Publications

Order by: publication date number of citations

• The Giant Radio Array for Neutrino Detection (GRAND) Project

  Bruno Lazarotto Lago

  SciPost Phys. Proc. 10, 027 (2022) · published 11 August 2022 | Toggle abstract · pdf

  GRAND is designed to detect ultra-high-energy cosmic particles -- specially neutrinos, cosmic rays and gamma rays using radio antennas. With $\sim$20 mountainous sites around the world it will cover a total area of 200,000 km$^{2}$. The planned sensitivity of 10$^{-10}$ GeV cm$^{-2}$ s$^{-1}$ sr$^{-1}$ above $5\times10^{17}$ eV will likely ensure the detection of cosmogenic neutrinos predicted by most common scenarios enabling neutrino astronomy. Furthermore, PeV--EeV neutrinos can test particle interactions at energies above those achieved in accelerators. The pathfinder stage GRANDProto300 is planned to start taking data in 2021. We present the current overall status of the project with emphasis on the neutrino physics.

  1 citation

• Effective field theory of fluctuating wall in open systems: from a kink in Josephson junction to general domain wall

  Keisuke Fujii, Masaru Hongo

  SciPost Phys. 12, 160 (2022) · published 13 May 2022 | Toggle abstract · pdf

  We investigate macroscopic behaviors of fluctuating domain walls in nonequilibrium open systems with the help of the effective field theory based on symmetry. Since the domain wall in open systems breaks the translational symmetry, there appears a gapless excitation identified as the Nambu-Goldstone (NG) mode, which shows the non-propagating diffusive behavior in contrast to those in closed systems. After demonstrating the presence of the diffusive NG mode in the $(2+1)$-dimensional dissipative Josephson junction, we provide a symmetry-based general analysis for open systems breaking the one-dimensional translational symmetry. A general effective Lagrangian is constructed based on the Schwinger-Keldysh formalism, which supports the presence of the gapless diffusion mode in the fluctuation spectrum in the thin wall regime. Besides, we also identify a term peculiar to the open system, which possibly leads to the instability in the thick-wall regime or the nonlinear Kardar-Parisi-Zhang coupling in the thin-wall regime although it is absent in the Josephson junction.

  1 citation

• Muon Decay

  W. Fetscher

  SciPost Phys. Proc. 5, 006 (2021) · published 6 September 2021 | Toggle abstract · pdf

  The decay of the muon has been studied at PSI with several precision measurements: The longitudinal polarization PL(E) with the muon decay parameters ξ′, ξ′′, the Time- Reversal Invariance (TRI) conserving transverse polarization PT1(E) with the muon de- cay parameters η, η′′, the TRI violating transverse polarization PT2(E), with α′/A, β′/A and the muon decay asymmetry with Pμξ. The detailed theoretical analysis of all mea- surements of normal and inverse muon decay has led for the first time to a lower limit |g V | > 0.960 ("V − A") and upper limits for nine other possible complex couplings, espe- cially the scalar coupling |g S | < 0.550 which had not been excluded before.

  1 citation

• Electric conductivity in non-Hermitian holography

  Zhuo-Yu Xian, David Rodríguez Fernández, Zhaohui Chen, Yang Liu, René Meyer

  SciPost Phys. 16, 004 (2024) · published 5 January 2024 | Toggle abstract · pdf

  We study the phase structure and charge transport at finite temperature and chemical potential in the non-Hermitian $\mathcal{PT}$-symmetric holographic model of [SciPost Phys. 9, 032 (2020)]. The non-Hermitian $\mathcal{PT}$-symmetric deformation is realized by promoting the parameter of a global U(1) symmetry to a complex number. Depending on the strength of the deformation, we find three phases: stable $\mathcal{PT}$-symmetric phase, unstable $\mathcal{PT}$-symmetric phase, and an unstable $\mathcal{PT}$-symmetry broken phase. In the three phases, the square of the condensate and also the spectral weight of the AC conductivity at zero frequency are, respectively, positive, negative, and complex. We check that the Ferrell-Glover-Tinkham sum rule for the AC conductivity holds in all the three phases. We also investigate a complexified U(1) rotor model with $\mathcal{PT}$-symmetric deformation, derive its phase structure and condensation pattern, and find a zero frequency spectral weight analogous to the holographic model.

  1 citation

• NISQ algorithm for the matrix elements of a generic observable

  Rebecca Erbanni, Kishor Bharti, Leong-Chuan Kwek, Dario Poletti

  SciPost Phys. 15, 180 (2023) · published 30 October 2023 | Toggle abstract · pdf

  The calculation of off-diagonal matrix elements has various applications in fields such as nuclear physics and quantum chemistry. In this paper, we present a noisy intermediate scale quantum algorithm for estimating the diagonal and off-diagonal matrix elements of a generic observable in the energy eigenbasis of a given Hamiltonian without explicitly preparing its eigenstates. By means of numerical simulations we show that this approach finds many of the matrix elements for the one and two qubits cases. Specifically, while in the first case, one can initialize the ansatz parameters over a broad interval, in the latter the optimization landscape can significantly slow down the speed of convergence and one should therefore be careful to restrict the initialization to a smaller range of parameters.

  1 citation

• Vision for QCD to the 2030s and Beyond

  George Sterman

  SciPost Phys. Proc. 8, 156 (2022) · published 14 July 2022 | Toggle abstract · pdf

  In this closing talk, I review some of the lessons we've learned about quantum chromodynamics, and reflect on what we may hope to learn in the coming years.

  1 citation

• Out-of-equilibrium dynamics of the Kitaev model on the Bethe lattice via coupled Heisenberg equations

  Oleksandr Gamayun, Oleg Lychkovskiy

  SciPost Phys. 12, 175 (2022) · published 25 May 2022 | Toggle abstract · pdf

  The Kitaev model on the honeycomb lattice, while being integrable via the spin-fermion mapping, has generally resisted an analytical treatment of the far-from-equilibrium dynamics due to the extensive number of relevant configurations of conserved charges. Here we study a close proxy of this model, the isotropic Kitaev spin-$1/2$ model on the Bethe lattice. Instead of relying on the spin-fermion mapping, we take a straightforward approach of solving Heisenberg equations for a tailored subset of spin operators. The simplest operator in this subset corresponds to the energy contribution of a single bond direction. As an example, we calculate the time-dependent expectation value of this observable for a factorized translation-invariant (or staggered-translation-invariant) initial state with arbitrary initial (staggered) polarization.

  1 citation

• Search for lepton flavour violation with the ATLAS experiment

  Brian Le on behalf of the ATLAS collaboration

  SciPost Phys. Proc. 1, 020 (2019) · published 19 February 2019 | Toggle abstract · pdf

  Lepton flavour violation (LFV) is a striking signature of potential beyond the Standard Model physics. The search for LFV with the ATLAS detector is reported in searches focusing on the decay of the Higgs boson, the Z boson and of a heavy neutral gauge boson, Z', using pp collisions data with a center of mass energy of 8 TeV and 13 TeV.

  1 citation

• Dynamics of parafermionic states in transport measurements

  Ida Egholm Nielsen, Jens Schulenborg, Reinhold Egger, Michele Burrello

  SciPost Phys. 15, 189 (2023) · published 8 November 2023 | Toggle abstract · pdf

  Advances in hybrid fractional quantum Hall (FQH)-superconductor platforms pave the way for realisation of parafermionic modes. We analyse signatures of these non-abelian anyons in transport measurements across devices with $\mathbb{Z}_6$ parafermions (PFs) coupled to an external electrode. Simulating the dynamics of these open systems by a stochastic quantum jump method, we show that a current readout over sufficiently long times constitutes a projective measurement of the fractional charge shared by two PFs. Interaction of these topological modes with the FQH environment, however, may cause poisoning events affecting this degree of freedom which we model by jump operators that describe incoherent coupling of PFs with FQH edge modes. We analyse how this gives rise to a characteristic three-level telegraph noise in the current, constituting a very strong signature of PFs. We discuss also other forms of poisoning and noise caused by interaction with fractional quasiparticles in the bulk of the Hall system. We conclude our work with an analysis of four-PF devices, in particular on how the PF fusion algebra can be observed in electrical transport experiments.

  1 citation

• On the intrinsic pinning and shape of charge-density waves in 1D Peierls systems

  Olivier Cépas, Pascal Quémerais

  SciPost Phys. 14, 051 (2023) · published 28 March 2023 | Toggle abstract · pdf

  Within the standard perturbative approach of Peierls, a charge-density wave is usually assumed to have a cosine shape of weak amplitude. In nonlinear physics, we know that waves can be deformed. What are the effects of the nonlinearities of the electron-lattice models in the physical properties of Peierls systems? We study in details a nonlinear discrete model, introduced by Brazovskii, Dzyaloshinskii and Krichever. First, we recall its exact analytical solution at integrable points. It is a cnoidal wave, with a continuous envelope, which may slide over the lattice potential at no energy cost, following Fröhlich's argument. Second, we show numerically that integrability-breaking terms modify some important physical properties. The envelope function may become discontinuous: electrons form stronger chemical bonds which are local dimers or oligomers. We show that an Aubry transition from the sliding phase to an insulating pinned phase occurs when the model is no longer integrable.

  1 citation