Papers

We introduce the flavoured lattice Schwinger model, a $(1{+}1)$-dimensional $U(1)$ lattice gauge theory in which the fermion doubling problem is resolved by staggering a $\mathbb{Z}_{2}$ flavour degree of freedom rather than staggering chirality. Unlike the standard approaches, this construction preserves an exact axial $U(1)$ symmetry at finite lattice spacing. We derive the continuum limit, showing that the model reduces to the two-flavour massless Schwinger model, with flavours $\alpha\in\{0,1\}$ sharing one dynamical $U(1)$ gauge field. The central result is a well-defined, regularised, gauge-invariant lattice axial charge $Q_{G}^{A}$ whose continuum non-conservation $\langle dQ_{G}^{A}/dt\rangle = -(2g/\pi)\!\int\! dx\,\langle E(x)\rangle$ arises as a direct dynamical consequence of minimal gauge coupling. A particle-hole transformation on the $\chi$ flavour exposes a hidden $U_{L}(2)\times U_{R}(2)$ chiral symmetry; non-Abelian bosonisation then identifies the model with a massive abelian Schwinger sector tensored with the level-$1$ $SU(2)$ Wess–Zumino–Witten model. Finally, we show that embedding the flavoured fermions in a ribbon-shaped $(2{+}1)$D Bernevig–Hughes–Zhang topological insulator and gauging the bulk in a constant background field factorises the boundary theory into two decoupled single-flavour Schwinger models, one on each edge, identifying the lattice factor of $2$ as one quantum of Schwinger anomaly per edge.

Scalar-induced gravitational waves (SIGWs) have recently attracted considerable interest, both as a possible explanation for the nanohertz signal reported by the Pulsar Timing Array (PTA) collaboration and for their connection with primordial black hole (PBH) physics. In addition to SIGWs, scalar-tensor-induced gravitational waves (STGWs) have emerged as a promising cosmological source of the stochastic gravitational wave background (SGWB). In this paper, we compute the STGWs generated during a generic matter-dominated (MD) era, as well as during an early matter-dominated (eMD) epoch followed by a sudden transition to the standard radiation-dominated (RD) stage, working in the Poisson gauge. We find that, in a purely MD age, the corresponding energy density rapidly dilutes, whereas in the presence of an eMD phase it remains non-vanishing due to the short duration of the eMD period. We then investigate whether the STGW signal could provide a dominant contribution to the NANOGrav 15-year dataset and we forecast the prospects for its detection with future observations by the Square Kilometre Array (SKA). In particular, we consider STGWs generated during both eMD and RD eras, including their linear-order contributions. We further inject the scalar-induced contribution, both as an additional component and as the only signal, and compare the spectra against the same datasets. Our results show that, although the SIGWs still appear to provide the dominant contribution and the posteriors are tightly constrained by the requirement of avoiding PBH overproduction, the GWs induced by scalar-tensor mixing constitute a viable target for future, more sensitive nano-Hz detectors of the SGWB.

We investigate the cosmological implications of non-polynomial quasi-topological gravity (NPQTG), a novel class of modified gravitational theories in which the background dynamics is encoded in a single function of the Hubble parameter. This framework provides a minimal and theoretically consistent extension of general relativity, incorporating higher-curvature effects while preserving second-order field equations and avoiding higher-derivative instabilities. We first establish the general conditions for cosmological viability and construct explicit realizations, including polynomial, quartic, power-law and non-polynomial models, demonstrating how different functional forms lead to distinct expansion histories. Focusing on the quartic and power-law cases, we show that the resulting cosmological evolution reproduces the standard thermal history of the Universe and gives rise to an effective dark-energy sector of geometric origin, with dynamical equation-of-state behavior that can lie in the quintessence or phantom regime. We then confront the models with observational data from Type Ia Supernovae, Cosmic Chronometers, and Baryon Acoustic Oscillations, using a Bayesian MCMC analysis. We find that both models provide an excellent fit to the data, remaining fully compatible with current constraints and statistically competitive with $\Lambda$CDM. Our results demonstrate that NPQTG offers a simple and efficient framework for describing late-time cosmic acceleration with dynamical dark energy, while maintaining theoretical consistency and observational viability.

It is known that the semiclassical approximation to the gravity path integral can be leveraged to explain certain inherently quantum aspects of gravity. One such aspect is the state-counting interpretation of the Bekenstein-Hawking entropy of black holes. A second aspect is the Page curve for the entanglement entropy of Hawking radiation, which agrees with expectations from unitarity. We show that these two questions are equivalent from the gravity path integral point of view. In particular, the Hawking's information loss puzzle gets resolved automatically by considering any (over)complete basis of black hole microstates which is compatible with black hole entropy. The tool which relates the two questions is a convex optimization problem for the von Neumann entropy of Hawking radiation.

We further develop a trace-anomaly-motivated gluonic scenario in which cold dark matter (CDM) is modeled as a long-lived color-singlet Bose-Einstein condensate seeded at the QCD confinement transition. Specifically, guided by the near-universality of the galactic acceleration scale $g^{}_\dagger \simeq (1\text{--}2)\times10^{-10}\,\mathrm{m\,s^{-2}}$ inferred from the RAR, we hypothesize that this relic gluonic condensate organizes, at galactic distances, into a spectrally rigid lowest-weight structure characterized by a protected infrared gap. Within an effective representation-theoretic framework, Lorentz covariance together with positive-energy lowest-weight unitarity naturally favors the AdS algebra $\mathfrak{so}(2,3)$ as the minimal algebraic structure supporting such a discrete tower of states. The resulting condensate produces, by construction, a cored halo profile with finite total mass $M_h$. Normalizing this profile by the observed approximate universality of the central DM surface density, $\Sigma_0\simeq141\,M_\odot\,\mathrm{pc}^{-2}$, yields a universal characteristic acceleration $g^{}_\star ={G\, M_h}/{r_{\rm c}^2} \simeq \pi^2 G\,\Sigma_0 \simeq 1.9\times10^{-10}\,\mathrm{m\,s^{-2}}$, independent of the particular halo scale; since $\Sigma_0$ fixes the final expression, the dependence on the collective correlation length $r_{\rm c}$ drops out. Notably, its predicted value lies well within the empirical range of the acceleration scale inferred from the RAR. We also provide an illustrative comparison with representative rotation curves from the SPARC database, indicating phenomenological compatibility of the finite-mass profile with realistic baryonic decompositions. This comparison is not a precision fit to the full SPARC sample, and the agreement with the RAR scale should not be interpreted as a first-principles derivation of the RAR itself.

Hilbert space fragmentation refers to exponential growth in the number of dynamically disconnected Krylov sectors with system size. It is taken as evidence of ergodicity breaking, since conventional symmetries generate at most a polynomial number of sectors. However, we demonstrate that generalized symmetries can fragment the Hilbert space. Models with higher-form, subsystem, and gauge symmetries can have exponentially many symmetry sectors. We further prove that non-invertible symmetries can induce additional fragmentation within individual symmetry sectors. Fragmentation in several known models arises from generalized symmetries, and the presence of exponentially many Krylov sectors therefore does not by itself imply ergodicity breaking. Finally, we show that disorder free localization arises naturally from Krylov-restricted thermalization when sectors lack translation invariance, requiring neither ergodicity breaking nor gauge symmetry.

We present an integral formulation of classical Yang-Mills theory coupled to fermionic and scalar matter fields in (1+1)-dimensional Minkowski spacetime. By reformulating the local dynamics in terms of loop-space holonomies, we demonstrate that the path independence of the holonomy eigenvalues constitutes a conservation law, yielding an infinite hierarchy of gauge-invariant, dynamically conserved charges. While a zero-curvature equation is associated with a necessary condition for this path invariance, we note that it is not strictly sufficient on its own. Employing a first-order symplectic formalism, we show that these non-abelian charges generate global symmetry transformations on the fundamental phase-space variables. We rigorously prove that these transformations preserve the physical dynamics, leaving the total Hamiltonian invariant up to first-class constraints. Furthermore, an analysis of the Poisson algebra reveals that these conserved charges are in involution, provided the boundary integration constant lies within the center of the gauge group. This exact, lower-dimensional framework provides a highly tractable setting to investigate the algebraic structures of these hidden symmetries and the meaning of the conserved charges as physical observables, establishing a classical foundation for exploring their role in the quantum regime, such as in strongly coupled lattice gauge theories.

Celestial symmetries of gravity and gauge theory can be enhanced to a $w_{1+\infty}$ algebra and an $S$-algebra respectively, when restricting to a single graviton/gluon helicity sector. Difficulties in combining both sectors in the full theory have been pointed out in the previous literature. In this work, we face this problem from the covariant phase space perspective and analyze in detail the structure of the mixed-helicity bracket of the higher-spin charges for both gravity and Yang–Mills theory. We show that, when restricting one of the two helicities to the wedge sector, a closed algebra can be obtained for all spins in terms of a notion of shadow charge we introduce. Furthermore, when focusing on the lower spin subalgebra sectors, in the case of gravity, we show that a dual mass extension of the BMS algebra can be consistently constructed; in the case of Maxwell theory, inclusion of magnetic charges allows us to recover a non-vanishing expression for the electromagnetic central charge previously obtained through different methods.

We present a pedagogical review of certain exact theoretical results concerning the physics of an imaginary world where one quark or more are deprived of their masses.

The observed unusual behaviors of the orbits of Trans-Neptunian objects as well as the gravitational anomalies detected by the Optical Gravitational Lensing Experiment can be explained by assuming the existence of a ninth planet in the Solar System, having a mass of the order of $5-10M_{\oplus}$, and located at the distance of 300-1000 AU from the Sun. Since no optical counterpart of Planet 9 was observed, it is reasonable to assume that it has a very low luminosity. Various proposals on the nature of Planet 9 have been advanced, including the possibility that it is a black hole, an axion or a dark matter star. We propose that dark matter heating of Planet 9 could generate a thermal radio flux that could allow its observational detection, even if Planet 9 is a very dark object. We estimate the dark matter impact parameter, the mass and the kinetic energy deposition rates, as well as the surface temperature of Planet 9. By adopting a specific model for the time evolution of the planet, and assuming a long time capture of dark matter, the surface temperature of Planet 9, and the spectral features of the emitted radiation are obtained. Our results indicate that dark matter capture may provide an efficient mechanism for the heating of Planet 9, and also provide a specific observational signature of the planet. The numerical evaluations depend on the unknown value of the dark matter-ordinary matter interaction cross-section, with the estimates obtained as a function of its ratio and the saturation cross section for dark matter to deposit its entire energy. For a value of this ratio of $10^{-10}$, and for a dark matter density of the order of $1.32\times 10^{-17}$ g/cm$^3$, in a few Gyrs the surface temperature of Planet 9 can reach values of the order of 200 K, or even higher, with a maximum wavelength of around $\lambda_{max}=1.44\times 10^{-3}$ cm, situated in the infrared domain.

Recent years have witnessed tremendous progress in developing a fine-grained low-dimensional holographic correspondence, specifically the construction of quantum mechanical boundary theories as holographic duals of two-dimensional gravity. In these developments, quantum chaos played a crucial role, both as source of universality and as a guiding principle for the matching of bulk and boundary signatures of gravity. In this article we review the construction of the chaos-assisted low-dimensional holographic correspondence for non-experts. We open with an introductory discussion of the two main protagonists of the theory, the SYK model and two-dimensional Jackiw-Teitelboim gravity. Within this framework we will discuss two independent 'bridges' between bulk and boundary physics, one pertaining to early time chaotic instabilities, the other to late time quantum chaos up to and including time scales of the order of the gravitational quantum level spacing. We will demonstrate that the resolution of these fine-grained quantum scales requires the extension of semiclassical gravity by elements of string theory. We conclude with an outlook towards higher dimensional generalizations of the chaotic holographic correspondence.

We present a real-time path-integral formulation of the quantum Fisher information for dynamical parameter estimation. For pure states undergoing unitary evolution, we show that the quantum Fisher information can be expressed as a connected symmetrized covariance of a time-integrated action deformation, equivalently as an integrated insertion of $\partial_\lambda S$ in the propagator. This reformulation avoids explicit state reconstruction by rewriting the quantum Fisher information in terms of real-time correlators that are natural targets for many-body methods. We further embed the construction into the Schwinger-Keldysh closed-time-path formalism, identifying the quantum Fisher information with the Keldysh component of an appropriate contour-ordered correlator generated by forward and backward propagating sources. Finally, using the Van Vleck-Gutzwiller approximation we re-derive the compact semiclassical quantum Fisher information expression, clarifying how classical trajectory data control leading-order metrological sensitivity.

Yang-Mills theory has extended well beyond its original role in describing the strong force and now emerges as an effective theory in condensed matter, ultracold atomic, and photonic systems. In these systems, the theory has been successful in explaining phenomena such as the spin-Hall effect, spin transport, and controlling the polarisation of light. Moreover, the ability to engineer and control synthetic non-Abelian gauge fields in these systems enables us to explore aspects of gauge dynamics inaccessible to high-energy experiments. In all the above mentioned cases, the state of the system evolves in an effective external Yang-Mills field. Thus, the study of test particle dynamics in such background fields is interesting in both the classical and quantum mechanical regimes. The background non-Abelian (color) gauge fields considered in this study are constant, and they generate uniform color magnetic fields or combined color electric and magnetic fields – which are relevant configurations. Despite the apparent simplicity of these backgrounds, the coupled evolution of real space motion and internal color degrees of freedom results in rich, nontrivial behaviour that is qualitatively distinct from the electrodynamic (Abelian) case, such as unbounded trajectories in a constant color magnetic field. In particular, particle trajectories encode signatures of the underlying gauge sources. Finally, the classical dynamics presented in this paper serves as a precursor to the complete quantum mechanical treatment to follow.

In quantum systems with a classical limit, advanced semiclassical methods provide the crucial link between phase-space structures, reflecting the distinction between chaotic, mixed or integrable classical dynamics, and the corresponding quantum properties. Well established techniques dealing with ergodic wave interference in the usual semiclassical limit $\hbar \to 0$, where the classical limit is given by Hamiltonian mechanics of particles, constitute a now standard part of the toolkit of theoretical physics. During the last years, these ideas have been extended into the field theoretical domain of systems composed of $N$ indistinguishable particles, aka quantum fields, displaying a different type of semiclassical limit $\hbar_{\rm eff}=1/N \to 0$ and accounting for genuine many-body quantum interference. The foundational concept behind this idea of many-body interference, the many-body version of the van Vleck-Gutzwillers semiclassical propagator, is explained in detail. Based on this the corresponding semiclassical many-body theory is reviewed. It provides a unified framework for understanding a variety of quantum chaotic phenomena addressed, including random-matrix spectral correlations in many-body systems, the universal morphology of many-body eigenstates, interference effects kin to mesoscopic weak localization, and the key to the scrambling of many-body correlations characterized by out-of-time-order correlators.

In this work, we investigate the scattering of spin-$3/2$ fermionic particles mediated by a Yukawa-like coupling in the context of the massive Rarita-Schwinger model. The interaction is introduced by replacing $m \to m_{\psi} + g\phi$ in the free spin-$3/2$ Lagrangian. The analysis is performed at both zero and finite temperatures. In the latter case, thermal effects are incorporated using the Thermofield Dynamics (TFD) formalism. In both regimes, we obtain the differential and total cross sections and examine their behavior in the short-range ($m_{\phi} \neq 0$) and long-range ($m_{\phi} = 0$) limits, in order to analyze the influence of zero- and finite-temperature effects.

The sine-Gordon model serves as a foundational $1+1$-dimensional quantum field theory with numerous applications in condensed matter physics. Despite its integrability, characterizing its finite-temperature behavior remains a significant theoretical challenge. Here we use the previously developed Method of Random Surfaces (MRS) to evaluate two-point and higher-order correlation functions. We cross-check these results with known analytical limits, demonstrating that the MRS provides reliable, non-perturbative data in intermediate regimes where traditional form-factor expansions and semiclassical methods are inapplicable. Furthermore, we derive an exact result for arbitrary $N$-point functions satisfying an appropriate selection rule, providing a direct computational method for complex multi-point observables at finite temperature. We also characterize the non-Gaussianity of correlations and demonstrate that the results align with intuitive theoretical expectations.

The complex Langevin approach is a promising method for the numerical treatment of systems with a sign problem, for which conventional lattice field theory techniques based on importance sampling cannot be applied. However, complex Langevin dynamics may fail to converge in some cases and converge to a wrong limit in others, motivating the development of various diagnostic tools over the years to assess the correctness of given simulation results. This work aims at providing a systematic comparison between the most prominent such correctness criteria. In particular, the main goal is to contrast their applicability, ease of use, and - most importantly - their predictive power. To this end, four simple but nontrivial models are considered and the criteria applied to each of them. It is found that no single correctness criterion is entirely foolproof on its own and that it is advisable in practice to employ multiple different criteria in combination. These conclusions are expected to carry over to more realistic theories as well.

The odd Euler ensemble, the locally stable attractor of the momentum-loop dynamics of freely decaying incompressible turbulence, has a self-similar energy spectrum \(E(k,t)=L^{-3/2}H(kL)\), \(L\sim\sqrt{\tilde\nu t}\), which does not depend on the dimension of space. We compute its scaling function as a Mellin–Barnes integral whose amplitude contains the ratio \(\zeta(p+15/2)/\zeta(p+17/2)\) of Riemann zeta functions; the odd ensemble differs from the even one by a prime-\(2\) Euler factor. The integral is evaluated by deforming the contour to Lefschetz thimbles. The non-trivial zeros of \(\zeta(s)\) generate a vertical wall of complex poles. As \(\xi=\log(k\sqrt{\tilde\nu t})\) increases, the thimble traps them in a Stokes staircase, first collectively and then a few at a time, and Berry smoothing turns each trapping into an analytic activation of an exponentially small oscillatory term. Assuming the Riemann Hypothesis and simplicity of the zeros, all these poles lie on one wall and their activations accumulate only at infinite time: the spectrum is analytic at every finite time and has an essential singularity at \(t=\infty\). The same analysis gives the second-order structure function, whose index falls continuously from \(2\) to \(0\) without an inertial plateau, and the decay laws, energy \(\propto t^{-5/4}\) and enstrophy \(\propto t^{-9/4}\). The operator representation and the stability of the Euler ensemble are derived in the first paper of this series, and the comparison with simulations and experiments is given in the third.

In the presence of confinement, small-data solutions to nonlinear dispersive equations can exhibit a gradual energy transfer from low to high frequencies, a mechanism driving the emergence of weakly turbulent dynamics. We show that such a forward energy transfer, manifested as arbitrary inflation of higher order Sobolev norms, occurs for small-data solutions of a quasilinear cubic wave equation on the Schwarzschild-AdS black hole exterior with Dirichlet conditions at infinity, for generic values of the mass parameter. This result is motivated by the question of nonlinear stability or instability of Schwarzschild-AdS as a solution to the Einstein vacuum equations, but the strategy of proof applies to a broader class of backgrounds exhibiting stable trapping of null geodesics. As an application, we obtain the analogous norm inflation statement on $\mathbb R \times \mathbb S^3_+$ for generic perturbations of the round metric on the hemisphere $\mathbb S^3_+$ preserving the trapping structure at the boundary.

We deform classical holomorphic Chern–Simons theory on a Calabi–Yau three-fold $X$ by deforming the complex structure by a deformation parameter $h \in\mathscr{H}^{0,1}(T^{1,0}X)$. The corresponding equations of motion admit new "instanton solutions" which which are invariant under re-scalings of $h$, and are perhaps more reminiscent of $G_2$-instantons for $G_2$ manifolds. We give examples of such instantons. In particular, when $h$ has non-vanishing Yukawa coupling ${\rm Yuk}(h,h,h)\neq 0$, it may be used to define a connection on ${\rm End}(T^{1,0}X)$ solving the instanton constraint. Interestingly, this connection gives rise to a hermitian (self-adjoint) connection for a real gauge theory on the real bundle ${\rm End}(TX)$ for only specific directions in deformation space, which may be classified using Morse theory. We quantize the deformed theory around these instanton backgrounds, and derive explicit expressions for the partition function in the limit where the complex structure deformation is large. We study anomalies, and the $h$-dependece of the partition function. In particular, coupling the theory to additional gravitational degrees of freedom, we find that the special directions in deformation space give rise to novel anomaly free theories on ${\rm End}(T^{1,0}X)$.

We show that fixed–$j$ holographic double deeply virtual Compton scattering (DDVCS), and its DVCS limit, give a fixed-scale structural match to the singlet conformal-OPE Wilson-kernel family of QCD in the leading-twist unpolarized singlet vector channel. The open-string $C_1(\delta,\vartheta)$ hypergeometric kernel was derived by Nishio–Watari; the new closed-string result is that the BPST upper Witten vertex gives the same family with a different near-boundary power count, because $\Delta_c(j)$ is fixed by the BPST trajectory rather than by open-Regge data. The Mellin exponent is therefore derived as $\delta_c(j)=j+\Delta_c(j)-2=2j+\gamma_c(j)$ rather than inserted by hand. The even open branch gives the parallel unprotected counterpart in the projected singlet vector amplitude. At $Q=\mu=\mu_0=\mu_\ast$, the point is not merely that equal-endpoint evolution is trivial; it is that the ultraviolet Witten vertex has already produced the fixed–$j$ conformal kernel before the lower conformal moment is matched. In the conformal partial-wave/CS representation, beta-proportional conformal-anomaly terms and scheme transformations are coefficient/evolution bookkeeping away from the matching point, not replacements for the projected fixed-scale hypergeometric $\eta/\xi$ Wilson-kernel family. The protected/unprotected $j=2$ split identifies the protected closed branch with the $(-)$ conformal partial wave and the even open branch with the unprotected $(+)$ counterpart; these are mixed singlet eigenchannels, not literal unmixed quark/gluon operators at finite $N_c$. Thus, once the lower Witten vertex is matched to constrained conformal moments, the DVCS/DDVCS deconvolution problem is organized in a physical operator basis rather than in arbitrary $x$-space profiles.

We show that the normalized non-normalizable photon profile fixed by the vacuum vector-current two-point function, when inserted into the fixed-$j$ hadronic Witten diagram, produces the fixed-$j$ conformal hard kernel in the leading-twist singlet vector channel of deeply virtual Compton scattering (DVCS) and double deeply virtual Compton scattering (DDVCS). For the near-boundary Brower–Polchinski–Strassler–Tan closed-string upper vertex, the Witten diagram yields the Gauss-hypergeometric Wilson-kernel family of the QCD conformal OPE, with the Mellin exponent derived from the explicit $z$-power count $\delta_c(j)=j+\Delta_c(j)-2$, not inserted as an ansatz. The lower Witten vertex is matched to, or provides a holographic representation of, the nonperturbative conformal moment; it is not a new hard kernel or a freely adjustable skewness profile. The matching is TT-projected, kernel-level, and fixed-scale in the conformal partial-wave/CS representation: finite coefficient normalizations, spin-$j$ source normalizations, scale factors, and lower hadronic matrix elements remain matched inputs. Together with the Nishio–Watari open branch and the protected/unprotected $j=2$ split, this structurally identifies the protected closed branch with the $(-)$ conformal partial wave and the even open branch with the unprotected $(+)$ counterpart in the projected fixed-$j$ singlet vector amplitude; these are mixed singlet eigenchannels, not literal unmixed quark/gluon operators at finite $N_c$. The conformal/Gegenbauer basis used in generalized parton distribution (GPD) deconvolution therefore has a second ultraviolet origin: it is selected both by the QCD OPE and by the near-boundary AdS Witten vertex.

Cosmology is living through fascinating times, where new observations from ground and space telescopes are questioning the established paradigm, the so-called Lambda Cold Dark Matter model. The particle nature of Dark Matter is severely constrained by underground experiments, while recent observations by galaxy surveys indicate that the cosmological constant (Lambda) may not be constant after all. Furthermore, observations at high redshift of fully-formed galaxies with massive black holes at their centers by the James Webb Space Telescope, as well as black holes with unexpected properties observed by gravitational wave detectors LIGO-Virgo, are driving an in-depth revision of our assumptions in models of structure formation and the evolution of the universe. I propose to explore two new paradigms to account for Dark Matter and Dark Energy, based on known physics without the need for new particles nor new degrees of freedom. I will extend the primordial spectrum of fluctuations to small scales with new statistical properties to provide a viable Primordial Black Hole scenario for Dark Matter, and will include non-equilibrium thermodynamics in the expanding universe, in the form of General Relativistic Entropic Acceleration, to explain Dark Energy. My proposal could provide a unified explanation for a plethora of interrelated multi-epoch, multi-scale and multi-probe observations from present and future Gravitational Wave detectors, Large Scale Structure observatories and Cosmic Microwave Background experiments. It emphasizes the need to develop new theoretical ideas hand-in-hand with observations to acquire a deeper understanding of our universe. If these ideas are correct, they will open a new window into the early universe and a new fundamental understanding of gravity in the late universe.

We discuss the effective field theory of large scale structure in terms of a single scalar degree of freedom, corresponding to the velocity potential of the matter fluid in a $\Lambda$CDM universe. This cosmic “pion” field is nonlinearly related to the overdensity and the gravitational potential, and corresponds to the Goldstone boson of spontaneously broken spacetime symmetry, allowing us to organize perturbation theory in a systematic way while keeping the symmetries manifest. We develop the effective field theory of the pion field to next-to-leading order, and we use it to calculate the corrections to the power spectrum and to check that these are consistent with the consistency relations of spontaneously broken spacetime symmetry. We compare our results against computer simulations for the evolution of large scale structure in the pion field picture, and we make use of N-body simulations to measure EFT coefficients and analyze the growth of additional degrees of freedom in the deep nonlinear regime. We conclude with a discussion of how the pion field picture may help suggest new variables for analyzing simulations and experimental surveys of large scale structure.

Energy correlators offer a clean probe of quantum chromodynamics, serving as an ideal laboratory to rigorously investigate non-perturbative power corrections. The recent discovery that linear corrections exhibit a universal anomalous scaling points to a deep, underlying theoretical structure. We uncover the quantum field-theoretic origin of this phenomenon in the energy-energy correlator using light-ray operators. Through an explicit loop calculation, we derive the one-loop anomalous dimension, revealing that the dijet operator must be combined with a specific triple-jet component. This provides a first-principles framework that connects operator theory with high-precision collider phenomenology.

A simple method is presented for deriving universal formulae for the correlators, frequently denoted $W_{g,n}(\{z_i\}), i=1,..n$, of a wide range of models of physical and mathematical interest. While many alternative methods exist for constructing such correlators, these formulae can be simply written in terms of one defining function and its derivatives. The method has been applied to the Airy and Bessel models, various minimal string and superstring theories, and their associated intersection theory settings, ordinary and various kinds of supersymmetric Weil-Petersson volumes, and more besides. For all these cases, their $W_{g,n}(\{z_i\})$ are just all specializations of the same universal formulae. A special variant of the method useful for ${N}{=}1$ supersymmetric cases is also presented. It allows for swift derivations of Norbury's three closed-form formulae for the volumes $V_{g,n}$ ($g{=}1,2,3$) of ${ N}{=}1$ supersymmetric Weil-Petersson volumes, and generalizations of them to a wider set of models. Moreover a new closed-form formula for the genus 4 case $V_{4,n}$ is derived. The straightforward method for how to derive such formulae for $g{>}4$ cases is described. Throughout, crucial roles are played by the underlying integrable KdV flows, as well as the Gel'fand-Dikii equation.

We calculate the response of an Unruh–DeWitt detector in a 2+1d spacetime that contains a BTZ black hole in a superposition of locations as viewed in a reference system associated with the detector. Upon performing a Quantum Reference Frame (QRF) transformation, this can also be seen as a detector in a superposition of locations in a single classical black hole spacetime. We use this to derive the form of the interaction of the detector and scalar field in such a superposition of spacetimes, ignoring backreaction. We define a measurement whose outcome probabilities contain a nonclassical contribution that would be absent for a black hole described by a classical mixture of positions. Finally, we compare our results with a previously studied setup involving a mass-superposed black hole by Foo et al. [Phys. Rev. Lett. 129, 181301 (2022)], and highlight a key difference. We show analytically how this difference arises and find singularities in the mass-superposed spectrum probed by the detector.

Wilson loop operators in ABJM theory provide a rich arena for studying defect conformal field theories (dCFTs) and the renormalization group (RG) flows connecting them. While these are well understood at weak coupling, a complete strong-coupling picture remains an open problem. In this paper, we present a systematic strong-coupling analysis of the fixed points and operator spectrum underlying defect RG flows in ABJM, via holography. By examining fluctuations of fundamental strings in the AdS$_4 \times \mathbb{CP}^3$ background around classical AdS$_2$ solutions, we map worldsheet excitations to the operators in the dual dCFT which are responsible for the flows and determine their scaling dimensions, including subleading corrections from one-loop worldsheet effects. We show how different boundary conditions on string coordinates correspond to distinct operators and provide a geometric realization of the RG flows through interpolating boundary conditions. We apply this framework to fermionic 1/2 BPS, bosonic 1/6 BPS, and non-supersymmetric Wilson loops, establishing a coherent strong-coupling picture in which the 1/2 BPS loop is IR stable, the 1/6 BPS loop acts as a saddle point, and the non-supersymmetric configuration emerges as a natural UV fixed point. We also advance a proposal for the holographic dual of a second non-supersymmetric loop, in terms of averaging over Dirichlet boundary conditions.

We investigate properties of the five-dimensional Chern–Simons AdS black hole coupled to $\mathrm{SU}(2)$ solitons by means of a minisuperspace approximation adapted to static, spherically symmetric configurations. The reduced action reproduces the known branch of solutions and provides a variational framework in which the boundary terms determine the conserved quantities and their conjugate variables. In particular, we recover the energy and the $\mathrm{U}(1)$ charge previously obtained by Hamiltonian methods, while the enlarged parameter space also reveals a momentum conjugate to the trace-torsion mode. The Euclidean action yields an entropy satisfying the first law of black hole thermodynamics. In contrast to many other torsional black hole models, the axial torsion parameter, describing the secondary black hole hair, together with the trace-torsion mode, contributes nontrivially to the entropy. The expression for the entropy obtained in this way is further confirmed by the other two methods found in the literature.

A rotating metric solution in Einstein-Gauss-Bonnet gravity with a negative cosmological constant was recently found in the Chern-Simons point. We construct a rotating thin shell gluing two spacetimes in Einstein-Gauss-Bonnet gravity, using the Davis junction conditions. We take the inner and outer spacetimes as replicas of the same rotating metric, with different values of mass and angular momentum. We show that the only possible thin shells either are vacuum thin shells or have a non-zero pressure in one tangential direction while the remaining stress tensor components vanish. We obtain the equation of motion for the shell, which resembles the continuity equation for a shell in General Relativity (GR), even though the quantity analogous to the intrinsic mass of the shell in GR is not connected to its stress tensor. We study the special case of vacuum thin shells connecting two spacetimes with zero hair. We obtain analytically the possible trajectories of the shell, and in certain situations we observe that the solution ceases to be valid. We find cases where the vacuum shell collapses and a naked singularity is formed. There two types of static vacuum thin shell solutions, one being stable occurring when both inner and outer spacetimes are overextremal, and the other unstable occurring when the horizons of inner and outer spacetimes approach each other, and are close to extremality.