The current paper presents a determination of $K_S^0$ and $\mathrm{\Lambda }/\overline{\mathrm{\Lambda }}$ fragmentation functions (FFs) from QCD analysis of single-inclusive electron-positron annihilation process (SIA). Our FFs determinations are performed at next-to-leading order (NLO), and for the first time, at next-to-next-to-leading order (NNLO) accuracy in perturbative quantum chromodynamics (pQCD) which is designated as SAK20 FFs. Each of these FFs is accompanied by their uncertainties which are determined using the “Hessian” method. Considering the hadron mass corrections, we clearly investigate the reliability of our results upon the inclusion of higher-order QCD correction. We provide comparisons of SAK20 FFs set with the available analysis from another group, finding in general a reasonable agreement, and also considerable differences. In order to judge the fit quality, our theoretical predictions are compared with the analyzed SIA datasets. SAK20 FFs at NLO and NNLO accuracy along with their uncertainties are made available in the standard LHAPDF format in order to use for predictions of present and future measurements in high-energy collisions such as LHC and RHIC.

The effect of nonperturbative and higher order perturbative corrections to all the free nucleon structure functions [$F_{iN}(x,Q^2);i=1–5$] in the deep inelastic scattering (DIS) of ${\nu }_{\tau }/{\overline{\nu }}_{\tau }$ on nucleon is studied. The target mass correction and higher twist effects are incorporated following the works of Kretzer et al. and Dasgupta et al., respectively. The evaluation of the nucleon structure functions has been performed by using the Martin–Motylinski– Harland-Lang–Thorne 2014 parametrization of the parton distribution functions. The calculations have been performed at the next-to-leading order. These nucleon structure functions are used to calculate the DIS cross section by further including the kinematical corrections due to $\tau$-lepton mass. Due to the inclusion of lepton mass two additional structure functions $F_{4N}(x,Q^2)$ and $F_{5N}(x,Q^2)$ become non-negligible. The results for the nucleon structure functions, differential and total scattering cross sections are presented. The various effects considered in this work are effective in the different regions of $x$ and $Q^2$, and quite important in the energy region of $E_{{\nu }_{\tau }/{\overline{\nu }}_{\tau }}<15\mathrm{GeV}$. A comparative study of our results with the existing results in the literature for the cross sections is made in the energy region of interest for the DUNE, SHiP, DsTau and HyperK experiments proposed to be done in the near future.

The presence of massive sterile neutrinos $N$ mixed with the active ones induces flavor violating processes in the charged lepton sector at the loop level. In particular, the amplitude of $H^0\to {\overline{\ell }}_i{\ell }_j$ is expected to be proportional to the product of heavy-light Yukawa couplings $y_i{y}_j=2s_{{\nu }_i}{s}_{{\nu }_j}{m}_N^2/v^2$, where $s_{{\nu }_{i,j}}$ express the heavy-light neutrino mixings. Here, we revisit these Higgs decays in the most generic extension of the neutrino sector, focusing on large values of $y_i$. We show that decoupling effects and a cancellation between the two dominant contributions to these processes makes the amplitude about 100 times smaller than anticipated. We find that perturbative values of $y_i$ giving an acceptable contribution to the $\rho$ parameter imply $\mathcal{B}(H^0\to {\overline{\ell }}_i{\ell }_j)<{10}^{-8}$ for any lepton flavors, a rate that is not accessible at current colliders.

We study holographic aspects of mixed state entanglement measures in various large $N$ top-down as well as bottom-up confining models. For the top-down models, we consider wrapped $D3$ and $D4$ brane gravity solutions, whereas, for the bottom-up confining model, the Einstein-Maxwell-dilaton gravity solution is considered. We study entanglement entropy, mutual information, entanglement wedge cross section, and entanglement negativity for the strip subsystems and find model-independent features of these entanglement measures in all confining theories. The entanglement negativity and entropy exhibit a phase transition at the same critical strip length $L_{\mathrm{crit}}$, at which the order of these measures changes from $\mathcal{O}(N^2)$ to $\mathcal{O}(N^0)$. The entanglement wedge cross section similarly shows an order change at $L_{\mathrm{crit}}$ and exhibits a discontinuous behavior each time a phase transition between different entangling surfaces occurs. We further test the inequality involving mutual information and entanglement wedge cross section and find that the latter always exceeds half of the former.

A Schrödinger picture description of the evolving quantum state of Hawking radiation is given, based on an ADM decomposition using time slicings that smoothly cross the horizon. This treatment avoids requiring a role for trans-planckian excitations, which can be viewed as artifacts of Hawking’s original calculation, and also supports arguments that radiation from black holes is produced in a “quantum atmosphere” with thickness comparable to the horizon size, rather than microscopically far from it. Particularly explicit formulas are given for the two-dimensional analog of the Schwarzschild geometry. This analysis is expected to generalize to other black holes, and to cosmology. The resulting quantum evolution also provides important background for investigating corrections to the Hawking process, as are necessary for restoring unitary evolution of black hole decay.

A major challenge common to all Galilean drop tests of the universality of free fall (UFF) is the required control over the initial kinematics of the two test masses upon release due to coupling to gravity gradients and rotations. In this work, we consider a space-borne test of the UFF based on atom interferometry and show that this detrimental effect can be mitigated at the ${10}^{-18}$ level given an initial differential position (velocity) uncertainty in the order of $\mu \mathrm{m}$ ($\mu \mathrm{m}/\mathrm{s}$) of the test masses. This corresponds to a relaxation of the source control by several orders of magnitude with respect to comparable mission scenarios, such as the STE-QUEST mission proposal reported in [D. N. Aguilera et al., Classical Quantum Gravity 31, 115010 (2014)]. Our twofold mitigation strategy extends a compensation mechanism that is already established in terrestrial experiments to satellite missions with varying gravity gradients and exploits the spectral distribution of the systematics. We assess the experimental feasibility and find that the moderate parameters of the proposed scheme are in line with technological capabilities. The described attenuation of the gravity-gradient-induced uncertainty removes one major obstacle in quantum tests of the UFF and allows us to consider mission scenarios with target accuracies beyond the state of the art.

The self-dual spacetime was derived from the mini-superspace approach, based on the polymerization quantization procedure in loop quantum gravity (LQG). Its deviation from the Schwarzschild spacetime is characterized by the polymeric function $P$, purely due to the geometric quantum effects from LQG. In this paper, we consider the observational constraints imposed on $P$ by using the Solar System experiments and observations. For this purpose, we calculate in detail the effects of $P$ on astronomical observations conducted in the Solar System, including the deflection angle of light by the Sun, gravitational time delay, perihelion advance, and geodetic procession. The observational constraints are derived by confronting the theoretical predictions with the most recent observations. Among these constraints, we find that the tightest one comes from the measurement of the gravitational time delay by the Cassini mission, which yields $0<P<5.5\times {10}^{-6}$. In addition, we also discuss the potential constraint that can be obtained in the near future by the joint European-Japanese BepiColombo project, and show that it could significantly improve the current constraints.

Generic features of models of inflation obtained from string compactifications are the correlations between the model parameters and the postinflationary evolution of the universe. Thus, the postinflationary evolution depends on the inflationary model parameters, and accurate inflationary predictions require that this be incorporated in the evolution of the primordial spectrum. The fibre inflation model is a promising model of inflation constructed in type IIB string theory. This model has two interesting features in its postinflationary evolution. The reheating temperature of the model is directly correlated with the model parameters. The model also necessarily predicts some dark radiation, which can be sizable for certain choices of discrete parameters in the model. We analyze this model in detail using publicly available codes—modechord and cosmomc with the latest Planck+BICEP2/Keck array data to constrain the model parameters and $N_{\text{pivot}}$ (the number of $e$-foldings between the horizon exit of the CMB pivot mode and the end of inflation). We also carry out the same analysis using the publicly available code cobaya. We find the results of both the analysis to be in agreement. Our analysis provides the basic methods necessary to extract precise inflationary prediction in string models incorporating correlations between model parameters and postinflationary evolution.

Being free of the initial singularity, bouncing cosmology serves as a promising alternative to inflation. However, how entropy production occurs during the postbounce phase is still unclear. In this work, we use a newly identified dark matter (DM) candidate called thermal equilibrium freeze-in DM (EQFIDM), which can directly freeze into thermal equilibrium shortly after a bounce, to trace the entropy-producing decay process of the residual bouncing field (RBF). Specifically, we present a model-independent formalism to obtain all nine possible types of entropy-producing RBF decay within a generic bouncing universe. We show that due to the different types of entropy production, the particle mass of this new DM candidate can range from the sub-keV scale to the super-TeV scale. From current Lyman-$\alpha$ forest observations, we find that although four of the possible types of entropy-producing processes have been excluded, five types remain, suggesting both warm and cold EQFIDM candidates with efficient entropy production mechanisms that are accommodated by the current observations. Then, we illustrate how the nature of the RBF can be constrained by current observations and investigate the potential of EQFIDM to alleviate the small-scale crisis.

We investigate the production of circularly polarized X and gamma-ray signals in cosmic accelerators such as supernova remnants and active galactic nuclei jets. Proton-proton and proton-photon collisions within these sites produce a charge asymmetry in the distribution of mesons and muons that eventually leads to a net circular polarization signal as these particles decay radiatively. We find that the fraction of circular polarization thus produced is at the level of $5\times {10}^{-4}$, regardless of the exact beam spectrum, as long as it is made predominantly of protons. While this fraction is very small, the detection of circular polarization signals in conjunction with high-energy neutrinos would provide an unambiguous signature of the presence of high-energy protons in cosmic accelerators. In supernovae shocks in particular, this would indicate the presence of relativistic protons hitting stationary protons and/or low-energy photons in the intergalactic or interstellar medium.

Next-generation neutrino experiments will push the limits in our understanding of astroparticle physics in the neutrino sector to energies orders of magnitude higher than the current state-of-the-art high-energy neutrino experiment, IceCube. These experiments will use neutrinos to tell us about the most extreme environments in the Universe while simultaneously leveraging these extreme environments as probes of neutrino properties at the highest energies accessible in the foreseeable future: $E\sim {10}^9\mathrm{GeV}$. At these energies neutrinos are readily absorbed in Earth. Assuming an isotropic distribution, by looking at how the flux varies as a function of the angle through Earth, we show that it is possible to extract the ${\nu }_{\tau }\text{−}N$ cross section with precision at the $\sim 20\%$ level ($1\sigma$ assuming Wilks’ theorem) given $N_{\text{events}}\sim 100$ events.

We carry out astrophysical inference for compact binary merger events in LIGO-Virgo’s first gravitational-wave transient catalog (GWTC-1) using a physically motivated calibration model. We demonstrate that importance sampling can be used to reduce the cost of what would otherwise be a computationally challenging analysis for signal-to-noise ratios of current gravitational-wave detections. We show that including the physical estimate for the calibration error distribution has negligible impact on the inference of parameters for the events in GWTC-1. Studying a simulated signal with matched filter signal-to-noise ratio $\mathrm{SNR}=200$, we project that a calibration error estimate typical of GWTC-1 is likely to be negligible for the current generation of gravitational-wave detectors. We argue that other sources of systematic error—from waveforms, prior distributions, and noise modeling—are likely to be more important. Finally, using the events in GWTC-1 as standard sirens, we infer an astrophysically informed improvement on the estimate of the calibration error in the LIGO interferometers.

Designs for future gravitational wave detection facilities feature silicon test masses at cryogenic temperatures to reduce thermal noise and thermally induced aberrations. Designers call for operation at 123 K or close to 18 K to exploit the vanishing thermal expansion of crystalline silicon. The amount of absorbed heat that can be radiatively removed from the test masses is limited at these temperatures, forcing complex cooling scenarios to be considered, including conduction through suspension wires. This is particularly relevant for the kilohertz class of detectors that aim for extremely high circulating power, i.e., roughly a factor 20 more than the world record at the time of writing, to reduce quantum noise. We explore the impact of raising the test mass temperature and show that a dedicated kilohertz-band cryogenic instrument can do so without significant sensitivity penalty, thereby boosting the radiative cooling rate and allowing higher power operation with simpler suspensions. We also explore the implications of operating cryogenic broadband detectors at elevated temperatures. The work presented here was instrumental in the development of the Neutron Star Extreme Matter Observatory kilohertz-band gravitational wave detector design concept.

Inspired by the observation of the fully-charm tetraquark $X(6900)$ state at LHCb, the production of $X(6900)$ in $\overline{p}p\to J/\psi J/\psi$ reaction is studied within an effective Lagrangian approach and Breit-Wigner formula. The numerical results show that the cross section of $X(6900)$ at the c.m. energy of 6.9 GeV is much larger than that from the background contribution. Moreover, we estimate dozens of signal events can be detected by the D0 experiment, which indicates that searching for the $X(6900)$ via antiproton-proton scattering may be a very important and promising way. Therefore, related experiments are suggested to be carried out.

We provide updates to the limits on solar emission of dark photons or more generally, any light vector particle coupled to the electron vector current. The recent 2019 and 2020 electronic recoil data from XENON1T now provide more stringent constraints on these models than the stellar energy loss in the sub-keV mass region. We also show that solar emission of dark photons does not provide a good fit to the recent XENON1T excess in the 2–5 keV energy bins. In contrast, the absorption of 2–4 keV mass dark photons that saturate the local dark matter mass density does provide a good fit to the excess, for mixing angles in the range $\epsilon \in (4–12)\times {10}^{-16}$, while satisfying astrophysical constraints. Similarly, other models utilizing the vector portal can fit the excess, including those with operators that directly couple the dark photon field strength to electron spin.

The latest search for the rare kaon decay $K^{+}\to {\pi }^{+}\nu \overline{\nu }$ by the NA62 experiment has produced evidence for it with a branching fraction consistent with the prediction of the standard model. The new result implies that in this decay, with the $\nu \overline{\nu }$ pair appearing as missing energy ($\cancel{E}$), the room for possible new physics is no longer sizable and that therefore its contributions to underlying four-particle $s\to d\cancel{E}$ operators with parity-even $ds$ quark bilinears have become significantly constrained. Nevertheless, we point out that appreciable manifestations from beyond the standard model induced by the corresponding operators with mainly parity-odd $ds$ quark bilinears could still occur in $K\to \pi \pi \cancel{E}$ modes, on which there are only minimal empirical details at present. We find in particular that new physics of this kind may enhance the branching fraction of $K_L\to {\pi }^0{\pi }^0\cancel{E}$ to values reaching its current experimental upper limit and the branching fractions of $K^{+}\to {\pi }^{+}{\pi }^0\cancel{E}$ and $K_L\to {\pi }^{+}{\pi }^{-}\cancel{E}$ to the levels of ${10}^{-7}$ and ${10}^{-6}$, respectively. Thus, quests for these decays in existing kaon facilities such as KOTO and NA62 or future ones could provide valuable information complementary to that gained from $K\to \pi \cancel{E}$.

Monte Carlo simulations of quantum field theories on a lattice become increasingly expensive as the continuum limit is approached since the cost per independent sample grows with a high power of the inverse lattice spacing. Simulations on fine lattices suffer from critical slowdown, the rapid growth of autocorrelations in the Markov chain with decreasing lattice spacing $a$. This causes a strong increase in the number of lattice configurations that have to be generated to obtain statistically significant results. In this paper, hierarchical sampling methods to tame this growth in autocorrelations are discussed. Combined with multilevel variance reduction techniques, this significantly reduces the computational cost of simulations for given tolerances ${\epsilon }_{\mathrm{disc}}$ on the discretization error and ${\epsilon }_{\mathrm{stat}}$ on the statistical error. For an observable with lattice errors of order $\alpha$ and an integrated autocorrelation time that grows like ${\tau }_{\mathrm{int}}\propto a^{-z}$, multilevel Monte Carlo can reduce the cost from $\mathcal{O}({\epsilon }_{\mathrm{stat}}^{-2}{\epsilon }_{\mathrm{disc}}^{-(1+z)/\alpha })$ to $\mathcal{O}({\epsilon }_{\mathrm{stat}}^{-2}|\log {\epsilon }_{\mathrm{disc}}{|}^2+{\epsilon }_{\mathrm{disc}}^{-1/\alpha })$ or $\mathcal{O}({\epsilon }_{\mathrm{stat}}^{-2}+{\epsilon }_{\mathrm{disc}}^{-1/\alpha })$. Even higher performance gains are expected for nonperturbative simulations of quantum field theories in $D$-dimensions. The efficiency of the approach is demonstrated on two nontrivial model systems in quantum mechanics, including a topological oscillator that is badly affected by critical slowdown due to freezing of the topological charge. On fine lattices, the new methods are several orders of magnitude faster than standard, single-level sampling based on hybrid Monte Carlo. For high resolutions, multilevel Monte Carlo can be used to accelerate even the cluster algorithm for the topological oscillator. Performance is further improved through perturbative matching. This guarantees efficient coupling of theories on the multilevel lattice hierarchy, which have a natural interpretation in terms of effective theories obtained by renormalization group transformations.

The transverse and longitudinal gluon propagators in the Landau gauge are studied in the two-color lattice QCD at nonzero quark chemical potential ${\mu }_q$. Parametrization of the momentum dependence of the propagators is provided for all values of chemical potential under study. We find that the longitudinal propagator is infrared suppressed at nonzero ${\mu }_q$ with suppression increasing with increasing ${\mu }_q$. The transverse propagator dependence on ${\mu }_q$ was found to be opposite: it is enhanced at large ${\mu }_q$. It is found, respectively, that the electric screening mass is increasing while the magnetic screening mass is decreasing with increasing ${\mu }_q$. Nice agreement between the electric screening mass computed from the longitudinal propagator and the Debye mass computed earlier from the singlet static quark-antiquark potential was found. We discuss how the dependence of the propagators on the chemical potential correlates with the respective dependence of the string tension. Additionally, we consider the difference between two propagators as a function of the momentum and make interesting observations.

We study a $\mathcal{P}\mathcal{T}$-symmetric scalar Euclidean field theory with a complex action, using both theoretical analysis and lattice simulations. This model has a rich phase structure that exhibits pattern formation in the critical region. Analytical results and simulations associate pattern formation with tachyonic instabilities in the homogeneous phase. Monte Carlo simulation shows that pattern morphologies vary smoothly, without distinct microphases. We suggest that pattern formation in this model may be regarded as a form of arrested spinodal decomposition. We extend our theoretical analysis to multicomponent $\mathcal{P}\mathcal{T}$-symmetric Euclidean scalar field theories and show that they give rise to new universality classes of local field theories that exhibit patterned behavior in the critical region. QCD at finite temperature and density is a member of the $Z(2)$ universality class when the Polyakov loop is used to distinguish confined and deconfined phases. This suggests the possibility of the formation of patterns of confined and deconfined matter in QCD in the critical region in the $\mu -T$ plane.

We study exclusive production of scalar ${\chi }_{c0}\equiv {\chi }_c(0^{++})$ and pseudoscalar ${\eta }_c$ charmonia states in proton-proton collisions at the LHC energies. The amplitudes for $gg\to {\chi }_{c0}$ as well as for $gg\to {\eta }_c$ mechanisms are derived in the $k_T$-factorization approach. The $pp\to pp{\eta }_c$ reaction is discussed for the first time. We have calculated rapidity, transverse momentum distributions, and such correlation observables as the distribution in relative azimuthal angle and $(t_1,t_2)$ distributions. The latter two observables are very different for ${\chi }_{c0}$ and ${\eta }_c$ cases. In contrast to the inclusive production of these mesons considered very recently in the literature, in the exclusive case, the cross section for ${\eta }_c$ is much lower than that for ${\chi }_{c0}$, which is due to a special interplay of the corresponding vertices and off-diagonal unintegrated gluon distributions used to calculate the cross sections. We present the numerical results for the key observables in the framework of potential models for the light-front quarkonia wave functions. We also discuss how different the absorptive corrections are for both considered cases.