Papers

We construct the Kerr-Schild classical double copy of the black string in the Randall-Sundrum II model, deriving the single and zeroth copies, and verifying the associated field equations. The single copy gauge field is independent of the holographic coordinate and satisfies a sourceless Maxwell equation on the curved background, in direct analogy with the Coulomb field of the Schwarzschild double copy. The zeroth copy scalar obeys a modified Klein-Gordon equation with a first-order derivative term along the extra dimension; a field redefinition yields a standard Klein-Gordon equation with effective mass $m^2 = 12/l^2$, induced by the warp factor. We further show that an alternative Kerr-Schild splitting, gravitationally equivalent to the canonical one, produces a physically inequivalent double copy: the gauge field is supported by a conserved but delocalized bulk current, and the zeroth copy satisfies a massless equation that carries no imprint of the warped extra dimension.

We propose a family of topological quantum critical points (tQCPs) separating non-invertible chiral topological orders in $(2+1)$ dimensions. We conjecture that these tQCPs can be captured by a family of scale-invariant field theories forming a non-compact scale-invariant manifold. A central feature of our proposal is topological shadowing: the underlying critical theory is rigorously constrained by the global topological data of the two adjacent gapped phases. These theories can be further projected into quantum field theories with universal non-local structures. The non-local coupling, however, controls dynamical observables along the scale-invariant manifold, including the VEV of Wilson loops and their exchange phase around the two non-contractible cycles of a torus. Despite the non-locality, our renormalization group calculations (up to two-loop order) strongly suggest that the theory shall maintain exact scale invariance. This supports, without supersymmetry, a continuous family of scale-invariant fixed points, which are further substantiated from a holographic perspective.

We examine several observable optical properties of a Skyrmion black hole (BH), focusing on the photon sphere, BH shadow, and photon trajectories. The Skyrme term, along with other geometric parameters of the spacetime, determines the photon sphere location and shapes the resulting BH shadow. Parameter variations produce observable departures from standard BH geometries, offering potential signatures of nonlinear field effects. We also analyze the sparsity of Hawking radiation and the associated energy emission spectra, showing how these quantities respond to the Skyrme coupling and background parameters. Our findings illuminate the connection between nonlinear field contributions and BH optics, with implications for observational and theoretical studies of modified gravity scenarios.

Second-order ordinary linear differential equations appear ubiquitously across physics, describing the behavior of systems from the quantum world of atoms to the classical world of gravitating bodies. We present a unified symmetry-based framework that provides a “litmus-test criterion” to determine when such a system admits a hierarchical ladder structure, and, whenever it does, explicitly constructs the ladder. This approach uncovers a previously underappreciated connection to supersymmetric quantum mechanics and a deep commonality among diverse physical problems. Applications to the quantum harmonic oscillator and dynamical tidal response of Kerr black holes are presented to illustrate the framework.

The Kerr-Schild double copy (KSDC) is well-known for relating exact classical solutions between Yang-Mills theory and theories of gravity. However, whether this correspondence provides a more fundamental mapping between the underlying symmetries of gauge theory and gravity remains an underdeveloped area of research in the contemporary double copy program. In this paper, we demonstrate that the KSDC correspondence does not provide a mapping between the residual symmetry structures of the Kerr-Schild ansatz in Yang-Mills theory and gravity. On the gauge theory side, residual symmetries form an infinite-dimensional algebra of functions along null directions. On the gravitational side, residual diffeomorphisms preserving the Kerr-Schild form of the Schwarzschild metric generate a conformal algebra on $S^2$, which decomposes into Killing vectors and proper conformal Killing vectors (CKVs). While the Killing sector reproduces the expected global isometries, the CKV sector yields an infinite-dimensional algebra after imposing asymptotic flatness and horizon regularity. This appears to contradict the fact that the Schwarzschild solution admits no proper conformal symmetries. We resolve this apparent contradiction by constructing a Weyl-compensated BRST complex, showing that the CKV sector is BRST-exact and therefore trivial in cohomology, so that the physical symmetry algebra reduces to the global isometries of Schwarzschild. This demonstrates that the KSDC introduces an enlarged symmetry structure at the level of the ansatz, but preserves physical symmetries after a cohomological reduction, revealing a fundamental mismatch between Yang-Mills and gravity at the level of residual symmetries.

We report a physical origin of tensionless strings, obtained by formulating string dynamics in finite-lifetime settings for the first time. Departing from the conventional paradigm of eternal strings, we construct an inertial worldsheet confined to a finite region of two-dimensional Minkowski spacetime, known as a causal diamond. This reveals a striking result: tensionless strings arise only at the moment of their birth. The ultra-shrinking limit of the diamond worldsheet realizes this birth configuration, thereby uncovering a new tensionless string phase characterized by a global, ultra-local Carrollian structure.

We study the double-logarithmic four-graviton Regge sector in $N$-extended supergravity. Its Mellin-space solution is already known in terms of parabolic-cylinder functions. We show that the same answer can be organized as a rank-two twisted period system, meaning that two closely related weighted integrals determine the full Mellin partial wave. These functions satisfy a simple pair of first-order differential equations and a recursion as the number of supersymmetries $N$ changes. This gives a uniform description of the full supergravity family, clarifies the relation between the positive-ray Euler integral and the earlier contour representation, and reproduces the same reduction rule through intersection theory. The reformulation also makes the special cases with four and six supersymmetries particularly transparent and yields a simple Hermite-polynomial construction for the low-even theories.

We study Bell-Clauser-Horne-Shimony-Holt (Bell-CHSH) violations in the vacuum state of free spinor fields in $(1+1)$-dimensional Minkowski spacetime. We construct explicit smooth compactly supported test functions with spacelike separated supports whose Bell-CHSH correlators converge to Tsirelson's bound $2\sqrt2$. In the massless case, after passage to the time-zero slice and a natural symmetry reduction, the problem reduces to the quadratic form of the Carleman operator on $L^2([0,\infty))$. Near-maximal Bell violation is then governed by the spectral edge $\pi$, and explicit near-extremizers are obtained from compactly supported cutoffs of the generalized eigenfunction $x^{-1/2}$. This also explains the appearance of the constant $\pi$ in earlier wavelet-based formulations. In the massive case, the same reduction leads to a Hankel operator with kernel $mK_1(m(x+y))$, where $K_1$ denotes the modified Bessel function of the second kind of order $1$, and exponentially damped variants of the massless test functions again yield Bell-CHSH values converging to $2\sqrt2$. Therefore, we establish a direct link between Bell-CHSH violations for free $(1+1)$-dimensional spinor fields and the spectral theory of Carleman and Hankel operators on the half-line.

We present a historical optical foundation for stationary vacuum Kerr–Schild spacetimes on a flat background and interpret it in modern double-copy language. In this setting, a complex optical seed \(\rho=-\theta-i\omega\), built from the expansion and signed twist of the Kerr–Schild congruence, is harmonic, while its inverse obeys an eikonal equation and reconstructs the congruence algebraically. Thus the local stationary geometry is organized by a single complex seed. In the overlap of the stationary Kerr–Schild and Petrov type–D Weyl double-copy framework, this seed furnishes a normalized representative of the zeroth-copy data, while its real part yields the Kerr–Schild profile and its gradient generates the single-copy gauge-field strength. The construction provides, without recourse to twistor methods, a spacetime realization of how a single complex seed builds the congruence, organizes the associated spacetime and gauge fields, and encodes the geometric content of the zeroth copy.

The KMOC (Kosower-Maybee-O'Connell) formalism establishes a bridge between quantum scattering amplitudes and classical observables in gravitational systems. In this work, we show how the weak-field limits of the four classical black hole metrics - Schwarzschild, Kerr, Reissner-Nordstrom, and Kerr-Newman - can be reproduced within this formalism. Starting from three-point amplitudes with exponential spin structure for both gravitational and electromagnetic interactions, we compute four-point scattering amplitudes and extract the momentum impulse via the KMOC formula. Matching these results with geodesic motion in a general metric allows us to reconstruct the metric components to leading order in G, a, and Q^2. For the Kerr-Newman case, we include interference terms between gravitational and electromagnetic interactions, which produce a Q^2 a/r^3 contribution to g_{t\phi} that does not appear in the Kerr or Reissner-Nordstrom weak-field limits separately. Our results are consistent with those of arXiv:1907.00431 [hep-th], where the Kerr-Newman metric is derived from minimal coupling amplitudes using the KMOC formalism arXiv:1908.04342 [hep-th]. All results are verified through their consistency with the well-known full metrics, though we emphasize that the KMOC formalism as applied here reproduces only the weak-field expansions, not the complete non-linear solutions.

We present a detailed study of quasinormal modes and greybody factors in the context of the parametrized quasinormal mode framework, in which modifications to general relativity are introduced as small corrections in the potential. We deduce the QNMs' and GBFs' dependence on the order of the modifications and their polynomial power. We also test the validity of the recently proposed QNM-GBF correspondence in the pQNM framework by inspecting the regime at which it breaks down.

In this article we develop a worldline technique based on the method of images to study the effective action associated to Yang-Mills theories on manifolds with boundaries. We consider the possibility of having either relative or absolute boundary conditions, which are particular types of mixed boundary conditions. Both vector fields and ghost fields are taken into account in this analysis. As a check of our construction, we compute the first three Seeley-DeWitt coefficients of the heat kernel asymptotics. Finally, we employ our technique to calculate the rate of gluon production due to a chromoelectric field background in the presence of a boundary.

We determine the normalization of the leading infrared renormalon of the chromomagnetic moment of a heavy quark. Estimates of higher order coefficients of the perturbative series are given. We compute the hyperfine splitting of the $B$ and $D$ mesons for the ground state with hyperasymptotic precision by including the leading terminant, associated with the first infrared renormalon. We fit the experimental data to the operator product expansion theoretical prediction with $\hat \mu^2_{G,\rm PV}$ as the free parameter. We obtain $\hat \mu^2_{G,\rm PV}=0.507(7)$ GeV$^2$ for the ground state.

Integration-by-parts (IBP) reduction of Feynman integrals to master integrals is a key computational bottleneck in precision calculations in high-energy physics. Traditional approaches based on the Laporta algorithm require solving large systems of equations, leading to memory consumption that grows rapidly with integral complexity. We present SAILIR (Self-supervised AI for Loop Integral Reduction), a new machine learning approach in which a transformer-based classifier guides the reduction of integrals one step at a time in a fully online fashion. The classifier is trained in an entirely self-supervised manner on synthetic data generated by a scramble/unscramble procedure: known reduction identities are applied in reverse to build expressions of increasing complexity, and the classifier learns to undo these steps. When combined with beam search and a highly parallelized, asynchronous, single-episode reduction strategy, SAILIR can reduce integrals of arbitrarily high weight with bounded memory. We benchmark SAILIR on the two-loop triangle-box topology, comparing against the state-of-the-art IBP reduction code Kira across 16 integrals of varying complexity. While SAILIR is slower in wall-clock time, its per-worker memory consumption remains approximately flat regardless of integral complexity, in contrast to Kira whose memory grows rapidly with complexity. For the most complex integrals considered here, SAILIR uses only 40% of the memory of Kira while achieving comparable reduction times. This demonstrates a fundamentally new paradigm for IBP reduction in which the memory bottleneck of Laporta-based approaches could be entirely overcome, potentially opening the door to precision calculations that are currently intractable.

Understanding the structure of operators that commute with $k$ identical replicas of unitary ensembles, also known as their $k$-commutants, is an important problem in quantum many-body physics with deep implications for the late-time behavior of physical quantities such as correlation functions and entanglement entropies under unitary evolution. In this work, we study the $k$-commutants of free-fermion unitary systems, which are heuristically known to contain $SO(k)$ and $SU(k)$ groups without and with particle number conservation respectively, with formal derivations of projectors onto these commutants appearing only very recently. We establish a complementary perspective by highlighting a larger $O(2k)$ replica symmetry (or $SU(2k)$ respectively) that the $k$-commutant transforms irreducibly under, which leads to a simple geometric understanding of the commutant in terms of coherent states parametrized by a Grassmannian manifold. We derive this structure by mapping the $k$-commutant to the ground state of effective ferromagnetic Heisenberg models, analogous to the ones that appear in the noisy circuit literature, which we solve exactly using standard representation theory methods. Further, we show that the Grassmannian manifold of the $k$-commutant is exactly the manifold of fermionic Gaussian states on $2k$ sites, which reveals a duality between real space and replica space in free-fermion systems. This geometric understanding also provides a compact projection formula onto the $k$-commutant, based on the resolution of identity for coherent states, which can prove advantageous in analytical calculations of averaged non-linear functionals of Gaussian states, as we demonstrate using some examples for the entanglement entropies. In all, this work provides a geometric perspective on the $k$-commutant of free-fermions that naturally connects to problems in quantum many-body physics.

We construct geometries describing the quantum backreaction of thermal fields in AdS$_3$. The solutions are obtained from branes in a four-dimensional AdS C-metric. They can be viewed as solutions of the semiclassical effective theory on the brane, which couples three-dimensional gravity to the CFT dual to the four-dimensional bulk. This brane construction is related by a double analytic continuation to earlier studies of quantum BTZ solutions. There are two families of solutions, labelled by the asymptotic mass. Solutions with negative mass correspond to the back-reaction of a thermal CFT state on global AdS$_3$. Solutions with positive mass have a horizon for zero back-reaction, which is replaced by a smooth origin in the back-reacted solution. We study the thermodynamics and first law on the brane, which we argue is realised in a two-brane setup where we include both the quantum BTZ brane and our quantum soliton brane.

Feynman integral reduction based on intersection theory provides an alternative to the traditional integration-by-parts method, yet its practical application has been constrained by the large number of variables required in the computation. In this Letter, we demonstrate that by employing the recently introduced branch representation, the reduction of $L$-loop Feynman integrals with an arbitrary number of external legs can be achieved through the computation of at most $(3L-3)$-variable intersection numbers. This constitutes a significant simplification compared to existing approaches, particularly for multi-leg integrals where the number of variables in conventional methods scales with the total number of propagators. We validate the proposed method through explicit calculations of two-loop diagrams, demonstrating substantial improvements in computational efficiency relative to both traditional intersection-theory approaches and standard integration-by-parts reduction techniques.

We observe that a large class of well behaved stationary and axisymmetric black hole solutions in general relativity and in the Einstein-Maxwell theory can be classified according to the properties of their background. Indeed all these backgrounds belong to a unique family which includes simultaneously all the known axisymmetric and regular backgrounds: the swirling, the Bertotti-Robinson, the Bonnor-Melvin universe, Witten's expanding bubble and also other novel, regular, rotating gravitational or electromagnetic environments. All these can be, fundamentally, traced back to the double Wick rotation of the topological generalisation of (accelerating) Kerr-Newman-NUT metric. We present a black hole embedded in an unexplored sector of the general background: Schwarzschild inside a generalised rotating (and possibly electromagnetic) universe. These results indicate that basically all the known analytical and exact single black hole solutions in the four-dimensional Einstein-Maxwell theory belong to the (accelerating) Kerr-Newman-NUT family embedded into backgrounds that are a subcase of the conjugated Kerr-Newman-NUT space-time with an angular manifold of arbitrary topology.

Considering $Z_4$ symmetry in Type I seesaw scenario, one could obtain mass-squared differences of light neutrinos, mixings and $CP$ violating phase within $3 \sigma$ confidence level based on neutrino oscillation data. This is possible with only three independent complex parameters for allowed Yukawa couplings and one real mass parameter for heavy right handed neutrino fields around electroweak scale. After considering only three more real parameters as coming from small soft-symmetry breaking terms, the lightest right handed neutrino could be considered as dark matter candidate via freeze-in mechanism and the other two heavier right handed neutrinos through their decays, could generate the baryonic asymmetry of the universe naturally via resonant leptogenesis.

Simulating lattice gauge theories on quantum computers presents unique challenges that drive the development of novel theoretical frameworks. The orbifold lattice approach offers a scalable method for simulating SU($N$) gauge theories in arbitrary dimensions. In this work, we present three improvements: (i) two new simplified Hamiltonians, (ii) an encoding of the SU(2) theory with smaller number of qubits, and (iii) a reduction in the requirement for large scalar masses to reach the Kogut-Susskind limit, achieved via the inclusion of an additional term in the Hamiltonian. These advancements significantly reduce circuit depth and qubit requirements for quantum simulations. We benchmarked these improvements using Monte Carlo simulations of SU(2) in (2+1) dimensions. Preliminary results demonstrate the effectiveness of these developments and further validate the use of noncompact variables as a promising framework for scalable quantum simulations of gauge theories.

In this work, we propose a novel experimental set-up using charged resonant gravitational wave detectors. We exploit the semi-classical analogue of the Gertsenshtein effect where the gravitational wave acts as an modulator for the optomechanical system. We consider a cavity QED scenario where the Weber bar is placed inside an electromagnetically shielded cavity. We observer that when the gravitational wave falls on the Weber bar, it emits photon which signifies the detection of gravitational waves by the resonant bars. The frequency controlled spontaneous emission scenario will shed a new light on future generation of efficient gravitational wave detector models.

In higher-dimensional Einstein-AdS gravity, it is well known that planar and static anti-de Sitter black holes can be endowed with multiple rotation parameters via a large-gauge transformation. However, a similar prescription fails when multiple NUT parameters are added, thereby obstructing the study of holographic properties with more than one NUT charge. To pave the way towards this direction, we construct explicit planar AdS spacetimes having multiple NUT parameters in two simple ways that allow one to circumvent the strong restrictions imposed by the vacuum field equations. First, motivated by momentum relaxation holographic models, we construct multi-NUT spaces in AdS with flat horizons by adding free scalar fields possessing an axionic profile. In our second approach, we build similar configurations in Einstein gravity with quadratic-curvature corrections. We end by presenting planar versions of the Kaluza-Klein monopole in AdS with different magnetic charges. As a byproduct, our strategy yields a simple way to generalize the Gross-Perry-Sorkin monopole to include the cosmological constant.

We present a constituent two-gluon description of the lowest-lying glueball states in pure Yang–Mills theory, calibrated against quenched lattice results. The framework incorporates an instanton-induced dynamical gluon mass, Casimir-scaled adjoint confinement, the short-distance adjoint Coulomb interaction, and instanton-induced central and tensor forces. The scalar $0^{++}$ glueball is found to be exceptionally compact, with a radius of order the instanton size, $\rho \sim \frac 13\,\mathrm{fm}$, consistent with lattice indications. By contrast, the tensor $2^{++}$ state remains spatially extended due to the centrifugal barrier. We also discuss the role of $S$-$D$ mixing. A semiclassical analysis further supports Regge behavior for excited states, in agreement with lattice results.

We investigate Hawking radiation in noncommutative spacetime. For a dynamical black hole formed by the collapse of a matter shell, we demonstrate that spacetime noncommutativity modifies the interaction between the radiation field and the background geometry. In particular, the collapsing shell is effectively shifted by an amount proportional to the momentum of an outgoing Hawking mode. While the nonlocality inherent in noncommutative spacetime invalidates the conventional arguments for the robustness of Hawking radiation, the radiation decays substantially after the scrambling time, resulting in an exponentially long evaporation time.

We construct simple analytical solutions of renormalization group equations for the running coupling and for the Green functions in QCD in the asymptotic regime. These solutions have an explicit form and subsequently sum up the leading, subleading, and so on logarithms in all orders of PT. They easily reproduce the inverse logarithm expansion and allow for further summation and improvement of the asymptotic behaviour.

It is shown that a duplication of the hypercharge, which is identical for the normal sector but different for the dark sector, may manifestly address neutrino mass and dark matter.

This work presents a comprehensive benchmark and validation of a recently proposed method called Effective Bethe Ansatz (EBA). It is a variational method that deforms the exact Bethe wavefunctions of one-dimensional spin chains at integrable points to approximate non-integrable systems. We apply this method to the non-integrable regime of the spin-1 bilinear-biquadratic chain. By performing EBA method starting from the two integrable endpoints, the Takhtajan-Babujian point and the Lai-Sutherland point, we systematically evaluate the accuracy of the EBA for the ground state and first excited state. Our validation is based on a direct comparison with exact diagonalization, assessing energy, fidelity, and entanglement entropy. The results confirm that the EBA provides a quantitatively accurate description in a finite window around the integrable points, while its fidelity and entanglement properties degrade in a controlled way as the perturbation increases. The method successfully captures key finite-size effects, such as level crossings, manifested as sharp drops in fidelity, and provides a probe to potential phase transitions. This study establishes the EBA as a reliable and efficient semi-analytical tool, clarifying its scope and limitations for studying low-energy physics in non-integrable quantum spin chains.

A metric is called universal if every symmetric conserved rank-two tensor constructed locally from the metric, the curvature, and covariant derivatives of the curvature is proportional to the metric. Such a metric solves arbitrary metric-based higher-curvature field equations after, at most, a change in the effective cosmological constant. A metric is called almost universal if the same field equations reduce instead to a finite set of algebraic conditions and a single linear scalar equation for a profile function. Universal and almost universal metrics are useful because they keep higher-curvature gravity under analytic control. Plane waves are a well-known example of universal metrics, while the Kerr-Schild-Kundt class of metrics including the $pp$-waves is almost universal. Here, we add a new member to this class of metrics and show that nonzero constant curvature $pp$-wave metrics are also almost universal. They reduce the generic gravity field equations to those of cosmological Einstein-Maxwell theory with null dust. The background of the $pp$-waves has the topology $\mathbb{R}^{1,1}\times S^{2}$ and provides the missing partner to the Nariai metric with ${\rm dS}^{2}\times S^{2}$ and the Bertotti-Robinson metric with ${\rm AdS}^{2}\times S^{2}$ topologies. These quantum-protected metrics are of clear interest. We exemplify our results by using the quadratic and cubic gravity theories.

We propose an effective Bethe ansatz (EBA) for solving quantum many-body systems near an integrable point. Our approach retains the functional form of the Bethe wave function while renormalizing the Bethe roots to account for integrability-breaking interactions. These effective roots are determined by minimizing physically motivated cost functions. The resulting off-shell Bethe states serve as approximate eigenstates of the non-integrable models. We assess the quality of the approximation using various physical observables, including the energy eigenvalue, state fidelity, and bipartite entanglement entropy. Our tests show that for models with weak integrability-breaking, the effective Bethe ansatz provides a high-quality approximation to the exact eigenstates over a wide range of deformation parameters. In contrast, for models with strong integrability-breaking interactions, the efficacy of the effective Bethe ansatz degrades relatively quickly as the deformation parameter increases. The efficacy of the method thus offers a useful probe for characterizing the strength of integrability breaking. Within its regime of accuracy, it also provides a new representation of the eigenstates of nearly integrable models, enabling one to exploit the algebraic structure inherited from integrability.

In this article, we report the results of comparing the effect of using trace of stress-energy tensor versus real-valued scalar field in Nonminimal Derivative Coupling gravitation model, respectively denoted as NMDC-T and NMDC-phi. We employ the model into an incompressible star and see the effect of both models NMDC-T and NMDC-phi on the compactness and mass-radius relation. We find that coupling parameters of NMDC-T is less sensitive than NMDC-phi.