Publications

Order by: publication date number of citations

• Integrability for Feynman integrals

  Florian Loebbert

  SciPost Phys. Proc. 14, 008 (2023) · published 23 November 2023 | Toggle abstract · pdf

  We give a brief overview of the Yangian symmetry of Feynman integrals. After a short introduction to the Yangian and integrability, we motivate the emergence of integrable structures for Feynman integrals via the fishnet limit of AdS/CFT. We discuss the resulting Yangian differential equations for massless fishnets in four dimensions as well as generalizations to massive propagators and generic dimensions. We also comment on the relation to momentum space conformal symmetry and on examples in dimensional regularization. Finally we sketch the recent application to fishnet integrals in two spacetime dimensions and the curious identification of Yangian invariants with period integrals of Calabi-Yau geometries.

  3 citations

• Quenching Factor estimation of Na recoils in NaI(Tl) crystals using a low-energy pulsed neutron beam measurement

  Mukund Raghunath Bharadwaj, G. Angloher, P. S. Barbeau, I. Dafinei, N. Di Marco, L. Einfalt, F. Ferroni, S. Fichtinger, A. Filipponi , T. Frank , M. Friedl , A. Fuss, Z. Ge , S. Hedges, M. Heikinheimo, K. Huitu, M. Kellermann, R. Maji, M. Mancuso, L. Pagnanini, F. Petricca, S. Pirro, F. Pröbst , G. Profeta, A. Puiu, F. Reindl , K. Schäffner, J. Schieck, D. Schmiedmayer , C. Schwertner , M. Stahlberg , A. Stendahl, M. Stukel , F. Wagner, S. Yue, V. Zema, Y. Zhu

  SciPost Phys. Proc. 12, 028 (2023) · published 4 July 2023 | Toggle abstract · pdf

  NaI(Tl) based scintillation detectors have become a staple in the field of direct dark matter searches, with the DAMA-LIBRA experiment being the standout for its reported observation of an annually modulating WIMP-like signal which is in direct contrast with other results. In order to accurately calibrate the energies of WIMP-induced nuclear recoil signals, precise measurements of the quenching factor of the NaI crystals are essential for each of these experiments, as it is well established that electron recoils and nuclear recoils have dissimilar scintillation light yields. In this contribution, we present first preliminary results of an ongoing systematic study that has been carried out by the COSINUS collaboration and Duke University to measure the quenching factor of Na recoils. Five ultra-pure NaI crystals, manufactured by the Shanghai Institute for Ceramics, each of which have varying Tl dopant concentrations, were irradiated with a mono-energetic neutron beam at the Triangle Universities National Laboratory, North Carolina, USA to extract the quenching factor values in the low recoil energies of 1-30keV$_{nr}$.

  3 citations

• Anatomy of the eigenstates distribution: A quest for a genuine multifractality

  Anton Kutlin, Ivan M. Khaymovich

  SciPost Phys. 16, 008 (2024) · published 9 January 2024 | Toggle abstract · pdf

  Motivated by a series of recent works, an interest in multifractal phases has risen as they are believed to be present in the Many-Body Localized (MBL) phase and are of high demand in quantum annealing and machine learning. Inspired by the success of the Rosenzweig-Porter (RP) model with Gaussian-distributed hopping elements, several RP-like ensembles with the fat-tailed distributed hopping terms have been proposed, with claims that they host the desired multifractal phase. In the present work, we develop a general (graphical) approach allowing a self-consistent analytical calculation of fractal dimensions for a generic RP model and investigate what features of the RP Hamiltonians can be responsible for the multifractal phase emergence. We conclude that the only feature contributing to a genuine multifractality is the on-site energies' distribution, meaning that no random matrix model with a statistically homogeneous distribution of diagonal disorder and uncorrelated off-diagonal terms can host a multifractal phase.

  3 citations

• Emergence of generalized hydrodynamics in the non-local Luttinger model

  Per Moosavi

  SciPost Phys. 9, 037 (2020) · published 11 September 2020 | Toggle abstract · pdf

  We propose the Luttinger model with finite-range interactions as a simple tractable example in 1+1 dimensions to analytically study the emergence of Euler-scale hydrodynamics in a quantum many-body system. This non-local Luttinger model is an exactly solvable quantum field theory somewhere between conformal and Bethe-ansatz integrable models. Applying the recent proposal of generalized hydrodynamics, we show that the model allows for fully explicit yet non-trivial solutions of the resulting Euler-scale hydrodynamic equations. Comparing with exact analytical non-equilibrium results valid at all time and length scales, we show perfect agreement at the Euler scale when the interactions are short range. A formal proof of the emergence of generalized hydrodynamics in the non-local Luttinger model is also given, and effects of long-range interactions are briefly discussed.

  3 citations

• Nonreciprocal superconducting transport and the spin Hall effect in gyrotropic structures

  Tim Kokkeler, Ilya Tokatly, F. Sebastian Bergeret

  SciPost Phys. 16, 055 (2024) · published 26 February 2024 | Toggle abstract · pdf

  The search for superconducting systems exhibiting nonreciprocal transport and, specifically, the diode effect, has proliferated in recent years. This trend has encompassed a wide variety of systems, including planar hybrid structures, asymmetric SQUIDs, and certain noncentrosymmetric superconductors. A common feature of such systems is a gyrotropic symmetry, realized on different scales and characterized by a polar vector. Alongside time-reversal symmetry breaking, the presence of a polar axis allows for magnetoelectric effects, which, when combined with proximity-induced superconductivity, results in spontaneous non-dissipative currents that underpin the superconducting diode effect. With this symmetry established, we present a comprehensive theoretical study of transport in a lateral Josephson junction composed of a normal metal supporting the spin Hall effect, and attached to a ferromagnetic insulator. Due to the presence of the latter, magnetoelectric effects arise without requiring external magnetic fields. We determine the dependence of the anomalous currents on the spin relaxation length and the transport parameters commonly used in spintronics to characterize the interface between the metal and the ferromagnetic insulator. Therefore, our theory naturally unifies nonreciprocal transport in superconducting systems with classical spintronic effects, such as the spin Hall effect, spin galvanic effect, and spin Hall magnetoresistance. We propose an experiment involving measurements of magnetoresistance in the normal state and nonreciprocal transport in the superconducting state. Such experiment would, on the one hand, allow for determining the parameters of the model and thus verifying with a greater precision the theories of magnetoelectric effects in normal systems. On the other hand, it would contribute to a deeper understanding of the underlying microscopic origins that determine these parameters.

  3 citations

• Confined vs. extended Dirac surface states in topological crystalline insulator nanowires

  Roni Majlin Skiff, Fernando de Juan, Raquel Queiroz, Subramanian Mathimalar, Haim Beidenkopf, Roni Ilan

  SciPost Phys. Core 6, 011 (2023) · published 13 March 2023 | Toggle abstract · pdf

  Confining two dimensional Dirac fermions on the surface of topological insulators has remained an outstanding conceptual challenge. Here we show that Dirac fermion confinement is achievable in topological crystalline insulators (TCI), which host multiple surface Dirac cones depending on the surface termination and the symmetries it preserves. This confinement is most dramatically reflected in the flux dependence of these Dirac states in the nanowire geometry, where different facets connect to form a closed surface. Using SnTe as a case study, we show how wires with all four facets of the $\langle 100 \rangle$ type display novel Aharonov-Bohm oscillations, while nanowires with the four facets of the $\langle 110 \rangle$ type such oscillations are absent due to strong confinement of the Dirac states to each facet separately. Our results place TCI nanowires as a versatile platform for confining and manipulating Dirac surface states.

  3 citations

• Quasi-localized vibrational modes, boson peak and sound attenuation in model mass-spring networks

  Shivam Mahajan, Massimo Pica Ciamarra

  SciPost Phys. 15, 069 (2023) · published 23 August 2023 | Toggle abstract · pdf

  We introduce an algorithm that constructs disordered mass-spring networks whose elastic properties mimic that of glasses by tuning the fluctuations of the local elastic properties, keeping fixed connectivity and controlling the prestress. In two dimensions, the algorithm reproduces the dependence of glasses' vibrational properties, such as quasi-localised vibrational modes and Boson peak, on the degree of stability. The sound attenuation displays Rayleigh scattering and disorder-broadening regimes at different frequencies, and the attenuation rate decreases with increased stability. Our results establish a strong connection between the vibrational features of disordered solids and the fluctuations of the local elastic properties and provide a new approach to investigating glasses' vibrational anomalies.

  3 citations

• A symbol and coaction for higher-loop sunrise integrals

  Andreas Forum, Matt von Hippel

  SciPost Phys. Core 6, 050 (2023) · published 12 July 2023 | Toggle abstract · pdf

  We construct a symbol and coaction for the $l$-loop sunrise family of integrals, both for equal-mass and generic-mass cases. These constitute the first concrete examples of symbols and coactions for integrals involving Calabi-Yau threefolds and higher. In order to achieve a symbol of finite length, we recast the differential equations satisfied by these integrals in a unipotent form. We augment the integrals in a natural way by including ratios of maximal cuts $\tau_i$. We discuss the relationship of this construction to constructions of symbols and coactions for multiple polylogarithms and elliptic multiple polylogarithms, and its connection to notions of transcendental weight.

  3 citations

• Spin-polarized two-dimensional electron/hole gases on LiCoO$_2$ layers.

  Santosh Kumar Radha, Walter R. L. Lambrecht

  SciPost Phys. 10, 057 (2021) · published 8 March 2021 | Toggle abstract · pdf

  First-principles calculations show the formation of a 2D spin polarized electron (hole) gas on the Li (CoO$_2$) terminated surfaces of finite slabs down to a monolayer, in remarkable contrast with the bulk band structure, which is stabilized by Li donating its electron to the CoO$_2$ layer forming a Co-$d-t_{2g}^6$ insulator. By mapping the first-principles computational results to a minimal tight-binding models corresponding to a non-chiral 3D generalization of the quadripartite Su-Schrieffer-Heeger (SSH4) model and symmetry analysis, we show that these surface states have topological origin.

  3 citations

• Theory Status - Puzzles in B Meson Decays and LFU?

  Svjetlana Fajfer

  SciPost Phys. Proc. 1, 010 (2019) · published 18 February 2019 | Toggle abstract · pdf

  Currently B meson puzzles motivate many studies of New Physics due to the observed deviations from the Standard Model predictions. There are two B meson puzzles, RD(∗) and RK(∗). The first one denotes the deviations in the decays driven by the charged current in the ratio of the decay widths for B → D(∗)τν and B → D(∗)μν, while the second one is related to the ratio of the decay widths for B → K (∗) μ+ μ− and B → K (∗) e+ e− transition. Also, the measured muon anomalous magnetic moment differs from the SM predictions. Usually, the effective Lagrangian approach containing New Physics effects is used to analyse RD(∗) and RK(∗). Among many models of New Physics, various leptoquark models are suggested to resolve both B meson anomalies. If New Physics is confirmed in B decays a number of processes at low and high energies should confirm its presence.

  3 citations