arXiv subjects

Enoch Leung

Publications and source records attributed to Enoch Leung.

9 recordsLinked to original sources

arXiv2026

Continuous symmetries and charge measurement of boundary operators in holography

We study holographic charge measurement for continuous internal symmetries. Charged boundary operators are characterized by Wilson lines of bulk gauge fields ending on the boundary, while charge measurement is performed using U-shaped defects hanging from the boundary. We derive universal features of this process from a low-energy point of view, and show how the hanging defect picture mimics the thickening regularization of continuous symmetry operators in field theory. Furthermore, we provide explicit top-down realizations in AdS/CFT setups in Type IIB string theory and M-theory, featuring Abelian as well as non-Abelian symmetries. In the case of Type IIB constructions, we analyze the brane dynamics underlying the charge measurement process. Along the way, we also characterize how hanging brane configurations can be regarded as being topological, and demonstrate how tachyon dynamics account for their fusion rules.

hep-th↗

arXiv2025

Non-Abelian Symmetry Operators from Hanging Branes in $AdS_5 \times S^5$

We investigate the holographic realization of topological operators for continuous non-Abelian symmetries in quantum field theories. As a concrete case study, we focus on Type IIB string theory on $AdS_5 \times S^5$ which admits an $SO(6)$ isometry, dual to the R-symmetry in 4d $N=4$ super Yang-Mills theory. We argue that symmetry operators for continuous symmetries are generally realized by bound states of D5-branes and KK monopoles hanging from the conformal boundary. Together they account for the contributions to the Gauss' law constraints from the self-dual 5-form flux and the Einstein-Hilbert term respectively. We also demonstrate how the D5-KK bound state measures the representation of the endpoint of Wilson lines constructed by D3-branes.

hep-th↗

arXiv2025

Anomaly-induced vanishing of brane partition functions

In the presence of 't Hooft anomalies, backgrounds for the symmetries of a quantum field theory can lead to non-conservation of Noether currents, or more generally, to the presence of charged insertions in the path integral. When there is a net background charge, the partition function evaluated on closed manifolds will vanish. For anomalous symmetries, this statement can also be understood as the anomaly theory giving rise to a non-trivial anomalous phase for the partition function even for "rigid" transformations which leave all background fields unchanged. We use the generalisation of this second viewpoint to the setting of anomalous higher-form symmetries in order to show vanishing of the partition function for a number of examples, both with and without a Lagrangian description. In particular, we show how to derive from these considerations the analogue of the Freed-Witten anomaly cancellation condition for the M5-brane, and also that for the D3-brane in S-fold backgrounds.

hep-th↗

arXiv2025

On the Physics of Higher Condensation Defects

We study the structure of topological defects for finite Abelian symmetries in quantum field theories, and argue on physical grounds that they satisfy the definition of a higher fusion category proposed by Johnson-Freyd. Our primary focus is on the requirement of Karoubi completeness, i.e. the factorization conditions on higher condensation defects. We demonstrate this on a tree of such defects, constructed by successive higher gauging, explicitly using Lagrangian techniques in a concrete four-dimensional example, before turning to more general field theories. Along the way we also comment on the phenomenon where decoupled topological field theories appear as fusion coefficients. We further discuss the categorical role of anomalies, and how they may affect the properties of (higher) condensation defects.

hep-th↗

arXiv2024

Non-Invertible Symmetries, Brane Dynamics, and Tachyon Condensation

We study the Symmetry Topological Field Theory in holography associated with 4d $\mathcal{N}=1$ Super Yang-Mills theory with gauge algebra $\mathfrak{su}(M)$. From this, all the bulk symmetry operators are computed and matched to various D-brane configurations. The fusion algebra of the operators emerges from brane dynamics. In particular, we show that the symmetry operators are purely determined from the center-of-mass modes of the branes. We identify the TQFT fusion coefficients with the relative motion of the branes. We also establish the origin of condensation defects, arising from fusion of non-invertible operators, as the consequence of tachyon condensation in brane-anti-brane pairs.

hep-th↗

arXiv2023

Einstein rings modulated by wavelike dark matter from anomalies in gravitationally lensed images

Unveiling the true nature of Dark Matter (DM), which manifests itself only through gravity, is one of the principal quests in physics. Leading candidates for DM are weakly interacting massive particles (WIMPs) or ultralight bosons (axions), at opposite extremes in mass scales, that have been postulated by competing theories to solve deficiencies in the Standard Model of particle physics. Whereas DM WIMPs behave like discrete particles ($\varrho$DM), quantum interference between DM axions is manifested as waves ($ψ$DM). Here, we show that gravitational lensing leaves signatures in multiply-lensed images of background galaxies that reveal whether the foreground lensing galaxy inhabits a $\varrho$DM or $ψ$DM halo. Whereas $\varrho$DM lens models leave well documented anomalies between the predicted and observed brightnesses and positions of multiply-lensed images, $ψ$DM lens models correctly predict the level of anomalies left over by $\varrho$DM lens models. More challengingly, when subjected to a battery of tests for reproducing the quadruply-lensed triplet images in the system HS 0810+2554, $ψ$DM is able to reproduce all aspects of this system whereas $\varrho$DM often fails. The ability of $ψ$DM to resolve lensing anomalies even in demanding cases like HS 0810+2554, together with its success in reproducing other astrophysical observations, tilt the balance toward new physics invoking axions.

astro-ph.CO↗

arXiv2022

M5-branes Probing Flux Backgrounds

We analyze the global symmetries and anomalies of 4d $\mathcal{N} = 1$ field theories that arise from a stack of $N$ M5-branes probing a class of flux backgrounds. These backgrounds consist of a resolved $\mathbb{C}^2 / \mathbb{Z}_k$ singularity fibered over a smooth Riemann surface of genus $g \geq 2$, supported by a non-trivial $G_4$-flux configuration labeled by a collection of $2(k-1)$ flux quanta, $\{N_i\}$. For $k=2$, this setup defines a non-trivial superconformal field theory (SCFT) in the IR, which is holographically dual to an explicit $AdS_5$ solution first described by Gauntlett, Martelli, Sparks, and Waldram. The generalization to $k \geq 3$ is hard to tackle directly within holography. Instead, in this paper we lay the groundwork for a systematic analysis of such a generalization by adopting anomaly inflow methods to identify continuous and discrete global symmetries of the 4d field theories. We also compute the 't Hooft anomalies for continuous symmetries at leading order in the limit of large $N$, $N_i$.

hep-th↗

arXiv2022

The Geometry of Decoupling Fields

We consider 4d field theories obtained by reducing the 6d (1,0) SCFT of $N$ M5-branes probing a $\mathbb C^2/\mathbb Z_k$ singularity on a Riemann surface with fluxes. We follow two different routes. On the one hand, we consider the integration of the anomaly polynomial of the parent 6d SCFT on the Riemann surface. On the other hand, we perform an anomaly inflow analysis directly from eleven dimensions, from a setup with M5-branes probing a resolved $\mathbb C^2/\mathbb Z_k$ singularity fibered over the Riemann surface. By comparing the 4d anomaly polynomials, we provide a characterization of a class of modes that decouple along the RG flow from six to four dimensions, for generic $N$, $k$, and genus. These modes are identified with the flip fields encountered in the Lagrangian descriptions of these 4d models, when they are available. We show that such fields couple to operators originating from M2-branes wrapping the resolution cycles. This provides a geometric origin of flip fields. They interpolate between the 6d theory in the UV, where the M2-brane operators are projected out, and the 4d theory in the IR, where these M2-brane operators are part of the spectrum.

hep-th↗

arXiv2018

Magnification Bias of Distant Galaxies in the Hubble Frontier Fields: Testing Wave vs. Particle Dark Matter Predictions

Acting as powerful gravitational lenses, the strong lensing galaxy clusters of the deep Hubble Frontier Fields (HFF) program permit access to lower-luminosity galaxies lying at higher redshifts than hitherto possible. We analyzed the HFF to measure the volume density of Lyman-break galaxies at $z > 4.75$ by identifying a complete and reliable sample up to $z \simeq 10$. A marked deficit of such galaxies was uncovered in the highly magnified regions of the clusters relative to their outskirts, implying that the magnification of the sky area dominates over additional faint galaxies magnified above the flux limit. This negative magnification bias is consistent with a slow rollover at the faint end of the UV luminosity function, and indicates a preference for Bose-Einstein condensate dark matter with a light boson mass of $m_\mathrm{B} \simeq 10^{-22} \, \mathrm{eV}$ over standard cold dark matter. We emphasize that measuring the magnification bias requires no correction for multiply lensed images (with typically three or more images per source), whereas directly reconstructing the luminosity function will lead to an overestimate unless such images can be exhaustively matched up, especially at the faint end that is accessible only in the strongly lensed regions. In addition, we detected a distinctive downward transition in galaxy number density at $z \gtrsim 8$, which may be linked to the relatively late reionization reported by Planck. Our results suggests that JWST will likely peer into an "abyss" with essentially no galaxies detected in deep NIR imaging at $z > 10$.

astro-ph.GA↗