Publications

Order by: publication date number of citations

• Probing quantum entanglement and collectivity effects in e+p collisions at HERA H1

  Chuan Sun

  SciPost Phys. Proc. 8, 147 (2022) · published 14 July 2022 | Toggle abstract · pdf

  Charged particle multiplicity spectra are measured at HERA H1 in DIS process at 319 GeV. The hadron entropy determined from the multiplicity spectra is compared to the gluon entropy predicted from a quantum-entanglement model. On the other hand, observed collective behaviours in high multiplicity pA, pp and ultra-peripheral PbPb collisions at RHIC and LHC motivate a study in ep collisions. Two- and multi-particle correlations are studied in DIS, as well as photoproduction events with collision energy <Wγp>~270 GeV.

• Lieb-Schultz-Mattis anomalies as obstructions to gauging (non-on-site) symmetries

  Sahand Seifnashri

  SciPost Phys. 16, 098 (2024) · published 9 April 2024 | Toggle abstract · pdf

  We study 't Hooft anomalies of global symmetries in 1+1d lattice Hamiltonian systems. We consider anomalies in internal and lattice translation symmetries. We derive a microscopic formula for the "anomaly cocycle" using topological defects implementing twisted boundary conditions. The anomaly takes value in the cohomology group $H^3(G,U(1)) × H^2(G,U(1))$. The first factor captures the anomaly in the internal symmetry group $G$, and the second factor corresponds to a generalized Lieb-Schultz-Mattis anomaly involving $G$ and lattice translation. We present a systematic procedure to gauge internal symmetries (that may not act on-site) on the lattice. We show that the anomaly cocycle is the obstruction to gauging the internal symmetry while preserving the lattice translation symmetry. As an application, we construct anomaly-free chiral lattice gauge theories. We demonstrate a one-to-one correspondence between (locality-preserving) symmetry operators and topological defects, which is essential for the results we prove. We also discuss the generalization to fermionic theories. Finally, we construct non-invertible lattice translation symmetries by gauging internal symmetries with a Lieb-Schultz-Mattis anomaly.

• High field magnetism of the triangular lattice antiferromagnet CsFeCl$_3$ under high pressure

  Katsuki Nihongi, Takanori Kida, Yasuo Narumi, Nobuyuki Kurita, Hidekazu Tanaka, Yoshiya Uwatoko, Koichi Kindo, Masayuki Hagiwara

  SciPost Phys. Proc. 11, 012 (2023) · published 5 June 2023 | Toggle abstract · pdf

  Magnetization measurements of the triangular lattice antiferromagnet CsFeCl$_{3}$ at 1.4 K for $H \parallel c$ were performed in pulsed high magnetic fields of up to 51 T under high pressures of up to 0.80 GPa. At ambient pressure, the magnetization below $H_{\rm c1}$ = 4 T is small, and then it changes steeply between $H_{\rm c1}$ and $H_{\rm c2}$ = 12 T, followed by a gradual increase in magnetization up to $H_{\rm m}$ = 33 T where a two-step metamagnetic transition occurs. With increasing pressure, the $H_{\rm c1}$ and $H_{\rm m}$ shifted to the low-field side, while the $H_{\rm c2}$ shifted to the opposite side. The change in $H_{\rm m}$ may depend on the difference in the single-ion anisotropies on pressure in the lowest $J$ = 1 and the excited $J$ = 2 states.

• Photoproduction of diffractive dijets in Pythia 8

  Ilkka Helenius

  SciPost Phys. Proc. 8, 145 (2022) · published 14 July 2022 | Toggle abstract · pdf

  The new framework for the simulations of hard diffractive events in photoproduction within Pythia 8 is presented. The model, originally introduced for proton-proton collisions, applies the dynamical rapidity gap survival probability based on the multiparton interaction model in Pythia. These additional interactions provide a natural explanation for the observed factorization-breaking effects in hard diffraction by filling up the rapidity gaps used to classify the events of diffractive origin. The generated cross sections are well in line with the existing data from HERA experiments and predictions for the future electron-ion collider are presented. In addition, also predictions for ultra-peripheral collisions at the LHC have been calculated where the factorization-breaking effects are found to be more pronounced.

• Hidden symmetry of Bogoliubov de Gennes quasi-particle eigenstates and universal relations in flat band superconducting bipartite lattices

  Georges Bouzerar, Maxime Thumin

  SciPost Phys. Core 7, 018 (2024) · published 9 April 2024 | Toggle abstract · pdf

  Unconventional flat band (FB) superconductivity, as observed in van der Waals heterostructures, could open promising avenues towards high-T$_c$ materials. In FBs, pairings and superfluid weight scale linearly with the interaction parameter, such an unusual behaviour justifies and encourages strategies to promote FB engineering. Bipartite lattices (BLs) which naturally host FBs could be particularly interesting candidates. Within Bogoliubov de Gennes theory and in the framework of the attractive Hubbard model in BLs, a hidden symmetry of the quasi-particle eigenstates is revealed. As a consequence, we demonstrate universal relations for the pairings and the superfluid weight that are independent of the characteristics of the hopping term. Remarkably, it is shown that these general properties are insensitive to disorder as long as the bipartite character is protected.

• Fluctuations and Selection Bias in 5 and 13 TeV p-p Collisions: Where are the jets?

  Thomas A. Trainor

  SciPost Phys. Proc. 10, 003 (2022) · published 10 August 2022 | Toggle abstract · pdf

  The ALICE collaboration recently reported high-statistics $\bf p_t$ spectra from 5 TeV and 13 TeV p-p collisions with intent to determine the role of jets in high-multiplicity collisions. In the present study a two-component (soft + hard) model (TCM) of hadron production in p-p collisions is applied to ALICE $\bf p_t$ spectra. As in previous TCM studies of A-B collision systems jet and nonjet contributions to $\bf p_t$ spectra are accurately separated over the entire $\bf p_t$ acceptance. The statistical significance of data-model differences is established leading to insights concerning selection bias and spectrum model validity.

• Transverse Momentum Dependent and collinear densities based on Parton Branching method

  S. Taheri Monfared, H. Jung

  SciPost Phys. Proc. 10, 008 (2022) · published 10 August 2022 | Toggle abstract · pdf

  We review the current status of collinear and Transverse Momentum Dependent densities based on the Parton Branching method. We investigate the performance of the PB-TMD evolution as well as PB-TMD parton shower with different configurations of the hard process in the four- and five-flavour schemes.

• Mechanically-driven stem cell separation in tissues caused by proliferating daughter cells

  Johannes C. Krämer, Edouard Hannezo, Gerhard Gompper, Jens Elgeti

  SciPost Phys. 16, 097 (2024) · published 8 April 2024 | Toggle abstract · pdf

  The homeostasis of epithelial tissue relies on a balance between the self-renewal of stem cell populations, cellular differentiation, and loss. Although this balance needs to be tightly regulated to avoid pathologies, such as tumor growth, the regulatory mechanisms, both cell-intrinsic and collective, which ensure tissue steady-state are still poorly understood. Here, we develop a computational model that incorporates basic assumptions of stem cell renewal into distinct populations and mechanical interactions between cells. We find that the model generates unexpected dynamic features: stem cells repel each other in the bulk tissue and are thus found rather isolated, as in a number of in vivo contexts. By mapping the system onto a gas of passive Brownian particles with effective repulsive interactions, that arise from the generated flows of differentiated cells, we show that we can quantitatively describe such stem cell distribution in tissues. The interaction potential between a pair of stem cells decays exponentially with a characteristic length that spans several cell sizes, corresponding to the volume of cells generated per stem cell division. Our findings may help understanding the dynamics of normal and cancerous epithelial tissues.

• Quasiparticle disintegration in fermionic superfluids

  Senne Van Loon, Jacques Tempere, Hadrien Kurkjian

  SciPost Phys. 12, 108 (2022) · published 28 March 2022 | Toggle abstract · pdf

  We study the fermionic quasiparticle spectrum in a zero-temperature superfluid Fermi gas, and in particular how it is modified by different disintegration processes. On top of the disintegration by emission of a collective boson ($1\to2$, subject of a previous study, PRL 124, 073404), we consider here disintegration events where three quasiparticles are emitted ($1\to3$). We show that both disintegration processes are described by a $t$-matrix self-energy (as well as some highly off-resonant vacuum processes), and we characterize the associated disintegration continua. At strong coupling, we show that the quasiparticle spectrum is heavily distorted near the $1\to3$ disintegration threshold. Near the dispersion minimum, where the quasiparticles remain well-defined, the main effect of the off-shell disintegration processes is to shift the location of the minimum by a value that corresponds to the Hartree shift in the BCS limit. With our approximation of the self-energy, the correction to the energy gap with respect to the mean-field result however remains small, in contrast with experimental measurements.

• Vertical and lateral manipulation of single Cs atoms on the semiconductor InAs(111)A

  Rian A. M. Ligthart, Cristophe Coinon, Ludovic Desplanque, Xavier Wallart, Ingmar Swart

  SciPost Phys. 16, 096 (2024) · published 5 April 2024 | Toggle abstract · pdf

  The tip of the scanning tunneling microscope can be used to position atoms and molecules on surfaces with atomic scale precision. Here, we report the controlled vertical and lateral manipulation of single Cs atoms on the InAs(111)A surface. The Cs adatom adsorbs on the In-vacancy site of the InAs(111)A—(2x2) surface reconstruction. Lateral manipulation is possible in all directions over the surface, not just along high-symmetry directions. Both pushing and pulling modes were observed in the height profile of the tip. We assembled two artificial structures, demonstrating the reliability of the manipulation procedures. Structures remained intact to a temperature of at least 44 K.