We calculate the low-lying spectra for the positive-parity $\mathrm{\Delta }$ and $N$ at two pion masses of 358 and 278 MeV using an isotropic clover action with two degenerate light-quark and one strange-quark flavors through the application of the generalized variational method within the distillation framework. The spectrum exhibits the general feature observed in previous calculations using an anistropic clover lattice, with a counting of states at least as rich as the quark model. Furthermore, we identify states that are hybrid in nature, where gluonic degrees of freedom play a structural role, indicating that such states appear as a feature of the excited baryon spectrum, irrespective of the lattice action, or the precise details of the smearing of the lattice interpolating operators used to identify such states.

We study the transition widths of $\mathrm{\Upsilon }(10753)$ and $\mathrm{\Upsilon }(11020)$ into standard bottomonium under the hypothesis that they correspond to the two lowest laying $1^{--}$ hybrid bottomonium states. We employ weakly coupled potential NRQCD an effective field theory incorporating the heavy-quark and multipole expansions. We consider the transitions generated by the leading order and next-to-leading order singlet-octet operators. In the multipole expansion the heavy-quark matrix elements factorize from the production of light-quark mesons by gluonic operators. For the leading order operator we compute the widths with a single ${\pi }^0$, $\eta$ or ${\eta }^{\prime }$ in the final state and for the next-to-leading operator for ${\pi }^{+}{\pi }^{-}$ or $K^{+}{K}^{-}$. The hadronization of the gluonic operators is obtained, in the first case, from the axial anomaly and a standard ${\pi }^0-\eta -{\eta }^{\prime }$ mixing scheme and, in the second case, we employ a coupled-channel dispersive representation matched to chiral perturbation theory for both the $S$- and $D$-wave pieces of the gluonic operator. We compare with experimental values and semi-inclusive widths. Our results strongly suggest that $\mathrm{\Upsilon }(11020)$ is indeed a hybrid bottomonium state.

We consider the production of electroweak $Z$ or $W^{\pm }$ bosons associated with $J/\psi$ mesons at the LHC conditions. Our attention is focused on new partonic subprocesses which yet have never been considered in the literature, namely, the charmed or strange quark excitation subprocesses followed by the charmed quark fragmentation $c\to J/\psi +c$. Additionally we take into account the effects of multiple quark and gluon radiation in the initial and final states. We find that the contributions from the new mechanisms are important and significantly reduce the gap between the theoretical and experimental results on the $J/\psi +Z$ and $J/\psi +W^{\pm }$ production cross sections.

The heavy quark drag and momentum diffusion coefficients in the presence of both the collisional and radiative processes have been studied in a hot viscous QCD medium. The thermal medium effects are incorporated by employing the effective fugacity quasiparticle model based on the lattice QCD equation of state. Viscous effects are embedded into the heavy quark transport through the near-equilibrium distribution functions of the constituent medium particles of the quark-gluon plasma. The viscous corrections to the momentum distributions have been estimated from the effective Boltzmann equation. The effect of shear viscous correction on drag and diffusion is investigated by considering the soft gluon radiation by heavy quarks along with the elastic collisional processes of the heavy quark with the light quarks and gluons within the quark-gluon plasma medium. The momentum and temperature dependence of the heavy quark transport coefficients are seen to be sensitive to the viscous coefficient of the quark-gluon plasma for the collisional and radiative processes. The collisional and radiative energy loss of the heavy quark in the viscous quark-gluon plasma has also been explored.

The graviton soft wall (GSW) model provides a unified description of the scalar glueball and meson spectra with a unique energy scale. This success has led us to extend the analysis to the description of the spectra of other hadrons. We use this model to calculate masses of the odd and even ground states of glueballs for various spins, and show that the GSW model is able to reproduce the Regge trajectory of these systems. In addition, the spectra of the $\rho$, $a_1$ and $\eta$ mesons will be addressed. Results are in excellent agreement with current experimental data. Furthermore such an achievement is obtained without any additional parameters. Indeed, the only two parameters appearing in these spectra are those that were previously fixed by the light scalar meson and glueball spectra. Finally, in order to describe the $\pi$ meson spectrum, a suitable modification of the dilaton profile function has been included in the analysis to properly take into account the Goldstone realization of chiral symmetry. The present investigation confirms that the GSW model provides an excellent description of the spectra of mesons and glueballs with only a small number of parameters unveiling a relevant predicting power.

It has been previously shown that a particular nonperturbative constituent-quark model of hadrons describes experimental measurements of electromagnetic form factors of light charged mesons through a small number of common phenomenological parameters, matching at the same time the quantum-chromodynamics (QCD) asymptotics for the $\pi$-meson form factor at large momentum transfer. Here we start with the determination of the $K^0$ electromagnetic form factor in this approach. Precise measurement of the $K^0$ charge radius makes it possible to constrain model parameters with high accuracy. Then, with all parameters fixed, we revisit the $K^{+}$ form factor and find that it matches experimental measurements in the infrared, lattice results at moderate momentum transfer, and the perturbative QCD asymptotics in the ultraviolet. In this way we obtain a narrow constraint on the $K^{+}$ charge radius, $⟨r_{K^{+}}^2⟩={0.403}_{-0.006}^{+0.007}{\mathrm{fm}}^2$, and extend the successful infrared-ultraviolet connection from $\pi$ to $K$ mesons.

We study the diffusion properties of the strongly interacting quark-gluon plasma (sQGP) and evaluate the diffusion coefficient matrix for the baryon (B), strange (S) and electric (Q) charges—${\kappa }_{q{q}^{\prime }}$ ($q,q^{\prime }=\mathrm{B},\mathrm{S},\mathrm{Q}$) and show their dependence on temperature $T$ and baryon chemical potential ${\mu }_{\mathrm{B}}$. The nonperturbative nature of the sQGP is evaluated within the dynamical quasiparticle model (DQPM) which is matched to reproduce the equation of state of the partonic matter above the deconfinement temperature $T_c$ from lattice QCD. The calculation of diffusion coefficients is based on two methods: (i) the Chapman-Enskog method for the linearized Boltzmann equation, which allows to explore nonequilibrium corrections for the phase-space distribution function in leading order of the Knudsen numbers as well as (ii) the relaxation time approximation (RTA). In this work we explore the differences between the two methods. We find a good agreement with the available lattice QCD data in case of the electric charge diffusion coefficient (or electric conductivity) at vanishing baryon chemical potential as well as a qualitative agreement with the recent predictions from the holographic approach for all diagonal components of the diffusion coefficient matrix. The knowledge of the diffusion coefficient matrix is also of special interest for more accurate hydrodynamic simulations.

In this work we investigate the minimal physical requirements needed for generating a speed of sound that surpasses its asymptotic conformal limit. It is shown that a peak in the speed of sound of homogeneous matter naturally emerges in the transition from a phase with broken chiral symmetry to one with a gapped Fermi surface. We argue that this could be relevant for understanding the peak in the speed of sound displayed by some of the current models for cold ultradense matter. A minimal model implementation of this mechanism is presented, based on the spontaneous breakdown of an approximate particle-antiparticle symmetry, and its thermodynamic properties are determined.

In this article we obtain a new set of nuclear parton distribution functions (nuclear PDFs) at next-to-leading order and next-to-next-to-leading order accuracy in perturbative QCD. The common nuclear deep-inelastic scattering (DIS) data analyzed in our study are complemented by the available charged-current neutrino DIS data with nuclear targets and data from Drell-Yan cross section measurements for several nuclear targets. In addition, the most recent DIS data from the Jefferson Lab CLAS and Hall C experiments are also added to our data sample. For these specific datasets, we consider the impact of target mass corrections and higher twist effects which are expected to be important in the region of large $x$ and intermediate-to-low $Q^2$. Our analysis is based on a publicly available open-source tool, APFEL, which has been modified to be applicable for our analysis of nuclear PDFs. Heavy-quark contributions to nuclear DIS are considered within the framework of the FONLL general-mass variable-flavor-number scheme. The most recent CT18 PDFs are used as baseline proton PDFs. The uncertainties of nuclear PDFs are determined using the standard Hessian approach. The results of our global QCD analysis are compared with existing nuclear PDF sets and with the fitted cross sections, for which our set of nuclear PDFs provides a very good description.

We present a comprehensive analysis of the $\gamma W$ interference radiative correction to the neutron $\beta$-decay matrix element. Within a dispersion relations approach, we compute the axial-vector part of the $\gamma W$ box amplitude ${\square }_A^{\gamma W}$ in terms of the isoscalar part of the $F_3^{\gamma W}$ interference structure function. Using the latest available phenomenology for $F_3^{\gamma W}$ from the nucleon elastic, resonance, deep-inelastic, and Regge regions, we find the real part of the box correction to be ${\square }_A^{\gamma W}=3.90(9)\times {10}^{-3}$. This improved correction gives a theoretical estimate of the CKM matrix element $|V_{ud}{|}^2=0.94805(26)$, which represents a $4\sigma$ violation of unitarity.

We investigate charged-current neutrino-nucleus deep inelastic scattering with particular interest in the relationship of short-range correlation (SRC) and the EMC effect. The structure functions $F_2^A(x,Q^2)$, $x{F}_3^A(x,Q^2)$ and ratios of differential cross sections are presented where the nuclei $A$ are chosen to be carbon, iron, and lead. We propose a kind of universal modification function which would provide a nontrivial test of SRC universality on the platform of neutrino-nucleus scattering and improve our understanding of nucleon structure substantially.

Gravitational collapse into a black hole has been extensively studied with classical sources. We develop a new formalism to simulate quantum fields forming a black hole. This formalism utilizes well-established techniques used for classical collapse by choosing a convenient coherent state, and simulates the matter fields quantum mechanically. Divergences are regularized with the cosmological constant and Pauli-Villars fields. Using a massless spherically symmetric scalar field as an example, we demonstrate the effectiveness of the formalism by reproducing some classical results in gravitational collapse, and identifying the difference due to quantum effects.

We propose a new kind of coherent state for the general $SO(D+1)$ formulation of loop quantum gravity in the ($1+D$)-dimensional space-time. Instead of Thiemann’s coherent state for $SO(D+1)$ gauge theory, our coherent spin-network state is given by constructing proper superposition over quantum numbers of the spin-networks with vertices labeled by the coherent intertwiners. Such superposition type coherent states are labeled by the so-called generalized twisted geometric variables which capture the geometric meaning of discretized general relativity. We study the basic properties of this kind of coherent state, i.e., the completeness and peakedness property. Moreover, we show that the superposition type coherent states are consistent with Thiemann’s coherent state for $SO(D+1)$ gauge theory in the large $\eta$ limit.

At leading order, the $S$-matrices in QED and gravity are known to factorize, providing unambiguous determinations of the parts divergent due to infrared contributions. The soft $S$-matrices defined in this fashion are shown to be defined entirely in terms of two-dimensional models on the celestial sphere, involving two real scalar fields, allowing us to express the soft $S$-matrices for real as well as virtual divergences as two-dimensional correlation functions. We discuss what this means for finding holographic representations of scattering amplitudes in QED and gravity and comment on simple double copy structures that arise during the analysis.

Of the contributions to the cosmological constant, zero-point energy contributions scale as ${\delta }^4(0)\sim {\mathrm{\Lambda }}^4$ where $\mathrm{\Lambda }$ is an ultraviolet cutoff used to regulate the calculations. I show that such contributions vanish when calculated in perturbation theory. This demonstration uses a little-known modification to perturbation theory found by Honerkamp and Meetz and by Gerstein, Jackiw, Lee, and Weinberg which comes into play when using cutoffs and interactions with multiple derivatives, as found in chiral theories and gravity. In a path integral treatment, the new interaction arises from the path integral measure and cancels the ${\delta }^4(0)$ contributions. This reduces the sensitivity of the cosmological constant to the high energy cutoff, although it does not resolve the cosmological constant problem. The feature removes one of the common motivations for supersymmetry. It also calls into question some of the results of the asymptotic safety program. Covariance and quadratic cutoff dependence are also briefly discussed.

We study the optical properties of the solar gravitational lens (SGL) while treating the Sun as an extended, axisymmetric and rotating body. The gravitational field of the Sun is represented using a set of zonal harmonics. We develop an analytical description of the intensity of light that is observed in the image plane in the strong interference region of a realistic SGL. This formalism makes it possible to model not only the point-spread function of point sources, but also actual observables, images that form in the focal plane of an imaging telescope positioned in the image plane. Perturbations of the monopole gravitational field of the Sun are dominated by the solar quadrupole moment, which results in forming an astroid caustic on the image plane. Consequently, an imaging telescope placed inside the astroid caustic observes four bright spots, forming the well-known pattern of an Einstein cross. The relative intensities and positions of these spots change as the telescope is moved in the image plane, with spots merging into bright arcs when the telescope approaches the caustic boundary. Outside the astroid caustic, only two spots remain and the observed pattern eventually becomes indistinguishable from the imaging pattern of a monopole lens at greater distances from the optical axis. We present results from extensive numerical simulations, forming the basis of our ongoing study of prospective exoplanet imaging with the SGL. These results are also applicable to describe a large class of gravitational lensing scenarios involving axisymmetric lenses that can be represented using zonal harmonics.

Autoparallel curves along with geodesic curves can arise as trajectories of physical test bodies. We explicitly derive autoparallels as effective post-Riemannian geometric constructs, and at the same time we argue against postulating autoparallels as fundamental equations of motion for test bodies in alternative gravity theories.

Current ground-based gravitational wave detectors are tuned to observe compact object mergers from stellar mass black holes and neutron stars; $\sim 50$ such events have been published to date. More exotic compact objects may exist, collisions of which would also generate copious gravitational waves. We model a stellar mass black hole inspiral into a stable, nonspinning, traversable wormhole, and find a characteristic waveform—an antichirp and/or burst—as the black hole outspirals into our region of the Universe. This is a characteristic signature which can be useful in wormhole searches in gravitational wave data or used to constrain wormhole geometries.

The quantity $T_0$, the cosmic microwave background (CMB) monopole, is an often neglected seventh parameter of the standard cosmological model. As well as its variation affecting the physics of the CMB, the measurement of $T_0$ is also used to calibrate the anisotropies via the orbital dipole. We point out that it is easy to misestimate the effect of $T_0$ because the CMB anisotropies are conventionally provided in temperature units. In fact the anisotropies are most naturally described as dimensionless and we argue for restoring the convention of working with $\mathrm{\Delta }T/T$ rather than $\mathrm{\Delta }T$. As a free cosmological parameter, $T_0$ most naturally only impacts the CMB power spectra through late-time effects. Thus if we ignore the COBE-FIRAS measurement, current CMB data only weakly constrain $T_0$. Even ideal future CMB data can at best provide a percent-level constraint on $T_0$, although adding large-scale structure data will lead to further improvement. The FIRAS measurement is so precise that its uncertainty negligibly affects most, but not all, cosmological parameter inferences for current CMB experiments. However, if we eventually want to extract all available information from CMB power spectra measured to multipoles $\ell \simeq 5000$, then we will need a better determination of $T_0$ than is currently available.

Relaxing the conventional assumption of a minimal coupling between the dark matter (DM) and dark energy (DE) fields introduces significant changes in the predicted evolution of the Universe. Therefore, testing such a possibility constitutes an essential task not only for cosmology but also for fundamental physics. In a previous communication [Phys. Rev. D 99, 043521 (2019)], we proposed a new null test for the $\mathrm{\Lambda }\mathrm{CDM}$ model based on the time dependence of the ratio between the DM and DE energy densities which is also able to detect potential signatures of interaction between the dark components. In this work, we extend that analysis avoiding the $\mathrm{\Lambda }\mathrm{CDM}$ assumption and reconstruct the interaction in the dark sector in a fully model-independent way using data from type Ia supernovae, cosmic chronometers and baryonic acoustic oscillations. According to our analysis, the $\mathrm{\Lambda }\mathrm{CDM}$ model is consistent with our model-independent approach at least at $3\sigma$ CL over the entire range of redshift studied. On the other hand, our analysis shows that the current background data do not allow us to rule out the existence of an interaction in the dark sector. Finally, we present a forecast for next-generation LSS surveys. In particular, we show that Euclid and SKA will be able to distinguish interacting models with about 4% of precision at $z\approx 1$.