A fundamental question in quantum chromodynamics (QCD) is the existence of a phase transition at large doping of quarks over antiquarks. We present the first prediction of a QCD critical point ($CP$) from a Bayesian analysis constrained by first principle results at zero doping. We employ the gauge/gravity duality to map QCD onto a theory of dual black holes. Predictions for the $CP$ location in different realizations of the model overlap at one sigma. Even if many prior samples do not include a $CP$, one is found in nearly 100% of posterior samples, indicating a strong preference for a $CP$.

Following recent experimental progress in the study of bottom baryons, we systematically calculate the mass spectra of ${\mathrm{\Lambda }}_b$, ${\mathrm{\Xi }}_b$, ${\mathrm{\Sigma }}_b$, ${\mathrm{\Xi }}_b^{\prime }$, and ${\mathrm{\Omega }}_b$ baryons with a quark-diquark picture in the framework of a relativistic flux tube model with spin-dependent interactions in the j-j coupling scheme. Furthermore, we calculate the strong decay width of bottom baryons decaying into a bottom baryon and a light pseudoscalar meson. Good agreement is found between the calculated masses and the experimentally available masses of singly bottom baryons. By analyzing both mass spectra and strong decay widths, we interpret ${\mathrm{\Sigma }}_b(6097)$ as a $1P(3/2^{-})$ state and ${\mathrm{\Xi }}_b(6100)$ as a $1P(1/2^{-})$ state of the ${\mathrm{\Xi }}_b$ baryon. The ${\mathrm{\Xi }}_b(6227)$ is identified to be an orbital excitation $1P$ of the ${\mathrm{\Xi }}_b^{\prime }$ baryon with $J^P=3/2^{-}$. Further, we determine ${\mathrm{\Xi }}_b(6327)$ and ${\mathrm{\Xi }}_b(6333)$ as a $1P(3/2^{-})$ state and $1P(5/2^{-})$ state, respectively, of ${\mathrm{\Xi }}_b^{\prime }$ baryon. From the obtained mass spectra, we construct the Regge trajectories in the $(J,M^2)$ plane, which are found to be essentially linear, parallel, and equidistant. Our predictions for higher orbital and radial excited states can help experimentalists identify missing excited states of singly bottom baryons.

The ground-breaking discovery of the first fully charmed tetraquark state $X(6900)$ in the $J/\psi J/\psi$ invariant mass distribution by the LHCb collaboration has inspired intensive theoretical studies. Various interpretations, such as molecular states, compact tetraquark states, and coupled-channel effects, have been proposed for these states. Of particular interest is the ongoing search for the triple-$J/\psi$ state–a fully-charmed hexaquark state. To deepen our understanding of the triple-$J/\psi$ state and to guide future experimental searches, we study the triple-$J/\psi$ system in this work employing the Gaussian expansion method and the $J/\psi J/\psi$ potential parametrized to yield a shallow bound state, as suggested in several theoretical works. Our results support a triple-$J/\psi$ bound state, even in cases where the attractive interaction between the two $J/\psi$ mesons is very weak. Moreover, our analysis implies the Efimov effect in the triple-$J/\psi$ system. In addition, we extend our investigation to the triple-$\mathrm{\Upsilon }(1S)$ system and obtain results similar to those for the triple-$J/\psi$ system.

The charge asymmetry in the process $e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}{\pi }^0$ is studied taking into account a longitudinal polarization of electrons (positrons). The asymmetry arises due to interference of amplitudes corresponding to production of pions in states with charge parity odd and charge parity even. It is a manifestation of $a_1(1260)$ meson in the intermediate state. Polarization leads to additional correlations in the differential cross section, which simplifies the experimental study of the process. It is shown that the charge asymmetry can reach several percent.

The first observation of the concurrent production of two $J/\psi$ mesons in proton-nucleus collisions is presented. The analysis is based on a proton-lead ($p\mathrm{Pb}$) data sample recorded at a nucleon-nucleon center-of-mass energy of 8.16 TeV by the CMS experiment at the CERN LHC and corresponding to an integrated luminosity of $174.6{\mathrm{nb}}^{-1}$. The two $J/\psi$ mesons are reconstructed in their ${\mu }^{+}{\mu }^{-}$ decay channels with transverse momenta $p_{\mathrm{T}}>6.5\mathrm{GeV}$ and rapidity $|y|<2.4$. Events where one of the $J/\psi$ mesons is reconstructed in the dielectron channel are also considered in the search. The $p\mathrm{Pb}\to J/\psi J/\psi +X$ process is observed with a significance of 5.3 standard deviations. The measured inclusive fiducial cross section, using the four-muon channel alone, is $\sigma (p\mathrm{Pb}\to J/\psi J/\psi +X)=22.0\pm 8.9(\mathrm{stat})\pm 1.5(\mathrm{syst})\mathrm{nb}$. A fit of the data to the expected rapidity separation for pairs of $J/\psi$ mesons produced in single (SPS) and double (DPS) parton scatterings yields ${\sigma }_{\mathrm{SPS}}^{p\mathrm{Pb}\to J/\psi J/\psi +X}=16.5\pm 10.8(\mathrm{stat})\pm 0.1(\mathrm{syst})\mathrm{nb}$ and ${\sigma }_{\mathrm{DPS}}^{p\mathrm{Pb}\to J/\psi J/\psi +X}=5.4\pm 6.2(\mathrm{stat})\pm 0.4(\mathrm{syst})\mathrm{nb}$, respectively. This latter result can be transformed into a lower bound on the effective DPS cross section, closely related to the squared average interparton transverse separation in the collision, of ${\sigma }_{\mathrm{eff}}>1.0\mathrm{mb}$ at 95% confidence level.

Generalized symmetries and their spontaneous breakdown serve as the fundamental concept to constrain the many-body entanglement structure, which allows us to characterize quantum phases of matter and emergent collective excitations. For example, emergent photons may be understood by spontaneous 1-form symmetry breaking, which results from a long-ranged entanglement structure between UV microscopic degrees of freedom. In this study, we show that emergent “gravity” may also arise in a similar fashion, where quotes have been used to emphasize that the symmetry-constrained gravitons show unconventional properties compared to usual gravitons. As the electric 1-form symmetry in Maxwell theory is realized as a global shift symmetry of the spatial component of the $\mathrm{U}(1)$ gauge field, generated by the electric field, we demonstrate that a constant shift of the Arnowitt-Deser-Misner (ADM) metric on the spatial hypersurface can be viewed as a global symmetry, generated by the ADM canonical momentum. Deriving a vector-type conserved charge from the variation of action, we construct a shift symmetry operator. Considering a Wick rotation, we demonstrate that a gravitational Wilson loop is charged under the action of this shift symmetry operator, which thus confirms the existence of a generalized global symmetry on the ADM hypersurface. Based on the Ward identity, we show that the spontaneous breaking of this global shift symmetry may give rise to a nonpropagating massless symmetric gauge field at the boundary of the hypersurface.

Orbital eccentricity in compact binaries is considered to be a key tracer of their astrophysical origin, and can be inferred from gravitational-wave observations due to its imprint on the emitted signal. For a robust measurement, accurate waveform models are needed. However, ambiguities in the definition of eccentricity can obfuscate the physical meaning and result in seemingly discrepant measurements. In this work we present a suite of 28 new numerical relativity simulations of eccentric, aligned-spin binary black holes with mass ratios between 1 and 6 and initial post-Newtonian eccentricities between 0.05 and 0.3. We then develop a robust pipeline for measuring the eccentricity evolution as a function of frequency from gravitational-wave observables that is applicable even to signals that span at least $\gtrsim 7$ orbits. We assess the reliability of our procedure and quantify its robustness under different assumptions on the data. Using the eccentricity measured at the first apastron, we initialize effective-one-body waveforms and quantify how the precision in the eccentricity measurement, and therefore the choice of the initial conditions, impacts the agreement with the numerical data. We find that even small deviations in the initial eccentricity can lead to non-negligible differences in the phase and amplitude of the waveforms. However, we demonstrate that we can reliably map the eccentricities between the simulation data and analytic models, which is crucial for robustly building eccentric hybrid waveforms, and to improve the accuracy of eccentric waveform models in the strong-field regime.

Black hole superradiance has proven to be very valuable in several realms of gravitational physics and holds a promising discovery potential. In this paper, we consider the superradiant instability of magnetically charged, rotating black holes and find a number of important differences with respect to neutral ones. Considering massive charged bosonic fields, we find that the instability timescale is much shorter, and this is true even if the black hole contains an order-one number of magnetic monopoles, or merely a single one, and possesses either low, moderate, or large values of angular momentum. In particular, the instability is drastically faster than the radiative-decay time of charged pions, potentially making it physically relevant. Furthermore, our analysis identifies the most unstable modes as a class of monopole spheroidal harmonics, which we dub north and south monopole modes, whose morphology is markedly different from the ones in standard superradiance since they extend along the rotational axis. For completeness, we also study the quasinormal mode spectrum and amplification factors of charged massless fields, finding no evidence of instabilities in that case.

Recent observations about the cosmic microwave background evidence a clear discrepancy between the scale of inflation and the Planck scale expected in the conventional inflationary picture, based on simple chaotic inflationary models. This paper explores a possible resolution of this conflict by considering a slight modification of the standard general relativity scenario, which naturally incorporates a cutoff scale consistent with the observations. This last scale of power suppression appears by the combined effect of the preinflationary background dynamics and an associated initial vacuum state for the cosmological perturbations, which differs from the conventional Bunch-Davies state of slow-roll inflation. We revise and correct previous discussions in the literature about the relation between this scale and the scale corresponding to the onset of inflation. The mechanism that produces this cutoff is intimately related to the criterion determining a privileged vacuum state for the primordial perturbations. We adhere to a recent proposal based on an asymptotic diagonalization of the Hamiltonian of the perturbations and leading to a nonoscillatory primordial power spectrum. With this choice, we are able to investigate analytically the model, studying in detail some physically interesting cases. These analytic calculations provide further support to our arguments about the relation between the different scales of the system.

The cosmic background (CB) is defined as the isotropic diffuse radiation field with extragalactic origin found across the electromagnetic spectrum. Different astrophysical sources dominate the CB emission at different energies, such as stars in the optical or active galactic nuclei in x rays. Assuming that dark matter consists of axions or axionlike particles with masses on the order of electron volts or higher, we expect an additional contribution to the CB due to their decay into two photons. Here, we model the CB between the optical and x-ray regimes and include the contribution of decaying axions. Through a comparison with the most recent direct and indirect CB measurements, we constrain the axion parameter space between masses $0.5–{10}^7\mathrm{eV}$ and improve previous limits on axion-photon coupling derived from the CB by roughly an order of magnitude, also reaching the QCD band. We further study the contribution of axions decaying in the Milky Way halo and characterize the axion parameters that would explain the tentative excess CB emission observed with the Long Range Reconnaissance Imager instrument on board the New Horizons probe.

We present a scattering amplitude formalism to study the tidal heating effects of nonspinning neutron stars incorporating both worldline effective field theory and relativistic stellar perturbation theory. In neutron stars, tidal heating arises from fluid viscosity due to various scattering processes in the interior. It also serves as a channel for the exchange of energy and angular momentum between the neutron star and its environment. In the interior of the neutron star, we first derive two master perturbation equations that capture fluid perturbations accurate to linear order in frequency. Remarkably, these equations receive no contribution from bulk viscosity due to a peculiar adiabatic incompressibility which arises in stellar fluid for nonbarotropic perturbations. In the exterior, the metric perturbations reduce to the Regge-Wheeler equation which we solve using the analytical Mano-Suzuki-Takasugi method. We compute the amplitude for gravitational waves scattering off a neutron star, also known as gravitational Raman scattering. From the amplitude, we obtain expressions for the electric quadrupolar static Love number and the leading dissipation number to all orders in compactness. We then compute the leading dissipation number for various realistic equations of state and estimate the change in the number of gravitational-wave cycles due to tidal heating during inspiral in the LIGO-Virgo-KAGRA band.

Regularized quantum information metrics are calculated for the scattering process $e^{-}{e}^{+}\to \gamma ,Z\to {\mu }^{-}{\mu }^{+}$ that has a witness photon entangled with the initial electron-positron state. Unitarity implies the correct regularization of divergences that appear in both the final density matrix and von Neumann entanglement entropies. The entropies are found to quantify uncertainty or randomness. The variation of information, entanglement entropy, and correlation between the muon’s and witness photon’s helicities are found to convey equivalent information. The magnitude of the muon’s expected helicity rises (falls) as the helicity entropy falls (rises). Area, or the scattering cross section, is a source of entropy for the muon’s helicity entropy and momentum entropy. The muon’s differential angular entropy distribution is similar to the differential angular cross section distribution, capturing the forward-backward asymmetry at high center-of-mass energies.

We study the rare semileptonic decays of $B_c$ mesons within the effective field theoretical framework of covariant confined quark model. The transition form factors corresponding to $B_c^{+}\to D^{(*)+}$ and $B_c^{+}\to D_s^{(*)+}$ are computed in the entire $q^2$ range. Using form factors, we compute the branching fractions and compare them with the available theoretical results. We also compute various physical observables such as forward-backward asymmetry, longitudinal and transverse polarizations, as well as clean angular observables.

This paper is a continuation of a study of the properties and applications of quantum stress tensor fluctuations. Here we treat the vacuum fluctuations of the electromagnetic energy-momentum flux operator which has been averaged in space and time. The probability distribution of these fluctuations depends upon the details of this averaging and may allow fluctuations very large compared to the variance. The possibility of detecting their effects on electrons will be considered. The averaging of the flux operator will arise from the interaction of an electron with a wave packet containing real photons. The vacuum radiation pressure fluctuations can exert a force on the electron in any direction, in contrast to the effect of scattering by real photons. Some numerical estimates of the effect will be given.

Three-body dynamics above threshold is required for the reliable extraction of many amplitudes and resonances from experiment and lattice QCD. The S-matrix principle of unitarity can be used to construct dynamical coupled-channel approaches in which three particles scatter off each other, rearranging two-body subsystems by particle exchange. This paper reports the development of a three-body coupled-channel, amplitude including pions and kaons. The unequal-mass amplitude contains two-body S- and P-wave subsystems (“isobars”) of all isospins, $I=0,1/2,1,3/2,2$, and it also allows for transitions within a given isobar. The $f_0(500)(\sigma ),f_0(980),\rho (700),K_0^{*}(700)(\kappa )$, and $K^{*}(892)$ resonances are included, apart from repulsive isobars. Different methods to evaluate the amplitude for physical momenta are discussed. Production amplitudes for $a_1$ quantum numbers are shown as a proof of principle for the numerical implementation.

Tetraquarks, bound states composed of two quarks and two antiquarks, have been the subject of intense study but are challenging to understand from first principles. We apply variational and Green’s function Monte Carlo methods to compute tetraquark ground-state energies in potential nonrelativistic QCD using a wide range of color and spatial wave functions. We find no evidence for bound tetraquarks composed of equal-mass quarks and antiquarks. Conversely, we find clear evidence for the existence of bound tetraquarks for sufficiently unequal quark/antiquark mass ratios at all overall mass scales where our effective theory results are applicable. We predict the critical mass ratios for bound state formation and study tetraquark bound states’ spatial and color structure at leading order and next-to-leading order in potential nonrelativistic QCD.