Gravitational form factors are often interpreted as providing access to stresses inside hadrons, in particular through Fourier transforms of the form factors $D$ and $\overline{c}$. Some researchers, however, have expressed skepticism of this interpretation. I revisit the question, and argue that it is indeed appropriate to interpret these quantities as stress distributions. I consider the hydrogen atom’s ground state as a familiar example, and use the pilot wave interpretation of quantum mechanics to give the distributions a clear meaning. A striking result is that $\overline{c}$—rather than $D$—quantifies the force law binding the system, which can be understood through Cauchy’s first law of motion.

We have investigated the process ${\mathrm{\Lambda }}_c^{+}\to {\pi }^{+}\eta n$ by taking into account the contributions from the nucleon resonance $N(1535)$ and the scalar meson $a_0(980)$, which could be dynamically generated by the interaction of the $S$-wave pseudoscalar meson-octet baryon and the $S$-wave pseudoscalar meson-pseudoscalar meson, respectively. Our results show that, in $\eta n$ invariant mass distribution, there is a significant near-threshold enhancement structure, which could be associated with $N(1535)$. On the other hand, one can find a clear cusp structure of $a_0(980)$ in ${\pi }^{+}\eta$ invariant mass distribution. We further estimate the ratio $R=\mathcal{B}({\mathrm{\Lambda }}_c^{+}\to a_0(980{)}^{+}n)/\mathcal{B}({\mathrm{\Lambda }}_c^{+}\to {\pi }^{+}\eta n)\approx 0.313$. Our results can be tested by BESIII, Belle II, and the proposed Super Tau-Charm Facility experiments in the future.

We revisit the notion of nuclear parton-to-pion fragmentation functions at next-to-leading order accuracy as an effective description of hadroproduction in nuclear environments such as in semi-inclusive lepton-nucleus deep-inelastic scattering and in single inclusive proton-nucleus collisions. We assess their viability in the face of very precise data collected for the latter at the CERN-LHC over the past decade as well as recent measurements of the former carried out by the CLAS experiment at JLab.

We conduct the first comprehensive P-wave four-body dynamical calculations of the fully charmed tetraquark systems within the quark potential model. We apply the Gaussian expansion method to solve the four-body Schrödinger equation, incorporating both dimeson and diquark-antidiquark spatial configurations. The matrix elements of P-wave states are calculated analytically using the infinitesimally shifted Gaussian basis functions. With the complex scaling method, we obtain several fully charmed P-wave resonant states with compact tetraquark configuration in the mass region of (7.0, 7.2) GeV, including states with exotic quantum numbers $J^{PC}=0^{--},1^{-+}$. However, we find no resonant states with the mass $M<7\mathrm{GeV}$ and width $\mathrm{\Gamma }<200\mathrm{MeV}$. Combining the present investigation with our previous results on S-wave fully charmed tetraquark systems [, Phys. Rev. D 109, 054034 (2024)], we find no candidates for the experimental states $X(6400)$ and $X(6600)$ in the quark model.

We carry out a comprehensive analysis of the Landau-Khalatnikov-Fradkin transformations for a charged fermion propagator at the two-loop level in quantum electrodynamics (QED). Starting with an arbitrary covariant gauge $\xi$ and space-time dimension $d$, we provide its explicit expressions in three- and four-dimensional QED. We begin with the tree-level fermion propagator in the Landau gauge and gauge-transform it to obtain an analytical expression for an all order result in an arbitrary covariant gauge. We expand it out to two loops both for the massless and massive propagators in three and four space-time dimensions. In addition to comparing with all earlier results in the literature wherever possible, we also study constraints of multiplicative renormalizabilty of our results in four-dimensional QED which are logarithmically divergent. Finally, we analyze representative solutions of the fermion propagator which correspond to dynamical chiral symmetry breaking and mass generation in QED. We study the gauge dependence of these emergent solutions, that of the Euclidean pole mass and the chiral fermion condensate.

To improve the theoretical understanding of multiquark states like $Z_b(10610)$ and $Z_b(10650)$, we calculate the heavy-meson heavy-(anti)meson scattering potential up to next-to-leading order, $\mathcal{O}(Q^2)$, within chiral effective field theory ($\chi \mathrm{EFT}$) employing a power counting scheme that explicitly keeps track with the large momentum scale $Q\sim \sqrt{2\mu \delta }$ (where $\delta =m_V-m_P$ is the vector-pseudoscalar mass difference and $\mu$ their reduced mass) introduced by the coupled channel dynamics. We provide expressions for the two-pion exchange (TPE) terms up to $\mathcal{O}(Q^2)$ and their partial-wave decomposition. We show that these potentials are well approximated by contact terms at $\mathcal{O}(Q^2)$, with minor residual nonanalytic TPE contributions, supporting $\chi \mathrm{EFT}$ convergence in the theoretical predictions for $Z_b(10610)$ and $Z_b(10650)$, as well as their spin partners. These findings are also relevant for $D^{(*)}{D}^{(*)}$ scattering, especially for the $T_{cc}$ state, for both physical and lattice quantum chromodynamics (QCD) data with moderately larger pion masses. We further demonstrate that the differences between isovector and isoscalar potentials for heavy mesons are naturally explained by the TPE contributions.

The early postmerger phase of a binary neutron-star coalescence is shaped by characteristic rotational velocities as well as violent density oscillations and offers the possibility to constrain the properties of neutron star matter by observing the gravitational wave emission. One possibility to do so is the investigation of gravitational wave damping through the bulk viscosity which originates from violations of weak chemical equilibrium. Motivated by these prospects, we present a comprehensive report about the implementation of the self-consistent and second-order formulation of the equations of relativistic hydrodynamics for dissipative fluids proposed by Müller, Israel, and Stewart. Furthermore, we report on the results of two test problems, namely the viscous damping of linear density oscillations of isolated nonrotating neutron stars and the viscous migration test, both of which confirm our implementation and can be used for future code tests. Finally, we present fully general-relativistic simulations of viscous binary neutron-star mergers. We explore the structural and thermal properties of binary neutron-star mergers with a constant bulk-viscosity prescription and investigate the impact of bulk viscosity on dynamical mass ejection. We find that inverse Reynolds numbers $\sim 1\%$ can be achieved for the highest employed viscosity thereby suppressing the dynamically ejected mass by a factor of $\sim 5$ compared to the inviscid case.

We apply the method of moments to the relativistic Boltzmann-Vlasov equation and derive the equations of motion for the irreducible moments of arbitrary tensor-rank of the invariant single-particle distribution function. We study two cases, in the first of which the moments are taken to be irreducible with respect to the little group associated with the timelike fluid four-velocity, while in the second case they are assumed to be also irreducible with respect to a spacelike four-vector orthogonal to the fluid four-velocity, which breaks the spatial isotropy to a rotational symmetry in the plane transverse to this vector. A systematic truncation and closure of the general moment equations leads, in the first case, to a theory of relativistic higher-order dissipative resistive magnetohydrodynamics. In the second case, we obtain a novel theory of dissipative resistive anisotropic magnetohydrodynamics, where the momentum anisotropy is, in principle, independent from that introduced by the external magnetic field.

Using renormalization group theory we show that oscillons in ($1+1$) dimensions can be obtained, at the leading nonlinear order, from $Q$-balls of universal complex field theories. For potentials with a nonzero cubic or quartic term the universal $Q$-ball theory is well approximated by the integrable complex sine-Gordon model. This allows us to generalize the usual perturbative expansion by Fodor et al. beyond the simplest unmodulated oscillon case. Concretely, we explain the characteristic amplitude modulations of excited oscillons as an effect of formation of a two-Q-ball (two-oscillon) bound state.

We study the behavior of the vacuum in Euclidean dynamical triangulations (EDT). Algorithmic improvements and better lattice spacing determinations allow us to test the properties of the emergent de Sitter geometries of our simulations to higher precision than previously possible. Although the agreement with de Sitter is good, the improved precision reveals deviations that can be interpreted as nontrivial vacuum dynamics, well described by a cosmological constant that runs with scale. The simulations show that the dominant running is quadratic and that the scale can be identified with the Hubble rate. Several key cross-checks support this picture, including consistent results across multiple lattice spacings and the fact that the null energy condition is not violated. The parameters of the running are fully determined by simulations, enabling predictions when extrapolated to the scales relevant for our Universe. This leads to a model for dark energy that is compatible with current observations, but which predicts deviations from the Standard Model of cosmology at the $\mathcal{O}({10}^{-3})$ level in observables that could be tested with future improvements in precision measurements.

The full width of the light isovector hybrid meson $H_{\mathrm{V}}$ with spin-parities $1^{-+}$ and content $(\overline{u}gu-\overline{d}gd)/\sqrt{2}$ is evaluated by considering the decays $H_{\mathrm{V}}\to {\rho }^{\pm }{\pi }^{\mp }$, $b_1^{\pm }{\pi }^{\mp }$, $f_1(1285)\pi$, $f_1(1420)\pi$, $\eta \pi$, and ${\eta }^{\prime }\pi$. To calculate the partial widths of these channels, we use the quantum chromodynamics (QCD) three-point sum rule method which is necessary to determine strong couplings at the corresponding hybrid-meson-meson vertices. It turns out that the main contribution to the full width $\mathrm{\Gamma }[H_{\mathrm{V}}]=(109.7\pm 16.0)\mathrm{MeV}$ of the hybrid meson comes from the processes $H_{\mathrm{V}}\to {\rho }^{\pm }{\pi }^{\mp }$ partial width of which amounts to $\approx 67\mathrm{MeV}$. The effects of the decays $H_{\mathrm{V}}\to b_1\pi$ and $H_{\mathrm{V}}\to f_1\pi ,f_1^{\prime }\pi$ are also sizeable: Their partial widths are equal to 13 MeV and 20 MeV, respectively. The decays to $\eta \pi$ and ${\eta }^{\prime }\pi$ mesons are subdominant reactions, nevertheless they form $\approx 9\%$ of the full width $\mathrm{\Gamma }[H_{\mathrm{V}}]$. Results obtained in this work may be interesting to unravel the tangle of predictions about $H_{\mathrm{V}}$ existing in the literature, as well as useful in analyses of different resonances.

We study the exclusive photoproduction of a ${\pi }^0\gamma$ pair with large invariant mass $M_{\gamma \pi }^2$, which is sensitive to the exchange of either two quarks or two gluons in the $t$ channel. In this paper, we show that the process involving two-gluon exchanges does not factorize in the Bjorken limit at the leading twist. This can be explicitly demonstrated by the fact that there exist diagrams, which contribute at the leading twist, for which Glauber gluons are trapped, due to the pinching of the contour integration of both the plus and minus component of the Glauber gluon momentum. For the same reason, ${\pi }^0$-nucleon scattering to two photons also suffers from the same issue. On the other hand, we stress that there are no issues with respect to collinear factorization for the quark channels. By considering an analysis of all potential reduced diagrams of leading pinch-singular surfaces, we argue that the quark channel is safe from Glauber pinches, and therefore, a collinear factorization in that case follows through without any problems. This means that processes where gluon exchanges are forbidden, such as the exclusive photoproduction of ${\pi }^{\pm }\gamma$ and ${\rho }^{0,\pm }\gamma$, are unaffected by the factorization breaking effects we point out in this paper.

We initiate the study of loop-level holographic correlators in the presence of defects. We present a unitarity method that constructs loop corrections from lower order data. As an example, we apply this method to 6D $\mathcal{N}=(2,0)$ theories with $\frac{1}{2}$-BPS surface defects and report the first holographic two-point function at one loop.

A discrepancy of approximately $5\sigma$ exists between the two known results for the tenth-order QED contribution to the anomalous magnetic moment of the electron, calculated from Feynman vertex diagrams without fermion loops. To investigate this, we decomposed this contribution into 389 parts based on a self-energy diagram representation, enabling a diagram-by-diagram numerical comparison of the two calculations. No significant discrepancies were found for individual diagrams. However, the numerical differences of the 98 diagrams sharing a common structure were not randomly distributed. The accumulation of these differences resulted in the $5\sigma$ discrepancy. A recalculation with increased statistics in the Monte Carlo integration was performed for these 98 diagrams. By replacing the old values with the new ones for these 98 integrals, we have obtained a revised result of $6.800\pm 0.128$, thereby resolving the discrepancy.

We determine the nucleon-sigma terms from lattice quantum chromodynamics (QCD). We find that the dominant excited state contamination in the nucleon three-point function with a scalar current is due to the transition between the nucleon and a S-wave scattering state of a nucleon and a scalar (sigma) meson. In this proof-of-concept study, we analyze a single $N_f=3$ ensemble with the unphysically large pion mass $M_{\pi }=429\mathrm{MeV}$. Excited state contamination is substantially reduced compared to the standard method when employing nucleon-sigma type interpolating operators within a generalized eigenvector analysis.

We derive an effective Kerr metric from an effective Schwarzschild metric inspired by loop quantum gravity using the Newman-Janis algorithm. The resulting spacetime is free from the classical ring singularity and does not allow the existence of closed timelike curves, due to a lower radial bound in its domain inherited from the spherically symmetric seed metric. We provide a possible interpretation of this lower bound by expressing the metric in generalized Painlevé-Gullstrand coordinates. We analyze the horizon structure and ergoregion highlighting the similarities and differences with the classical Kerr spacetime. The study of the trajectory of a zero angular momentum observer reveals two novel effects purely due to quantum gravity: one related to the frame dragging and the other to the repulsive behavior in the deep quantum region. We derive an effective separation Carter constant and the geodesic equations. Finally, we specialize the geodesic analysis to equatorial circular trajectories, obtaining a modified third Kepler law and the equation defining the photon sphere.

We consider SQCD for $N_f<N_c$. We use a brane configuration in type IIA string theory to propose a Seiberg dual. The brane configuration that realizes the magnetic theory contains $N_f$ branes and $N_c-N_f$ antibranes, leading to an $SU(N_c-N_f)$ gauge theory with $N_f$ flavors. The potential between the branes triggers a RG flow, and we argue that the IR theory realizes the Affleck-Dine-Seiberg superpotential. We use both field theory arguments, in particular, anomaly matching, and a lift of the type IIA brane configuration to $M$ theory, in order to support our proposal.

We show that the gravitational waveform emitted by a binary on an eccentric orbit can be naturally decomposed into a series of harmonics. The frequencies of these harmonics depend upon the radial frequency, $f_{\mathrm{r}}$, determined by the time to return to apoapsis, and the azimuthal frequency, $f_{\varphi }$, determined by the time to complete one orbit relative to a fixed axis. These frequencies differ due to periapsis advance. Restricting to the (2, 2) multipole, we find that the frequencies can be expressed as $f=2f_{\varphi }+k{f}_{\mathrm{r}}$. We introduce a straightforward method of generating these harmonics and show that the majority of the signal power is contained in the $k=-1,0,1$ harmonics for moderate eccentricities. We demonstrate that by filtering these three leading harmonics, we are able to obtain a good estimate of the orbital eccentricity from their relative amplitudes.

The present work shows that the second law of thermodynamics gets naturally satisfied during the entire cosmic evolution of the Universe starting from inflation to the late dark energy era, without imposing any exotic condition. This makes the interconnection between cosmology and thermodynamics more concrete. Consequently, it also depicts that why the matter fields are not in thermal equilibrium with the apparent horizon during most of the cosmic era of the Universe, except for the fluids with $\omega =-1/3$ leading to the transitions of the Universe from an accelerating to a decelerating era and vice-versa.

The canonical cosmological model to explain the recent acceleration of the universe relies on a cosmological constant, and most dynamical dark energy and modified gravity model alternatives are based on scalar fields. Still, further alternatives are possible. One of these involves vector fields: under certain conditions, they can lead to accelerating universes while preserving large-scale homogeneity and isotropy. We report quantitative observational constraints on a model previously proposed by Armendáriz-Picón and known as the cosmic triad. We consider several subclasses of the model, which generically is a parametric extension of the canonical $\mathrm{\Lambda }$ Cold Dark Matter ($\mathrm{\Lambda }\mathrm{CDM}$) model, as well as two possible choices of the triad’s potential. Our analysis shows that any deviations from this limit are constrained to be small. In particular the preferred present-day values of the matter density and the dark energy equation of state are fully consistent with those obtained, for the same datasets, in flat $\mathrm{\Lambda }\mathrm{CDM}$ and $w_0\mathrm{CDM}$. The constraints mildly depend on the priors on the dark energy equation of state, specifically on whether phantom values thereof are allowed, while the choice of potential does not play a significant role since any such potential is constrained to be relatively flat.