Papers

To clearly identify the mechanism behind the suppression of heavy quarkonium in relativistic heavy-ion collisions, we study $\Upsilon$ production at RHIC energies by solving its transport equation driven solely by the suppression rates. By calculating the nuclear modification factor and comparing it with experimental data, we find that the sudden suppression governed by the color-screening temperature cannot simultaneously describe both the ground and excited states of the $\Upsilon$, whereas the continuous suppression induced by thermal decay successfully reproduces all the $\Upsilon$ measurements. This provides strong evidence that inelastic scatterings with thermal partons, rather than color screening, dominate quarkonium suppression in heavy-ion collisions.

We discuss the tension one encounters in trying to solve, simultaneously, the $U(1)$ and strong-$CP$ problems in QCD with light quarks and a small $\bar{\theta}$ angle within QCD itself. We do so by considering the low-energy expansion of a $1$PI effective action $\Gamma$, a functional of a properly chosen set of gauge-invariant (composite) operators. After enforcing Ward-identity constraints on $\Gamma$, we prove, under minor assumptions, that $CP$ violation at small non-vanishing $\bar{\theta}$ can be avoided only if the anomaly-induced contribution to the pseudoscalar mass matrix is completely negligible when compared to its non-anomalous counterpart - that is, only if the $U(1)$ problem is not solved. The topological susceptibility in QCD and a precise generalization of the one in pure Yang-Mills theory emerge as the most important players in establishing the above tension and in determining the corrections to various known results at leading order in $\bar{\theta}$.

We present HEPLocalAgent, an open source local interface that builds a bounded class of collider simulation workflows from natural language requests. A locally served language model proposes a typed workflow representation, and deterministic software then restores recognized user stated quantities, builds the HEP tool inputs, validates the supported workflow, and presents the artifacts for approval before execution. In a same response comparison on 47 evaluable model request cases, the first structured proposal gave 7 unmodified artifacts satisfying the external benchmark scorer, against 19 after the full deterministic pipeline. Under the fixed representation normalization defined by the benchmark, the counts were 11 and 43. The direction of improvement is unchanged. The gap between the two views arises because the released builder and the benchmark scorers disagree on three bookkeeping conventions, namely launch form, two fixed control lines, and the output directory name, not on physics content. Four of seven approved workflows ran to completion on the managed local software stack, with cross sections consistent between repeats. In a separate challenge set, 57 of 96 problematic requests still reached the approval stage after part of the request was dropped, defaulted, or reinterpreted. No tested unsafe payload was retained in an executable artifact before the approval gate, but this does not establish operating system level containment. The deterministic backend supports MadGraph, Pythia8, Delphes, and a restricted MadAnalysis 5 plan. Reliable natural language routing to the MadAnalysis stage was not demonstrated in the tested examples. Version 1 should therefore be seen as an inspectable, validation gated workflow constructor requiring expert approval rather than an autonomous or scientifically self validating agent.

Scientists increasingly want to drive research software by natural-language request, but fluent output helps only if it becomes a correct machine-readable artifact. We introduce HEPToolBench, a benchmark of 28 collider-simulation tasks scored by deterministic, task-specific scorers, plus a three-task structured-debugging extension. We evaluate 42 deployments, from small locally served open-weight models to hosted frontier systems. The central experiment compares direct generation of native HEP-tool syntax with a schema-mediated interface where the model returns a typed representation that deterministic software serializes. Across five matched requests, the mean score rises from 0.418 to 0.902 and task passes from 21/210 to 159/210, with 41 of 42 deployments improving; eleven deployments, seven locally served open-weight models, go from 0/5 passes under native syntax to 5/5 under the structured interface. Values use the corrected v1.2.1 contract, in which the two native scorers that had enforced operational conventions absent from their own prompts are rescored prompt-faithfully cohort-wide. One asymmetry remains: native scorers score the recorded response verbatim and reject Markdown-fenced replies, whereas structured scorers recover JSON from such wrappers; no full-cohort rescoring under a single symmetric extraction rule has been done. An audit of archived responses from 17 locally served deployments shows this does not explain their gains: passes remain six to ten times more frequent under the structured interface when both sides use the same extraction rule. A task pass alone does not guarantee runtime or scientific viability. Within this scope, moving syntax generation into deterministic software can substantially improve reliability for both small local and frontier models. Prompts, scorers, responses, and regeneration scripts are released for independent evaluation and extension.

In this paper, a minimal-length inspired deformation of hot and dense chiral quark matter is formulated within a \(2+1\)-flavor Nambu-Jona-Lasinio framework. The deformation is based on a complete Jacobi-consistent three-dimensional quadratic GUP algebra and modifies the microscopic phase-space density of states while leaving the quasiparticle spectrum unchanged, leading to a thermodynamically closed mean-field theory with coupled light and strange gap equations. The analysis shows that ultraviolet phase-space suppression weakens dynamical chiral symmetry breaking, lowers the light and strange constituent masses, and shifts the light-sector chiral transition boundary, including its crossover and critical endpoint toward lower temperature and chemical potential. The numerical results are obtained from a single self-consistent solution of the coupled gap equations, and explicit endpoint comparisons show that the temperature-dependent and chemical-potential dependent results are mutually consistent. The result is a systematic effective-model study of how minimal-length inspired ultraviolet deformations reorganize coupled chiral dynamics and bulk quark-matter thermodynamics.

The pronounced maximum ("horn") in the $K^+/\pi^+$ excitation function observed in central Pb+Pb collisions is well established feature of collision-energy dependence, but its dependence on system size remains poorly understood. We confront hadronic (SMASH) and partonic (PHSD) transport, Glauber core-corona, canonical-ensemble suppression, and the two-phase statistical model of the early stage (SMES) with $K^+/\pi^+$ data spanning the complete NA61/SHINE system-size ladder (p+p, Be+Be, Ar+Sc, Xe+La) together with NA49 Pb+Pb and STAR Au+Au, quantifying every comparison by $\chi^2$. No single framework describes the full range: core-corona is preferred for intermediate systems, SMES with canonical strangeness conservation for heavy systems, and none reproduces the small-system data. Neither transport model generates the horn, with or without partonic degrees of freedom. The data exhibit a step-like enhancement of $K^+/\pi^+$ between Be+Be and Ar+Sc, quantified within the core-corona framework by a step from $\fcore \approx 0.22$ (Be+Be) to $\fcore \approx 0.58$ (Ar+Sc). The strangeness saturation factor $\gs$ rises in two distinct steps, separating geometric core formation from thermodynamic equilibration. The $(K^+/\pi^+)/(K^-/\pi^-)$ double ratio, which at fixed $\sqrts$ cancels the system-independent $\mu_B$ contribution, shows a step between light and heavy systems at a global significance of $3.7\sigma$, providing evidence for genuine strangeness enhancement beyond the pair-production baseline. Preliminary Xe+La data favor core-corona ($\chindf = 5.8$) over SMASH ($\chindf = 23.3$); finalized spectra will sharpen the CC/SMES discrimination at the $27\%$ level.

We report on the calculation of heavy-to-light form factors at $\mathcal{O}(\alpha_s^3)$ and on selected phenomenological applications in inclusive $B$-decays. After outlining the loop calculation, we extract the hard function in $\bar B \to X_s \gamma$, and discuss our recent progress and preliminary results for the N$^3$LO corrections to partial decay rates in $\bar B \to X_u l \bar \nu_l$, important for the inclusive determination of $|V_{ub}|$. In particular, we establish relations for heavy-quark parameters in the shape-function scheme to four loops and improve a particular model of the $B$ meson shape-function.

A proof is given that the six fixed points of the massless 1-loop renormalization group running of the CKM matrix in the Standard Model found previously at 1-loop are fixed points to all orders in perturbation theory. A previous proof required an extra assumption on the running which is eliminated in the proof presented here.

Applications of the concept of a hydrodynamic attractor have been mostly constrained to the context of hydrodynamization in heavy ion collisions. Deepening the understanding of the general phenomenon requires generalizing it to other contexts in order to see which facettes are truly universal and not a peculiarity of equilibrating conformal Bjorken flow. As part of this endeavor, this work aims to study the behaviour in a system that does not hydrodynamize, but nevertheless loses memory through expansion. We find that the system goes through three stages. At early times, expansion drives the ratio $P_L/\epsilon$ to converge to $-1$ as $\tau^{-2}$. This memory loss is partially restored at intermediate times, when interaction dominated degrees of freedom through expansion dominated evolution grow quadraticallly in time. At late times, interactions shuffle of information in state space without significant memory loss or restoration.

Neutral-current interactions of atmospheric neutrinos in large liquid scintillator detectors offer a new opportunity to study single-signal events (hereafter singles), characterized by a prompt energy deposition on the MeV-to-GeV scale and no identified delayed signal. In this work, we systematically investigate the model dependence of atmospheric-neutrino singles due to the primary neutrino-nucleus interaction, residual-nucleus de-excitation, and secondary interactions in the scintillator. Our results show that the dominant model dependence originates from the primary neutrino-nucleus interaction, especially for neutral-current processes on carbon, whereas de-excitation is essential for the singles selection yet leads to relatively small spectral variations among realistic models. Secondary-interaction effects are also subdominant overall. We further present the predicted event rates and prompt-energy spectra for neutral-current singles, along with the charged-current contribution. Separately, we estimate the low-energy contribution from elastic scattering of sub-\SI{100}{\MeV} atmospheric neutrinos on free protons. These results highlight the physics potential of current and future large liquid scintillator detectors, such as the Jiangmen Underground Neutrino Observatory, to study atmospheric-neutrino singles, probe neutrino-nucleus interaction models, and improve background estimates for rare-event searches.

The classification and regression of particle collision events constitute a persistent computational challenge in experimental high energy physics, where large volumes of simulated data must be processed with both speed and precision. This work carries out a systematic comparison of four classical machine learning architectures, support vector machines (SVM), artificial neural networks (ANN), convolutional neural networks (CNN), and long short-term memory (LSTM) networks against their quantum counterparts: quantum SVM (QSVM), quantum neural networks (QNN), quantum CNN (QCNN), and quantum LSTM (QLSTM). All models are trained on simulated proton-proton collision events with electron-positron and muon-antimuon final states from the CERN Open Data portal, using transverse-momentum components as input features and transverse-momentum magnitude as the regression target. Classical architectures, and in particular the CNN and LSTM, achieve marginally better quantitative performance under current hardware and dataset constraints. Quantum models, however, reach competitive accuracy with substantially fewer trainable parameters: the QCNN reproduces the performance of the deep classical CNN using only four qubits and a circuit of depth three, pointing to a genuine parameter-efficiency advantage on near-term quantum devices. A baseline analysis confirms that the regression problem is non-trivial for shallow polynomial fits, supporting the relevance of the architectural comparison. These results characterize the trade-offs between classical and quantum approaches under realistic, resource-constrained conditions and provide a benchmark for future studies on actual quantum hardware.

We probe the possibilities of efficiently constructing simple Feynman diagrams into quantum devices. More precisely, we study Drell-Yan lepton pair creation at the partonic level of the form q qbar -> gamma/Z -> l- l+. We develop quantum gates that build up the relevant diagrams using simple Feynman rules, such as vertex and propagator gates V and P. We show how the quantum circuit may compute simultaneous amplitudes in the phase space and how to reach the full integrated cross section from the outputs. In addition to this, we also show how the circuit is able to simultaneously isolate the interference effects of the contributing diagrams by a simple basis rotation. The circuit design is made to be general, and thus this work constitutes a step towards the implementation of arbitrary scattering process computations and efficient interference analyses.

We systematically investigate the magnetic moments (MMs) and radiative decay widths of S-wave doubly heavy tetraquark states based on chromomagnetic interaction (CMI). They provide a complementary probe to distinguish compact from molecule structures in addition to the mass spectrum and strong decay properties. Using the CMI eigenvectors, we compute the MMs and M1 transition rates for the tetraquarks in the compact configuration. We predict the MM of the observed $T_{cc}(3875)^+$ with $I(J^P)=0(1^+)$ to be 0.45 $\mu_N$ when treating it as a compact tetraquark state, whereas the MM of the $0(1^+)$ $DD^*$ molecule is about $-0.07\,\mu_N$. Five radiative transition channels related to the $T_{cc}(3875)^+$ are identified with widths ranging from $6.07$ keV to $306.37$ keV. Our results show that the MMs of the $J^P=1^+$ $bc\bar{q}\bar{q}^\prime$ ($q/q^\prime=u,d,s$) and $J^P=1^+$ $QQ\bar{n}\bar{s}$ ($Q=b,c; n=u,d$) states are influenced by the diquark-spin mixing. Through the analyses of radiative transitions between different tetraquark states, we find that such processes in the $QQ\bar{n}\bar{n}^\prime$, $QQ\bar{s}\bar{s}$, and $bc\bar{n}\bar{s}$ cases may serve to reveal the tetraquark structures of the initial or final states. We also define the magnetic coupling matrices characterizing the MMs of the tetraquark system with $J^P=1^+$, with which the range of MM can be constrained. The present study provides a valuable reference point for the search of exotic states in future particle physics experiments.

We investigate the neutrino flux from the Sun and Earth, as well as the heating of Jupiter and white dwarfs, induced by the annihilation of spin-$1/2$ dark matter particles captured through their electromagnetic interactions with nuclei. Using current data, we derive constraints on the electromagnetic moments and compare them with existing bounds from direct dark matter searches, laboratory experiments, and astrophysical observations. We find that celestial bodies provide leading constraints in several regions of parameter space: the Earth is particularly sensitive to millicharged dark matter, while massive white dwarfs provide powerful probes of the magnetic dipole moment, charge radius, and anapole moment in regions where direct searches lose sensitivity. We illustrate the implications of these constraints in simplified models of Dirac and Majorana dark matter with radiatively generated electromagnetic moments, as we discuss the complementarity between capture in celestial bodies and other dark matter searches.

We present a physics-informed deep-neural-network extraction of unpolarized transverse-momentum-dependent parton distribution functions (TMDPDFs) in impact-parameter space from Drell–Yan data. The perturbative contribution is computed with a resummed $W$ term using $\mathrm{N}^{3}\mathrm{LL}$ evolution, strict-NLO hard and operator-product-expansion matching, and smooth profile scales at small and large $b_T$. A compact feature-wise linear modulation network learns only a shared nonperturbative factor $F_{NP}(x,b_T)$; the collinear PDFs, hard factor, evolution kernel, matching coefficients, and Fourier–Bessel transform remain fixed. The primary result is a smooth light-flavor $b_T$-space TMD ensemble and its cross-section-level validation. The reported $k_T$ distributions are regularized finite-$b_T$ Hankel transforms, not independent momentum-space fits. As a separate robustness test, a smooth finite-$Y$ transition is applied to 24 additional Tevatron points extending to $q_T/Q\simeq0.30$. The nominal 329-point fit is unchanged, and the results remain stable when $F_{\rm NP}$ is held fixed while the transition profile is varied. An independent 122-bin Tevatron $\mathrm{N}^{3}\mathrm{LL}+\mathrm{NNLO}$ $W+Y$ grid provides a direct perturbative benchmark. A separate $W+Y$ candidate using the specified non-LHCb finite-$Y$ inputs is retained as an identifiability study.

Long-lived particles that decay inside the tracker are searched for via the spatial displacement of their decay vertices. However, the same decays also arrive late, providing a handle made available by a precision timing layer at the HL-LHC that displaced-vertex searches do not exploit. We study the exotic decay of a Higgs boson produced through vector-boson fusion (VBF), $pp\to hjj$ with $h\to ss$, in which the long-lived scalar decays as $s\to b\bar b$, and use the VBF tag jets to identify the hard-scatter vertex. Its prompt central tracks, timed by a CMS-MTD-like barrel layer that also times the central tracks of the displaced vertex, define a per-event start time, turning each displaced vertex into a four-dimensional object. Because a fast simulation cannot determine the absolute normalization of the heavy-flavour and instrumental displaced-vertex backgrounds, we take as the primary result a normalization-free figure of merit: the ratio of the timing-enhanced sensitivity to the spatial-only sensitivity. Adding the timing layer improves this ratio by a factor of $\simeq2.8$ at a nominal working point and by up to an order of magnitude for a tighter delayed-vertex requirement, because the heavy-flavour background that survives the spatial selection is prompt in collision time. The improvement increases with decay length, extending sensitivity into the long-lifetime regime in which purely spatial searches lose tracker acceptance. The gain is essentially mass-independent at a decay length of $\ctau\simeq100\mm$, where the trend with scalar mass reverses: lighter scalars benefit more at short lifetimes because of their larger boost, whereas heavier scalars benefit more at long lifetimes as the lighter states leak out of the tracker.

This white paper summarizes scientific challenges and AI/ML research opportunities identified through the FAIRS Japan 2024 unconference process. The discussion focuses on three major physics domains: accelerator physics, cosmology and astrophysics, and neutrino physics. Although each domain has distinct scientific goals and experimental constraints, several common technical themes emerge: high-dimensional reconstruction, fast and accurate simulation, uncertainty propagation, simulation-to-data mismatch, anomaly detection, real-time decision-making, and shared infrastructure.

Finite-volume extrapolation (FVE) is essential for extracting physical observables in the lattice calculation. While rigorous FVE formulations are well established for short-range potentials in both two- and three-body systems, long-range interactions with force ranges comparable to the lattice size $L$ remain challenging. Extending a previous data-driven scheme for two-body systems, we apply symbolic regression (PySR) to uncover universal three-body FVE formulae. For short-range potentials, we reproduce the two limiting cases, i.e. $\kappa_3\gg\kappa_2$ and $\kappa_3\sim\kappa_2$. For pure long-range potentials, we obtain a dedicated analytic expression, and after incorporating short-range contributions, we uncover a unified formula consistent with the original PySR solution, which performs excellently in the intermediate force range around 1 fm. This work demonstrates that combining machine learning with physical constraints can yield novel analytical results inaccessible to conventional theoretical tools, advancing data-driven methodologies in hadron physics.

Light low-energy cosmic ray antinuclei constitute powerful probes for detecting dark matter or other sources of new physics in our Galaxy. This ASTRA Initiative Mission Concept reviews the theoretical motivation, highlighting the transformative potential and current experimental status. Motivated by exciting tentative results, it makes a clear case for the need for the next flagship mission to confirm or refute claims of cosmic antinuclei as signs of new physics.

Relativistic heavy-ion collisions are the only known means of creating the quark-gluon plasma, a deconfined state of QCD matter. Hydrodynamic modeling has established that this medium behaves as a strongly coupled, low-viscosity fluid, but typically assumes that its quark and gluon composition reaches chemical equilibrium by the onset of the hydrodynamic phase. This assumption remains uncertain: gluon-dominated initial states suggest that quark production continues well into the hydrodynamic stage, with potentially different rates for light and strange quarks. This dissertation develops a dynamical framework for light and strange quark chemical equilibration. Incomplete equilibration of each flavor is described through time-dependent quark fugacities that modify both the equation of state and the particlization of the medium. Implemented within a multistage framework of fluctuating initial conditions, viscous hydrodynamics, particlization, and hadronic transport, the model is used to study the effects of equilibration on the hydrodynamic evolution and on hadronic and electromagnetic observables. The framework is embedded within a Bayesian analysis in which Gaussian process emulators trained on the model calculations infer the initial light and strange quark fugacities, their equilibration timescales, and selected transport coefficients from Au+Au collision data at RHIC. The strange sector is found to begin substantially undersaturated, more suppressed than the light sector; the data further favor a slower approach to equilibrium for strangeness, though the timescales themselves remain weakly constrained. These results favor a quark-gluon plasma whose flavor composition is still approaching chemical equilibrium during the hydrodynamic phase rather than fixed at its outset, and motivate extensions to collision systems of differing size and energy.

Helicity amplitudes give the most complete description of a variety of scattering reactions used in studies of strong interactions, but they cannot be measured directly: experiments record bilinear combinations of them folded through a detector response, and conventional analyses recover them through multiple stages that introduce discrete ambiguities and require a separate extraction of the absolute cross sections. Here we replace that chain with a single Bayesian inference that determines the experimentally identifiable amplitude parameters directly from detector-level measurements. A score-based diffusion model, trained on a forward simulator, provides the full posterior in each kinematic bin, with the detector response carried by the forward model and positivity of the spin-density matrix guaranteed by the parameterization. The observable amplitude content in electroproduction of final particles grows with polarization of beams and targets, providing additional sensitivity to underlying phases. In simulation, the posterior achieves empirical coverage at or above the nominal level and delivers the angular observables and the separated contributions from longitudinal and transverse photons with their correlations retained. It transfers without retraining to a realistic detector response absent from training and remains reliable in the weakly constrained nucleon-helicity-flip sector, where per-bin likelihood maximization degrades. The result is a general framework for a broad class of inverse problems, phase retrieval, quantum-state tomography, and partial-wave analysis are further instances. Its core requires only a forward simulation of the complete measurement process, instrumental effects are handled within one statistically consistent posterior, applicable across exclusive vector-meson programs at Jefferson Lab, COMPASS, HERMES, and the future Electron-Ion Collider.

Nambu–Jona-Lasinio (NJL) models of color-superconducting quark matter suffer from cutoff artifacts once temperature or quark chemical potential become comparable to the model cutoff. These artifacts can be removed employing a renormalization-group (RG) consistent regularization scheme. In this article we perform a systematic study of neutral beta-equilibrated quark matter within the three-flavor NJL model with RG consistent regularization. Varying the coupling constant in the scalar diquark channel, we map out the phase diagram in the plane of chemical potential and temperature, and identify the gapless domains. We particularly focus on the melting pattern of the color-flavor locked (CFL) phase. At larger couplings the CFL phase melts through a so-called $d$SC phase, as expected from leading-order Ginzburg–Landau analyses. Lowering the coupling, the phase structure becomes markedly richer: While at large densities the CFL phase still melts through a $dSC$ phase, we find a $uSC$ phase at lower chemical potential. These phases, $uSC$ and $dSC$ meet at a doubly critical point whose existence had been anticipated long ago but was never demonstrated explicitly in a model.

We compute high frequency gravitational wave radiation in shockwave collisions of a light mass compact object with energy $\mu_L$ off a heavy compact object (black hole) with energy $\mu_H \gg \mu_L$. A formal solution is obtained in terms of shockwave propagators that provide snapshots of $O(\mu_L\mu_H^n)$ tidal response functions sensitive to classical and potentially semi-classical dynamics of black hole formation. In a perturbative expansion, the first nontrivial contribution of $O(\mu_L\mu_H)$ is the emission of a graviton from the Lipatov vertex generated by the fusion of two reggeized gravitons. For graviton frequencies $\omega\rightarrow 0$, the Lipatov amplitude reduces to the ultrarelativistic limit of the single-graviton exchange Weinberg amplitude. At $O(\mu_L\mu_H^2)$, the Lipatov amplitude includes a piece accounting for the rescattering of the graviton off a reggeized graviton and another, corresponding to graviton emission from a vertex fusing three reggeized gravitons. These nontrivial contributions again simplify to the Weinberg radiative amplitude for two-graviton exchange in the soft limit. We highlight throughout double copy structures to gluon radiation in dilute-dense collisions of Yang-Mills shockwaves. We relate our shockwave results to the eikonal multiple scattering framework of Veneziano et al.

The computational treatment of non-Gaussian entanglers could pose a significant challenge when extending the Multi-Scale Entanglement Renormalization Ansatz (MERA) to interacting quantum field theories. A natural strategy is therefore to consider polynomial entanglers for which the Baker-Campbell-Hausdorff (BCH) expansion terminates at finite order. In this work, we identify an algebraic obstruction that limits the universality classes accessible to this family of entanglers. Working within the wavelet MERA (wMERA) framework applied to the interacting $\phi^4$ theory in two dimensions, we show analytically that the effective potential generated by any finite-BCH polynomial entangler is necessarily of Landau form in the generic case, establishing mean-field universality for the full class; in non-generic, degenerate cases the resulting exponent departs from mean-field but still fails to reproduce the Ising value. As a numerical illustration, the critical exponent $\beta$ remains consistent with its mean-field value $\beta = 1/2$ across all ansätze considered, with no drift toward the Ising value $\beta = 1/8$ as the nonlocality range or variational complexity increases. Reproducing non-mean-field criticality therefore might require non-polynomial or infinite-BCH constructions.

We study how virtual next-to-leading-order electroweak corrections affect the quantum observables of entanglement and magic in lepton–lepton collisions. Treating the outgoing particles as multi-qudit systems, $\textit{i.e.}$, qubits for spin-$\tfrac{1}{2}$ fermions and qutrits for massive vector bosons, we compute entanglement entropy and the stabilizer second Rényi entropy for the processes $\ell^+\ell^- \to \tau^-\tau^+,\, ZZ$ at one-loop accuracy. We show that radiative corrections coherently modify the quantum structure of the final state, shifting regions of maximal entanglement and altering the generated magic relative to leading order. Our results demonstrate that these quantum observables provide novel, precision-sensitive probes of electroweak dynamics at future lepton colliders and open a path toward their use in searches for new physics.

The rare decays $K^+\to\pi^+\nu\bar\nu$ and $K_L\to\pi^0\nu\bar\nu$ are among the most precisely predicted flavor observables, enabling determinations of the CKM matrix and its CP-violating phase, as well as providing sensitivity to new physics at scales far beyond the reach of colliders. We propose a dedicated rare-kaon program at Fermilab, exploiting the high-intensity proton complex currently under construction for its neutrino programs and potential collider R&D. In this letter, we estimate the achievable kaon flux and project the sensitivity to the aforementioned kaon golden modes, as well as the reach on new dynamics in the UV with an EFT framework. Such a program could measure both modes with unprecedented precision, probe new physics up to $\mathcal{O}(100)$ TeV, and determine the unitarity triangle from kaon processes alone. All this can be achieved while sharing infrastructure with other frontier programs.

We propose time-domain astrometric weak lensing of multiply imaged quasars as a probe of substellar dark matter (DM) halos. In $\Lambda$CDM, each macro-image's light traverses many microhalos, producing a stochastic centroid motion with a calculable red power spectrum. Halos with crossing times longer than the survey impart a relative angular acceleration between image pairs. The response peaks at subhalo scale radii 0.005-2 pc and masses $3\times10^{-6}$-$10^2\,M_\odot$, 12-14 orders of magnitude below the smallest detected DM structures, down to the damping cutoffs of a 100 GeV thermal relic. We forecast the sensitivity of ten-year campaigns with 300 epochs for two benchmark systems: the galaxy-lensed quadruple B1422+231 at a 0.1 $\mu$as per-epoch precision forecast for extended-path intensity correlation, and the cluster-lensed triple SDSS J1029+2623 at 1 $\mu$as. The angular-acceleration channel reaches the standard $\Lambda$CDM microhalo population with a variance signal-to-noise ratio of order ten for the galaxy lens (order unity after stellar microlensing subtraction) and 0.35 for the cluster under the optimistic assumption that 10% of the projected mass density at the image positions resides in surviving microhalos. A positive detection would: raise universal lower bounds on the DM particle mass to $\gtrsim400$ keV for fermions and $\gtrsim10^{-12}$ eV for bosons; constrain the DM kinetic decoupling temperature to $\gtrsim 10$ MeV; and be sensitive to the running of the spectral tilt at the 0.01 level over 15-20 e-folds of the primordial curvature power spectrum. A robust null result across well-characterized lenses would constrain microhalo survival and/or imply violations of the above inequalities. These signatures motivate differential astrometric observations with extreme 0.1-1 $\mu$as light-centroiding precision on multiply imaged quasars. [Abridged]

Post-inflationary axion theories with domain wall number $N>1$ suffer from a domain wall problem. We show analytically, and confirm via simulations, that there is a region of phenomenologically viable parameter space for such theories with additional PQ-violating operators. Contrary to the conventional picture, in such theories the beyond-QCD PQ violation destroys the axion strings before the QCD axion potential becomes cosmologically relevant. This regime is realized for axion decay constants $f_a \lesssim 10^{10} \, \rm GeV$, pointing to a QCD axion mass in the $10^{-3}-10^{-2}\,{\rm eV}$ range. The required additional PQ violation induces a neutron electric dipole moment within two orders of magnitude of the current experimental limit, placing it within the reach of upcoming neutron electric dipole moment experiments.

We propose a new approach to axion-like particle (ALP) searches based on long, coiled optical fibers in an external magnetic field. We develop the theoretical framework required to describe photon-ALP conversion in this geometry by incorporating transverse boundary conditions and fiber bending. For solid silica fibers with refractive index considerably larger than unity, we show that the leading signal is a phase shift of the photon, with negligible loss due to ALP production. This setup has the potential to set new constraints in the regime of large ALP mass. We further identify parameter regions in which boundary effects become important, in particular for hollow-core fibers, where signals due to ALPs can be significantly enhanced.

It has been known that in sufficiently strong uniform magnetic fields, the ground state of quantum chromodynamics (QCD) supports a spatially modulated condensate of neutral pions, dubbed chiral soliton lattice (CSL). In this paper, we investigate whether a similar ordered ground state might exist when the external magnetic field is nonuniform, as appropriate for potential phenomenological applications, including heavy-ion collisions and neutron stars. To that end, we use the low-energy effective field theory of QCD, restricted to the neutral pions as the sole low-energy degrees of freedom in strong magnetic fields. In the limit of vanishing pion mass, we achieve a complete characterization of magnetic fields supporting a CSL-like ground state. Moreover, for a simple but infinite family of magnetic fields, we find the corresponding CSL state analytically. Going away from the massless limit requires full numerical minimization of the energy functional. Here we provide some sample numerical results, focusing on the qualitative differences as compared to the situations with a uniform magnetic field or a vanishing pion mass. The main conclusion remains unchanged: while bending the magnetic field typically reduces the energy gain due to the neutral pion condensation, a CSL-type ground state is still possible. As a byproduct of our work, we map the location of the CSL phase in the phase diagram of QCD in a uniform magnetic field and finite volume.