Papers

At fixed three-momentum, massive Dirac neutrino one-particle states span a 4D space of particle–antiparticle identity and helicity. We show that helicity flip, charge conjugation, and their product close an internal $SU(2)$ pseudospin subalgebra within $SU(4)$, distinct from the Wigner little group. Its helicity generator is the lepton-number-weighted spin rotation $U_1=2LJ_2$. The lepton-number $L$ and helicity $\mathcal H_h$ grade the 16 generators $\tau_\mu\otimes\sigma_\nu$, organizing the $\Delta L=2$ sector. Helicity-preserving directions $\tau_{1,2}\otimes\sigma_{0,3}$ carry the pseudo-Dirac mixing $\kappa_{\rm pD}=\Delta m^2/4E$ (active–sterile), while helicity-flipping directions $\tau_{1,2}\otimes\sigma_{1,2}$ carry the neutrinoless double-beta decay mass factor (active–active). Furthermore, charge conjugation matches the $U_2$ generator. The Majorana condition is thus a projection onto the $U_2=+1$ eigenspace, where only the Wigner algebra survives. This framework algebraically classifies Majorana masses and pseudo-Dirac splittings without assuming neutrinos are Majorana particles.

In the standard curvature-perturbation scenario, PBHs form from the collapse of superhorizon curvature fluctuations after horizon re-entry. The predicted abundance is exponentially sensitive to the collapse threshold and hence to the shape of the primordial curvature profile. In this work we develop a finite-action framework to describe curvature-profile dispersion around representative peak profiles. Using a multipolar Fourier-Bessel decomposition, we separate the local peak variables of the Gaussian field from residual radial and angular deformations, normalized by their Gaussian action. We apply the formalism to spherical numerical-collapse examples in order to isolate the effect of radial shape dispersion. For finite-width spectra, and in the presence of logarithmic local non-Gaussianity, we compute the collapse threshold as a function of a coherent shape variable and combine the result with peak statistics. We find that the dominant contribution to the PBH abundance is not necessarily the conditional-mean reference profile, nor simply the profile with the lowest threshold. Instead, it is selected by a competition between the Gaussian cost of realizing a coherent deformation and the exponential gain associated with lowering the collapse threshold. Broad spectra and negative non-Gaussianity can make rare shape deformations dominate the abundance. In the examples studied here, the dominant branches can correspond to several-sigma coherent shape fluctuations while enhancing the integrated abundance by orders of magnitude. Equivalently, including shape dispersion can reduce the power-spectrum amplitude required to obtain a fixed PBH abundance. Our results show that residual profile dispersion is a genuine statistical ingredient in PBH formation and can be quantitatively important for accurate abundance estimates.

The black hole information paradox has motivated extensive study of how and when information escapes from evaporating black holes. Here we address the analogous question for cosmological horizons: when does an individual Hawking pair begin to carry information out of a de Sitter horizon? We study this problem in a class of two-dimensional flow geometries that interpolate smoothly between an asymptotic AdS$ _2 $ boundary and a dS$ _2 $ static patch. Modeling the emission of a Hawking pair via a probe state constructed from local operators and their modular conjugates, we promote the centaur algebra of observables to a Type II$ _\infty $ factor through the crossed-product construction. This allows us to compute the entropy difference between the thermofield-double reference state and the Hawking-pair state. We find that this difference traces a characteristic mini-Page curve for the cosmological horizon: it starts near zero, reaches a minimum near $ \tau \approx \beta/8 $ before increasing again. We interpret the location of the minimum as the time at which quantum information begins to escape the cosmological horizon. Extending the analysis to the microcanonical ensemble, we show that the algebraic entropy coincides with the generalized entropy of an entanglement wedge cut that tracks the emitted particle along the horizon. Furthermore, the relative modular flow generated between the two states yields a Lyapunov exponent $\lambda =2\pi/\beta$, identifying the scrambling time as the scale at which the information carried by the pair becomes accessible to a static-patch observer.

Bulk reconstruction is a central problem in AdS/CFT, and entanglement wedge reconstruction is its subregion version. We argue that this subregion statement should be separated from the stronger holographic quantum error correction interpretation, in which one region-independent logical bulk operator has code-preserving representatives in several boundary regions. A simple locality argument shows that such a common reconstruction must commute with the code-preserving local algebras in the complementary regions. This is the mechanism realized in HaPPY-type codes: the erased regions are blind to a protected logical algebra. An ordinary finite $N$ holographic CFT does not have such a protected invisible sector for supergravity fields. Its low-energy local observables, in particular, suitably smeared stress tensors, detect the physical support and gravitational dressing of ordinary bulk operators, up to possible center or superselection data. Thus, there is no such holographic quantum error correction and the $N=\infty$ agreement of global and subregion HKLL formulae is a free-theory statement. What remains is entanglement wedge reconstruction without holographic quantum error correction, or subregion complementarity: each boundary region has its own code-preserving low-energy algebra and its own region-adapted bulk interpretation, rather than a shared logical operator.

We construct a measure that exhibits two aspects of a new type of universality and dramatically simplifies the integration of tensors $T_{a_1,a_2,\ldots,a_D} \in \mathbb{C}$ ($a_1,\ldots,a_D=1,\ldots,N$) at large $N$. In contrast to matrix integration, in which matrix traces canonically yield the integrand, tensors need additional information (equivalent to a $D$-coloured graph $B$) to contract their indices and form a tensor trace $B(T)$. We show that, whenever each $B_1,\ldots, B_n$ can be obtained by a recursive construction known as melonicity, then the leading order in $N$ of the integral of $ {B_1}(T) {B_2}(T) \cdots {B_n}(T) $ is independent of the – often intricate – combinatorics of the traces $B_i$, but also, to our surprise, independent of $D$ as far as $D\geq 3$. Instead, at large $N$, these integrals are some functions (indexed by $n$) of the number of vertices $2p_i$ of $B_i$ which we call melonic polynomials. Melonic traces cumulants with respect to any ('interacting') measure \[ \exp\Big\{-N^{D-1} \sum_{i=1}^m g_i {B_i}(T)\Big\} \mathrm{d}\mu_0(T) \quad (g_1,\ldots,g_m \in \mathbb{R}, \mathrm{d}\mu_0(T) =\text{the tensor Gaussian}) \] with each $B_i$ melonic, can be computed with our universal measure that replaces each $B_i$ by a canonical trace depending only on $p_i$. We prove that any two melonic tensor models are indistinguishable at large-$N$, independently of the number of tensor indices (first universality aspect), and of the fine-grainedness of their interactions (second universality), being a sufficient condition that the couplings (the parameters $g_i$ above) agree and their respective traces are monomials with the same degree in $T$.

In this note we explore numerically the finite Bernoulli convolutions. We show that with a suitable choice of parameter, it might serve as a toy model for intermittent energy cascade in fully developed turbulence. We then show how the crossings of $\beta$-expansions distribute in $\beta$, and suggest that it might highlight the parameters with enhanced overlap structure that are related to measures that are singular continuous. We later introduce a notion of order to the $\beta$-expansions based on the lexicographical order of the $N$-binary words, and observe that for most sampled adjacent pairs when $\beta=2$, the distance in their order increases exponentially when $\beta$ decreases from 2 to 1. This suggests 'chaotic' behavior, with the 'Lyapunov exponents' bunched into several clusters that depend on $N$. We end the note with some 'order plots' and an interesting connection between the finite $\beta$-compactum with $\beta=g$ (g being the golden ratio) and binary reflected Gray code.

We express the generalized entropy (GE) of the Hawking radiation in the final stage of an evaporating rotating regular black hole (BH) by writing the mass of the BH as $m_{\rm ext} + \alpha$, where $m_{\rm ext}$ represents the mass at the extremal limit and $\alpha$ is a parameter. Generally, entropy is non-negative. Based on this fact, we assume that, in the GE considered in this study, the signs of the contributions from the area term and the correction term remain unchanged throughout the entire evaporation process of the BH. Therefore, we regard $\alpha$ at which the correction term vanishes as its lower bound and determine it. As a result, we find that such a value of $\alpha$ is finite. Denoting this value by $\alpha_2$, this result indicates that the mass of the BH cannot become smaller than $m_{\rm ext} + \alpha_2$, which can be interpreted as the emergence of a remnant at the final stage of BH evaporation. The BH considered in this study is a rotating regular BH. The regularization is motivated by the possibility that the fine structure of the central region becomes relevant in the final stage of evaporation. A rotating BH is considered from the viewpoint of generality.

We investigate the optical properties of a rotating black hole immersed in a Hernquist dark matter halo. The spacetime is generated from a static Hernquist black hole through the noncomplexification version of the Newman-Janis procedure, yielding a Kerr-like geometry whose halo contribution is encoded in the radial function $\Delta(r)$ \cite{AraujoFilho:2026hernquist}. We derive the null geodesic equations, effective potentials, radial acceleration, and representative three-dimensional photon trajectories around the event horizon and ergoregion. Using the separability of the Hamilton-Jacobi equation, we obtain the critical impact parameters of unstable spherical photon orbits and construct the shadow contours for a distant observer. The rotation parameter mainly shifts and distorts the shadow, whereas the Hernquist halo enlarges the photon capture region and increases the apparent shadow size. Comparing the area-equivalent shadow diameter with the Event Horizon Telescope measurements of Sgr A$^\ast$ and M87$^\ast$, we constrain the dimensionless halo parameter $\hat{\rho}=M^2\rho$. The strongest restriction comes from Sgr A$^\ast$, giving $\hat{\rho}\sim(2.7-3.8)\times10^{-3}$ at $1\sigma$ and $\hat{\rho}\sim(4.1-5.2)\times10^{-3}$ at $2\sigma$. We also analyze strong- and weak-field gravitational lensing. In the strong-field regime, the halo shifts the unstable photon orbit and critical impact parameter, controlling the logarithmic deflection angle and the position of relativistic images. In the weak-field regime, the halo contributes already to the leading bending angle and enhances deviations from Kerr as $\rho$ grows. From the Einstein ring of ESO325-G004, we further obtain $0\leq\hat{\rho}\lesssim0.00939$ at $1\sigma$ and $0\leq\hat{\rho}\lesssim0.01963$ at $2\sigma$.

Conformal field theory provides universal predictions for Loschmidt amplitudes following quenches from product states to critical Hamiltonians. Building on this observation, we develop a route to extracting conformal data from real-time dynamics without preparing critical low-energy states. After analytic continuation, the Loschmidt amplitude is described by a boundary-CFT partition function on a strip, whose transverse transfer matrix encodes both the boundary operator spectrum and the central charge. Local space-time perturbations of the amplitude are governed by equilibrium correlation functions, and therefore provide access to critical exponents. In parallel, generalized temporal entropies exhibit scaling with time analogous to the equilibrium scaling of spatial entanglement entropy. We show that the low-lying boundary spectrum can be reconstructed from the system-size dependence of finite-chain Loschmidt echoes, whose damped oscillations encode differences of boundary scaling dimensions. Finally, we propose a finite-size scaling protocol that can extract these quantities from simulations or experiments on state-of-the-art quantum platforms.

In these notes, basic concepts and necessary formulas for the modeling of elastic lepton-nucleon and quasielastic lepton-nucleus scattering using relativistic models are discussed. Certain theoretical developments are presented in meticulous detail, particularly those rarely found in papers or standard textbooks. In order to highlight the discrepancies between models and evaluate the impact of various nuclear effects, theoretical predictions are compared with inclusive electron scattering data. These notes are designed for Master's or PhD students embarking on their research in the field of neutrino-nucleus interactions at intermediate energies (ranging from several hundred MeV to a few GeV). They are intended to serve as a supplemental guide, never as a substitute for traditional textbooks on Scattering Theory and Quantum Field Theory. Currently, these notes are included in the course `Relativistic Quantum Theory: Nuclear Processes', which is integrated into both the Interuniversity Master in Nuclear Physics (https://master.us.es/fisicanuclear/index.php/) and the Erasmus Mundus Joint Master Degree in Nuclear Physics (https://www.emm-nucphys.eu/en), with the University of Seville as one of the partner institutions. Previously, this material was part of the course `Weak Interactions', within the same Master's programs.

Testing General Relativity (GR) with black hole ringdowns has conventionally focused on attempting to detect shifts away from the quasinormal mode (QNM) frequencies of the Kerr metric. It has recently been argued, however, that the ringdown signal will also be contaminated with the QNM frequencies of any new fields that are present in a beyond-GR scenario, provided that they couple nonminimally to gravity. We study black hole perturbations for the shift-symmetric Horndeski action, which includes all interactions between a massless scalar and gravity that lead to second order equations upon variation. We perturb linearly in the field and also employ a perturbative expansion in the scalar charge per unit black hole mass, $q$. Assuming that the scalar amplitude is suppressed by $q$, we demonstrate that, to order $q^2$, the coupling between the scalar and the Gauss-Bonnet invariant is the only term that contributes to both frequency shifts and contamination, and that the two effects appear at the same perturbative order. If the assumption about the suppression of the scalar amplitude is relaxed, contamination can appear at leading order in $q$, and hence dominate over frequency shifts. In this case, contamination also receives subleading corrections from an additional coupling

We develop a general framework for the statistics of mixed-dimensional excitations subject to intertwined conservation laws, extending the familiar Fermi statistics with conserved particle number. We define statistics microscopically through a hopping-operator algebra: a local operator subalgebra (LOsA) generated by operators that locally move or deform excitations while preserving the conservation law. Nontrivial statistics arise when this subalgebra is nontrivial. We first focus on LOsAs that encode pointed conservation laws. These give rise to invertible excitations, whose fusion rules are exactly those of the symmetry defects of a higher group $\cG$. For such $\cG$-conserved excitations in $d$-dimensional space, we show that the corresponding LOsA – and hence the statistics it defines – is classified by a cohomology class $[\omega] \in H^{d+2}(B\cG;\R/\Z)$, where changing $[\omega]$ by a coboundary corresponds merely to a rephasing of the local operators. We further provide a holographic realization: excitations with this prescribed conservation law and statistics live on the boundary of a $\cG$ higher-group gauge theory in $(d+1)$-dimensional space, twisted by $[\omega]$. More generally, non-pointed conservation laws and the associated statistics of non-invertible excitations are defined by a pair: a LOsA together with its excitation-complex representation. This is equivalent to the pair consisting of a LOsA and its Hilbert-space representation, which is the data defining a generalized symmetry. Consequently, non-pointed conservation laws and their statistics in $d$-dimensional space are classified by fusion $d$-categories, just as generalized symmetries are. The higher-group results above are the fully-pointed special cases of this more general classification.

The total angular momentum current can be decomposed into orbital and spin contributions in different ways, known as pseudo-gauges. This freedom leads to ambiguities in the definition of local-equilibrium density operators, which in turn affect estimates of spin polarization in heavy-ion collisions. In this work, the pseudo-gauge ambiguity, together with other ambiguities associated with improvements of conserved currents, is reformulated in terms of spurious symmetries corresponding to conserved currents with vanishing total charge. A prescription for the unambiguous definition of a local-equilibrium density operator is introduced using the currents associated with genuine symmetries. The resulting density operator is invariant under transformations that add improvement terms to local currents, including the energy-momentum tensor.

A limiting case is worked out in which the causal action principle for causal fermion systems describing Minkowski space gives rise to the linear Fock space dynamics of perturbative quantum field theory including non-abelian gauge fields and Dirac fields.

We study one-loop effects in the near-extremal thermodynamics of BTZ and warped BTZ black holes, with particular emphasis on the fate of eigenmodes that become zero modes in the extremal throat. Our analysis is formulated in three-dimensional Topologically Massive Gravity, a higher derivative theory characterized by the presence of a gravitational Chern–Simons term, and it makes use of the Newman–Penrose formulation. For BTZ, we compare the near-horizon computation with the full-geometry eigenvalue problem and identify how the Schwarzian and rotational sectors are lifted at small temperature. We then extend the same strategy to warped BTZ. We find that rotational modes are essential for a consistent near-extremal treatment of both BTZ and warped BTZ black holes, and cannot be discarded without first specifying the boundary conditions.

We develop the Gram/Wishart/Stiefel formulation of the \(N=2\), large–\(d\) planar endpoint theory of lattice BFSS/BMN matrix quantum mechanics on the lattice. The endpoint variables become rank–two Wishart eigenvalues and relative Stiefel angles, expressing the holonomy invariants \(A\), \(B\), and \(R^2=A^2+B^2\) in radial and angular Gram data. The large-\(R\) aligned contribution \(-A\) is absorbed into the Gaussian sector, producing the shifted mass \((\alpha_\Lambda)_{\rm eff}=\alpha_\Lambda-1/2\). The exact \(O(2)\) angular integral encodes this sector in a rank–two Bessel kernel. The pure \(-A\) theory, exactly solvable in Cartesian variables, fixes the leading Bessel/HCIZ structure: its exponential selects alignment, while its prefactor removes the spurious doubled Wishart entropy. We then apply this structure to the transverse \(B\)-type expansion and its non-polynomial toy completion. Finite polynomial truncations lead to an apparent large–\(d\) perturbativity bound incompatible with the continuum limit, but this bound is shown to be an artifact of truncation. After summing the local transverse completion and balancing the compensating \(+A\) term, the Wishart saddle is recovered with the physical shifted mass. The resulting continuum behavior reproduces the universal \(-2d\) contribution of the \(D_\Lambda\)-channel, while the genuinely anisotropic \(\beta_\Lambda\)-channel lies outside the scope of a pure transverse \(B\)-type description. Finally, we outline the emergent Grassmannian geometry encoded by the two endpoint planes. Their relative angular fluctuations form a \(2(d-2)\)-dimensional sector, whose entropy interpretation is developed in the sequel. For \(d\ge4\), the two planes generically span a relational four-dimensional subspace of \(\mathbb R^d\).

We present significant improvements to the AMFlow package for the numerical computation of dimensionally regularized Feynman integrals. Several new features are introduced to reduce computational cost, including an alternative recursion mode, a high-performance differential equation solver, support for state-of-the-art integration-by-parts reducers and other useful improvements. We benchmark the new version on a three-loop five-point topology and find that both the symbolic and numerical performance are significantly improved.

We define a gauge-invariant and renormalized off-shell mass function in quantum field theory. The conventional self-energy is gauge-dependent off-shell. We generalize the self-energy, together with the corresponding vertex function, to be gauge-invariant and process-independent. To do this, we extend the pinch technique to an arbitrarily long fermion line. The Ward-Takahashi identity acting locally at each vertex cancels the gauge-dependent piece exactly, leaving the Feynman-gauge self-energy. On-shell renormalization then yields a mass function that is gauge-invariant, scheme-independent and equal to the physical mass at the pole; the same self-energy also yields an infrared-finite scalar mass function directly comparable with Schwinger-Dyson and lattice determinations. The cancellation is local to the internal fermion line and holds entirely off-shell, so the self-energy is well-defined on each internal segment of an amplitude with arbitrarily many external photons; we demonstrate this explicitly by computing the minimal off-shell Compton amplitude.

We extend Nielsen's geometric approach for quantum complexity from closed to open quantum systems, whose dynamics is governed by Lindbladian evolution. In this framework, complexity is defined through an optimal-control problem on the space of mixed states, with a cost assigned to both unitary and non-unitary generators. We show that the resulting geometric structure differs fundamentally from the Riemannian geometry that emerges in the case of unitary evolution. In the open-system setting, the natural geometry is typically sub-Finslerian. Dissipation makes the geodesics non-reversible, while the admissible tangent directions are restricted by the physically allowed controls. We analyze several physically motivated examples, including a single qubit subject to depolarizing and amplitude-damping channels, as well as the damped harmonic oscillator. We show that, similarly to the unitary case, varying the penalty factors in the cost functional modifies the geometric properties through changes in the flag curvature, the Finslerian analog of sectional curvature. Our results provide a geometric framework for quantifying the abstract notion of complexity in dissipative quantum systems, with potential connections to experimentally realizable setups.

A covariant reconstruction framework for Kantowski–Sachs (KS) geometries sourced by Chaplygin-type and polytropic fluids in teleparallel $F(T)$ gravity is developed using the coframe–spin-connection formalism and the teleparallel invariant approach. The matter sector is modelled by nonlinear equations of state, including the generalized Chaplygin gas $p=-A/\rho^{\alpha}$ and a polytropic law $p=K\rho^{\Gamma}$. The corresponding conservation laws determine the dependence of the fluid density on the anisotropic KS volume $V=A_2A_3^2$. These source scalings are then inserted into the symmetric part of the covariant teleparallel field equations and used to reconstruct the functional form of $F(T)$ directly from the KS dynamics. Power-law and exponential ansätze generate distinct invariant reconstruction branches. In the power-law sector, the Chaplygin fluid produces mixed constant-plus-power source terms, while the polytropic sector generates density powers controlled by the polytropic index. In the exponential sector, the natural reconstruction variable is the shifted invariant $X=T_0-T$, leading to shifted teleparallel de Sitter branches. The reconstructed models are interpreted as local anisotropic cosmological sectors and, for contracting angular KS scale factors, as local Kantowski–Sachs black-hole-interior reconstruction branches. The analysis is local and branch-dependent; leading-order viability is assessed through \(F_T>0\) and \(F_{TT}>0\), while a complete perturbative stability analysis is left for future work. The reconstruction is entirely driven by nonlinear matter conservation laws, thereby reversing the standard reconstruction strategy in which the gravitational Lagrangian is prescribed a priori.

We study linear gravito-electromagnetic perturbations of a slowly rotating 4-derivative corrected Kerr-Newman (KN) black hole (BH), using a perturbative approach beyond the KN geometry up to first order in angular momentum, first order in the higher-derivative parameters ci, i = 1,2...8, and 14th order in the BH electric charge. We derive the corrected coupled radial master equations for both axial and polar perturbation sectors. We extend the asymptotic iteration method (AIM) to apply to coupled second-order ordinary differential equations (ODEs) and employ it to compute the quasinormal frequencies (QNFs) of the system.Our results show pronounced isospectrality breakings between the two parity sectors, induced by c6,c7 and c8,particularly for high charge BH.This indicate the equations for the two parity sectors lose the transformation symmetry that relates them in the KN case.The very tiny frequency shifts induced by c4 support the interpretation that this parameter represents a redundant degree of freedom in the effective field theory.Finally, we parameterize the QNFs via a analytical fitting procedure for broader applicability.

The electric and magnetic carrollian limits of $N=1$ supergravity in $D=4$ spacetime dimensions are explicitly derived. The approach is general and applies also to extended supergravity models

Regular black holes in Horndeski theories must have stable horizons and regular centers. We study static, spherically symmetric, asymptotically flat configurations with a time-independent scalar. The horizon branch on which the scalar kinetic term $X$ remains nonzero is generically obstructed by divergent propagation speeds or ghost/gradient instabilities, aside from special degeneracies. On the regular branch, where $X$ vanishes at the horizon, analyticity at the relevant $X=0$ endpoints reduces the leading scalar equation to finite sets of Taylor coefficients. For nondegenerate shift-symmetric theories this gives a nonperturbative current no-hair theorem: the scalar is constant and the metric is Schwarzschild, hence centrally singular for nonzero ADM mass. For non-shift-symmetric positive-power couplings, the corresponding exclusion applies to the perturbative branch continuously connected to Schwarzschild. We also classify marginal nonanalytic departures: covariant regularity fixes the scalar-Gauss-Bonnet chain as the unique marginal nonanalytic completion. Hairy black holes in this completion evade the analytic current step but remain centrally singular.

Quantum computing has emerged as a promising framework for addressing computationally demanding problems in collider physics. In recent years, a growing number of quantum algorithms have been proposed for applications ranging from event generation and parton shower simulation to the evaluation of scattering amplitudes, loop and phase-space integration, and optimization problems relevant to experimental analysis. We provide a concise overview of the main ideas behind these developments, with emphasis on the potential advantages of quantum approaches in comparison with classical methods, as well as on the current limitations imposed by noisy intermediate-scale quantum hardware.

Suggestions of a late-time phantom crossing from DESI baryon acoustic oscillation measurements, combined with cosmic microwave background and Type-Ia supernova observations, have renewed interest in non-standard dark energy models. In this Letter, we propose a new realization of a low redshift phantom crossing using only well understood ingredients from fermion condensation and general relativity. Our construction relies on the interplay between effective quintom-like dark energy and backreaction from non-linear structure formation. The full cosmological evolution is consistent with $\Lambda$CDM until low redshift, where the backreaction starts to become prominent and a phase transition occurs. At this point, the total dark energy equation of state first crosses $w_{\text{DE}}=-1$ from above. For benchmark values of the backreaction energy density, a second crossing from below occurs at a lower redshift, as suggested by recent observation. Fitting our theoretical model with CPL parametrization, we find the result is consistent with the combined DESI+CMB+SNIa data analysis with DESY5, PantheonPlus, and Union3 datasets. Specifically, for backreaction density parameter $\Omega_{\rm BR}(z=0) = 0.0572$, the CPL parametrization gives the phantom crossing redshift $z_* \simeq 0.35$, $w_0 \simeq -0.76 $ and $w_a \simeq -0.93$.

We present a new class of exact solutions in Einstein-Gauss-Bonnet gravity in 2+1 dimensions that generalize the C-metric. This set of metrics equals the C-metric multiplied by a factor which, along with the massless scalar field, depends on a single variable whose value governs the structure of the spacetime. As in Einstein gravity there are three classes of metrics, but within each class we find six distinct subclasses of solutions. After discussing their basic structure, we concentrate only on one subclass that is locally AdS. In the zero-coupling limit, this subclass of solutions not only remains well defined and recovers the C-metric but also encompasses two previously unknown representations of the AdS spacetime. Furthermore, we establish the existence of a domain wall and delineate its energy conditions. We also find new classes of solutions of non-constant curvature, whose interpretation remains to be understood.

We present a novel rotating black hole solution surrounded by a Hernquist dark matter halo, obtained by applying the Newman–Janis algorithm to the exact Schwarzschild–Hernquist spacetime. The resulting Kerr–Hernquist geometry provides an axisymmetric background for investigating scalar-field dynamics in realistic dark matter environments. Using the analytical asymptotic matching method, we derive the quasibound-state spectrum, identify the conditions for scalar cloud formation and the black hole bomb instability, and obtain an analytic expression for the superradiant scattering amplification factor. We show that the halo preserves the hydrogen-like structure of the quasibound-state spectrum while introducing corrections governed by the combination $\rho_0 r_0^3$. Increasing the halo density and scale radius enhances the scalar-field binding energy, lowers the critical field mass for scalar cloud formation, suppresses the growth rate of the superradiant instability for co-rotating modes ($m_\ell>0$), and accelerates the decay of counter-rotating modes ($m_\ell<0$). Furthermore, the dark matter halo reduces both the magnitude and frequency range of superradiant amplification, thereby weakening energy extraction from the black hole. These results demonstrate that the Kerr–Hernquist geometry provides a unified framework for studying quasibound states, scalar clouds, black hole bombs, and superradiant scattering, while revealing how a Hernquist dark matter halo leaves observable imprints on the spectrum and stability of rotating black holes.

In this work, I analyze the zero modes of a one-loop semiclassical Yang-Mills theory in \(3+1\)d. I find that zero modes are generated by gauge redundancy of the background field. Proper gauge fixing, achieved by introducing a bosonic ghost term, together with zeta-function regularization, yields a finite one-loop effective action in closed form that reproduces the well-known one-loop Yang-Mills beta function.

The free massless Majorana field in 1+1 dimensions is employed to study the Bell-CHSH inequality in Quantum Field Theory. Use of the modular wedge localization enables us to show the near saturation of the Tsirelson bound.

In this work, we present a \(3+1d\) scalar QED model in a constant self-dual magnetic field configuration. We provide exact closed form analytic calculations of the partition function, the \(\beta\)-function, and the propagators. To our knowledge, we present the first closed-form finite expression for the matter field propagators in a self-dual background, which is made accessible by working entirely in the Landau level basis. This theory serves as a toy model for charged particles in parallel electric and magnetic fields, with natural extensions to studies of \(3+1d\) chiral magnetic effects and pulsar physics.