The central speed of sound (SS) measures the stiffness of the equation of state (EOS) of superdense neutron star (NS) matter. Its variations with density and radial coordinate in NSs in conventional analyses often suffer from uncertainties of the specific nuclear EOS used. Using the central SS and NS mass/radius scaling obtained from solving perturbatively the scaled Tolman-Oppenheimer-Volkoff (TOV) equations, we study the variations of SS, trace anomaly and several closely related properties of NSs in an EOS-model-independent manner. We find that the SS increases with the reduced central pressure ${\widehat{P}}_{\mathrm{c}}\equiv P_{\mathrm{c}}/{ϵ}_{\mathrm{c}}$ (scaled by the central energy density ${ϵ}_{\mathrm{c}}$), and the conformal bound for SS tends to break down for NSs with masses higher than about $1.9M_{\odot }$. The ratio $P/ϵ$ is upper bounded as $P/ϵ\lesssim 0.374$ around the centers of stable NSs. We demonstrate that it is an intrinsic property of strong field gravity and is more relevant than the perturbative QCD bound on it. While a sharp phase transition at high densities characterized by a sudden vanishing of SS in cores of massive NSs are basically excluded, the probability for a continuous crossover signaled by a peaked radial profile of SS is found to be enhanced as ${\widehat{P}}_{\mathrm{c}}$ decreases, implying it likely happens near the centers of massive NSs. Moreover, a new and more stringent causality boundary as $R_{\max }/\mathrm{km}\gtrsim 4.73M_{\mathrm{NS}}^{\max }/M_{\odot }+1.14$ for the NS mass-radius curve is found to be excellently consistent with observational data on NS masses and radii. Furthermore, new constraints on the ultimate energy density and pressure allowed in NSs before collapsing into black holes are obtained and compared with earlier predictions in the literature.

The atmospheric lepton fluxes play a crucial role in many particle and astroparticle physics experiments, e.g., in establishing the neutrino signal and the muon background for neutrino oscillation measurements, or the atmospheric background for astrophysical neutrino searches. The Matrix Cascade Equations (MCEq) code is a numerical tool used to model the atmospheric lepton fluxes by solving a system of coupled differential equations for particle production, interaction, and decay at extremely low computational costs. Previously, the MCEq framework accommodated only longitudinal development of air showers, an approximation that works well for neutrino and muon fluxes at high energies ($\mathcal{O}(10\mathrm{GeV})$ and above). However, for accurate calculations of atmospheric lepton angular distributions at lower energies, the lateral component of hadronic cascades becomes significant. We introduce “2D MCEq,” an efficient numerical approach for combined longitudinal and angular evolution of air showers that retains the low computational complexity. The accuracy of the 2D MCEq is affirmed by its benchmark comparison with the standard Monte Carlo code corsika. Our method can be used for two-dimensional evolution of hadronic cascades in arbitrary media and paves the way for efficient three-dimensional calculations of atmospheric neutrino fluxes.

Extreme mass ratio inspirals (EMRIs) are among the primary targets for the Laser Interferometer Space Antenna (LISA). The extreme mass ratios of these systems result in relatively weak gravitational wave signals, that can be individually resolved only for cosmologically nearby sources (up to $z\approx 2$). The incoherent piling up of the signal emitted by unresolved EMRIs generate a confusion noise, that can be formally treated as a stochastic GW background (GWB). In this paper, we estimate the level of this background considering a collection of astrophysically motivated EMRI models, spanning the range of uncertainties affecting EMRI formation. To this end, we employed the innovative augmented analytic kludge waveforms and used the full LISA response function. For each model, we compute the GWB SNR and the number of resolvable sources. Compared to simplified computations of the EMRI signals from the literature, we find that for a given model the GWB SNR is lower by a factor of $\approx 2$ whereas the number of resolvable sources drops by a factor of 3 to 5. Nonetheless, the vast majority of the models result in potentially detectable GWB which can also significantly contribute to the overall LISA noise budget in the 1–10 mHz frequency range.

The anomalous orbits of trans-Neptunian objects (TNOs) can be explained by the planet 9 hypothesis. We propose that the planet 9 can be an axion star. Axion stars are gravitational bound clusters condensed by QCD axions or axionlike particles (ALPs), which we call axions for brevity. We find that the probability of capturing an axion star by the solar system is the same order of magnitude as the probability of capturing a free floating planet (FFP), and even higher for the case of axion star, with axion star mass $5M_{\oplus }\approx 1.5\times {10}^{-5}{M}_{\odot }$ and ${\mathrm{\Omega }}_{\mathrm{AS}}/{\mathrm{\Omega }}_{\mathrm{DM}}\simeq 1/10$. Although axion star can emit monochromatic signals through two-photon decay, we find that the frequency of decay photon is either not within the frequency range of the radio telescope, or the decay signal is too weak to be detected. Therefore, if planet 9 is composed by an axion star, it may be difficult to distinguish it from an isolated primordial black hole by spontaneous decay of axion.

Transient gravitational waves (aka gravitational wave bursts) within the nanohertz frequency band could be generated by a variety of astrophysical phenomena such as the encounter of supermassive black holes, the kinks or cusps in cosmic strings, or other as-yet-unknown physical processes. Radio pulses emitted from millisecond pulsars could be perturbed by passing gravitational waves; hence, the correlation of the perturbations in a pulsar timing array can be used to detect and characterize burst signals with a duration of $\mathcal{O}(1–10)\mathrm{years}$. We propose a fully Bayesian framework for the analysis of the pulsar-timing-array data, where the burst waveform is generically modeled by piecewise straight lines, and the waveform parameters in the likelihood can be integrated out analytically. As a result, with merely three parameters (in addition to those describing the pulsars’ intrinsic and background noise), one is able to efficiently search for the existence and the sky location of a burst signal. If a signal is present, the posterior of the waveform can be found without further Bayesian inference. We demonstrate this model by analyzing simulated datasets containing a stochastic gravitational wave background and a burst signal generated by the parabolic encounter of two supermassive black holes.

We investigate the interactions of the ${\chi }_{c1}(4274)$ state with light mesons in the hot hadron gas formed in heavy-ion collisions. The vacuum and thermally averaged cross sections of production of ${\chi }_{c1}(4274)$ accompanied by light pseudoscalar and light vector mesons as well as the corresponding inverse processes are estimated within the context of an effective Lagrangian approach. The results suggest non-negligible thermal cross sections, with larger magnitudes for most of the suppression reactions than those for production. This might be a relevant feature to be considered in the analysis of future data collected in heavy-ion collisions.

This work is devoted to the study of the $\{\beta \}$ expansion of the perturbative expressions for the $e^{+}{e}^{-}$ annihilation Adler function $D(Q^2)$ and for the related renormalization group functions, namely, for the photon vacuum polarization function and its anomalous dimension $\gamma ({\alpha }_s)$ in QCD at the $\mathcal{O}({\alpha }_s^4)$ order. We emphasize that $\gamma ({\alpha }_s)$ is not a conformal-invariant contribution to $D(Q^2)$; therefore, for a consistent analysis, it is necessary to decompose its higher-order perturbation theory coefficients in powers of the $\beta$-function coefficients in the same way as for the Adler function. The arguments in favor of this statement are given. The comparison of the $\overline{\mathrm{MS}}$ and principal of maximum conformality and Brodsky-Lepage-Mackenzie scale approximants are demonstrated. We comment briefly on theoretical and phenomenologically related consequences of this comparison.

We extend the previously developed small-$x$ parton shower algorithm to include the kinematic constraint effect and $k_t$ resummation effect. This work enables the Monte Carlo generator to simultaneously resum large-$k_t$ and small-$x$ logarithms in the saturation regime for the first time. It is an important step towards simulating processes involving multiple well separated hard scales, such as dijet production in eA collisions at the EIC.

Bandlimited approaches to quantum field theory offer the tantalizing possibility of working with fields that are simultaneously both continuous and discrete via the Shannon sampling theorem from signal processing. Conflicting assumptions in general relativity (smooth spacetime) and quantum field theory (high-energy deviations from low-energy emergent smoothness) motivate the use of such an appealing analytical tool that could thread the needle to meet both requirements. Bandlimited continuous quantum fields are isomorphic to lattice theories—yet without requiring a fixed lattice. Any lattice with a required minimum spacing can be used. This is an isomorphism that avoids taking the limit of the lattice spacing going to zero. In this work, we explore the consequences of this isomorphism, including the emergence of effectively continuous symmetries in quantum lattice theories. One obtains conserved lattice observables for these continuous (Noether) symmetries, as well as a duality of locality from the two perspectives. We expect this work and its extensions to provide useful tools for considering numerical lattice models of continuous quantum fields (e.g., lattice gauge theories) arising from the availability of discreteness without a fixed lattice, as well as offering new insights into emergent continuous symmetries in lattice models and possible laboratory demonstrations of these phenomena.

We analyze data from the dark matter direct detection experiments PandaX-4T, LUX-ZEPLIN and XENONnT to place bounds on neutrino electromagnetic properties (magnetic moments, millicharges, and charge radii). We also show how these bounds will improve at the future facility DARWIN. In our analyses we implement a more conservative treatment of background uncertainties than usually done in the literature. From the combined analysis of all three experiments we can place very strong bounds on the neutrino magnetic moments and on the neutrino millicharges. We show that even though the bounds on the neutrino charge radii are not very strong from the analysis of current data, DARWIN could provide the first measurement of the electron neutrino charge radius, in agreement with the Standard Model prediction.

Axionlike dark matter whose symmetry breaking occurs after the end of inflation predicts enhanced primordial density fluctuations at small scales. This leads to dense axion minihalos (or miniclusters) forming early in the history of the Universe. Condensation of axions in the minihalos leads to the formation and subsequent growth of axion stars at the cores of these halos. If, like the QCD axion, the axionlike particle has attractive self-interactions there is a maximal mass for these stars, above which the star rapidly shrinks and converts an $\mathcal{O}(1)$ fraction of its mass into unbound relativistic axions. This process would leave a similar (although in principle distinct) signature in cosmological observables as a decaying dark matter fraction, and thus is strongly constrained. We place new limits on the properties of axionlike particles that are independent of their nongravitational couplings to the standard model.

We study several previous corrections and contributions to the muon $g-2$, starting from the dark photon hypothesis to the dark $Z$. We explore the inputs from a dark $Z$ boson virtual mediator in a first order loop. We consider not only the QED-like contributions in the theory but also weak interactions. We obtain a new factor that adds corrections to the form factor associated with the anomalous magnetic moment. We show that our result is favorable in new, unexplored windows in the mass-coupling parameter space.

Composite topological structures such as superheavy “quasistable strings” (QSS) and “walls bounded by strings” (WBS) arise in realistic extensions of the Standard Model of high energy physics. We show that the gravitational radiation emitted in the early universe by these two unstable structures with a dimensionless string tension $G\mu \approx {10}^{-6}$ is consistent with the NANOGrav evidence of low frequency gravitational background as well as the recent LIGO-VIRGO constraints, provided the superheavy strings and monopoles experience a certain amount of inflation. For the case of walls bounded by strings, the domain walls arise from the spontaneous breaking of a remnant discrete gauge symmetry around the electroweak scale. The quasistable strings, on the other hand, arise from a two step breaking of a local gauge symmetry. The monopoles appear from the first breaking and get connected to strings that arise from the second breaking. Both composite structures decay by emitting gravitational waves over a wide frequency range. The Bayes factors for QSS and WBS relative to the inspiraling supermassive black hole binaries are estimated to be about 60 and 30 respectively, which are comparable with that of metastable strings and cosmic superstrings.

We study a nonuniversal $U(1{)}_X$ extension of the Standard Model with an extended scalar sector of two doublets and one singlet plus three additional exotic quarks and two exotic charged leptons on the fermionic sector. In order to obtain the observed fermion mass hierarchy, an additional ${\mathbb{Z}}_2$ discrete symmetry is imposed, where the heaviest fermions acquire their masses from three different scales determined by two Higgs doublets and one singlet, whereas the lightest fermions obtain their masses from effective operators up to dimension seven. From chiral anomalies cancellation, the model also includes heavy right-handed neutrinos which get massive via an inverse seesaw mechanism, reproducing the observed mass differences for the active neutrinos. We analyze phenomenological consequences of the model in view of the so-called flavor anomalies, namely the latest measurement made by Fermilab of the anomalous magnetic moment of the muon $g-2$, and additionally, the fit to semileptonic $B$ meson decays made by different flavor groups, dominated mainly by the LHCb 2020 data. We obtain that the model can explain the former at the $1\sigma$ level by means of contributions coming from charged $W^{+}$ bosons interacting with exotic Majorana neutrinos at one-loop level, with the $Z^{\prime }$ boson contribution itself coming from the $U(1{)}_X$ symmetry being negligible. However, we find that the model is able to accommodate the $b\to s{\ell }^{+}{\ell }^{-}$ transitions associated to the $B$ meson anomalies only at the $2\sigma$ level via tree-level $Z^{\prime }$ boson exchange, while simultaneously respecting various constraints from the recent $R_{K^{(*)}}$ measurements made by the LHCb, neutrino trident production and $B_s-{\overline{B}}_s$ oscillations.

We calculate the nucleon electric dipole moment (EDM) from the $\theta$ term with overlap fermions on three domain wall lattices with different sea pion masses at lattice spacing 0.11 fm. Due to the chiral symmetry conserved by the overlap fermions, we have well-defined topological charge and chiral limit for the EDM. Thus, the chiral extrapolation can be carried out reliably at nonzero lattice spacings. We use three to four different partially quenched valence pion masses for each sea pion mass and find that the EDM dependence on the valence and sea pion masses behaves oppositely, which can be described by partially quenched chiral perturbation theory. With the help of the cluster decomposition error reduction technique, we determine the neutron and proton EDM at the physical pion mass to be $d_n=-0.00148(14)(31)\overline{\theta }\mathrm{e}·\mathrm{fm}$ and $d_p=0.0038(11)(8)\overline{\theta }\mathrm{e}·\mathrm{fm}$. This work is a clear demonstration of the advantages of using chiral fermions in the nucleon EDM calculation and paves the road to future precise studies of the strong $CP$ violation effects.

At the TeV scale, low-energy precision observations of neutron characteristics provide unique probes of novel physics. Precision studies of neutron decay observables are susceptible to beyond the Standard Model (BSM) tensor and scalar interactions, while the neutron electric dipole moment, $d_n$, also has high sensitivity to new BSM $CP$-violating interactions. To fully utilize the potential of future experimental neutron physics programs, matrix elements of appropriate low-energy effective operators within neutron states must be precisely calculated. We present results from the QCDSF/UKQCD/CSSM Collaboration for the isovector charges $g_T$, $g_A$ and $g_S$ of the nucleon, $\mathrm{\Sigma }$ and $\mathrm{\Xi }$ baryons using lattice QCD methods and the Feynman-Hellmann theorem. We use a flavor symmetry breaking method to systematically approach the physical quark mass using ensembles that span five lattice spacings and multiple volumes. We extend this existing flavor-breaking expansion to also account for lattice spacing and finite volume effects in order to quantify all systematic uncertainties. Our final estimates of the nucleon isovector charges are $g_T=1.010(21{)}_{\mathrm{stat}}(12{)}_{\mathrm{sys}},g_A=1.253(63{)}_{\mathrm{stat}}(41{)}_{\mathrm{sys}}$ and $g_S=1.08(21{)}_{\mathrm{stat}}(03{)}_{\mathrm{sys}}$ renormalized, where appropriate, at $\mu =2\mathrm{GeV}$ in the $\overline{\mathrm{MS}}$ scheme.

Using proton-proton collisions at center-of-mass energies 7, 8, and 13 TeV, with a total integrated luminosity of $9{\mathrm{fb}}^{-1}$, the LHCb collaboration has performed amplitude analyses of the $B^{+}\to D^{+}{D}^{-}{K}^{+}$, $B^{+}\to D^{-}{D}_s^{+}{\pi }^{+}$, and $B^0\to {\overline{D}}^0{D}_s^{+}{\pi }^{-}$ decays, observing that new $T_{cs}$ and $T_{c\overline{s}}$ resonances are required in order to explain the experimental data. These signals could be the first observation of tetraquark candidates that do not contain a heavy quark-antiquark pair; in fact, they consist of four different flavors of quarks, one of which is a doubly charged open-charm state. We present herein an analysis of the $T_{cs}$ and $T_{c\overline{s}}$ states, which is an extension of our recently published study of similar $T_{cc}^{+}$ exotic candidates. Our theoretical framework is a constituent-quark-model-based coupled-channels calculation of $q{q}^{\prime }\overline{s}\overline{c}$ and $cq\overline{s}{\overline{q}}^{\prime }$ tetraquark sectors for $T_{cs}$ and $T_{c\overline{s}}$ structures, respectively. We explore the nature, and pole position, of the singularities that appear in the scattering matrix with spin-parity quantum numbers: $J^P=0^{\pm }$, $1^{\mp }$, and $2^{\pm }$. The constituent quark model has been widely used in the heavy quark sector, and thus all model parameters are already constrained from previous works. This makes our predictions robust and parameter-free. We find many singularities in the solution of various scattering-matrix problems which are either virtual states or resonances, but not bound states. Some of them fit reasonably well with the experimental observations of the spin-parity, mass, and width of $T_{cs}$ and $T_{c\overline{s}}$ candidates, and thus tentative assignments are made.

Leading $\mathrm{\Lambda }$ (LL) production in $ep$ collisions at high energies is investigated using the color dipole formalism and taking into account the nonlinear QCD effects. In particular, the impact of the absorptive effects on the LL spectra are estimated considering the kinematical range that will be probed by the Electron Ion Collider and by the Large Hadron electron Collider. Our results indicate that the LL spectrum is strongly suppressed at small photon virtualities. These results suggest that absorptive effects are not negligible and should be taken into account in order to extract the kaon structure function from data on leading $\mathrm{\Lambda }$ production.

Ultralight bosonic particles are fascinating candidates of dark matter (DM). It behaves as classical waves in our Galaxy due to its large number density. There have been various methods proposed to search for the wavelike DM, such as methods utilizing interferometric gravitational-wave detectors. Understanding the characteristics of DM signals is crucial to extract the properties of DM from data. While the DM signal is nearly monochromatic with the angular frequency of its mass, the amplitude and phase are gradually changing due to the velocity dispersion of DMs in our Galaxy halo. The stochastic amplitude and phase should be properly taken into account to accurately constrain the coupling constant of DM from data. Previous works formulated a method to obtain the upper bound on the coupling constant incorporating the stochastic effects. One of these works compared the upper bound with and without the stochastic effect in a measurement time that is much shorter than the variation timescale of the amplitude and phase. In this paper, we extend their formulation to arbitrary measurement time and evaluate the stochastic effects. Moreover, we investigate the velocity-dependent signal for dark photon DM including an uncertainly of the velocity. We demonstrate that our method accurately estimates the upper bound on the coupling constant with numerical simulations. We also estimate the expected upper bound of the coupling constant of axion DM and dark photon DM from future experiments in a semianalytic way. The stochasticity especially affects constraints on a small mass region. Our formulation offers a generic treatment of the ultralight bosonic DM signal with the stochastic effect.