Papers

Attractors are effective low-dimensional structures, defined in a chosen set of observables, that trajectories from different initial states approach; hydrodynamic attractors are those on which the late-time evolution is governed by hydrodynamic constitutive relations. Motivated by nuclear collisions and ultracold atomic gases, this chapter distinguishes attractorization (the loss of sensitivity to some directions in the space of initial states) from hydrodynamization (the onset of validity of hydrodynamic constitutive relations). Using mainly conformal, boost-invariant Bjorken flow, we compare Müller-Israel-Stewart-type theories, kinetic theory, holography, and classical Yang-Mills fields. Forward attraction, produced by the decay of non-hydrodynamic modes, is distinguished from pullback attraction, which can select a unique regular solution, and from expansion-driven attraction, which can suppress initial-state sensitivity before microscopic relaxation, with or without a subsequent fluid regime. Divergent gradient expansions and their transseries completions, the state-space picture, and adiabatic hydrodynamization provide complementary descriptions. Applications to nuclear collisions include particle production, transverse energy and flow, the initialization of and linear response around attracting backgrounds, jet quenching, and attractor-informed modifications of hydrodynamic models. For ultracold Fermi gases, we review theoretical proposals for bulk-channel attractors under scattering-length drives and distinguish them from recent measurements of short-time contact and momentum-distribution dynamics.

We develop a theory of a dark baryon dark matter candidate that interacts with nuclei dominantly through inelastic scattering mediated by a transition magnetic dipole operator. Models are presented that can elegantly explain both the scattering rate and the size of the inelastic splitting to be consistent with the one event observed at LZ\@. Elastic scattering is suppressed due to accidental symmetries within the strongly-coupled sector. The nuclear response is dominated by a spin-dependent structure factor, thus we find a large range of masses, $1 \; {\rm TeV} \lesssim m_\chi \lesssim 50 \; {\rm TeV}$, and mass splitting of $100 \; {\rm keV} \lesssim \delta \lesssim 500 \; {\rm keV}$ can fit the data for a variety of possible dark matter velocity distributions. The models predict that some nuclear scattering events will be accompanied by a simultaneous photon signal with energy $\delta$, which not only distinguishes this model from other inelastic dark matter explanations but also enables directional detection in conventional direct detection experiments. We briefly comment on the dark matter abundance, indirect detection signals (including the models' significantly weaker constraints from dark matter annihilation in the Sun), and the associated collider signals that arise from the meson sector of the theory.

We derive the two-loop anomalous dimension relevant for the resummation of subleading non-global and, for the first time, also clustering logarithms within the framework of effective field theory. Special emphasis is put on the choice of the renormalization scheme. We show that the modified minimal subtraction scheme is problematic since it requires extra dimensions to set up the parton shower to perform the resummation. We discuss a set of modified dipole subtraction schemes which are free from this complication and can be used to obtain a frame-independent result for the renormalization-group evolution. We implement the leading-color limit of our result in the Marzili framework and numerically verify the scheme independence for gap-between-jets cross sections.

Supermassive black holes (SMBHs) in "little red dots" (LRDs) discovered by the James Webb Space Telescope (JWST) may result from runaway mergers of primordial black holes (PBHs) in clusters—through long-short mode coupling on small scales in the early Universe. In this framework, we derive the SMBH mass function, together with the compactness and overmassive features of LRDs. We also estimate that the dense gas residing in PBH clusters is consistent with LRD observations. In addition, SMBHs formed from PBH clusters can help accelerate galaxy formation at high redshifts, thus alleviating tension with $\Lambda$CDM cosmology.

Motivated by recent progress in data-driven approaches, we introduce a machine-learning (ML)-informed Debye mass, extracted from lattice-informed inputs, exclusively in the complex-valued heavy-quark Kent State University (KSU) potential. The resulting complex potential is used to solve the real-time Schrödinger equation within the quantum trajectories (QTraj) framework for the evolution of bottomonium in the quark-gluon plasma. We then compute the nuclear modification factors and double ratios for bottomonium $\Upsilon(1S)$, $\Upsilon(2S)$, and $\Upsilon(3S)$ states in Pb-Pb collisions at $\sqrt{s_{NN}} = 5.02$ TeV. We compare our ML-induced results with those from the original KSU model and with experimental measurements from ALICE, ATLAS, and CMS collaborations. We find that the machine-learned Debye mass leads to improved agreement with data, particularly for excited states, highlighting the utility of machine learning in modeling in-medium QCD effects.

The LZ experiment reported a nuclear recoil with anomalous energy $E_R=248$ keV, around the typical neutron motion in xenon. This motivates interpreting the event as the disappearance of a bound neutron, either through spontaneous decay or a dark-matter-induced reaction. If the energy released is large, the predicted recoil spectrum is broad around the observed value; only $\sim10\%$ of xenon events avoid extra nuclear activity; the disappearance rate is target-independent and mildly constrained by oxygen experiments. In the special case of near-threshold DM-induced neutron disappearance, it can be open in xenon and closed in oxygen, the quiet fraction rises to $\sim30\%$, the recoil spectrum turns into lines.

The LUX-ZEPLIN (LZ) experiment has reported an inelastic nuclear-recoil candidate at $E_{\rm nr}=248\pm23_{\rm stat}\pm23_{\rm sys}\,{\rm keV}$. We test whether endothermic pseudo-Dirac dark matter coupled to a kinetically mixed dark photon can account for this event while reproducing the observed relic abundance. A five-parameter fit using an energy-only LZ likelihood and a relic-density likelihood favors TeV-scale dark matter with a mass splitting of a few hundred keV, and a GeV-scale mediator. The recoil energy places the splitting near its kinematic ceiling, while secluded annihilation fixes the dark gauge coupling to a good approximation as a function of the dark-matter mass. Representative points predict $\mathcal{O}(1)$ accepted LZ event candidate and the observed DM relic density. Because the preferred splitting lies below the $e^+e^-$ threshold, the viability of the minimal model depends on the late-time excited-state abundance; a transition dipole can provide additional depletion, and the required light mediator remains testable in accelerator searches.

The ATLAS Collaboration has reported measurements of the transverse momentum ($p_{\rm{T}}$) spectra of charged hadrons in proton-proton ($p+p$), proton-lead ($p+Pb$), and lead-lead ($Pb+Pb$) collisions at a nucleon-nucleon center-of-mass energy of $\sqrt{s_{\rm{NN}}}~=$~5.02~TeV within the rapidity interval $-2.5<y<2.0$. In the present work, we investigate medium effects on charged-hadron production in $p+Pb$ and $Pb+Pb$ collisions using a phenomenological modified Tsallis parametrization that accounts for transverse collective flow in the low-to-intermediate $p_{\rm{T}}$ region and medium-induced parton energy loss at high $p_{\rm{T}}$. The modified parametrization provides a consistent description of the measured spectra over the full investigated $p_{\rm{T}}$ range across different centrality classes. The extracted energy-loss exponent $\alpha$, which characterizes the energy dependence of parton energy loss, is found to lie in the range 0.59$-$0.73 for $p+Pb$ collisions and 0.32$-$0.59 for $Pb+Pb$ collisions. In addition, the extracted parameters exhibit a clear centrality dependence, reflecting enhanced collective effects in central collisions. These results provide quantitative insight into the interplay between transverse collective flow and medium-induced parton energy loss in charged-hadron production at LHC energies.

The LUX-ZEPLIN (LZ) experiment has recently reported a nuclear-recoil candidate at $E_R=248\pm23_{\rm stat}\pm23_{\rm sys}\,{\rm keV}$ in an exposure of $2.84\,{\rm tonne\,yr}$. At this unusually high recoil energy, the spin-independent (SI) xenon response is strongly suppressed, motivating dark matter interactions with a harder recoil spectrum. We show that elastic spin-dependent (SD) scattering through the nonrelativistic operator $\mathcal O_4=\mathbf S_{\rm DM}\cdot\mathbf S_N$ provides a simple realization of such a spectrum. We consider singlet-doublet Majorana dark matter, for which a diagonal $Z$ coupling generates the required SD interaction. The accompanying Higgs-mediated SI interaction would generically produce too many low-energy recoils, but can be suppressed along a Higgs blind spot while retaining a nonzero $Z$ coupling. We find a region of the Higgs blind spot that simultaneously predicts an $\mathcal O(1)$ event rate in the LZ high-recoil window and reproduces the observed thermal relic abundance. The same SD interaction leads to solar capture, allowing this region to be tested independently with solar-neutrino searches. Current IceCube limits already probe part of the LZ-compatible thermal parameter space, while a viable region remains. Additional xenon exposure and improved solar-neutrino searches can therefore provide complementary tests of this interpretation.

We investigate the sensitivity of a future high-energy muon collider (MuCs) to the inert scalar sector of the Inert Doublet Model (IDM) through a comprehensive set of $2\to4$ electroweak gauge-boson fusion processes. The scalar spectrum consists of two CP-even neutral scalars: $h$ and $H$, one CP-odd neutral scalar $A$, and a pair of charged scalars $H^\pm$. We assume the neutral scalar $H$ to be the lightest inert state and the dark matter (DM) candidate, while the observed $125$~GeV Higgs boson is identified with the scalar of the Standard Model-like doublet. We consider charged Higgs pair production: $\mu^+\mu^-\to H^+H^-\nu\bar{\nu}$ induced by WW fusion, as well as the associated channels: $\mu^+\mu^-\to HH^\pm\mu^\mp\nu$ and $\mu^+\mu^-\to AH^\pm\mu^\mp\nu$, induced by $WZ$ and $W\gamma$ fusion. Owing to their Vector Boson Fusion (VBF) origin, the corresponding cross sections increase significantly with collider energy, making them particularly well suited for exploration at a high-energy MuCs. We first study the $2\to 2$ subprocesses $WW\to H^+ H^-$ and $WV\to H^+ S_i$, $V=Z, \gamma$ and $S_i=H$ or $A$ and establish the destructive interference among the contributing diagrams. After imposing theoretical consistency requirements and current experimental constraints, including those from DM and collider searches, we evaluate the corresponding signal rates at $\sqrt{s}=3$, $10$, and $20$~TeV. We further perform a detector-level Monte Carlo analysis combined with a cut-based signal-background selection. Our results demonstrate that the sensitivity to inert scalar production increases significantly with collision energy, establishing the 10 and 20~TeV MuCs stages as powerful probes of the IDM inert scalar sector.

In our previous work [C. Lorcé et al., Phys. Lett. B 868 (2025) 139792], we investigated the 2D spatial distributions of transverse total angular momentum, including orbital angular momentum and intrinsic spin, relative to the canonical center (or center of spin). In the present work, we extend this analysis in two directions. First, we study the corresponding transverse boost distributions relative to the canonical center. Second, since the definition of generalized angular momentum density depends crucially on the choice of pivot, we analyze how the spatial distributions of transverse total angular momentum and boost are modified when they are defined relative to different relativistic centers, viz.~the relativistic centers of mass, energy, and spin. Considering spin-1/2 targets, we derive the corresponding 2D spatial distributions in the transverse plane, and further investigate how the spatial patterns evolve under longitudinal Lorentz boosts. Additionally, we provide the corresponding light-front distributions in the transverse plane, establishing a clear connection between the instant-form and light-front descriptions of transverse angular momentum and boost.

The LUX-ZEPLIN (LZ) Collaboration has reported a high-energy candidate event LZ230616 with a reconstructed nuclear recoil energy $E_R=248\pm23_{\rm stat}\pm23_{\rm sys}~{\rm keV}$. We investigate a possible interpretation in terms of inelastic scattering between two Majorana dark matter states mediated by an axionlike particle coupled to gluons. The positive mass splitting suppresses low-energy recoils, while the momentum dependence of the interaction reshapes the high-energy spectrum. We treat the dark-sector and gluonic couplings independently and retain the momentum-dependent nucleon form factors and xenon nuclear responses. Using an approximate single-event likelihood, we find that, for $m_a=0.3~{\rm GeV}$, a narrow spectrum near the candidate energy arises at $m_\chi\simeq0.35~{\rm TeV}$ and $\delta\simeq330~{\rm keV}$, although this configuration requires a large coupling product and is highly sensitive to the Galactic halo speed cutoff. Our analysis establishes the kinematic and coupling requirements for subsequent tests using the thermal relic abundance and laboratory constraints on the mediator.

Representing multi-loop scattering amplitudes as linear combinations of multivalued transcendental functions with process-dependent rational coefficients has long been understood to be advantageous. In general, these transcendental functions satisfy a system of differential equations with coupled homogeneous blocks. When these coupled blocks can be removed through algebraic basis transformations, the relation between the rational and algebraic bases is universal and minimal. Here, we ask whether an analogous universal and minimal relation exists when decoupling requires transformations involving complete elliptic integrals. We elaborate on the method proposed in ref. arXiv:2504.20897, in which we suggested that a basis constructed using an elliptic generalization of leading singularities may provide an answer to this question. We extend this analysis to the off-diagonal blocks of the rational differential equations satisfied by the bases obtained through this construction. We find that the $\epsilon$ dependence of these blocks can be organized into a universal structure that is preserved under the decoupling transformation used to express the solutions in terms of iterated integrals.

We show that the Chiral Mean-Field model (CMF) can produce a phase diagram with three critical points: the nuclear liquid-gas transition, quark deconfinement, and a strangeness driven transition. The strangeness driven transition separates a mainly nucleonic phase from one dominated by hyperons and baryon resonances. We discuss the compositional change in these transitions and their possible signatures in heavy-ion collisions and neutron star mergers.

In a companion paper, we demonstrated that static axion field gradients sourced by dense nuclear matter (axion hair) can dominate the near-field electrodynamics of old rotation-powered pulsars, leading to new constraints on light QCD axions and on CP-violating axion-nucleon interactions. This article provides the extended theoretical and numerical framework underlying those results. We begin by providing a detailed description of the sourcing of axion hair from dense nuclear matter, computing self-consistent field profiles for each interaction across the relevant parameter space. We then study the modification to the electrodynamics induced in the polar gap region by these axion gradients; this is done at the analytic level by studying the modification induced by axion field gradients on the effective discharge parameter (computed in the force-free limit of the split monopole magnetic field configuration, and looking at leading deviations from the force-free limit for dipolar field configurations), and numerically by developing dedicated 1D particle-in-cell simulations which capture the leading order dynamical behavior near the star. Our results demonstrate that axion hair serves to either enhance acceleration, or enhance screening, where the relevant effect changes between the northern and southern hemispheres of the star, and between the field lines which support out-flowing and return currents.

We explore a radiative neutrino mass model based on the topology T4-3-i, which is a one-loop completion of the Weinberg operator. We focus on its T4-3-i-C1 realization, containing an inert scalar doublet, a real scalar triplet, a Majorana fermion triplet, and a Dirac singlet fermion. An exact $Z_2$ symmetry forbids the tree-level type-III term and stabilizes the lightest $Z_2$-odd particle, leaving the one-loop topology as the leading source of neutrino mass. The model accomodate a neutral CP-even scalar dark matter candidate and predicts a rank two neutrino mass matrix, and thus one neutrino is massless. A combined analysis incorporating theoretical and experimental constraints reveals viable solutions to both neutrino mass orderings, with the inverted ordering predicting larger values of $m_{\beta\beta}$, $m_\beta$, and $\sum_i m_i$, thereby enhancing its testability through future beta-decay, neutrinoless double beta decay, and cosmological probes. Within the same viable parameter region, the observed dark matter relic abundance is accounted for by annihilation and coannihilation processes, while the electroweak triplet sector gives rise to prompt, displaced, or long-lived particle signatures, offering complementary collider probes to dark matter and low-energy searches.

We study chiral matching of dimension-7 (dim-7) baryon-number-violating operators in low-energy effective field theory. We show that all dim-7 operators can be classified into two distinct Lorentz structures and their chirality-flipped counterparts, and we derive their leading-order hadronic realizations in chiral perturbation theory. As an application, we systematically investigate $\Delta I=3/2$ nucleon decays, including $n\to \ell^-\pi^+$, $p\to \ell^- \pi^+\pi^+$, and $n\to \ell^- \pi^+ (\pi^0, \eta)$, with $\ell=e,~\mu$. Using existing experimental bounds on $n\to \ell^-\pi^+$, we set stringent constraints on the relevant Wilson coefficients and derive improved lower limits on the partial lifetimes of the six three-body modes from their correlations with the two-body modes. We further present a concrete ultraviolet model that generates the dim-7 operators and the associated $\Delta I=3/2$ nucleon decays at leading order. Our results pave the way for exploring dim-7 contributions to nucleon decays and motivate future searches for these exotic modes.

We present a new extension to the toolbox of parton-distribution reweighting methods, which enables a general user to study the impact of an updated theory prediction on the results of a pre-existing parton-distribution global analysis. This new method is a combination of the well-known reweighting method with a new deweighting variant where a dataset is removed from the original analysis in an approximate way. Specific use cases of this method could include e.g. testing the impact of updating the treatment of an observable from N$^n$LO to N$^{n+1}$LO precision in the global analysis, or including previously ignored electroweak, mass, resummation, or higher-twist effects, or even testing the impact of some beyond-standard-model physics. We discuss the implementation of this method in the Hessian formalism, and show its use in a single case study, where we update the treatment of dimuon production in neutrino-induced DIS with the novel semi-inclusive DIS approach.

We investigate backward Compton scattering in which an incident vortex (vx) photon collides head-on with a plane-wave (pw) electron and both final-state particles are projected onto vortex states, $\gamma_{\rm vx}+e^-_{\rm pw}\to\gamma_{\rm vx}+e^-_{\rm vx}$. We derive analytically the scattering amplitude and differential cross sections in the energy and cone angle of either final particle. Rotational symmetry implies a selection rule associated with the conservation of the total angular momentum along the collision axis. A Bessel-Gaussian wave packet is adopted for the incident photon to provide a physical normalization and regularize the boundary singularities of ideal Bessel states. We present numerical results for a $10~{\rm MeV}$ electron colliding with a vortex photon of central energy $1~{\rm MeV}$ or $10~{\rm keV}$. The final-photon distributions exhibit strong energy–angle correlations, topological-charge-dependent interference fringes, and systematic shifts of their dominant peaks, allowing different topological charge sectors to be enhanced through angular or energy post-selection. For a longitudinally polarized incident electron, the dominant channels favor final photons of matching helicity. For the $1~{\rm MeV}$ photon benchmark, the final electron can likewise be produced as a MeV-scale vortex state with a sizable cone angle and a large angular-momentum projection. These results demonstrate that triple-vortex backward Compton scattering offers a potential means of generating and controlling high-energy vortex photons and electrons.

Following important experimental developments, tests of the Diffuse Supernova Neutrino Background (DSNB) are entering a new phase that might lead to a discovery. This motivates the development of simple and broadly applicable tools for comparing theoretical predictions and interpreting experimental results. We show that, over the energy range relevant to current detectors, the DSNB is well described by an exponential spectrum, characterized by the differential flux at 20 MeV, $\phi_{20}$, and a spectral energy scale, $E_0$. We fit the spectra of 24 representative models and demonstrate that the exponential description provides an excellent approximation. We then recast the recent Super-Kamiokande results in the $(\phi_{20},E_0)$ plane, showing that model-specific best fits and upper bounds can be interpreted naturally within this framework. Our results indicate that, above realistic detection thresholds, and until the precision phase is reached, the observable DSNB is effectively a two-parameter phenomenon. We advocate that the $(\phi_{20},E_0)$ parameterization be adopted as a standard, to be used routinely to report future theoretical predictions and experimental results.

The high-energy nuclear recoil event with recoil energy $E_R \approx 248\text{ keV}$ observed by the LZ collaboration provides an exciting hint toward a model with a $1.1\text{ TeV}$ Higgsino inelastic dark matter. Such a recoil energy requires a mass splitting of order ($\delta \approx 350\text{ keV}$) between the two nearly-degenerate neutral states. We show that within the framework of the MSSM, the model predicts a nearly-degenerate charged Higgsino state, chargino, whose mass splitting from the neutral states is of order $\mathcal{O}(350)$~MeV. The subsequent decays of such charginos once produced at colliders would lead to a sub-centimeter charged track or tracklet (with lifetime $\tau \approx 0.025\text{ ns}$) at the detector. We show that such a scenario is not constrained by the current LHC bounds, and could be tested at future high-energy colliders, including HL-LHC, 100 TeV $pp$ colliders, and muon colliders. The most critical requirement is how short a track or tracklet can be reconstructed.

We investigate the transverse-spin asymmetry $A^{\sin\phi_{S_\Lambda}}_{UUT}$ for transversely polarized $\Lambda$ production in semi-inclusive deep inelastic scattering with an unpolarized electron beam and an unpolarized nucleon target. The spin-dependent asymmetry is sensitive to the twist-3 T-odd quark-gluon-quark fragmentation function $\tilde{D}_{T}$, which describes the correlation between an unpolarized fragmenting quark and the transverse polarization of the produced hadron. We calculate $\tilde{D}_{T}$ of the $\Lambda$ hyperon within a diquark model and investigate its contribution to the asymmetry. We determine the model parameters by fitting the fragmentation functions $D_1$ and $G_1$ to the DSV parametrization. Using the numerical results of the model and the available parametrization of the unpolarized parton distribution function $f_1$, we predict the asymmetry in the electroproduction of the $\Lambda$ hyperon in the kinematic regions of the EIC and the EicC. We also examine the impact of including the strange-quark contribution on the transverse-spin asymmetry. In our phenomenological analysis, we include the QCD evolution of the parton distribution function $f_1$ and the fragmentation function $\tilde{D}_{T}$. The results show that the asymmetry is sizable and can be significantly modified by the strange-quark contribution.

The poorly constrained density dependence of the nuclear symmetry energy introduces significant uncertainties in the equation of state (EOS) of dense nuclear matter and, consequently, in neutron-star properties. We systematically investigate how uncertainties in the symmetry energy $E_{\rm sym}$ and its slope $L$ at saturation density $n_0$ affect NS properties within the relativistic mean-field (RMF) framework, including the effects of nonlinear $\sigma$-$\delta$ coupling and possible admixture of dark matter(DM) . For fixed $E_{\rm sym}(n_0)$ and $L(n_0)$, we find that the $\sigma$-$\delta$ coupling with $g_{\sigma\delta}=-0.004$ induces an abnormal softening of the EOS, which simultaneously increasing the maximum NS mass and reducing the stellar radius and tidal deformability. A similar behavior is found in the presence of DM with Fermi momentum $k_F^{\rm DM}=50~\mathrm{MeV}$ at $E_{\rm sym}(n_0)=36~\mathrm{MeV}$. In this case, the RMF EOS satisfies the tidal-deformability constraint from GW170817. We further find that the surface curvature of NSs is strongly correlated with the stiffness of $E_{\rm sym}$, with softer symmetry energy corresponding to larger surface curvature. Our results also indicate that the behavior of $E_{\rm sym}$ around $n_0$ is mainly governed by isoscalar rather than isovector parameters.

In our previous studies, we calculated the cross-section for the production of free $\mu^{+}\mu^{-}$ pairs using a probability function dependent on the impact parameter, and also, we computed bound-free $e^{+}e^{-}$ pair production cross section. In this study, unlike the others, we obtained the cross section for the production of bound-free $e^{+}e^{-}$ pairs using the probability function dependent on the impact parameter. Here also, we simultaneously calculated the cross sections for producing free $\mu^{+}\mu^{-}$ with bound-free $e^{+}e^{-}$ pairs in relativistic $Pb+Pb$ collisions at the LHC with Lorentz factors at $\gamma=1500$ and $\gamma=3000$ reported in the literature. Our calculation is based on second-order perturbation theory, implemented by using Monte Carlo integration techniques. We present impact parameter dependent pair production probabilities for free $\mu^{+}\mu^{-}$ and bound-free $e^{+}e^{-}$ pair production processes. Notably, the bound-free $e^{+}e^{-}$ pair production was evaluated by using a formalism adapted from that of free $\mu^{+}\mu^{-}$ pair production. Our results obtained here for the free $\mu^{+}\mu^{-}$ with bound-free $e^{+}e^{-}$ pair production cross sections are compared with those from other theoretical methods available in the literature. This study aims to provide predictions that can be tested against future experimental data, thereby offering a valuable check for quantum electrodynamics (QED) in strong electromagnetic fields.

We characterize several quantum resources carried by the spins of the $\tau^{+}\tau^{-}$ pair produced in $e^{+}e^{-}$ annihilation. At the Belle-II energy, $\sqrt{s}=10.579\,\mathrm{GeV}$, Bell nonlocality, steerability, entanglement of formation, and coherence are governed by the production angle and are largest for transverse emission, $\vartheta=\pi/2$. Their common kinematic origin is exposed by expressing the spin state as a velocity and angle-dependent mixture of a separable contribution and a maximally entangled component. Within the physical production domain, this representation connects the weakly correlated threshold state at $\sqrt{s}=2m_{\tau}$ to the Bell-state limit approached at ultrarelativistic energies. We then propagate the two-spin state through a phenomenological correlated-dephasing channel to determine how environmental memory and inter-channel classical correlations affect the available resources. Memory effects generate collapses and revivals that are absent from the monotonic Markovian evolution. The analysis therefore separates the kinematic mechanism that creates the spin correlations from the noise properties that control their subsequent survival.

We evaluate the transport coefficients, namely the shear viscosity $\eta$ and the spatial diffusion coefficient of heavy quarks $D_s$, within a Quasi-Particle Model (QPM). In particular, for the first time this has been done by exploiting novel lQCD data at $N_f=3+1$. In such a framework, in which the gluons are massive, the interactions among quarks and gluons have been evaluated via the scattering matrices evaluated from tree level Feynman diagrams. As far as the evaluation of $D_s$ is concerned, the Fokker-Planck approximation for the relativistic Boltzmann equation has been employed for the diffusion of both charm and bottom quarks in either a $N_f=3$ and a $N_f=3+1$ bulk. We have developed a dual-component Chapman-Enskog formalism for the ratio $\eta/s$ (being $s$ the entropy density) of a mixture of quarks and gluons. The temperature dependence of the shear viscosity is then compared to the results from a Green-Kubo approach, based on the numerical resolution of the relativistic Boltzmann equation with a stochastic implementation of the collision integral. Finally, using the above results, we compare the strong and weak coupling regimes for the ratio $(2\pi T D_s)/(4\pi \eta/s)$.

Interest in axions and axion-like particles has resurged, driven by their role in solving the strong CP problem and their appeal as dark matter candidates. The luminosity of the tip of the red giant branch (TRGB) offers a key observable for probing these particle properties. This work aims to improve existing bounds on the axion-electron coupling by adopting a differential observable that is less sensitive to distance, interstellar extinction, the zero-point of bolometric corrections (BCs), and other systematic uncertainties. We use the bolometric magnitude difference between the TRGB and the RGB bump (RGBB) as a distance-independent constraint, applied to three globular clusters of intermediate-to-high metallicity: NGC 104 (47 Tuc), NGC 362, and NGC 5904 (M5). Using photometric catalogs of RGB stars, we determine V- and I-band magnitudes of both features and convert them to bolometric values. After validating that our stellar models reproduce the observed RGBB luminosity, we perform a maximum likelihood analysis with Monte Carlo simulations to propagate uncertainties and derive new bounds on the coupling. A combined analysis of the three clusters yields a maximum likelihood at $g_{13} = g_{ae}/10^{-13} = 0.8$ and a 95% C.L. upper limit of 1.49. Although slightly less stringent than recent bounds from larger multi-cluster samples, this limit is substantially more robust. Under reasonable mass-loss assumptions, $g_{13} \gtrsim 7.5$ is ruled out, as it predicts the disappearance of the HB and AGB phases routinely observed in globular clusters, a limit more than an order of magnitude stronger than current direct experimental bounds such as XENONnT. We demonstrate the effectiveness of this differential, distance-independent method for constraining physics beyond the Standard Model. Applying it to a wider sample of globular clusters would further refine the constraint on $g_{ae}$.

We investigate the momentum-space structure of the gauge-invariant gluon energy-momentum tensor (EMT) for spin-$0$ and spin-$\tfrac{1}{2}$ hadrons in the light-front formalism. We parameterize the nonlocal gluon EMT in terms of so-called gluon gravitational transverse-momentum-dependent distributions (gravitational TMDs) and derive their connections to twist-2 and twist-3 gluon TMDs. Moreover, we demonstrate that particular components of the gluon EMT encode information about the average kinetic four-momentum of gluons and the internal mechanical properties of hadrons-such as pressure and shear distributions.

We develop a nonperturbative functional renormalization group framework within the LPA' to solve the Wetterich flow equation for the $Z_2$-symmetric real singlet extension of the Standard Model at finite temperature, without a low-order polynomial truncation of the loop corrections to the effective potential, using a physics-informed neural network (PINN) representation. In contrast to conventional truncations based on low-order field expansions, our hybrid tree-level-plus-neural-network ansatz yields a continuous, mesh-free description of the effective potential over the full field and scale range. As a proof of concept, we apply the framework to the finite-temperature effective potential relevant to the electroweak phase transition: one-dimensional field-space slices at two benchmark temperatures, and a two-dimensional reconstruction at T=100 GeV yielding a two-step bounce action. The flow is implemented in a multi-domain setup in scale and field space with derivative matching conditions ensuring smoothness and numerical stability. Gauge and Yukawa sectors are incorporated via independently computed perturbative two-loop running couplings, and anomalous dimensions are included in the flow at the LPA' level. We benchmark the network against resummed perturbation theory and against a grid-based relaxation solver of the same equation. Finally, we introduce a soft consistency constraint that keeps the solution close, in sign and order of magnitude, to perturbation theory across the field-space domain. We find this constraint necessary, rather than merely helpful, for selecting a physically sensible solution of the flow equation. The converged result nevertheless retains a residual dependence on this guidance – through hand-tuned weights and an analytic thermal target – which we identify as the central open problem for mesh-free FRG treatments of this kind.

We apply transfer learning (TL) to construct data-driven models of inclusive electron-nucleus cross sections. Starting from an ensemble of deep neural networks pretrained on \(^{12}\)C data, we fine-tune the models separately for \(^{3}\)He, \(^{6}\)Li, \(^{16}\)O, \(^{27}\)Al, \(^{40}\)Ca, and \(^{56}\)Fe. The resulting models improve for all targets, marginally so for oxygen, where the carbon baseline is already adequate, although their predictive robustness depends on the amount, coverage, and precision of the available target data. We systematically study how model performance depends on the number of fine-tuned layers, on the fraction and selection of the training data, and on the overlap between the source and target kinematic domains. The layer-wise analysis shows that oxygen requires only shallow adaptation, whereas helium, calcium, and iron require substantially deeper fine-tuning. Lithium represents the least robust case because of its limited dataset, while aluminum demonstrates a strong sensitivity to a small subset of highly constraining measurements. For selected kinematic configurations outside the coverage of the carbon training data, the adapted models remain consistent with the measurements within their estimated uncertainties. Finally, we compare the resulting predictions with those of the phenomenological F1F2 model.