Publications

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• Lecture notes on normalizing flows for lattice quantum field theories

  Miranda C. N. Cheng, Niki Stratikopoulou

  SciPost Phys. Lect. Notes 110 (2026) · published 7 January 2026 | Toggle abstract · pdf

  Numerical simulations of quantum field theories on lattices serve as a fundamental tool for studying the non-perturbative regime of the theories, where analytic tools often fall short. Challenges arise when one takes the continuum limit or as the system approaches a critical point, especially in the presence of non-trivial topological structures in the theory. Rapid recent advances in machine learning provide a promising avenue for progress in this area. These lecture notes aim to give a brief account of lattice field theories, normalizing flows, and how the latter can be applied to study the former. The notes are based on the lectures given by the first author in various recent research schools.

• Simplified template cross sections – Stage 1.1 and 1.2

  Nicolas Berger, Claudia Bertella, Matteo Bonanomi, Nihal Brahimi, Thomas P. Calvet, Milene Calvetti, Valerio Dao, Marco Delmastro, Michael Duehrssen-Debling, Paolo Francavilla, Yacine Haddad, Sarah Heim, Jelena Jovicevic, Oleh Kivernyk, Maria Moreno Llacer, Jonathon M. Langford, Changqiao Li, Giovanni Marchiori, Josh A. McFayden, Johannes K. L. Michel, Predrag Milenovic, Carlo E. Pandini, Edward Scott, Frank J. Tackmann, Kerstin Tackmann, Lorenzo Viliani, Meng Xiao, Hongtao Yang

  SciPost Phys. Comm. Rep. 15 (2026) · published 7 January 2026 | Toggle abstract · pdf

  Simplified Template Cross Sections (STXS) have been adopted by the LHC experiments as a common framework for Higgs measurements. Their purpose is to reduce the theoretical uncertainties that are directly folded into the measurements as much as possible, while at the same time allowing for the combination of the measurements between different decay channels as well as between experiments. We report the complete, revised definition of the STXS kinematic bins (stage 1.1 and stage 1.2), which have been used for the measurements by the ATLAS and CMS experiments using the full LHC Run 2 datasets. The main focus is on the four dominant Higgs production processes, namely gluon-fusion, vector-boson fusion, production in association with a vector boson and in association with a $t\bar t$ pair. We also comment briefly on the treatment of other production modes.

• Hopf exceptional points

  Tsuneya Yoshida, Emil J. Bergholtz, Tomáš Bzdušek

  SciPost Phys. 20, 001 (2026) · published 7 January 2026 | Toggle abstract · pdf

  Exceptional points at which eigenvalues and eigenvectors of non-Hermitian matrices coalesce are ubiquitous in the description of a wide range of platforms from photonic or mechanical metamaterials to open quantum systems. Here, we introduce a class of Hopf exceptional points (HEPs) that are protected by the Hopf invariants (including the higher-dimensional generalizations) and which exhibit phenomenology sharply distinct from conventional exceptional points. Saliently, owing to their $\mathbb{Z}_2$ topological invariant related to the Witten anomaly, three-fold HEPs and symmetry-protected five-fold HEPs act as their own \enquote{antiparticles}. Furthermore, based on higher homotopy groups of spheres, we predict the existence of multifold HEPs and symmetry-protected HEPs with non-Hermitian topology captured by a range of finite groups (such as $\mathbb{Z}_3$, $\mathbb{Z}_{12}$, or $\mathbb{Z}_{24}$) beyond the periodic table of Bernard-LeClair symmetry classes.

• One-loop amplitudes for $t\bar{t}j$ and $t\bar{t}\gamma$ productions at the LHC through $\mathcal{O}(\epsilon^2)$

  Souvik Bera, Colomba Brancaccio, Dhimiter Canko, Heribertus Bayu Hartanto

  SciPost Phys. 19, 165 (2025) · published 24 December 2025 | Toggle abstract · pdf

  We present analytic expressions for the one-loop QCD helicity amplitudes contributing to top-quark pair production in association with a photon or a jet at the Large Hadron Collider (LHC), evaluated through $\mathcal{O}(\epsilon^2)$ in the dimensional regularisation parameter, $\epsilon$. These amplitudes are required to construct the two-loop hard functions that enter the NNLO QCD computation. The helicity amplitudes are expressed as linear combinations of algebraically independent components of the $\epsilon$-expanded master integrals, with the corresponding rational coefficients written in terms of momentum-twistor variables. We derive differential equations for the pentagon functions, which enable efficient numerical evaluation via generalised power series expansion method.

• Boundary criticality of complex conformal field theory: A case study in the non-Hermitian 5-state Potts model

  Yin Tang, Qianyu Liu, Qicheng Tang, Wei Zhu

  SciPost Phys. 19, 164 (2025) · published 24 December 2025 | Toggle abstract · pdf

  Conformal fields with boundaries give rise to rich critical phenomena that can reveal information about the underlying conformality. While most existing studies focus on Hermitian systems, here we explore boundary critical phenomena in a non-Hermitian quantum 5-state Potts model which exhibits complex conformality in the bulk. We identify free, fixed and mixed conformal boundary conditions and observe the conformal tower structure of energy spectra, supporting the emergence of conformal boundary criticality. We also studied the duality relation between different conformal boundary conditions under the Kramers-Wannier transformation. These findings should facilitate a comprehensive understanding for complex CFTs and stimulate further exploration on the boundary critical phenomena within non-Hermitian strongly-correlated systems.

• A short introduction to cosmology and its current status

  Pedro G. Ferreira, Alexander Roskill

  SciPost Phys. Lect. Notes 109 (2025) · published 24 December 2025 | Toggle abstract · pdf

  The current cosmological model, known as the $\Lambda$-Cold Dark Matter model (or $\Lambda$CDM for short) is one of the most astonishing accomplishments of contemporary theoretical physics. It is a well-defined mathematical model which depends on very few ingredients and parameters and is able to make a range of predictions and postdictions with astonishing accuracy. It is built out of well-known physics – general relativity, quantum mechanics and atomic physics, statistical mechanics and thermodynamics – and predicts the existence of new, unseen components. Again and again it has been shown to fit new data sets with remarkable precision. Despite these successes, we have yet to understand the unseen components of the Universe and there has been evidence for inconsistencies in the model. In these lectures, we lay the foundations of modern cosmology.

• Tensorization of neural networks for improved privacy and interpretability

  José Ramón Pareja Monturiol, Alejandro Pozas-Kerstjens, David Pérez-García

  SciPost Phys. Core 8, 095 (2025) · published 24 December 2025 | Toggle abstract · pdf

  We present a tensorization algorithm for constructing tensor train/matrix product state (MPS) representations of functions, drawing on sketching and cross interpolation ideas. The method only requires black-box access to the target function and a small set of sample points defining the domain of interest. Thus, it is particularly well-suited for machine learning models, where the domain of interest is naturally defined by the training dataset. We show that this approach can be used to enhance the privacy and interpretability of neural network models. Specifically, we apply our decomposition to (i) obfuscate neural networks whose parameters encode patterns tied to the training data distribution, and (ii) estimate topological phases of matter that are easily accessible from the MPS representation. Additionally, we show that this tensorization can serve as an efficient initialization method for optimizing MPS in general settings, and that, for model compression, our algorithm achieves a superior trade-off between memory and time complexity compared to conventional tensorization methods of neural networks.

• The Curious Case of Bhasan Char: Island Relocation and the Politics of Refugee Containment in the ‘Global South’

  Tazreena Sajjad

  Mig. Pol. 4, 006 (2025) · published 24 December 2025 | Toggle abstract · pdf

  On October 9, 2021, the Bangladesh Ministry of Disaster Management and Relief, and the U.N. High Commissioner for Refugees (UNHCR) signed a Memorandum of Understanding (MoU) to establish a common framework for humanitarian services for Rohingya refugees on Bhasanchar, an island 37 miles from the mainland in the Bay of Bengal. Bangladesh’s plan to relocate 100,000 Rohingya to Bhasanchar offers an opportunity to analyze the complex nature of refugee-hosting in the Global South, bringing into focus how a Global South host, rather than being a passive actor, can attempt a context-specific strategy to generate normative and financial support for its role in accommodating a displaced population. This research aims to make three main contributions. First, it seeks to situate the case of the Rohingya refugee population in Bangladesh within the literature on migration diplomacy and refugee rentierism. Second, it seeks to modify and expand on the refugee rentier state literature by demonstrating how a host country can pursue a path of ‘normative modelling,’ rather than blackmailing or backscratching for purely economic aims. It shows that states may seek to set new norms for refugee hosting for the purpose of gaining international recognition and accolades, in addition to economic support. As such, it finds the existing models of refugee rentierism constrained by its roots in realist IR theory, and suggests a constructivist correction, in which identity and norm setting are relevant to understanding the state’s policy choices. Third, in examining the use of ‘internal offshoring’ i.e. using one’s own territory for redistribution of a population (in this case from a congested refugee camp), it problematizes how Global North practices of extraterritorial ‘offshoring’ such as Australia’s use of the Nauru and Manus islands for immigration detention have served as the framework for understanding Bangladesh’s strategy. While the research outlines the grounds for valid concerns about Bhasanchar, an examination of the political economy of land use in Bangladesh offers a nuanced understanding of the island relocation plan. Such an analysis underscores how imposing the border externalization practices framework inaccurately casts Bangladesh as a case of ‘negative norm absorption’ of migrant deterrence practices, rather than capturing how char (island) living has long been a part of riverine Bangladesh’s sociocultural and economic practices and obfuscates the country’s attempt at norm modeling for refugee accommodation.

• Deriving the non-perturbative gravitational dual of quantum Liouville theory from BCFT operator algebra

  Lin Chen, Ling-Yan Hung, Yikun Jiang, Bing-Xin Lao

  SciPost Phys. 19, 163 (2025) · published 23 December 2025 | Toggle abstract · pdf

  We demonstrate that, by utilizing the boundary conformal field theory (BCFT) operator algebra of the Liouville CFT, one can express its path-integral on any Riemann surface as a three dimensional path-integral with appropriate boundary conditions, generalising the recipe for rational CFTs. This serves as a constructive method for deriving the quantum holographic dual of the CFT, which reduces to Einstein gravity in the large central charge limit. As a byproduct, the framework provides an explicit discrete state-sum of a 3D non-chiral topological theory constructed from quantum $6j$ symbols of $\mathcal{U}_q(sl(2,\mathbb{R}))$ with non-trivial boundary conditions, representing a long-sought non-perturbative discrete formulation of 3D pure gravity with negative cosmological constant, at least within a class of three manifolds. This constitutes the first example of an exact holographic tensor network that reproduces a known irrational CFT with a precise quantum gravitational interpretation.

• Monodromies of CFT correlators on the Lorentzian cylinder

  Suman Kundu, Shiraz Minwalla, Abhishek Navhal

  SciPost Phys. 19, 162 (2025) · published 23 December 2025 | Toggle abstract · pdf

  While correlators of a CFT are single valued in Euclidean Space, they are multi-valued - and have a complicated sheet structure - in Lorentzian space. Correlators on $R^{1,1}$ are well known to access a finite number of these sheets. In this paper, we demonstrate the spiral nature of lightcones on $S^1 × $ time, which allows the time-ordered correlators of a $CFT_2$ on this spacetime - the Lorentzian cylinder - to access an infinite number of sheets of the correlator. We present a complete classification, both of the sheets accessed as well as of the various distinct causal configurations that lie on a particular sheet. Our construction provides a physical interpretation for an infinite number of sheets of the correlator, while, however, leaving a larger infinity of these sheets uninterpreted.