The $\tau$ lepton anomalous magnetic moment $a_{\tau }=\frac{g_{\tau }-2}{2}$ was measured, so far, with a precision of only several percents, despite its high sensitivity to physics beyond the Standard Model such as compositeness or supersymmetry. A new study is presented to improve the sensitivity of the $a_{\tau }$ measurement with photon-photon interactions from ultraperipheral lead-lead collisions at the LHC. The theoretical approach used in this work is based on an effective Lagrangian and on a photon flux implemented in the madgraph5 Monte Carlo simulation. Using a multivariate analysis to discriminate the signal from the background processes, a sensitivity to the anomalous magnetic moment $a_{\tau }=0_{+0.015}^{-0.019}$ is obtained at 95% confidence level with a dataset corresponding to an integrated luminosity of $2{\mathrm{nb}}^{-1}$ of lead-lead collisions and assuming a conservative 10% systematic uncorrelated uncertainty for signal and background. The present results using multivariate analysis are compared to similar results obtained using sequential cuts, as done in previous measurements, showing an improvement of about 35% in the sensitivity to $a_{\tau }$.

We compute correlation functions of local operator insertions on the $1/2$ Bogomol’nyi-Prasad-Sommerfield Wilson lines of $\mathcal{N}=4$ Chern-Simons-matter theories in three dimensions. We study the algebra preserved by the defect conformal field theory supported on the line, identify the superdisplacement multiplet, and discuss some of its weak-coupling realizations. By employing a superspace description, we present the four-point functions of the superdisplacement and show how they are determined by functions of cross ratios. Within an analytic bootstrap approach, we derive these functions at leading and next-to-leading order at strong coupling, obtaining a result in agreement with appropriate orbifolds of the ABJM case considered in Bianchi et al. [Analytic bootstrap and Witten diagrams for the ABJM Wilson line as defect CFT1, J. High Energy Phys. 08 (2020) 143].

In this paper, we carry out the entanglement calculations on the coherent intertwiners. We first consider the entanglement introduced by the group averaging of the tensor-product-type intertwiner on a 4-valents vertex. Then, we calculate explicitly the entanglement carried by the gauge-invariant coherent intertwiner with four legs. Our numerical results show that the entanglement can be controlled by the local semiclassical geometry described by the coherent intertwiner. We also extend our analytical calculation to the coherent intertwiners with an arbitrary number of legs. Especially, we apply the previous results to the entanglement of the spin-network state labeled by coherent intertwiners, with the network puncturing a boundary by its vertices. We show that the entanglement of such spin-network state is not only determined by the area of the boundary but also carries a quantum correction controlled by the semiclassical geometry associated to the vertices puncturing the boundary.

According to the Bañados-Silk-West (BSW) effect, two particles moving toward a black hole can collide near the horizon with an unbounded energy in the center-of-mass frame. This requires one of the particles to have fine-tuned parameters in such a way that the time component of generalized momentum is zero $X=0$. Thus the existence of such trajectories is a necessary condition for the BSW effect. However, it is insufficient since the forward-in-time condition requires $X>0$ outside the horizon. We examine this condition for different types of particles and horizons and find configurations for which the BSW effect is possible. In doing so, we take into account a finite force of unspecified nature exerted on particles. It includes relationships between numbers characterizing the rate with which four-velocity, acceleration, and metric functions change near the horizon. For some aforementioned relations, parameters of a system control the sign of $X$; in other cases they are required for $X$ to be a real quantity. In the simplest case of free particles the BSW effect for the Kerr or Kerr-Newman black hole is impossible if a fine-tuned particle has a negative energy, so in this sense a combination of the Penrose process and the BSW effect is forbidden.

We study time symmetric initial data for asymptotically anti–de Sitter spacetimes with conformal boundary containing a spatial circle. Such $d$-dimensional initial datasets can contain ($d-2$)-dimensional minimal surfaces if the circle is contractible. We compute the minimum energy of a large class of such initial data as a function of the area $A$ of this minimal surface. The statement $E\ge E_{\min }(A)$ is analogous to the Penrose inequality which bounds the energy from below by a function of the area of a ($d-1$)-dimensional minimal surface.

We investigate future singularities originating from the anisotropy in the Universe. We formulate a new class of singularities in the homogeneous and anisotropic universe, comparing them with the known singularities in the homogeneous and isotropic universe. We also discuss the physical consequences of the new singularities. Moreover, we develop a novel reconstruction method for the anisotropic universe by introducing four scalar fields to reconstruct cosmological models in which future singularities appear. We present an explicit example where the anisotropy may grow in the future up to singularity.

We study the structure of static spherical stars composed of nonrelativistic matter in linear massive gravity with or without the Fierz-Pauli (FP) tuning. Adopting a polytropic equation of state, we construct master differential equations for the stellar profile function, which is fourth order in the FP theory or sixth order in generic non-FP theories, where the difference in the differential order reflects the presence of a ghost spin-0 graviton in the latter. In both cases, even when the spin-0 ghost is present, we find exact solutions with finite radius for the polytropic indices $n=0$ and 1. Analyzing the dependences of the stellar radius, mass, and Yukawa charge on the graviton masses, we observe that a discontinuous behavior arises in the massless limit of the FP theory similarly to the van Dam-Veltman-Zakharov discontinuity, while it is absent in non-FP theories. We discuss rough observational constraints on the graviton masses.

We consider the thermodynamic properties of an exact black hole solution obtained in Weyl geometric gravity theory, by considering the simplest conformally invariant action, constructed from the square of the Weyl scalar, and the strength of the Weyl vector only. The action is linearized in the Weyl scalar by introducing an auxiliary scalar field, and thus it can be reformulated as a scalar-vector-tensor theory in a Riemann space, in the presence of a nonminimal coupling between the Ricci scalar and the scalar field. In static spherical symmetry, this theory admits an exact black hole solution, which generalizes the standard Schwarzschild-de Sitter solution through the presence of two new terms in the metric, having a linear and a quadratic dependence on the radial coordinate, respectively. The solution is obtained by assuming that the Weyl vector has only a radial component. After studying the locations of the event and cosmological horizons of the Weyl geometric black hole, we investigate in detail the thermodynamical (quantum properties) of this type of black holes, by considering the Hawking temperature, the entropy, specific heat and the Helmholtz energy functions on both the event and the cosmological horizons. The Weyl geometric black holes have thermodynamic properties that clearly differentiate them from similar solutions of other modified gravity theories. The obtained results may lead to the possibility of a better understanding of the properties of the black holes in alternative gravity, and of the relevance of the thermodynamic aspects in black hole physics.

We propose a cosmological lingering phase for the initial state prior to inflation which would help address the singularity problem of inflation. The Universe begins with a constant (Hagedorn) temperature and then transitions into an inflationary universe while preserving the null energy condition (NEC). We first consider the phase space of positive spatial curvature models within general relativity and with matter sources that respect the NEC. Depending on the duration of the postlingering inflation, these models can produce a small amount of observable spatial curvature in the cosmic microwave background. We also discuss how lingering can arise with or without spatial curvature in theories of quantum gravity when considering the thermodynamic scaling of particles and its impact on the early Universe. The string theory dilaton is essential to the dynamics. There are many open questions that remain.

We include the effect of the frictional force caused by interactions between cosmic strings and the particles of the background plasma in the computation of the Stochastic Gravitational Wave Background generated by cosmic string loops. Although our results show that friction leads to a partial suppression of the emission of gravitational radiation by cosmic string loops, we also find that loop production is very intense in the early stages of the Kibble regime. We show that, in many instances, this leads to a prominent signature of friction in the ultrahigh frequency range of the spectrum, in the form of a secondary peak. The signature of friction is not only sensitive to cosmic string properties but also to the initial conditions of the network and its surroundings. A detection of this signature would then allow us to extract information about the physics of the early Universe that cannot be uncovered when probing the rest of the Stochastic Gravitational Wave Background spectrum.

We present the angular diameter distance measurement obtained with the baryonic acoustic oscillation (BAO) feature from galaxy clustering in the completed Dark Energy Survey, consisting of six years (Y6) of observations. We use the Y6 BAO galaxy sample, optimized for BAO science in the redshift range $0.6<z<1.2$, with an effective redshift at $z_{\mathrm{eff}}=0.85$ and split into six tomographic bins. The sample has nearly 16 million galaxies over 4,273 square degrees. Our consensus measurement constrains the ratio of the angular distance to sound horizon scale to $D_M(z_{\mathrm{eff}})/r_d=19.51\pm 0.41$ (at 68.3% confidence interval), resulting from comparing the BAO position in our data to that predicted by planck $\mathrm{\Lambda }\mathrm{CDM}$ via the BAO shift parameter $\alpha =(D_M/r_d)/(D_M/r_d{)}_{\mathrm{PLANCK}}$. To achieve this, the BAO shift is measured with three different methods, angular correlation function (ACF), angular power spectrum (APS), and projected correlation function (PCF), obtaining $\alpha =0.952\pm 0.023$, $0.962\pm 0.022$, and $0.955\pm 0.020$, respectively, which we combine to $\alpha =0.957\pm 0.020$, including systematic errors. When compared with the $\mathrm{\Lambda }\mathrm{CDM}$ model that best fits planck data, this measurement is found to be 4.3% and $2.1\sigma$ below the angular BAO scale predicted. To date, it represents the most precise angular BAO measurement at $z>0.75$ from any survey and the most precise measurement at any redshift from photometric surveys. The analysis was performed blinded to the BAO position, and it is shown to be robust against analysis choices, data removal, redshift calibrations, and observational systematics.

In this paper, we present and validate the galaxy sample used for the analysis of the baryon acoustic oscillation (BAO) signal in the Dark Energy Survey (DES) Y6 data. The definition is based on a color and redshift-dependent magnitude cut optimized to select galaxies at redshifts higher than 0.6, while ensuring a high-quality photo-$z$ determination. The optimization is performed using a Fisher forecast algorithm, finding the optimal $i$-magnitude cut to be given by $i<19.64+2.894z_{\mathrm{ph}}$. For the optimal sample, we forecast an increase in precision in the BAO measurement of $\sim 25\%$ with respect to the Y3 analysis. Our BAO sample has a total of 15,937,556 galaxies in the redshift range $0.6<z_{\mathrm{ph}}<1.2$, and its angular mask covers $4,273.42{\mathrm{deg}}^2$ to a depth of $i=22.5$. We validate its redshift distributions with three different methods: directional neighborhood fitting algorithm (DNF), which is our primary photo-$z$ estimation; direct calibration with spectroscopic redshifts from VIPERS, which is a spectroscopic galaxy sample that overlaps with our BAO sample and is complete within our selection cuts; and clustering redshift using SDSS galaxies. The fiducial redshift distribution is a combination of these three techniques performed by modifying the mean and width of the DNF distributions to match those of VIPERS and clustering redshift. In this paper, we also describe the methodology used to mitigate the effect of observational systematics, which is analogous to the one used in the Y3 analysis. This paper is one of the two dedicated to the analysis of the BAO signal in DES Y6. In its companion paper, we present the angular diameter distance constraints obtained through the fitting to the BAO scale.

Viscous unified dark matter models aim to describe the dark sector of the Universe, as the dark matter fluid itself gives rise to an accelerated expansion due to a negative bulk viscous pressure. However, in most studies, radiation is often disregarded as a minor factor in dynamical system analyses, overlooking whether radiation domination is achievable. In this paper, we rigorously examine this critical aspect for common parametrizations of bulk viscosity, denoted as $\xi$, within two general classes of viscous unified models. Our findings reveal significant inconsistencies in models where $\xi \propto H^{1-2s}{\rho }_m^s$ with $s\le 0$, and surprisingly, in models where $\xi \propto {\rho }_m^s$ with exponents $s<0$, as they both fail to produce a radiation-dominated era—an undesirable outcome for any cosmological model. Moreover, the exponent $s$ must lye within the interval $0\le s<1/2$ for the latter model to correctly describes the cosmological evolution. These results underscore the need of including these constraints as a prior in statistical analyses of observational data, with implications for current statistical inferences for the second model, where both prior and best-fit values of $s$ often fall outside the acceptable range.

In this work, we elaborate further on a cosmological model of inflation that characterizes Chern-Simons (CS) gravity models inspired from string theory. Such models are known to belong to the class of the so-called string-inspired running vacuum cosmologies. In particular, by applying methods of dynamical systems, commonly used in scalar-field cosmology, we examine in detail, for the first time to our knowledge, the passage from a preinflationary era dominated by a stiff-axion-matter equation of state, characteristic of the model, to inflation of the running vacuum model (RVM) type. By a careful discussion of the formation of the condensate of the CS gravitational anomaly term, induced by populations of primordial gravitational waves at the end of the stiff-axion-matter era, we show that an effectively linear axion-monodromy potential arises. This eventually causes the transition from the matter to the RVM inflation. By taking into account terms that have previously been ignored in the relevant literature of weak-graviton quantization, we show that the effect of such terms is to diminish the value of the condensate by half, remaining, however, in the same order of magnitude. This, in turn, implies that the qualitative conclusions of previous works on the subject remain valid. Moreover, on assuming the approximate cosmic-time independence of the gravitational-CS condensate, we also provide an estimate of the number of sources of the primordial gravitational waves, upon the requirement of respecting the trans-Planckian conjecture.

Gravitational waves (GWs) emanating from binary black holes (BBHs) encode vital information about their sources, enabling us to infer critical properties of the BBH population across the Universe, including mass, spin, and eccentricity distribution. While the masses and spins of binary components are already recognized for their insights into formation, eccentricity stands out as a distinct and quantifiable indicator of formation and evolution. However, despite its significance, eccentricity is notably absent from most parameter estimation analyses associated with GW signals. To evaluate the precision with which the eccentricity distribution can be deduced, we generated two synthetic populations of eccentric binary black holes (EBBHs) characterized by nonspinning, nonprecessing dynamics, and mass ranges between $10$ and $50M_{\odot }$. This was achieved using an eccentric power law model, encompassing 100 events with eccentricity distributions set at ${\sigma }_{\epsilon }=0.05$ and ${\sigma }_{\epsilon }=0.15$. This synthetic EBBH ensemble contrasts against a circular binary black holes collection to discern how parameter inferences would vary without eccentricity. Employing Markov chain Monte Carlo techniques, we constrained model parameters, including the event rate ($\mathcal{R}$), minimum mass ($m_{\min }$), maximum mass ($m_{\max }$), and ${\sigma }_{\epsilon }$ which is uncertainty in eccentricity. Our analysis demonstrates that eccentric population inference can identify the signatures of even modest eccentricity distribution. In addition, our study shows that an analysis neglecting eccentricity may draw biased conclusions of population inference for the larger values of eccentricity distribution.

Gravitational waves in the postmerger phase of binary neutron star mergers may become detectable with planned upgrades of existing gravitational-wave detectors or with more sensitive next-generation detectors. The construction of template banks for the postmerger phase can facilitate signal detection and parameter estimation. Here, we investigate the performance of an artificial neural network in predicting simulation-based waveforms in the frequency domain (restricted to the magnitude of the frequency spectrum and to equal-mass models) that depend on three parameters that can be inferred through observations, neutron star mass, tidal deformability, and the gradient of radius versus mass. Compared to a baseline study using multiple linear regression, we find that the artificial neural network can predict waveforms with higher accuracy and more consistent performance in a cross-validation study. We also demonstrate, through a recalibration procedure, that future reduction of uncertainties in empirical relations that are used in our hierarchical scheme will result in more accurate predicted postmerger spectra.

We compute spectral functions in a scalar ${\varphi }^4$-theory in three spacetime dimensions via the spectral functional renormalization group. This approach allows for the direct, manifestly Lorentz covariant computation of correlation functions in Minkowski spacetime, including a physical on-shell renormalization. We present numerical results for the spectral functions of the two- and four-point correlation functions for different values of the coupling parameter. These results agree very well with those obtained from another functional real-time approach, the spectral Dyson-Schwinger equation.

Motivated by recent theoretical predictions about the existence of a $B\overline{B}$ bound state [also denoted as $X(10550)$], in this work we estimate the production of the $S$-wave $B^{+}{B}^{-}$ molecule via $\mathrm{\Upsilon }(4S)$ radiative decays. In particular, we make use of effective Lagrangian approach and the compositeness condition to calculate the $X(10550)$ production rate via $\mathrm{\Upsilon }(4S)\to \gamma X(10550)$ decays employing triangle diagrams. Our results show that the partial decay width of this reaction is of the order of 0.5–192 keV for a respective binding energy of 1–100 MeV, corresponding to a branching fraction of ${10}^{-5}–{10}^{-3}$. These findings suggest that the existence of the $X(10550)$ might be checked via the analysis of the mentioned decay in present and future experiments.

With the available experimental results on ${\chi }_{cJ}(J=0,1,2)$ decays, we explore the decays of ${\chi }_{cJ}\to {\mathcal{B}}_8{\overline{\mathcal{B}}}_8$ and ${\chi }_{cJ}\to {\mathcal{B}}_{10}{\overline{\mathcal{B}}}_{10}$ based on the SU(3) flavor symmetry. In addition, we give an extensive discussion on the possible contributions from the SU(3) breaking effect and ${\mathrm{\Sigma }}^0-\mathrm{\Lambda }$ mixing. With the decay amplitude determined from an effective Hamiltonian, we also present the expected branching fractions for those unobserved decay modes, e.g., ${\chi }_{cJ}\to n\overline{n}$ and ${\chi }_{cJ}\to \mathrm{\Lambda }{\overline{\mathrm{\Sigma }}}^0+\overline{\mathrm{\Lambda }}{\mathrm{\Sigma }}^0$, which are expected to be observed at the BESIII experiment and the future planned Super Tau-Charm facilities. Our results provide valuable insights that will aid in advancing our understanding of the mechanisms and characteristics of ${\chi }_{cJ}$ decays.