Within the functional renormalization group framework, we present a fluid-dynamical approach to solving flow equations for models living in a multidimensional field space. To this end, the underlying exact flow equation of the effective potential is reformulated as a set of nonlinear advection-diffusion-type equations which can be solved using the Kurganov-Tadmor central scheme, a modern finite-volume discretization from computational fluid dynamics. We demonstrate the effectiveness of our approach by performing explicit benchmark tests using ($0+0$)-dimensional models with two discretized field-space directions or two symmetry invariants. Our techniques can be directly applied to flow equations of effective potentials of general (fermion-)boson systems with multiple invariants or condensates, as we also demonstrate for two concrete examples in three spacetime dimensions.

The substructure of the $\mathrm{\Delta }(1232)$ resonance is studied in the $p{\gamma }^{*}\to \mathrm{\Delta }(1232)$ transition via helicity amplitudes within a quark-model framework that treats baryons as three-quark systems and includes both quark-core and meson-cloud contributions. In the calculation of the transition amplitudes, the proton wave function is Lorentz boosted from the proton rest frame to the $\mathrm{\Delta }(1232)$ resonance rest frame. The comparison of the calculated amplitudes $A_{1/2}$, $A_{3/2}$, and $S_{1/2}$ with experimental data indicates a non-negligible $L=2$ admixture in the $\mathrm{\Delta }(1232)$, about 80% of the $\mathrm{\Delta }(1232)$ wave function in the S wave and 20% in the D wave. In particular, the $S_{1/2}$ amplitude is found to be dominated by the $L=2$ quark-core component rather than the $L=0$ part. The results challenge the traditional understanding that the $\mathrm{\Delta }(1232)$ baryon is dominantly an $L=0$ state.

We present a comprehensive analysis of the decay ${\mathrm{\Lambda }}_c^{-}\to \mathrm{\Lambda }(\to p\pi ){\mu }^{-}{\overline{\nu }}_{\mu }$ within a model-independent effective field theory framework. Previous studies have been restricted to the three-body decay ${\mathrm{\Lambda }}_c^{+}\to \mathrm{\Lambda }{\mu }^{+}{\nu }_{\mu }$ and considered only left-handed neutrinos within the low-energy effective theory (LEFT). In this work, we extend the analysis to the complete four-body angular distribution for the first time, incorporating the indirect constraints implied by the Standard Model effective field theory (SMEFT) on the LEFT Wilson coefficients. We also include the effects of right-handed neutrino (RHN) operators, enabling a unified treatment of both left- and right-handed neutrino interactions in the $c\to s\mu {\nu }_{\mu }$ transition. Using the global bounds derived from LEFT observables and their SMEFT correlations, we study the impact of allowed new-physics scenarios on a variety of observables, including differential decay rates, forward-backward asymmetries, polarization asymmetries of the final-state hadron and lepton, and the angular coefficients (${\mathcal{M}}_0$ to ${\mathcal{M}}_9$) in the 4-body angular distribution. Our analysis reveals significant deviations from the Standard Model in the observables ${\mathcal{P}}_L^{\mathrm{\Lambda }}$ and ${\mathcal{M}}_1$ for $C_{RL}^V$ and $C_{RR}^V$, and striking $T$-odd effects in ${\mathcal{M}}_7$ for complex $C_{RL}^V$. These features provide sensitive probes of vector-type new physics, such as leptoquark or right-handed current models. The predicted patterns can be tested in forthcoming measurements at BESIII, LHCb, and Belle II, where polarization-sensitive observables in ${\mathrm{\Lambda }}_c$ decays are becoming experimentally accessible.

We study the interaction between photons, dark photons, and axions at future lepton colliders, focusing on single-photon events with missing energy as the experimental signature. We find that future facilities such as the International Linear Collider, Circular Electron-Positron Collider, and Future Circular Collider will be sensitive to the axion–photon–dark photon coupling down to the order of ${10}^{-4}{\mathrm{GeV}}^{-1}$ for dark photon masses around $\mathcal{O}(10\mathrm{GeV})$, assuming that the axion is extremely light and escapes detection. We further show that longitudinal beam polarization at the International Linear Collider can enhance the signal significance by a factor of 4, providing the strongest projected reach in the model parameter space. Existing constraints from Large Electron-Positron II are analyzed for comparison. Furthermore, the mass of dark photon can be determined by measuring the sharp dropoff in the distribution of the recoil mass.

We introduce a generalized definition of the isothermal compressibility (${\kappa }_{T,{\sigma }_Q^2}$) calculable by keeping net conserved charge fluctuations rather than total number densities constant. We present lattice QCD results for this isothermal compressibility, expressed in terms of fluctuations of conserved charges that are related to baryon ($B$), electric charge ($Q$), and strangeness ($S$) quantum numbers. This generalized isothermal compressibility is compared with hadron resonance gas model calculations as well as with heavy-ion collision data obtained at RHIC and the LHC. We find ${\kappa }_{T,{\sigma }_Q^2}=13.8(1.3){\mathrm{fm}}^3/\mathrm{GeV}$ at $T_{\mathrm{pc},0}=156.5(1.5)\mathrm{MeV}$ and ${\widehat{\mu }}_B=0$. This finding is consistent with the rescaled result of the ALICE Collaboration, where we replaced the number of charged hadrons ($N_{\mathrm{ch}}$) by the total number of hadrons ($N_{\mathrm{tot}}$) at freeze-out. Normalizing this result with the QCD pressure ($P$) we find that the isothermal compressibility on the pseudocritical line stays close to that of an ideal gas, i.e., $P{\kappa }_{T,{\sigma }_Q^2}\simeq 1$.

We develop the threshold resummation formalism for semi-inclusive deep-inelastic scattering (SIDIS) using their factorization property and renormalization group invariance. This allows us to obtain the soft and virtual (SV) and next-to SV (NSV) corrections for the SIDIS cross section beyond second order in QCD as well as to systematically resum threshold logarithms to all orders in Mellin space. Thanks to the recent results on next-to-next-to-leading order (NNLO) QCD corrections for the SIDIS and four loop results on the vector form factor and Altarelli-Parisi splitting functions in QCD, we obtain all the SV corrections at fourth order in strong coupling constant $a_s$ except a pure delta function term resulting from the real emissions. The numerical analysis on the impact of resummed contributions at next-to-next-to leading logarithmic ($\overline{\mathrm{NNLL}}$) accuracy matched with the exact fixed order $\mathrm{NNLO}$ results on the cross section demonstrates very good perturbative stability of the perturbation prediction, including the reduced dependence on the renormalization and factorization scales ${\mu }_R$ and ${\mu }_F$.

The spatial distributions of $[ud]$ diquark and heavy-light diquark of the SU(3)-flavor antitriplet charmed baryons are investigated by the two singly Cabibbo-suppressed hadronic weak decays, ${\mathrm{\Lambda }}_c\to \mathrm{\Lambda }{K}^{+}$ and ${\mathrm{\Lambda }}_c\to {\mathrm{\Sigma }}^0{K}^{+}$ within the nonrelativistic constituent quark model. The above two spatial distributions are reflected by the two parameters ${\alpha }_{\rho }$ and ${\alpha }_{\lambda }$, which are the harmonic oscillator strength parameters of the charmed baryons. These two parameters obtain strong constraints from the decay widths of ${\mathrm{\Lambda }}_c\to \mathrm{\Lambda }{K}^{+}$ and ${\mathrm{\Lambda }}_c\to {\mathrm{\Sigma }}^0{K}^{+}$. The larger the harmonic oscillator parameter is, the more compact the spatial distribution will become. The current ${\alpha }_{\rho }$ and ${\alpha }_{\lambda }$ indicate that neither the light diquark nor the heavy-light diquark turns out to favor a compact structure. In addition, some selection rules, including the “$\mathrm{\Lambda }$ selection rule,” can be useful for the search of excited baryons in the heavy-flavor baryon hadronic weak decays.

We present flux-integrated charged-current ${\nu }_{\mu }$ cross-section measurements on argon for final states containing exactly one ${\pi }^{\pm }$ and no other hadrons except nucleons. The analysis uses data from the MicroBooNE experiment in the Booster Neutrino Beam, corresponding to $1.11\times {10}^{21}$ protons on target. Total and single-differential cross-section measurements are provided within a phase space restricted to muon momenta above 150 MeV, pion momenta above 100 MeV, and muon-pion opening angles smaller than 2.65 rad. Differential cross sections are reported with respect to the scattering angles of the muon and pion relative to the beam direction, their momenta, and their combined opening angle. The differential cross section with respect to muon momentum is based on a subset of selected events with the muon track fully contained in the detector, whereas the cross section with respect to pion momentum is based on a subset of selected events rich in pions that have not hadronically scattered on the argon before coming to rest. The latter has not been measured on argon before. The total cross section is measured as $(3.75\pm 0.07(\mathrm{stat})\pm 0.80(\mathrm{syst}))\times {10}^{-38}{\mathrm{cm}}^2/\mathrm{Ar}$ at a mean energy of approximately 0.8 GeV. Comparisons of the measured cross sections with predictions from multiple neutrino-nucleus interaction generators show good overall agreement, except at very forward muon angles.

We deployed the Mobile Skipper Testing Apparatus $\sim 33\mathrm{m}$ away from the Compact Muon Solenoid collision point, the first skipper-CCD detector probing low-energy particles produced in high-energy collisions at the Large Hadron Collider. In this work, we search for beam-related events using data collected in 2024 during beam-on and beam-off periods. The dataset corresponds to integrated luminosities of $113.3{\mathrm{fb}}^{-1}$ and $1.54{\mathrm{nb}}^{-1}$ for the proton-proton and Pb-Pb collision periods, respectively. We report observed event rates in a model-independent framework across two ionization regions: $\le 20e^{-}$ and $>20e^{-}$. For the low-energy region, we perform a likelihood analysis to test the null hypothesis of no beam-correlated signal. We found no significant correlation during proton-proton and Pb-Pb collisions. For the high-energy region, we present the energy spectra for both collision periods and compare event rates for images with and without luminosity. We observe a slight increase in the event rate following the Pb-Pb collisions, coinciding with a rise in the single-electron rate, which will be investigated in future work. Using the low-energy proton-proton results, we place 95% confidence level constraints on the mass-millicharge parameter space of millicharged particles. Overall, the results in this work demonstrate the viability of skipper-CCD technology to explore new physics at high-energy colliders and motivate future searches with more massive detectors.

Deriving the Yukawa couplings and the resulting fermion masses and mixing angles of the Standard Model (SM) from a more fundamental theory remains one of the central outstanding problems in theoretical high-energy physics. It has long been recognized that string theory provides a framework within which this question can, at least in principle, be addressed. While substantial progress has been made in studying flavor physics in string compactifications over the past few decades, a concrete string construction that reproduces the full set of observed SM flavor parameters remains unknown. Here, we take a significant step in this direction by identifying two explicit $E_8\times E_8$ heterotic string models compactified on a Calabi-Yau threefold with Abelian, holomorphic, and polystable vector bundles with minimal supersymmetric (MS) SM spectrum. Subject to reasonable assumptions about the moduli, we show that these models reproduce the correct values of the quark and charged lepton masses, as well as the quark mixing parameters, at some point in their moduli spaces. The resulting four-dimensional theories are $\mathcal{N}=1$ supersymmetric, contain no exotic fields, and realize a $\mu$-term suppressed to the electroweak scale. While the issues of moduli stabilization and supersymmetry breaking are not addressed here; our main result constitutes a proof of principle: There exist choices of topology and moduli within heterotic string compactifications which allow for an MSSM spectrum with the correct flavor parameters.

Recent proposals equate the size of Einstein-Rosen (ER) bridges in Jackiw-Teilboim (JT) gravity to spread complexity of a dual, double-scaled Sachdev-Ye-Kitaev theory (DSSYK). We show that the auxiliary “chord basis” of these proposals is an extrapolation from a subexponential part of the finite-dimensional physical Krylov basis of a spreading thermofield double state. The physical tridiagonal Hamiltonian coincides with the DSSYK approximation on the initial Krylov basis, but deviates markedly over an exponentially large part of the state space. We nonperturbatively extend the identification of ER bridge size and spread complexity to the complete Hilbert space, and show that it saturates at late times. We use methods for tridiagonalizing random Hamiltonians to study all universality classes to which large-N SYK theories and JT gravities can belong. The saturation dynamics depends on the universality class, and displays “white hole” physics at late times where the ER bridge shrinks from maximum size to a plateau. We describe extensions of our results to higher dimensions.

The two-parameter inhomogeneous and time-dependent Pimentel solution of Brans-Dicke theory is analyzed to probe and extend the new thermal view in which general relativity is the zero-temperature (equilibrium) state of scalar-tensor gravity. As the parameters vary, we uncover phenomenology not found before with other exact solutions, nor contemplated thus far in the general theory. In the process, we also discuss the anomalous limit to general relativity of the Pimentel geometry and show how the Mars solution of the Einstein equations is its Einstein frame version, elucidating the relation between these geometries.

We present a semianalytical binary black hole (BBH) metric approximation that models the entire evolution of the system from inspiral to merger. The metric is constructed as a boosted Kerr-Schild superposition following post-Newtonian (PN) trajectories at the fourth PN order in the inspiral phase. During merger, we interpolate the binary metric in time to a single black hole remnant with properties obtained from numerical relativity fitting formulas. The new metric can model BBHs with arbitrary spin direction, mass ratio, and eccentricity at any stage of their evolution in a fast and computationally efficient way. We analyze the properties of our new metric and compare it with a full numerical relativity evolution. Hamiltonian constraints are well behaved even at merger, and the mass and spin measured self-consistently on the black hole apparent horizon deviate on average only $\lesssim 10\%$ compared to the full numerical evolution. We perform general relativistic magneto-hydrodynamical simulations for two cases: merging black holes in a uniform gas, and inspiralling black holes accreting from a magnetized circumbinary disk. We demonstrate that, in both cases, the properties of the gas, such as the accretion rate, are remarkably similar between the two approaches, with small average differences. We demonstrate that our approximate metric significantly reduces computational cost compared to full numerical relativity, enabling a new class of high-resolution, long-term binary accretion simulations. The numerical implementation of the metric is now open source and optimized for numerical work.

Deforming the algebra of constraint is a well-known approach to effective loop quantum cosmology. More generally, it is a consistent way to modify gravity from the Hamiltonian perspective. In this framework, the Hamiltonian (scalar) constraint is usually the only one to be holonomy corrected. As a heuristic hypothesis, we consider the possibility to also correct the diffeomorphism and Gauss constraints. It is shown that it is impossible to correct the diffeomorphism constraint without correcting the Gauss one, while maintaining a first-class algebra. However, if all constraints are corrected, the algebra can be closed. The resulting differential equations to be fulfilled by the corrections (of the background and of the perturbations) are derived.

The coupling between matter fields and gravity (encoded in the geometry of spacetime) can be realized in various ways. Most commonly, a minimal coupling principle is employed, meaning that all matter fields, except spinors, couple only to the spacetime metric, while spinors additionally couple to the spacetime connection. Nonminimal couplings between matter fields and spacetime curvature can arise, for example, from quantum field theory on curved spacetime through renormalization corrections, in gauge theories of gravity, and in effective field theories. In this article, we consider a nonminimal coupling $F^{\mu \nu }{\tilde{R}}_{\mu \nu }$ between the field strength tensor of the electromagnetic field $F_{\mu \nu }$ and the antisymmetric part of the Ricci tensor ${\tilde{R}}_{[\mu \nu ]}$ in Riemann-Cartan geometry, which is based on a general metric-compatible connection with torsion. We find an exact four-dimensional vacuum solution that generalizes the Reissner-Nordström black hole from Einstein-Maxwell and reveals new interactions between the intrinsic torsion-spin charge and the electric charge. Qualitatively, this solution exhibits two distinct features: the effective charge is not constrained to be positive, and the sign of the electric charge influences its gravitational effects. We also derive slowly rotating solutions in three dimensions, representing a generalized slowly rotating BTZ black hole solution with couplings among the magnetic and electric charges, the angular momentum, and the intrinsic torsion-spin charge.

The ultrahigh frequency (above 10 kHz) gravitational wave (GW) window provides a unique opportunity to detect primordial GWs, free from astrophysical foregrounds that dominate lower frequencies. A stochastic GW background in this range is generically predicted from cosmological phase transitions and topological defects associated with grand unification and other ultrahigh energy theories. We establish a universal quantum limit framework for various detection schemes, setting a fundamental bound on GW detectability. Our analysis reveals that backgrounds in the kHz–MHz range are in principle observable, whereas higher-frequency signals lie below the quantum limit. These results offer theoretical guidance for future detector designs and open new avenues for probing early universe physics.

While theoretically established for decades, the Penrose process—energy extraction from rotating black holes—still lacks clear observational evidence. A promising theoretical framework posits magnetic reconnection in the ergosphere as a trigger, causing a plasmoid to separate into an escaping positive-energy fragment and an infalling negative-energy one. In this work, we investigate the observational imprints of this scenario. We treat the energized plasmoid as a hotspot and calculate its light curves for a realistic plasma magnetization. In particular, we further compare with the scenario in which the plasmoid, after fragmentation, falls into the black hole with positive energy, while all other conditions remain unchanged. Our results reveal that the process of fragmentation generates distinct flares, whose characteristics depend heavily on whether the infalling fragment carries negative or positive energy. We propose that these differences serve as identifiable signatures of the Penrose process.

Spacetimes in general relativity can be uniquely decomposed into a set of multipole moments. Given the usefulness of moments in the categorization of radiation patterns, tidal deformations, and other phenomena associated with compact objects, a number of studies have explored their construction in beyond-Einstein theories of gravity. It is shown here that uniqueness does not necessarily extend across theories: by comparing a few static and spherically symmetric solutions in different theories, we find that two distinct objects can possess the same Geroch-Hansen moments. Moreover, two metrics can match and yet take different moments. Implications of this result are explored in the context of black-hole shadows and “universal” relations hinging on moment computations.

We investigate cosmic structure formation in the framework of a path-integral formulation of an $N$-particle ensemble in phase space, dubbed resummed kinetic field theory (RKFT), up to one-loop perturbative order. In particular, we compute power spectra of the density contrast, the divergence and curl of the momentum density and arbitrary $n$-point cumulants of the stress tensor. In contrast to earlier works, we propose a different method of sampling initial conditions, with a Gaussian initial phase-space density. Doing so, we exactly reproduce the corresponding results from Eulerian standard perturbation theory (SPT) at one-loop order, showing that formerly found deviations can be fully attributed to inconsistencies in the previous sampling method. Since, in contrast to SPT, the full phase-space description does not assume a truncation of the Vlasov hierarchy, our findings suggest that nonperturbative techniques are required to accurately capture the physics of cosmic structure formation.

Accurate and efficient simulation-based emulators are essential for interpreting cosmological survey data down to nonlinear scales. Multifidelity emulation techniques reduce simulation costs by combining high- and low-fidelity data, but traditional regression methods such as Gaussian processes struggle with scalability in sample size and dimensionality. In this work, we present T2N-MusE, a neural network framework characterized by (i) a novel two-step multifidelity architecture, (ii) a two-stage Bayesian hyperparameter optimization, (iii) a two-phase $k$-fold training strategy, and (iv) a per-$z$ principal component analysis strategy. We apply T2N-MusE to selected data from the goku simulation suite, covering a 10-dimensional cosmological parameter space, and build emulators for the matter power spectrum over a range of redshifts with different configurations. We find the emulators outperform our earlier Gaussian process models significantly and demonstrate that each of these techniques is efficient in training neural networks or/and effective in improving generalization accuracy. We observe a reduction in the mean error by more than a factor of 5 and in the worst-case error by approximately a factor of 8 in leave-one-out cross-validation, relative to previous work. This framework has been used to build the most powerful emulator for the matter power spectrum, gokunemu, and will also be used to construct emulators for other statistics in future.