We present a phenomenological study on the role of charm contribution and $SU(2)$ isospin symmetry in the extraction of the $\mathrm{\Lambda }$ polarizing fragmentation functions from $e^{+}{e}^{-}\to {\mathrm{\Lambda }}^{\uparrow }({\overline{\mathrm{\Lambda }}}^{\uparrow })h+X$ annihilation processes. We adopt the well-established transverse-momentum-dependent factorization formalism, within the Collins-Soper-Sterman evolution scheme at next-to-leading logarithm accuracy, carefully exploiting the role of the nonperturbative component of the polarizing fragmentation function. We then discuss the impact of these results on the predictions for transverse $\mathrm{\Lambda }$, $\overline{\mathrm{\Lambda }}$ polarization in semi-inclusive deep inelastic scattering processes at typical energies of the future Electron-Ion Collider.

We address the proton spin puzzle with a fully relativistic and nonperturbative approach based on a light-front quantized Hamiltonian with quantum chromodynamics (QCD) input. From this, we calculate the effects from incorporating a dynamical gluon on the proton’s gluon densities, helicity distribution, and orbital angular momentum that constitute the proton spin sum rule. We predict about 26% of the proton’s spin is carried by the gluon’s helicity and about 1.3% by its orbital angular momentum in low-momentum transfer experiments. Our approach also provides a good quality description of the proton’s quark distribution functions following QCD scale evolution.

Using a data sample of $(1.0087\pm 0.0044)\times {10}^{10}J/\psi$ events collected with the BESIII detector, the decays of $J/\psi \to \gamma {\pi }^0(\eta ,{\eta }^{\prime })\to \gamma \gamma \gamma$ are studied. Newly measured branching fractions are $\mathcal{B}(J/\psi \to \gamma {\pi }^0)=(3.34\pm 0.02\pm 0.09)\times {10}^{-5}$, $\mathcal{B}(J/\psi \to \gamma \eta )=(1.096\pm 0.001\pm 0.019)\times {10}^{-3}$, and $\mathcal{B}(J/\psi \to \gamma {\eta }^{\prime })=(5.40\pm 0.01\pm 0.11)\times {10}^{-3}$, where the first uncertainties are statistical and the second are systematic. These results are consistent with the world average values within two standard deviations. The ratio of partial widths $\mathrm{\Gamma }(J/\psi \to \gamma {\eta }^{\prime })/\mathrm{\Gamma }(J/\psi \to \gamma \eta )$ is measured to be $4.93\pm 0.13$. The singlet-octet pseudoscalar mixing angle ${\theta }_P$ is determined to be ${\theta }_P=-(22.11\pm 0.26)°$ or $-(19.34\pm 0.34)°$ with two different phenomenological models.

We present a new technique, “tau polarimetry,” for measuring the longitudinal beam polarization present in an $e^{+}{e}^{-}$ collider through the analysis of $e^{+}{e}^{-}\to {\tau }^{+}{\tau }^{-}$ events. By exploiting the sensitivity of $\tau$ decay kinematics to the longitudinal polarization of the beams, we demonstrate that the longitudinal polarization can be measured with a 3 per mil systematic uncertainty at the interaction point using a technique that is independent of spin and beam transport modeling. Using $424.2\pm 1.8{\mathrm{fb}}^{-1}$ of BABAR data at $\sqrt{s}=10.58\mathrm{GeV}$, the average longitudinal polarization of the PEP-II $e^{+}{e}^{-}$ collider has been measured to be $⟨P⟩=0.0035\pm 0.0024_{\mathrm{stat}}\pm 0.0029_{\mathrm{sys}}$. The systematic uncertainty studies are described in detail, which can serve as a guide for future applications of tau polarimetry. A proposed $e^{-}$ beam longitudinal polarization upgrade to the SuperKEKB $e^{+}{e}^{-}$ collider would benefit from this technique.

In this work, we wish to address the question—whether the quasinormal modes, the characteristic frequencies associated with perturbed black hole spacetimes, central to the stability of these black holes, are themselves stable. Though the differential operator governing the perturbation of black hole spacetimes is self-adjoint, the boundary conditions are dissipative in nature, so that the spectral theorem becomes inapplicable, and there is no guarantee regarding the stability of the quasinormal modes. Following Jaramillo et al. [Phys. Rev. X 11, 031003 (2021)], we have provided a general method of transforming to the hyperboloidal coordinate system, for both asymptotically flat and asymptotically de Sitter spacetimes which neatly captures the dissipative boundary conditions, and the differential operator becomes non-self-adjoint. Employing the pseudospectrum analysis and numerically implementing the same through Chebyshev’s spectral method, we present how the quasinormal modes will drift away from their unperturbed values under external perturbation of the scattering potential. Intriguingly, for strong enough perturbation, even the fundamental quasinormal mode, associated with gravitational perturbations, drifts away from its unperturbed position for asymptotically de Sitter black holes, in stark contrast to the case of asymptotically flat black holes. Besides presenting several other interesting results, specifically for asymptotically de Sitter black holes, we also discuss the implications of the instability of the fundamental quasinormal mode on the strong cosmic censorship conjecture.

Graviton-photon oscillation is the conversion of gravitational waves to electromagnetic waves and vice versa in the presence of a background electromagnetic field. We investigate this phenomenon in a cosmological scenario considering a background cosmic magnetic field and assuming different gravitational frameworks. We obtain the damping term that characterizes the attenuation of the conversion probability in cosmological backgrounds. This is a general feature that is present even for standard general relativity. Furthermore, we show that the effects of decoherence, which are due to the interaction with the cosmological expansion and with the additional degrees of freedom of alternative theories of gravity, can be relevant to the phenomenon of graviton-photon mixing.

We study the interactions between ’t Hooft-Polyakov magnetic monopoles and the domain walls formed by the same order parameter within an $SU(2)$ gauge theory. We observe that the collision leads to the erasure of the magnetic monopoles, as suggested by Dvali et al. [Phys. Rev. Lett. 80, 2281 (1998)]. The domain wall represents a layer of vacuum with un-Higgsed $SU(2)$ gauge symmetry. When the monopole enters the wall, it unwinds, and the magnetic charge spreads over the wall. We perform numerical simulations of the collision process and, in particular, analyze the angular distribution of the emitted electromagnetic radiation. As in the previous studies, we observe that erasure always occurs. Although not forbidden by any conservation laws, the monopole never passes through the wall. This is explained by entropy suppression. The erasure phenomenon has important implications for cosmology, as it sheds a very different light on the monopole abundance in postinflationary phase transitions and provides potentially observable imprints in the form of electromagnetic and gravitational radiation. The phenomenon also sheds light on fundamental aspects of gauge theories with coexisting phases, such as confining and Higgs phases.

We present an estimation of the noise induced by scattered light inside the main arms of the Einstein Telescope (ET) gravitational wave detector. Both ET configurations for high- and low-frequency interferometers are considered, for which we propose baffle layouts. The level of scattered light and the ET laser beam clipping losses are intimately related to the baffle inner aperture. We discuss how this translates into minimum requirements on the vacuum pipe radius, a critical parameter in the ET design. The noise estimations are computed using analytical calculations complemented with numerical tools and depend on a number of baseline parameters we use as input in the calculations. We conclude that the scattered light noise can be maintained at acceptable levels such that it does not compromise the ET performance, provided some requirements are met.

We propose a novel strategy for disentangling proton collisions at hadron colliders such as the LHC that considerably improves over the current state of the art. Employing a metric inspired by optimal transport problems as the cost function of a graph neural network, our algorithm is able to compare two particle collections with different noise levels and learns to flag particles originating from the main interaction amidst products from up to 200 simultaneous pileup collisions. We thereby sidestep the critical task of obtaining a ground truth by labeling particles and avoid arduous human annotation in favor of labels derived in situ through a self-supervised process. We demonstrate how our approach—which, unlike competing algorithms, is trivial to implement—improves the resolution in key objects used in precision measurements and searches alike and present large sensitivity gains in searching for exotic Higgs boson decays at the High-Luminosity LHC.

In this paper, we investigate the time-dependent angular analysis of $B_s^0\to \varphi \varphi$ decay to search for new physics signals via $CP$-violating observables. We work with a new physics Hamiltonian containing both left- and right-handed chromomagnetic dipole operators. The hierarchy of the helicity amplitudes in this model gives us a new scheme of experimental search, which is different from the ones LHCb has used in its analysis. To illustrate this new scheme, we perform a sensitivity study using two pseudo datasets generated using LHCb’s measured values. We find the sensitivity of $CP$-violating observables to be of the order of 5–7% with the current LHCb statistics. In addition, we present a revised version of the table of coefficients of time-dependent terms in the angular decay distribution with precisely defined quantities. Moreover, we show that Belle(II)’s $B_d^0\to \varphi K_s$ and LHCb’s $B_s^0\to \varphi \varphi$ measurements could be coupled within our model to obtain the chirality of the new physics.

The front form of Hamiltonian dynamics provides a framework within QCD in which interaction terms are invariant under seven of ten Poincaré transformations and the vacuum structure is simple. However, canonical expressions are divergent and must be regulated before attempting to define an eigenvalue problem. The renormalization-group procedure for effective particles (RGPEP) provides a systematic way of renormalizing Hamiltonians and obtaining counterterms. One of its achievements is the description of asymptotic freedom with a running coupling defined as the coefficient of the three-gluon-vertex operators in the renormalized Hamiltonian. Yet, the results we obtain need a deeper understanding, since the coefficient function shows a finite cutoff dependence, at least in the third-order terms of the perturbative expansion. In this work, we present an RGPEP computation of the three-gluon vertex with a different regularization scheme based on massive gluons. Our calculation shows that the three-gluon Hamiltonian interaction term has a finite limit as the gluon mass vanishes, but the finite function $h(x)$ that was obtained in previous calculations as a consequence of the finite dependence on the regularization is different. This result indicates a need for understanding how to eliminate finite regularization effects from Hamiltonians for effective quarks and gluons in QCD. Nevertheless, it is remarkable that all terms depending on the gluon mass cancel out in the limit of vanishing gluon mass in a nontrivial way, even when each term individually diverges in such a limit.

We present a new class of dark matter (DM) models wherein the Standard Model (SM) is extended with a new $SU(2{)}_{\mathrm{D}}$ dark gauge sector. In this framework, the stability of DM is provided by the conservation of a $U(1)$ global symmetry which, upon appropriate charge assignments for the $SU(2{)}_{\mathrm{D}}$ multiplets, effectively leads to a ${\mathbb{Z}}_2$ symmetry subgroup. The origin of the global $U(1)$ symmetry which ensures the stability of DM can be justified in the form of a dark electroweak (EW) sector or through an underlying composite structure. The key ingredient of the model is a vectorlike (VL) fermion doublet of $SU(2{)}_{\mathrm{D}}$, the members of which are singlets of the SM EW gauge group, which mediate the interactions between the dark sector and the SM, via new Yukawa interactions. This class of models, labeled as fermion portal vector DM (FPVDM), allows multiple realizations, depending on the properties of the VL partner and the scalar potential. After spontaneous breaking of the $SU(2{)}_{\mathrm{D}}$ symmetry via a new scalar doublet, the ensuing massive vector bosons with nonzero dark isospin are DM candidates. The new class of FPVDM models suggested here has numerous phenomenological implications for collider and noncollider studies. As a practical example, we discuss here in detail a realization involving a VL top partner assuming no mixing between the two physical scalars of the theory, the SM Higgs boson and its counterpart in the dark sector. We, thus, provide bounds on this setup from both collider and astroparticle observables.

We compute the heavy quarkonium complex potential in a magnetic field of arbitrary strength generated in the relativistic heavy-ion collision. First, the one-loop gluon polarization tensor is obtained in the presence of an external, constant, and homogeneous magnetic field using the Schwinger proper time formalism in Euclidean space. The gluon propagator is computed from the gluon polarization tensor, and it is used to calculate the dielectric permittivity in the presence of the magnetic field. The modified dielectric permittivity is then used to compute the heavy quarkonium complex potential. We find that the heavy quarkonium complex potential is anisotropic in nature, which depends on the angle between the quark-antiquark ($Q\overline{Q}$) dipole axis and the direction of the magnetic field. We discuss the effect of the magnetic field strength and the angular orientation of the dipole on the heavy quarkonium potential. We discuss how the magnetic field influences the thermal widths of quarkonium states. Further, we also discuss the limitation of the strong-field approximation as done in literature in the light of heavy-ion observables, as the effect of the magnetic field is very nominal to the quarkonium potential.

We derive a “classical-quantum” approximation scheme for a broad class of bipartite quantum systems from fully quantum dynamics. In this approximation, one subsystem evolves via classical equations of motion with quantum corrections, and the other subsystem evolves quantum mechanically with equations of motion informed by the evolving classical degrees of freedom. Using perturbation theory, we derive an estimate for the growth rate of entanglement of the subsystems and deduce a “scrambling time”—the time required for the subsystems to become significantly entangled from an initial product state. We argue that a necessary condition for the validity of the classical-quantum approximation is consistency of initial data with the generalized Bohr correspondence principle. We illustrate the general formalism by numerically studying the fully quantum, fully classical, and classical-quantum dynamics of a system of two oscillators with nonlinear coupling. This system exhibits parametric resonance, and we show that quantum effects quench parametric resonance at late times. Lastly, we present a curious late-time scaling relation between the average value of the von Neumann entanglement of the interacting oscillator system and its total energy: $S\sim 2/3\ln E$.

A new duality is proposed in four-dimensional flat space, which exchanges between spin and orbital degrees of freedom. This is motivated by a Hodge decomposition of the angular-momentum bivector for massive fields, along which spin and orbital angular momentum are Hodge duals of one another. The duality respects Poincarè symmetry and is shown to transform between complementary spacelike regions, projecting a fixed three-dimensional de Sitter world-tube (around the center of mass) into the bulk of four-dimensional spacetime and vice versa. This state of affairs is interpreted as a realization of the holographic principle. The dual theory living on that tube turns out to be noncommutative and entirely defined by the Casimir elements of the Poincarè algebra. In fact, the mass is now an ultraviolet cutoff. This naturally suggests that, for a Poincarè or just Lorentz-invariant quantum theory with massive fields of nonzero spin, spacetime is quantized at the fundamental level.

It is usually accepted that quantum dynamics described by the Schrödinger equation that determines the evolution of states from one Cauchy surface to another is unitary. However, it has been known for some time that this expectation is not borne out in the conventional setting in which one envisages the dynamics on a fixed Hilbert space. Indeed it is not even true for linear quantum field theory on Minkowski space if the chosen Cauchy surfaces are not preserved by the flow of a timelike Killing vector. This issue was elegantly addressed and resolved by Agullo and Ashtekar who showed that in a general setting quantum dynamics in the Schrödinger picture does not take place in a fixed Hilbert space. Instead, it takes place on a nontrivial bundle over time, the Hilbert bundle, whose fiber at a given time is a Hilbert space at that time. In this article, we postulate a Schrödinger equation that incorporates the effect of change in vacuum during time evolution by including the Bogoliubov transformation explicitly in the Schrödinger equation. More precisely, for a linear (real) Klein-Gordon field on a globally hyperbolic spacetime we write down a Schrödinger equation that propagates states between arbitrary chosen Cauchy surfaces, thus describing the quantum dynamics on a Hilbert bundle. We show that this dynamics is unitary if a specific tensor on the canonical phase space satisfies the Hilbert-Schmidt condition. The generalized unitarity condition of Agullo-Ashtekar follows quite naturally from our construction.

The violation of the Bell-Clauser-Horne-Shimony-Holt inequality in the vacuum state of a relativistic free real scalar field is established by means of the Tomita-Takesaki construction and the direct computation of the correlation functions of Weyl operators.

We present the predictions with standard sirens at gravitational-wave detectors, such as the Laser Interferometer Space Antenna (LISA) and the Einstein Telescope (ET), for interacting dark energy theories. We focus on four models characterized by couplings between the dark energy field and the dark matter fluid arising from conformal or disformal transformations of the metric, along with an exponential self-interacting potential. To this purpose we construct mock catalogs and perform a Markov chain Monte Carlo analysis by considering ET and LISA standard sirens, and also their combination with baryon acoustic oscillation (BAO) and supernovae Ia (SNIa) data. We find that in all four models considered, the accuracy on the $H_0$ parameter increases by 1 order of magnitude at $1\sigma$ when compared to the $\mathrm{SNIa}+\mathrm{BAO}$ data set, possibly shedding light in the future on the origin of the $H_0$ tension. The combination of standard sirens with $\mathrm{SNIa}+\mathrm{BAO}$ allows to improve the accuracy on some coupling and exponential parameters, hinting at future prospects for constraining interactions in the dark sector.

We study the classical dynamics of the Nambu-Goto strings with a null symmetry in curved spacetimes admitting a null Killing vector field. The Nambu-Goto equation is reduced to first-order ordinary differential equations and is always integrable in contrast to the case of non-null symmetries where integrability requires additional spacetime symmetries. It is found that in the case of null symmetry, an almost contact structure associated with the metric dual 1-form $\eta$ of the null Killing vector field emerges naturally. This structure determines the allowed class of string worldsheets in such a way that the tangent vector fields of the worldsheet lie in $\ker \mathrm{d}\eta$. In the special case that the almost contact structure becomes a contact structure, its Reeb vector field completely characterizes the worldsheet. We apply our formulation to the strings in the $pp$-waves, the Einstein static universe and the Gödel universe. We also study their worldsheet geometry in detail.

We establish a new relation between classical observables for scattering and bound orbits of a massive probe particle in a Kerr background. We find an exact representation of the Hamilton-Jacobi action in terms of the conserved charges that admits an analytic continuation, for both the radial and polar contributions, for a general class of geodesics beyond the equatorial case. Remarkably, this allows to extend the boundary to a bound dictionary and provides an efficient method to compute the deflection angles and time delay for scattering orbits, as well as frequency ratios for bound orbits, in the probe limit but at all orders in the perturbative expansion.