Publications

Order by: publication date number of citations

• Inferring correlated distributions: Boosted top jets

  Ezequiel Alvarez, Manuel Szewc, Alejandro Szynkman, Santiago Tanco, Tatiana Tarutina

  SciPost Phys. Core 8, 087 (2025) · published 26 November 2025 | Toggle abstract · pdf

  Improving the understanding of signal and background distributions in signal-region is a valuable key to enhance any analysis in collider physics. This is usually a difficult task because –among others– signal and backgrounds are hard to discriminate in signal-region, simulations may reach a limit of reliability if they need to model non-perturbative QCD, and distributions are multi-dimensional and many times may be correlated within each class. Bayesian density estimation is a technique that leverages prior knowledge and data correlations to effectively extract information from data in signal-region. In this work we extend previous works on data-driven mixture models for meaningful unsupervised signal extraction in collider physics to incorporate correlations between features. Using a standard dataset of top and QCD jets, we show how simulators, despite having an expected bias, can be used to inject sufficient inductive nuance into an inference model in terms of priors to then be corrected by data and estimate the true correlated distributions between features within each class. We compare the model with and without correlations to show how the signal extraction is sensitive to their inclusion and we quantify the improvement due to the inclusion of correlations using both supervised and unsupervised metrics.

• On the difference between thermalization in open and isolated quantum systems: A case study

  Archak Purkayastha, Giacomo Guarnieri, Janet Anders, Marco Merkli

  SciPost Phys. 19, 136 (2025) · published 25 November 2025 | Toggle abstract · pdf

  Thermalization of isolated and open quantum systems has been studied extensively. However, being the subject of investigation by different scientific communities and being analysed using different mathematical tools, the connection between the isolated (IQS) and open (OQS) approaches to thermalization has remained opaque. Here we demonstrate that the fundamental difference between the two paradigms is the order in which the long time and the thermodynamic limits are taken. This difference implies that they describe physics on widely different time and length scales. Our analysis is carried out numerically for the case of a double quantum dot (DQD) coupled to a fermionic lead, also known as the interacting resonant level model in quantum impurity physics. We show how both OQS and IQS thermalization can be explored in this model on equal footing, allowing a fair comparison between the two. We find that while the quadratically coupled (free) DQD experiences no isolated thermalization, it of course does experience open thermalization. For the non-linearly interacting DQD coupled to a fermionic lead, the many-body interaction in the DQD breaks the integrability of the whole system. We find that this system shows strong evidence of both OQS and IQS thermalization in the same dynamics, but at widely different time scales, consistent with reversing the order of the long time and the thermodynamic limits.

• NLO finite system size corrections to $2\to2$ scattering in $\phi^4$ theory using newly derived sum of sinc functions

  Jean F. Du Plessis, William A. Horowitz

  SciPost Phys. Proc. 15, 002 (2024) · published 2 April 2024 | Toggle abstract · pdf

  Previously an equation of state for the relativistic hydrodynamics encountered in heavy-ion collisions at the LHC and RHIC has been calculated using lattice gauge theory methods. This leads to a prediction of very low viscosity, due to the calculated trace anomaly. Finite system corrections to this trace anomaly could challenge this calculation, since the lattice calculation was done in an effectively infinite system. In order to verify this trace anomaly it is sensible to add phenomenologically relevant finite system corrections. We investigate massive $\phi^4$ theory with periodic boundary conditions on $n$ of the 3 spatial dimensions. $2\to2$ NLO scattering is then computed. Using a newly derived formula for an arbitrary dimensional sum of sinc functions, we show that the NLO finite size corrections preserve unitarity.

• From Rindler fluid to dark fluid on the holographic cutoff surface

  Rong-Gen Cai, Gansukh Tumurtushaa, Yun-Long Zhang

  SciPost Phys. Proc. 4, 003 (2021) · published 13 August 2021 | Toggle abstract · pdf

  As an approximation to the near horizon regime of black holes, the Rindler fluid was proposed on an accelerating cutoff surface in the flat spacetime. The concept of the Rindler fluid was then generalized into a flat bulk with the cutoff surface of the induced de Sitter and FRW universe, such that an effective description of dark fluid in the accelerating universe can be investigated.

• Rashba spin-orbit coupling and nonlocal correlations in disordered 2D systems

  Yongtai Li, Gour Jana, Chinedu E. Ekuma

  SciPost Phys. 19, 135 (2025) · published 24 November 2025 | Toggle abstract · pdf

  We present an extension of the dynamical cluster approximation (DCA) that incorporates Rashba spin-orbit coupling (SOC) to investigate the interplay between disorder, spin-orbit interaction, and nonlocal spatial correlations in disordered two-dimensional systems. By analyzing the average density of states, momentum-resolved self-energy, and return probability, we demonstrate how Rashba SOC and nonlocal correlations jointly modify single-particle properties and spin-dependent interference. The method captures key features of the symplectic universality class, including SOC-induced delocalization signatures at finite times. We benchmark the DCA results against those obtained from the numerically exact kernel polynomial method, finding good agreement. This validates the computationally efficient, mean-field-based DCA framework as a robust tool for exploring disorder, spin-orbit coupling, and nonlocal correlation effects in low-dimensional systems, and paves the way for simulating multiorbital and strongly correlated systems that were previously inaccessible due to computational limitations.

• Multicomponent one-dimensional quantum droplets across the mean-field stability regime

  I. A. Englezos, P. Schmelcher, S. I. Mistakidis

  SciPost Phys. 19, 133 (2025) · published 24 November 2025 | Toggle abstract · pdf

  The Lee-Huang-Yang (LHY) energy correction at the edge of the mean-field stability regime is known to give rise to beyond mean-field structures in a wide variety of systems. In this work, we analytically derive the LHY energy for two-, three- and four-component one-dimensional bosonic short-range interacting mixtures across the mean-field stability regime. For varying intercomponent attraction in the two-component setting, quantitative deviations from the original LHY treatment emerge being imprinted in the droplet saturation density and width. On the other hand, for repulsive interactions an unseen early onset of phase-separation occurs for both homonuclear and heteronuclear mixtures. Closed LHY expressions for the fully-symmetric three- and four-component mixtures, as well as for mixtures comprised of two identical components coupled to a third independent component are provided and found to host a plethora of mixed droplet states. Our results are expected to inspire future investigations in multicomponent systems for unveiling exotic self-bound states of matter and unravel their nonequilibrium quantum dynamics.

• Emergent Kitaev materials in synthetic Fermi-Hubbard bilayers

  Daniel González-Cuadra, Alejandro Bermudez

  SciPost Phys. 19, 130 (2025) · published 18 November 2025 | Toggle abstract · pdf

  We investigate the emergence of bond-directional spin-spin interactions in a synthetic Fermi-Hubbard bilayer that can be realized with ultracold fermions in Raman optical lattices. The model exploits synthetic dimensions to couple two honeycomb layers, each corresponding to a different hyperfine atomic state, via Raman-assisted tunneling and, moreover, via an inter-layer Hubbard repulsion due to the cold-atom scattering. In the strong-coupling regime at half filling, we derive effective spin Hamiltonians for the kinetic exchange featuring Kitaev, Heisenberg, off-diagonal exchange ($\Gamma$-couplings), as well as tunable Dzyaloshinskii-Moriya interactions. We identify specific configurations that generate both ferromagnetic and antiferromagnetic Kitaev couplings with various perturbations of relevance to Kitaev materials, providing a tunable platform that can explore how quantum spin liquids emerge from itinerant fermion systems. We analyze the Fermi-liquid and Mott-insulating phases, highlighting a correspondence between Dirac and Majorana quasi-particles, with possible phase transitions thereof. In an extreme anisotropic limit, we show that the model reduces to an inter-layer ribbon in a quasi-1D ladder, allowing for a numerical study of the correlated ground state using matrix product states. We find a transition from a symmetry-protected topological insulator to a Kitaev-like regime characterized by nonlocal string order. Our results establish that cold-atom quantum simulators based on Raman optical lattices can be a playground for extended Kitaev models, bridging itinerant fermionic systems and spin-liquid physics.

• Search for lepton flavour violating decays involving tau leptons in the final state at CMS

  Luca Guzzi

  SciPost Phys. Proc. 17, 016 (2025) · published 23 July 2025 | Toggle abstract · pdf

  In the Standard Model (SM) lepton flavour numbers are approximately conserved at energies accessible to current experiments, where lepton flavour violation is extremely suppressed. The observation of neutrino oscillations, however, proves that neutrinos are massive particles and allows for additional Lepton Flavour Violating (LFV) processes also at low energies. Nevertheless, these processes are predicted with very low branching ratios and are sensitive to new physics effects, which could manifest as an enhancement in the decay probability. Similarly, Lepton Flavour Universality Violating (LFUV) observables allows for the test of the SM and the study of beyond the SM theories. The latest CMS results from the Higgs, B-physics and exotica groups are presented on the search for LFV and LFUV with tau leptons in the final state. The results are based on data collected in proton-proton collisions at the centre-of-mass energy of 13 TeV.

• A Fermi surface descriptor quantifying the correlations between anomalous Hall effect and Fermi surface geometry

  Elena Derunova, Jacob Gayles, Yan Sun, Michael W. Gaultois, Mazhar N. Ali

  SciPost Phys. Core 8, 085 (2025) · published 18 November 2025 | Toggle abstract · pdf

  In the last few decades, basic ideas of topology have completely transformed the prediction of quantum transport phenomena. Following this trend, we go deeper into the incorporation of modern mathematics into quantum material science focusing on geometry. Here we investigate the relation between the geometrical type of the Fermi surface and Anomalous and Spin Hall Effects. An index, $\mathbb{H}_F$, quantifying the hyperbolic geometry of the Fermi surface, shows a universal correlation (R$^2$ = 0.97) with the experimentally measured intrinsic anomalous Hall conductivity, of 16 different compounds spanning a wide variety of crystal, chemical, and electronic structure families, including those where topological methods give R$^2$ = 0.52. This raises a question about the predictive limits of topological physics and its transformation into a wider study of bandstructures' and Fermi surfaces' geometries and relating them to the quantum geometry theory of a more general metric of eigenstates, opening horizon for the prediction of phenomena beyond topological understanding.

• Searches for new phenomena in final states with taus using the ATLAS detector

  Giuseppe Carratta

  SciPost Phys. Proc. 17, 014 (2025) · published 23 July 2025 | Toggle abstract · pdf

  Many theories beyond the Standard Model predict new phenomena, such as leptoquarks, vector like leptons, $Z'$ and $W'$ bosons, supersymmetry, new scalars or heavy leptons, in final states with isolated, high-$p_{T}$ taus. Searches for new physics with such signatures, produced either resonantly or non-resonantly, are performed using the ATLAS experiment at the LHC. The most recent results at $\sqrt{s} =$ 13 TeV in proton-proton collision, are presented in this contribution.