Papers

Sterile neutrinos are well-motivated dark matter candidates, but their conventional production through active-sterile mixing is tightly constrained by X-ray searches and structure-formation observations. We propose a distinct production mechanism operating entirely within a sterile sector: two sterile neutrinos, $N_1$ and $N_2$, coupled to a singlet scalar $\phi$, with $N_1$ the dark matter candidate and $N_2$ held in equilibrium through frequent scattering induced by its scalar interaction. Thermal self-energies induced by the $N_2$ and $\phi$ backgrounds generate both a temperature-dependent mass splitting and an off-diagonal mixing between $N_1$ and $N_2$. As the Universe cools, the in-medium levels can undergo a level crossing, leading to resonantly enhanced conversion of the thermal $N_2$ population into $N_1$. We formulate the conversion using a density-matrix kinetic equation that consistently incorporates coherent $N_1$-$N_2$ conversion, collisional decoherence, and thermal repopulation of $N_2$. For a narrow resonance, the integrated conversion probability admits a simple analytic form that coincides with the Landau-Zener result, despite the underlying collisionally damped dynamics. In the weak-conversion regime relevant for freeze-in, this correspondence provides a robust analytic description of the resonant production. We derive the resulting dark matter abundance and identify the conditions for cosmological stability of $N_1$ and for resonant conversion to dominate over direct scattering and decay production. The resulting relic abundance scales as $Y_1\propto g_{12}^2 g_{22}M_{\rm Pl}/m_1$, making the dark matter energy density approximately independent of $m_1$. This mechanism provides a new route to sterile-neutrino dark matter that does not require appreciable active-sterile mixing.

We revisit the light tetraquark states with quantum numbers $J^{PC}=1^{++}$ using QCD sum rules, focusing on a complete set of derivative-free diquark-antidiquark interpolating currents. By calculating the operator product expansion up to dimension-eight condensates, we extract the ground-state mass of the hidden-strange $us\bar{u}\bar{s}$ tetraquark from both Laplace sum rules (LSR) and finite-energy sum rules (FESR). Our combined analysis yields $M_{us\bar{u}\bar{s}} = 1.45\pm0.11$~GeV, which agrees well with the mass of the $a_1(1420)$ resonance and supports its tetraquark interpretation. Furthermore, we perform Gaussian sum rule (GSR) analyses to probe radial excitations, adopting a two-resonance narrow-width model. The GSR fit reveals a heavier state with mass $m_2 = 1.86\pm0.12$~GeV and a relative coupling $r = 0.15\pm0.03$ for the lighter state, indicating that the $a_1(1930)$ is a promising candidate for a compact $1^{++}$ tetraquark. We also discuss the dominant decay modes of these tetraquark candidates, emphasizing hidden-strange channels such as $K^*K$ and $f_0(980)\pi$, which can be tested in future experiments.

We derive the scalar propagator in a thermal medium under global rotation without restricting the spacetime points to a common comoving trajectory. The resulting propagator retains an explicit dependence on the radial coordinates, reflecting the lack of translational invariance in the transverse plane, and therefore cannot in general be formulated solely in momentum space. We show that the usual free Feynman propagator is exactly recovered in the nonrotating limit, providing a first consistency check of the formulation. As a nontrivial test, we apply the propagator to the interacting $\lambda\phi^4$ theory at finite temperature and rotation. The one-loop scalar self-energy obtained within the Matsubara formalism correctly separates into vacuum and medium contributions and reproduces the standard finite-temperature result when $\Omega\to0$. We subsequently construct the effective potential including screening effects through ring resummation and, for $\Omega/T\ll1$, evaluate the rotational corrections up to $\mathcal{O}(\Omega^4)$. Within this model, the resulting effective potential exhibits the expected thermal restoration of the spontaneously broken $\mathbb{Z}_2$ symmetry, while global rotation favors symmetry restoration and enhances this effect as the transverse size of the system increases. These results provide complementary consistency checks of the rotating scalar propagator and highlight the need to retain its explicit position-space structure in more general perturbative calculations.

In this work, we systematically investigate the baryon-baryon interactions in singly bottomed dibaryon systems within the chiral quark model and search for possible bound states. By exploring the baryon-baryon interaction, we find that low-isospin channels tend to generate deeper attractive interactions and are prone to form bound states. We also find that decuplet-decuplet systems tend to show stronger attraction and support a larger number of bound states, whereas octet-octet systems generally exhibit weaker attraction and fewer bound solutions. The binding behavior of octet-decuplet systems generall lies between these two cases. Several bound states are obtained, which are $\Delta\Sigma_b^*$ with $IJ=\frac{1}{2}0$, $\frac{1}{2}1$, $\frac{1}{2}2$, $\frac{1}{2}3$, and $\frac{3}{2}3$, the $\Delta\Sigma_b$ with $IJ=\frac{1}{2}1$, $\frac{1}{2}2$, $\frac{3}{2}1$, and $\frac{3}{2}2$, the $N\Sigma_b^*$ with $IJ=\frac{1}{2}2$, the $\Sigma\Sigma_b$ with $IJ=00$, $01$, and $11$, the $\Sigma\Sigma_b^*$ with $IJ=01$ and $02$, the $\Sigma^*\Sigma_b$ with $IJ=01$ and $02$, and the $\Sigma^*\Sigma_b^*$ with $IJ=00$, $01$, $02$, $03$, and $13$. Further investigations of the corresponding scattering processes are still required to determine whether these bound-state candidates can be identified. These states deserve further experimental investigation.

Working through next-to-next-to-leading order (NNLO) accuracy in pionless effective field theory, we compute the isovector magnetic-dipole contribution to the scalar deuteron magnetic polarizability. The polarizability follows from detailed balance and a dispersion integral with the two magnetic current counter-terms fixed by the thermal $np\to d\gamma$ rate. The conventional $\rho$ and $Z$ expansion schemes differ by $12.3\%$ at next-to-leading order but agree to $0.165\%$ at NNLO, resulting an apparent scheme dependence and supplying an independent convergence diagnostic. We obtain $\beta_{M0}^{(M1_v)}=0.0789\pm0.0010~\mathrm{fm}^{3}$, a $1.3\%$ uncertainty, compared with $4.9\%$ previously.

Complex experiments infer theory parameters through a coupled chain of physical models and data reduction. We formulate the theoretical–operational model (TOM) as a typed factorization of this forward prediction and study how changes of preparation, phenomenon modelling, readout, backgrounds, and analysis project onto the local manifold generated by the physics parameters. For a smooth prediction and a locally identifiable weighted least-squares estimate, the resulting response map separates each model deformation into a parameter-equivalent component and a residual component that cannot be absorbed by a change of the fitted physics parameters. This gives local criteria for robustness, exact degeneracy, and partial degeneracy of parameter inference. The construction is applied to charged-lepton-flavour-violating muon–electron conversion in aluminium. A one-bin conversion-rate model exhibits an exact normalization degeneracy. In a two-template model of the elastic–inelastic spectrum, a common signal normalization is absorbed by the fitted conversion rate without changing an operator-sensitive nuclear-response ratio, whereas a relative elastic–inelastic efficiency change is exactly parameter-equivalent to a change of that ratio at first order. A numerical Run-I example based on published Mu2e spectra shows that a \(100\,\mathrm{keV}/c\) momentum-scale mismatch is only partially parameter-equivalent: its projection ratio onto the local tangent space generated by the elastic normalization \(R_0\) and the logarithmic inelastic-to-elastic response ratio \(\rho\) is \(\eta=0.331\), while most of the weighted spectral deformation remains as a residual shape. TOM thereby provides a local theoretical description of parameter robustness and degeneracy at the interface of particle/nuclear phenomenology and experimental realization.

We study the stability of collective neutrino oscillations using a distributional approach motivated by the statistical mechanics of Kuramoto synchronization. Treating the ensemble of neutrino flavor polarization vectors in the thermodynamic limit $N\to\infty$, we derive an exact nonlinear Fokker–Planck (continuity) equation for the one-body distribution $F(\vec{\mathbf{S}},\omega,t)$ on the flavor sphere. This equation admits a two-parameter family of azimuthally symmetric stationary solutions, whose stability we analyze by linearizing around them. The resulting eigenvalue condition determines the growth or decay rate of small perturbations from any initial distribution – not merely from a state close to full flavor coherence – thereby going significantly beyond the conventional linear stability analysis of collective modes. In special limits the condition reproduces known synchronization thresholds in the two-beam model, providing a non-trivial check of the framework. We present analytical results for the eigenvalue equation and explore stability phase diagrams for physically relevant frequency distributions.

We investigate the cosmological moduli problem (CMP) in the context of supersymmetric models where discrete R-symmetries are used to suppress the mu term, and where mu is regenerated via Kim–Nilles superpotential operators. In such theories, a global U(1)_{PQ} emerges as an accidental, approximate symmetry which solves the strong CP problem. R-parity is also generated as accidental but approximate, where RPV operators gain a (f_a/m_P)^n suppression. When n=1, the thermally-produced LSPs may decay before BBN in the early universe, leaving axion-only dark matter of the SUSY DFSZ type. Meanwhile, the dominant cosmological constraint on light stringy moduli previously came from the modulus-induced WIMP overproduction problem. WIMP overproduction is now ameliorated by the RPV WIMP decays, but the moduli-induced BBN bound may be exacerbated by convolving long-lived modulus decay with long-lived RPV WIMP decay: long-lived particle (LLP) cascade decays. In this context, moduli as light as m_\phi ~ 130 TeV may be allowed which can reconcile naturalness with the presence of stringy moduli in the early universe.

Recent NLO analyses of inclusive Higgs production indicate that high-energy resummation corrections can reach the 10% level, highlighting the growing impact of high-energy QCD dynamics on electroweak observables from LHC to FCC energies. We extend this precision program to Drell-Yan plus jet production by deriving high-energy-resummed predictions for rapidity and transverse-momentum distributions of electroweak bosons. Fixed-order NLO accuracy is consistently combined with next-to-leading energy-logarithmic resummation (NLL/NLO). We outline a JETHAD-DYnamis-POWHEG matching strategy that retains polarization and angular correlations while enabling realistic lepton-level kinematics. This setup provides the first high-energy-resummed description of rapidity-separated electroweak-boson plus jet final states. The resulting framework offers a precision-oriented description of Drell-Yan observables for present LHC measurements and the High-Luminosity LHC, where percent-level theoretical control will become increasingly important.

At high-energy colliders, enormous numbers of feebly interacting particles beyond the Standard Model can be produced with negligible missing-energy signatures in the main detectors. These particles can travel macroscopic distances and decay inside a distant large-volume detector, leaving visible signals. In this sense, we may not need new detectors to search for very long-lived particles. In this paper, we show that long-lived dark particles produced in rare meson decays in proton-proton collisions during LHC Run 3 and at the HL-LHC can leave observable imprints in KM3NeT detectors such as ORCA. If no anomalous signal has been observed in ORCA to date, our projected sensitivity for LHC Run 3 will correspond to one of the strongest limits on kaon decays into light long-lived particles.

Jets are central to the physics programs of both current and future colliders, from precision Standard Model measurements and searches for new physics at the Large Hadron Collider to studies of nucleon structure at the future Electron-Ion Collider. Motivated by these applications, we explore quantum machine learning for jet classification and present a permutation-invariant Quantum Graph Neural Network (QGNN) applied to particle-cloud representations of jets. We apply the model to two such discrimination tasks: quark vs. gluon and up vs. down quark flavor tagging, with the latter being, to our knowledge, the first application of a quantum model to this problem. In the ideal simulation, the QGNN performs competitively against the Particle Flow Network and traditional QCD observables. We further deploy scaled-down models to IBM and IonQ quantum processing units (QPUs), where we train and evaluate them, obtaining promising results. Finally, we perform an interpretability analysis to characterize the observables learned by the quantum model, relating them to generalized angularities for the quark-gluon study and to jet charge for the flavor study.

The mathematically elegant and promising idea of supersymmetry faces severe challenges as its conventional weak-scale realizations are increasingly constrained by the lack of experimental evidence of superpartners. However, we point out that the prediction of new (seemingly non-existing) supersymmetric particles is not a necessity: if we slightly relax our expectations from the supersymmetric models, generators $Q^a_\alpha$ of $N$-extended supersymmetry can be readily interpreted as carrying a quantum number of the internal gauge group, thus connecting particles with different gauge properties. In this view, operators $Q^a_\alpha$ remain “square roots” of translations, but do not by themselves generate symmetries of the model. They merely represent transformations that mathematically relate bosonic and fermionic fields; it is only the gauge-invariant combinations of the form $\sum_a \{Q^a_\alpha, \bar Q_{a\beta}\}$ that correspond to spacetime momenta and thus represent symmetries of the model. With this conceptual modification, the simplest Yang-Mills supersymmetric model no longer connects vector bosons with hypothetical gauginos, but with far less exotic chiral fermions, e.g.\ with left-handed leptons. Further adding an $SU(2)$ doublet of Higgs scalars no longer introduces Higgsinos, but a fermion that naturally corresponds to the right-handed lepton, with the familiar Yukawa term showing up as a mathematical necessity. Despite giving up the requirement that operators $Q^a_\alpha$ alone generate symmetries of the action, this approach to supersymmetry is strikingly mathematically similar to standard SUSY, raising hopes that many of the favorable properties of standard supersymmetry can be retained, while potentially reconciling the idea of supersymmetry with experimental data. The approach is still quite restrictive: the relative coefficients of such models are strongly determined.

The existence of right-handed (RH) neutrinos is strongly motivated by the observation of small neutrino masses and as a means to shed light on the origin of parity violation in the Standard Model (SM). Experimental searches for the corresponding mass eigenstates, referred to as heavy neutral leptons (HNLs), have been carried out in a variety of experiments and within different HNL models. In the current work we use the SM effective field theory with added RH neutrinos, known as $\nu$SMEFT, to study GeV-scale HNL production in $e^+e^-$ collisions at the Belle~II experiment. We focus on leptonic decays of long-lived HNLs that produce a displaced vertex in the Belle~II detector. Accounting for detection efficiency and backgrounds, we estimate the sensitivity of Belle~II to the new-physics scale of four-fermion, Higgs-current, and dipole operators in $\nu$SMEFT. We find that for most operators, the search we propose probes large regions of parameter space that are not excluded by other searches.

We propose using supernova microlensing to search for ultracompact minihalos and other extended dark structures seeded by enhanced primordial small-scale power. Unlike conventional microlensing searches, which are often optimized for primordial black holes, cosmological supernovae are sensitive to lenses with physical sizes comparable to their Einstein radii (up to $\sim {\rm pc}\left(M/10^4M_\odot\right)^{1/2}$ scale), opening a qualitatively different region of dark object parameter space. We compute the extended object detection efficiency relative to point lenses. We then show how projected limits on the abundance of ultracompact minihalos can be mapped, in benchmark formation scenarios, onto constraints on the primordial power spectrum. With the Vera C. Rubin Observatory expected to deliver an unprecedented LSST supernova sample, supernova microlensing is poised to become a timely and complementary probe of small-scale structure and the physics of the early Universe.

We study the structure of leading hadronization effects and the contributions of massive electroweak gauge boson exchange in the $\tau_1$ and $\tau_{1a}$ 1-Jettiness global event shapes for deep inelastic scattering (DIS). The leading hadronization effects in $\tau_1$ acquire a non-trivial dependence on the hard scattering kinematics. This kinematic dependence is explicitly calculable, so that the leading hadronization effects in $\tau_1$, $\tau_{1a}$, and DIS thrust are universal and described by the same underlying shape function. The additional calculable kinematic dependence in $\tau_1$ provides an independent lever arm for simultaneously constraining hadronization effects in these observables. We present corresponding results at the N$^3$LL+${\cal O}(\alpha_s^2)$ level of accuracy. We extend previous results by including the contributions mediated by the exchange of the massive $Z$ and $W$ electroweak gauge bosons for neutral current (NC) and charged current (CC) DIS, respectively, including ${\cal O}(\alpha_s)$ QCD corrections to obtain N$^2$LL+${\cal O}(\alpha_s)$ results. We compare theoretical predictions to Pythia simulation and demonstrate the universality of leading hadronization effects across NC and CC DIS processes and a wide range of kinematics relevant to HERA and the EIC.

We determine the gauge-invariant identity, mass scale and ultraviolet stability of the dark matter candidate arising from \(G(2)\to SU(3)_C\) in the exceptional \(G(2)\!-\!E_6\!-\!E_7\) construction. The broken \(G(2)\) sector contains odd \(1^{+-}\) and \(0^{--}\) channels, whereas the scalar \(0^{++}\sim X\bar X\) state is even and unprotected. For \(m_X\simeq5.7\times10^{13}\,\mathrm{GeV}\), weak-binding reference masses are \(M_{2X}\simeq1.14\times10^{14}\,\mathrm{GeV}\) and \(M_{3X}\simeq1.71\times10^{14}\,\mathrm{GeV}\), while the exact pole masses remain nonperturbative. Gauge-invariant Fröhlich–Morchio–Strocchi (FMS) operators, Hall–Post bounds, \(Y\)-junction arguments and the pure-\(SU(3)\) glue spectrum favor \(1^{+-}\) in their controlled regimes without excluding a deeply bound \(0^{--}\) state. We then test whether this dark grading survives the full chiral exceptional embedding. An on-shell analysis finds no independent purely dark odd operator through dimension seven: the first nonvanishing basis appears at dimension nine. So the minimal one-copy exceptional embedding does not provide an exact ultraviolet dark \(G\)-parity. Moving the dark Higgs from the common \(\mathbf{1463}_H\) parent to a separated \(\mathbf{1539}_H\) removes the scalar-parent obstruction and the relevant dimension-nine exceptional parents vanish on the selected pure-dark component in the undressed limit. A genuinely gauged or geometric \(\mathbb Z_{2,D}\) would therefore leave a bosonic parity after dark Higgsing. Its extension to the mirror-free theory nevertheless fails because the required \(G(2)\) conjugation also conjugates color, \(\mathbf3_C\leftrightarrow\bar{\mathbf3}_C\). The remaining obstruction to exact dark matter stability is therefore ultraviolet and chiral, rather than low-energy or purely scalar.

LUX-ZEPLIN (LZ) has reported one event compatible with a $248~\mathrm{keV}$ nuclear recoil. While initial attention has focused on inelastic dark matter, that interpretation depends sensitively on the uncertain high-speed tail of the Galactic halo. We develop instead an elastic realisation of the pseudoscalar-pseudoscalar interaction $L_4=(\bar\chi i\gamma^5\chi)(\bar N i\gamma^5N)$, whose contact templates give one of the largest local significances identified by LZ. The minimal model presented involves Dirac fermion dark matter and a pseudoscalar mediator. The pseudoscalar arises from a complex singlet and the minimal gauge-invariant UV completion also requires a single multi-TeV vector-like heavy quark. A representative model which realises thermal freeze-out has $m_\chi\sim 400~{\rm GeV}$ and $m_a\sim 1~{\rm GeV}$. The simplest model breaks from the isoscalar/isovector assumption, and the recoil spectrum lies between LZ's elastic $O_4^v$ and contact $L_4^v$ templates, suggesting a local significance of $2.6$-$3.2\sigma$.

The recent observation of an isolated nuclear recoil at $248\pm 23\pm 23$ keV energy by the LUX-ZEPLIN (LZ) experiment has motivated the community to look for a new physics explanation, as the Standard Model background estimation fails to accommodate it. Most of the existing literature hitherto considers a galactic halo dark matter with a heavier partner. In this work, we traverse the alternate route of atmospheric neutrino ($\nu$) up-scattering, thus producing a massive beyond standard model (BSM) particle $\chi$ with mass $m_\chi$. The kinematic requirement of such a scattering demands a higher energy of the incoming neutrinos than elastic scattering, explaining the absence of excess events from solar $\nu$ scattering. However, for high energy neutrinos in the tail of the atmospheric neutrino flux, the kinematic threshold no longer prevents events at low recoil energies. To avoid an excess of such events, we consider a momentum dependent operator, which suppresses the event rate at low recoil energies and allows a single event in the high recoil energy window. Such up-scattering on nuclei ($\mathcal{N}$), $\nu \mathcal{N}\to \chi \mathcal{N}$, can be naturally realized in sterile neutrino models, though we keep our analysis generic without specifying $\chi$. We identify the region of parameter space that can produce such an isolated event, assuming a pseudoscalar mediator with mass $m_\phi$ that couples to the $\nu$-$\chi$ pair with strength $y_\chi$ and to up quarks with strength $y_u$. For example, $m_\chi \simeq 1.13$~GeV, $m_\phi \simeq 494$~MeV and $\sqrt{y_\chi y_u} \simeq 0.33$ can account for the observed event while remaining allowed by other existing constraints.

The LUX-ZEPLIN experiment has reported a single nuclear recoil at $248\pm23({\rm stat})\pm23({\rm sys})\keV$ in an extended search window. Inelastic dark matter, in which the scattering is endothermic, is a natural mechanism for producing a signal at such high energy. We fit the event to the dark matter mass and the mass splitting between two dark matter states, and find that the data favour a splitting pushed close to the kinematic limit set by the escape speed of the halo. The signal is then supplied by dark matter in the tail of the halo speed distribution. This drives a strongly seasonal signal: annual modulation rises above $50\%$ across the favoured region of parameter space and even reaches $100\%$ for some parameters, implying the signal vanishes for part of the year. Such a strong modulation distinguishes this interpretation sharply from a non-modulating signal, and we quantify the number of events needed to establish it. Experiments with larger target masses than LZ's, notably XLZD and PandaX, will be able to test this directly.

The LZ experiment has reported a single 248 keV nuclear recoil event in their $2.84$ ton-yr exposure on a xenon target. The absence of lower nuclear recoil events is naturally explained by inelastically scattering dark matter (DM), for which the nuclear recoil energy spectra are shifted upwards from zero. Excitingly, the observed rate and spectra are consistent with a thermal $1.1$ TeV higgsino that explains all of DM with a mass splitting $\delta \sim 370 - 490$ keV between the two lowest-lying Majorana states, with the range depending on the underlying DM velocity distribution. In this work, however, we show that higgsino DM with these properties would generically produce more higher-energy recoil events in a high-energy sideband along the LZ $S1c$ energy axis, while the LZ experiment reports no events in that bin. This suggests a possible tension which could be further explored by the LZ Collaboration, as the acceptance in that bin is not public. We further show that a non-thermal $\sim$500 GeV higgsino may evade the sideband constraint and that future experiments using heavy targets can potentially test the higgsino interpretation of the event either way.

The high-recoil event reported by LUX–ZEPLIN motivates a TeV Higgsino with a sub-MeV neutral-state splitting. Away from cancellations, such a small gap in the MSSM points to electroweak-gaugino masses of order $10^7\,\mathrm{GeV}$, far above the Higgsino mass. We show that the non-universal boundary condition $M_1^G/M_2^G=-3/5$ at the $\mathrm{SU}(5)$ GUT scale cancels the leading bino and wino contributions and is preserved by homogeneous one-loop evolution down to the Higgsino scale. The remaining finite-gaugino terms admit a controlled tree-level solution with a wino mass near $120\TeV$ for a $350\keV$ gap, a $1.091\TeV$ Higgsino and $\tan\beta=10$. We identify mixed $\mathrm{SU}(5)$ representations that realize the required gaugino ratio and examine the radiative sensitivity and spectrum consistency of this construction. Because the inelastic $Z$ coupling remains essentially unsuppressed, a full-density thermal Higgsino is still subject to the published solar-capture bounds under their astrophysical and transport assumptions.

Minimal dark matter extended to include a Majorana and a Dirac multiplet coupled through the Higgs — the HC-MDM model — provides a compelling and predictive framework. We show that in certain limits of this model, the mass splitting and the inelastic interaction are representation-independent, while the thermal-relic masses are representation-dependent. We then show that this model can account for the high-energy recoil event recently reported by LUX-ZEPLIN (LZ) while also respecting thermal-relic, elastic-scattering, and solar-capture constraints. Generic inelastic DM models do not connect all these tests and generic Higgsino models do not survive them.

We present the first QCD determination of an energy-dependent form factor for a two-hadron scattering state. In particular, we calculate the QCD contribution to the forward electromagnetic $\pi^+\pi^+ + \gamma\to\pi^+\pi^+$ amplitude at $m_\pi\approx 400$~MeV using lattice QCD. Because lattice calculations are performed in a finite Euclidean spacetime, where asymptotic scattering states are absent, this amplitude cannot be accessed directly from correlation functions. Instead, we can constrain this and related amplitudes nonperturbatively using a finite-volume formalism that requires two ingredients: the discrete finite-volume spectrum and finite-volume matrix elements of the electromagnetic current. We calculate three-point correlation functions coupling $\pi^+\pi^+$ finite-volume states and extract the corresponding electromagnetic matrix elements. Combining these results with the previously determined spectrum, we constrain the infinite-volume $\pi^+\pi^+ + \gamma\to\pi^+\pi^+$ amplitude in the forward limit. Using constraints from Lorentz symmetry, unitarity, and analyticity, we describe this amplitude in terms of a single real-valued energy-dependent two-hadron form factor. The resulting amplitude and form factor agree with the Ward-Takahashi identity across all energies and moving frames considered, providing the first QCD validation of this finite-volume approach and a pathway toward first-principles studies of the electromagnetic structure and electroweak responses of resonances and multi-hadron bound states.

We present lattice QCD results for the CP violating pion-nucleon coupling $\bar{g}_0$ induced by the QCD $\overline\Theta$ term from the analysis of three 2+1+1-flavor ensembles generated with highly improved staggered quarks (HISQ) by the MILC collaboration. These ensembles are at lattice spacing $a\approx 0.09~\text{fm}$ and pion masses of 313, 226 and 138 MeV, respectively. The coupling $\bar{g}_0$ is extracted in two ways. First, from the matrix element of the correlation between the pesudoscalar current and the topological charge evaluated between the nucleon ground state. The data for correlation functions with both the pseudoscalar and axial vector exhibit large contamination from the $N\pi$ excited state. We show that these can be controlled at the leading order using chiral perturbation theory ($\chi$PT) and the axial Ward identity (AWI, also called the partially conserved axial current (PCAC) relation). The result after removing the $N\pi$ contamination and extrapolating to the physical pion mass is, however, noisy: $\bar{g}_0/(2F_\pi)=-7(63)\times 10^{-3} \,{\overline{\Theta}}$. The more precise result $\bar{g}_0/(2F_\pi)=17.4(1.9)\times 10^{-3} \,{\overline{\Theta}}$ is obtained using low energy effective field theory methods or equivalently the AWI. Since contamination from the $N\pi$ excited states arises in the calculation of many nucleon matrix elements, we give an extended discussion on them and the use of the AWI for controlling them in the calculation of $\bar g_0$.

Open-system lattice gauge theory (LGT) has so far been developed predominantly in Abelian settings, leaving open how genuinely non-Abelian gauge structure reshapes dissipative real-time dynamics. Here, we study a $1+1$D SU(2) Yang–Mills LGT with dynamical matter coupled to a thermal scalar environment through a gauge-preserving Lindblad evolution, which we solve using tensor networks. Starting from a quark–antiquark pair connected by a chromoelectric flux string, we find that the thermal medium melts the string by delocalizing the color charges and screening the flux; on resonance, this dissipative melting competes with and delays coherent string breaking. The thermalization time is non-monotonic in the environment coupling, decreasing through environment-assisted transport at weak dissipation before increasing in a quantum-Zeno regime. In the strong-dephasing limit, a Schrieffer–Wolff expansion maps the dynamics to a classical exclusion process and yields the Liouvillian thermalization time analytically. Beyond these generic open-system effects, the non-Abelian matter structure produces a systematic mesonic bias in the steady state, while the thermalization time decreases with temperature, in contrast to the Abelian Schwinger model trend and in qualitative agreement with pNRQCD studies of the quark–gluon plasma. These results establish a gauge-preserving framework for thermalization and string dynamics in open non-Abelian lattice gauge theories.

Understanding real-time string dynamics in three spatial dimensions is essential for connecting quantum simulations of lattice gauge theories (LGTs) to the physical dimensionality of QED and QCD, where transverse fluctuations and competing local processes proliferate. We present the first real-time simulations of string breaking in $3+1$D lattice quantum electrodynamics. Using tree tensor networks, we simulate the quench dynamics of electric flux strings in a $3\!+\!1$D U(1) LGT with dynamical matter. At strong coupling, the string breaks resonantly at a sharp resonance condition of mass and gauge couplings, converting electric energy into matter–antimatter pairs that screen the static charges. Off resonance, we classify all competing channels—pair production, string deformations and extensions, and flux loops—whose multiplicity, extensive for pair production and flux loops, depletes the string sector even far from resonance. A channel-resolved perturbation theory quantitatively reproduces these dynamics and their Fourier spectrum. Our results establish diagnostics and benchmarks for upcoming quantum simulators of higher-dimensional LGTs.

We investigate the fragmentation dynamics underlying the production of fully heavy tetraquarks by means of the TQ4Q2.0 collinear FF set, covering scalar ($0^{++}$), axial-vector ($1^{+-}$), and tensor ($2^{++}$) configurations. The fragmentation inputs are determined within NRQCD factorization for the complete set of relevant partonic channels and are subsequently evolved across heavy-flavor thresholds through the HF-NRevo scheme. Perturbative uncertainties associated with fragmentation-scale variations are consistently propagated together with nonperturbative effects encoded in color-composite long-distance matrix elements. Attention is devoted to the axial-vector sector, whose fragmentation pattern makes it especially sensitive to intrinsic-charm contributions at LHC and FCC energies. TQ4Q2.0 therefore provides an uncertainty-aware framework for exploring fully heavy tetraquark production over a broad kinematic range and for connecting exotic-hadron spectroscopy with the partonic structure of the proton.

The Future Circular Electron-Positron Collider (FCC-ee) will probe aspects of the Higgs boson and the electroweak scale with unprecedented precision via associated Higgs production with a $Z$ boson. We focus on the Two-Higgs-Doublet Model (2HDM) to frame the FCC-ee's precision constraints within a small, concrete parameter space at next-to-leading order. We demonstrate that the projected precision of the FCC-ee's 240 GeV run will enable a precise analysis of Beyond-the-Standard-Model (BSM)-relevant Higgs-sector interactions near the alignment limit. As the key aspects of the 2HDM that drive deviations of the cross section from its Standard Model expectation (presence of new scalar states, Higgs mixing, and non-trivial inter-Higgs couplings) are also typically present in extensions more complex than the 2HDM, this demonstrates the FCC-ee's indirect potential for unveiling BSM physics around the electroweak scale.

We analyze general properties of cusped defect lines embedded in generic conformal field theories (CFTs). We prove that suitably defined cusp scaling operators transform like primary operators under general conformal transformations. We show that, via the cusp operator expansion (COE), defects of general shape can be expanded in a basis of cusped defects. These findings are checked and exemplified in the case of the localized magnetic field defect. Finally, we derive analytic constraints on dynamical cusp data by making use of a crossing equation, and discuss possible numerical bootstrap applications of our results.

The properties of compact stars with a strong first-order phase transition to quark matter and with an additional fluid of self-interacting bosonic dark matter (DM) are studied. We find that the inclusion of DM changes considerably the stability of mass-radius configurations relative to the naive one-fluid criterion. For compact star configurations with similar masses and different radii, so-called twin stars, the presence of DM removes the unstable segment between the hadronic and the hybrid branch, so that the stable mass-radius sequence becomes continuous after the onset of the phase transition to quark matter. We furthermore find stable ultra-compact objects (UCOs), defined by a total compactness $C = M_\text{tot}/R_\text{grav} \ge 1/3$. We observe two distinct classes of UCOs: a DM-halo class with $f_\text{DM} \gtrsim 0.9$, and a DM-core class at $f_\text{DM} \lesssim 0.02$. The two classes can be separated by the surface redshift of the normal matter, which reaches $z=0.73$–$0.77$ for the DM-core class and stays below $0.45$ for the DM-halo class. Finally, we find hybrid star solutions of 'ultimate twins' with similar mass and visible radius, but different dark matter content, leading to different tidal deformabilities and surface redshifts. Future X-ray and gravitational measurements of ultra-compact neutron stars with radii and masses outside the allowed neutron star range can thereby probe the presence and the properties of DM in addition to a first-order phase transition to quark matter.