Publications

Order by: publication date number of citations

• Excitations of static isolated fermions in the Higgs phase of gauge Higgs theory

  Kazue Matsuyama, Jeff Greensite

  SciPost Phys. Proc. 6, 012 (2022) · published 31 May 2022 | Toggle abstract · pdf

  A spectrum of localized excitations of isolated static fermions has been discovered in several different gauge Higgs theories. In lattice numerical simulations, we show that the charged elementary particles can have the spectrum of excitations in the Higgs phase of SU(3) gauge Higgs theory, q=2 Abelian Higgs theory, Landau-Ginzburg theory, and in chiral U(1) gauge Higgs theory. Possibly these excited states of the isolated fermions can be observed in ARPES studies of conventional superconductors. Also, we consider that similar kinds of excitations could exist in other gauge Higgs theories, such as the electroweak sector of the Standard Model.

• Quenching a Fermi superfluid across the BEC-BCS crossover

  Moritz Breyer, Daniel Eberz, Andreas Kell, Michael Köhl

  SciPost Phys. 18, 053 (2025) · published 14 February 2025 | Toggle abstract · pdf

  We study the response of a Fermi superfluid to a rapid change of the interaction strength. For a broad range of quench parameters, the order parameter exhibits damped oscillations, however, we also identify quench regimes in which these oscillations are absent. By comparing our data to a numerical model we find that the damping time constants are explainable by a dephasing in a local density approximation, however, the oscillation frequencies, while being comparable to the superconducting order parameter, display in detail significant differences to the integrable BCS (Bardeen-Cooper-Schrieffer) model.

• Exact solution for two $\delta$-interacting bosons on a ring in the presence of a $\delta$-barrier: Asymmetric Bethe Ansatz for spatially odd states

  Maxim Olshanii, Mathias Albert, Gianni Aupetit-Diallo, Patrizia Vignolo, Steven G. Jackson

  SciPost Phys. Core 8, 083 (2025) · published 12 November 2025 | Toggle abstract · pdf

  In this article, we apply the recently proposed Asymmetric Bethe Ansatz method to the problem of two one-dimensional, short-range-interacting bosons on a ring in the presence of a $\delta$-function barrier. Only half of the Hilbert space—namely, the two-body states that are odd under point inversion about the position of the barrier—is accessible to this method. The other half is presumably non-integrable. We consider benchmarking the recently proposed $1/g$ expansion about the hard-core boson point [D. Sen, Int. J. Mod. Phys. A 14, 1789 (1999); A. G. Volosniev et al., Nat. Commun. 5, 5300 (2014)] as one application of our results. Additionally, we find that when the $\delta$-barrier is converted to a $\delta$-well with strength equal to that of the particle-particle interaction, the system exhibits the spectrum of its non-interacting counterpart while its eigenstates display features of a strongly interacting system. We discuss this phenomenon in the "Summary and Future Research" section of our paper.

• Quantum spin nematic liquid in the low-dimensional anisotropic magnets -S=1/2 delta spin chain with the anisotropic ferromagnetic interaction in magnetic field-

  Toru Sakai, Rito Furuchi, Hiroki Nakano, Kiyomi Okamoto

  SciPost Phys. Proc. 11, 001 (2023) · published 5 June 2023 | Toggle abstract · pdf

  The magnetization process of the $S=1/2$ delta chain with the anisotropic ferromagnetic interaction is investigated using the numerical diagonalization of finite-size clusters. It is found that the spin nematic liquid phase appears in higher magnetization region, as well as the SDW liquid one in lower region.

• Generalized lattices, conformal manifolds, and symmetries

  Shlomo S. Razamat, Michal Shemesh, Aelly Zeltzer

  SciPost Phys. 19, 069 (2025) · published 24 September 2025 | Toggle abstract · pdf

  We consider supersymmetric conformal quantum field theories (SCFTs) with degrees of freedom labeled by lattice data. We will assume that in terms of the corresponding lattice the interactions are nearest neighbor and exactly marginal. For example, one can construct such theories by coupling many copies of a single SCFT with exactly marginal deformations. In particular, we discuss the interplay between conformal manifolds of such theories and their global, on-site and lattice, symmetries. We show that one can interpret certain current non-conservation equations for symmetries broken by the interactions as conservation equations including the lattice directions. Moreover, we discuss a class of exactly marginal deformations which are labeled by lattice holonomies that are topological on the lattice. We discuss concrete examples of such constructions and comment on their relevance to compactifications of SCFTs.

• Identifying biases of the Majorana scattering invariant

  Isidora Araya Day, Antonio L. R. Manesco, Michael Wimmer, Anton R. Akhmerov

  SciPost Phys. Core 8, 047 (2025) · published 4 July 2025 | Toggle abstract · pdf

  The easily accessible experimental signatures of Majorana modes are ambiguous and only probe topology indirectly: for example, quasi-Majorana states mimic most properties of Majoranas. Establishing a correspondence between an experiment and a theoretical model known to be topological resolves this ambiguity. Here we demonstrate that already theoretically determining whether a finite system is topological is by itself ambiguous. In particular, we show that the scattering topological invariant—a probe of topology most closely related to transport signatures of Majoranas—has multiple biases in finite systems. For example, we identify that quasi-Majorana states also mimic the scattering invariant of Majorana zero modes in intermediate-sized systems. We expect that the bias due to finite size effects is universal, and advocate that the analysis of topology in finite systems should be accompanied by a comparison with the thermodynamic limit. Our results are directly relevant to the applications of the topological gap protocol.

• Introduction to string theory

  Carlo Maccaferri, Fabio Marino, Beniamino Valsesia

  SciPost Phys. Lect. Notes 90 (2025) · published 29 January 2025 | Toggle abstract · pdf

  These are lecture notes of the introductory String Theory course held by one of the authors for the master program of Theoretical Physics at Turin University. The world-sheet approach to String Theory is pedagogically introduced in the framework of the bosonic string and of the superstring.

• Electromagnetic multipole expansions and the logarithmic soft photon theorem

  Geoffrey Compère, Dima Fontaine, Kevin Nguyen

  SciPost Phys. Core 8, 066 (2025) · published 10 October 2025 | Toggle abstract · pdf

  We study the general structure of the electromagnetic field in the vicinity of spatial infinity. Starting from the general solution of the sourced Maxwell equations written in terms of multipole moments as obtained by Iyer and Damour, we derive the expansion of the electromagnetic field perturbatively in the electromagnetic coupling. At leading order, where the effect of long-range Coulombic interactions between charged particles is neglected, we discover infinite sets of antipodal matching relations satisfied by the electromagnetic field, which extend and sometimes correct previously known relations. At next-to-leading order, electromagnetic tails resulting from these Coulombic interactions appear, which affect the antipodal matching relations beyond those equivalent to the leading soft photon theorem. Moreover, new antipodal matching relations arise, which we use to re-derive the classical logarithmic soft photon theorem of Sahoo and Sen. Our analysis largely builds upon that of Campiglia and Laddha, although it invalidates the antipodal matching relation which they originally used in their derivation. The antipodal matching relations and the proof of the classical logarithmic soft photon theorem agree with an earlier analysis of Bhatkar, which we generalize using other methods.

• Interaction and collision of skyrmions in chiral antiferromagnets

  George Theodorou, Bruno Barton-Singer, Stavros Komineas

  SciPost Phys. 18, 037 (2025) · published 30 January 2025 | Toggle abstract · pdf

  Skyrmions in an antiferromagnet can travel as solitary waves in stark contrast to the situation in ferromagnets. Traveling skyrmion solutions have been found numerically in chiral antiferromagnets. We study head-on collision events between two skyrmions. We find that the result of the collision depends on the initial velocity of the skyrmions. For small velocities, the skyrmions shrink as they approach, then bounce back and eventually acquire almost their initial speed. For larger velocities, the skyrmions approach each other and shrink until they become singular points at some finite separation and are eventually annihilated. Considering skyrmion energetics, we can determine the regimes of the different dynamical behaviors. Using a collective co-ordinate approach, we reproduce the dynamics of the collisions including the variation of the size of the skyrmions and collapse above a critical velocity.

• Muons in showers with energy $\boldsymbol{E_{0} \geq}$ 5 EeV and QGSjetII-04 and EPOS LHC models of hadronic interactions. Is there a muon deficit in the models?

  Stanislav Knurenko, Igor Petrov

  SciPost Phys. Proc. 13, 032 (2023) · published 29 September 2023 | Toggle abstract · pdf

  The paper presents data on the muon component with a threshold $\varepsilon_{thr} ≥$ 1 GeV. Air showers were registered at the Yakutsk array during almost 50 years of continuous air shower observations. The characteristics of muons are compared with calculations of QGSjetII-04 and EPOS LHC models for a proton and an iron nucleus. There is a muon deficit in the models, at energies greater than 5 EeV. To make an agreement between experimental data and simulations on muons, further tuning of the models is required.