Motivated by gravitational wave observations of binary black hole mergers, we present a procedure to compute the leading-order nonlinear gravitational wave interactions around a Kerr black hole. We describe the formalism used to derive the equations for second-order perturbations. We develop a procedure that allows us to reconstruct the first-order metric perturbation solely from knowledge of the solution to the first-order Teukolsky equation, without the need of Hertz potentials. Finally, we illustrate this metric reconstruction procedure in the asymptotic limit for the first-order quasinormal modes of Kerr. In a companion paper [J. L. Ripley et al., Phys. Rev. D 103, 104018 (2021)] we present a numerical implementation of these ideas.

We study cross correlations between line intensity and weak lensing maps to search for axionlike particles (ALPs). Radiative decay of eV-mass ALPs can contribute to cosmic background emissions at optical and infrared wavelengths. Line intensity mapping is a unique means of measuring the background emission at a given photon frequency. If ALPs constitute the abundance of cosmic dark matter, line intensity maps can correlate with large-scale structures probed by weak gravitational lensing effects in galaxy-imaging surveys. We develop a theoretical framework to predict the cross-correlation. We then explore potentiality of probing ALPs with the cross-correlation in upcoming galaxy-imaging and spectral surveys. Assuming SPHEREx and the Vera Rubin Observatory’s Legacy Survey of Space and Time (LSST), we find that the cross-correlation by the ALP decay can be greater than the astrophysical-line counterparts at wavelength of $\sim 3000\mathrm{nm}$ for ALPs with a particle mass of $m_a\sim 1\mathrm{eV}$ and a particle-to-two-photons coupling of $g_{a\gamma \gamma }\sim 1\times {10}^{-11}{\mathrm{GeV}}^{-1}$. We also predict that a null detection of the cross-correlation can place a $2\sigma$-level upper bound of $g_{a\gamma \gamma }\lesssim {10}^{-11}{\mathrm{GeV}}^{-1}$ for eV-mass ALPs, improving the current constraint by a factor of $\sim 10$. We then make a forecast of expected constraints on ALP parameters in SPHEREx and LSST by Fisher analysis, providing a guideline of searching for the ALP decay with the large-scale structure data.

GW170817 has led to the first example of multimessenger astronomy with observations from gravitational wave interferometers and electromagnetic telescopes combined to characterize the source. However, detections of the early inspiral phase by the gravitational wave detectors would allow the observation of the earlier stages of the merger in the electromagnetic band, improving multimessenger astronomy and giving access to new information. In this paper, we introduce a new machine-learning-based approach to produce early-warning alerts for an inspiraling binary neutron star system, based only on the early inspiral part of the signal. We give a proof of concept to show the possibility to use a combination of small convolutional neural networks trained on the whitened detector strain in the time domain to detect and classify early inspirals. Each of those is targeting a specific range of chirp masses dividing the binary neutron star category into three subclasses: light, intermediate, and heavy. In this work, we focus on one LIGO detector at design sensitivity and generate noise from the design power spectral density. We show that within this setup it is possible to produce an early alert up to 100 seconds before the merger for the best-case scenario. We also present some future upgrades that will enhance the detection capabilities of our convolutional neural networks. Finally, we also show that the current number of detections for a realistic binary neutron star population is comparable to that of matched filtering and that there is a high probability to detect GW170817- and GW190425-like events at design sensitivity.

We demonstrate the role of $D_{(s)}^{*}$ and their contributions in the quasi-two-body decays $B_{(s)}\to D_{(s)}h{h}^{\prime }$ ($h,h^{\prime }=\{\pi ,K\}$) in the perturbative QCD approach, stemming from the quark flavor changing $\overline{b}\to \overline{c}{q}_2{\overline{q}}_1$ and $\overline{b}\to c\overline{q_1}\overline{q_2}$ with $q_1,q_2=\{s/d,u\}$. The main motivation of this study is the measurement of significant derivations from the simple phase-space model in the channels $B_{(s)}\to D_{(s)}h{h}^{\prime }$ at $B$ factories and LHC, which are now clarified as the Breit-Wigner-tail effects from the corresponding intermediate resonant states $D_{(s)}^{*}$. We confirm that these effects from $D^{*}$ are small ($\sim 5\%$) in the quasi-two-body $B_{(s)}\to D\pi \pi (K)$ decaying channels and predict the tiny ($<1\%$) contributions from $D^{*}$ in the $B_{(s)}\to D_{s}K\pi (K)$ decaying channels. Our result that the $B_s\to DK\pi (K)$ decaying channel contributions were only from the Breit-Wigner-tail effect of $D_s^{*}$ is in agreement with the current LHCb measurement. We recommend that the Belle-II and the LHCb Collaborations restudy the processes $B^{+}\to {\overline{D}}^{*0}{\pi }^{+}(K^{+})\to D^{-}{\pi }^{+}{\pi }^{+}(K^{+})$ to reveal the structure of $D^{*0}$ and the strong decay $D^{*0}\to D^{+}{\pi }^{-}$.

The expressions of the shear viscosity and the bulk viscosity components in the presence of an arbitrary external magnetic field for a system of hot charged scalar bosons (spin 0) as well as for a system of hot charged Dirac fermions (spin $\frac{1}{2}$) have been derived by employing the one-loop Kubo formalism. This is done by explicitly evaluating the thermomagnetic spectral functions of the energy-momentum tensors using the real time formalism of finite temperature field theory and the Schwinger proper time formalism. In the present work, a rich quantum field theoretical structure in the expressions of the viscous coefficients in nonzero magnetic field are found, which are different from their respective expressions obtained earlier via kinetic-theory-based calculations; though, in the absence of a magnetic field, the one-loop Kubo and the kinetic-theory-based expressions for the viscosities are known to be identical. We have identified that Kubo and kinetic-theory-based results of viscosity components follow a similar kind of temperature and magnetic field dependency. The relaxation time and the synchrotron frequency in the kinetic theory formalism are realized to be connected, respectively, with the thermal width of propagator and the transitions among the Landau levels of the charged particles in the Kubo formalism. We believe that the connection of the latter quantities is quite new and probably the present work is the first time addressing this interpretation along with the new expressions of viscosity components, not seen in existing works.

Electroweakly interacting massive particles (EWIMPs), in other words, new massive particles that are charged under the electroweak interaction of the Standard Model (SM), are often predicted in various new physics models. EWIMPs are probed at hadron collider experiments not only by observing their direct productions but also by measuring their quantum effects on Drell-Yan processes for SM lepton pair productions. Such effects are known to be enhanced especially when the dilepton invariant mass of the final state is close to the EWIMP threshold, namely twice the EWIMP mass. In such a mass region, however, we have to carefully take nonperturbative effects into account, because the EWIMPs become nonrelativistic and the prediction may be significantly affected by, e.g., bound states of the EWIMPs caused by the electroweak interaction. We study such nonperturbative effects using the nonrelativistic effective field theory of the EWIMPs, and found that those indeed affect the differential cross section of the Drell-Yan processes significantly, though the effects are smeared due to the finite energy resolution of the lepton measurement at the Large Hadron Collider experiment.

We show that the canonical seesaw mechanism implemented by the $U(1{)}_{B-L}$ gauge symmetry provides two-component dark matter naturally. The seesaw scale that breaks $B-L$ defines a residual gauge symmetry to be $Z_6=Z_2\otimes Z_3$, where $Z_2$ leads to the usual matter parity, while $Z_3$ is newly recognized, transforming quark fields nontrivially. The dark matter components—that transform nontrivially under the matter parity and $Z_3$, respectively—can gain arbitrary masses, despite the fact that the $Z_3$ dark matter may be heavier than the light quarks $u$, $d$. This dark matter setup can address the XENON1T anomaly recently observed and other observables, given that the dark matter masses are nearly degenerate, heavier than the electron and the $B-L$ gauge boson $Z^{\prime }$, as well as the fast-moving $Z_3$ dark matter has a large $B-L$ charge, while the $Z^{\prime }$ is viably below the beam dump experiment sensitive regime.

Nonrelativistic dark matter (DM) can be accelerated by scattering on high-energy cosmic-ray (CR) electrons. This process leads to a subpopulation of relativistic or semirelativistic DM which extends the experimental reach for direct detection in the sub-GeV mass regime. In this paper we examine the current and future potential of this mechanism for constraining models of light dark matter. In particular, we find that Super-Kamiokande and XENON1T data can already provide leading constraints on the flux of dark matter that has been accelerated to high energies from cosmic ray electrons. We also examine future projected sensitivities for DUNE and Hyper-K, and contrary to previous findings, conclude that DUNE will be able supersede Super-K bounds on cosmic-ray upscattered DM for a variety of DM models.

We investigate a model of dark sector based on non-Abelian $SU(2{)}_D$ gauge symmetry. This dark gauge symmetry is broken into discrete $Z_2$ via vacuum expectation values of two real triplet scalars, and an $SU(2{)}_D$ doublet Dirac fermion becomes $Z_2$—odd particles whose lighter component makes stable dark matter candidate. The standard model and dark sector can be connected via the scalar mixing and the gauge kinetic mixing generated by higher dimensional operators. We then discuss relic density of dark matter and implications to collider physics in the model. The most unique signatures of this model at the LHC would be the dark scalar (${\mathrm{\Phi }}_1^{{(}^{\prime })}$) productions where it subsequently decays into: (1) a fermionic dark matter (${\chi }_l$) and a heavy dark fermion (${\chi }_h$) pair, ${\mathrm{\Phi }}_1^{{(}^{\prime })}\to {\overline{\chi }}_l{\chi }_h({\overline{\chi }}_h{\chi }_l)$, followed by ${\chi }_h$ decays into ${\chi }_l$ and non-Abelian dark gauge bosons ($X_i$’s) which decays into SM fermion pair ${\overline{f}}_{\mathrm{SM}}{f}_{\mathrm{SM}}$ resulting in the reaction $pp\to {\mathrm{\Phi }}_1^{{(}^{\prime })}\to {\overline{\chi }}_h{\chi }_l({\overline{\chi }}_l{\chi }_h)\to f_{\mathrm{SM}}{\overline{f}}_{\mathrm{SM}}{\chi }_l{\overline{\chi }}_l$, (2) a pair of $X_i$’s followed by $X_i$ decays into a DM pair or the SM fermions resulting in the reaction, $pp\to {\mathrm{\Phi }}_1^{{(}^{\prime })}\to X_i{X}_i\to {\overline{\chi }}_l{\chi }_l{f}_{\mathrm{SM}}{\overline{f}}_{\mathrm{SM}}$ or even number of $f_{\mathrm{SM}}{\overline{f}}_{\mathrm{SM}}$ pairs.

The parton quasidistribution functions approach provides a path to computing parton distribution functions (PDFs) using lattice QCD. This approach requires matrix elements of a power-divergent operator in a nucleon at high momentum and one generically expects discretization effects starting at first order in the lattice spacing $a$. Therefore, it is important to demonstrate that the continuum limit can be reliably taken and to understand the size and shape of lattice artifacts. In this work, we report a calculation of isovector unpolarized and helicity PDFs using lattice ensembles with $N_f=2+1+1$ Wilson twisted mass fermions, a pion mass of approximately 370 MeV, and three different lattice spacings. Our results show a significant dependence on $a$, and the continuum extrapolation produces a better agreement with phenomenology. The latter is particularly true for the antiquark distribution at small momentum fraction $x$, where the extrapolation changes its sign.

In this work, we find the light front densities for momentum and forces, including pressure and shear forces, within hadrons. This is achieved by deriving relativistically correct expressions relating these densities to the gravitational form factors $A(t)$ and $D(t)$ associated with the energy momentum tensor. The derivation begins from the fundamental definition of density in a quantum field theory, namely the expectation value of a local operator within a spatially localized state. We find that it is necessary to use the light front formalism to define a density that corresponds to the internal hadron structure. When using the instant form formalism, it is impossible to remove the spatial extent of the hadron wave function from any density, and—even within instant form dynamics—one does not obtain a Breit frame Fourier transform for a properly defined density. Within the front formalism, we derive new expressions for various mechanical properties of hadrons, including the mechanical radius, as well as for stability conditions. The multipole ansatz for the form factors is used as an example to illustrate all of these findings.

We review arguments that chiral symmetry breaking is triggered when the quark bilinear condensate’s dimension passes through one ($\gamma =1$). This is supported by gap equations and more recently holographic models. Confinement may then be a separate property of the pure Yang-Mills theory below the scale of the dynamically generated quark mass, occurring at the scale of the pole in the deep IR running. Here, we use perturbative results for the running of the gauge coupling and $\gamma$ in asymptotically free $\mathrm{SU}(N)$ gauge theories with matter in higher dimension representations to seek the best candidate theories where confinement and chiral symmetry breaking can be maximally separated. For example, SU(2) gauge theory with a single Weyl quark in the $S_3$ (dimension 4) representation may have a factor of 20 separation in scale. Such a theory could be simulated on the lattice to test the separation. We also propose studying multirepresentation theories where the higher dimension representation forms a condensate at one scale that can be quite separate from the condensation scale of the second representation matter. The confinement scale would presumably be below the second scale. For example, SU(3) gauge theory with a Weyl adjoint fermion and ten fundamental quarks may have a separation of a factor of 20 also.

We consider the associated production of Higgs boson and hadronic jet(s) in $pp$ collisions at the LHC for the first time using the $k_T$-factorization approach. Our analysis is based on the off-shell gluon-gluon fusion subprocess, where nonzero transverse momenta of initial gluons are taken into account and covers $H\to \gamma \gamma$, $H\to Z{Z}^{*}\to 4l$ (with $l=e$, $\mu$), and $H\to W^{+}{W}^{-}\to e^{\pm }{\mu }^{\mp }\nu \overline{\nu }$ decay channels. The transverse momentum dependent (TMD) (or unintegrated) gluon densities in a proton are taken from Catani-Ciafaloni-Fiorani-Marchesini evolution equation. To simulate the kinematics of the produced jets, the TMD parton shower implemented into the Monte Carlo event generator cascade is applied. The comparison of our results with the latest experimental data taken by the CMS and ATLAS Collaborations at $\sqrt{s}=8$ and 13 TeV is presented. Our predictions are compared also with the results of conventional higher-order perturbative QCD calculations. We highlight observables, which are sensitive to the TMD gluon densities in a proton.

Explicit expressions for quantum fluctuations of energy in subsystems of a hot relativistic gas of spin-$1/2$ particles are derived. The results depend on the form of the energy-momentum tensor used in the calculations, which is a feature described as pseudogauge dependence. However, for sufficiently large subsystems the results obtained in different pseudogauges converge and agree with the canonical-ensemble formula known from statistical physics. As different forms of the energy-momentum tensor of a gas are a priori equivalent, our finding suggests that the concept of quantum fluctuations of energy in very small thermodynamic systems is pseudogauge dependent. On the practical side, the results of our calculations determine a scale of coarse graining for which the choice of the pseudogauge becomes irrelevant.

We consider examples of long-lived false vacua in quantum field theory that arise from so-called ‘universes’. These false vacua are protected by a ($d-1$)-form global symmetry, where $d$ is the dimension of spacetime. The lifetimes of the false vacua are set by UV data: the tension of ($d-2$)-branes charged under a ($d-2$)-form gauge symmetry. The lifetimes can be made parametrically long even when the difference in energy density between the false and true vacua is large compared to the natural scales of the field theory. We study examples of near-eternal false vacua in Abelian gauge theories in two dimensions and in four-dimensional QCD. In both cases, it is possible to view the ($d-1$)-form symmetries as arising from a modification of the sum over instantons. We find that the modification of the instanton sum in 4d QCD leads to a higher-group symmetry structure involving the 3-form and conventional 0-form global symmetries.

We examine a quantized massive scalar field in ($1+1$)-dimensional spatially compact cosmological spacetimes in which the early time and late time expansion laws provide distinguished definitions of Fock “in” and “out” vacua, with the possible exception of the spatially constant sector, which may become effectively massless at early or late times. We show, generalizing the work of Ford and Pathinayake, that when such a massive zero mode occurs, the freedom in the respective in and out states is a family with two real parameters. As an application, we consider massive untwisted and twisted scalar fields in the ($1+1$)-dimensional spatially compact Milne spacetime, where the untwisted field has a massive in zero mode. We demonstrate, by a combination of analytic and numerical methods, that the choice of the massive in zero mode state has a significant effect on the response of an inertial Unruh-DeWitt detector, especially in the excitation part of the spectrum. The detector’s peculiar velocity with respect to comoving cosmological observers has the strongest effect in the in vacuum of the untwisted field, where it shifts the excitation and deexcitation resonances toward higher values of the detector’s energy gap.

Entanglement entropy (EE) in interacting field theories has two important issues: renormalization of UV divergences and non-Gaussianity of the vacuum. In this paper, we investigate them in the framework of the two-particle irreducible formalism. In particular, we consider EE of a half space in an interacting scalar field theory. It is formulated as ${\mathbb{Z}}_M$ gauge theory on Feynman diagrams: ${\mathbb{Z}}_M$ fluxes are assigned on plaquettes and summed to obtain EE. Some configurations of fluxes are interpreted as twists of propagators and vertices. The former gives a Gaussian part of EE written in terms of a renormalized 2-point function while the latter reflects non-Gaussianity of the vacuum.

We have studied the induced one-loop energy-momentum tensor of a massive complex scalar field within the framework of nonperturbative quantum electrodynamics (QED) with a uniform electric field background on the Poincaré patch of the two-dimensional de Sitter spacetime (${\mathrm{d}\mathrm{S}}_2$). We also consider a direct coupling the scalar field to the Ricci scalar curvature which is parametrized by an arbitrary dimensionless nonminimal coupling constant. We evaluate the trace anomaly of the induced energy-momentum tensor. We show that our results for the induced energy-momentum tensor in the zero electric field case, and the trace anomaly are in agreement with the existing literature. Furthermore, we construct the nonperturbative, regularized, one-loop effective Lagrangian of scalar QED in $\mathrm{d}{\mathrm{S}}_2$ from the induced energy-momentum tensor.

In the presence of a black hole, light sources connect to observers along multiple paths. As a result, observed brightness fluctuations must be correlated across different times and positions in black hole images. Photons that execute multiple orbits around the black hole appear near a critical curve in the observer sky, giving rise to the photon ring. In this paper, a novel observable is proposed: the two-point correlation function of intensity fluctuations on the photon ring. This correlation function is analytically computed for a Kerr black hole surrounded by stochastic equatorial emission, with source statistics motivated by simulations of a turbulent accretion flow. It is shown that this two-point function exhibits a universal, self-similar structure consisting of multiple peaks of identical shape: while the profile of each peak encodes statistical properties of fluctuations in the source, the locations and heights of the peaks are determined purely by the black hole parameters. Measuring these peaks would demonstrate the existence of the photon ring without resolving its thickness, and would provide estimates of black hole mass and spin. With regular monitoring over sufficiently long timescales, this measurement could be possible via interferometric imaging with modest improvements to the Event Horizon Telescope.

We study the polarizations of gravitational waves (GWs) in two classes of extended gravity theories. As a preparatory yet complete study, we formulate the polarizations in linear massive gravity (MG) with generic mass terms of non-Fierz–Pauli type by identifying all the independent variables that obey Klein–Gordon-type equations. The dynamical degrees of freedom (dofs) in the generic MG consist of spin-2 and spin-0 modes, the former breaking down into two tensor (helicity-2), two vector (helicity-1), and one scalar (helicity-0) components, while the latter just corresponding to a scalar. We find convenient ways of decomposing the two scalar modes of each spin into distinct linear combinations of the transverse and longitudinal polarizations with coefficients directly expressed by the mass parameters, thereby serving as a useful tool in measuring the masses of GWs. Then we analyze the linear perturbations of generic higher-curvature gravity (HCG) whose Lagrangian is an arbitrary polynomial of the Riemann tensor. When expanded around a flat background, the linear dynamical dofs in this theory are identified as massless spin-2, massive spin-2, and massive spin-0 modes. As its massive part encompasses the identical structure to the generic MG, GWs in the generic HCG provide six massive polarizations on top of the ordinary two massless modes. In parallel to MG, we find convenient representations for the scalar-polarization modes directly connected to the parameters of HCG. In the analysis of HCG, we employ two distinct methods; One takes full advantage of the partial equivalence between the generic HCG and MG at the linear level, whereas the other relies upon a gauge-invariant formalism. We confirm that the two results agree. We also discuss methods to determine the theory parameters by GW-polarization measurements. It is worth stressing that our method for determining the theory parameters does not require measuring the propagation speeds, whether absolute or relative, or the details of the waveforms of the GWs.