We propose to replace the exact amplitudes used in Monte Carlo event generators for trained machine learning regressors, with the aim of speeding up the evaluation of slow amplitudes. As a proof of concept, we study the process $gg\to ZZ$, whose leading-order amplitude is loop induced. We show that gradient boosting machines like xgboost can predict the fully differential distributions with errors below 0.1%, and with prediction times $\mathcal{O}({10}^3)$ faster than the evaluation of the exact function. This is achieved with training times $\sim 23\mathrm{minutes}$ and regressors of size $\lesssim 22\mathrm{Mb}$. We also find that xgboost performs well over the entire phase space, while interpolation gives much larger errors in regions where the function is peaked. These results suggest a possible new avenue to speed up Monte Carlo event generators.

Symmetries play important roles in the understanding of hadron structures and spectroscopy. Motivated by the discovery of the doubly charmed tetraquark $T_{cc}^{+}(3875)$, we study the ground states of the doubly heavy tetraquarks with the QCD inspired heavy antiquark-diquark symmetry in the constituent quark model. Six ground states of $T_{QQ}(Q=c,b)$ are predicted and the lightest $T_{cc}$ state has a mass of $3875.8\pm 7.6\mathrm{MeV}$ and spin-parity $1^{+}$, which are consistent with those of the observed $T_{cc}^{+}(3875)$. In addition, the magnetic moments of the predicted tetraquarks $T_{cc}^{+}(3876)$ and $T_{bb}^{-}(10396)$ are also estimated in the same model, which provide further information to distinguish the structures of the $T_{QQ}$ states.

We investigate the worldline quantum field theory (WQFT) formalism for scalar QED and observe that a generating function emerges from WQFT, from which the scattering angle ensues. This generating function bears important similarities to the radial action in that it requires no consideration of exponentiation of lower-order contributions. We demonstrate the computations of this generating function and the resulting scattering angle of a binary system coupled to an electromagnetic field up to the third order in the post-Minkowskian expansion.

In this paper we propose a new way to detect sublunar-mass primordial black holes (PBHs) by direct observations of the Earth-Moon binary system. Our method is based on treating PBH as a perturbation term, by assuming that the PBH is sweeping across the Solar System with a sublunar mass and is far away from the Earth-Moon binary (much greater than 1 AU). This perturbation treatment allows us to develop a framework to calculate the orbits of a generic binary system such as the Earth-Moon binary system. Our numerical results show that the Earth-Moon distance is sensitive to the initial values of the system. In most cases, the long-duration interactions between the PBH and the Earth-Moon system can induce lasting imprints on the Earth-Moon’s orbit, and these imprints can accumulate over time, eventually giving rise to observable deviations which can be used to infer the properties of the PBH.

We complete the nonlocal-in-time effective-one-body (EOB) formalism of the conservative dynamics for massless scalar-tensor (ST) theories at third post-Newtonian (PN) order. The nonlocal-in-time EOB Hamiltonian is obtained by mapping the order-reduced Hamiltonian corresponding to the nonlocal-in-time Lagrangian derived in [Phys. Rev. D 99, 044047 (2019)]. To transcribe the dynamics within the EOB formalism, we use a strategy of order-reduction of nonlocal dynamics to a local ordinary action-angle Hamiltonian. We then map this onto the EOB Hamiltonian to determine the nonlocal-in-time ST corrections to the EOB potentials $(A,B,Q_e)$ at 3PN order.

We determine the general local-in-time effective-one-body (EOB) Hamiltonian for massless scalar-tensor (ST) theories at third post-Newtonian (PN) order. Starting from the Lagrangian derived in Bernard [Phys. Rev. D 99, 044047 (2019)], we map it to the corresponding ordinary Hamiltonian describing the two-body interaction in ST theories at 3PN level. Using a canonical transformation, we then map this onto an EOB Hamiltonian so as to determine the ST corrections to the 3PN-accurate EOB potentials $(A,B,Q_e)$ at 3PN. We then focus on circular orbits and compare the effect of the newly computed 3PN terms, also completed with finite-size and nonlocal-in-time contributions, on predictions for the frequency at the innermost stable circular orbit. Our results will be useful to build high-accuracy waveform models in ST theory, which could be used to perform precise tests against general relativity using gravitational wave data from coalescing compact binaries.

We propose a novel and simple scenario to explain baryon asymmetry and dark matter (DM) by utilizing an early matter-dominated era (EMDE) caused by a heavy metastable particle. Within the EMDE, lack of pressure enhances the formation of primordial black holes (PBHs) which can then contribute to the relic abundance of DM. The eventual decay of heavy metastable particle that has baryon number and $CP$-violating interactions reheats the Universe and gives rise to baryon asymmetry. Since in this setup, PBH serves as a DM candidate, the particle physics model may not require new stable degrees of freedom which leads to more freedom in the model-building side. As an example, we show that a modulus field which dominates the energy density of the Universe prior to its decay, may explain both DM and baryon asymmetry in the Universe in the context of the minimally supersymmetric Standard Model while the lightest superparticle is not stable and cannot be a DM candidate due to the $R$-parity violating interactions needed for baryogenesis.

LISA is a space-based mHz gravitational-wave observatory, with a planned launch in 2034. It is expected to be the first detector of its kind, and will present unique challenges in instrumentation and data analysis. An accurate preflight simulation of LISA data is a vital part of the development of both the instrument and the analysis methods. The simulation must include a detailed model of the full measurement and analysis chain, capturing the main features that affect the instrument performance and processing algorithms. Here, we propose a new model that includes, for the first time, proper relativistic treatment of reference frames with realistic orbits, a model for onboard clocks and clock synchronization measurements, proper modeling of total laser frequencies (including laser locking), frequency planning and Doppler shifts, better treatment of onboard processing, and updated noise models. We then introduce two implementations of this model, lisanode and lisa instrument. We demonstrate that TDI processing successfully recovers gravitational-wave signals from the significantly more realistic and complex simulated data. lisanode and lisa instrument are already widely used by the LISA community and, for example, currently provide the mock data for the LISA data challenges.

A primordial black hole (PBH) is interesting to people for its ability of explaining dark matter as well as supermassive astrophysical objects. In the normal inflation scenario, the generation of PBHs usually requires an enhanced power spectrum of scalar perturbation at the end of inflation era, which is expected when the dispersion relation of the inflaton field gets modified. In this work, we study a kind of inflation model called the Dirac-Born-Infeld-inspired nonminimal kinetic coupling (DINKIC) model, where the dispersion relation is modified by a square root existing in the field Lagrangian. We discuss the enhancement of scalar power spectrum due to the modified dispersion relation, as well as the abundance of PBHs produced by the Press-Schechter collapse mechanism. We also discuss the formation of scalar-induced gravitational waves by linear scalar perturbations.

We implement a multigroup and discrete-ordinate neutrino transport model in spherical symmetry which allows to simulate collective neutrino oscillations by including realistic collisional rates in a self-consistent way. We utilize this innovative model, based on strategic parameter rescaling, to study a recently proposed collisional flavor instability caused by the asymmetry of emission and absorption rates between ${\nu }_e$ and ${\overline{\nu }}_e$ for four different static backgrounds taken from different stages in a core-collapse supernova simulation. Our results confirm that collisional instabilities generally exist around the neutrinosphere during the supernova accretion and postaccretion phase, as suggested by Johns [arXiv:2104.11369.]. However, the growth and transport of flavor instabilities can only be fully captured by models with global simulations as done in this work. With minimal ingredient to trigger collisional instabilities, we find that the flavor oscillations and transport mainly affect (anti)neutrinos of heavy lepton flavors around their decoupling sphere, which then leave imprints on their energy spectra in the free-streaming regime. For electron (anti)neutrinos, their properties remain nearly intact. We also explore various effects due to the decoherence from neutrino-nucleon scattering, artificially enhanced decoherence from emission and absorption, neutrino vacuum mixing, and inhomogeneous matter profile, and discuss the implication of our work.

Time-delay interferometry (TDI) is the data processing technique that cancels the large laser phase fluctuations affecting the heterodyne Doppler measurements made by unequal-arm space-based gravitational wave interferometers. The space of all TDI combinations was first derived under the simplifying assumption of a stationary array, for which the three time-delay operators commute. In this model, any element of the TDI space can be written as a linear combination of four TDI variables, the generators of the “first-generation” TDI space. To adequately suppress the laser phase fluctuations in a realistic array configuration, the rotation of the array and the time dependence of the six interspacecraft light travel times has to be accounted for. In the case of the Laser Interferometer Space Antenna (LISA), a European Space Agency mission characterized by slowly time varying armlengths, it has been possible to identify data combinations that, to first order in the interspacecraft velocities, either exactly cancel or suppress the laser phase fluctuations below the level identified by the noise sources intrinsic to the heterodyne measurements (the so-called “secondary” noises). Here we reanalyze the problem of exactly canceling the residual laser noise terms linear in the interspacecraft velocities. We find that the procedure for obtaining elements of the second-generation TDI space can be generalized in an iterative way. This allows us to “lift up” the generators of the first-generation TDI space and construct elements of the higher order TDI space whose gravitational wave sensitivities are equal to those of their first-generation counterparts.

The nucleon axial coupling constant $g_A$ is calculated in the presence of an external uniform magnetic field using finite energy sum rules. The correlation function of proton, neutron and axial-vector currents is calculated both the hadronic and the QCD sector. Once the axial contribution in the form factor is isolated, a double sum rule is considered, i.e., the usual QCD contour integration for the external moments of both the proton and neutron current. The effects of the external magnetic field come mainly through the in-medium current-nucleon coupling constants ${\lambda }_N(B)$ and the hadronic thresholds $s_0(B)$ provided by the nucleon-nucleon correlators. As a result, the axial coupling constant decreases in the presence of the magnetic field.

We propose a phenomenological extended vector meson dominance model for the baryon electromagnetic structure, and it is found that the current experimental data on the $\mathrm{\Sigma }$ and $\mathrm{\Xi }$ electromagnetic form factors in the timelike region can be well described. Meanwhile, we can also reproduce the ratios of the total cross sections of reactions $e^{+}{e}^{-}\to {\mathrm{\Sigma }}^{+}{\overline{\mathrm{\Sigma }}}^{-}$, ${\mathrm{\Sigma }}^0{\overline{\mathrm{\Sigma }}}^0$, and ${\mathrm{\Sigma }}^{-}{\overline{\mathrm{\Sigma }}}^{+}$, which are $9.7\pm 1.3:3.3\pm 0.7:1$ at center-of-mass energies from 2.3864 GeV to 3.02 GeV. We also analytically continue the expression of the form factors to spacelike region and estimate the charge radii of the $\mathrm{\Sigma }$ and $\mathrm{\Xi }$ hyperons. The obtained result of the charge radius for the ${\mathrm{\Sigma }}^{-}$ is in agreement with the experimental data.

The modified vacuum fluctuations of quantum fields in the presence of a perfectly reflecting mirror lead to divergent velocity dispersions of a charged test particle. Here, it is shown that when the mirror is modeled by a material medium described by a Drude-like susceptibility, these dispersions become regular, thus elucidating that the origin of the divergences that appear in the previous treatments is related to the assumption of idealized boundary conditions. As a consequence of implementing this more realistic description, the dispersion curves acquire an oscillatory behavior caused by the effective mass of the field modes inside the dispersive medium. Additionally, it is found that the effects over the particle are delayed when compared to the perfect mirror limit, a phenomenon attributed to the imperfect reflection of field modes on the mirror. Therefore, although idealized boundary conditions are simplifying hypotheses, their usage might hide or significantly modify relevant physical phenomena.

Ultralight scalars could extract energy and angular momentum from a Kerr black hole (BH) because of superradiant instability. Multiple modes labeled with $nlm$ grow while rotating around the BH, emitting continuous gravitational waves (GWs). In this work, we carefully study the contribution of the subdominant modes with $n\ge 1$ in the evolution of the BH-condensate system. We find that the BH still evolves along the Regge trajectory of the $n=0$ modes even with the presence of the subdominant modes. The interference of the dominant and the subdominant modes produces beats in the emitted GWs, which could be used to distinguish the BH-condensate systems from other monochromatic GW sources, such as neutron stars.

We consider a new physics model, where the Standard Model (SM) is extended by hyperchargeless $Y=0$ triplet fermions and a Higgs triplet with hypercharge $Y=2$. The first two generation fermion triplets are even under the $Z_2$ transformation. In contrast, the third fermion triplet and scalar triplet are odd under the same $Z_2$ transformation. It is a unifying framework for the simultaneous explanation of neutrino mass and mixing, dark matter, baryogenesis, inflation, and reheating temperature of the Universe. The two $Z_2$ even neutral fermions explain the neutrino low energy variables, whereas the third one can serve as a viable dark matter candidate, explaining the exact relic density. The scalar triplet is coupled nonminimally to gravity and forms the inflaton. We calculate the inflationary parameters and find them consistent with the new Planck-2018 constraints. We also do the reheating analysis for the inflaton decays/annihilations to relativistic SM particles. The triplet fermions associated with $Z_2$ even sector can provide the observed baryon asymmetry of the Universe at the TeV scale.

Basis transformations often involve Fierz and other relations that are only valid in $D=4$ dimensions. In general $D$ spacetime dimensions, however, evanescent operators have to be introduced in order to preserve such identities. Such evanescent operators contribute to one-loop basis transformations as well as to two-loop renormalization group running. We present a simple procedure on how to systematically change basis at the one-loop level by obtaining shifts due to evanescent operators. As an example we apply this method to derive the one-loop basis transformation from the Buras, Misiak and Urban basis useful for next-to-leading order QCD calculations, to the Jenkins, Manohar and Stoffer basis used in the matching to the standard model effective theory.

We present results for the static energy in ($2+1+1$)-flavor QCD over a wide range of lattice spacings and several quark masses, including the physical quark mass, with ensembles of lattice-gauge-field configurations made available by the MILC Collaboration. We obtain results for the static energy out to distances of nearly 1 fm, allowing us to perform a simultaneous determination of the scales $r_1$ and $r_0$, as well as the string tension $\sigma$. For the smallest three lattice spacings we also determine the scale $r_2$. Our results for $r_0/r_1$ and $r_0\sqrt{\sigma }$ agree with published ($2+1$)-flavor results. However, our result for $r_1/r_2$ differs significantly from the value obtained in the ($2+1$)-flavor case, which is most likely due to the effect of the charm quark. We also report results for $r_0$, $r_1$, and $r_2$ in fm, with the former two being slightly lower than published ($2+1$)-flavor results. We study in detail the effect of the charm quark on the static energy by comparing our results on the finest two lattices with the previously published ($2+1$)-flavor QCD results at similar lattice spacing. We find that for $r>0.2\mathrm{fm}$ our results on the static energy agree with the ($2+1$)-flavor result, implying the decoupling of the charm quark for these distances. For smaller distances, on the other hand, we find that the effect of the dynamical charm quark is noticeable. The lattice results agree well with the two-loop perturbative expression of the static energy incorporating finite charm mass effects. This is the first time that the decoupling of the charm quark is observed and quantitatively analyzed on lattice data of the static energy.