Perimeter Institute

A bstract The Checkerboard conformal field theory is an interesting representative of a large class of non-unitary, logarithmic Fishnet CFTs (FCFT) in arbitrary dimension which have been intensively studied in the last years. Its planar Feynman graphs have the structure of a regular square lattice with checkerboard colouring. Such graphs are integrable since each coloured cell of the lattice is equal to an R-matrix in the principal series representations of the conformal group. We compute perturbatively and numerically the anomalous dimension of the shortest single-trace operator in two reductions of the Checkerboard CFT: the first one corresponds to the Fishnet limit of the twisted ABJM theory in 3D, whereas the spectrum in the second, 2D reduction contains the energy of the BFKL Pomeron. We derive an analytic expression for the Checkerboard analogues of Basso-Dixon 4-point functions, as well as for the class of Diamond-type 4-point graphs with disc topology. The properties of the latter are studied in terms of OPE for operators with open indices. We prove that the spectrum of the theory receives corrections only at even orders in the loop expansion and we conjecture such a modification of Checkerboard CFT where quantum corrections occur only with a given periodicity in the loop order.

Fast radio bursts (FRBs) are microsecond-to-millisecond-duration radio transients¹ that originate mostly from extragalactic distances. The FRB emission mechanism remains debated, with two main competing classes of models: physical processes that occur within close proximity to a central engine2, 3–4; and relativistic shocks that propagate out to large radial distances5, 6, 7–8. The expected emission-region sizes are notably different between these two types of models⁹. Here we present the measurement of two mutually coherent scintillation scales in the frequency spectrum of FRB 20221022A¹⁰: one originating from a scattering screen located within the Milky Way, and the second originating from its host galaxy or local environment. We use the scattering media as an astrophysical lens to constrain the size of the observed FRB lateral emission region⁹ to ≲3 × 10⁴ kilometres. This emission size is inconsistent with the expectation for the large-radial-distance models5, 6, 7–8, and is more naturally explained by an emission process that operates within or just beyond the magnetosphere of a central compact object. Recently, FRB 20221022A was found to exhibit an S-shaped polarization angle swing¹⁰, most likely originating from a magnetospheric emission process. The scintillation results presented in this work independently support this conclusion, while highlighting scintillation as a useful tool in our understanding of FRB emission physics and progenitors.

Fast radio bursts (FRBs) last for milliseconds and arrive at Earth from cosmological distances. Although their origins and emission mechanisms are unknown, their signals bear similarities with the much less luminous radio emission generated by pulsars within our Miky Way Galaxy¹, with properties suggesting neutron star origins2,3. However, unlike pulsars, FRBs typically show minimal variability in their linear polarization position angle (PA) curves⁴. Even when marked PA evolution is present, their curves deviate significantly from the canonical shape predicted by the rotating vector model (RVM) of pulsars⁵. Here we report on FRB 20221022A, detected by the Canadian Hydrogen Intensity Mapping Experiment Fast Radio Burst project (CHIME/FRB) and localized to a nearby host galaxy (about 65 Mpc), MCG+14-02-011. This FRB shows a notable approximately 130° PA rotation over its about 2.5 ms burst duration, resembling the characteristic S-shaped evolution seen in many pulsars and some radio magnetars. The observed PA evolution supports magnetospheric origins6, 7–8 over models involving distant shocks9, 10–11, echoing similar conclusions drawn from tempo-polarimetric studies of some repeating FRBs12,13. The PA evolution is well described by the RVM and, although we cannot determine the inclination and magnetic obliquity because of the unknown period or duty cycle of the source, we exclude very short-period pulsars (for example, recycled millisecond pulsars) as the progenitor.

A bstract We explore the properties of Ω-deformed M-theory, with particular focus on the ${\mathbb{C}}_{\epsilon_1}$ ℂ ϵ 1 × ${\mathbb{C}}_{\epsilon_2}$ ℂ ϵ 2 × ${\mathbb{C}}_{\epsilon_3}$ ℂ ϵ 3 background and coupling to Ω-deformed M2 and M5 brane world-volume theories.

A bstract Surface operators are nonlocal probes of gauge theories capable of distinguishing phases that are not discernible by the classic Wilson-’t Hooft criterion. We prove that the correlation function of a surface operator with a chiral primary operator in $\mathcal{N}$ N = 4 super Yang-Mills is a finite polynomial in the Yang-Mills coupling constant. Surprisingly, in spite of these observables receiving nontrivial quantum corrections, we find that these correlation functions are exactly captured in the ’t Hooft limit by supergravity in asymptotically AdS 5 × S ⁵ [1] ! We also calculate exactly the surface operator vacuum expectation value and the correlator of a surface operator with 1/8-BPS Wilson loops using supersymmetric localization. We demonstrate that these correlation functions in $\mathcal{N}$ N = 4 SYM realize in a nontrivial fashion the conjectured action of S -duality. Finally, we perturbatively quantize $\mathcal{N}$ N = 4 SYM around the surface operator singularity and identify the Feynman diagrams that, when summed over, reproduce the exact result obtained by localization.

A bstract We employ two-dimensional chiral algebra techniques to produce solutions of certain differential and integral equations which occur in the context of the Analytic Geometric Langlands Program. In particular, we build “Multiplication Kernels” K 3 ( x, x′, x′′ ) which intertwine the action of $\mathfrak{s}{\mathfrak{l}}_2$ s l 2 Gaudin Hamiltonians on three sets of variables.

We study the back-reaction of quantum systems onto classical ones. Taking the starting point that semi-classical physics should be described at all times by a point in classical phase space and a quantum state in Hilbert space, we consider an unravelling approach, describing the system in terms of a classical-quantum trajectory. We derive the general form of the dynamics under the assumptions that the classical trajectories are continuous and the evolution is autonomous, and the requirement that the dynamics is linear and completely positive in the combined classical-quantum state. This requirement is necessary in order to consistently describe probabilities, and forces the dynamics to be stochastic when the back-reaction is non-zero. The resulting equations of motion are natural generalisations of the standard semi-classical equations of motion, but since the resulting dynamics is linear in the combined classical-quantum state, it does not lead to the pathologies which usually follow from evolution laws based on expectation values. In particular, the evolution laws we present account for correlations between the classical and quantum system, which resolves issues associated with other semi-classical approaches. In addition, despite a breakdown of predictability in the classical degrees of freedom, the quantum state evolves deterministically conditioned on the classical trajectory, provided a trade-off between decoherence and diffusion is saturated. As a result, the quantum state remains pure when conditioned on the classical trajectory. To illustrate these points, we numerically simulate a number of semi-classical toy models, including one of vacuum fluctuations as a source driving the expansion of the universe. Finally, we discuss the application of these results to semi-classical gravity, and the black-hole information problem.

A bstract The biadjoint scalar partial amplitude, {m}_n\left(\mathbbm{I},\mathbbm{I}\right) m n I I , can be expressed as a single integral over the positive tropical Grassmannian thus producing a Global Schwinger Parameterization . The first result in this work is an extension to all partial amplitudes m n ( α , β ) using a limiting procedure on kinematic invariants that produces indicator functions in the integrand. The same limiting procedure leads to an integral representation of ϕ ⁴ amplitudes where indicator functions turn into Dirac delta functions. Their support decomposes into C n /2−1 regions, with C q the q th -Catalan number. The contribution from each region is identified with a m n /2+1 ( α , \mathbbm{I} I ) amplitude. We provide a combinatorial description of the regions in terms of non-crossing chord diagrams and propose a general formula for ϕ ⁴ amplitudes using the Lagrange inversion construction. We start the exploration of ϕ p theories, finding that their regions are encoded in non-crossing ( p – 2)-chord diagrams. The structure of the expansion of ϕ p amplitudes in terms of ϕ ³ amplitudes is the same as that of Green functions in terms of connected Green functions in the planar limit of Φ p− 1 matrix models. We also discuss possible connections to recent constructions based on Stokes polytopes and accordiohedra.

The Large Hadron Collider’s high luminosity era presents major computational challenges in the analysis of collision events. Large amounts of Monte Carlo (MC) simulation will be required to constrain the statistical uncertainties of the simulated datasets below these of the experimental data. Modelling of high-energy particles propagating through the calorimeter section of the detector is the most computationally intensive MC simulation task. We introduce a technique combining recent advancements in generative models and quantum annealing for fast and efficient simulation of high-energy particle-calorimeter interactions.

In the AdS/CFT correspondence, a direct scattering in the bulk may not have a local boundary analog. A nonlocal implementation on the boundary requires O(1/GN) mutual information. This statement is formalized by the connected wedge theorem, which can be proven using general relativity within AdS3 but also argued for using quantum information theory on the boundary, suggesting that the theorem applies to any holographic duality. We examine scattering within the static patch of asymptotically dS3 spacetime, which is conjectured to be described by a quantum theory on the stretched horizon in static patch holography. We show that causality on the horizon induced from null infinities $\mathcal{I}$± is consistent with the theorem. Specifically, signals propagating in the static patch are associated with local operators at $\mathcal{I}$±. Our results suggest a novel connection between static patch holography and the dS/CFT correspondence.

The precise origins of fast radio bursts (FRBs) remain unknown. Multiwavelength observations of nearby FRB sources can provide important insights into the enigmatic FRB phenomenon. Here we present results from a sensitive, broadband X-ray and radio observational campaign of FRB 20200120E, the closest known extragalactic repeating FRB source (located 3.63 Mpc away in an ~10-Gyr-old globular cluster). We place deep limits on the persistent and prompt X-ray emission from FRB 20200120E, which we use to constrain possible origins for the source. We compare our results with various classes of X-ray sources, transients and FRB models. We find that FRB 20200120E is unlikely to be associated with ultraluminous X-ray bursts, magnetar-like giant flares or an SGR 1935+2154-like intermediate flare. Although other types of bright magnetar-like intermediate flares and short X-ray bursts would have been detectable from FRB 20200120E during our observations, we cannot entirely rule them out as a class. We show that FRB 20200120E is unlikely to be powered by an ultraluminous X-ray source or a young extragalactic pulsar embedded in a Crab-like nebula. We also provide new constraints on the compatibility of FRB 20200120E with accretion-based FRB models involving X-ray binaries. These results highlight the power of multiwavelength observations of nearby FRBs for discriminating between FRB models.

How can detector click probabilities respond to spatial rotations around a fixed axis, in any possible physical theory? Here, we give a thorough mathematical analysis of this question in terms of “rotation boxes”, which are analogous to the well-known notion of non-local boxes. We prove that quantum theory admits the most general rotational correlations for spins 0, 1/2, and 1, but we describe a metrological game where beyond-quantum resources of spin 3/2 outperform all quantum resources of the same spin. We prove a multitude of fundamental results about these correlations, including an exact convex characterization of the spin-1 correlations, a Tsirelson-type inequality for spins 3/2 and higher, and a proof that the general spin-J correlations provide an efficient outer SDP approximation to the quantum set. Furthermore, we review and consolidate earlier results that hint at a wealth of applications of this formalism: a theory-agnostic semi-device-independent randomness generator, an exact characterization of the quantum (2, 2, 2)-Bell correlations in terms of local symmetries, and the derivation of multipartite Bell witnesses. Our results illuminate the foundational question of how space constrains the structure of quantum theory, they build a bridge between semi-device-independent quantum information and spacetime physics, and they demonstrate interesting relations to topics such as entanglement witnesses, spectrahedra, and orbitopes.

A bstract In CFTs, the partition function of a line defect with a cusp depends logarithmically on the size of the line with an angle-dependent coefficient: the cusp anomalous dimension. In the first part of this work, we study the general properties of the cusp anomalous dimension. We relate the small cusp angle limit to the effective field theory of defect fusion, making predictions for the first couple of terms in the expansion. Using a concavity property of the cusp anomalous dimension we argue that the Casimir energy between a line defect and its orientation reversal is always negative (“opposites attract”). We use these results to determine the fusion algebra of Wilson lines in $\mathcal{N}$ N = 4 SYM as well as pinning field defects in the Wilson-Fisher fixed points. In the second part of the paper we obtain nonperturbative numerical results for the cusp anomalous dimension of pinning field defects in the Ising model in d = 3, using the recently developed fuzzy-sphere regularization. We also compute the pinning field cusp anomalous dimension in the O ( N ) model at one-loop in the ε -expansion. Our results are in agreement with the general theory developed in the first part of the work, and we make several predictions for impurities in magnets.

This study presents a machine learning-based procedure to automate the charge tuning of semiconductor spin qubits with minimal human intervention, addressing one of the significant challenges in scaling up quantum dot technologies. This method exploits artificial neural networks to identify noisy transition lines in stability diagrams, guiding a robust exploration strategy leveraging neural network uncertainty estimations. Tested across three distinct offline experimental datasets representing different single-quantum-dot technologies, this approach achieves a tuning success rate of over 99% in optimal cases, where more than 10% of the success is directly attributable to uncertainty exploitation. The challenging constraints of small training sets containing high diagram-to-diagram variability allowed us to evaluate the capabilities and limits of the proposed procedure.

A bstract We present efficient data-driven approaches to predict the value of subdivergence-free Feynman integrals (Feynman periods) in ϕ ⁴ -theory from properties of the underlying Feynman graphs, based on a statistical examination of almost 2 million graphs. We find that the numbers of cuts and cycles determines the period to better than 2% relative accuracy. Hepp bound and Martin invariant allow for even more accurate predictions. In most cases, the period is a multi-linear function of the properties in question. Furthermore, we investigate the usefulness of machine-learning algorithms to predict the period. When sufficiently many properties of the graph are used, the period can be predicted with better than 0.05% relative accuracy. We use one of the constructed prediction models for weighted Monte-Carlo sampling of Feynman graphs, and compute the primitive contribution to the beta function of ϕ ⁴ -theory at L ∈ {13, … , 17} loops. Our results confirm the previously known numerical estimates of the primitive beta function and improve their accuracy. Compared to uniform random sampling of graphs, our new algorithm is 1000-times faster to reach a desired accuracy, or reaches 32-fold higher accuracy in fixed runtime. The dataset of all periods computed for this work, combined with a previous dataset, is made publicly available. Besides the physical application, it could serve as a benchmark for graph-based machine learning algorithms.

A bstract We study ’t Hooft lines in four-dimensional holomorphic-topological Chern-Simons theory. We relate them to Q-operators in the theory of integrable systems. We give a physical interpretation of the fundamental TQ and QQ relations satisfied by Q-operators and conventional transfer matrices.

A bstract Metastable ‘false’ vacuum states are an important feature of the Standard Model of particle physics and many theories beyond it. Describing the dynamics of a phase transition out of a false vacuum via the nucleation of bubbles is essential for understanding the cosmology of vacuum decay and the full spectrum of observables. In this paper, we study vacuum decay by numerically evolving ensembles of field theories in 1+1 dimensions from a metastable state. We demonstrate that for an initial Bose-Einstein distribution of fluctuations, bubbles form with a Gaussian spread of center-of-mass velocities and that bubble nucleation events are preceded by an oscillon — a long-lived, time-dependent, pseudo-stable configuration of the field. Defining an effective temperature from the long-wavelength amplitude of fluctuations in the ensemble of simulations, we find good agreement between theoretical finite temperature predictions and empirical measurements of the decay rate, velocity distribution and critical bubble solution. We comment on the generalization of our results and the implications for cosmological observables.

A bstract We describe how to implement the conformal bootstrap program in the context of the embedding space OPE formalism introduced in previous work. To take maximal advantage of the known properties of the scalar conformal blocks for symmetric-traceless exchange, we construct tensorial generalizations of the three-point and four-point scalar conformal blocks that have many nice properties. Further, we present a special basis of tensor structures for three-point correlation functions endowed with the remarkable simplifying property that it does not mix under permutations of the external quasi-primary operators. We find that in this approach, we can write the M -point conformal bootstrap equations explicitly in terms of the standard position space cross-ratios without the need to project back to position space, thus effectively deriving all conformal bootstrap equations directly from the embedding space. Finally, we lay out an algorithm for generating the conformal bootstrap equations in this formalism. Collectively, the tensorial generalizations, the new basis of tensor structures, as well as the procedure for deriving the conformal bootstrap equations lead to four-point bootstrap equations for quasi-primary operators in arbitrary Lorentz representations expressed as linear combinations of the standard scalar conformal blocks for spin- ℓ exchange, with finite ℓ -independent terms. Moreover, the OPE coefficients in these equations conveniently feature trivial symmetry properties. The only inputs necessary are the relevant projection operators and tensor structures, which are all fixed by group theory. To illustrate the procedure, we present one nontrivial example involving scalars S and vectors V , namely ⟨ SSSV ⟩.