-energy particle collisions relies heavily on the performance of full event generators, which include the calculation of the hard process and the subsequent parton shower step. With the continuous improvement of quantum devices, dedicated algorithms are needed to exploit the potential quantum that computers can provide. We propose general and extendable algorithms for quantum gate computers to facilitate calculations of helicity amplitudes and the parton shower process. The helicity amplitude calculation exploits the equivalence between spinors and qubits and the unique features of a quantum computer to compute the helicities of each particle involved simultaneously, thus fully utilizing the quantum nature of the computation. This advantage over classical computers is further exploited by the simultaneous computation of s- and t-channel amplitudes for a $2\to 2$ process. The parton shower algorithm simulates collinear emission for a two-step, discrete parton shower. In contrast to classical implementations, the quantum algorithm constructs a wave function with a superposition of all shower histories for the whole parton shower process, thus removing the need to explicitly keep track of individual shower histories. Both algorithms utilize the quantum computers ability to remain in a quantum state throughout the computation and represent a first step towards a quantum computing algorithm describing the full collision event at the LHC.

Calculations in field theory are usually accomplished by employing some variants of perturbation theory, for instance, using loop expansions. These calculations result in asymptotic series in powers of small coupling parameters, which as a rule are divergent for finite values of the parameters. In this paper, we describe a method allowing for the extrapolation of such asymptotic series to finite values of the coupling parameters and even to their infinite limits. The method is based on self-similar approximation theory. This theory approximates well a large class of functions, rational, irrational, and transcendental. We present a method resulting in self-similar factor approximants allowing for the extrapolation of functions to arbitrary values of coupling parameters from only the knowledge of expansions in powers of small coupling parameters. The efficiency of the method is illustrated by several problems of quantum field theory.

One of the assumptions of simplified models is that there are a few new particles and interactions accessible at the LHC and all other new particles are heavy and decoupled. The effective field theory (EFT) method provides a consistent method to test this assumption. Simplified models can be augmented with higher order operators involving the new particles accessible at the LHC. Any UV completion of the simplified model will be able to match onto these beyond the Standard Model EFTs (BSM-EFT). In this paper, we study the simplest simplified model: the Standard Model extended by a real gauge singlet scalar. In addition to the usual renormalizable interactions, we include dimension-5 interactions of the singlet scalar with Standard Model particles. As we will show, even when the cutoff scale is 3 TeV, these new effective interactions can drastically change the interpretation of Higgs precision measurements and scalar searches. In addition, we discuss how power counting in a BSM-EFT depends strongly on the processes and parameter space under consideration. Finally, we propose a ${\chi }^2$ method to consistently combine the limits from new particle searches with measurements of the Standard Model. Unlike imposing a hard cutoff on heavy resonance rates, our method allows fluctuations in individual channels that are consistent with global fits.

Particle production in two-photon interactions at hadronic collisions is becoming increasingly relevant in the LHC physics program as a way to improve our understanding of the Standard Model and search for signals of New Physics. A key ingredient for the study of these interactions in $pp$ collisions is the description of the photon content of the proton, which allow us to derive predictions for the cross sections associated with events where occur the proton dissociation (nonexclusive processes) and for those where both incident protons remain intact (exclusive processes). In this paper, a detailed comparison of the different models for the elastic and inelastic photon distributions found in the literature is presented and the current theoretical uncertainty is estimated. The impact on the invariant mass distribution for the dimuon production is analyzed. Moreover, the relative contribution of nonexclusive events is estimated and its dependence on the invariant mass of the pair is presented. We demonstrate that the predictions for production of pairs with large invariant mass is strongly dependent on the model assumed to describe the elastic and inelastic photon distributions and that the ratio between nonexclusive and exclusive cross sections present a mild energy dependence. Finally, our results indicate that a future experimental analysis of the nonexclusive events will be useful to constrain the photon content of proton.

We study the behavior of a free massive scalar wave-packet near the Cauchy horizon of an ${\mathrm{AdS}}_2$ black hole and find that it becomes infinitely differentiable for smooth initial data, independently of the parameters describing the spacetime or the scalar. This indicates a violation of the strong cosmic censorship conjecture at the classical level. We discuss our result in connection with some recent observations of violation of the conjecture for certain nearly extremal black holes.

Focusing on the novel phenomenon of several enhancement structures existing in the invariant mass spectrum of a $J/\psi$ pair, which was reported by LHCb very recently, we find a new dynamical mechanism based on the special reactions, where all the possible combinations of a double charmonium directly produced by a proton-proton collision are transitioned into final-state $J/\psi J/\psi$. Under this framework, totally different from the popular tetraquark explanation, the LHCb experimental data of the line shape of the $J/\psi$-pair invariant mass spectrum can be well mimicked. Since the proposed dynamical mechanism is universal enough, we further predict the possible enhancement structures existing in the $\mathrm{\Upsilon }(1S)$-pair invariant mass spectrum, which may provide a realistic approach to test the new mechanism proposed in this work and form a new task for the LHCb and CMS experiments.

Algebraic properties of the Becchi-Rouet-Stora-Tyutin (BRST) symmetry associated to the twisted gauge symmetry occurring in the $\kappa$-Poincaré invariant gauge theories on the $\kappa$-Minkowski space are investigated. We find that the BRST operation associated to the gauge invariance of the action functional can be continuously deformed together with its corresponding Leibniz rule, into a nilpotent twisted BRST operation, leading to a twisted BRST symmetry algebra which may be viewed as a noncommutative analog of the usual Yang-Mills BRST algebra.

We present the first known integrable relativistic field theories with interacting massive and massless sectors, and we demonstrate that knowledge of the massless sector is essential for understanding of the spectrum of the massive sector. Terms in this spectrum polynomial in the spatial volume (the accuracy for which the Bethe ansatz would suffice in a massive theory) require not just Lüscher-like corrections (usually exponentially small) but the full Thermodynamic Bethe Ansatz (TBA) integral equations. We are motivated by the implications of these ideas for $\mathrm{AdS}/\mathrm{CFT}$, but present here only field-theory results.

We examine stability of summation by parts (SBP) numerical schemes that use hyperboloidal slices to include future null infinity in the computational domain. This inclusion serves to mitigate outer boundary effects and, in the future, will help reduce systematic errors in gravitational waveform extraction. We also study a setup with truncation error matching. Our SBP-Stable scheme guarantees energy balance for a class of linear wave equations at the semidiscrete level. We develop also specialized dissipation operators. The whole construction is made at second-order accuracy in spherical symmetry but could be straightforwardly generalized to higher order or spectral accuracy without symmetry. In a practical implementation, we evolve first a scalar field obeying the linear wave equation and observe, as expected, long-term stability and norm convergence. We obtain similar results with a potential term. To examine the limitations of the approach, we consider a massive field, whose equations of motion do not regularize and whose dynamics near null infinity, which involve excited incoming pulses that cannot be resolved by the code, is very different to that in the massless setting. We still observe excellent energy conservation, but convergence is not satisfactory. Overall, our results suggest that compactified hyperboloidal slices are likely to be provably effective whenever the asymptotic solution space is close to that of the wave equation.

We study the motion of charged particles in a family of five-dimensional solutions describing either a black hole or topological star with a fifth compact dimension stabilized by a magnetic flux. The particle’s trajectory is shown to move along the surface of a Poincaré cone. The radial motion shows a rich structure where the existence of various bound, plunging, or escaping trajectories depend on the constants of motion. Curves of energy and angular momentum corresponding to spherical orbits show a swallow-tail structure highly reminiscent to phase transitions of thermodynamics. When the momentum along the compact direction is varied, the is a critical point beyond which the swallow-tail kink disappears and becomes a smooth curve.