Publications

Order by: publication date number of citations

• Inverted pendulum driven by a horizontal random force: statistics of the never-falling trajectory and supersymmetry

  Nikolai A. Stepanov, Mikhail A. Skvortsov

  SciPost Phys. 13, 021 (2022) · published 16 August 2022 | Toggle abstract · pdf

  We study stochastic dynamics of an inverted pendulum subject to a random force in the horizontal direction (Whitney's problem). Considered on the entire time axis, the problem admits a unique solution that always remains in the upper half plane. We formulate the problem of statistical description of this never-falling trajectory and solve it by a field-theoretical technique assuming a white-noise driving. In our approach based on the supersymmetric formalism of Parisi and Sourlas, statistic properties of the never-falling trajectory are expressed in terms of the zero mode of the corresponding transfer-matrix Hamiltonian. The emerging mathematical structure is similar to that of the Fokker-Planck equation, which however is written for the "square root" of the probability distribution function. Our results for the statistics of the non-falling trajectory are in perfect agreement with direct numerical simulations of the stochastic pendulum equation. In the limit of strong driving (no gravitation), we obtain an exact analytical solution for the instantaneous joint probability distribution function of the pendulum's angle and its velocity.

• Returning CP-observables to the frames they belong

  Jona Ackerschott, Rahool Kumar Barman, Dorival Gonçalves, Theo Heimel, Tilman Plehn

  SciPost Phys. 17, 001 (2024) · published 2 July 2024 | Toggle abstract · pdf

  Optimal kinematic observables are often defined in specific frames and then approximated at the reconstruction level. We show how multi-dimensional unfolding methods allow us to reconstruct these observables in their proper rest frame and in a probabilistically faithful way. We illustrate our approach with a measurement of a CP-phase in the top Yukawa coupling. Our method makes use of key advantages of generative unfolding, but as a constructed observable it fits into standard LHC analysis frameworks.

• Variational quantum gate optimization at the pulse level

  Sean Greenaway, Francesco Petiziol, Hongzheng Zhao, Florian Mintert

  SciPost Phys. 16, 082 (2024) · published 22 March 2024 | Toggle abstract · pdf

  We experimentally investigate the viability of a variational quantum gate optimization protocol informed by the underlying physical Hamiltonian of fixed-frequency transmon qubits. Through the successful experimental optimization of two and three qubit quantum gates the utility of the scheme for obtaining gates based on static effective Hamiltonians is demonstrated. The limits of such a strategy are investigated through the optimization of a time-dependent, Floquet-engineered gate, however parameter drift is identified as a key limiting factor preventing the implementation of such a scheme which the variational optimization protocol is unable to overcome.

• Real-time ab initio description of the photon-echo mechanisms in extended systems: the case study of bulk GaAs

  Marco D'Alessandro, Davide Sangalli

  SciPost Phys. 12, 193 (2022) · published 13 June 2022 | Toggle abstract · pdf

  In this paper we present an ab initio real-time analysis of free polarization decay and photon echo in extended systems. As a prototype material, we study bulk GaAs driven by ultra-short laser pulses of 10 fs (energy spread of 0.4 eV), with frequency tuned in the continuum of the optical spectrum. We compute the electronic polarization P(t), and define a computational procedure to extract the echo signal in the dipole approximation. Results are obtained in both the low and high field regime, and compared with a two-levels system (TLS) model, with parameters extracted from the ab initio simulations. ab initio results are in optimal agreement with the TLS in the low-field case, whereas some differences are observed in the high-field regime where the multi-band nature of GaAs becomes relevant. In the high field regime we compute the pulse area, and look for fluences with pulse area close to {\pi}. We highlight that such fluences are well below the damage threshold of GaAs. However a unique value of the area cannot be defined, due to the strong dependence of the transition dipoles in the energy window excited by the laser pulse.

• Unitary Howe dualities in fermionic and bosonic algebras and related Dirac operators

  Guner Muarem

  SciPost Phys. Proc. 14, 038 (2023) · published 24 November 2023 | Toggle abstract · pdf

  In this paper we use the canonical complex structure $\mathbb{J}$ on $\mathbb{R}^{2n}$ to introduce a twist of the symplectic Dirac operator. This can be interpreted as the bosonic analogue of the Dirac operators on a Hermitian manifold. Moreover, we prove that the algebra of these Dirac operators is isomorphic to the Lie algebra $\mathfrak{su}(1,2)$ which leads to the Howe dual pair $(U(n),\mathfrak{su}(1,2))$.

• The origin and evolution of wide Jupiter mass binary objects in young stellar clusters

  Simon Portegies Zwart, Erwan Hochart

  SciPost Astro. 3, 001 (2024) · published 2 July 2024 | Toggle abstract · pdf

  The recently observed population of 540 free-floating Jupiter-mass objects, including 40 dynamically soft pairs, and two triples, in the Trapezium cluster have raised interesting questions on their formation and evolution. We test various scenarios for the origin and survivability of these free floating Jupiter-mass objects and Jupiter-mass Binary Objects (JuMBOs) in the Trapezium cluster. The numerical calculations are performed by direct $N$-body integration of the stars and planets in the Trapezium cluster starting with a wide variety of planets in various configurations. We discuss four models: $\mathcal{SPP}$, in which selected stars have two outer orbiting Jupiter-mass planets; $\mathcal{SPM}$, where selected stars are orbited by Jupiter-mass planet-moon pairs; $\mathcal{ISF}$ in which JuMBOs form in situ with the stars, and $\mathcal{FFC}$, where we introduce a population of free-floating single Jupiter-mass objects, but no initialised binaries. Models $\mathcal{FFC}$ and $\mathcal{SPP}$ fail to produce enough JuMBOs. Models $\mathcal{SPM}$ can produce sufficient free-floaters and JuMBOs, but requires unusually wide orbits for the planet-moon system around the star. The observed JuMBOs and free-floating Jupiter-mass objects in the Trapezium cluster are best reproduced if they formed in pairs and as free-floaters together with the other stars in a smooth (Plummer) density profile with a virial radius of $\sim 0.5$pc. A fractal (with fractal dimension 1.6) stellar density distribution also works, but requires relatively recent formations ($\raise-.5ex\hbox{$\buildrel>\over\sim$} 0.2$Myr after the other stars formed) or a high ($\raise-.5ex\hbox{$\buildrel>\over\sim$} 50$%) initial binary fraction. This would make the primordial binary fraction of JuMBOs even higher than the already large observation fraction of $\sim 8$% (42/540). The fraction of JuMBOs will continue to drop with time, and the lack of JuMBOs in Upper Scorpius could then result in its higher age, causing more JuMBOs to be ionized. We then also predict that the interstellar density of Jupiter-mass objects (mostly singles with some $\sim 2$% lucky surviving binaries) is $\sim 0.05$ per pc$^{-3}$ (or around 0.24 per star).

• Sea Asymmetry from Polarized W Boson Production

  C. Cocuzza, A. Metz, N. Sato

  SciPost Phys. Proc. 8, 025 (2022) · published 11 July 2022 | Toggle abstract · pdf

  We present the results of a global QCD analysis of helicity parton distribution functions (PDFs) that includes the latest polarized W-lepton production data from the STAR collaboration at the Relativistic Heavy-Ion Collider (RHIC). This data allows the first extraction of a nonzero helicity light-quark sea asymmetry within a simultaneous global QCD analysis of unpolarized and helicity PDFs.

• Relativistic kinematics in flat and curved space-times

  Patrick Moylan

  SciPost Phys. Proc. 14, 037 (2023) · published 24 November 2023 | Toggle abstract · pdf

  Almost immediately after the seminal papers of Poincaré (1905,1906) and Einstein (1905) on special relativity, wherein Poincaré established the full covariance of the Maxwell-Lorentz equations under the scale-extended Poincaré group and Einstein explained the Lorentz transformation using his assumption that the one-way speed of light in vacuo is constant and the same for all inertial observers (Einstein's second postulate), attempts were made to get at the Lorentz transformations from basic properties of space and time but avoiding Einstein's second postulate. Various such approaches usually involve general consequences of the relativity principle, such as a group structure to the set of all admissible inertial transformations and also assumptions about causality and/or homogeneity of space-time combined with isotropy of space. The first such attempt is usually attributed to von Ignatowsky in 1911. It was followed shortly thereafter by a paper of Frank and Rothe published in the same year. Since then, papers have continued to be written on the subject even up to the present. We elaborate on some of the results of such papers paying special attention to a 1968 paper of Bacri and Lévy-Leblond where possible kinematical groups include the de Sitter and anti-de Sitter groups and lead to special relativity in de Sitter and anti-de Sitter spaces.

• Annihilating dark matter search with 12 years of Fermi LAT data in nearby galaxy clusters

  Charles Thorpe-Morgan, D. Malyshev, C.-A. Stegen, Andrea Santangelo, J. Jochum

  SciPost Phys. Proc. 12, 071 (2023) · published 10 July 2023 | Toggle abstract · pdf

  Galaxy clusters contain an abundance of dark matter making them attractive laboratories for indirect DM searches. This work details a search for signals of pair annihilation from WIMP dark matter in the GeV gamma ray regime. We perform this search in five low $z$ and high galactic latitude galaxy clusters (Centaurus, Coma, Virgo, Perseus and Fornax); using nearly 12 years of Fermi/LAT data. Through the non-detection of this characteristic signal, we derive constraints on the annihilation cross-section of DM pair annihilation into the $b\overline{b}$, $W^+W^-$ and $\gamma\gamma$ channels. The limits obtained are of a comparable magnitude to those of recently derived from Fermi/LAT observations of dwarf spheroidal galaxies.

• Hadron Production in terms of Green's Functions in Non-Equilibrium Matter

  A. V. Koshelkin

  SciPost Phys. Proc. 10, 037 (2022) · published 11 August 2022 | Toggle abstract · pdf

  Following the quark-hadron duality concept, we show that the number of hadrons generated in the deconfinement matter is entirely determined by the exact non-equilibrium Green's functions of partons in the medium and the vertex function governing the probability of the confinement-deconfinement phase transition. In such an approach, compactifying the standard (3+1) chromodynamics into $ QCD_{xy} + QCD_{zt}$, the rate of the hadrons produced in particle collisions is derived in the explicit form provided that the hadronization is the first order phase transition. The pion production is found to be in good agreement to the experimental results on the pion yield in pp collisions.