We present the first analytic results of next-to-next-to-next-to-leading-order (${\mathrm{N}}^3\mathrm{LO}$) QCD corrections to the top-quark decay width. We focus on the dominant leading color contribution, which includes light-quark loops. At next-to-next-to-leading order (NNLO), this dominant contribution accounts for 95% of the total correction. By utilizing the optical theorem, the ${\mathrm{N}}^3\mathrm{LO}$ corrections are related to the imaginary parts of the four-loop self-energy Feynman diagrams, which are calculated with differential equations. The results are expressed in terms of harmonic polylogarithms, enabling fast and accurate evaluation. The third-order QCD corrections decrease the leading-order decay width by 0.667%, and the scale uncertainty is reduced by half compared to the NNLO result. The most precise prediction for the top-quark width is now 1.321 GeV for $m_t=172.69\mathrm{GeV}$. Additionally, we obtain the third-order QCD corrections to the dilepton invariant mass spectrum and decay width in the semileptonic $b\to u$ transition. The perturbative series in the on-shell mass scheme exhibits poor convergence behavior. In the $\overline{\mathrm{MS}}$ mass scheme, the scale dependence is greatly improved. A more precise determination of the CKM matrix element $V_{ub}$ could be obtained with such higher-order corrections.

Laser Interferometer Space Antenna (LISA) will observe gravitational waves from galactic binaries (GBs) of white dwarfs or neutron stars. Some of these objects are among the most magnetic astrophysical objects in the Universe. Magnetism, by secularly disrupting the orbit, can eventually affect the gravitational waves emission and could then be potentially detected and characterized after several years of observations by LISA. Currently, the data processing pipeline of the LISA Data Challenge (LDC) for GBs does not consider either magnetism or eccentricity. Recently, it was shown [Bourgoin et al., [Phys. Rev. D 105, 124042 (2022)]] that magnetism induces a shift on the gravitational wave frequencies. Additionally, it was argued that, if the binary’s orbit is eccentric, the presence of magnetism could be detected by LISA. In this work, we explore the consequences of a future data analysis conducted on quasicircular and magnetic GB systems using the current LDC tools. We first show that a single eccentric GB can be interpreted as several GBs and this can eventually bias population studies deduced from LISA’s future catalog. Then, we confirm that for quasicircular orbits, the secular magnetic energy of the system can be inferred if the signal-to-noise ratio of the second harmonic is high enough to be detected by traditional quasimonochromatic source searching algorithms. LISA observations could therefore bring new insights on the nature and origin of magnetic fields in white dwarfs or neutron stars.

We calculate the form factors for the $B\to D^{*}\ell {\nu }_{\ell }$ decay in $2+1$ flavor lattice QCD. For all quark flavors, we employ the Möbius domain-wall action, which preserves chiral symmetry to a good precision. Our gauge ensembles are generated at three lattice cutoffs $a^{-1}\sim 2.5$, 3.6, and 4.5 GeV with pion masses as low as $M_{\pi }\sim 230\mathrm{MeV}$. The physical lattice size $L$ satisfies the condition $M_{\pi }L\ge 4$ to control finite volume effects (FVEs), while we simulate a smaller size at the smallest $M_{\pi }$ to directly examine FVEs. The bottom quark masses are chosen in a range from the physical charm quark mass to $0.7a^{-1}$ to control discretization effects. We extrapolate the form factors to the continuum limit and physical quark masses based on heavy meson chiral perturbation theory at next-to-leading order. Then the recoil parameter dependence is parametrized using a model independent form leading to our estimate of the decay rate ratio between the tau ($\ell =\tau$) and light lepton ($\ell =e$, $\mu$) channels $R(D^{*})=0.252(22)$ in the Standard Model. A simultaneous fit with recent data from the Belle experiment yields $|V_{cb}|=39.19(91)\times {10}^{-3}$, which is consistent with previous exclusive determinations, and shows good consistency in the kinematical distribution of the differential decay rate between the lattice and experimental data.

One of the main challenges in the numerical modeling of binary neutron-star mergers are long-term simulations of the postmerger remnant over timescales of the order of seconds. When this modeling includes all the aspects of the complex physics accompanying the remnant, the computational costs can easily become enormous. To address this challenge in part, we have developed a novel hybrid approach in which the solution from a general-relativistic magnetohydrodynamics (GRMHD) code solving the full set of the Einstein equations in Cartesian coordinates is coupled with another GRMHD code in which the Einstein equations are solved under the conformally flat condition (CFC). The latter approximation has a long history and has been shown to provide an accurate description of compact objects in nonvacuum spacetimes. An important aspect of the CFC approximation is that the elliptic equations need to be solved only for a fraction of the steps needed for the underlying hydrodynamical/magnetohydrodynamical evolution, thus allowing for a gain in computational efficiency that can be up to a factor of $\sim 6(230)$ in three-dimensional (two-dimensional) simulations. We present here the basic features of the new code, the strategies necessary to interface it when importing both two- and three-dimensional data, and a novel and robust approach to the recovery of the primitive variables. To validate our new framework, we have carried out a number of tests with various coordinates systems and different numbers of spatial dimensions, involving a variety of astrophysical scenarios, including the evolution of the postmerger remnant of a binary neutron-star merger over a timescale of one second. Overall, our results show that the new code, bhac+, is able to accurately reproduce the evolution of compact objects in nonvacuum spacetimes and that, when compared with the evolution in full general relativity, the CFC approximation reproduces accurately both the gravitational fields and the matter variables at a fraction of the computational costs. This opens the way for the systematic study of the secular matter and electromagnetic emission from binary-merger remnants.

In this work, we investigate spectral complexity and Krylov complexity in quantum billiard systems at finite temperature. We study both circle and stadium billiards as paradigmatic examples of integrable and nonintegrable quantum-mechanical systems, respectively. We show that the saturation value and timescale of spectral complexity may be used to probe the nonintegrability of the system since we find that when computed for the circle billiard, it saturates at a later timescale compared to the stadium billiards. This observation is verified for different temperatures. Furthermore, we study the Krylov complexity of the position operator and its associated Lanczos coefficients at finite temperature using the Wightman inner product. We find that the growth rate of the Lanczos coefficients saturates the conjectured universal bound at low temperatures. Additionally, we also find that even a subset of the Lanczos coefficients can potentially serve as an indicator of integrability, as they demonstrate erratic behavior specifically in the circle billiard case, in contrast to the stadium billiard. Finally, we also study Krylov entropy and verify its early-time logarithmic relation with Krylov complexity in both types of billiard systems.

The violation of the Bell inequality is one of the hallmarks of quantum mechanics and can be used to rule out local deterministic alternative descriptions. We utilize the data analysis published by the LHCb Collaboration on the helicity amplitudes for the decay $B^0\to J/\psi K^{*}(892{)}^0$ to compute the entanglement among the polarizations of the final vector mesons and the violation of the Bell inequality that it entails. We find that quantum entanglement can be detected with a significance well above $5\sigma$ (nominally $84\sigma$) and Bell inequality is violated with a significance well above $5\sigma$ (nominally $36\sigma$)—thereby firmly establishing these distinguishing feature of quantum mechanics at high energies in a collider setting and in the presence of strong and weak interactions. Entanglement is also present and the Bell inequality is violated in other decays of the $B$ mesons into vector mesons, but with lesser significance.

Line-intensity mapping (LIM) is quickly attracting attention as an alternative technique to probe large-scale structure and galaxy formation and evolution at high redshift. LIM one-point statistics are motivated because they provide access to the highly non-Gaussian information present in line-intensity maps and contribute to break degeneracies between cosmology and astrophysics. Now that promising surveys are underway, an accurate model for the LIM probability distribution function (PDF) is necessary to employ one-point statistics. We consider the impact of extended emission and limited experimental resolution in the LIM PDF for the first time. We find that these effects result in a lower and broader peak at low intensities and a lower tail towards high intensities. Focusing on the distribution of intensities in the observed map, we perform the first model validation of LIM one-point statistics with simulations and find good qualitative agreement. We also discuss the impact on the covariance, and demonstrate that if not accounted for, large biases in the astrophysical parameters can be expected in parameter inference. These effects are also relevant for any summary statistic estimated from the LIM PDF, and must be implemented to avoid biased results. The comparison with simulations shows, however, that there are still deviations, mostly related with the modeling of the clustering of emitters, which encourage further development of the modeling of LIM one-point statistics.

Neutrino interactions are essential for an accurate understanding of the binary neutron star merger process. In this article, we extend the code infrastructure of the well-established numerical-relativity code BAM that until recently neglected neutrino-driven interactions. In fact, while previous work allowed already the usage of nuclear-tabulated equations of state and employing a neutrino leakage scheme, we are moving forward by implementing a first-order multipolar radiation transport scheme ($M1$) for the advection of neutrinos. After testing our implementation on a set of standard scenarios, we apply it to the evolution of four low-mass binary systems, and we perform an analysis of ejecta properties. We also show that our new ejecta analysis infrastructure is able to provide numerical relativity-informed inputs for the codes POSSIS and Skynet, for the computation of kilonova lightcurves and nucleosynthesis yields, respectively.

We compute the nucleon axial and pseudoscalar form factors using three $N_f=2+1+1$ twisted-mass fermion ensembles with all quark masses tuned to approximately their physical values. The values of the lattice spacings of these three physical point ensembles are 0.080, 0.068, and 0.057 fm and spatial sizes 5.1, 5.44, and 5.47 fm, respectively, yielding $m_{\pi }L>3.6$. Convergence to the ground-state matrix elements is assessed using multistate fits. We study the momentum dependence of the three form factors and check the partially conserved axial-vector current (PCAC) hypothesis and the pion pole dominance (PPD). We show that in the continuum limit, the PCAC and PPD relations are satisfied. We also show that the Goldberger-Treimann relation is approximately fulfilled and determine the Goldberger-Treiman discrepancy. Our final results are $g_A=1.245(28)(14)$ for the nucleon axial charge, $⟨r_A^2⟩=0.339(48)(06){\text{fm}}^2$ for the axial radius, $g_{\pi NN}\equiv \underset{Q^2\to -m_{\pi }^2}{lim}{G}_{\pi NN}(Q^2)=13.25(67)(69)$ for the pion-nucleon coupling constant, and $G_P(0.88m_{\mu }^2)\equiv g_P^{*}=8.99(39)(49)$ for the induced pseudoscalar form factor at the muon capture point.

We perform a new general-relativistic viscous-radiation hydrodynamics simulation for supernovalike explosions associated with stellar core collapse of rotating massive stars to a system of a black hole and a massive torus, paying particular attention to large-mass progenitor stars with the zero-age main-sequence mass of $M_{\mathrm{ZAMS}}=20$, 35, and $45M_{\odot }$ of Aguilera-Dena et al. [Astrophys. J. 901, 114 (2020) ]. Assuming that a black hole is formed in a short timescale after the onset of the stellar collapse, the new simulations are started from initial data of a spinning black hole and infalling matter that self-consistently satisfy the constraint equations of general relativity. It is found that, with a reasonable size of the viscous parameter, the supernovalike explosion is driven by the viscous heating effect in the torus around the black hole, irrespective of the progenitor mass. The typical explosion energy and ejecta mass for the large-mass cases ($M_{\mathrm{ZAMS}}=35$ and $45M_{\odot }$) are $\sim {10}^{52}\mathrm{erg}$ and $\sim 5M_{\odot }$, respectively, with ${}^{56}\mathrm{Ni}$ mass larger than $0.15M_{\odot }$. These are consistent with the observational data of stripped-envelope and high-energy supernovae such as broad-lined type Ic supernovae. This indicates that rotating stellar collapses of massive stars to a black hole surrounded by a massive torus can be a central engine for high-energy supernovae. By artificially varying the angular velocity of the initial data, we explore the dependence of the explosion energy and ejecta mass on the initial angular momentum and find that the large explosion energy $\sim {10}^{52}\mathrm{erg}$ and large ${}^{56}\mathrm{Ni}$ mass $\ge 0.15M_{\odot }$ are possible only when a large-mass compact torus with mass $\gtrsim 1M_{\odot }$ is formed.

A lattice QCD computation of the coupled channel $\pi \mathrm{\Sigma }–\overline{K}N$ scattering amplitudes in the $\mathrm{\Lambda }(1405)$ region is detailed. Results are obtained using a single ensemble of gauge field configurations with $N_{\mathrm{f}}=2+1$ dynamical quark flavors and $m_{\pi }\approx 200\mathrm{MeV}$ and $m_K\approx 487\mathrm{MeV}$. Hermitian correlation matrices using both single baryon and meson-baryon interpolating operators for a variety of different total momenta and irreducible representations are used. Several parametrizations of the two-channel scattering $K$-matrix are utilized to obtain the scattering amplitudes from the finite-volume spectrum. The amplitudes, continued to the complex energy plane, exhibit a virtual bound state below the $\pi \mathrm{\Sigma }$ threshold and a resonance pole just below the $\overline{K}N$ threshold.

Crystalline materials are promising candidates as substrates or high-reflective coatings of mirrors to reduce thermal noises in future laser interferometric gravitational wave detectors. However, birefringence of such materials could degrade the sensitivity of gravitational wave detectors, not only because it can introduce optical losses, but also because its fluctuations create extra phase noise in the arm cavity reflected beam. In this paper, we analytically estimate the effects of birefringence and its fluctuations in the mirror substrate and coating for gravitational wave detectors. Our calculations show that the requirements for the birefringence fluctuations in silicon substrate and AlGaAs coating will be on the order of ${10}^{-8}$ and ${10}^{-10}\mathrm{rad}/\sqrt{\mathrm{Hz}}$ at 100 Hz, respectively, for future gravitational wave detectors. We also point out that optical cavity response needs to be carefully taken into account to estimate optical losses from depolarization.

We derive robust bounds on the equation of state (EOS) at finite baryon chemical potential using QCD inequalities and input from recent lattice-QCD calculations of thermodynamic properties of matter at nonzero isospin chemical potential. We use lattice data to deduce an upper bound on the baryon density of the symmetric nuclear matter at a given baryon chemical potential and a lower bound on the pressure as a function of the energy density. We also use constraints from perturbative calculations of the QCD EOS at high density derived in earlier work and causality to delineate robust bounds on the EOS of isospin symmetric matter at densities relevant to heavy-ion collisions.

The thermal photon emissivity of the quark-gluon plasma is determined by the in-medium spectral function of the electromagnetic current at lightlike kinematics, $\sigma (\omega )$. In this work, we present the first lattice QCD results on moments of $\sigma (\omega )/\omega$, defined by the weight function $1/({\omega }^2+(2\pi Tn{)}^2)$, $n\in \mathbb{Z}$ and computed without encountering an inverse problem. We employ two dynamical flavors of $\mathrm{O}(a)$-improved Wilson fermions at a temperature $T\approx 250\mathrm{MeV}$ and perform the continuum limit. We compare our results for the first two moments to those obtained dispersively by integrating over the spectral function computed at weak coupling by Arnold, Moore and Yaffe.

Neutrino-neutrino scattering could have a large secret component that would turn neutrinos within a supernova (SN) core into a self-coupled fluid. Neutrino transport within the SN core, emission from its surface, expansion into space, and the flux spectrum and time structure at Earth might all be affected. We examine these questions from first principles. First, diffusive transport differs only by a modified spectral average of the interaction rate. We next study the fluid energy transfer between a hot and a cold blackbody surface in plane-parallel and spherical geometry. The key element is the decoupling process within the radiating bodies, which themselves are taken to be isothermal. For a zero-temperature cold plate, mimicking radiation into free space by the hot plate, the energy flux is 3%–4% smaller than the usual Stefan-Boltzmann law. The fluid energy density just outside the hot plate is numerically 0.70 of the standard case, the outflow velocity is the speed of sound $v_{\mathrm{s}}=c/\sqrt{3}$, conspiring to a nearly unchanged energy flux. Our results provide the crucial boundary condition for the expansion of the self-interacting fluid into space, assuming an isothermal neutrino sphere. We also derive a dynamical solution, assuming the emission suddenly begins at some instant. A neutrino front expands in space with luminal speed, whereas the outflow velocity at the radiating surface asymptotically approaches $v_{\mathrm{s}}$ from above. Asymptotically, one thus recovers the steady-state emission found in the two-plate model. A sudden end to neutrino emission leads to a fireball with constant thickness equal to the duration of neutrino emission.

Motivated by cosmological Hartle-Hawking and microcanonical density matrix prescriptions for the quantum state of the Universe we develop a Schwinger-Keldysh in-in formalism for generic nonequilibrium dynamical systems with the initial density matrix. We build the generating functional of in-in Green’s functions and expectation values for a generic density matrix of the Gaussian type and show that the requirement of particle interpretation selects a distinguished set of positive/negative frequency basis functions of the wave operator of the theory, which is determined by the density matrix parameters. Then we consider a special case of the density matrix determined by the Euclidean path integral of the theory, which in the cosmological context can be considered as a generalization of the no-boundary pure state to the case of the microcanonical ensemble, and show that in view of a special reflection symmetry its Wightman Green’s functions satisfy Kubo-Martin-Schwinger periodicity conditions which hold despite the nonequilibrium and nonstationary nature of the physical setup. Rich analyticity structure in the complex plane of the time variable reveals the combined Euclidean-Lorentzian evolution of the theory, which depending on the properties of the initial density matrix can be interpreted as a decay of a classically forbidden quantum state.

The second Gravitational-Wave Transient Catalog, GWTC-2, reported on 39 compact binary coalescences observed by the Advanced LIGO and Advanced Virgo detectors between 1 April 2019 $15:00$ UTC and 1 October 2019 $15:00$ UTC. Here, we present GWTC-2.1, which reports on a deeper list of candidate events observed over the same period. We analyze the final version of the strain data over this period with improved calibration and better subtraction of excess noise, which has been publicly released. We employ three matched-filter search pipelines for candidate identification, and estimate the probability of astrophysical origin for each candidate event. While GWTC-2 used a false alarm rate threshold of 2 per year, we include in GWTC-2.1, 1201 candidates that pass a false alarm rate threshold of 2 per day. We calculate the source properties of a subset of 44 high-significance candidates that have a probability of astrophysical origin greater than 0.5. Of these candidates, 36 have been reported in GWTC-2. We also calculate updated source properties for all binary black hole events previously reported in GWTC-1. If the eight additional high-significance candidates presented here are astrophysical, the mass range of events that are unambiguously identified as binary black holes (both objects $\ge 3M_{\odot }$) is increased compared to GWTC-2, with total masses from $\sim 14M_{\odot }$ for GW190924_021846 to $\sim 182M_{\odot }$ for GW190426_190642. Source properties calculated using our default prior suggest that the primary components of two new candidate events (GW190403_051519 and GW190426_190642) fall in the mass gap predicted by pair-instability supernova theory. We also expand the population of binaries with significantly asymmetric mass ratios reported in GWTC-2 by an additional two events (the mass ratio is less than 0.65 and 0.44 at 90% probability for GW190403_051519 and GW190917_114630 respectively), and find that two of the eight new events have effective inspiral spins ${\chi }_{\mathrm{eff}}>0$ (at 90% credibility), while no binary is consistent with ${\chi }_{\mathrm{eff}}<0$ at the same significance. We provide updated estimates for rates of binary black hole and binary neutron star coalescence in the local Universe.

We point out a problem with the formulation and derivations of sum rules for quark fragmentation functions that impacts their validity in QCD, but which potentially points toward an improved understanding of final states in inclusive hard processes. Fragmentation functions give the distribution of final-state hadrons arising from a parton exiting a hard scattering, and the sum rules for momentum, electric charge, etc. express conservation of these quantities. The problem arises from a mismatch between the quark quantum numbers of the initial quark and the fact that all observed final-state hadrons are confined bound states with color zero. We point that, in a confining theory like QCD, the Wilson line in the operator definition of a fragmentation function entails that the final state in a fragmentation function includes a bound state in the external field generated by the Wilson line. We justify this with the aid of general features of string hadronization. The anomalous bound states are restricted to fractional momentum $z=0$. They tend to invalidate sum rules like the one for charge conservation when applied to the fragmentation functions inferred from experimental data but not the momentum sum rule. We propose to exploit our ideas in future studies as a way to relate the fragmentation functions extracted from inclusive cross sections to more detailed nonperturbative descriptions of final state hadronization. We also describe scenarios wherein the traditional sum rules might remain approximately valid with a reasonably high degree of accuracy.

Ultracold atomic gases can undergo phase transitions that mimic relativistic vacuum decay, allowing us to empirically test early Universe physics in tabletop experiments. We investigate the physics of these analog systems, going beyond previous analyses of the classical equations of motion to study quantum fluctuations in the cold-atom false vacuum. We show that the fluctuation spectrum of this vacuum state agrees with the usual relativistic result in the regime where the classical analogy holds, providing further evidence for the suitability of these systems for studying vacuum decay. Using a suite of semiclassical lattice simulations, we simulate bubble nucleation from this analog vacuum state in a 1D homonuclear potassium-41 mixture, finding qualitative agreement with instanton predictions. We identify realistic parameters for this system that will allow us to study vacuum decay with current experimental capabilities, including a prescription for efficiently scanning over decay rates, and show that this setup will probe the quantum (rather than thermal) decay regime at temperatures $T\lesssim 10\mathrm{nK}$. Our results help lay the groundwork for using upcoming cold-atom experiments as a new probe of nonperturbative early Universe physics.

Most tests of general relativity with gravitational-wave observations rely on inferring the degree to which a signal deviates from general relativity in conjunction with the astrophysical parameters of its source, such as the component masses and spins of a compact binary. Due to features of the signal, measurements of these deviations are often highly correlated with the properties of astrophysical sources. As a consequence, prior assumptions about astrophysical parameters will generally affect the inferred magnitude of the deviations. Incorporating information about the underlying astrophysical population is necessary to avoid biases in the inference of deviations from general relativity. Current tests assume that the astrophysical population follows an unrealistic fiducial prior chosen to ease sampling of the posterior—for example, a prior flat in component masses—which is inconsistent with both astrophysical expectations and the distribution inferred from observations. We propose a framework for fortifying tests of general relativity by simultaneously inferring the astrophysical population using a catalog of detections. Although this method applies broadly, we demonstrate it concretely on massive graviton constraints and parametrized tests of deviations to the post-Newtonian phase coefficients. Using observations from LIGO-Virgo-KAGRA’s third observing run, we show that concurrent inference of the astrophysical distribution strengthens constraints and improves overall consistency with general relativity. We provide updated constraints on deviations from the theory, finding that, upon modeling the astrophysical population, the 90%-credible upper limit on the mass of the graviton improves by 25% to $m_g\le 9.6\times {10}^{-24}\mathrm{eV}/c^2$ and the inferred population-level post-Newtonian deviations move $\sim 0.4\sigma$ closer to zero.