Publications

Order by: publication date number of citations

• The fermionic double smeared null energy condition

  Duarte Fragoso, Lihan Guo

  SciPost Phys. Core 8, 045 (2025) · published 26 June 2025 | Toggle abstract · pdf

  Energy conditions are crucial for understanding why exotic phenomena such as traversable wormholes and closed timelike curves remain elusive. In this paper, we prove the Double Smeared Null Energy Condition (DSNEC) for the fermionic free theory in 4-dimensional flat Minkowski spacetime, extending previous work on the same energy condition for the bosonic case [J. R. Fliss and B. Freivogel, SciPost Phys. 12, 084 (2022); J. R. Fliss et al., SciPost Phys. 14, 024 (2023)] by adapting Fewster and Mistry's method [C. J. Fewster and B. Mistry, Phys. Rev. D 68, 105010 (2003)] to the energy-momentum tensor $T_{++}$. A notable difference from previous works lies in the presence of the $\gamma_0 \gamma_+$ matrix in $T_{++}$, causing a loss of symmetry. This challenge is addressed by making use of its square-root matrix. We provide explicit analytic results for the massless case as well as numerical insights for the mass-dependence of the bound in the case of Gaussian smearing.

• Properties of non-relativistic string theory

  E.A. Bergshoeff, J. Lahnsteiner, L. Romano, C. Simsek

  SciPost Phys. Proc. 4, 001 (2021) · published 13 August 2021 | Toggle abstract · pdf

  We show how Newton-Cartan geometry can be generalized to String Newton-Cartan geometry which is the geometry underlying non-relativistic string theory. Several salient properties of non-relativistic string theory in this geometric background are presented and a discussion of possible research for the future is outlined.

• A sharp transition in quantum chaos and thermodynamics of mass deformed SYK model

  Tomoki Nosaka

  SciPost Phys. Proc. 4, 006 (2021) · published 13 August 2021 | Toggle abstract · pdf

  We review our recent work [arXiv:2009.10759] where we studied the chaotic property of the two coupled Sachdev-Ye-Kitaev systems exhibiting a Hawking-Page like phase transition. By computing the out-of-time-ordered correlator in the large N limit by using the bilocal field formalism, we found that the chaos exponent of this model shows a discontinuous fall-off at the phase transition temperature. Hence in this model the Hawking-Page like transition is correlated with a transition in chaoticity, as expected from the relation between a black hole geometry and the chaotic behavior in the dual field theory.

• Search for upward-going air showers with the fluorescence detector of the Pierre Auger Observatory

  Emanuele De Vito

  SciPost Phys. Proc. 16, 029 (2025) · published 15 July 2025 | Toggle abstract · pdf

  The fluorescence detector (FD) of the Pierre Auger Observatory is sensitive to upward-going air showers for energies above $10^{17}$ eV. Given its operation time and wide field of view, the FD has the potential to support or constrain the recent "anomalous" observations by the ANITA detector, interpreted as upward-going air showers of unexplained nature. We have used 14 years of data collected by the FD to search for upward-going showers using a set of quality selection criteria defined using 10% of the full data sample. To distinguish candidates from false positives, calculate the exposure and obtain the expected background, dedicated simulations for signal (upward-going events) and background (downward-going events) have been performed. Results of the analysis after unblinding the data set are presented. Finally, the exposure and sensitivity for the specific scenario of a signal being ascribed to tau lepton decay are calculated and the corresponding upper limits are shown as a function of primary energy and in different zenith angle ranges.

• Probing $\delta_{CP}$ phase and charged lepton flavour violation with $A_4$ flavor symmetry and deviations to tri-bi-maximal mixing via $z_2 \times z_2$ invariant perturbation in the neutrino sector

  Gayatri Ghosh

  SciPost Phys. Proc. 16, 025 (2025) · published 15 July 2025 | Toggle abstract · pdf

  In this work, a flavour theory of a neutrino mass model based on $A_{4}$ symmetry is considered to explain the phenomenology of CP violation phase and charged lepton flavour violation. The spontaneous symmetry breaking of $A_{4}$ symmetry in this model leads to tribimaximal mixing in the neutrino sector at a leading order. $\mathrm{A} z_{2} × z_{2}$ invariant perturbations in this model is introduced in the neutrino sector which leads to testable predictions of $\theta_{13}$ and $\mathbf{C P}$ violation. We consider an effective theory with an $A_{4} × z_{2} × z_{2}$ symmetry, which after spontaneous symmetry breaking at high scale which is much higher than the electroweak scale leads to charged lepton flavour violation processes once the heavy Majorana neutrino mass degeneracy is lifted either by renormalization group effects or by a soft breaking of the $A_{4}$ symmetry.

• Andreev bound states at boundaries of polarized 2D Fermi superfluids with s-wave pairing and spin-orbit coupling

  Kadin Thompson, Joachim Brand, Ulrich Zuelicke

  SciPost Phys. 14, 115 (2023) · published 16 May 2023 | Toggle abstract · pdf

  A topological superfluid phase characterized by an emergent chiral-p-wave pair potential is expected to form in a two-dimensional Fermi superfluid subject to s-wave pairing, spin-orbit coupling and a large-enough Zeeman splitting. Andreev bound states appear at phase boundaries, including Majorana zero modes whose existence is assured by the bulk-boundary correspondence principle. Here we study the physical properties of these subgap-energy bound states at step-like interfaces using the spin-resolved Bogoliubov-de$\,$Gennes mean-field formalism and assuming small spin-orbit coupling. Extending a recently developed spin-projection technique based on Feshbach partitioning [SciPost Phys. 5, 016 (2018)] combined with the Andreev approximation allows us to obtain remarkably simple analytical expressions for the bound-state energies as well as the majority and minority spin components of their wave functions. Besides the vacuum boundary, where a majority-spin Majorana excitation is encountered, we also consider the boundary between the topological and a nontopological superfluid phase that can appear in a coexistence scenario due to the first-order topological phase transition predicted for this system. At this superfluid-superfluid interface, we find a localized chiral Majorana mode hosted by the minority-spin sector. Our theory further predicts majority-spin subgap-energy bound states similar to those found at a Josephson junction between same-chirality p-wave superfluids. Their presence affects the Majorana mode due to a coupling of minority and majority spin sectors only in the small energy range where their spectra overlap. Our results may inform experimental efforts aimed at realizing and characterizing unconventional Majorana quasiparticles.

• Time-dependent Schwinger boson mean-field theory of supermagnonic propagation in 2D antiferromagnets

  Martijn D. Bouman, Johan H. Mentink

  SciPost Phys. 17, 159 (2024) · published 9 December 2024 | Toggle abstract · pdf

  Understanding the speed limits for the propagation of magnons is of key importance for the development of ultrafast spintronics and magnonics. Recently, it was predicted that in 2D antiferromagnets, spin correlations can propagate faster than the highest magnon velocity. Here we gain deeper understanding of this supermagnonic effect based on time-dependent Schwinger boson mean-field theory. We find that the supermagnonic effect is determined by the competition between propagating magnons and a localized quasi-bound state, which is tunable by lattice coordination and quantum spin value $S$, suggesting a new scenario to enhance magnon propagation.

• Monopole breaking of Chern-Weil symmetries

  Eduardo García-Valdecasas, Matthew Reece, Motoo Suzuki

  SciPost Phys. 18, 162 (2025) · published 20 May 2025 | Toggle abstract · pdf

  Gauge theories in $d$ dimensions with a nontrivial fundamental group admit a $(d-3)$-form magnetic symmetry and a $(d-5)$-form instantonic symmetry. These are examples of Chern-Weil symmetries, with conserved currents built out of the gauge field strength, which can only be explicitly broken through violations of the Bianchi identity. For U(1) gauge theory, it is clear that magnetic monopoles violate not only the $(d-3)$-form magnetic symmetry but also lower-form symmetries like the instantonic symmetry. It is also known that an improved instanton number symmetry current, which is conserved, can be constructed in the case that the magnetic monopole admits a dyonic excitation. We study the generalization to other gauge groups, showing that magnetic monopoles also violate instantonic symmetries for nonabelian groups like PSU($n$), and that dyon modes can restore such symmetries. Furthermore, we show that in many (but not all) examples where a gauge group $G$ is Higgsed to a gauge group $H$, the structure of monopoles and dyons emerging from the Higgsing process explicitly breaks the instantonic symmetries of $H$ to those of $G$. The meaning of explicit breaking of a $(d-5)$-form symmetry is clearest for $d > 4$, but these results also extend to $d = 4$, where the breaking is interpreted as an obstruction to coupling the theory to a background axion field.

• Classification of topological insulators and superconductors with multiple order-two point group symmetries

  Ken Shiozaki

  SciPost Phys. Core 8, 088 (2025) · published 28 November 2025 | Toggle abstract · pdf

  We present a method for computing the classification groups of topological insulators and superconductors in the presence of $\mathbb{Z}_2^{× n}$ point group symmetries, for arbitrary natural numbers $n$. Each symmetry class is characterized by four possible additional symmetry types for each generator of $\mathbb{Z}_2^{× n}$, together with bit values encoding whether pairs of generators commute or anticommute. We show that the classification is fully determined by the number of momentum- and real-space variables flipped by each generator, as well as the number of variables simultaneously flipped by any pair of generators. As a concrete illustration, we provide the complete classification table for the case of $\mathbb{Z}_2^{× 2}$ point group symmetry.

• Exact solution of the Izergin-Korepin Gaudin model with periodic and open boundaries

  Xiaotian Xu, Pei Sun, Xin Zhang, Junpeng Cao, Tao Yang

  SciPost Phys. Core 8, 041 (2025) · published 21 May 2025 | Toggle abstract · pdf

  We study the Izergin-Korepin Gaudin models with both periodic and open integrable boundary conditions, which describe quantum systems exhibiting novel long-range interactions. Using the Bethe Ansatz approach, we derive the eigenvalues of the Gaudin operators and the corresponding Bethe Ansatz equations.