Opening speech by the INPP Director

• Christos Markou

Opening speech by the APCTP Director

• Jae-Hyung Jeon (APCTP)

TBA

• Emmanouil Floratos (National and Kapodistrian University of Athens (GR))

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• Jae-Hyung Jeon (APCTP)

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• Vassilios Constantoudis (INN)

Chaos or Noise? Identifying the Origin of Irregular Dynamics from Time Series Using Machine Learning

• Jong-Min Park (Asia Pacific Center for Theoretical Physics (APCTP))

Many time series observed in nature exhibit irregular and seemingly unpredictable fluctuations. Determining whether such behavior originates from chaotic dynamics or from intrinsic stochastic fluctuations is a longstanding challenge in nonlinear science and time-series analysis. Although a variety of methods have been developed for this purpose, reliable discrimination remains difficult because stochastic processes can often mimic characteristic signatures of chaos. In this talk, I will present a learning-based framework for distinguishing chaotic dynamics from stochastic processes using time-series data. The proposed approach is motivated by the observation that conventional short-term prediction methods can be misled by stochastic processes with strong temporal correlations, which may exhibit apparent predictability despite the absence of an underlying deterministic rule. To overcome this limitation, we introduce a cross-prediction strategy in which the future change of a variable is predicted from its current value. This prediction task requires not only short-term predictability but also the ability to infer the deterministic structure governing the dynamics, providing a more stringent test for chaos. Implemented using reservoir computing, the framework yields a simple quantitative criterion for distinguishing chaos from noise based on the coefficient of determination between true and predicted future changes. Applications to a wide range of synthetic chaotic and stochastic systems reveal a clear separation between the two classes. We further apply the method to several empirical datasets previously analyzed in the literature and obtain classifications largely consistent with existing evidence. These results demonstrate that the proposed approach provides a simple, robust, and broadly applicable tool for distinguishing chaos from noise from time-series observations.

Adaptive transitions in networks of coupled non-linear oscillators

• Astero Provata (INN)

Adaptive coupling in networks of interacting nonlinear oscillators has gained recent attention due to the many applications both in biological and in artificial neural networks, where synaptic plasticity or adaptive coupling are considered as key factors in the learning processes. In our studies, we apply adaptive connectivity rules in exemplary networks consisting of leaky-integrate-and-fire (LIF) or FitzHugh-Nagumo (FHN) oscillators. For such networks, in the absence of adaptivity (i.e., for constant network connectivity), hybrid synchronization patterns (solitaries, chimeras and bump states) have been observed [1]. When the coupling strengths get modified, influenced by the nodal state variables (nodal potentials), then the network dynamics undergoes structural transitions crossing domains of different complexity/synchrony [2-3]. Coupling adaptivity (plasticity) may be realized via Hebbian learning adjusted by the Oja rule (also called 'forgetting' rule) to prevent the network link weights from growing without bounds. The resulting adaptive transitions become evident when the time scales governing the coupling dynamics are much slower than the ones governing the nodal dynamics (nodal potentials). Namely, when the coupling time scales are slow, the network has the time to realize and demonstrate different synchronization regimes before reaching the final steady state. The transitions are characterized by abrupt changes of the average coupling weights and of the Kuramoto order parameter as the network evolves in time [2-3]. The emergence of adaptive transitions demonstrate how the interplay of distinct time scales can profoundly influence the evolution and the collective behavior in dynamical systems. Literature [1] Y. Kuramoto and D. Battogtokh Coexistence of Coherence and Incoherence in Nonlocally Coupled Phase Oscillators Nonlinear Phenomena in Complex Systems 5 380 (2002) http://www.j-npcs.org/online/vol2002/v5no4/v5no4p380.pdf [2]. A. Provata, G. C. Boulougouris and J. Hizanidis Adaptive transitions in FitzHugh-Nagumo networks with Hebb-Oja coupling rules Journal of Statistical Mechanics: Theory and Experiment, Volume 2026, 044004 (2026) https://doi.org/10.1088/1742-5468/ae5c93 [3]. A. Provata, G. C. Boulougouris and J. Hizanidis Synchronization transitions in spiking networks with adaptive coupling Chaos, Solitons & Fractals, Volume 200, 117128 (2025) https://doi.org/10.1016/j.chaos.2025.117128

TBA

• Roni Muslim (APCTP)

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• Konstadinos Sfetsos (National and Kapodistrian University of Athens (GR))

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• Nikolaos Tetradis (National and Kapodistrian University of Athens (GR))

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• Alexadros Kehagias

Emergent $\text{AdS}_{d+1}$ Geometry from Functional Renormalization Group in the Massless Critical Limit

• Ki Seok Kim (POSTECH)

We present a holographic dual description for the O(N) vector model in $d$-dimensional Euclidean space within the functional renormalization group (FRG) framework. By iterating Wilsonian renormalization group transformations, the extra-dimensional scale coordinate is identified as the radial direction of an emergent $(d+1)$-dimensional bulk spacetime. We construct a bidirectional holographic dictionary that maps non-perturbative fluctuations to the emergent bulk metric warping factors. Under the massless critical configuration, the emergent gravitational vacuum reduces to an Anti-de Sitter ($\text{AdS}_{d+1}$) geometry, satisfying the local energy conditions.

TBA

• Manuela Kulaxizi

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• Dimitrios Zoakos

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• Fotis Farakos (NTUA)

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• Kostas Filippas (NCSR Demokritos, Institute of Nuclear and Particle Physics)

Two-loop amplitudes for Higgs boson production in association with a bottom-quark pair at the LHC

• Heribertus Bayu Hartanto (Asia Pacific Center for Theoretical Physics (APCTP), Pohang, South Korea)

I will first review the phenomenological importance of Higgs boson production in association with a bottom-quark pair (Hbb production) at the LHC. I will then discuss the computation of two-loop scattering amplitudes, the principal bottleneck in obtaining NNLO QCD predictions, and their application to cross-section calculations.

Automating two-loop amplitude computation with HELAC2LOOP

• Konstantinos Papadopoulos

TBA

• Aris-George-Baldur Spourdalakis (NSCR Demokritos)

Three-loop Feynman integrals for leading-colour diboson production at hadron colliders

• Mattia Pozzoli (University of Bologna and INFN)

In this talk, I will present results for planar families of Feynman integrals for a four-point three-loop kinematics, with two non-degenerate external masses. These integrals are necessary to compute the three-loop amplitude for the production of two vector bosons, which are relevant for N3LO QCD corrections to this process. After grouping the integrals into nine integral families, we compute them through differential equations. To this end, for all integral families we construct a basis of pure master integrals, satisfying canonical differential equations. Compared to the two-loop case, this step is more complicated not only because of the larger number of master integrals, but also by the appearance of new square roots in the alphabet. We evaluate the master integrals by solving the differential equations using generalised power series expansions.

TBA

• Dhimiter Canko (Università di Bologna)

Novel cluster-algebraic letters for 5- and 6-point QCD processes

• Georgios Papathanasiou (National and Kapodistrian University of Athens)

By breaking dual conformal invariance, we transform cluster-algebraic predictions for the alphabet of 9-point amplitudes in N=4 super Yang-Mills theory to analogous predictions for 5- and 6-point processes in QCD. We start by obtaining, for the first time, candidate letters for 6-point processes with one massive external leg, and discover that they surprisingly also contain nested square roots. We confirm that our results essentially contain the alphabet of all 1-loop integrals with these kinematics, and in their massless limit also the recently computed alphabet of finite, planar 2-loop amplitudes for 6-point massless QCD processes. In the latter case, we additionally find 162 letters that may appear at higher loops. We similarly produce candidate letters for 5-point 2-mass processes, whose comparison with the literature reveals a nontrivial overlap that also includes new letters.

TBA

• Panagiotis Dimitrakis (IQCQT)

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• Karl Jakobs (University of Freiburg (DE))

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• Shohei Okawa (APCTP)

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• Vassilis Spanos (Department of Physics National and Kapodistrian University of Athens)

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• Theodoros Papanikolaou (University of Patras)

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• Konstantinos Zoubos

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• Giuseppe Bevilacqua (NCSR Demokritos)