We derive a linearly causal and stable third-order relativistic fluid-dynamical theory from the Boltzmann equation using the method of moments. For this purpose, we demonstrate that such a theory must include novel degrees of freedom, corresponding to irreducible tensors of ranks 3 and 4. The equations of motion derived in this work are compared with numerical solutions of the Boltzmann equation, considering an ultrarelativistic, classical gas in the highly symmetric Bjorken flow scenario. These solutions are shown to be in good agreement for a wide range of values of shear viscosity and initial temperatures.

The properties of the pion quasiparticle in hot and dense isospin medium, including the screening mass, pole mass, and thermal width, as well as their relationships with the pion superfluid phase transition, are investigated in the framework of two-flavor ($N_f=2$) soft-wall $\mathrm{AdS}/\mathrm{QCD}$ models. We extract the screening mass of the pion from the pole of the spatial two-point retarded correlation function. The screening masses of both neutral and charged pions increase monotonously with the increasing of temperature. However, the isospin chemical potential ${\mu }_I$ would depress the screening masses of the charged pions, $m_{{\pi }^{\pm },\mathrm{scr}}$. With the increasing of ${\mu }_I$, $m_{{\pi }^{\pm },\mathrm{scr}}$ monotonically decrease to zero on the boundary between the normal phase and the pion superfluid phase, while the screening mass of the neutral pion, $m_{{\pi }^0,\mathrm{scr}}$, remains almost unchanged. We also extracted the pole mass $m_{\mathrm{pole}}$ and thermal width $\mathrm{\Gamma }$ of the pion from the pole of temporal two-point retarded correlation function, i.e., the corresponding quasinormal frequencies, $\omega =m_{\mathrm{pole}}-i\mathrm{\Gamma }/2$. The pole masses of the three modes (${\pi }^0,{\pi }^{+},{\pi }^{-}$) are splitting at finite ${\mu }_I$. The thermal widths of the three modes increase with temperature. Furthermore, the pole mass and thermal width of ${\pi }^{+}$ decrease almost monotonically with the increasing of ${\mu }_I$, reaching zero at ${\mu }_I={\mu }_I^c$, simultaneously. It indicates that ${\pi }^{+}$ becomes a massless Goldstone boson as a result of the pion superfluid phase transition.

Many components of data analysis in high-energy physics and beyond require morphing one dataset into another. This is commonly solved via reweighting, but there are advantages of preserving weights and shifting the data points instead. Normalizing flows are machine learning models that have shown impressive precision on a variety of particle physics tasks. Naively, normalizing flows cannot be used for morphing because they require knowledge of the probability density of the starting dataset; in most cases in particle physics, we can generate more examples, but we do not know densities explicitly. We propose a protocol called flows for flows for training normalizing flows to morph one dataset into another even if the underlying probability density of neither dataset is known explicitly. This enables a morphing strategy trained with maximum likelihood estimation, a setup that has been shown to be highly effective in related tasks. We study variations on this protocol to explore how far the data points are moved to statistically match the two datasets. Furthermore, we show how to condition the learned flows on particular features in order to create a morphing function for every value of the conditioning feature. For illustration, we demonstrate flows for flows on toy examples as well as a collider physics example involving dijet events.

Evidence for a stochastic gravitational wave background in the nHz frequency band is recently reported by four pulsar timing array collaborations NANOGrav, EPTA, CPTA, and PPTA. It can be interpreted by gravitational waves from collapsing domain walls in the early universe. We assume such domain walls arising from the spontaneous breaking of a $Z_2$ symmetry in a scalar field theory, where a tiny $Z_2$-violating potential is required to make domain walls unstable. We propose that this $Z_2$-violating potential is radiatively induced by a feeble Yukawa coupling between the scalar field and a fermion field, which is also responsible for dark matter production via the freeze-in mechanism. Combining the pulsar timing array data and the observed dark matter relic density, we find that the model parameters can be narrowed down to small ranges.

The absence of semitauonic decays of charmed hadrons makes the decay processes mediated by the quark-level $c\to d{\tau }^{+}{\nu }_{\tau }$ transition inadequate for probing a generic new physics (NP) with all kinds of Dirac structures. To fill in this gap, we consider in this paper the quasielastic neutrino scattering process ${\nu }_{\tau }+n\to {\tau }^{-}+{\mathrm{\Lambda }}_c$, and propose searching for NP through the polarizations of the $\tau$ lepton and the ${\mathrm{\Lambda }}_c$ baryon. In the framework of a general low-energy effective Lagrangian, we perform a comprehensive analysis of the (differential) cross sections and polarization vectors of the process both within the Standard Model and in various NP scenarios, and scrutinize possible NP signals. We also explore the influence on our findings due to the uncertainties and the different parametrizations of the ${\mathrm{\Lambda }}_c\to N$ transition form factors, and show that they have become one of the major challenges to further constrain possible NP through the quasielastic scattering process.

Both parameters in the Higgs field’s potential, its mass and quartic coupling, appear fine-tuned to near-critical values, which gives rise to the hierarchy problem and the metastability of the electroweak vacuum. Whereas such behavior appears puzzling in the context of particle physics, it is a common feature of dynamical systems, which has led to the suggestion that the parameters of the Higgs potential could be set through some dynamical process. In this article, we discuss how this notion could be extended to physics beyond the Standard Model (SM). We first review in which sense the SM Higgs parameters can be understood as near-critical and show that this notion can be extrapolated in a unique way for a generic class of SM extensions. Our main result is a prediction for the parameters of such models in terms of their corresponding Standard Model effective field theory Wilson coefficients and corresponding matching scale. For generic models, our result suggests that the scale of new (bosonic) physics lies close to the instability scale. We explore the potentially observable consequences of this connection, and illustrate aspects of our analysis with a concrete example. Lastly, we discuss implications of our results for several mechanisms of dynamical vacuum selection associated with various beyond-the-Standard-Model constructions.

We propose a minimal extension of the Standard Model by incorporating sterile neutrinos and a QCD axion to account for the mass and mixing hierarchies of quarks and leptons and to solve the strong $CP$ problem and by introducing $G_{\mathrm{SM}}\times {\mathrm{\Gamma }}_N\times U(1{)}_X$ symmetry. We demonstrate that the Kähler transformation corrects the weight of modular forms in the superpotential and show that the model is consistent with the modular and $U(1{)}_X$ anomaly-free conditions. This enables a simple construction of a modular-independent superpotential for scalar potential. Using minimal supermultiplets, we demonstrate a level-3 modular form-induced superpotential. Sterile neutrinos explain small active neutrino masses via the seesaw mechanism and provide a well-motivated $U(1{)}_X$-breaking scale, whereas gauge singlet scalar fields play crucial roles in generating the QCD axion, heavy neutrino mass, and fermion mass hierarchy. The model predicts a range for the $U(1{)}_X$-breaking scale from ${10}^{13}$ to ${10}^{15}\mathrm{GeV}$ for $1\mathrm{TeV}<m_{3/2}<{10}^6\mathrm{TeV}$. In the supersymmetric limit, all Yukawa coefficients in the superpotential are given by complex numbers with an absolute value of unity, implying a democratic distribution. Performing numerical analysis, we study how model parameters are constrained by current experimental results. In particular, the model predicts that the value of the quark Dirac $CP$ phase falls between 38° to 87°, which is consistent with experimental data, and the favored value of the neutrino Dirac $CP$ phase is around 250°. Furthermore, the model can be tested by ongoing and future experiments on axion searches, neutrino oscillations, and $0\nu \beta \beta$ decay.

We investigate the ten independent local form factors relevant to the $b$-baryon decay ${\mathrm{\Lambda }}_b\to \mathrm{\Lambda }{\ell }^{+}{\ell }^{-}$, combining information of lattice QCD and dispersive bounds. We propose a novel parametrization of the form factors in terms of orthonormal polynomials that diagonalizes the form factor contributions to the dispersive bounds. This is a generalization of the unitarity bounds developed for meson-to-meson form factors. In contrast to ad hoc parametrizations of these form factors, our parametrization provides a degree of control of the form-factor uncertainties at large hadronic recoil. This is of phenomenological interest for theoretical predictions of, e.g., ${\mathrm{\Lambda }}_b\to \mathrm{\Lambda }\gamma$ and ${\mathrm{\Lambda }}_b\to \mathrm{\Lambda }{\ell }^{+}{\ell }^{-}$ decay processes.

For further decoding the inner structure of the two excited ${\mathrm{\Xi }}_b$ states observed by LHCb, we perform a systematical study of the strong decays of the low-lying $1D$-wave ${\mathrm{\Xi }}_b$ and ${\mathrm{\Xi }}_b^{\prime }$ excitations using the quark pair creation model within the $j-j$ coupling scheme. Combined with the measured masses and decay properties of ${\mathrm{\Xi }}_b(6327{)}^0$ and ${\mathrm{\Xi }}_b(6327{)}^0$, the two excited states can be explained as $1D$ $\lambda$-mode ${\mathrm{\Xi }}_b$ states ${\mathrm{\Xi }}_b|J^P={\frac{3}{2}}^{+},2{⟩}_{\lambda \lambda }$ and ${\mathrm{\Xi }}_b|J^P={\frac{5}{2}}^{+},2{⟩}_{\lambda \lambda }$, respectively. If such a view is correct, ${\mathrm{\Xi }}_b^{\prime }\pi$ and ${\mathrm{\Xi }}_b^{\prime *}\pi$ could be other interesting channels for experimental exploration of the ${\mathrm{\Xi }}_b(6327{)}^0$ and ${\mathrm{\Xi }}_b(6327{)}^0$, respectively. The calculations are good and consistent with the results within the chiral quark model. In addition, for the other missing $1D$-wave ${\mathrm{\Xi }}_b$ and ${\mathrm{\Xi }}_b^{\prime }$ excitations, our predictions indicate that: (i) the two $\rho$-mode $1D{\mathrm{\Xi }}_b$ states are likely to be moderate states with a width of $\mathrm{\Gamma }\sim 50\mathrm{MeV}$. The $J^P=3/2^{+}$ state dominantly decays into ${\mathrm{\Sigma }}_{b}K$ and ${\mathrm{\Xi }}_b^{\prime }\pi$, while the $J^P=5/2^{+}$ state decays primarily through ${\mathrm{\Sigma }}_b^{*}K$ and ${\mathrm{\Xi }}_b^{\prime *}\pi$; (ii) The $\lambda$-mode $1D$ ${\mathrm{\Xi }}_b^{\prime }$ states may be moderate states with widths of about several MeV to dozens of MeV. Most of the $\lambda$-mode $1D$ ${\mathrm{\Xi }}_b^{\prime }$ states mainly decay into the $1P$-wave bottomed baryon via the pionic decay processes. Meanwhile, several $\lambda$-mode $1D$ ${\mathrm{\Xi }}_b^{\prime }$ states have significant decay rates into $\mathrm{\Lambda }B$; (iii) While, the $\rho$-mode $1D$ ${\mathrm{\Xi }}_b^{\prime }$ states are predicted to be very broad states with a width of about several hundreds of MeV, it is a great challenge to explore the $\rho$-mode $1D$ ${\mathrm{\Xi }}_b^{\prime }$ states in experiments because of their broad widths.

We perform the linear analysis of causality and stability for a minimal extended spin hydrodynamics up to second order of the gradient expansion. The first order spin hydrodynamics, with a rank-3 spin tensor being antisymmetric for only the last two indices, are proved to be acausal and unstable. We then consider the minimal causal spin hydrodynamics up to second order of the gradient expansion. We derive the necessary causality and stability conditions for this minimal causal spin hydrodynamics. Interestingly, the satisfaction of the stability conditions relies on the equations of state for the spin density and chemical potentials. Moreover, different with the conventional relativistic dissipative hydrodynamics, the stability of the theory seems to be broken at the finite wave vector when the stability conditions are fulfilled at small and large wave vector limits. It implies that the behavior in small and large wave vector limits may be insufficient to determine the stability conditions for spin hydrodynamics in linear mode analysis.

AI-supported algorithms, particularly generative models, have been successfully used in a variety of different contexts. This work employs a generative modeling approach to unfold detector effects specifically tailored for exclusive reactions that involve multiparticle final states. Our study demonstrates the preservation of correlations between kinematic variables in a multidimensional phase space. We perform a full closure test on two-pion photoproduction pseudodata generated with a realistic model in the kinematics of the Jefferson Lab CLAS g11 experiment. The overlap of different reaction mechanisms leading to the same final state associated with the CLAS detector’s nontrivial effects represents an ideal test case for AI-supported analysis. Uncertainty quantification performed via bootstrap provides an estimate of the systematic uncertainty associated with the procedure. The test demonstrates that GANs can reproduce highly correlated multidifferential cross sections even in the presence of detector-induced distortions in the training datasets, and provides a solid basis for applying the framework to real experimental data.

Continuous tensor networks give a variational ansatz for the ground state of the quantum field theories (QFTs). Notable examples are the continuous matrix product state (cMPS) and the continuous multiscale entanglement renormalization ansatz (cMERA). While cMPS is just adapted to the nonrelativistic QFTs, only the Gaussian cMERA is well understood, which we cannot use to approximate the ground state of the interacting relativistic QFTs. But, instead, cMERA also corresponds to a real-space renormalization group flow in the context of the wave functions. In this paper, we investigate the backward Gaussian cMERA renormalization group flow of the class of cMPS by putting the standard cMPS at the IR scale. At the UV scale, for the bosonic systems in the thermodynamic limit, we achieve the variational class of states that has been proposed recently, as the relativistic cMPS (RCMPS) is adapted to the relativistic QFTs without requiring one to introduce of any additional IR or UV cutoff. We also extend the RCMPS to fermionic systems and theories on a finite circle.

We present precise resummed predictions for Higgs boson rapidity distribution through bottom quark annihilation at next-to-next-to-leading logarithmic (NNLL) accuracy matched to next-to-next-to-leading order and at next-to-next-to-next-to-leading logarithmic (N3LL) accuracy matched to next-to-next-to-next-to-leading order soft-virtual in the strong coupling. Exploiting the universal behavior of soft radiation near the threshold, we determine the analytic expressions for the process-dependent and universal perturbative ingredients for threshold resummation in double singular limits of partonic threshold variables $z_1$, $z_2$. Subsequently, the threshold resummation is performed in the double Mellin space within the standard QCD framework. The new third-order process-dependent nonlogarithmic coefficients are determined using three-loop bottom quark form factor and third-order quark soft distribution function in rapidity distribution. The effect of these new resummed coefficients are studied at the 13 TeV LHC. We observe a better perturbative convergence in the resummed predictions on the Higgs rapidity spectrum in bottom quark annihilation. We also find that the NNLL and N3LL corrections are sizeable which typically are of the order of $-2.5\%$ and $-1.5\%$ over the respective available fixed orders with the scale uncertainty remaining at the same level as the fixed order.

In this work, we study the role of triangle singularity in the $J/\psi \to \gamma \overline{p}\mathrm{\Delta }$ decay. We find that through a triangle mechanism, involving a triangle loop composed of $\omega$, $\pi$, and $p$, this decay may develop a triangle singularity and produce a visible peak in the invariant mass $M_{\gamma \mathrm{\Delta }}$ around 1.73 GeV with a width of 0.02 GeV. Such a triangle mechanism may also cause significant spin effects on the final $\mathrm{\Delta }$, which can be detected by measuring its spin density matrix elements. Our calculations show that the branching ratio due to the triangle mechanism is $\mathrm{Br}(J/\psi \to \gamma \overline{p}\mathrm{\Delta },\mathrm{\Delta }\to \pi p)=1.058\times {10}^{-6}$. Hopefully, this reaction can be investigated at BESIII and future experiments, e.g., Super Tau-Charm Facility, and the narrow width of the induced structure, the moving triangle singularity position, and the distinct features of the spin density matrix elements of the $\mathrm{\Delta }$ may serve as signals for the triangle singularity mechanism.

The prospects of searches for anomalous production of hadronically decaying weak boson pairs at proposed high-energy muon colliders are reported. Muon-muon collision events are simulated at $\sqrt{s}=6$, 10, and 30 TeV, corresponding to an integrated luminosity of 4, 10, and $10{\mathrm{ab}}^{-1}$, respectively. Simulated $\mu \mu \to \mathrm{W}\mathrm{W}+\nu \nu /\mu \mu$ events are used to set expected constraints on the structure of quartic vector boson interactions in the framework of a dimension-8 effective field theory. Similarly, $\mu \mu \to \mathrm{W}\mathrm{W}/\mathrm{Z}\mathrm{Z}+\nu \nu$ events are used to report constraints on the product of the cross section and branching fraction for vector boson fusion production of a heavy neutral Higgs boson decaying to weak boson pairs. These results are interpreted in the context of the Georgi-Machacek model.

We present an updated Standard Model (SM) estimate of the inclusive $b\to s\overline{\ell }\ell$ rate at a high dilepton invariant mass ($q^2\ge 15{\mathrm{GeV}}^2$). We show that this estimate is in good agreement with the result obtained summing the SM predictions for the leading one-body modes ($K$ and $K^{*}$) and the subleading nonresonant $K\pi$ channel (for which we also present an updated estimate). On the contrary, the semi-inclusive sum based on data exhibits a deficit compared to the inclusive SM prediction in the muon modes. The statistical significance of this deficit does not exceed $2\sigma$ but is free from uncertainties on hadronic form factors and fully compatible with the deficit observed at low-$q^2$ on the exclusive modes. The implications of these results in conjunction with other SM tests on $b\to s\overline{\mu }\mu$ modes are briefly discussed.

We study the dynamics of an electron wave packet in a strong constant crossed electromagnetic field accounting for radiative corrections due to interaction of the electron with the vacuum fluctuations. We evaluate a wave packet composed of the solutions to the Dyson-Schwinger equation, which describes electron propagation without emission of real photons. Spacetime dependence of the wave packet is obtained analytically for a short time interval, the more restricted from above the wider is the packet in momentum space. The radiative corrections alter the electron wave function, resulting in particular in a damping of the wave packet. The expectation value of the Dirac spin operator also gets modified.

We explore the possibility that an $SU(2{)}_L$ triplet scalar with hypercharge $Y=0$ is the origin of the 95 GeV diphoton excess. For a small mixing angle with the Standard Model Higgs, its neutral component has naturally a sizable branching ratio to $\gamma \gamma$ such that its Drell-Yan production via $pp\to W^{*}\to H{H}^{\pm }$ is sufficient to obtain the desired signal strength, where $H^{\pm }$ is the charged Higgs component of the triplet. The predictions of this setup are (1) The $\gamma \gamma$ signal has a $p_T$ spectrum different from gluon fusion but similar to associated production. (2) Photons are produced in association with tau leptons and jets, but generally do not fall into the vector-boson fusion category. (3) The existence of a charged Higgs with $m_{H^{\pm }}\approx (95\pm 5)\mathrm{GeV}$ leading to $\sigma (pp\to \tau \tau \nu \nu )\approx 0.4\mathrm{pb}$, which is of the same level as the current limit and can be discovered with Run 3 data. (4) A positive definite shift in the $W$ mass as suggested by the current global electroweak fit.

In this work, we investigate the real-time dynamics of quenching a state from phase separation in a holographic model of first-order phase transition. In addition to the typical phase-separated and high-energy final states, we have discovered a novel dynamical process that drives the system to a low-temperature supercooled final state within a narrow range of quench parameters. The critical behavior is also revealed during the fully nonlinear dynamics. Following a sudden quench with critical parameters, the phase separation can be attracted to a critical nucleus. Specifically, the critical nucleus will subsequently shrink in size and eventually disappear for supercritical parameters, where the system is actually supercooled with a temperature lower than the initial one. While for subcritical parameters, the nucleus will grow in size and finally reform a phase separation, where the absorbed quenching energy is reflected in the increment of the latent heat.

In this paper, we present a holographic realization of spontaneous chiral symmetry breaking and confinement. The latter is realized by building a solution of 5D Einstein-dilaton gravity leading to a confining quark antiquark potential. The 4D currents and the quark mass operator associated with chiral symmetry breaking and creation of meson states are mapped to 5D fields whose dynamics is given by a non-Abelian Higgs action. We introduce a nonminimal dilaton coupling to the tachyon potential which has two parameters, one of them controlling the presence or absence of spontaneous chiral symmetry breaking and the other controlling the sign of the quark condensate as the quark mass grows. We calculate the masses of vector, scalar, axial-vector, and pseudoscalar mesons, focusing on the effect of chiral symmetry breaking on the spectrum. In the chiral limit we identify the emergence of a massless state in the pseudoscalar meson spectrum, i.e., the pion. We calculate all meson decay constants and confirm that the pion satisfies the Gell-Mann-Oakes relation in the light quark regime.