The possible existence of nucleon-antinucleon bound states has been studied for decades. We investigate the $e^{+}{e}^{-}\to p\overline{p}$ and $e^{+}{e}^{-}\to n\overline{n}$ cross sections in the nonrelativistic effective field theory framework. The proton-antiproton and neutron-antineutron coupled-channel final state interactions are considered and found responsible for near-threshold enhancements. Both the proton-neutron mass difference and the Coulomb interaction between $p$ and $\overline{p}$ are considered, and the $N\overline{N}$ strong interactions are taken into account through a short-distance optical potential. By fitting the low energy constants in the amplitudes to the data for the near-threshold $e^{+}{e}^{-}\to N\overline{N}$ cross sections from the BESIII and SND collaborations, a $N\overline{N}$ quasibound state is found just above the $p\overline{p}$ threshold, and another $N\overline{N}$ pole is found on the unphysical Riemann sheet, farther away from the threshold. The constructed coupled-channel amplitude with Coulomb effects also offers a framework that can be used directly in experimental analyses on fine structures near the $N\overline{N}$ thresholds.

The BESIII Collaboration has recently reported a new resonance structure in the cross-section analyses of the $e^{+}{e}^{-}\to \rho \pi$ and $e^{+}{e}^{-}\to \rho (1450)\pi$ processes, displaying characteristics akin to an $\omega$ meson. However, its measured mass, $M=2119\pm 11\pm 15\mathrm{MeV}$, significantly deviates from the predictions of the unquenched relativized potential model for conventional $\omega$ vector meson spectroscopy. To address this discrepancy, we propose a $4S-3D$ mixing scheme and investigate the corresponding decay properties within this framework. Our analysis demonstrates that the mixed state ${\omega }_{4S-3D}^{\prime }$ exhibits excellent agreement with the observed resonance, not only in mass and width but also in the products of its dielectron width and branching ratios, ${\mathrm{\Gamma }}_{e^{+}{e}^{-}}^{\mathcal{R}}\times {\mathcal{B}}_{\mathcal{R}\to \rho \pi }$ and ${\mathrm{\Gamma }}_{e^{+}{e}^{-}}^{\mathcal{R}}\times {\mathcal{B}}_{\mathcal{R}\to \rho (1450)\pi \to {\pi }^{+}{\pi }^{-}{\pi }^0}$. The determined mixing angle, $\theta =-({31.1}_{-3.1}^{+2.1})°$, strongly supports the interpretation of this structure as the ${\omega }_{4S-3D}^{\prime }$ state. Furthermore, we predict dominant decay channels for ${\omega }_{4S-3D}^{\prime }$ and its partner state ${\omega }_{4S-3D}^{\prime \prime }$. These predictions, together with the proposed mixing mechanism, provide crucial guidance for future experimental studies aimed at probing this structure and rigorously testing the $4S-3D$ mixing hypothesis.

Spin squeezing has been explored in atomic systems as a tool for quantum sensing, improving experimental sensitivity beyond the spin standard quantum limit for certain measurements. To optimize absolute metrological sensitivity, it is beneficial to consider macroscopic spin ensembles, such as nuclear spins in solids and liquids. Coupling a macroscopic spin ensemble to a parametrically-modulated resonant circuit can create collective spin squeezing by generating spin correlations mediated by the circuit. We analyze the squeezing dynamics in the presence of decoherence and finite spin polarization, showing that achieving 7 dB spin squeezing is feasible in several nuclear spin systems. The metrological benefit of squeezing a macroscopic spin ensemble lies in the suppression of technical noise sources in the spin detection system relative to the spin projection noise. This expands the experimental sensitivity bandwidth when searching for signals of unknown frequency and can improve the resonant signal-to-noise ratio. Squeezing macroscopic spin ensembles may prove to be a useful technique for fundamental physics experiments aimed at detecting spin interactions with oscillating background fields, such as ultralight dark matter.

Tensor networks provide a powerful tool for studying many-body quantum systems, particularly making quantum simulations more efficient. In this article, we construct a tensor network representation of the spin network states, which correspond to $SU(2)$ gauge-invariant discrete field theories. Importantly, the spin network states play a central role in the loop quantum gravity (LQG) approach to the Planck scale physics. Our focus is on the Ising-type spin networks, which provide a basic model of quantum space in LQG. It is shown that the tensor network approach improves the previously introduced methods of constructing quantum circuits for the Ising spin networks by reducing the number of qubits involved. It is also shown that the tensor network approach is convenient for implementing holographic states involving the bulk-boundary conjecture, which contributes to establishing a link between LQG and holographic duality.

We obtain an action for a generalized conformal mechanics (GCM) coupled to Jackiw-Teitelboim (JT) gravity from a double scaling limit of the motion of a charged massive particle in the near-horizon geometry of a near-extremal spherical black hole. When JT gravity is treated in the classical approximation, the backreaction of the particle’s wave function on the time-reparametrization mode (and therefore the bulk metric) vanishes while the conformal symmetry in GCM is reparametrized in a state-dependent way. We also construct the semi-classical Hilbert space of the full theory by explicitly solving the general time-dependent normalizable solutions of the Schrödinger equation for GCM, and show that the time-reparametrization mode can be inferred from the measurement of suitable observables. Since the full theory of the GCM coupled to JT gravity is amenable to quantization, it can lead to a solvable model for a detector coupled to quantum gravity.

We propose a new “universal expansion” for one-loop amplitudes with arbitrary number of gluons in $D$ dimensions, which holds for general gauge theories with gluons, fermions, and scalars in the loop, including pure and supersymmetric Yang-Mills theories. It expresses the $n$-gluon amplitudes as a linear combination of universal scalar-loop amplitudes with $n-m$ gluons and $m$ scalars, multiplied by gauge-invariant building blocks (defined for general gauge theories); the integrands of these scalar-loop amplitudes are given in terms of tree-level objects attached to the scalar loop, or by differential operators acting on the most important part which is proportional to $D$ (with $m=0$). We present closed-formula for these one-loop integrands and prove them by showing that the single cuts are correctly reproduced by the gluing of an additional pair of gluons (fermions, scalars) in the forward limit, plus $n$ gluons in a tree amplitude.

We bring the Kerr-Newman spacetime into the Bondi-Sachs gauge by means of zero angular momentum, null geodesics. We compute the memory effect produced at the black hole horizon by a transient gravitational shock wave, which from future null infinity is seen as a Bondi-Metzner-Sachs supertranslation. This results in a change of the supertransformation charges at infinity between the spacetime geometries defined by the black hole before, and after, the shockwave scattering. For an extremal Kerr-Newman black hole, we give the complementary description of this process in the near-horizon limit, as seen by an observer hovering over the horizon. In this limit, we compute the supertransformation charges and compare them to those calculated at null infinity. We analyze the effect of these transformations on the electromagnetic gauge field and explore the self-interaction between this and the angular momentum of the black hole.

We study inflation in a recently proposed gravitational effective field theory describing the trace anomaly. The theory requires an additional scalar which is massless in the early universe. This scalar—referenced as an anomalyon—couples to the familiar matter and radiation through the gauge field trace anomaly. We derive a class of cosmological solutions that deviate from the standard inflationary ones only slightly, in spite of the fact that the anomalyon has a sizable time dependent background. On the other hand, the scalar cosmological perturbations in this theory are different from the conventional inflationary perturbations. The inflaton and anomalyon perturbations mix, and one of the diagonal combinations gives the standard nearly scale-invariant adiabatic spectrum, while the other combination has a blue power spectrum at short distance scales. We argue that this blue spectrum can lead to the formation of primordial black holes (PBHs) at distance scales much shorter than the ones tested in cosmic microwave background observations. The resulting PBHs can be heavy enough to survive to the present day Universe. For natural values of the parameters involved the PBHs would constitute only a tiny fraction of the dark matter, but with fine-tunings perhaps all of dark matter could be accounted by them. We also show that the theory predicts primordial gravitational waves which are almost identical to the standard inflationary ones.

We study the primordial black hole (PBH) reheating scenario, where PBHs originate in a general cosmological background. In this scenario, ultralight PBHs with masses $M\lesssim {10}^8\mathrm{g}$ temporarily dominate the Universe and reheat it via Hawking radiation before big bang nucleosynthesis (BBN). We investigate whether the induced gravitational wave (GW) spectrum associated with PBH reheating contains information about the pre-PBH-dominated stage, namely the initial equation of state $w$ (after inflation). We first derive the transfer functions of curvature fluctuations for general $w$ with adiabatic and isocurvature initial conditions. We find that, in general, a stiffer equation of state enhances the induced GW amplitude as it allows for a longer PBH-dominated phase compared to the radiation-dominated case. We also find that the spectral slope of GWs induced by primordial curvature fluctuations is sensitive to $w$, while the spectral slope of GWs induced by PBH number density fluctuations is not. Lastly, we derive constraints of the initial PBH abundance as a function of $w$, using BBN and cosmic microwave background (CMB) observations. A stiffer equation of state leads to stricter constraints on the initial energy density fraction, as induced GWs are enhanced. Interestingly, we find that such induced GW signals may enter the observational window of several future GW detectors, such as LISA and the Einstein Telescope. Our formulas, especially the curvature fluctuation transfer functions, are applicable to any early matter-dominated universe scenario.

We explore the potential for extracting the longitudinal proton structure function $F_L$ at the future Electron Ion Collider (EIC) through a Rosenbluth separation method. The impacts of differing assumptions on sample sizes, systematic uncertainties, and beam energy scenarios are investigated. With a sufficiently large number of center-of-mass energy configurations and well-controlled systematics, the EIC will measure $F_L$ to an unprecedented precision, even with relatively modest luminosities. The accessible kinematic range complements both fixed-target and Hadron-Electron Ring Accelerator data. In the most optimistic scenarios, the EIC data will be a highly competitive direct probe of the proton gluon density.

In a nonrelativistic quark model framework, we carry out a calculation of the mass spectrum for the low-lying $1S$ all-heavy pentaquark states by adopting the explicitly correlated Gaussian method. The obtained states are compact and lie far above the lowest dissociation baryon-meson threshold. Moreover, using the obtained masses and wave functions we evaluate the fall-apart decay properties within a quark-exchange model. The results show that the $1S$ all-heavy pentaquark states have a fairly narrow fall-apart width, which scatters in the range of $\sim 0.1–4.0\mathrm{MeV}$. Their dominant fall-apart decay channels may be ideal for searching for their signals in future experiments.

We investigate the effects of nonthermally produced dark matter on large-scale structure formation, focusing on the gravitino dark matter. Our analysis shows that large-scale structure measurements from the Sloan Digital Sky Survey (SDSS) luminous red galaxy (LRG) data offer a promising approach to probing nonthermally produced gravitinos. Specifically, if gravitinos resulting from neutralino decay constitute a fraction $F_{\mathrm{dec}}=0.35(0.1)$ of the dark matter component, the data exclude binolike neutralino with a mass $m_{{\chi }_1^0}\lesssim 25(11)\mathrm{GeV}$ at 95% C.L. Furthermore, this constraint appears to be largely independent of the gravitino mass.

At present, the study of the charm-quark Yukawa coupling at the Large Hadron Collider mainly focuses on the Higgs decay processes. Such signal suffers from overwhelming QCD background and derives its sensitivity primarily from the $Vh$ associated production channel. In addition, sensitivity to a possible $CP$ phase in charm-quark Yukawa at the hadron collider is not discussed. We investigate the charm-Higgs associated production signal that contains a potentially detectable interference term between $cch$ Yukawa coupling mediated diagrams and $ggh$ coupling mediated diagram. Such an interference term is sensitive to the relative $CP$ phase between contributing diagrams. High dimensional kinematic information is exploited by machine learning techniques to separate the different contribution, and sensitivity on the coupling is derived. Assuming a real ${\kappa }_c$ modification framework, the $1\sigma$ bound of $-5.6<{\kappa }_c<5.6$ (HL-LHC) and $-1.51<{\kappa }_c<1.62$ (FCC) are achieved. When allowing for $CP$ phase in the charm Yukawa, a combined $1\sigma$ bound of $0.32<|{\kappa }_c|<1.69$, $-77°<\alpha <77°$ (HL-LHC) and $0.70<|{\kappa }_c|<1.29$, $-55°<\alpha <55°$ (FCC) can be achieved on the magnitude and $CP$ phase of the coupling, respectively.

The axioms of quantum mechanics require that the Hamiltonian of any closed system is self-adjoint, so that energy levels are real and time evolution preserves probability. On the other hand, non-Hermitian Hamiltonians with $\mathcal{PT}$ symmetry can have both real spectra and unitary time evolution. In this paper, we study in detail a pair of quantum oscillators coupled by an imaginary bilinear term, both in quantum mechanics and in quantum field theory. We discuss explicitly how such Hamiltonians lead to perfectly sound physical theories with real spectra and unitary time evolution, in spite of their non-Hermiticity. We also analyze two-point correlation functions and their associated Källen-Lehmann representation. In particular, we discuss the intimate relation between positivity violation of the spectral functions and the nonobservability of operators in a given correlation function. Finally, we conjecture that positivity violation of some spectral functions of the theory could be a generic sign of the existence of complex pairs of energy eigenvalues (i.e., a $\mathcal{PT}$-broken phase) somewhere in its parameter space.

We examine possible additive corrections to the Bekenstein-Hawking (BH) entropy of black holes due to very general classical and quantal modifications of general relativity. In general, black-hole entropy is subject to the generalized second law of thermodynamics. For the case of binary-black-hole coalescence, the difference in corrections to the inspiral and remnant black-hole entropies is shown, within this law, to be bounded by the difference in the corresponding BH entropies. This latter difference has been measured by several groups attempting to validate Hawking’s area theorem on black-hole horizons, by analyzing gravitational-wave data from possible binary-black-hole mergers. The former difference—that between corrections to remnant and inspiral black-hole entropies beyond the BH entropy, is thus constrained by a bound measured from observational data. We examine the implications of this constraint for general binary-black-hole coalescence. If calculated entropy corrections follow the essential pattern of BH entropies dictated by the Hawking area theorem, consistency with the observational bound is shown to be guaranteed. If they do not, these corrections are then nontrivially constrained by the observational bound.

Cosmological observations from big bang nucleosynthesis and the cosmic microwave background (CMB) offer crucial insights into the Early Universe, enabling us to trace its evolution back to lifetimes as short as 0.01 s. Upcoming CMB spectrum measurements will achieve unprecedented precision, allowing for more accurate extraction of information about the primordial neutrinos. This provides an opportunity to test whether their properties align with the predictions of the standard cosmological model or indicate the presence of new physics that influenced the evolution of the MeV-temperature plasma. A key component in understanding how new physics may have affected primordial neutrinos is solving the neutrino Boltzmann equation. In this paper, we address this question by developing a novel approach—neutrino direct simulation Monte Carlo (DSMC). We discuss it in depth, highlighting its model independence, transparency, and computational efficiency—features that current state-of-the-art methods lack. Then, we introduce a proof-of-concept implementation of the neutrino DSMC and apply it to several toy scenarios, showcasing key aspects of the primordial plasma’s evolution in the presence of new physics.

The Galactic gamma-ray flux can be described as the sum of two components: the first is due to the emission from an ensemble of discrete sources, and the second is formed by the photons produced by cosmic rays propagating in interstellar space and interacting with gas or radiation fields. The source component is partially resolved as the contributions from individual sources, but a fraction is unresolved and appears as a diffuse flux. Both the unresolved source flux and the interstellar emission flux encode information of great significance for high energy astrophysics, and therefore the separation of these two contributions is very important. In this work we use the distributions in celestial coordinates of the objects contained in the catalogs obtained by the extensive air showers telescopes HAWC and LHAASO to estimate the total luminosity of the Galactic gamma-ray sources and the contribution of unresolved sources to the diffuse gamma-ray flux. This analysis suggests that while the flux from unresolved sources is measurable and important, the dominant contribution to the diffuse flux over most of the celestial sphere is interstellar emission.

Gravitational-wave (GW) detections of electromagnetically bright compact binary coalescences can provide an independent measurement of the Hubble constant $H_0$. In order to obtain a measurement that could help arbitrate the existing tension on $H_0$, one needs to fully understand any source of systematic biases for this approach. In this study, we aim to understand the impact of instrumental calibration errors (CEs) on the measurements of the luminosity distance, $D_L$, and the inferred $H_0$ value. We simulate binary neutron star mergers (BNSs), as detected by a network of Advanced LIGO and Advanced Virgo interferometers at their design sensitivity. We artificially add CEs equal to exceptionally large values experienced in LIGO-Virgo’s third observing run (O3). We find that for individual BNSs at a network signal-to-noise ratio of 50, the systematic errors on $D_L$—and hence $H_0$—are still smaller than the statistical uncertainties. The biases become more significant when we combine multiple events to obtain a joint posterior on $H_0$. In the rather unrealistic case that the data around each detection is affected by the same CEs corresponding to the worst offender of O3, the true $H_0$ value would be excluded from the 90% credible interval after we combine $\sim 40$ sources. If instead, 10% of the sources suffer from severe CEs, the true value of $H_0$ is included in the 90% credible interval even after 100 sources.

The observations of compact star inspirals from LIGO/Virgo, combined with mass and radius measurements from NICER, provide a valuable tool to study the highly uncertain equation of state (EOS) of dense matter at the densities characteristic of compact stars. In this work, we use a Bayesian statistical method to constrain the solid states of strange-cluster matter, called strangeon matter, as the putative basic units of the ground state of bulk strong matter, incorporating the mass and radius measurements of PSR $\mathrm{J}0030+0451$, PSR $\mathrm{J}0740+6620$, and the recent data for the $1.4M_{\odot }$ pulsar PSR J0437-4715. We also include constraints from gravitational wave events GW170817 and GW190814. Under the prior assumption of a finite number of quarks in a strangeon, $N_{\mathrm{q}}$, our analysis reveals that current mass-radius measurements favor a larger $N_{\mathrm{q}}$. Specifically, the results support the scenario where a strangeon forms a stable bound state with $N_{\mathrm{q}}=18$, symmetric in color, flavor, and spin spaces, with a relatively strong Bayesian evidence. The comparative analyses of the posterior EOS parameter spaces derived from the three-parameter model and two-parameter model demonstrate a consistent prediction under identical observational constraints. In particular, our results reveal that the most probable values of the maximum mass are found to be ${3.58}_{-0.12}^{+0.16}{M}_{\odot }$ (${3.65}_{-0.16}^{+0.18}{M}_{\odot }$) at the 90% confidence level for three-parameter (two-parameter) EOS, based on the joint analysis of PSR $\mathrm{J}0030+0451$, PSR $\mathrm{J}0740+6620$, PSR J0437-4715, GW170817, and GW190814. Correspondingly, the radii for $1.4M_{\odot }$ and $2.1M_{\odot }$ stars are ${12.04}_{-0.31}^{+0.27}\mathrm{km}$ (${12.16}_{-0.31}^{+0.26}\mathrm{km}$), and ${13.43}_{-0.32}^{+0.31}\mathrm{km}$ (${13.60}_{-0.34}^{+0.29}\mathrm{km}$), respectively. The tidal deformability ${\mathrm{\Lambda }}_{1.4}$ for a $1.4M_{\odot }$ star is ${205}_{-32.53}^{+32.49}$ (${212.36}_{-32.66}^{+53.71}$). These results may impact the research of multiquark states, which could potentially improve our understanding of the nonperturbative strong interaction.