SciPost Phys. 19, 162 (2025) ·
published 23 December 2025
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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.
SciPost Phys. Proc. 7, 047 (2022) ·
published 22 June 2022
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Multi-loop scattering amplitudes constitute a serious bottleneck in current high-energy physics computations. Obtaining new integrand level representations with smooth behaviour is crucial for solving this issue, and surpassing the precision frontier. In this talk, we describe a new technology to rewrite multi-loop Feynman integrands in such a way that non-physical singularities are avoided. The method is inspired by the Loop-Tree Duality (LTD) theorem, and uses geometrical concepts to derive the causal structure of any multi-loop multi-leg scattering amplitude. This representation makes the integrand much more stable, allowing faster numerical simulations, and opens the path for novel re-interpretations of higher-order corrections in QFT.
SciPost Phys. Proc. 7, 046 (2022) ·
published 22 June 2022
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I present results for soft anomalous dimensions through three loops for many QCD processes. In particular, I give detailed expressions for soft anomalous dimensions in various processes with electroweak and Higgs bosons as well as single top quarks and top-antitop pairs.
SciPost Phys. Proc. 3, 026 (2020) ·
published 25 February 2020
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A novel approach that allows access to long-sought information on the Hyperon-Nucleon (YN) interaction was developed by producing a hyperon beam within a few-body nuclear system, and studying final-state interactions. The determination of polarisation observables, and specifically the beam spin asymmetry, in exclusive reactions allows a detailed study of the various final-state interactions and provides us with the tools needed to isolate kinematic regimes where the YN interaction dominates. High-statistics data collected using the CLAS detector housed in Hall-B of the Thomas Jefferson laboratory allows us to obtain a large set of polarisation observables and place stringent constraints on the underlying dynamics of the YN interaction.
SciPost Phys. 19, 037 (2025) ·
published 13 August 2025
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By using the Bogoliubov perturbation theory we describe the self-bound ground state and excited breathing states of $N$ two-dimensional bosons with zero-range attractive interactions. Our results for the ground state energy $B_N$ and size $R_N$ improve previously known large-$N$ asymptotes and we better understand the crossover to the few-body regime. The breathing oscillations, absent at the mean-field level, result from the quantum-mechanical breaking of the mean-field scale symmetry. The breathing-mode frequency scales as $\Omega\propto |B_N|/\sqrt{N}$ at large $N$.
Mig. Pol. 4, 006 (2025) ·
published 24 December 2025
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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.
SciPost Phys. Proc. 7, 045 (2022) ·
published 22 June 2022
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We study the non-linear background field redefinitions arising at the quantum level in a spontaneously broken effective gauge field theory. The non-linear field redefinitions are crucial for the symmetric (i.e. fulfilling all the relevant functional identities of the theory) renormalization of gauge-invariant operators. In a general $R_\xi$-gauge the classical background-quantum splitting is also non-linearly deformed by radiative corrections. In the Landau gauge these deformations vanish to all orders in the loop expansion.
Jorge Expósito Patiño, Hannes Robert Rüter, David Hilditch
SciPost Phys. 19, 112 (2025) ·
published 27 October 2025
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Electromagnetism plays an important role in a variety of applications in gravity that we wish to investigate. To that end, in this work, we present an implementation of the Maxwell equations within the adaptive-mesh pseudospectral numerical relativity code BAMPS. We perform a thorough analysis of the evolution equations as a first order symmetric hyperbolic system of PDEs. This includes both the construction of the characteristic variables for use in our penalty boundary communication scheme, as well as radiation controlling, constraint preserving outer boundary conditions which, for the first time in a numerical context, are shown to be boundary-stable. After choosing a formulation of the Maxwell constraints that we may solve for initial data, we move on to show a suite of numerical tests. Our simulations, both within the Cowling approximation, and in full non-linear evolution, demonstrate rapid convergence of error with resolution, as well as consistency with known quasinormal decay rates on the Kerr background. Finally we evolve the electrovacuum equations of motion with strong data, a good representation of typical critical collapse runs.
SciPost Phys. 19, 114 (2025) ·
published 28 October 2025
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We reformulate tree-level amplitudes in open superstring theory (type-I) in terms of stringy Tr$(\phi^3)$ amplitudes with various kinematical shifts in the "curve-integral" formulation: while the bosonic-string amplitude with $n$ pairs of "scaffolding" scalars comes from a particularly simple shift of the Tr$(\phi^3)$ one (corresponding to $n$ length-$2$ cycles), the analogous superstring amplitude requires "correction" terms given by bosonic-string amplitudes with longer, even-length "cycles", which are also Tr$(\phi^3)$ ones at shifted kinematics dictated by the cycles; in total it is expressed as a sum of $(2n-3)!!$ shifted amplitudes originated from the expansion of a reduced Pfaffian. Upon taking $n$ scaffolding residues, this leads to a new formula of the $n$-gluon superstring amplitude, which is manifestly symmetric in $n-1$ legs, as a gauge-invariant combination of mixed bosonic string amplitudes with gluons and scalars, which come from length-$2$ cycles and longer ones respectively (the total sum is associated with the expansion a $n× n$ symmetrical determinant); the corresponding prefactors are nested commutators of $2n$-gon kinematical variables, which nicely become traces of field-strengths for those legs corresponding to scalars in the mixed amplitudes. These interesting linear combinations of bosonic string amplitudes must guarantee the cancellation of tachyon poles and $F^3$ vertices etc., and they give new relations between the superstring amplitude and its bosonic-string building blocks to all orders in the $\alpha'$ expansion (the first order gives a new formula for gluon amplitudes with a single $F^3$ insertion in terms of Yang-Mills-scalar amplitudes). We provide both the worldsheet and "curve-integral" derivations, and discuss applications to heterotic and type II cases.
SciPost Phys. 19, 117 (2025) ·
published 29 October 2025
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The control of antiferromagnetic order can pave the way to large storage capacity as well as fast manipulation of stored data. Here achieving a steady-state of sublattice magnetization after switching is crucial to prevent loss of stored data. The present theoretical approach aims to obtain instantaneous stable states of the order after reorienting the Néel vector in open quantum antiferromagnets using time-dependent Schwinger boson mean-field theory. The Lindblad formalism is employed to couple the system to the environment. The quantum theoretical approach comprises differences in the effects of dephasing, originating from destructive interference of different wave vectors, and spin-lattice relaxation. We show that the spin-lattice relaxation results in an exponentially fast convergence to the steady-state after full ultrafast switching.
