arXiv subjects

Tung Tran

Publications and source records attributed to Tung Tran.

At least 19 recordsLinked to original sources

arXiv2026

Worldline Higher Spin Gravity

We propose a worldline formulation of higher-spin gravity (HSG) in $\mathrm{AdS}_4$, based on a simple twistor action. Taken at face value, the model describes only the free propagation of massless higher-spin fields. The central observation of this work is that the model admits a natural double-line interpretation, which supplies a geometric prescription for gluing worldlines at interaction vertices, in close parallel with the joining of strings in string theory. Building on this picture, we construct $\mathrm{AdS}$-covariant vertex operators for all massless higher-spin fields, show that they satisfy the Bargmann-Wigner equations, and use them to compute the n-point correlation functions of type-A and type-B HSG as worldline path integrals of these vertex operators. In the boundary limit these correlators reproduce the higher-spin current correlators of free boson and free fermion vector models. We further discuss the embedding of the worldline theory into Poisson sigma model, where the doubled-line structure acquires a geometric origin as the two edges of an open string worldsheet, together with several consequences of this enlarged framework -- fractional branes, loop expansion, unoriented projection, and the prospect of a worldsheet formulation of HSG.

hep-th↗

arXiv2026

LCA: Local Classifier Alignment for Continual Learning

A fundamental requirement for intelligent systems is the ability to learn continuously under changing environments. However, models trained in this regime often suffer from catastrophic forgetting. Leveraging pre-trained models has recently emerged as a promising solution, since their generalized feature extractors enable faster and more robust adaptation. While some earlier works mitigate forgetting by fine-tuning only on the first task, this approach quickly deteriorates as the number of tasks grows and the data distributions diverge. More recent research instead seeks to consolidate task knowledge into a unified backbone, or adapting the backbone as new tasks arrive. However, such approaches may create a (potential) \textit{mismatch} between task-specific classifiers and the adapted backbone. To address this issue, we propose a novel \textit{Local Classifier Alignment} (LCA) loss to better align the classifier with backbone. Theoretically, we show that this LCA loss can enable the classifier to not only generalize well for all observed tasks, but also improve robustness. Furthermore, we develop a complete solution for continual learning, following the model merging approach and using LCA. Extensive experiments on several standard benchmarks demonstrate that our method often achieves leading performance, sometimes surpasses the state-of-the-art methods with a large margin.

cs.AI↗

arXiv2025

Three-dimensional non-relativistic chiral massive higher-spin gravity

We obtain a non-relativistic chiral massive higher-spin gravity in a deformed $AdS_3$ spacetime by applying a Lifshitz deformation and subsequent null reduction to chiral massless higher-spin gravity in $AdS_4$. Intriguingly, the vertices of this non-relativistic theory are less constrained than the ones of the original $4d$ chiral massless theory since we do not have enough dynamical generators to fix the couplings uniquely. Anticipating higher-spin interactions should be suppressed, we propose a simple approximate mass-spin relation which interpolates between the relativistic and non-relativistic regimes. With the proposed mass-spin relation, we observe that that higher-spin interactions indeed become suppressed at large spins, consistent with low-energy physics. We conjecture that the holographic dual of the non-relativistic chiral massive higher-spin gravity proposed in this work is a $2d$ non-relativistic Landau-Ginzburg theory in the light-cone gauge. This non-relativistic theory is expected to describe a two-fluid system with a $\lambda$-point constrained in one spatial dimension.

hep-th↗

arXiv2025

Chiral higher-spin symmetry of the celestial twistor sphere

We study the chiral higher-spin symmetry algebras $\mathfrak{ca}$ of various twistorial higher-spin theories. These symmetries play the roles of asymptotic symmetries on the celestial twistor sphere, which constrain the observables of twistorial theories. To first order in quantum correction, we show that the chiral algebras associated with anomaly-free holomorphic twistorial higher-spin theories are associative themselves. On the other hand, the chiral algebras associated with anomalous holomorphic twistorial higher-spin theories only become associative upon including suitable axionic currents. When computing $4d$ form factors in terms of correlation functions between higher-spin currents on the celestial twistor sphere, we observe that there are some non-vanishing higher-spin form factors. This observation, however, is only well justified for the case of theories with Yang-Mills-like interactions. We also give some brief comments on the case of higher-derivative interactions.

hep-th↗

arXiv2025

Anomaly-free twistorial higher-spin theories

We present twistor BV actions that encompasses many classically consistent bosonic holomorphic twistorial higher-spin theories with vanishing cosmological constant. Upon quantization, these actions are shown to be quantum consistent, i.e. no gauge anomaly, for some subclasses of twistorial higher-spin theories. Anomaly-free twistorial theories can be identified through an index theorem, which is a higher-spin extension of the Hirzebruch-Riemann-Roch index theorem. We also discuss the anomaly cancellation mechanisms on twistor space to render anomalous theories quantum consistent at one loop.

hep-th↗

arXiv2025

Self-dual pp-wave solutions in chiral higher-spin gravity

We show that chiral higher-spin gravity with a vanishing cosmological constant admits a class of exact self-dual pp-wave solutions derived from harmonic scalar functions and two principal spinors. These solutions satisfy both the linear and non-linear equations of motion, as they annihilate all higher-order vertices, leading to the equations of motion for free fields on a self-dual background sourced by a positive-helicity spin-2 field. Our method employs a simple light-cone ansatz for positive-helicity chiral higher-spin fields, along with a modified Kerr-Schild ansatz adapted for the self-dual gravity framework.

hep-th↗

arXiv2024

$\mathfrak{hs}$-extended gravity from the IKKT matrix model

We elaborate further on the one-loop effective action of the IKKT model on 3 + 1 dimensional covariant quantum spacetime in the presence of fuzzy extra dimensions. In particular, we describe the one-loop effective action in terms of a remarkable $SO(1, 9)$ character, which allows to evaluate the pertinent traces over the internal modes explicitly. This also allows to estimate the higher-order contributions (in the internal flux $\mathcal{F}_{\mathtt{IJ}}$) to the one-loop effective action in a systematic way. We show that all higher-order contributions are generally suppressed and UV finite, which justifies the previous treatment of the induced gravitational action. We also obtain explicit expressions for the effective Newton constant, and determine the dynamics of the Kaluza-Klein scale $\Delta_{\mathcal{K}}$ of the fuzzy extra dimensions $\mathcal{K}$.

hep-th↗

arXiv2024

Quantum $\mathfrak{hs}$-Yang-Mills from the IKKT matrix model

We study the one-loop effective action of the higher-spin gauge theory induced by the IKKT matrix model on a $\mathcal{M}^{1,3}\times \mathcal{K}$ background, where $\mathcal{M}^{1,3}$ is an FLRW cosmological spacetime brane and $\mathcal{K}$ are compact fuzzy extra dimensions. In particular, we show that all non-abelian ($\mathfrak{hs}$-valued) gauge fields in this model acquire mass via quantum effects, thus avoiding no-go theorems. This leads to a massive non-abelian quantum $\mathfrak{hs}$-Yang-Mills theory, whose detailed structure depends on $\mathcal{K}$. The stabilization of $\mathcal{K}$ at one loop is understood as a result of the coupling between $\mathcal{K}$ and the $U(1)$-flux bundle on space-time. This flux stabilization induces the KK scale into the $\mathcal{N} = 4$ SYM sector of the model, which break superconformal symmetry.

hep-th↗

arXiv2023

Spinorial description for Lorentzian $\mathfrak{hs}$-IKKT

We introduce a novel spinorial description for the higher-spin gauge theory induced by the IKKT matrix model on an FLRW spacetime with Lorentzian signature, called Lorentzian $\mathfrak{hs}$-IKKT theory. The new description is based on Weyl spinors transforming under the space-like isometry subgroup $SL(2,\mathbb{C})$ of the structure group $SO(2, 4) \simeq SU(2,2)$. It allows us to exploit the full power of the spinor formalism in Lorentzian signature, in contrast to a previous formalism based on the compact subgroup $SU(2)_L\times SU(2)_R$ of $SU(2,2)$. Some cubic vertices of the Yang-Mills sector and the corresponding scattering amplitudes are computed. We observe that the $n$-point (for $n \geq 4$) tree-level amplitudes are typically non-trivial on-shell, but exponentially suppressed in the late-time regime. While Lorentz invariance of the higher-spin amplitudes is not manifest, it is expected to be restored by higher-spin gauge invariance.

hep-th↗

arXiv2023

Interactions in the IKKT matrix model on covariant quantum spacetime

We study the interactions of the higher-spin gauge theory arising from the IKKT matrix model on a covariant quantum FLRW quantum space-time $\mathcal{M}^{1,3}_{\mathtt{J}}$, denoted as HS-IKKT. In particular, we elaborate some of the vertices and observe that they are not manifestly Lorentz invariant in the unitary formulation. We argue that Lorentz invariance of HS-IKKT can be recovered since Lorentz transformations are part of the gauge invariance in the covariant formulation. This statement is verified for some vertices with the lowest number of derivatives. The lowest-derivative sector of this theory is expected to be governed by an ``almost''-Lorentz-invariant Yang-Mills theory coupled to emergent gravity.

hep-th↗

arXiv2023

Spinorial higher-spin gauge theory from IKKT in Euclidean and Minkowski signatures

We explore the semi-classical relation between the fuzzy 4-hyperboloid $H_N^4$ and non-compact quantized twistor space $\mathbb{P}^{1,2}$ at large $N$. This provides two backgrounds $N$ of the IKKT matrix model via two natural stereographic projections, leading to higher-spin gauge theories with Euclidean and Minkowski signature denoted by HS-IKKT. The resulting higher-spin gauge theory can be understood as an uplift of $\mathcal{N} = 4$ super Yang-Mills to twistor space. The action of HS-IKKT is written using a spinor formalism in both Euclidean and Minkowski signature. We then compute the tree-level amplitudes of the massless sector within the Yang-Mills part of the HS-IKKT model in the flat limit in Euclidean signature. All $n$-point tree-level scattering amplitudes for $n \geq 4$ of this sector are found to vanish in the flat limit.

hep-th↗

arXiv2023

Constraining higher-spin S-matrices

There are various no-go theorems that tightly constrain the existence of local higher-spin theories with non-trivial S-matrix in flat space. Due to the existence of higher-spin Yang-Mills theory with non-trivial scattering amplitudes, it makes sense to revisit Weinberg's soft theorem - a direct consequence of the Lorentz invariance of the S-matrix that does not take advantage of unitarity and parity invariance. By working with the chiral representation - a representation originated from twistor theory, we show that Weinberg's soft theorem can be evaded and non-trivial higher-spin S-matrix is possible. In particular, we show that Weinberg's soft theorem is more closely related to the number of derivatives in the interactions rather than spins. We also observe that all constraints imposed by gauge invariance of the S-matrix are accompanied by polynomials in the soft momentum of the emitted particle where the zeroth order in the soft momentum is charge conservation law.

hep-th↗

arXiv2022

Twistor approach to higher-spin theories and matrix model

We discuss recent endeavours in connecting twistor theory to higher-spin theories and the IKKT- matrix model. Starting with a brief review on higher-spin algebra hs in four-dimensional target space, we elucidate how higher-spin symmetry can be encoded in hs-valued sections/holomorphic differential forms on (non-commutative) twistor space. This provides an efficient way to construct local higher-spin theories in spacetime from some actions on (non-commutative) twistor space. Remarkably, some higher-spin theories obtained within the framework of twistor theory can have non-trivial scattering amplitudes in flat space.

hep-th↗

arXiv2022

A Twistorial Description of the IKKT-Matrix Model

We consider the fuzzy 4-sphere $S_N^4$ as a background in the IKKT matrix model and explore the relation between $S_N^4$ and fuzzy twistor space in the semi-classical limit. A novel description for the IKKT-matrix model in terms of spinorial indices is given, which is reminiscent of $\mathcal{N}=4$ super-symmetric Yang-Mills (SYM) in $4d$. On fuzzy twistor space, the interactions of the IKKT model are of gravitational type. The higher-spin (HS) gauge theory emerging in this limit from the IKKT model, denoted as HS-IKKT, on fuzzy twistor space is shown to be a higher-spin extension of $\mathcal{N}=4$ SYM, with vertices that have more than two derivatives. We obtain its (Euclidean) spacetime action using the Penrose transform. Although this is a gravitational theory, it shares many features with the higher-spin extensions of Yang-Mills in $4d$ flat space obtained in arXiv:2105.12782, arXiv:2107.04500. The tree-level amplitudes of the HS-IKKT are studied in the semi-classical flat limit. The self-dual sector of the IKKT model is obtained by dropping some parts of the cubic- and the quartic interactions, which is shown to reduce to a BF-type action on commutative deformed projective twistor space.

hep-th↗

arXiv2022

Higher-spin Yang-Mills, amplitudes and self-duality

The existence of interacting higher-spin theories is tightly constrained by many no-go theorems. In this paper, we construct a chiral, higher-spin generalization of Yang-Mills theory in flat space which avoids these no-go theorems and has non-trivial tree-level scattering amplitudes with some higher-spin external legs. The fields and action are complex, so the theory is non-unitary and parity-violating, yet we find surprisingly compact formulae for all-multiplicity tree-level scattering amplitudes in the maximal helicity violating (MHV) sector, where the two negative helicity particles have identical but arbitrary spin. This is possible because the theory admits a perturbative expansion around its self-dual sector. Using twistor theory, we prove the classical integrability of this self-dual sector and show that it can be described on spacetime by an infinite tower of interacting massless scalar fields. We also give a twistor construction of the full theory, and use it to derive the formula for the MHV amplitude.

hep-th↗

arXiv2022

Toward a twistor action for chiral higher-spin gravity

A covariant twistor action for chiral higher-spin theory in (A)dS and flat space is constructed in terms of a holomorphic Chern-Simons theory on twistor space. The action reproduces all known cubic vertices of chiral higher-spin theory in flat space. The spacetime action of the holomorphic Chern-Simons theory in flat space is also obtained.

hep-th↗

arXiv2021

Twistor Constructions for Higher-spin Extensions of (Self-dual) Yang-Mills

We present the inverse Penrose transform (the map from spacetime to twistor space) for self-dual Yang-Mills (SDYM) and its higher-spin extensions on a flat background. The twistor action for the higher-spin extension of SDYM (HS-SDYM) is of BF-type. By considering a deformation away from the self-dual sector of HS-SDYM, we discover a new action that describes a higher-spin extension of Yang-Mills theory (HS-YM). The twistor action for HS-YM is a straightforward generalization of the Yang-Mills one.

hep-th↗

arXiv2021

Actions for Self-dual Higher Spin Gravities

Higher Spin Gravities are scarce, but covariant actions for them are even scarcer. We construct covariant actions for contractions of Chiral Higher Spin Gravity that represent higher spin extensions of self-dual Yang-Mills and self-dual Gravity theories. The actions give examples of complete higher spin theories both in flat and (anti)-de Sitter spaces that feature gauge and gravitational interactions. The actions are based on a new description of higher spin fields, whose origin can be traced to early works on twistor theory. The new description simplifies the structure of interactions. In particular, we find a covariant form of the minimal gravitational interaction for higher spin fields both in flat and anti-de Sitter space, which resolves some of the puzzles in the literature.

hep-th↗