Publications

Order by: publication date number of citations

• Relative cluster entropy for power-law correlated sequences

  Anna Carbone, Linda Ponta

  SciPost Phys. 13, 076 (2022) · published 30 September 2022 | Toggle abstract · pdf

  We propose an information-theoretical measure, the \textit{relative cluster entropy} $\mathcal{D_{C}}[P \| Q] $, to discriminate among cluster partitions characterised by probability distribution functions $P$ and $Q$. The measure is illustrated with the clusters generated by pairs of fractional Brownian motions with Hurst exponents $H_1$ and $H_2$ respectively. For subdiffusive, normal and superdiffusive sequences, the relative entropy sensibly depends on the difference between $H_1$ and $H_2$. By using the \textit{minimum relative entropy} principle, cluster sequences characterized by different correlation degrees are distinguished and the optimal Hurst exponent is selected. As a case study, real-world cluster partitions of market price series are compared to those obtained from fully uncorrelated sequences (simple Browniam motions) assumed as a model. The \textit{minimum relative cluster entropy} yields optimal Hurst exponents $H_1=0.55$, $H_1=0.57$, and $H_1=0.63$ respectively for the prices of DJIA, S\&P500, NASDAQ: a clear indication of non-markovianity. Finally, we derive the analytical expression of the relative cluster entropy and the outcomes are discussed for arbitrary pairs of power-laws probability distribution functions of continuous random variables.

• A benchmark study of dioxygen complexes based on coupled cluster and density functional theory

  Marcel Swart, Marc Reimann

  SciPost Chem. 3, 001 (2024) · published 13 August 2024 | Toggle abstract · pdf

  A set of five compounds containing peroxo, superoxo or bis-μ-oxo moieties has been studied in the gas phase using CCSD(T)/aug-cc-pVQZ, also in combination with Goodson’s continued fraction approach. The corresponding analytical frequencies corroborate assignments of bands from experiments, and thus provide a consistent set of reference data that can be used for benchmarking a range of density functional approximations. A total of 100 density functionals have been checked for the general bond lengths, the specific peroxo/superoxo bond lengths, angles, and vibrational frequencies. There is not one density functional that performs equally well for all of these properties, not even within one class of density functionals.

• Quenched dynamics and pattern formation in clean and disordered Bogoliubov-de Gennes superconductors

  Bo Fan, Antonio Miguel García García

  SciPost Phys. 17, 049 (2024) · published 13 August 2024 | Toggle abstract · pdf

  We study the quench dynamics of a two dimensional superconductor in a square lattice of size up to $200× 200$ employing the self-consistent time dependent Bogoliubov-de Gennes (BdG) formalism. In the clean limit, the dynamics of the order parameter for short times, characterized by a fast exponential growth and an oscillatory pattern, agrees with the Bardeen-Cooper-Schrieffer (BCS) prediction. However, unlike BCS, we observe for longer times a universal exponential decay of these time oscillations. We show explicitly that the origin of this exponential decay is the full emergence of spatial inhomogeneities of the order parameter characterized by the exponential growth of its variance. The addition of a weak disorder does not alter these results qualitatively. In this region, the spatial inhomogeneities rapidly develop into an intricate spatial structure consisting of ordered fragmented stripes in perpendicular directions where the order parameter is heavily suppressed. As the disorder strength increases, the fragmented stripes gradually turn into a square lattice of approximately circular spatial regions where the condensate is heavily suppressed. A further increase of disorder leads to the deformation and ultimate destruction of this lattice. We show these emergent spatial patterns are sensitive to the underlying lattice structure. We explore suitable settings for the experimental confirmation of these findings.

• Functional renormalization group for fermions on a one dimensional lattice at arbitrary filling

  Lucas Désoppi, Nicolas Dupuis, Claude Bourbonnais

  SciPost Phys. 17, 054 (2024) · published 15 August 2024 | Toggle abstract · pdf

  A formalism based on the fermionic functional-renormalization-group approach to interacting electron models defined on a lattice is presented. One-loop flow equations for the coupling constants and susceptibilities in the particle-particle and particle-hole channels are derived in weak-coupling conditions. It is shown that lattice effects manifest themselves through the curvature of the spectrum and the dependence of the coupling constants on momenta. This method is then applied to the one-dimensional extended Hubbard model; we thoroughly discuss the evolution of the phase diagram, and in particular the fate of the bond-centered charge-density-wave phase, as the system is doped away from half-filling. Our findings are compared to the predictions of the field-theory continuum limit and available numerical results.

• Ambitions for theory in the physics of life

  William Bialek

  SciPost Phys. Lect. Notes 84 (2024) · published 15 August 2024 | Toggle abstract · pdf

  Theoretical physicists have been fascinated by the phenomena of life for more than a century. As we engage with more realistic descriptions of living systems, however, things get complicated. After reviewing different reactions to this complexity, I explore the optimization of information flow as a potentially general theoretical principle. The primary example is a genetic network guiding development of the fly embryo, but each idea also is illustrated by examples from neural systems. In each case, optimization makes detailed, largely parameter-free predictions that connect quantitatively with experiment.

• On the Virasoro fusion kernel at $c=25$

  Sylvain Ribault, Ioannis Tsiares

  SciPost Phys. 17, 058 (2024) · published 22 August 2024 | Toggle abstract · pdf

  We find a formula for the Virasoro fusion kernel at $c=25$, in terms of the connection coefficients of the Painlevé VI differential equation. Our formula agrees numerically with previously known integral representations of the kernel. The derivation of our formula relies on a duality $c\to 26-c$ that is obeyed by the shift equations for the fusion and modular kernels. We conjecture that for $c<1$ the fusion and modular kernels are not smooth functions, but distributions.

• Energy magnetization and transport in systems with a non-zero Berry curvature in a magnetic field

  Archisman Panigrahi, Subroto Mukerjee

  SciPost Phys. Core 6, 052 (2023) · published 31 July 2023 | Toggle abstract · pdf

  We demonstrate that the well-known expression for the charge magnetization of a sample with a non-zero Berry curvature can be obtained by demanding that the Einstein relation holds for the electric transport current. We extend this formalism to the transport energy current and show that the energy magnetization must satisfy a particular condition. We provide a physical interpretation of this condition, and relate the energy magnetization to circulating energy currents in Chern insulators due to chiral edge states. We further recover the expression for the energy magnetization with this alternative formalism. We also solve the Boltzmann Transport Equation for the non-equilibrium distribution function in 2D for systems with a non-zero Berry curvature in a magnetic field. This distribution function can be used to obtain the regular Hall response in time-reversal invariant samples with a non-zero Berry curvature, for which there is no anomalous Hall response.

• Self-force framework for transition-to-plunge waveforms

  Lorenzo Küchler, Geoffrey Compère, Leanne Durkan, Adam Pound

  SciPost Phys. 17, 056 (2024) · published 16 August 2024 | Toggle abstract · pdf

  Compact binaries with asymmetric mass ratios are key expected sources for next-generation gravitational wave detectors. Gravitational self-force theory has been successful in producing post-adiabatic waveforms that describe the quasi-circular inspiral around a non-spinning black hole with sub-radian accuracy, in remarkable agreement with numerical relativity simulations. Current inspiral models, however, break down at the innermost stable circular orbit, missing part of the waveform as the secondary body transitions to a plunge into the black hole. In this work we derive the transition-to-plunge expansion within a multiscale framework and asymptotically match its early-time behaviour with the late inspiral. Our multiscale formulation facilitates rapid generation of waveforms: we build second post-leading transition-to-plunge waveforms, named 2PLT waveforms. Although our numerical results are limited to low perturbative orders, our framework contains the analytic tools for building higher-order waveforms consistent with post-adiabatic inspirals, once all the necessary numerical self-force data becomes available. We validate our framework by comparing against numerical relativity simulations, surrogate models and the effective one-body approach.

• Forward trijet production and saturation

  Andreas van Hameren

  SciPost Phys. Proc. 8, 022 (2022) · published 11 July 2022 | Toggle abstract · pdf

  We present a multi-parton extension of the so-called small-$\boldsymbol{x}$ Improved Transverse Momentum Dependent (ITMD) factorization for hadroproduction of three or more jets in the forward rapidity region, allowing to study gluon saturation using such processes.

• India based neutrino observatory, physics reach and status report

  D. Indumathi

  SciPost Phys. Proc. 13, 024 (2023) · published 29 September 2023 | Toggle abstract · pdf

  The India-based Neutrino Observatory (INO) is a proposed underground facility located in India that will primarily house the magnetised Iron CALorimeter (ICAL) detector to study atmospheric neutrinos produced by interactions of cosmic rays with Earth's atmosphere. The physics goal is to to make precision measurements of the neutrino mixing and oscillation parameters through such a study. We present here the results from detailed simulations studies, as well as a status report on the project. In particular, we highlight the sensitivity of ICAL to the open issue of the neutrino mass ordering, which can be determined independent of the CP phase at ICAL.