arXiv subjects

Nadav Drukker

Publications and source records attributed to Nadav Drukker.

At least 19 recordsLinked to original sources

arXiv2026

Flowing with Displacements and Tilts: Surface Operators in $O(N)$ Models

Defect conformal field theories have special operators of protected dimension known as displacements and tilts. They arise due to the breaking of global symmetries by the defect and the normalisations of their two-point functions are characteristics of the defect. In the case of surface defects, these normalisations are related to some of the anomaly coefficients in the surface effective action. To study these operators and their flows between different defect renormalization group fixed points we present an elegant approach using conformal perturbation theory that easily reproduces the known examples from the critical Wilson-Fisher $O(N)$ model in $4-\varepsilon$ dimensions and allows us to construct new ones in other multiscalar theories. In all the systems that we study the flows are short and under full control, as is the change of the displacement and tilt normalizations. We point out some novel features like the existence of vortices when the defect conformal manifold is not simply connected. In addition to regular human labour, this work relied heavily on generative AI; see full disclosure in methodology section.

hep-th↗

arXiv2026

Crosscap Defects

We introduce a novel class of defects, termed crosscap defects, in conformal field theory (CFT) in general dimensions. These arise from quotienting the spacetime by a $Z_2$ automorphism, and provide higher-codimension generalisations of CFT on real projective space ($RP^{d}$). Crosscap defects extend along a $p$-dimensional fixed locus of the $Z_2$ action and preserve an $SO(p+1,1)\times PO(d-p)$ subgroup of the conformal group. The two-point functions of operators in this setup exhibit three operator product expansion channels: bulk, image, and defect. These lead to several crosscap crossing equations, which we present. We analyse conformal block decompositions and show that the blocks are identical to defect CFT blocks up to a redefinition of cross ratios. As concrete examples, we study crosscap defects in the $O(N)$ model at the Gaussian and Wilson--Fisher fixed points in the $\varepsilon$-expansion. We compute explicitly the associated CFT data as a function of $p$ and find that, unlike standard defects, displacement and tilt operators are absent for generic $p$. They provide examples of defect conformal manifolds without exactly marginal operators.

hep-th↗

arXiv2025

Nonlinearly Realised Defect Symmetries and Anomalies

Conformal defects -- extended objects in conformal field theories -- carry localised excitations inherited from symmetry currents, known as the displacements and tilts. They capture the linear response of the defect to deformations of its shape or of its profile along internal symmetry directions. There is no universal formula for deformations beyond the linear order and this is subject to ambiguities of coordinate choices on coset spaces and scheme dependence in the quantum theory. We analyse the exact match between the two and identify the scheme independent quantities capturing nonlinearly realised symmetries. This leads to universal integral identities for correlation functions in the presence of tilts and displacements. We present several applications of them. We also study possible anomalies, recovering known ones, finding new expressions for them, and uncovering new ones.

hep-th↗

arXiv2025

Transdimensional Defects

This note introduces a novel paradigm for conformal defects with continuously adjustable dimensions. Just as the standard $\varepsilon$ expansion interpolates between integer spacetime dimensions, a new parameter, $δ$, is used to interpolate between different integer-dimensional defects. The ensuing framework is explored in detail for defects of dimension $p=2+δ$ in both free and interacting $O(N)$ bulk conformal field theories (CFTs) in $d=4-\varepsilon$. Comprehensive calculations are performed to first and second order in $\varepsilon$ and to high or all orders in $δ$. Additionally, in the large-$N$ limit, the interpolation between defects of dimensions $p=1$ and $p=2$ is analysed for spacetime dimensions $4\leq d\leq 6$. The new parameter $δ$ provides a natural enrichment of the space of defect CFTs and allows to find new integer dimension or co-dimension defects.

hep-th↗

arXiv2025

Fine Spectrum from Crude Analytic Bootstrap

The magnetic line defect in the $O(N)$ model gives rise to a non-trivial one-dimensional defect conformal field theory of theoretical and experimental value. This model is considered here in $d=4-\varepsilon$ and the full spectrum of defect operators with dimensions close to one, two and three at order $\varepsilon$ is presented. The spectrum of several classes of operators of dimension close to four and operators of large charge are also discussed. Analytic bootstrap techniques are used extensively, and efficient tools to deal with the unmixing of nearly degenerate operators are developed. Integral identities are also incorporated, and it is shown that they lead to constraints on some three-point function coefficients and anomalous dimensions to order $\varepsilon^2$.

hep-th↗

arXiv2023

Vortex loop operators and quantum M2-branes

We study M2-branes in $AdS_4\times S^7/{\mathbb Z}_k$ dual to 1/2 and 1/3 BPS vortex loop operators in ABJM theory and compute their one-loop correction beyond the classical M2-brane action. The correction depends only on the parity of $k$ and is independent of all continues parameters in the definition of the vortex loops. The result for odd $k$ agrees with the answers for the 1/2 BPS Wilson loop in the $k=1$ theory and for even $k$ with the one in the $k = 2$ theory. Combining with the classical part, we find that the natural expansion parameter seems to be $1/\sqrt{kN}$ rather than $1/\sqrt{N}$. This provides a further setting where semiclassical quantisation can be applied to M2-branes and produces new results inaccessible by other methods.

hep-th↗

arXiv2023

Quantum holographic surface anomalies

Expectation values of surface operators suffer from logarithmic divergences reflecting a conformal anomaly. In a holographic setting, where surface operators can be computed by a minimal surface in $AdS$, the leading contribution to the anomaly comes from a divergence in the classical action (or area) of the minimal surface. We study the subleading correction to it due to quantum fluctuations of the minimal surface. In the same way that the divergence in the area does not require a global solution but only a near-boundary analysis, the same holds for the quantum corrections. We study the asymptotic form of the fluctuation determinant and show how to use the heat kernel to calculate the quantum anomaly. In the case of M2-branes describing surface operators in the ${\cal N}=(2,0)$ theory in 6d, our calculation of the one-loop determinant reproduces expressions for the anomaly that have been found by less direct methods.

hep-th↗

arXiv2023

1/3 BPS loops and defect CFTs in ABJM theory

We address a longstanding question of whether ABJM theory has Wilson loop operators preserving eight supercharges (so 1/3 BPS). We present such Wilson loops made of a large supermatrix combining two 1/2 BPS Wilson loops. We study the spectrum of operator insertions into them including the displacement operator and several others and study their correlation functions. Another natural construction arising in this context are Wilson loops with alternating superconnections. This amounts to including "defect changing operators" along the loop, similar to a discrete cusp. This insertion is topological and preserves two supercharges. We study the multiplet of this operator and how it can be used to introduce further operators. We also construct the defect conformal manifold arising from marginal defect operators.

hep-th↗

arXiv2022

Ironing out the crease

The crease is a surface operator folded by a finite angle along an infinite line. Several realisations of it in the 6d ${\mathcal N}=(2,0)$ theory are studied here. It plays a role similar to the generalised quark-antiquark potential, or the cusp anomalous dimension, in gauge theories. We identify a finite quantity that can be studied despite the conformal anomalies ubiquitous with surface operators and evaluate it in free field theory and in the holographic dual. We also find a subtle difference between the infinite crease and its conformal transform to a compact observable comprised of two glued hemispheres, reminiscent of the circular Wilson loop. We prove by a novel application of defect CFT techniques for the $SO(2,1)$ symmetry along the fold that the near-BPS behaviour of the crease is determined as the derivative of the compact observable with respect to its angle, as in the bremsstrahlung function. We also comment about the lightlike limit of the crease in Minkowski space.

hep-th↗

arXiv2022

Knitting Knots & the Framing Anomaly

We study the twisting fault emerging in circular knitting and its relation to the mathematical concepts of framing curves and the Gauss linking integral. We create three knitted bands with framing zero, one, and negative two, and use three different techniques to compute the framing using the Gauss linking integral. We also briefly mention the connection to in Chern-Simons gauge theory.

math.HO↗

arXiv2022

Classifying BPS bosonic Wilson loops in 3d ${\cal N}=4$ Chern-Simons-matter theories

We study the possible BPS Wilson loops in three-dimensional ${\cal N}=4$ Chern-Simons-matter theory which involve only the gauge field and bilinears of the scalars. Previously known examples are the analogues of the Gaiotto-Yin loops preserving four supercharges and "latitude" loops preserving two. We carry out a careful classification and find, in addition, loops preserving three supercharges, further inequivalent classes of loops preserving two supercharges and loops preserving a single supercharge. For each of the classes of loops, we present a representative example and analyse their full orbit under the broken symmetries.

hep-th↗

arXiv2022

Broken global symmetries and defect conformal manifolds

Just as exactly marginal operators allow to deform a conformal field theory along the space of theories known as the conformal manifold, appropriate operators on conformal defects allow for deformations of the defects. When a defect breaks a global symmetry, there is a contact term in the conservation equation with an exactly marginal defect operator. The resulting defect conformal manifold is the symmetry breaking coset and its Zamolodchikov metric is expressed as the 2-point function of the exactly marginal operator. As the Riemann tensor on the conformal manifold can be expressed as an integrated 4-point function of the marginal operators, we find an exact relation to the curvature of the coset space. We confirm this relation against previously obtained 4-point functions for insertions into the 1/2 BPS Wilson loop in ${\cal N} = 4$ SYM and 3d ${\cal N} = 6$ theory and the 1/2 BPS surface operator of the 6d ${\cal N} = (2, 0)$ theory.

hep-th↗

arXiv2022

BPS surface operators and calibrations

We present here a careful study of the holographic duals of BPS surface operators in the 6d ${\cal N}=(2,0)$ theory. Several different classes of surface operators have been recently identified and each class has a specific calibration form - a 3-form in $AdS_7\times S^4$ whose pullback to the M2-brane world-volume is equal to the volume form. In all but one class, the appropriate forms are closed, so the action of the M2-brane is easily expressed in terms of boundary data, which is the geometry of the surface. Specifically, for surfaces of vanishing anomaly, it is proportional to the integral of the square of the extrinsic curvature. This can be extended to the case of surfaces with anomalies, by taking the ratio of two surfaces with the same anomaly. This gives a slew of new expectation values at large $N$ in this theory. For one specific class of surface operators, which are Lagrangian submanifolds of ${\mathbb R}^4\subset {\mathbb R}^6$, the structure is far richer and we find that the M2-branes are special Lagrangian submanifold of an appropriate six-dimensional almost Calabi-Yau submanifold of $AdS_7\times S^4$. This allows for an elegant treatment of many such examples.

hep-th↗

arXiv2022

Cutting and Sewing Riemann Surfaces in Mathematics, Physics and Clay

A series of ceramic artworks are presented, inspired by the author's research connecting theoretical physics to the beautiful theory of Riemann surfaces. More specifically the research is related to the classification of curves on the surfaces based on a description of them as built from basic building blocks known as "pairs of pants". The relevant background on this mathematics of these two dimensional spaces is outlined, some of the artistic process is explained: Both the conceptual ideas and their implementation. Many photos of the ceramics are included to illustrate this and the connected physics problem is briefly mentioned.

physics.pop-ph↗

arXiv2022

Conformal and non-conformal hyperloop deformations of the 1/2 BPS circle

We construct new large classes of BPS Wilson hyperloops in three-dimensional ${\cal N}=4$ quiver Chern-Simons-matter theory on $S^3$. The main strategy is to start with the 1/2 BPS Wilson loop of this theory, choose any linear combination of the supercharges it preserves, and look for deformations built out of the matter fields that still preserve that supercharge. This is a powerful generalization of a recently developed approach based on deformations of 1/4 and 1/8 BPS bosonic loops, which itself was far more effective at discovering new operators than older methods relying on complicated ansatze. We discover many new moduli spaces of BPS hyperloops preserving varied numbers of supersymmetries and varied subsets of the symmetries of the 1/2 BPS operator. In particular, we find new bosonic operators preserving 2 or 3 supercharges as well as new families of loops that do not share supercharges with any bosonic loops, including subclasses of both 1/8 and 1/4 BPS loops that are conformal.

hep-th↗

arXiv2022

M2-doughnuts

We present a family of new M2-brane solutions in $AdS_7\times S^4$ that calculate toroidal BPS surface operators in the $\mathcal{N}=(2,0)$ theory. These observables are conformally invariant and not subject to anomalies so we are able to evaluate their finite expectation values at leading order at large $N$. In the limit of a thin torus we find a cylinder, which is a natural surface generalization of both the circular and parallel lines Wilson loop. We study and comment on this limit in some detail.

hep-th↗

arXiv2021

Defect CFT in the 6d (2,0) theory from M2 brane dynamics in AdS$_7 \times$S$^4$

Surface operators in the 6d (2,0) theory at large $N$ have a holographic description in terms of M2 branes probing the AdS$_7 \times S^4$ M-theory background. The most symmetric, 1/2-BPS, operator is defined over a planar or spherical surface, and it preserves a 2d superconformal group. This includes, in particular, an $SO(2,2)$ subgroup of 2d conformal transformations, so that the surface operator may be viewed as a conformal defect in the 6d theory. The dual M2 brane has an AdS$_3$ induced geometry, reflecting the 2d conformal symmetry. Here we use the holographic description to extract the defect CFT data associated to the surface operator. The spectrum of transverse fluctuations of the M2 brane is found to be in one-to-one correspondence with a protected multiplet of operator insertions on the surface, which includes the displacement operator. We compute the one-loop determinants of fluctuations of the M2 brane, and extract the conformal anomaly coefficient of the spherical surface to order $N^0$. We also briefly discuss the RG flow from the non-supersymmetric to the 1/2-BPS defect operator, and its consistency with a "$b$-theorem" for the defect CFT. Starting with the M2 brane action, we then use AdS$_3$ Witten diagrams to compute the 4-point functions of the elementary bosonic insertions on the surface operator, and extract some of the defect CFT data from the OPE. The 4-point function is shown to satisfy superconformal Ward identities, and we discuss a related subsector of "twisted" scalar insertions, whose correlation functions are constrained by the residual superconformal symmetry.

hep-th↗

arXiv2021

Notes on hyperloops in N=4 Chern-Simons-matter theories

We present new circular Wilson loops in three-dimensional N=4 quiver Chern-Simons-matter theory on S^3. At any given node of the quiver, a two-parameter family of operators can be obtained by opportunely deforming the 1/4 BPS Gaiotto-Yin loop. Including then adjacent nodes, the coupling to the bifundamental matter fields allows to enlarge this family and to construct loop operators based on superconnections. We discuss their classification, which depends on both discrete data and continuous parameters subject to an identification. The resulting moduli spaces are conical manifolds, similar to the conifold of the 1/6 BPS loops of the ABJ(M) theory.

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