Papers

The phase structure of strongly interacting matter at high baryon density remains an open problem in QCD, with important implications for the internal structure and magnetic properties of neutron stars. We reexamine the emergence of a quark spin-polarized (QSP) phase in cold, dense quark matter within the two-flavor Nambu-Jona-Lasinio model with tensor interactions, focusing on its dependence on regularization. We compare the traditional regularization scheme (TRS), where a sharp momentum cutoff is applied to both vacuum and medium contributions, with the medium separation scheme (MSS), where ultraviolet-divergent vacuum terms are isolated while finite medium-dependent phase-space contributions remain cutoff free. The two prescriptions lead to qualitatively different results. In TRS, the QSP condensate eventually collapses at high chemical potential, leading to nonmonotonic thermodynamic behavior and, for some couplings, violations of causality. In MSS, the QSP condensate instead increases monotonically with density, the equation of state remains causal, and the associated spontaneous magnetization grows toward high density. The persistence of spin polarization at high density may provide a microscopic contribution to the strong magnetic fields of compact stars, including magnetars. An exploratory hybrid-star construction further shows that the QSP phase can significantly modify the equation of state, stability trends, and mass-radius relations. These results highlight the importance of a consistent treatment of medium phase space and demonstrate the potential impact of a persistent spin-polarized quark phase on neutron-star physics.

Using two fitted coupled-channel one-loop chiral amplitudes, we investigate the strong-interaction energy shift and decay width of the hypothetical Coulomb-bound $K^+ K^-$ hadronic atom, kaonium. We obtain ground-state widths of 1.67 and 0.92 keV, which are both larger than previous kaonium predictions, including the 0.30 keV result obtained from a non-perturbative treatment based on leading-order chiral perturbation theory. Although the $K^+ K^-$ scattering lengths obtained from the two one-loop amplitudes have nearly equal imaginary parts, their real parts have opposite signs; thus, the leading absorptive contributions to the widths are similar, while the Coulomb corrections act in opposite directions. The kaonium width therefore depends on both the real and imaginary parts of the near-threshold strong amplitude. Despite the increased ground-state width, the first three $s$-wave levels remain separated. In photon fusion, at fixed pole area and resonance position, the increase in the intrinsic width has a negligible effect on the line shape after including Belle's experimental resolution.

One of the most important discoveries at the LHC is the presence of effects associated with quark-gluon plasma (QGP) formation in proton-proton (pp) collisions. The origin of these observations remains unknown. Since event selection in many studies relies on multiplicity-based estimators known to introduce selection biases, alternative approaches must be explored to elucidate the origin of these phenomena. This contribution presents a comparison of different event classifiers used in LHC experiments, aiming to assess their mutual compatibility. Results for pp collisions at $\sqrt{s}=13$ TeV simulated with PYTHIA 8 indicate that the different classifiers introduce biases that can obscure any evidence of QGP formation in small systems. However, these biases are significantly reduced or absent in events triggered with flattenicity. This finding motivates the application of flattenicity in dijet acoplanarity studies used to search for jet quenching effects. While multiplicity-based estimators produce an azimuthal broadening in high-multiplicity compared with minimum-bias pp collisions, even in PYTHIA 8 that does not incorporate jet quenching, events triggered with flattenicity show no such broadening. This suggests that this novel tool could be exploited by LHC experiments to refine jet-quenching searches in small systems.

We test the hypothesis that Newton's gravitational constant underwent a rapid transition approximately $73$-$130\,{\rm Myr}$ ago, as proposed in some resolutions of the Hubble tension. Fully convective red dwarf stars with masses below $\sim0.35\,M_\odot$ have thermal timescales comparable to the proposed transition look-back times, so an appreciable present-day memory can remain. We show that a rapid step in $G$ induces measurable changes in their radii and confront these predictions with mass-radius measurements of eight red dwarfs in detached eclipsing binaries. We find that the $G$-step models proposed to resolve the Hubble tension, corresponding to a $4\%$ change in $G$ at a look-back time of $73\,{\rm Myr}$ and an $11\%$ change at $130\,{\rm Myr}$, are excluded at significances of $3.1\sigma$ and $4.0\sigma$, respectively.

A reinterpretation of ATLAS searches targeting $b$-tagged dijet resonances and monotop-alike signatures at a center-of-mass energy of 13 TeV is presented using $pp$ collision data corresponding to integrated luminosities of 139 $\mathrm{fb}^{-1}$. These searches are used to constrain a baryon-number-violating new physics model that introduces two scalar mediators $X_{1}$ and $X_{2}$ to simultaneously address the baryon asymmetry of the universe and the dark matter relic abundance. By exploiting heavy-flavor signatures and allowing for jet-rich final states, this reinterpretation provides complementary sensitivity to the model relative to non-flavor-tagged inclusive dijet searches and conventional monotop reinterpretations. Assuming the mediators decay either into a pair of down-type quarks or into a top quark and a dark matter candidate, we translate the experimental upper limits into the model's parameter space. 95% confidence level exclusion limits are derived in the $\lambda_1$-$\lambda_2$ coupling plane for benchmark mediator masses of 1.5, 1.75, and 2.0 TeV. For all three benchmark masses, the $b$-tagged dijet reinterpretation excludes $\lambda_1 > 0.45$, while the bottom-squark reinterpretation excludes the region with $\lambda_1 > 0.3$ and $\lambda_2 > 0.6$, within the respective validated parameter domains.

We present a next-to-leading order + parton shower generator for $t$- and $s$-channel single-top production in hadron colliders, for a leptonically-decaying top, including off-shell and non-resonant effects. The generator, publicly available in the POWHEG BOX RES framework, describes the hadro-production of a $b$-jet and a leptonically decaying $W$-boson, accompanied by an additional jet, i.e. $pp\to \ell^{+} \nu_{\ell}\, j_b\, j $ and $pp\to \ell^{-} \bar{\nu}_{\ell}\, j_{\bar{b}}\, j $, where $j_b$ ($j_{\bar{b}}$) is a jet containing a bottom (anti)quark, and $j$ is a generic jet. We also provide an interface to the Pythia parton shower, suited to matching in the presence of decaying resonances such as the top quark. Our matching is designed to combine the advantages of a five-flavour calculation with the description of bottom quark mass effects in final-state jets. We perform a phenomenological study using fiducial cuts and discuss shower effects.

Relativistic heavy quarks equilibrate even when their microscopic drag and momentum diffusion violate the Einstein relation. We investigate how equilibration proceeds as a function of the coupling and compared to simplified Fokker-Planck models. To do this, we present a detailed calculation of the momentum-transfer kernel in weakly coupled non-Abelian plasmas through strict $\mathcal{O}(g^4)$, and study the resulting dynamics at leading order in the inverse heavy-quark mass. Beyond leading logarithm, its non-Gaussian structure plays a crucial role in equilibration. We examine closely the analytic structure of the evolution kernel, determine the large-order asymptotics of the momentum-transfer cumulants, and show how the kernel's bounded analytic domain fixes asymmetric exponential tails at the level of the momentum transfer probability. Strongly coupled $\mathcal{N}=4$ SYM also features an approximately Gaussian core and exponential tails, but differs in the nature of the kernel's singularities and the velocity dependence of the transport coefficients and tail exponents. These differences have distinct dynamical consequences: for the parameters studied, the persistence of the relativistic population in steeply falling spectra is largely explained by drag alone at very weak coupling, whereas fluctuation-induced survivor bias produces a large relative enhancement at strong coupling. Nevertheless, the shared qualitative structure between weak and strong coupling points the way towards a practical phenomenological description of heavy quarks anchored in first-principles field theory.

Vector-boson polarization provides a sensitive probe of new physics in the electroweak sector. Rare processes and suppressed longitudinal contributions make optimal polarization separation essential to exploit the available data. We show that parton-level differential polarization fractions define optimal observables and a fundamental sensitivity limit for polarized cross-section measurements. Their conditional expectations retain all experimentally accessible polarization information, yielding the best achievable sensitivity within the assumed model, and can be learned by neural networks for unbinned or binned inference. Measuring their distributions combines polarization sensitivity with the model independence of fiducial cross sections, probing deviations beyond constant rescalings of polarized contributions. We demonstrate the approach in inclusive ZZ production.

We demonstrate that Maxwell electrodynamics interacting with a planar Chern-Simons interface does not have plane wave solutions localized on the interface. We re-examine the derivation of such waves presented by N. Kaloper in [Phys.Rev.D114(2026)L051903] and show that at an intermediate step certain terms were missed in an equation therein. Taking these terms into account changes the final conclusion of [Phys.Rev.D114(2026)L051903]. We also show that the method used in [arXiv:2606.12513 [hep-th]] to reproduce the same result is not consistent.

A light force carrier can mediate long-range interactions between dark matter particles and facilitate the formation of bound states. Models incorporating these features have attracted considerable attention in recent years, with significant advances in both the theoretical understanding of such bound states and their impact on the parameter space consistent with the observed dark matter relic abundance. However, the relevant results and their consistent implementation in Boltzmann equations remain technically intricate, requiring careful treatment or the use of specialized tools. This complexity has hindered broader adoption of these findings and restricted their use to a small number of expert groups. To address this challenge, we propose a simple prescription based on the analytic limits of the relevant rates, which allows standard freeze-out computations to be refined through a straightforward semi-analytical prescription that captures the main features of the full calculation. We illustrate this approach for a $U(1)$ dark matter model with a light force carrier, including Sommerfeld enhancement and bound-state effects.

We examine Higgsino dark matter (DM) as a potential explanation of the $248~\mathrm{keV}$ nuclear-recoil event of interest reported by the LUX-ZEPLIN (LZ) experiment, taking into account IceCube constraints on DM annihilation in the Sun. In the nearly pure Higgsino limit, two neutral Majorana states separated by a small mass splitting $\delta$ are connected by an off-diagonal coupling to the $Z$ boson, providing a natural realization of inelastic DM. Using a likelihood analysis, we identify 90% confidence regions compatible with the LZ event and consistent with the null results of IceCube searches, both with and without including a constraint from the absence of events in the LZ high-energy sideband. In our LZ analysis, we consider the DM distribution in the Standard Halo Model alone as well as possible enhancements of the high-speed tail induced by the Large Magellanic Cloud (LMC). We present four variants of bounds from IceCube on Higgsino dark matter, depending on various assumptions on cooling channels in the Sun, motivated by severe theoretical uncertainties about Higgsino-nucleon elastic scattering (unimportant for direct detection but crucial for IceCube bounds). Whereas the thermal Higgsino with a mass of $1.1~\mathrm{TeV}$ remains only marginally compatible with both the LZ event and the IceCube limits when the LMC-induced high-speed tail is included and both elastic cooling in the Sun and the LZ high-energy sideband constraint are neglected, higher mass Higgsinos are excellent candidates for the LZ event in light of IceCube constraints. Depending on the halo distribution, cooling interactions, and whether the LZ high-energy sideband is included, the compatible regions in the Higgsino parameter space $(m_\chi,\delta)$ extend from masses of $\sim2~\mathrm{TeV}$ to hundreds of TeV or higher, with mass splittings ranging approximately from $350$ to $525~\mathrm{keV}$.

Jet vetoes are central to precision measurements of Higgs-boson properties at the Large Hadron Collider, where they are used to suppress backgrounds containing hard QCD radiation. We present the first prediction for the Higgs jet-vetoed cross section at the third logarithmic order in QCD, consistently combining the next-to-next-to-next-to-leading order calculation with state-of-the-art next-to-next-to-next-to-leading logarithmic resummation. At phenomenologically relevant veto scales ($p_T^{\rm v}\sim30$ GeV) and jet radii ($R=0.4$), the resummation increases the fixed-order prediction by about $3\%$, and their combination leads to a residual perturbative uncertainty of approximately $3\%$. Our results mark a milestone in the precise description of jet-vetoed Higgs-production at hadron colliders, reaching the level of precision relevant for the high-luminosity phase of the LHC.

We present a phenomenology-driven overview of opportunities and outstanding challenges in baryon electroweak transitions, focusing on hyperon and charmed-baryon processes for which lattice-QCD results are available, including semileptonic decays and selected radiative, dileptonic, and neutrino-induced channels. We identify semileptonic decays of strange and charmed baryons as a particularly promising domain for synergy between phenomenology, experiment, and lattice QCD. Particular emphasis is placed on the determination of vector and axial form factors, the precision and model-independent extraction of $|V_{us}|$ from hyperon semileptonic decays including radiative corrections, and on searches for non-standard interactions through lepton-flavor- and CP-violating observables. We examine the momentum dependence of form factors in ground-state transitions, highlight the emerging $\Xi_c \to \Xi$ semileptonic puzzle stemming from tensions between lattice-QCD predictions and experimental measurements, discuss inclusive decay rates, and outline strategies for extending these studies to transitions involving excited baryon states. For completeness, we review also results involving beauty-baryon decays.

We supplement McMule, a Monte Carlo framework that provides QED corrections up to next-to-next-to-leading order (NNLO) in the fine structure constant $\alpha$, with the inelastic two-photon exchange (TPE) contribution, based on the data-driven dispersive calculation of Tomalak, Pasquini and Vanderhaeghen, which we extend to the $Q^2\rightarrow 0$ limit that enables applications in the low-$Q^2$ region relevant for upcoming low-energy experiments. We present results for two experimental settings: the future MAGIX@MESA experiment and the ISR@MAMI measurement. For MAGIX@MESA kinematics, the inelastic TPE is small, comparable to the proton-side NLO corrections and subdominant to both the leptonic radiative corrections and the full NNLO QED corrections once a 1 MeV photon-energy cut is applied. For the ISR@MAMI kinematics, NNLO QED corrections modify the radiative tail below the elastic peak at the 10% level.

We present the first calculation of the third-order corrections to the rapidity anomalous dimension for jet-veto cross sections. This is a crucial ingredient for the resummation of these scattering observables in key processes such as colour-singlet and heavy-quark-pair production at hadron colliders. More precisely, our results enable the next-to-next-to-next-to-leading logarithmic (N$^3$LL) resummation of the jet-veto cross section for colour singlet production at the LHC, with immediate phenomenological relevance. The anomalous dimension is extracted from a calculation of the three-loop soft function in soft-collinear effective field theory, and is presented as a function of the jet radius $R$ for the clustering algorithms of the generalised-$k_t$ family. To handle the complexity associated with the clustering algorithm, we formulate a semi-numerical computational approach. This strategy is itself a result of the paper, and can be extended to the calculation of other anomalous dimensions and soft functions at three loops.

$B$-mesogenesis is a low-temperature baryogenesis mechanism, that uses $CP$-violation of the $B$ mesons in the standard model to fulfill the Sakharov conditions. It requires a late period of matter domination by a scalar field $\Phi$ that decays into $b\bar b$ quarks, reheating the Universe below the QCD phase transition. We investigate the impact of this mechanism on Big Bang Nucleosynthesis, with respect to the reheating temperature $T_{rh}$, and the mass of $\Phi$. Injection of hadrons skewing neutron/proton interconversions are the most important effect, followed by neutrino heating from $\Phi$ decays. For $M_\Phi\lesssim 100\,$GeV, $T_{rh}$ must be $\gtrsim 10\,$MeV.

EOS is an open-source software package for a variety of computational tasks in flavor physics. In this article, we describe new developments for version 1.1 of this software and discuss changes with respect to version 1.0. These developments and changes include theory predictions for additional decay and scattering processes, such as semileptonic charm decays, hadronic tau decays, and $e^+e^- \to$ hadrons scattering. Overall, these changes have contributed 1063 additional (pseudo-)observables. Beyond the physics capabilities of the software, the changes include improving the quality and reducing the computational costs of posterior sampling; providing a more versatile and testable figure framework; and improving the overall user experience.

In this work, we investigate final-state interaction effects in $B^{\mp}\to K^+K^- \pi^{\mp}$ decays above 3 GeV with a twofold objective: (i) to study $CP$ asymmetry, and (ii) to search for possible signatures of the $X(3700)$ state (also denoted as $X(3720)$). We consider both tree-level and resonant contributions, with the latter arising from a triangle mechanism $B^{\mp} \to \bar{D}^0 D^{\ast \mp} (\to \pi^{\mp} D^0) \to K^+K^- \pi^{\mp}$, in which the $D \bar D \to K \bar K$ rescattering process carries the signature of the exotic $X(3700)$ state. We analyze the dependence of our results on the relative phase between the tree-level and resonant contributions, as well as on other relevant parameters. We estimate the differential mass distribution in the region where the $X(3700)$ may leave a trace, and the $CP$ asymmetry driven by final-state interactions. Our findings are compared with available data for the differential mass distributions and the $CP$ asymmetry. Taken together, these results may contribute to a better understanding of the properties of exotic states and the role of $CP$ asymmetry in $B$-meson phenomenology.

The mathematical methods and approaches used in our analytical calculations of electromagnetic corrections to the leptonic anomaly $a_L$, which is caused by a special class of Feynman diagrams with insertions of the vacuum polarization operator, are presented and examined in detail. The developed methods are essentially based on the Mellin–Barnes transform for the propagators of massive particles with subsequent application of the PSLQ algorithm to solve the emerging functional equations. Functional equations are also used in the procedure of analytic continuation of a particular type of hypergeometric functions to the entire complex plane of their parameters. It is shown that these approaches make it possible to obtain explicit expressions for radiative corrections of rather high orders.

Quantum entanglement in $\tau^+\tau^-$ production provides a direct probe of non-classical spin correlations in a relativistic quantum system, with the $\tau$ decay products serving as spin analyzers. We investigate the detector-level feasibility of such measurements in $e^+e^-\to\tau^+\tau^-$ at the Super Tau-Charm Facility (STCF) at $\sqrt{s}=7$ GeV, using the $\rho\rho$ and $\pi\rho$ decay channels. Signal and dominant background processes are simulated with the full STCF detector and reconstruction framework. Dedicated reconstruction and event-selection procedures yield overall signal efficiencies of approximately $4.5\%$ and $4.8\%$, with corresponding purities of about $87.6\%$ and $93.2\%$ for the $\rho\rho$ and $\pi\rho$ channels, respectively. From the reconstructed decay kinematics, the $\tau^+\tau^-$ spin-density matrix is inferred and the concurrence $C[\rho]$ together with the Bell-sensitive quantity $m_{12}[C]$ are evaluated in a selected fiducial region. For the benchmark requirement $|\cos\theta|<0.2$ and an integrated luminosity of $1~\mathrm{ab}^{-1}$, the projected relative precision on $C[\rho]$ is about $2.2\%$ in both channels, while that on $m_{12}[C]$ is approximately $1.4\%$ for $\rho\rho$ and $1.5\%$ for $\pi\rho$, including statistical and detector-resolution uncertainties. The reconstructed $m_{12}[C]$ shows a larger separation from its reference threshold in the $\rho\rho$ channel, making this topology particularly sensitive to Bell-type spin correlations. These results demonstrate the detector-level feasibility of probing quantum entanglement and non-classical spin correlations in hadronic $\tau$ decays at STCF.

As an alternative to standard dark matter freeze-out via two-body annihilation, strongly interacting massive particles are proposed to regulate their relic abundance through three/four-body self-annihilation. During such freeze-out, dark matter must undergo both number reduction and energy dissipation. The former requires number-reducing processes, and the latter requires an efficient energy-dissipation mechanism. In this work, we propose a novel mechanism where internal Bremsstrahlung processes establish kinetic equilibrium between dark matter and radiation, and thus dissipate energy. More appealingly, this mechanism can be naturally realized in a class of strong dynamics models with flavor-universal quarks and a light axion. To demonstrate our results in a $Sp(4)_c$ dark-color model, we compute all relevant interaction terms and numerically solve the full Boltzmann equations. The same mechanism can also be applied to vector dark matter models.

Cosmic birefringence, the isotropic rotation of the plane of linear polarization of photons from sources at cosmological distances, can be generated by different parity-violating mechanisms. While the net rotation angle of a single polarized source carries little information about its physical origin, sources at various redshifts $z$ can be used to distinguish between different origins. Parity-sensitive correlations of the $E$- and $B$-mode polarization fields of the cosmic microwave background measured on large and small angular scales probe sources at $z\simeq 10$ and $1100$, respectively. Thus, the detailed shape of the $EB$ power spectrum is sensitive to the redshift evolution of the birefringence source. In this paper, we calculate the $EB$ power spectrum due to a neutrino-asymmetry current, and compare it to axion dark energy and dark matter using a common Chern–Simons framework. We find that the $EB$ power spectrum due to a neutrino asymmetry is suppressed at low multipoles, $\ell\lesssim 20$, similar to the dark matter case. This can be clearly distinguished from the dark energy case, which has no such suppression. Large-scale polarization measurements, including LiteBIRD, can therefore distinguish late-time dark energy birefringence from that generated at higher redshifts by axion dark matter or neutrino asymmetry. We also find that the evolution of the neutrino density during recombination alters the shape of the $EB$ power spectrum at high multipoles. This signature can be used to distinguish between the neutrino and axion dark matter interpretations, using ground-based experiments such as the Simons Observatory.

We construct the quantized electromagnetic field and the corresponding photon propagators in a rigidly rotating cylindrical reference frame. Starting from covariant Maxwell theory, we formulate the gauge-fixed field equations and solve them in cylindrical coordinates. The vector nature of the electromagnetic field requires distinguishing orbital and intrinsic angular momentum, with the total angular momentum as the natural quantum number. We construct the two independent physical photon modes in terms of Bessel functions by solving the coupled differential equations, and provide an alternative construction based on a covariant basis of vector eigenfunctions generated by a covariantly constant tetrad. After normalizing the modes with the Maxwell inner product, we quantize the electromagnetic field and define the corresponding photon states and greater and lesser two-point functions. The physical time-ordered propagator is obtained directly from the quantized modes, with its transverse dependence encoded in polarization kernels that retain the cylindrical spatial structure and its spectral poles exhibiting the rotational energy shift. The full gauge-fixed photon propagator is constructed in two complementary ways: from the scalar Green function combined with the tensor transformation of the inertial Feynman-gauge propagator, and from the covariant vector eigensystem through its spectral decomposition and the Fock–Schwinger proper-time representation. We verify that both constructions satisfy the Green-function equation for the complete gauge-fixed Maxwell operator, providing the propagator required for covariant perturbative calculations with internal photon lines.

Cosmic-string loops generate a broadband gravitational-wave background (GWB) that is typically modeled via two distinct formalisms: a discrete harmonic expansion, commonly used in pulsar-timing-array (PTA) studies, and a continuous burst superposition, employed in ground-based GWB searches. In this work, we formally unify the two formalisms, showing that they provide discrete and continuous representations of the same underlying radiation process and converge on the scale-invariant spectrum plateau. On the rising low-frequency branch, where the first few harmonics dominate, the discrete nature becomes important, causing the two formalisms to diverge. Within this unified framework, the spectral calculation is more consistent across frequency bands, enabling multi-band inference. Leveraging this physical insight, we perform joint Bayesian inference across four representative loop-distribution models using the NANOGrav, EPTA, and LIGO–Virgo–KAGRA (LVK) datasets. By jointly sampling the string tension $G\mu$ alongside the average cusp and kink numbers $\{N_c, N_k\}$, the loop-radiation uncertainties are accounted for. We find that employing the harmonic expansion strengthens the LVK bounds by $21\%-31\%$ for three of these models. Additionally, the stringent LVK bounds preclude three of these models from explaining the observed PTA common signal. For the sole surviving model, our multi-band analysis improves the inferred limit on $G\mu$.

We study the formation of $\mathcal{N}$-quark baryons during the confinement crossover of an $SU(\mathcal{N})$ gauge theory containing quarks in the fundamental representation, with masses around or below the confinement scale. We assume stepwise baryon formation through the successive fusion of pairs of quark-clusters, with color interaction rates obeying quadratic Casimir scaling. We include the complete set of reactions between $SU(\mathcal{N})$ antisymmetric clusters dressed with their specific spin-flavor multiplicities. We show that at large $\mathcal{N}$, baryon formation is hindered by a Casimir bottleneck, such that fusion of few-quark clusters in the initial steps of the baryon assembly chain is strongly outweighed by cluster destruction processes. We find that for $\mathcal{N}=12\,(18)$ the baryon-to-meson yield ratio is suppressed down to $10^{-12}\,(10^{-23})$ of its value at $\mathcal{N}=3$. We embed the mechanism in a vectorlike three-flavor model whose lightest baryon can be electrically neutral, while axial-anomaly-induced couplings and dimension-six operators induce decays of the unstable mesons and charged baryons safely before big-bang nucleosynthesis. The relic density of cosmologically stable neutral $\mathcal{N}$-baryons is thus set during confinement at values so small that, for sufficiently large $\mathcal{N}$, the baryon masses required to saturate the dark matter energy density exceed by several orders of magnitude the unitarity bound on annihilation cross sections.

The internal structure of hadrons is governed by nonperturbative Quantum Chromodynamics (QCD). This dissertation presents first-principles calculations of partonic observables using lattice QCD and effective field theory, with controlled systematic uncertainties, advancing from collinear structure to transverse-momentum-dependent distributions (TMDs) that encode the three-dimensional partonic structure of hadrons. Within the large momentum effective theory (LaMET) framework, this work presents state-of-the-art calculations of pion distribution amplitudes and systematic studies of nucleon parton distributions, with control of renormalization, excited-state contamination, Fourier-transform systematics, and power corrections. A Coulomb-gauge formulation of quasi-distributions simplifies ultraviolet structure by avoiding Wilson-line related linear divergences, with Gribov-copy effects found to be negligible at current statistical precision. Building on these developments, this dissertation reports lattice determinations of nucleon TMD parton distributions, the Collins-Soper kernel, the intrinsic soft function, and pion TMD observables. These results provide nonperturbative inputs for global QCD analyses and the precision hadron-structure program, including the Electron-Ion Collider. In parallel, this work explores machine-learning acceleration of lattice gauge simulations through neural field transformations embedded in Hybrid Monte Carlo. In two-dimensional U(1) tests, the method reduces autocorrelation and improves performance toward finer lattice spacing, suggesting potential applications to more efficient lattice QCD simulations.

We investigate high energy neutrinos (HE$\nu$s) from the decay of superheavy dark matter (DM) produced during a cosmological first order phase transition. Adopting the filtered DM production mechanism, we revisit the relic abundance calculation by incorporating recent progress in determining the bubble wall velocity from hydrodynamics. We show that DM with mass $m_{\text{DM}}\simeq 4.4\times10^{8}~\text{GeV}$ can reproduce the observed relic abundance and accommodate ultra high energy neutrino events such as KM3-230213A, while the same phase transition simultaneously generates a stochastic gravitational wave (GW) background. Although the GW signal (which peaks at $10^{4}\,\text{Hz}$) is not yet observable in this example, at lower DM masses $m_{\text{DM}} \lesssim10^{6}~\text{GeV}$, the neutrino spectrum shifts into the energy range relevant for IceCube observations, while the associated GW signal moves to lower frequencies and can reach the projected sensitivities of Cosmic Explorer, BBO, and DECIGO. This gives a multimessenger connection between HE$\nu$s and GWs, with both signals connected to DM production in a first order phase transition.

The effective action at one-loop for the quantum electrodynamics (QED) in the presence of background vectors and tensors that break the Lorentz symmetry is calculated in this work. We highlight that just the Lorentz symmetry violation through the Dirac matrices in the fermionic sector is considered since investigations in others sectors of the extended QED has been explored in recent papers. Using the proper time method, we show that some background vectors and tensors do not contribute to the effective action at one-loop and in the linear approximation. Thereby, only two background tensors contribute to the effective action at one-loop for small components of these tensors, and that a new combination of cubic and quartic non-linear electrodynamics emerge in the weak field regime.

Prompt-photon production with recoiling QCD radiation is crucial for new-physics searches, determinations of parton distribution and fragmentation functions, and jet-quenching studies in heavy-ion collisions. We present the first fully differential NNLO QCD predictions for photon-associated identified-hadron production at the LHC. We compare predictions obtained with different fragmentation function (FF) sets to ALICE and ATLAS data at $\sqrt{s}=5.02\,{\rm TeV}$. Our calculation provides an important theoretical ingredient for FF global fits and offers a precision proton–proton baseline for photon-tagged heavy-ion studies.

We present an elementary recursive construction of Hermitian projectors on multi-quark ${\rm SU}(N)$ color states, based on the characterization of these states by their quadratic Casimir, and using the birdtrack pictorial technique.