The recent result of the Dark Energy Spectroscopic Instrument (DESI) in combination with other cosmological data shows evidence of the evolving dark energy parametrized by the $w_0{w}_a\mathrm{CDM}$ model. We interpret this result in terms of a quintessential scalar field and demonstrate that it can explain the DESI result even though it becomes eventually phantom in the past. Relaxing the assumption on the functional form of the equation-of-state parameter $w=w(a)$, we also discuss a more realistic quintessential model. The implications of the DESI result for Swampland conjectures, cosmic birefringence, and the fate of the Universe are discussed as well.

In the framework of linearized quantum gravity, we study the quantum gravitational interaction between two nonpointlike objects induced by fluctuating gravitomagnetic fields in vacuum. We find that, in addition to the quantum gravitational interaction induced by fluctuating gravitoelectric fields previously studied, there exists a quantum gravitomagnetic interaction. This interaction originates from the interaction between the instantaneous localized mass currents in nonpointlike objects induced by the fluctuating gravitomagnetic fields. Using fourth-order perturbation theory, we derive the explicit form of the quantum gravitomagnetic interaction energy, which shows an $r^{-10}$ dependence in the near regime and an $r^{-11}$ dependence in the far regime, where $r$ is the distance between the two objects. This interaction energy is expected to be significant when the gravitomagnetic polarizability of the objects is large.

We construct a regular bound state of two extremal black holes in type IIB supergravity with opposite charges. The bound state resembles the Schwarzschild black hole from the asymptotics to the photon ring and has the same mass and charges as the Schwarzschild black hole. On the one hand, we show that the bound-state entropy admits a microscopic description in terms of branes and antibranes in string theory. On the other hand, we demonstrate that the entropy approaches half of the Schwarzschild entropy as the mass becomes significantly larger than the Kaluza-Klein scales used to regularize the geometry. This opens up the possibility of a brane/antibrane interpretation of the Schwarzschild entropy in string theory.

We discuss various questions that emerge in connection with the Lie-algebraic deformation of the ${\mathbb{CP}}^1$ sigma model in two dimensions. First, we supersymmetrize the original model endowing it with the minimal $\mathcal{N}=(0,2)$ and extended $\mathcal{N}=(2,2)$ supersymmetries. Then we derive the general hypercurrent anomaly in both cases. In the latter case this anomaly is one-loop but is somewhat different from the standard expressions one can find in the literature because the target manifold is nonsymmetric. We also show how to introduce the twisted masses and the $\theta$ term, and study the Bogomol’nyi–Prasad–Sommerfield equation for instantons, in particular the value of the topological charge. Then we demonstrate that the second loop in the $\beta$ function of the nonsupersymmetric Lie-algebraic sigma model is due to an infrared effect. To this end we use a supersymmetric regularization. We also conjecture that the above statement is valid for higher loops too, similar to the parallel phenomenon in four-dimensional $\mathcal{N}=1$ super-Yang-Mills. In the second part of the paper we develop a special dimensional reduction—namely, starting from the two-dimensional Lie-algebraic model we arrive at a quasi-exactly solvable quantum-mechanical problem of the Lamé type.

We derive the soft effective action in ($d+2$)-dimensional Abelian gauge theories from the on-shell action obeying Neumann boundary conditions at timelike and null infinity and Dirichlet boundary conditions at spatial infinity. This allows us to identify the on-shell degrees of freedom on the boundary with the soft modes living on the celestial sphere. Following the work of Donnelly and Wall, this suggests that we can interpret soft modes as entanglement edge modes on the celestial sphere and study entanglement properties of soft modes in Abelian gauge theories.

We provide the leading near conformal corrections on a cylinder to the scaling dimension of the lowest-lying fixed isospin charge $Q$ operators defined at the lower boundary of the quantum chromodynamics conformal window, ${\tilde{\mathrm{\Delta }}}_Q={\tilde{\mathrm{\Delta }}}_Q^{*}+{(\frac{m_{\sigma }}{4\pi \nu })}^2{Q}^{\frac{\mathrm{\Delta }}{3}}{B}_1+{(\frac{m_{\pi }(\theta )}{4\pi \nu })}^4{Q}^{\frac{2}{3}(1-\gamma )}{B}_2+\mathcal{O}(m_{\sigma }^4,m_{\pi }^8,m_{\sigma }^2{m}_{\pi }^4).$ Here, ${\tilde{\mathrm{\Delta }}}_Q/r$ is the classical ground state energy of the theory on $\mathbb{R}\times S_r^3$ at fixed isospin charge while ${\tilde{\mathrm{\Delta }}}_Q^{*}$ is the scaling dimension at the leading order in the large charge expansion. In the conformal limit $m_{\sigma }=m_{\pi }=0$, the state-operator correspondence implies ${\tilde{\mathrm{\Delta }}}_Q={\tilde{\mathrm{\Delta }}}_Q^{*}$. The near-conformal corrections are expressed in powers of the dilaton and pion masses in units of the chiral symmetry breaking scale $4\pi \nu$ with the $\theta$-angle dependence encoded directly in the pion mass. The characteristic $Q$-scaling is dictated by the quark mass operator anomalous dimension $\gamma$ and the one characterizing the dilaton potential $\mathrm{\Delta }$. The coefficients $B_i$ with $i=1,2$ depend on the geometry of the cylinder and properties of the nearby conformal field theory.

In this paper, we consider the convergence properties of the polarization tensor of graphene obtained in the framework of thermal quantum field theory in three-dimensional spacetime. During the last years, this problem attracted much attention in connection with the calculation of the Casimir force in graphene systems and the investigation of the electrical conductivity and reflectance of graphene sheets. There are contradictory statements in the literature, especially on whether this tensor has an ultraviolet divergence in three dimensions. Here, we analyze this problem using the well-known method of dimensional regularization. It is shown that the thermal correction to the polarization tensor is finite at any $D$, whereas its zero-temperature part behaves differently for $D=3$ and 4. For $D=3$, it is obtained by analytic continuation with no subtracting of infinitely large terms. As for the spacetime of $D=4$, the finite result for the polarization tensor at zero temperature is found after subtracting the pole term. Our results are in agreement with previous calculations of the polarization tensor at both zero and nonzero temperature. This opens the possibility for a wider application of the quantum-field-theoretical approach in investigations of graphene and other two-dimensional novel materials.

We explore the necessary conditions for 1-form symmetries to emerge in the long-distance limit when they are explicitly broken at short distances. A minimal requirement is that there exist operators which become topological at long distances and that these operators have nontrivial correlation functions. These criteria are obeyed when the would-be emergent symmetry is spontaneously broken, or is involved in ’t Hooft anomalies. On the other hand, confinement, i.e. a phase with unbroken 1-form symmetry, is nearly incompatible with the emergence of 1-form symmetries. We comment on some implications of our results for QCD as well as the idea of Higgs-confinement continuity.

We explicitly express the Minkowski vacuum of a massless scalar field in terms of the particle notion associated with suitable spherical conformal killing fields. These fields are orthogonal to the light wave fronts originating from a sphere with a radius of $r_H$ in flat spacetime: a bifurcate conformal killing horizon that exhibits semiclassical features similar to those of black hole horizons and Cauchy horizons of spherically symmetric black holes. Our result highlights the quantum aspects of this analogy and extends the well-known decomposition of the Minkowski vacuum in terms of Rindler modes, which are associated with the boost Killing field normal to a pair of null planes in Minkowski spacetime (the basis of the Unruh effect). While some features of our result have been established by the theorems of Kay and Wald in the 1990s—on quantum field theory in stationary spacetimes with bifurcate Killing horizons—the added value we provide here lies in the explicit expression of the vacuum.

The computation of the amplitude, $\alpha$, of asymptotic standing wave tails of weakly delocalized, stationary solutions in a fifth-order Korteweg–de Vries equation is revisited. Assuming the coefficient of the fifth order derivative term, ${\epsilon }^2\ll 1$, a new derivation of the “beyond all orders in $\epsilon$” amplitude, $\alpha$, is presented. It is shown by asymptotic matching techniques, extended to higher orders in $\epsilon$, that the value of $\alpha$ can be obtained from the asymmetry at the center of the unique solution exponentially decaying in one direction. This observation, complemented by some fundamental results of Hammersley and Mazzarino [Proc. R. Soc. A 424, 19 (1989)], not only sheds new light on the computation of $\alpha$ but also greatly facilitates its numerical determination to a remarkable precision for so small values of $\epsilon$, which are beyond the capabilities of standard numerical methods.

In this study, we explore the impact of an additional dimension, as proposed in Kaluza-Klein’s theory, on the Casimir effect within the context of Lorentz invariance violation (LIV), which is represented by the “aether field.” We demonstrate that the Casimir energy is directly influenced by the presence of the fifth dimension, as well as by the aether parameter. Consequently, the force between the plates is also subject to variations of these parameters. Furthermore, we examine constraints on both the size of the extra dimension and the aether field parameter based on experimental data. The LIV parameter can provide insights into addressing the size-related challenges in Kaluza-Klein’s theory and offers a mean to establish an upper limit on the size of the extra dimension. This helps to rationalize the difficulties associated with its detection in current experiments.

In this study, we look into binaries undergoing gravitational radiation during a hyperbolic passage. Such hyperbolic events can be a credible source of gravitational waves in future detectors. We systematically calculate fluxes of gravitational radiation from such events in the presence of dark matter with different profiles, also considering the effects of dynamical friction. We provide an estimate for the braking index and show how it evolves due to the presence of the dark matter medium. We also investigate the binary dynamics through the changes in the orbital parameters by treating the potential due to a dark matter spike and the dynamical friction effects as a perturbation term. An insight into the effects of such a medium on the binaries from the corresponding osculating elements opens up avenues to study binary dynamics for such events.

We present new, simple analytical formulas to accurately describe light rays in spherically symmetric static spacetimes. These formulas extend those introduced by Beloborodov and refined by Poutanen for the Schwarzschild metric. Our enhanced formulas are designed to be applicable to a broader range of spacetimes, making them particularly valuable for describing phenomena around compact objects like neutron stars and black holes. As an illustration of their application, we present analytical studies of images of thin accretion disks surrounding black holes and explore their associated polarimetry.

The nongravitational interaction between the dark components of the Universe could lead to the variation of dark matter energy density standard evolution law. When we assume this scenario, the dark matter energy density follows ${\rho }_{dm}\sim (1+z{)}^{3+\epsilon (z)}$ [where $\epsilon (z)=0$ corresponds to the standard dark matter density evolution]. In this paper, we perform a Bayesian analysis to test three parametrizations for $\epsilon (z)$, namely, $\epsilon (z)={\epsilon }_0$, $\epsilon (z)={\epsilon }_0+{\epsilon }_1\frac{z}{1+z}$, and $\epsilon (z)={\epsilon }_0+{\epsilon }_1\frac{z(1+z)}{1+z^2}$, where the first one is motivated through fundamental grounds and the others are on phenomenological grounds. Through the Gaussian process regression, our method uses galaxy cluster gas mass fraction measurements, Type Ia supernovae observations, cosmic chronometers, and Baryon Acoustic Oscillations data. No specific cosmological model is considered. In all possibilities analyzed, the standard evolution law ($\epsilon (z)=0$) is within $2\sigma \mathrm{C}.\mathrm{L}.$ The investigated cases generally indicated scenarios of inconclusive or weak evidence toward the simplest model from the Bayesian standpoint.

Sensitivity forecasts inform the design of experiments and the direction of theoretical efforts. To arrive at representative results, Bayesian forecasts should marginalize their conclusions over uncertain parameters and noise realizations rather than picking fiducial values. However, this is typically computationally infeasible with current methods for forecasts of an experiment’s ability to distinguish between competing models. We thus propose a novel simulation-based methodology capable of providing expedient and rigorous Bayesian model comparison forecasts without relying on restrictive assumptions.

We introduce a multifield dark energy model with a nonflat field-space metric, in which one field is dynamical while the others have constant spatial gradients. The model is predictive at the background level, leading to an early dark energy component at high redshifts and a suppressed fraction of late-time anisotropy. Both features have simple expressions in terms of the curvature scale of the field-space, and correspond to stable points in the phase space of possible solutions. Because of the coupling between time and space-dependent scalar fields, vector field perturbations develop tachyonic instabilities at scales below the Hubble radius, thus being potentially observable in the number count of galaxies. Overall, the presence of a nontrivial field-space curvature also leads to the appearance of instabilities on scalar perturbations, which can impact the matter density distribution at large scales.

Using an excursion-set approach, we revisit the initial spatial clustering of Primordial Black Holes (PBHs) originating from the Hubble reentry of large Gaussian density fluctuations in the early Universe. We derive the two-point correlation functions of PBHs, properly accounting for the “cloud-in-cloud” mechanism. Our expressions naturally and intrinsically correlate the formation of pairs of PBHs, which is a key difference with the Poisson model of clustering. Our approach effectively includes short-range exclusion effects and clarifies the clustering behaviors at small scale: PBHs are anticorrelated at short distances. Using a scale-independent collapse threshold, we derive explicit expressions for the excess probability to find pairs of PBHs separated by a distance $r$, as well as the excess probability to find pairs with asymmetric mass ratio. Our framework is model independent by construction, and we discuss possible other applications.

The $\beta$-skeleton approach can be conveniently utilized to construct the cosmic web based on the spatial geometry distribution of galaxies, particularly in sparse samples. This method plays a key role in establishing the three-dimensional structure of the Universe and serves as a tool for quantitatively characterizing the nature of the cosmic web. This study is the first application of $\beta$-skeleton information as weights in mark weighted correlation functions (MCFs), presenting a novel statistical measure. We have applied the $\beta$-skeleton approach to the CMASS NGC galaxy samples from SDSS BOSS DR12 in the redshift interval $0.45\le z\le 0.55$. Additionally, we applied this approach to three COLA cosmological simulations with different settings (${\mathrm{\Omega }}_m=0.25$, ${\mathrm{\Omega }}_m=0.31$, ${\mathrm{\Omega }}_m=0.4$) for comparison. We measured three MCFs, each weighted by (i) the number of neighboring galaxies around each galaxy, (ii) the average distance of each galaxy from its surrounding neighbors, and (iii) the reciprocal of the average distance of each galaxy from its surrounding neighbors. By comparing measurements and calculating corresponding ${\chi }^2$ statistics, we observe high sensitivity to the cosmological parameter ${\mathrm{\Omega }}_m$ through a joint analysis of the two-point correlation and three MCFs.

Cosmological probes constructed in large-scale surveys are independent of the underlying theory of gravity, and their relativistic descriptions are indeed applicable to any theory of gravity. It was shown that the presence of fluctuations with wavelengths much larger than the characteristic scales of the surveys has no impact on cosmological probes if the matter content is adiabatic and the Einstein equations are used. In this paper we study the sensitivity of cosmological probes to infrared fluctuations in the Horndeski theory. We find that the extra degree of freedom (dof) in the Horndeski scalar field can induce sensitivity to infrared fluctuations in the cosmological probes, even when the matter components are adiabatic on large scales. A generalized adiabatic condition including the extra dof, in contrast, guarantees that cosmological probes are devoid of infrared sensitivity, and this solution corresponds to the adiabatic modes à la Weinberg in the Horndeski theory, which can be removed by a coordinate transformation in the infrared limit. We discuss the implications of our findings and the connections to the initial conditions.