Three major misconceptions concerning quantized tachyon fields, the energy spectrum unbounded from below, the frame-dependent and unstable vacuum state, and the noncovariant commutation rules, are shown to be a result of misrepresenting the Lorentz group in a too small Hilbert space. By doubling this space we establish an explicitly covariant framework that allows for the proper quantization of the tachyon fields eliminating all of these issues. Our scheme that is derived to maintain the relativistic covariance also singles out the two-state formalism developed by Aharonov et al. [Phys. Rev. 134, B1410 (1964)] as a preferred interpretation of the quantum theory.

A new quantum link microstructure was proposed for the lattice quantum chromodynamics (QCD) Hamiltonian, replacing the Wilson gauge links with a bilinear of fermionic qubits, later generalized to D-theory. This formalism provides a general framework for building lattice field theory algorithms for quantum computing. We focus mostly on the simplest case of a quantum rotor for a single compact U(1) field. We also make some progress for non-Abelian setups, making it clear that the ideas developed in the U(1) case extend to other groups. These in turn are building blocks for $1+0$-dimensional ($1+0$-D) matrix models, $1+1$-D sigma models and non-Abelian gauge theories in $2+1$ and $3+1$ dimensions. By introducing multiple flavors for the U(1) field, where the flavor symmetry is gauged, we can efficiently approach the infinite-dimensional Hilbert space of the quantum O(2) rotor with increasing flavors. The emphasis of the method is on preserving the symplectic algebra exchanging fermionic qubits by sigma matrices (or hard bosons) and developing a formal strategy capable of generalization to a $\mathrm{SU}(3)$ field for lattice QCD and other non-Abelian $1+1$-D sigma models or $3+1$-D gauge theories. For U(1), we discuss briefly the qubit algorithms for the study of the discrete $1+1$-D sine-Gordon equation.

We study the entanglement entropy of Hamiltonian SU(2) lattice gauge theory in $2+1$ dimensions on linear plaquette chains and show that the entanglement entropies of both ground and excited states follow Page curves. The transition of the subsystem size dependence of the entanglement entropy from the area law for the ground state to the volume law for highly excited states is found to be described by a universal crossover function. Quantum many-body scars in the middle of the spectrum, which are present in the electric flux truncated Hilbert space, where the gauge theory can be mapped onto an Ising model, disappear when higher electric field representations are included in the Hilbert space basis. This suggests the continuum ($2+1$)-dimensional SU(2) gauge theory does not have such scarred states.

In the present work, a relativistic relation that connects the difference of interacting and noninteracting integrated two-particle correlation functions in finite volume to infinite volume scattering phase shift through an integral is derived. We show that the difference of integrated finite volume correlation functions converges rapidly to its infinite volume limit as the size of the periodic box is increased. The fast convergence of our proposed formalism is illustrated by analytic solutions of a contact interaction model, the perturbation theory calculation, and also the Monte Carlo simulation of a complex ${\varphi }^4$ lattice field theory model.

We present the application of microcanonical inflection point analysis (MIPA)—a novel and powerful method for the systematic identification and classification of phase transitions (PTs)—to the microcanonical formulation of lattice gauge theories. Specifically, we explore how this approach sheds light on collective phenomena such as the emergence of topological order in quantum field theories. As a case study, we show how to systematically characterize PTs in 4D $U(1)$ lattice electrodynamics. Beyond identifying the well-established deconfinement PT (DPT) associated with pair dissolution, classified as a first-order PT, we uncover two higher-order PTs not observed before. Thanks to the application of the MIPA, we identify an independent third-order PT in the confined phase and indications of a dependent third-order PT in the deconfined (Coulomb) phase. To gain physical insights into these PTs, we numerically compute the average number density of monopolar and pair defects as a function of energy. Notably, our findings reveal that the pair dissolution mechanism extends beyond a singular transitional phenomenon coinciding with the DPT. Instead, it encompasses a spectrum of transitional phenomena, as indicated by the rates of acceleration and deceleration in the dissolution of pairs as a function of energy. Finally, we briefly discuss how such a method can be extended to more complex quantum field theories on a lattice.

The scalar mesons have been established for a long time, but their nature is still an open question. In this paper, we investigate the potential of categorizing their $SU(3{)}_f$ representations via $J/\psi \to SV$ and $\gamma S$, offering a criterion that may illuminate this issue. Here, $S$ ($V$) denotes scalar (vector) mesons. Using the $SU(3{)}_f$ symmetry with the current data, we find that $f_0(500)$ and $f_0(980)$ are mostly made of singlet and octet $SU(3{)}_f$ representations, respectively, with the singlet-octet mixing angle of $\theta =(82.9\pm 4.4)°$. This conclusion is consistent with the caculations of the quark-antiquark ($q\overline{q}$) hypothesis. For the scalar mesons in the range of 1–2 GeV, we discuss the mixings between $q\overline{q}$ and glueballs. Our numerical results suggest that $f_0(1710)$ is likely composed of the scalar glueball. We urge our experimental colleagues to measure $J/\psi \to \rho a_0(980,1450,1710)$, $K^{*}(892{)}^{\pm }{K}^{*}(700,1430,1950{)}^{\mp }$, and $\omega f_0(500)$, which provide useful information in the $SU(3{)}_f$ analysis.

Observing the mass shifts of mesons immersed in nuclear matter is interesting, as the changes are expected to shed light on the effects of chiral symmetry breaking on the origin of hadron masses. At the same time, it is important to understand the momentum dependence of the masses for spin-1 mesons, as the changes manifest differently across the two polarization modes. Here, the mass shifts of $K_1^{\pm }$ mesons with finite three-momentum in nuclear medium are studied in the QCD sum rule approach. We find that the mass of $K_1^{+}$ ($K_1^{-}$) meson is increased(decreased) by the nontrivial momentum effect in both the transverse and longitudinal modes. Specifically, compared to its rest mass in the nuclear medium, in the transverse mode, the mass of $K_1^{+}(K_1^{-})$ is observed to shift by $+2(-55)\mathrm{MeV}$, while in the longitudinal mode, the mass shift is $+13(-11)\mathrm{MeV}$, all at a momentum of 0.5 GeV. Exploring the medium modifications of $K_1$ meson through kaon beams at J-PARC will provide insights on the partial restoration of chiral symmetry in nuclear matter.

We study quantum chromodynamics in the chiral large $N_c$ limit which contains a left-handed Weyl fermion in the fundamental representation, a left-handed Weyl fermion in the two index antisymmetric representation and $(N_c-3)$ left-handed Weyl fermions in the antifundamental representation of the $SU(N_c)$ gauge group. We construct gauge singlet composite operators and study their masses and correlation functions at large $N_c$. It is shown that all hadron masses scale as $\sim N_c^0{n}_q$ where $n_q$ is the number of constituent quarks in the hadron. In addition by simple gluon exchange considerations it is seen that scattering amplitudes between hadrons have the same $N_c$ scaling as the mass of the lightest hadron involved. This is the case provided the hadrons in the scattering amplitude share a sufficiently large number of constituent quarks. The chiral large $N_c$ extension also allows for other nontrivial processes. For instance we consider two different baryonium states that are unique to this extension and that decay via emissions of two- and three-quark hadrons. Also other nontrivial scattering processes are considered. Finally, we study composites made of a mix of left- and right-handed fields. We categorize multiple groups of hadrons within the full spectrum according to their flavor structure. Within these groups all $n$-point functions scale the same.

In this work, we evaluate the $X(3872)$ to $\psi (2S)$ yield ratio ($N_X/N_{\psi (2S)}$) in Pb-Pb collisions, taking into account the interactions of the $\psi (2S)$ and $X(3872)$ states with light mesons in the hadron gas formed at the late stages of these collisions. We employ an effective Lagrangian approach to estimate the thermally averaged cross sections for the production and absorption of the $\psi (2S)$ and use them in the rate equation to determine the time evolution of $N_{\psi (2S)}$. The multiplicity of these states at the end of the mixed phase is obtained from the coalescence model. The multiplicity of $X(3872)$, treated as a bound state of $(D{\overline{D}}^{*}+\mathrm{cc})$ and also as a compact tetraquark, was already calculated in previous works. Knowing these yields, we derive predictions for the ratio ($N_X/N_{\psi (2S)}$) as a function of the centrality, of the center-of-mass energy, and of the charged hadron multiplicity measured at midrapidity $[d{N}_{ch}/d\eta (\eta <0.5)]$. Finally, we make predictions for this ratio in Pb-Pb collisions at $\sqrt{s_{NN}}=5.02\mathrm{TeV}$ to be measured by the ALICE Collaboration in run 3. Our findings suggest that the molecular configuration generates a ratio compatible with the data, whereas the ratio obtained with the tetraquark configuration is 50 times smaller.

In the present work, the strong decays of the newly observed $P_{cs}(4338)$ as well as its high isospin cousin $P_{cs}(4460)$ are studied via the QCD sum rules. According to conservation of isospin, spin, and parity, the hadronic coupling constants in four decay channels are obtained; then, the partial decay widths are obtained. The total width of the $P_{cs}(4338)$ coincides with the experimental data nicely, while the predictions for the $P_{cs}(4460)$ can be testified in the future experiment and shed light on the nature of the $P_{cs}(4338)$.

We propose novel methods to determine the $\mathrm{\Upsilon }(4S)\to B^{+}{B}^{-}$ and $\mathrm{\Upsilon }(4S)\to B^0{\overline{B}}^0$ decay rates. The precision to which they and their ratio are known yields at present a limiting uncertainty around 2% in measurements of absolute $B$ decay rates, and thus in a variety of applications, such as precision determinations of elements of the Cabibbo-Kobayashi-Maskawa matrix and flavor-symmetry relations. The new methods we propose are based in one case on exploiting the $\mathrm{\Upsilon }(5S)$ datasets, in the other case on the different average number of charged tracks in $B^{\pm }$ and $B^0$ decays. We estimate future sensitivities using these methods and discuss possible measurements of $f_d/f_u$ at the (HL-)LHC.

This study aims to develop second-order relativistic viscous magnetohydrodynamics (MHD) derived from kinetic theory within an extended relaxation time approximation (momentum/energy dependent) for the collision kernel. The investigation involves a detailed examination of shear stress tensor evolution equations and associated transport coefficients. The Boltzmann equation is solved using a Chapman-Enskog-like gradient expansion for a charge-conserved conformal system, incorporating a momentum-dependent relaxation time. The derived relativistic nonresistive, viscous second-order MHD equations for the shear stress tensor reveal significant modifications in the coupling with dissipative charge current and magnetic field due to the momentum dependence of the relaxation time. By utilizing a power law parametrization to quantify the momentum dependence of the relaxation time, the anisotropic magnetic field-dependent shear coefficients in the Navier-Stokes limit have been investigated. The resulting viscous coefficients are seen to be sensitive to the momentum dependence of the relaxation time.

We present the first search for the leptonic decays $D^{*+}\to e^{+}{\nu }_e$ and $D^{*+}\to {\mu }^{+}{\nu }_{\mu }$ by analyzing a data sample of electron-positron collisions recorded with the BESIII detector at center-of-mass energies between 4.178 and 4.226 GeV, corresponding to an integrated luminosity of $6.32{\mathrm{fb}}^{-1}$. No significant signal is observed. The upper limits on the branching fractions for $D^{*+}\to e^{+}{\nu }_e$ and $D^{*+}\to {\mu }^{+}{\nu }_{\mu }$ are set to be $1.1\times {10}^{-5}$ and $4.3\times {10}^{-6}$ at 90% confidence level, respectively.

Our Universe is permeated with interstellar plasma, which prevents propagation of low-frequency electromagnetic waves. Here, we show that two dramatic consequences arise out of such suppression; (i) if plasma permeates the light ring of a black hole, electromagnetic modes are screened entirely from the gravitational-wave signal, changing the black hole spectroscopy paradigm; (ii) if a near vacuum cavity is formed close to a charged black hole, as expected for near equal-mass mergers, ringdown “echoes” are excited. The amplitude of such echoes decays slowly and could thus serve as a silver bullet for plasmas near charged black holes.

We present a superfluid dark star model consisting of relativistic dark bosons with two-body self-interaction. The obtained masses, radii, and tidal deformability depend in a simple way on the boson mass and interaction strength. We report first results on binary mergers: the distinctive amplitude and frequency of the emitted gravitational waves are well within reach of terrestrial interferometers.

We explicitly compute the Neveu-Schwarz sector conventional type-I superstring tree-level amplitudes at five points after compactifying to 4D, express the QFT building block in the helicity basis, and give several attempts toward arbitrary $n$ points. More specifically, we consider the interaction of one first excited level and otherwise massless states of conventional type-I superstrings, where the four-dimensional states can, for instance, be realized via D3 branes. We construct the amplitude by using the Berends-Giele currents. From the recursion of Berends-Giele currents, we can generate the higher point amplitude. We also apply the BCFW recursion with massive external legs shifted and get the amplitude for arbitrary $n$ points.

We consider the D3-D7 model and use the spectral function of a probe fermion on D7 to analyze the first order phase transition from the black-hole embedding phase to another black-hole embedding phase in the presence of the finite density and temperature. From the fermionic spectral functions, we study the temperature dependence of the decay rate, and we observe various phenomena that support the first order phase transition including jump in it at the critical temperature that corresponds to the first order phase transition.

In this paper, we utilize the effective corrections of the $\overline{\mu }$ scheme in loop quantum black holes to obtain a four-dimensional spherically symmetric metric with a cosmological constant. By imposing the areal gauge on the components of Ashtekar variables in the classical theory and applying the holonomy corrections, we derive the equations of motion, which can be solved to obtain the expression for the effective metric in the Painlevé-Gullstrand coordinates. Compared to the classical de Sitter (anti–de Sitter) spacetime, the loop quantum gravity (LQG) correction sets an upper bound on the cosmological constant as $\mathrm{\Lambda }<\frac{3}{{\gamma }^2\mathrm{\Delta }}$. The thermodynamic properties of black holes have also been calculated. We interestingly found that for a small black hole, the temperature of the LQG black hole decreases as the mass decreases, which is quite different with the classical scenario. Moreover, our result shows that a logarithmic term appeared as the leading order correction to the Beikenstein-Hawking entropy. Furthermore, the LQG corrections also introduce an extra phase transition in the black hole’s heat capacity at smaller radius.

It has been shown that non-Abelian solitonic vortex string supported in four-dimensional (4D) $\mathcal{N}=2$ supersymmetric QCD (SQCD) with the U(2) gauge group and $N_f=4$ quark flavors becomes a critical superstring. This string propagates in the ten-dimensional space formed by a product of the flat 4D space and an internal space given by a Calabi-Yau noncompact threefold, namely, the conifold. The spectrum of low-lying closed string states was found and interpreted as a spectrum of hadrons in 4D $\mathcal{N}=2$ SQCD. In particular, the lowest string state appears to be a massless Bogomol’nyi-Prasad-Sommerfield (BPS) baryon associated with the deformation of the complex structure modulus $b$ of the conifold. It was recently shown that the Coulomb branch of the associated string sigma model which opens up at strong coupling can be described by $\mathcal{N}=2$ Liouville theory. Building on these results we switch on quark masses in 4D $\mathcal{N}=2$ SQCD and study the interpolation of the initial U(2) SQCD with $N_f=4$ quarks to the final SQCD with the U(4) gauge group and $N_f=8$ quarks. To find the true string vacuum which arises due to the mass deformation we solve the effective supergravity equations of motion associated with the deformed world sheet Liouville theory. We show that the massless BPS baryon $b$ survives the deformation and that finding of the spectrum of low-lying massive hadrons in the final SQCD is linked to the Calogero problem.

The integrated correlator of four superconformal stress-tensor primaries in $SU(N)$ $\mathcal{N}=4$ super Yang-Mills (SYM) theory in the perturbative limit takes a remarkably simple form, where the $L$-loop coefficient is given by a rational multiple of $\zeta (2L+1)$. In this paper, we extend the previous analysis of expressing the perturbative integrated correlator as a linear combination of periods of $f$-graphs, graphical representations for loop integrands, to the nonplanar sector at four loops. At this loop order, multiple zeta values make their first appearance when evaluating periods of nonplanar $f$-graphs, but cancel nontrivially in the weighted sum. The remaining single zeta value, along with the rational number prefactor, makes a perfect agreement with the prediction from supersymmmetric localization.