We propose a method to ease the challenges of exploring multidimensional parameter spaces in beyond-the-Standard Model theories. We evaluate the model likelihood for any choice of parameters by sampling the theory parameters intelligently and building a kernel density estimator. By reducing the number of expensive Monte Carlo simulations, this method provides an efficient way to test complex theories. We illustrate our technique to set new limits on a short-lived heavy neutrino $N$, proposed as an explanation of anomalies in neutrino experiments. Using a search for lepton pairs in the T2K near detector, we find exclusion limits on the model parameters in a vast region of parameter space, fully exploiting the advantages of our new method. With a single Monte Carlo simulation, we obtain the differential event rate for arbitrary choices of model parameters, allowing us to cast limits on any slice of the model parameter space. We conclude that $N$ particles with lifetimes greater than $c{\tau }^0\gtrsim 3\mathrm{cm}$ are excluded by T2K data. We also derive model-independent constraints in terms of the total rate, lifetime, and $N$ mass and provide an approximated analytical formula. This method can be applied in other branches of physics to explore the landscape of theory parameters efficiently.

In some extensions of the Standard Model (SM), two neutrons are allowed to decay into two sterile antineutrinos ($nn\to \overline{\chi }\overline{\chi }$) via new scalar bosons. This process violates both the baryon number ($\mathcal{B}$) and the lepton number ($\mathcal{L}$) by two units but conserves their difference $(\mathcal{B}-\mathcal{L})$. Neutron stars contain a large number of neutrons, and thus the $nn\to \overline{\chi }\overline{\chi }$ process can be greatly enhanced inside a neutron star. This process could result in nontrivial effects that are different from the SM predictions and can be explored through astrophysical and laboratory observations. Furthermore, a large number of sterile antineutrinos, which may be dark matter candidates, can be emitted from the interior of the neutron star. The properties of the emitted particles show a particular pattern that can be uniquely determined by the mass and radius of the neutron star. In addition, the dineutron decay may contribute to the orbital-period change of the binary systems containing neutron stars. We analyze the possibility of constraining the mass of the new scalar bosons using the observations of the binary’s orbital-period changes. It is found that the mass of the new scalar bosons is roughly restricted in the range from 1 TeV to several TeV, which is possibly within the reach of direct searches at the LHC or future high-energy experiments. The joint analysis which combines the astrophysics and particle phenomenology could provide an excellent opportunity for the study of the new physical effects beyond the SM.

Current experimental data guarantees the presence of physics beyond the Standard Model in the neutrino sector. The responsible physical description might show itself through virtual effects on low-energy observables. In particular, massive neutrinos are able to produce contributions to the triple gauge coupling $WW\gamma$. The present paper deals with the calculation, estimation and analysis of one-loop contributions from Majorana neutrinos to the Lorentz-covariant $WW\gamma$ parametrization. Our calculations show that $CP$-odd effects vanish exactly, whereas $CP$-even contributions, $\mathrm{\Delta }\kappa$ and $\mathrm{\Delta }Q$, remain. According to our estimations, the effects from heavy neutrinos with masses in the range of hundreds of GeVs dominate over those from light neutrinos. This investigation shows that contributions from heavy Majorana neutrinos to the anomaly $\mathrm{\Delta }\kappa$ could be as large as $\sim \mathcal{O}({10}^{-3})$, one order of magnitude below the Standard-Model contribution. We find that the International Linear Collider, sensitive to triple gauge couplings participating in $WW$ production, might measure these effects in electron-positron collisions at a center-of-mass energy of 800 GeV, as long as heavy-neutrino masses are $\gtrsim 300\mathrm{GeV}$ and below $\sim 1500\mathrm{GeV}$.

We investigate efficiency of a gauge-covariant neural network and an approximation of the Jacobian in optimizing the complexified integration path toward evading the sign problem in lattice field theories. For the construction of the complexified integration path, we employ the path optimization method. The two-dimensional U(1) gauge theory with the complex gauge-coupling constant is used as a laboratory to evaluate the efficiency. It is found that the gauge-covariant neural network, which is composed of the Stout-like smearing, can enhance the average phase factor, as the gauge-invariant input does. For the approximation of the Jacobian, we test the most drastic case in which we perfectly drop the Jacobian during the learning process. It reduces the numerical cost of the Jacobian calculation from $\mathcal{O}(N^3)$ to $\mathcal{O}(1)$, where $N$ means the number of degrees of freedom of the theory. The path optimization using this Jacobian approximation still enhances the average phase factor at expense of a slight increase of the statistical error.

This work develops neural-network-based preconditioners to accelerate solution of the Wilson-Dirac normal equation in lattice quantum field theories. The approach is implemented for the two-flavor lattice Schwinger model near the critical point. In this system, neural-network preconditioners are found to accelerate the convergence of the conjugate gradient solver compared with the solution of unpreconditioned systems or those preconditioned with conventional approaches based on even-odd or incomplete Cholesky decompositions, as measured by reductions in the number of iterations and/or complex operations required for convergence. It is also shown that a preconditioner trained on ensembles with small lattice volumes can be used to construct preconditioners for ensembles with many times larger lattice volumes, with minimal degradation of performance. This volume-transferring technique amortizes the training cost and presents a pathway towards scaling such preconditioners to lattice field theory calculations with larger lattice volumes and in four dimensions.

We study the critical behavior of the three-dimensional Gross-Neveu (GN) model with $N_f$ four-component Dirac fermionic flavors and quartic interactions, at the chiral ${\mathbb{Z}}_2$ transition in the massless ${\mathbb{Z}}_2$-symmetric limit. For this purpose, we consider a lattice GN model with staggered Kogut-Susskind fermions and a scalar field coupled to the scalar bilinear fermionic operator, which effectively realizes the attractive four-fermion interaction. We perform Monte Carlo simulations for $N_f=4$, 8, 12, 16. By means of finite-size scaling analyses of the numerical data, we obtain estimates of the critical exponents, which are compared with the large-$N_f$ predictions obtained using the continuum GN field theory. We observe a substantial agreement. This confirms that lattice GN models with staggered fermions provide a nonperturbative realization of the GN quantum field theory, even though the lattice interactions explicitly break the flavor $\mathrm{U}(N_f)\otimes \mathrm{U}(N_f)$ symmetry of the GN field theory, which is only recovered in the critical limit.

We compute the chromopolarizabilities of the fully heavy baryons ${\mathrm{\Omega }}_{QQ{Q}^{\prime }}$ ($Q,Q^{\prime }=b$, $c$) in the framework of potential nonrelativistic quantum chromodynamics. At leading order, the fully heavy hadrons are considered as ground chromo-Coulombic bound states. We find that the chromopolarizability ${\beta }_{\mathrm{\Omega }}$ of a fully heavy baryon $QQQ$ is 2.6 times the chromopolarizability ${\beta }_{\psi }$ of the quarkonium $\overline{Q}Q$ with the same heavy quark flavor $Q$. This result is accurate up to the correction of the order 0.3 for $Q=b$ and provides an order-of-magnitude estimate for $Q=c$. We discuss the dependence of the ratio ${\beta }_{\mathrm{\Omega }}/{\beta }_{\psi }$ on the heavy quark mass $m_Q$ and the strong coupling constant ${\alpha }_s$ as well as on the ratio of the masses $m_{Q^{\prime }}/m_Q$, in the case not all quarks in the baryon are identical. Since the chromopolarizability of heavy hadrons defines the strength of their interaction at low energies mediated by soft gluons, which at long range hadronize into pairs of pions and kaons, our findings argue in favor of the existence of near-threshold states composed of pairs of fully heavy baryons.

The three-body $\eta K^{*}{\overline{K}}^{*}$, $\pi K^{*}{\overline{K}}^{*}$, and $K{K}^{*}{\overline{K}}^{*}$ systems are investigated within the framework of fixed-center approximation to the Faddeev equations, where $K^{*}{\overline{K}}^{*}$ is treated as the scalar meson $f_0(1710)$. The interactions between $\pi$, $\eta$, $K$, and $K^{*}$ are taken from the chiral unitary approach. By scattering the $\eta$ meson on the clusterized $(K^{*}{\overline{K}}^{*}{)}_{f_0(1710)}$ system, we find a peak in the modulus squared of the three-body scattering amplitude and it can be associated as a bound state with quantum numbers $I^G(J^{PC})=0^{+}(0^{-+})$. Its mass and width are around 2054 and 60 MeV, respectively. This state could be associated with the $\eta (2100)$ meson. For the $\pi (K^{*}{\overline{K}}^{*}{)}_{f_0(1710)}$ scattering, we find a bump structure around 1900–2000 MeV with quantum numbers $1^{-}(0^{-+})$, while for the $K(K^{*}{\overline{K}}^{*}{)}_{f_0(1710)}$ system, there are three structures. One of them is quite stable and its mass is about 2130 MeV. It is expected that these theoretical predictions here could be tested by future experimental measurements, such as by the BESIII, BelleII, and LHCb Collaborations.

The Higgs boson pair production via gluon-gluon fusion and vector boson fusion in the $b\overline{b}{\mu }^{+}{\mu }^{-}$ final state at the LHC is studied to probe the Higgs self-coupling ${\kappa }_{\lambda }$ and the four-boson HHVV coupling ${\kappa }_{2\mathrm{V}}$ for the first time. A cut-based analysis and a machine-learning analysis using boosted decision trees are performed with categorizations and optimizations depending on the variations of these couplings. The expected sensitivities are extracted with different integrated luminosities assumed up to the full high-luminosity LHC runs. The expected upper limit at 95% confidence level on the Higgs boson pair production is calculated as 47 (28) times the Standard Model cross section using the cut-based method (boosted decision trees) for the gluon-gluon fusion production and 928 for the vector boson fusion production, assuming an integrated luminosity of $3000{\mathrm{fb}}^{-1}$. The expected constraints on the couplings at 95% confidence level are calculated to be $-13.8<{\kappa }_{\lambda }<19.1$ ($-10.0<{\kappa }_{\lambda }<15.5$) and $-3.4<{\kappa }_{2\mathrm{V}}<5.5$ using the cut-based method (boosted decision trees), respectively, assuming an integrated luminosity of $3000{\mathrm{fb}}^{-1}$.

We present a novel lepton-nucleus event generator: ACHILLES, A CHIcago Land Lepton Event Simulator. The generator factorizes the primary interaction from the propagation of hadrons in the nucleus, which allows for a great deal of modularity, facilitating further improvements and interfaces with existing codes. We validate our generator against high-quality electron-carbon scattering data in the quasielastic regime, including the recent CLAS/e4v reanalysis of existing data. We find promising agreement in both inclusive and exclusive distributions. By varying the assumptions on the propagation of knocked-out nucleons throughout the nucleus, we estimate a component of theoretical uncertainties. We also propose novel observables that will allow for further testing of lepton-nucleus scattering models. ACHILLES is readily extendable to generate neutrino-nucleus scattering events.

We investigate a hypothesis that energy accumulation and the subsequent release in NaI(Tl) may lead to pulselike events in the few-keV energy regime, a phenomenon suggested by the crystal manufacturing company Saint-Gobain, who provided the crystals for DAMA/LIBRA. While we observed delayed long-lasting (days) light emission in a 3-inch NaI(Tl) crystal after exposing it to UV light, the delayed light consists primarily of single photons that are uncorrelated with each other. We also observe delayed light emission in NaI(Tl) following gamma radiation and large ionization events like cosmic-ray muons. We found that irradiating the crystal with red light after UV exposure significantly suppressed delayed photon emissions.

A determination of the $CP$-even fraction $F_{+}$ in the decay $D^0\to K^{+}{K}^{-}{\pi }^{+}{\pi }^{-}$ is presented. Using $2.93{\mathrm{fb}}^{-1}$ of $e^{+}{e}^{-}\to \psi (3770)\to D\overline{D}$ data collected by the BESIII detector, one charm meson is reconstructed in the signal mode and the other in a $CP$ eigenstate or the decay $D\to K_{S,L}^0{\pi }^{+}{\pi }^{-}$. Analysis of the relative rates of these double-tagged events yields the result $F_{+}=0.730\pm 0.037\pm 0.021$, where the first uncertainty is statistical and the second is systematic. This is the first model-independent measurement of $F_{+}$ in $D^0\to K^{+}{K}^{-}{\pi }^{+}{\pi }^{-}$ decays.

The Migdal effect has received much attention from the dark matter direct detection community, in particular due to its power in setting leading limits on sub-GeV particle dark matter. However, it is crucial to obtain experimental confirmation of the Migdal effect through nuclear scattering using Standard Model probes. In this work, we extend existing calculations of the Migdal effect to the case of neutron-nucleus scattering, with a particular focus on neutron scattering angle distributions in silicon. We identify kinematic regimes wherein the assumptions present in current calculations of the Migdal effect hold for neutron scattering and demonstrate that these include viable neutron calibration schemes. We then apply this framework to propose an experimental strategy to measure the Migdal effect in cryogenic silicon detectors using an upgrade to the NEXUS facility at Fermilab.

A tantalizing hint of isotropic cosmic birefringence has been found in the $EB$ cross-power spectrum of the cosmic microwave background (CMB) polarization data with a statistical significance of $3\sigma$. A pseudoscalar field coupled to the CMB photons via the Chern-Simons term can explain this observation. The same field may also be responsible for early dark energy (EDE), which alleviates the so-called Hubble tension. Since the EDE field evolves significantly during the recombination epoch, the conventional formula that relates $EB$ to the difference between the $E$- and $B$-mode autopower spectra is no longer valid. Solving the Boltzmann equation for polarized photons and the dynamics of the EDE field consistently, we find that currently favored parameter space of the EDE model yields a variety of shapes of the $EB$ spectrum, which can be tested by CMB experiments.

We find electric string solutions in Yang-Mills-Higgs theory.

We derive a representation for a lattice U(1) gauge theory with exponential convergence in the number of states used to represent each lattice site that is applicable at all values of the coupling. At large coupling, this representation is equivalent to the Kogut-Susskind electric representation, which is known to provide a good description in this region. At small coupling, our approach adjusts the maximum magnetic field that is represented in the digitization as in this regime the low-lying eigenstates become strongly peaked around zero magnetic field. Additionally, we choose a representation of the electric component of the Hamiltonian that gives minimal violation of the canonical commutation relation when acting upon low-lying eigenstates. For $(2+1)$ dimensions with 4 lattice sites the expectation value of the plaquette operator can be calculated with only 7 states per lattice site with per-mille level accuracy for all values of the coupling constant.

We report on a measurement of the ${\mathrm{\Omega }}_c^0$ lifetime using ${\mathrm{\Omega }}_c^0\to {\mathrm{\Omega }}^{-}{\pi }^{+}$ decays reconstructed in $e^{+}{e}^{-}\to c\overline{c}$ data collected by the Belle II experiment and corresponding to $207{\mathrm{fb}}^{-1}$ of integrated luminosity. The result, $\tau ({\mathrm{\Omega }}_c^0)=243\pm 48(\mathrm{stat})\pm 11(\mathrm{syst})\mathrm{fs}$, agrees with recent measurements indicating that the ${\mathrm{\Omega }}_c^0$ is not the shortest-lived weakly decaying charmed baryon.

A covariant twistor action for chiral higher-spin theory in anti–de Sitter and flat space is constructed in term of a holomorphic Chern-Simons theory on twistor space. The action reproduces all known cubic vertices of chiral higher-spin theory in flat space. The spacetime action of the holomorphic Chern-Simons theory in flat space is also obtained.

We show that the scalar-tensor theory that arises in a rigorous $D\to 3$ limit of Lovelock gravity up to cubic order admits a holographic $c$-theorem and verify that the value of the $c$-function at the UV fixed point matches with the Weyl anomaly coefficient (up to an irrelevant factor). The constructed $c$-function is the same as one that follows from the “naive limit,” which is obtained by scaling the couplings by a factor of $\frac{1}{D-3}$, and then setting $D=3$.

An isolated critical point is a peculiar thermodynamic critical point that occurs in the phase diagram of hyperbolic black holes in $K$th-order Lovelock gravity in higher dimensions (with $K$ odd) for special tuned Lovelock coupling constants. It corresponds to a “merger” of two swallowtails and is characterized by nonstandard critical exponents. Upon employing a recent proposal for assigning a topological charge to thermodynamic critical points, we argue that the isolated critical point offers an interpretation corresponding to the onset of a topological phase transition of a vortex-antivortex pair.