Einstein-Cartan gravity, which is an alternative formulation of general relativity, introduces new degrees of freedom contained in the torsion field which encodes the torsion feature of spacetime. Interestingly, the torsion field couples to all fermions through its axial-vector mode with a universal coupling $\eta =1/8$ which is possible to change under the quantum effects. We argue that Einstein-Cartan gravity provides a significant portal to probe the $A^{\prime }$ dark gauge boson which resides in the dark sector existing as an invisible world parallel to our own and couples to the standard model (SM) particles through only the kinetic mixing. For the (very) small kinetic mixing, searches for the $A^{\prime }$ from Drell-Yan processes are insensitive due to the suppressed production cross section and the considerable SM backgrounds. However, through the mediation of torsion field the $pp$ collisions produce dark-sector fermions which would significantly produce the $A^{\prime }$ due to unsuppressed dark gauge coupling. We explore the potential production modes of the $A^{\prime }$ through bremsstrahlung off dark-sector fermion and the cascade decays. Einstein-Cartan gravity suggests the torsion mass $\gtrsim \mathcal{O}(4)\mathrm{TeV}$ for $\eta$ varying around the classical value since the present scenarios would tend to produce the $A^{\prime }$ with the high boost and large missing transverse momentum from dark-sector fermions where the SM backgrounds are low. On the other hand, the $A^{\prime }$ search via Einstein-Cartan portal can reach even for the signal events to be not large and is also sensitive to the (very) small kinetic mixing as long as the decay channels of the $A^{\prime }$ to dark-sector particles are inaccessible.

We focus on the chiral and heavy quark mass expansion of meson masses and decay constants. We propose a light-front QCD formalism for the evaluation of these quantities, consistent with chiral perturbation theory and heavy quark effective theory.

Inspired by the LHCb’s newest observation of two new excited ${\mathrm{\Xi }}_b^0$ states, we systematically study the strong decays of the low-lying $\lambda$ and $\rho$ modes $1D$-wave ${\mathrm{\Xi }}_b$ and ${\mathrm{\Xi }}_b^{\prime }$ baryons using the chiral quark model within the $j\text{−}j$ coupling scheme. Based on the measured masses and strong decay properties of ${\mathrm{\Xi }}_b(6327{)}^0$ and ${\mathrm{\Xi }}_b(6333{)}^0$, we explain the two states as the $\lambda$-mode $1D{\mathrm{\Xi }}_b$ states with $J^P=3/2^{+}$ and $J^P=5/2^{+}$, respectively. Moreover, under this assignment, another dominant decay channel of ${\mathrm{\Xi }}_b(6327{)}^0$ is ${\mathrm{\Xi }}_b^{\prime }\pi$ and that of ${\mathrm{\Xi }}_b(6333{)}^0$ is ${\mathrm{\Xi }}_b^{*}\pi$. Hence, the decay modes ${\mathrm{\Xi }}_b^{\prime }\pi$ and ${\mathrm{\Xi }}_b^{*}\pi$ may be another ideal channel as well to decode the inner structure of ${\mathrm{\Xi }}_b(6327{)}^0$ and ${\mathrm{\Xi }}_b(6333{)}^0$, respectively. For other unseen $1D{\mathrm{\Xi }}_b$ and ${\mathrm{\Xi }}_b^{\prime }$ states, our results indicate (i) that ${\mathrm{\Xi }}_b|J^P={\frac{3}{2}}^{+},2{⟩}_{\rho }$, and ${\mathrm{\Xi }}_b|J^P={\frac{5}{2}}^{+},2{⟩}_{\rho }$ are most likely to be narrow states with a width of $\mathrm{\Gamma }\simeq (12-30)\mathrm{MeV}$, and dominantly decay into ${\mathrm{\Sigma }}_{b}K$ and ${\mathrm{\Sigma }}_b^{*}K$, respectively, and (ii) that the $1D{\mathrm{\Xi }}_b^{\prime }$ baryons are not broad states, and the widths vary in the range of $\mathrm{\Gamma }\simeq (14-46)\mathrm{MeV}$. These states have a good potential to be observed in their dominant decay processes.

In this work, we investigate the $\mathrm{\Upsilon }(10753)\to \mathrm{\Upsilon }(nS){\pi }^{+}{\pi }^{-}$ ($n=1$, 2, 3) processes by considering the hadronic loop mechanism, where $\mathrm{\Upsilon }(10753)$ is assigned to a conventional bottomonium in the $4S\text{−}3D$ mixing scheme. Our results of the concerned processes own considerable branching ratios, which can reach up to the order of magnitude of ${10}^{-4}–{10}^{-3}$. We indicate that the measured ${\mathrm{\Gamma }}_{e^{+}{e}^{-}}\times \mathcal{B}[\mathrm{\Upsilon }(10753)\to \mathrm{\Upsilon }(nS){\pi }^{+}{\pi }^{-}]$ values given by Belle can be reproduced well. This fact supports the former bottomonium assignment to the $\mathrm{\Upsilon }(10753)$ in the $4S\text{−}3D$ mixing scheme. Obviously, it is a good opportunity for the ongoing Belle II experiment if the predicted result in this work can be tested further.

We show that spatial curvature has a significant effect on the existence of entanglement islands in cosmology. We consider a homogeneous, isotropic universe with thermal radiation purified by a reference spacetime. Arbitrarily small positive curvature guarantees that the entire universe is an island. Proper subsets of the time-symmetric slice of a closed or open universe can be islands, but only if the cosmological constant is negative and sufficiently large in magnitude.

We present a comprehensive comparison between the numerical relativity (NR) angular momentum flux at infinity and the corresponding quantity entering the radiation reaction in teobresums, an effective one body (EOB) waveform model for nonprecessing coalescing black hole binaries on quasicircular orbits. This comparison prompted us to implement two changes in the model: (i) including next-to-quasi-circular corrections in the $\ell =m$, $\ell \le 5$ multipoles entering the radiation reaction and (ii) consequently updating the NR-informed spin-orbital sector of the model. This yields a new waveform model that presents a higher self-consistency between waveform and dynamics and an improved agreement with NR simulations. We test the model computing the EOB/NR unfaithfulness ${\overline{F}}_{\mathrm{EOB}/\mathrm{NR}}$ over all 534 spin-aligned configurations available through the Simulating eXtreme Spacetime catalog, notably using the noise spectral density of Advanced LIGO, Einstein Telescope and Cosmic Explorer, for total mass up to $500M_{\odot }$. We find that the maximum unfaithfulness ${\overline{F}}_{\mathrm{EOB}/\mathrm{NR}}^{\max }$ is mostly between ${10}^{-4}$ and ${10}^{-3}$, and the performance progressively worsens up to $\sim 5\times {10}^{-3}$ as the effective spin of the system is increased. We perform similar analyses on the seobnrv4hm model, which delivers ${\overline{F}}_{\mathrm{EOB}/\mathrm{NR}}^{\max }$ values uniformly distributed versus effective spin and mostly between ${10}^{-3}$ and ${10}^{-2}$. We conclude that the improved teobresums model already represents a reliable and robust first step towards the development of highly accurate waveform templates for third generation detectors.

Dynamical effects in general relativity have been finally, relatively recently observed by LIGO [B. P. Abbott et al., Living Rev. Relativity 19, 1 (2016).]. These effects correspond to gravitational waves created by the coalescence of black holes or neutron stars billions of years ago and billions of light years away from their sources. To be able to measure these signals, great care has to be taken to minimize all sources of noise in the detector. One of the sources of noise is called Newtonian noise, the name based on the notion that close by sources would create essentially instantaneous Newtonian gravitational fields. In this article we present an analysis of the dynamical (time dependent) nature of the Newtonian noise. In that respect, it is a misnomer to call it Newtonian noise, because the Newtonian theory does not afford any dynamical notion of the gravitational field. We will, in fact, do our analysis in the context of Einsteinian general relativity. The dynamical aspects of the nature of the Newtonian noise have heretofore been disregarded as they were considered negligible. However, we demonstrate that they are indeed not far from the realm of being measurable. They could be used to validate Einsteinian general relativity or to give valuable information on the true dynamical nature of gravity. One fundamental question, for example, is a direct measurement the speed of propagation of gravitational effects and the verification that it is indeed the same as the speed of light? We propose a simple laboratory experiment that could affirm or deny this proposition. We also analyze the possibility of the detection of large geophysical events, such as earthquakes. We find that large seismic events seem to be easily observable with the present ensemble of gravitational wave detectors. The ensemble of gravitational wave detectors could easily serve as a system of early warning for otherwise catastrophic seismic events.

The correspondence between the thermodynamic energy equation satisfied by a closed comoving volume and the conservation equation satisfied by the energy-momentum tensor of the matter inside the comoving volume is extended to a more general system with an arbitrary cosmological horizon and a heat source. The energy of the system consisting of a cosmological horizon and the internal matter could be conserved by defining a surface energy on the horizons. Therefore, energy conservation and energy-momentum tensor conservation can always be consistent for such a system. On the other hand, from the perspective of classical thermodynamics, one can define an effective pressure at the cosmological horizon to guarantee that the thermodynamic energy equation inside the horizon is consistent with the energy-momentum tensor conservation equation of the matter inside the horizon. These systems can satisfy the generalized second law of thermodynamics under appropriate conditions. The definitions of the surface energy and the effective pressure are extended to the gravity theory with nonminimal coupling between geometry and matter, in which geometry could be regarded as a heat source.

Spatial extension has been hailed as a “smoking gun” in the gamma-ray search of dark galactic subhalos, which would appear as unidentified sources for gamma-ray telescopes. In this work, we study the sensitivity of the Fermi-LAT to extended subhalos using simulated data based on a realistic sky model. We simulate spatial templates for a set of representative subhalos, whose parameters were derived from our previous work with $N$-body cosmological simulation data. We find that detecting an extended subhalo and finding an unequivocal signal of angular extension requires, respectively, a flux 2 to 10 times larger than in the case of a pointlike source. By studying a large grid of models, where parameters such as the WIMP mass, annihilation channel, or subhalo model are varied significantly, we obtain the response of the LAT as a function of the product of annihilation cross-section times the $J$ factor. Indeed, we show that spatial extension can be used as an additional “filter” to reject subhalos candidates among the pool of unidentified LAT sources, as well as a smoking gun for positive identification. For instance, typical angular extensions of a few tenths of a degree are expected for the considered scenarios. Finally, we also study the impact of the obtained LAT sensitivity to such extended subhalos on the achievable dark matter constraints, which are a few times less constraining than comparable point-source limits.

There have been recent debates about whether $\overline{\mathrm{MS}}$ parton densities exactly obey positivity bounds (including the Soffer bound) and whether the bounds should be applied as a constraint on global fits to parton densities and on nonperturbative calculations. A recent paper [Candido et al., Can $\overline{\mathrm{MS}}$ parton distributions be negative?, J. High Energy Phys. 11 (2020) 129] appears to provide a proof of positivity in contradiction with earlier work by other authors. We examine their derivation and find that its primary failure is in the apparently uncontroversial statement that bare parton density (or distribution) function (pdfs) are always positive. We show that under the conditions used in the derivation, that statement fails. This is associated with the use of dimensional regularization for both UV divergences (space-time dimension $n<4$) and for collinear divergences, with $n>4$. Collinear divergences appear in massless partonic quantities convoluted with bare pdfs, in the approach used by these and other authors, which we call “track B.” Divergent UV contributions are regulated and are positive when $n<4$, but can and often do become negative after analytic continuation to $n>4$. We explore ramifications of this idea and provide some elementary calculations in a model QFT that show how this situation can generically arise in reality. We examine the connection with the origin of the track B method. Our examination pinpoints considerable difficulties with track B that render it either wrong or highly problematic and explain that a different approach, which appears in some literature and that we call track A, does not suffer from this set of problems. The issue of positivity highlights that track-B methods can lead to wrong results of phenomenological importance. From our analysis we identify the restricted situations in which positivity tends to be violated.

Vacuum stability requires that the scalar potential is bounded from below. Whether or not this is true depends only on the scalar quartic interactions, but even so the analysis is arduous and has only been carried out for a limited set of models. Complementing the existing literature, this work contains the necessary and sufficient conditions for two $SU(n)$ invariant potentials to be bounded from below. In particular, expressions are given for models with the fundamental and the 2-index (anti)symmetric representations of this group. A sufficient condition for vacuum stability is also provided for models with the fundamental and the adjoint representations. Finally, some considerations are made concerning the model with the gauge group $SU(2)$ and the scalar representations 1, 2, and 3; such a setup is particularly important for neutrino mass generation and lepton number violation.

Possibilities for the measurement of the longitudinal structure function in diffraction $F_{\mathrm{L}}^{\mathrm{D}}$ at the future U.S. Electron Ion Collider are investigated. The sensitivity to $F_{\mathrm{L}}^{\mathrm{D}}$ arises from the variation of the reduced diffractive cross section with center-of-mass energy. Simulations are performed with various sets of beam energy combinations and for different assumptions on the precision of the diffractive cross section measurements. Scenarios compatible with current EIC performance expectations lead to an unprecedented precision on $F_{\mathrm{L}}^{\mathrm{D}}$ at the 5–10% level in the best measured regions. While scenarios with data at a larger number of center-of-mass energies allow the extraction of $F_{\mathrm{L}}^{\mathrm{D}}$ in the widest kinematic domain and with the smallest uncertainties, even the more conservative assumptions lead to precise measurements. The ratio $R^{\mathrm{D}}$ of photoabsorption cross sections for longitudinally to transversely polarized photons can also be obtained with high precision using a separate extraction method.

The theoretical results for the total cross sections and polarization components of the ${\tau }^{+}$ lepton produced in the charged current induced $|\mathrm{\Delta }S|=1$ quasielastic ${\overline{\nu }}_{\tau }-N$ scattering leading to hyperons ($\mathrm{\Lambda }$, $\mathrm{\Sigma }$) have been presented assuming T invariance. The theoretical uncertainties arising due to the use of different vector, axial-vector, and pseudoscalar form factors as well as the effect of SU(3) symmetry breaking have been studied. We have also presented, for the first time, a comparison of the total cross sections for the production of $e$, $\mu$, $\tau$ leptons to facilitate the implications of lepton flavor universality in the $|\mathrm{\Delta }S|=1$ quasielastic reactions induced by the antineutrinos of all flavors i.e., ${\nu }_l$; $l=e$, $\mu$, $\tau$.

Model-independent reactor isotopic cross sections per fission are determined by global fits of the reactor antineutrino data from high-enriched-uranium (HEU) reactor rates, low-enriched-uranium (LEU) reactor rates, and reactor fuel evolution data. Taking account of the implicit quasilinear relationship between the fission fractions of ${}^{239}\mathrm{Pu}$ and ${}^{241}\mathrm{Pu}$ in the LEU reactor data, the inverse-beta-decay (IBD) yields and their correlations of the fissionable isotopes ${}^{235}\mathrm{U}$, ${}^{238}\mathrm{U}$, and Pu’s are obtained. The data-driven isotopic IBD yields provide an anomaly-free model for the reactor isotopic cross sections per fission, where better than 1% accuracy of the expected reactor IBD yields can be achieved for future experiments.

The QCD axion is a well-motivated addition to the standard model to solve the strong $CP$ problem. If the axion acquires mass dominantly from a hidden sector, it can be as heavy as $O(1)\mathrm{GeV}$, and the decay constant can be as low as $O(100)\mathrm{GeV}$ without running into the axion quality problem. We propose new search strategies for such heavy QCD axions at the Belle II experiment, where the axions are expected to be produced via $B\to Ka$. We find that a subsequent decay $a\to 3\pi$ with a displaced vertex leads to a unique signal with essentially no background, and that a dedicated search can explore the range $O(1–10)\mathrm{TeV}$ of decay-constant values. We also show that $a\to \gamma \gamma$ can cover a significant portion of currently unexplored region of $150\lesssim m_a\lesssim 500\mathrm{MeV}$.

We continue the study of a recently constructed holographic QCD model supplemented with a magnetic field. We consider the holographic dual of a quark-antiquark pair and investigate its entropy beyond the deconfinement phase transition in terms of interquark distance, temperature and magnetic field. We obtain a clear magnetic field dependence in the strongly decreasing entropy near deconfinement and in the entropy variation for growing interquark separation. We uncover various supporting evidence for inverse magnetic catalysis. The emergent entropic force is found to become stronger with magnetic field, promoting the quarkonium dissociation. We also probe the dynamical dissociation of the quarkonium state, finding a faster dissociation with magnetic field. At least the static predictions should become amenable to a qualitative comparison with future lattice data.

We show that the canonical purification of an evaporating black hole after the Page time consists of a short, connected, Lorentzian wormhole between two asymptotic boundaries, one of which is unitarily related to the radiation. This provides a quantitative and general realization of the predictions of $\mathrm{ER}=\mathrm{EPR}$ in an evaporating black hole after the Page time; this further gives a standard $\mathrm{AdS}/\mathrm{CFT}$ calculation of the entropy of the radiation (without modifications of the homology constraint). Before the Page time, the canonical purification consists of two disconnected, semiclassical black holes. From this, we construct two bipartite entangled holographic CFT states, with equal (and large) amount of entanglement, where the semiclassical dual of one has a connected ERB and the other does not. From this example, we speculate that measures of multipartite entanglement may offer a more complete picture into the emergence of spacetime.

Fluid and ultralight bosonic dark matter can interact through gravity to form stable fermion-boson stars, which are static and regular mixed solutions of the Einstein-Euler-(complex, massive)-Klein-Gordon system. In this work we study the dynamical formation via gravitational cooling of a spherical mixed white-dwarf–boson star, whose properties depend on the boson particle mass and the mass of the boson star. Due to the accretion of bosonic dark matter, the white dwarf migrates to a denser and more compact object with a boson star core, thus modifying its gravitational redshift and altering the electromagnetic radiation emitted from the photosphere. We discuss the implications of the changes in the gravitational redshift that in principle could be produced by any type of dark matter and that might lead to small discrepancies in the estimation of masses and radii derived from white-dwarf observations.

Gravitational lenses are examined in a de Sitter (dS) background, for which the existence of the dS horizon is taken into account and hyperbolic trigonometry is used together with the hyperbolic angular diameter distance. Spherical trigonometry is used to discuss a gravitational lens in anti–de Sitter (AdS) background. The difference in the form among the dS/AdS lens equations and the exact lens equation in Minkowski background begins at the third order, when a small angle approximation is used in terms of lens and source planes. The angular separation of lensed images is decreased by the third-order deviation in the dS lens equation, while it is increased in AdS. In the present framework on the dS/AdS backgrounds, we discuss also the deflection angle of light, which does not include any term of purely the cosmological constant. Despite the different geometry, the deflection angle of light rays in hyperbolic and spherical geometry can take the same form. Through a coupling of the cosmological constant with lens mass, the separation angle of multiple images is larger (smaller) in dS (AdS) than in the flat case, for a given mass, source direction, and angular diameter distances among the lens, receiver and source.

Upcoming observing campaigns with improved detectors will yield numerous detections of gravitational waves from neutron star binary inspirals. Rare loud signals together with numerous signals of moderate strength promise stringent constraints on the properties of neutron star matter, with a projected radius statistical uncertainty of 50–200 m with $\mathcal{O}(2000)$ sources. Given this precision we revisit all analysis assumptions and identify sources of systematic errors, quantify their impact on radius extraction, and discuss their relative importance and ways to mitigate them.