Papers

The 4th International Symposium on the History of Particle Physics spanned two decades, from approximately 1980 to 2000. In this opening keynote lecture, I survey developments in particle physics from the prehistory of the $J/\psi$ discovery to the early nineteen-eighties. I offer context for the contributions that follow in the symposium program.

We develop a quantum algorithmic framework for the efficient simulation of Yang–Mills theories, including the $\mathrm{SU}(3)$ gauge theory in Quantum Chromodynamics (QCD). The framework uses maximal-tree gauge in terms of gauge field variables that removes all local gauge redundancies. In the resulting gauge-fixed formulation and digitization in the field-amplitude basis, we show that Hamiltonian time evolution admits an efficient implementation based on quantum singular value transformation (QSVT). We derive upper bounds on the total number of qubits and gate complexity, finding polynomial scaling with the inverse simulation precision $1/\varepsilon_s$, lattice volume $\mathcal{V}$, gauge coupling $g$, and target energy scale $E$. Our results provide a rigorous complexity-theoretic demonstration that non-Abelian Yang–Mills theories can be simulated efficiently on quantum computers, paving the way toward first-principles quantum simulations of non-perturbative QCD dynamics.

We propose an anomaly-free and renormalizable axial $U_A(1)_{L_\mu-L_\tau}$ model and study its experimental signatures for $A'$ masses from the MeV scale to the TeV scale. The opposite charges of the left- and right-handed charged leptons forbid the usual muon and tau Yukawa interactions. Their masses are instead generated by a singlet scalar and heavy vector-like leptons through a universal-seesaw mechanism. We focus on heavy vector-like leptons, small light–heavy mixing, and $m_s\gtrsim10~\mathrm{GeV}$. In this limit, the observables considered here depend mainly on $(m_{A'},g_X)$, while the other model parameters are restricted by mixing and perturbativity. We confront this benchmark with current experimental searches. For neutrino trident production, our finite-$m_\mu$ calculation shows that $A'$ modifies the axial weak coefficient, rather than the vector coefficient relevant to the usual $L_\mu-L_\tau$ model. The longitudinal mode enhances muon bremsstrahlung and gives a negative contribution to $(g-2)_\mu$; the latter dominates over the scalar contribution in our benchmark. Combining these results with invisible meson decays and four-muon resonance searches, we summarize the phenomenological constraints in the $(m_{A'},g_X)$ plane. For $m_{A'}\gg m_\mu$, vector and axial final-state-radiation rates become nearly identical, so the corresponding collider limits can be obtained by rate matching. At a future muon collider, the total rate alone does not fully resolve the interaction structure, whereas angular distributions, especially the forward–backward asymmetry in $\mu^+\mu^-\to\tau^+\tau^-$, retain direct sensitivity to chirality.

This work studies the collider phenomenology of long-lived doubly charged scalars. After reviewing the existing searches for the doubly charged scalar in both the prompt and the long-lived regimes, we identify an intermediate range of proper decay length, namely, $\mathcal{O}(0.1~\mathrm{mm}) \lesssim c\tau \lesssim \mathcal{O}(100~\mathrm{mm})$, where conventional searches lose sensitivity. We investigate the prospects for probing the doubly charged scalar both in the presence and in the absence of the $\Delta L=2$ Yukawa coupling of the $SU(2)_{L}$ complex triplet. In the presence of this coupling, $H^{\pm\pm}$ can be long-lived only for masses in the range $100$-$150~\mathrm{GeV}$, whereas in the fermiophobic scenario (i.e., in the absence of the $\Delta L=2$ coupling), the range extends to $\mathrm{TeV}$ scale. We propose a displaced-vertex search at the HL-LHC for doubly charged scalars with masses up to $\approx 1~\mathrm{TeV}$ and $c\tau=10$-$100~\mathrm{mm}$ in the fermiophobic scenario, while a benchmark point with a doubly charged scalar of mass $120~\mathrm{GeV}$ and $c\tau = 5~\mathrm{mm}$ is considered when the complex triplet scalar couples to leptons. We show that a cut on the invariant mass of the displaced vertex as reconstructed from the associated tracks can strongly suppress Standard Model backgrounds. We present projected limits on the Drell-Yan pair-production cross section for the doubly charged scalar at $\sqrt{s}=14~\mathrm{TeV}$ with an integrated luminosity of $3000~\mathrm{fb}^{-1}$, considering two illustrative assumptions for the residual background. Displaced-vertex searches thus probe a region complementary to those covered by prompt and heavy stable charged-particle searches.

Motivated by a considerable release of data on first two excited states of the doubly strange baryon, $\Xi(1620)$ and $\Xi(1690)$, from different experimental collaborations in recent years, we investigate meson-baryon interactions in a coupled-channel approach. The systems are composed of pseudoscalar and vector mesons and the calculations are done for the total spin 1/2 and isospin 1/2 configuration. The tree-level interactions are deduced from Lagrangians based on chiral and hidden local symmetries. Specifically, we make an attempt to describe (1) data on the $K^-\Lambda$ femtoscopic correlation function coming from $p\,p$ and $Pb\,Pb$ collisions, and (2) the available data on invariant mass distributions for different systems: $\pi\Xi$, $\bar K \Sigma$ and $\bar K \Lambda$. We find that the amplitude which yields the correlation function close to the data results in mass distributions of different meson-baryon systems that are in discordance with the experimental data and vice-versa.

We present discussions on the possibility of emerging hidden scale symmetry, as a pseudo-conformal phase in super dense baryonic matter, using the velocity of sound as a criterion for a scale symmetry window in hadronic dense matter. In the density dependent mean field approach à la Brown-Rho scaling, it has been observed that the interplay between vector mesons and $ \chi$, one of the strongly correlated effects between hadrons, is nontrivial such that the trace of the energy momentum tensor becomes density-independent in the super dense regime and the sound velocity approaches the conformal sound velocity for the pseudo-conformal phase. It is suggested that in the pseudo conformal phase the rearrangement terms induced by density dependent couplings do not spoil the hidden scale symmetry in the compact star matter. We elaborate further on the astrophysically observable quantities of the compact stars and the implications for the parity doubling and the quark-hadron transitions.

The flavor structure of the Standard Model (SM) remains one of the most compelling questions in particle physics, with the third generation being particularly intriguing due to its significantly larger masses and comparatively less precisely measured properties. These features make third-generation flavor transitions particularly interesting in context of search for physics beyond the SM. In this work, we investigate flavor-violating transitions between the third and the first two generations, mediated by the neutral gauge bosons ($Z/\gamma$), within the framework of the SM Effective Field Theory (SMEFT), using dipole and Higgs-current operators. We determine the optimal sensitivities using the optimal observable technique (OOT) at different center-of-mass energies of the upcoming Future Circular Collider in the $e^+e^-$ mode (FCC-ee). We further derive complementary constraints on the relevant SMEFT operators from low-energy flavor-violating observables and heavy fermion decay channels. Our analysis also reveals characteristic interference patterns among the dipole contributions, which depend on the underlying flavor transition and exhibit distinct behavior between the $Z$ pole and higher-energy FCC-ee stages. The FCC-ee provides a complementary and direct probe of flavor-violating interactions at the electroweak scale, with the projections showing improved sensitivity for several interactions and comparable sensitivity to existing flavor constraints for several others. This highlights the importance of a systematic assessment across the different FCC-ee energy stages, which provides a comprehensive picture of its potential to explore flavor-violating phenomena and its complementarity with low-energy flavor experiments.

The efficient sampling of high-dimensional phase spaces is a major challenge for Monte Carlo event generators, as for high-multiplicity final states the evaluation of scattering matrix elements becomes computationally expensive. We here introduce a training strategy that significantly reduces the cost of adapting the samplers, while delivering samplers that outperform the current benchmarks. The method exploits the nested structure of phase spaces, where an $(N+1)$-particle phase space factorises into an $N$-particle and a one-particle phase space. We thereby assume that an efficient sampler for the corresponding $N$-particle phase space is already available, as is the case in stacks of QCD $X+n$-jets processes. By augmenting an $N$-particle to an $(N+1)$-particle dataset, we obtain a training sample that more closely resembles the integrand and is statistically larger than, for example, a uniformly sampled one. Starting the adaptation phase of the sampler with a well-sampled $N$-particle core accelerates learning of the full $(N+1)$-particle phase-space density. Since the augmented sample is only used as an initial proposal distribution, unbiased Monte Carlo estimates are still guaranteed by exact event weighting. The approach is agnostic to the trained sampler and can be applied to machine-learning-based methods as well as more traditional algorithms such as VEGAS. We demonstrate the reduction in matrix-element evaluations and final performance increase for jet-associated Drell–Yan and top-pair production at the LHC, using Continuous Normalising Flow samplers.

Extracting transverse momentum dependent parton distribution functions (TMD PDFs) from semi-inclusive deep inelastic scattering (SIDIS) data is a central goal of the nucleon structure program at Jefferson Lab and the future Electron-Ion Collider. Traditional extraction methods rely on parameterized functional forms and iterative fitting, which can limit the flexibility of the resulting distributions and make uncertainty quantification cumbersome. We present a conditional diffusion model that learns to map raw SIDIS event kinematics directly to TMD PDFs, bypassing explicit functional assumptions. Evaluated on simulated SIDIS data at CLAS12 kinematics, the model recovers the underlying TMD with informative uncertainties that narrow steadily with increasing event statistics, and produces reliable estimates even with as few as 1,000 conditioning events, a statistics-limited regime directly relevant to ongoing and planned experiments.

We review and extend recent progress on QCD-like phases at nonzero temperature and chemical potentials within the gauge-gravity duality. We focus on the Witten-Sakai-Sugimoto model, a top-down approach based on string theory which allows for a unified treatment of mesons, baryons and quarks. Phases such as pion condensation, baryonic and quarkyonic matter are located in the phase diagram, and we discuss predictions as well as weaknesses and limitations of this holographic approach. One of the novelties included in this review is the first holographic construction of a pionic phase between BEC and BCS regimes, which however is found to be metastable. We also discuss future directions in holographic QCD, within the model used here and in a wider context.

We investigate the effect of the GUP on the Lamb shift of a two-level atom interacting with a real massless scalar quantum field, within the DDC formalism. For an atom undergoing inertial motion, uniform acceleration, and uniform circular motion, we analyze the separate contributions of vacuum fluctuations and radiation reaction. We first derive the statistical functions of the field along the atom's trajectories for the three types of motion, expressing them as frequency integrals, and then employ them to calculate the vacuum fluctuation and radiation reaction contributions to the radiative level shift. We show that the GUP-modified Lamb shift of the two-level atom arises entirely from vacuum fluctuations and acquires additional corrections proportional to $\beta$. We focus in particular on the acceleration-dependent GUP corrections. For a uniformly accelerated atom, the GUP corrections comprise thermal and nonthermal parts. At low accelerations, the thermal part exhibits nonmonotonic behavior, and is proportional to $a^4$ in the limit $a/\omega_0 \to 0$; the nonthermal part, by contrast, grows nonlinearly and monotonically, exceeding the thermal part by nearly two orders of magnitude at large accelerations. For an atom in uniform circular motion, the GUP corrections are purely nonthermal and also display a nonlinear, monotonic dependence on acceleration, increasing or decreasing steeply according to the sign of $\beta$. For the same $\beta$, the corrections are larger in uniform circular motion than in uniformly accelerated motion, since the former involves terms proportional to both $a^2$ and $a^3$, whereas the latter contains only $a^2$ terms.

We present a detailed NLO+PS study of Higgs-boson production in association with charm and bottom quarks, with particular focus on the modelling of the H+c final state. We systematically compare predictions in massive and massless flavour schemes, quantify scale and flavour-scheme uncertainties, and assess the impact of interference and loop-induced contributions. Special emphasis is placed on the Higgs production via charm Yukawa fusion, for which we compare NLO+PS predictions with a NNLO+PS calculation of $c\bar{c}H$ production in the four-flavour scheme at 13.6 TeV. Based on these results, we provide the first practical recommendations for the simulation of $c\bar{c}H$ production in LHC analyses.

We study collective slow flavor conversion (SFC) of supernova neutrinos with multi-energy, multi-angle simulations for three representative neutrino spectra in the early accretion, late accretion, and cooling phases, in which multiple crossings between the initial electron- and heavy-lepton-flavor spectra are present. By numerically solving the neutrino quantum kinetic equations in a local periodic box, we find that SFC triggered predominantly by the spatially inhomogeneous instabilities drives the system toward a spatially coarse-grained, quasi-stationary state, whose flavor conversion probability depends strongly on energy, angle, and the neutrino mass ordering. While we find that not all of the initial spectral crossings are completely erased in the final state, a simple, box-like analytical prescription inspired by studies of fast flavor conversions, which eliminates the spectral crossings, can reasonably approximate the post-SFC spectra. Using the initial and post-SFC spectra, we also evaluate the changes of the corresponding $\nu_e$ and $\bar\nu_e$ heating rates as well as the absorption equilibrium electron fraction ($Y_e$). Within the considered scenarios, we find that the heating rates are generally enhanced by up to $\sim 80\%$ due to the net conversion of $\nu_x$ to $\nu_e$ (and $\bar\nu_x$ to $\bar\nu_e$) above their crossing energy, provided that the energy spectra above the crossing energy differ substantially. For the absorption equilibrium $Y_e$, spectra changes due to SFC increase it by $\sim 0.03$ due to the relatively more enhanced $\nu_e$ absorption rate than $\bar\nu_e$, which potentially drives supernova materials to be more proton-rich. These results highlight the importance of energy-dependent treatments of SFC for supernova neutrinos.

For a relativistically decoupled thermal relic, the dark-matter energy-to-entropy ratio scales as $\rho_{\rm DM}/s\sim 10^{-3}m_{\rm DM}$. This is the familiar hot-dark-matter abundance relation. Immediately after weak-sphaleron freeze-out, the baryon asymmetry can be parametrized as $\rho_{\rm baryon}/s\sim 10^{-4}|\mu_B|$. Here $\mu_B$ is the baryon-number chemical potential. We propose a new class of models, called chemical-potential-matched dark matter ($\mu$DM), in which $|\mu_B|\sim m_{\rm DM}$, thereby providing a new route to the baryon-dark matter coincidence. As a concrete example of $\mu$DM, we consider an Affleck-Dine field whose excitations constitute dark matter. We also briefly discuss spontaneous electroweak baryogenesis associated with axion-like-particle walls. In the absence of entropy dilution, this coincidence mechanism generically points to dark matter in the eV-keV mass range. Its momentum distribution can nevertheless be cold if thermal production is dominated by Bose-enhanced stimulated emission. Alternatively, entropy dilution after both the dark-matter and baryon yields are fixed allows masses up to the MeV scale.

We investigate a $\mathbb{Z}_3$-symmetric extension of the Standard Model consisting of a right-handed neutrino ($N_R$), a dark fermion ($\chi$) that dominates the relic density and a dark complex scalar ($S$) that facilitates a strong first-order electroweak phase transition (SFOEWPT). The observed relic abundance, is achieved through the combined effects of annihilation, semi-annihilation, and dark-sector conversion processes over a broad region of parameter space consistent with a SFOEWPT. We further investigate the resulting multi-messenger signatures, including loop-induced direct detection, indirect detection through gamma-ray observations, and gravitational wave signals, with the latter lying within the projected sensitivities of future space-based detectors such as LISA, BBO, and DECIGO.

The conversion between baryon and lepton numbers has a significant impact on the mechanisms for dynamically generating the matter-antimatter asymmetry in the present universe. Under the traditional wisdom, such conversion originates from the so-called electroweak sphaleron processes. In this work we find that in association with a proper scalar and the other TeV new physics, the baryon-lepton conversion can still keep efficient after the electroweak sphalerons are no longer active. Moreover this scenario can provide a solution to the puzzle of neutron lifetime and predict some decay modes of multi-nucleons to multi-leptons.

Fermionic domain-wall Skyrmions arise in the chiral soliton lattice of two flavor chiral perturbation theory in a magnetic field as the ground state and are associated with baryons of the underlying theory of quantum chromodynamics. We analyze the electromagnetic screening characteristics of domain-wall Skyrmions that give insight into baryon density on the magnetic field and chemical potential phase diagram. At zero temperature, using the moduli effective theory, it is found Skyrmion density is saturated up to the Fermi momenta on the disk of the chiral soliton lattice orthogonal to the magnetic field. We further study chiral perturbation theory coupled to quantum electrodynamics leading to finite temperature screening, wherein a static fermionic domain-wall Skyrmion screening is predicted through a combined Debye mass/length.

We present a general approach for calculating new electron-electron interactions with atomic structure theory, include dominant many-body effects, and extract bounds for parity-odd cases. The procedure is valid for any mediator mass and improves previous calculations by including many-body corrections to the new interaction through the time-dependent Hartree-Fock method. Bounds on coupling strengths are then extracted for scalar-pseudoscalar and vector-axial vector interactions by comparison with experimental atomic electric dipole moments and parity non-conserving (PNC) transitions respectively. In the latter case, our calculations rule out any coupling-mass ratio |g^e_V g^e_A|/m_X^2 greater than 10^-11 MeV^-2 above m_X ~ 10 MeV, covering a previously unconstrained mass region. We also report an updated calculation of the regular (Standard Model) electron-electron Z^0 exchange contribution to the 6s-7s PNC transition amplitude E_PNC in cesium.

We analyze the complementarity between direct detection (DD) and indirect detection (ID) searches of sub-GeV dark matter (DM) in the context of two realistic models: the vector-portal (dark photon) and scalar-portal (higgs-portal) models. For DD we focus on the latest constraints on the DM-electron scattering from the present DAMIC-M experiment as well as its future projection. For ID we consider several existing X-rays/gamma-rays and cosmic-ray ($e^\pm$) observations as well as the upcoming MeV telescope COSI to obtain the corresponding bounds and projections on the DM annihilation rate, which are then translated in terms of the DM-electron scattering cross-section and compared with the DD bounds/projections. We properly take into account astrophysical and galactic propagation uncertainties. We find that the complementarity between DAMIC-M and ID works best for the vector-portal model, especially for the case where the vector mediator is heavier than the DM particle: in this case, the present DAMIC-M bound becomes comparable to (or better than, for some astrophysical configurations) the combined ID limit for $3\,{\rm MeV} \lesssim m_{\rm DM} \lesssim 20\,{\rm MeV}$. For other cases and mass ranges, the ID is in general more constraining and can also, for some mass ranges, constrain the parameter space below the neutrino floor, which is inaccessible to DD experiments.

A photon can decay into an electron-positron pair in the presence of an intense laser pulse by a process known as nonlinear Breit-Wheeler pair production (NBWPP). For a sufficiently intense pulse, the probability of NBWPP for a high-energy gamma photon scales more favorably with the interaction time than with the field intensity. In contrast to typical stationary-focus Gaussian (SFG) laser pulses, a flying-focus (FF) pulse features a focal point that moves at a programmable velocity. Here, we show that a FF pulse counterpropagating with a high-energy photon beam while its focus copropagates with the beam at the speed of light enhances the NBWPP yield relative to an equal-energy SFG pulse. Numerical simulations show that a Joule-class tightly-focused FF pulse allows for an enhancement of the pair-production yield by 12%, 29% and 76% for a photon of 10, 20 and 50 GeV energy, respectively. Thus, in this regime, FF pulses are more efficient at producing electron-positron pairs than conventional SFG pulses.

Paleo-detectors are a proposed approach to the direct detection of dark matter (DM) based on the observation of DM-induced nuclear recoils. Rather than relying on large detector masses required for conventional detectors, paleo-detectors exploit extremely long integration times, using small samples of naturally occurring minerals that have resided deep underground and accumulated damage tracks over geological timescales of order a gigayear. In this contribution, we review recent theoretical predictions for the sensitivity of paleo-detectors to WIMP-nucleus interactions within the framework of a Non-Relativistic Effective Field Theory (NREFT). We discuss both elastic and inelastic scattering processes and consider isoscalar couplings, taking into account backgrounds from neutrinos and radiogenic sources. We present projected sensitivities of paleo-detectors for different readout and exposure scenarios and compare the reach of paleo-detectors to that of conventional direct-detection experiments. For DM masses in the range $1\ \mathrm{GeV}/c^2$-$10\ \mathrm{GeV}/c^2$, paleo-detectors are expected to achieve sensitivities exceeding those of conventional experiments for WIMP-nucleus interactions mediated by all NREFT operators, with only a weak dependence on the read-out scenario or target mineral. For larger DM masses, $10\ \mathrm{GeV}/c^2$-$5\ \mathrm{TeV}/c^2$, paleo-detectors are projected to attain sensitivities comparable to or surpassing conventional experiments for interactions mediated by several NREFT operators, depending on the specific read-out scenario and choice of target mineral.

IceCube has recently detected a diffuse population of high-energy neutrinos arising from the Milky Way. We use this high-significance detection to place new limits on dark matter (DM) annihilation to neutrinos with two complementary approaches. The first method uses the background-subtracted Galactic longitude distribution of shower events to place a conservative bound on the DM annihilation cross section that does not rely on any assumed Galactic cosmic ray emission model; the resulting limits on the velocity-averaged annihilation cross section improve upon existing bounds by factors of a few. The second method uses the template-dependent neutrino energy spectra from the Inner Galaxy, inferred under different Galactic cosmic ray emission models. This complementary approach shows that the inferred Galactic neutrino intensities are already sensitive to DM contributions near the thermal-relic benchmark for a range of TeV-scale DM masses, though this comparison is more model-dependent. Our results demonstrate that measurements of diffuse Galactic neutrino emission can be used as a powerful probe of DM annihilation into neutrinos. Future observations with IceCube-Gen2 and KM3NeT will substantially extend this sensitivity, potentially allowing a decisive test of the thermal freeze-out mechanism with Galactic neutrino observations.

Accelerator-based experiments at the intensity frontier, in which a high-energy beam impinges on a nuclear target, serve as powerful probes of the light dark matter paradigm. Such experiments require precise modeling of the target nucleus for reliable signal predictions. We present the application of a many-body ab initio method to calculate light dark matter mediator production signal rates at electron fixed-target experiments, using chiral effective field theory interactions. Considering both elastic and quasi elastic scattering, we compute cross sections using a Monte Carlo event generator implementation informed by ab initio nuclear elastic form factors and spectral functions for three representative nuclei, $^{20}$Ne, $^{34}$Si, and $^{56}$Fe, at varying electron beam energies. We compare our results to a commonly used phenomenological parameterization, finding an increased signal yield by up to two orders of magnitude with our quasi elastic treatment and an agreement for lighter mediators.

In recent years, significant progress has been made in the development of automated tools that match the parameters of new physics models and the appropriate low-energy Effective Field Theories. This work introduces an extensible, hybrid tool, OperatorToC++, that combines the strengths of Mathematica and C++ to facilitate the next steps beyond the matching. OperatorToC++ efficiently tackles the complexities within the analytical matched expressions such as intricate loop-functions and lengthy sums and products involving tensor objects. It then translates and bundles the results into C++ classes and functions which provide a convenient platform for further numerical analyses. Finally, it offers the possibility of calling the compiled Wilson coefficient methods as Python functions, thus enabling to link them with the vast Python library ecosystem for High Energy Physics workflows.

We present FlaSR, a Mathematica package for the automatic generation of higher-order amplitude and amplitude-squared $SU(2)$ flavor sum rules, with a particular emphasis on $U$-spin. The package is based on recent insights into the mathematical structure of flavor sum rules. Given a system of symmetry-related processes defined by a list of particle multiplets in the initial and final states, together with the transformation properties of the symmetry-limit Hamiltonian, the package generates the full list of processes and outputs amplitude and amplitude-squared sum rules for the system. For amplitude sum rules, the package generates the complete set at all orders in symmetry breaking for which such relations exist. For amplitude-squared sum rules, which translate directly into sum rules among physical observables, the current version of the package is not guaranteed to generate the complete set. We illustrate the scope of the package with a range of representative examples.

Energy correlators are universal observables, well defined across a wide range of theories and spacetime dimensions, from gauge theory and conformal field theory to string theory. Energy correlators are constrained by three fundamental properties: pointwise positivity of the energy flux, global positivity originating from their interpretation as state norms in a unitary theory, and energy conservation organizing multi-point energy correlators into an infinite consistent hierarchy. We argue that the most general solution to the infinite hierarchy positivity problem of energy correlators is given by the event distribution formula, which expresses energy correlators as moments of the measure on the space of probability measures on the celestial sphere. We work out in detail implications of positivity for two- and three-point energy correlators and show that it implies nontrivial two-sided bounds on their multipole expansion coefficients. The bounds obtained by requiring consistency of the infinite hierarchy of energy correlators are strictly stronger than those obtained by imposing positivity of the two- and three-point correlators alone. For the low-spin multipole coefficients studied in the paper, the derived bounds are optimal in the sense that their extrema are realized by finite mixtures of finite-particle events. We further demonstrate consequences of positivity in energy correlators in collider physics and conformal field theories.

Event triggering sits at the heart of high-energy physics, where the rare events of interest must be retained while an overwhelming background is discarded under tight latency and bandwidth budgets. This work compares four classical machine learning models, namely a support vector machine, an artificial neural network, a convolutional network and a long short-term memory network, with four hybrid quantum counterparts, on a trigger-like binary classification task built from CMS open data. The label is defined by an invariant-mass window, and the inputs combine reconstructed kinematics with physics-motivated derived variables: the pseudorapidity difference, the wrapped azimuthal difference, the angular separation and the total transverse momentum. The quantum models run under a fixed resource budget of eight qubits, a principal-component compression to sixteen features and state-vector simulation. Every model shares the same stratified split, the same preprocessing and a common decision threshold, and performance is reported through accuracy, ROC-AUC, F1-score, precision and recall. The strongest classical model is the artificial neural network, at 93.53 percent accuracy and 0.9819 ROC-AUC, while the strongest quantum model is the quantum convolutional network, at 90.89 percent accuracy and 0.9731 ROC-AUC, with the quantum neural network close behind. The quantum-kernel and recurrent quantum approaches trail both, which places the trainable hybrid embeddings ahead within this budget. The study is meant as a controlled reference point rather than a claim of quantum advantage.

We investigate the problem of confinement of massive ghost, which violates the unitarity of the physical S-matrix, in quadratic gravity on the basis of a manifestly covariant and local canonical operator formalism. First, we reconsider the manifestly covariant quantization of quadratic gravity in the de Donder gauge (the harmonic gauge) from the viewpoint of dipole fields. Next, we also reconsider a possible mechanism of confinement of the massive ghost and derive an effective Lagrangian for asymptotic fields of a BRST quartet where the asymptotic field corresponding to the massive ghost is found to obey a dipole field equation as in the Froissart model, which is a characteristic feature in our formalism. To understand quantum aspects of our theory, we perform a manifestly covariant quantization of the effective Lagrangian in two different ways based on the three-dimensional Fourier transform and the four-dimensional Fourier transform, and derive the same result that the quantum Fock space is spanned by multipole states.

Left–right symmetric theories with generalized parity restrict the bare QCD angle to a CP-conserving value and relate the physical strong-CP phase \(\bar\theta\) to a CP-odd parity-breaking parameter \(\eps\). We show that, in the Dirac-neutrino realization, imposing a sectorial reality condition on the Dirac lepton Yukawa matrices turns observable leptonic CP violation from an independent input into a branch-dependent prediction. Parity reconstructs the right-handed leptonic mixing matrix, whereas leptonic reality requires it to be rephasing-equivalent to the complex conjugate of the left-handed one. For generic three-generation Yukawas, compatibility is equivalent to the vanishing of a single Jarlskog-type CP-odd invariant. In the physical Dirac hierarchy, for fixed oscillation data, mass ordering, and discrete leptonic branch, compatibility determines the PMNS Jarlskog invariant as a function of the lightest neutrino mass and \(\eps\). We derive its leading analytic behavior and obtain the nonlinear compatibility branches numerically. In compressed mixed-sign Dirac-neutrino spectra, small signed mass sums can amplify a tiny parity deformation into order-one values of the normalized PMNS Jarlskog invariant, including maximal CP violation. The corresponding quark reconstruction independently provides a calculable, branch-dependent conversion between \(\eps\) and \(\bar\theta\). Together, the leptonic and quark relations define a family of correlations among leptonic CP violation, the absolute neutrino mass scale, and strong CP.

We formulate a theoretical framework for the evolution of QCD jets in vacuum and in the quark–gluon plasma through the resummation of large energy logarithms. Exploiting the strong hierarchy between the hard scale of the jet and the energy scale associated with jet energy loss, we show that jet observables near threshold can be formulated in terms of Wilson-line correlators obeying Banfi-Marchesini-Smye (BMS) evolution. In this description, soft radiation resolves the internal color structure of the jet, leading to a hierarchy of non-linear evolution equations that govern the evolution of color coherence and the emergence of decoherent energy loss. For jets propagating through a QCD medium, we demonstrate that medium-induced interactions modify the boundary conditions of the evolution while leaving its ultraviolet structure unchanged. This separation of scales provides a unified description of vacuum-like radiation, medium-induced energy loss, and color coherence. In the large-$N_c$ limit, the resulting evolution is closely related to the Balitsky-Kovchegov equation of high-energy QCD, allowing concepts from saturation physics to be applied to jet quenching. In particular, the medium coherence angle plays a role analogous to the saturation scale and acquires the same asymptotic scaling behavior under evolution. Our framework establishes a perturbative foundation for the study of color coherence effects in jet quenching and provides a unified picture of soft jet evolution in vacuum and in dense QCD matter.