Publications

Order by: publication date number of citations

• Josephson current through the SYK model

  Luca Dell'Anna

  SciPost Phys. 17, 120 (2024) · published 24 October 2024 | Toggle abstract · pdf

  We calculate the equilibrium Josephson current through a disordered interacting quantum dot described by a Sachdev-Ye-Kitaev model fully contacted by two BCS superconductors, such that all modes of the dot contribute to the coupling, which encodes hopping and spin-flip processes. We show that, at zero temperature and at the conformal limit, i.e. in the strong interacting limit, the Josephson current is suppressed by $U$, the strength of the interaction, as ln(U)/U and becomes universal, namely it gets independent on the superconducting gap. At finite temperature, instead, it depends on the ratio between the gap and the temperature. A proximity effect exists but the self-energy corrections induced by the coupling with the superconducting leads seem subleading as compared to the interaction self-energy and the tunneling matrix for large number of particles. Finally we compare the results of the original four-fermion model with those obtained considering zero interaction, two-fermions and a generalized $q$-fermion model.

• Towards two- and three-loop QCD corrections to the width difference in $B_s-\bar{B}_s$ mixing

  Vladyslav Shtabovenko

  SciPost Phys. Proc. 7, 025 (2022) · published 21 June 2022 | Toggle abstract · pdf

  In this work we address the issue of large perturbative uncertainties in the theory prediction for $\Delta \Gamma_s$, the width difference in the $B^0_s - \bar{B}^0_s$ mixing process. To this aim we complete important steps towards the full analytic result for the previously unknown Wilson coefficients from the matching between $|\Delta B|=1$ and $|\Delta B|=2$ effective Hamiltonians at next-to-next-leading order (NNLO) in the strong coupling constant. We provide a thorough discussion of technical and conceptual difficulties behind this computation and give an outlook regarding the availability of the new NNLO theory prediction for $\Delta \Gamma_s$.

• Topological dipole insulator

  Ho Tat Lam, Jung Hoon Han, Yizhi You

  SciPost Phys. 17, 137 (2024) · published 18 November 2024 | Toggle abstract · pdf

  We expand the concept of two-dimensional topological insulators to encompass a novel category known as topological dipole insulators (TDIs), characterized by conserved dipole moments along the $x$-direction in addition to charge conservation. By generalizing Laughlin's flux insertion argument, we prove a no-go theorem and predict possible edge patterns and anomalies in a TDI with both charge $U^e(1)$ and dipole $U^d(1)$ symmetries. The edge of a TDI is characterized as a quadrupolar channel that displays a dipole $U^d(1)$ anomaly. A quantized amount of dipole gets transferred between the edges under the dipolar flux insertion, manifesting as 'quantized quadrupolar Hall effect' in TDIs. A microscopic coupled-wire Hamiltonian realizing the TDI is constructed by introducing a mutually commuting pair-hopping terms between wires to gap out all the bulk modes while preserving the dipole moment. The effective action at the quadrupolar edge can be derived from the wire model, with the corresponding bulk dipolar Chern-Simons response theory delineating the topological electromagnetic response in TDIs. Finally, we enrich our exploration of topological dipole insulators to the spinful case and construct a dipolar version of the quantum spin Hall effect, whose boundary evidences a mixed anomaly between spin and dipole symmetry. Effective bulk and the edge action for the dipolar quantum spin Hall insulator are constructed as well.

• Sustaining a temperature difference

  Matteo Polettini, Alberto Garilli

  SciPost Phys. 9, 030 (2020) · published 2 September 2020 | Toggle abstract · pdf

  We derive an expression for the minimal rate of entropy that sustains two reservoirs at different temperatures $T_0$ and $T_\ell$. The law displays an intuitive $\ell^{-1}$ dependency on the relative distance and a characterisic $\log^2 (T_\ell/T_0)$ dependency on the boundary temperatures. First we give a back-of-envelope argument based on the Fourier Law (FL) of conduction, showing that the least-dissipation profile is exponential. Then we revisit a model of a chain of oscillators, each coupled to a heat reservoir. In the limit of large damping we reobtain the exponential and squared-log behaviors, providing a self-consistent derivation of the FL. For small damping "equipartition frustration" leads to a well-known balistic behaviour, whose incompatibility with the FL posed a long-time challenge.

• Comparison of $pp$ and $p \bar{p}$ differential elastic cross sections and observation of the exchange of a Colorless $C$-odd gluonic compound

  C. Royon

  SciPost Phys. Proc. 10, 023 (2022) · published 11 August 2022 | Toggle abstract · pdf

  We describe the discovery of the colorless $C$-odd gluonic compound, the odderon, by the D0 and TOTEM Collaborations by comparing elastic differential cross sections measured in $pp$ and $p \bar{p}$ interactions at high energies.

• Constraints on the spectrum of field theories with non-integer $O(N)$ symmetry from quantum evanescence

  Weiguang Cao, Xiaochuan Lu, Tom Melia

  SciPost Phys. Core 7, 055 (2024) · published 14 August 2024 | Toggle abstract · pdf

  We identify constraints in the energy spectra of quantum theories that have a global $O(N)$ symmetry, where $N$ is treated as a continuous parameter. We point out that a class of evanescent states fall out of the spectrum at integer values of $N$ in pairs, via an annihilation mechanism. This forces the energies of the states in such a pair to approach equality as $N$ approaches a certain integer, with both states disappearing at precisely integer $N$ and the point of would-be degeneracy. These constraints occur between different irreducible representations of the analytic continuation of $O(N)$ and hold non-perturbatively. We give examples in the spectra of the critical $O(N)$ model.

• Top quark pair and single top cross sections and ttX (CMS)

  Ravindra K Verma

  SciPost Phys. Proc. 8, 108 (2022) · published 13 July 2022 | Toggle abstract · pdf

  Latest results on inclusive and differential top quark pair and single top quark production cross sections are presented using proton-proton collision data collected by the CMS experiment. The differential cross sections are measured as a function of various kinematic observables of the top quarks and the jets and leptons of the event final state. The results are confronted with precise theory calculations and used to constrain Standard Model parameters. Measurements are performed also with high pT top quarks, i.e., in boosted regimes.

• Cosmic censorship of trans-Planckian field ranges in gravitational collapse

  Himanshu Chaudhary, Chethan Krishnan

  SciPost Phys. 9, 036 (2020) · published 11 September 2020 | Toggle abstract · pdf

  A classical solution where the (scalar) field value moves by an ${\cal O}(1)$ range in Planck units is believed to signal the breakdown of Effective Field Theory (EFT). One heuristic argument for this is that such a field will have enough energy to be inside its own Schwarzschild radius, and will result in collapse. In this paper, we consider an inverse problem: what kind of field ranges arise during the gravitational collapse of a classical field? Despite the fact that collapse has been studied for almost a hundred years, most of the discussion is phrased in terms of fluid stress tensors, and not fields. An exception is the scalar collapse made famous by Choptuik. We re-consider Choptuik-like systems, but with the emphasis now on the evolution of the scalar. We give strong evidence that generic spherically symmetric collapse of a massless scalar field leads to super-Planckian field movement. But we also note that in every such supercritical collapse scenario, the large field range is hidden behind an apparent horizon. We also discuss how the familiar perfect fluid models for collapse like Oppenheimer-Snyder and Vaidya should be viewed in light of our results.

• Effective field theory descriptions of Higgs boson pair production

  Lina Alasfar, Luca Cadamuro, Christina Dimitriadi, Arnaud Ferrari, Ramona Gröber, Gudrun Heinrich, Tom Ingebretsen Carlson, Jannis Lang, Serhat Ördek, Laura Pereira Sánchez, Ludovic Scyboz, Jörgen Sjölin

  SciPost Phys. Comm. Rep. 2 (2024) · published 16 October 2024 | Toggle abstract · pdf

  Higgs boson pair production is traditionally considered to be of particular interest for a measurement of the trilinear Higgs self-coupling. Yet it can offer insights into other couplings as well, since -- in an effective field theory (EFT) parameterisation of potential new physics -- both the production cross section and kinematical properties of the Higgs boson pair depend on various other Wilson coefficients of EFT operators. This note summarises the ongoing efforts related to the development of EFT tools for Higgs boson pair production in gluon fusion, and provides recommendations for the use of distinct EFT parameterisations in the Higgs boson pair production process. This document also outlines where further efforts are needed and provides a detailed analysis of theoretical uncertainties. Additionally, benchmark scenarios are updated. We also re-derive a parameterisation of the next-to-leading order (NLO) QCD corrections in terms of the EFT Wilson coefficients both for the total cross section and the distribution in the invariant mass of the Higgs boson pair, providing for the first time also the covariance matrix. A reweighting procedure making use of the newly derived coefficients is validated, which can be used to significantly speed up experimental analyses.

• Precision physics with the proton spectrometer and diffractive physics measurements from CMS

  Cristophe Royon

  SciPost Phys. Proc. 15, 030 (2024) · published 3 April 2024 | Toggle abstract · pdf

  We describe recent results from CMS and TOTEM on hard diffraction, diffractive jets and jet gap jet events. We also give the first sensitivities and limits on quartic anomalous couplings and axion-like particles at high mass using the LHC as a $\gamma \gamma$ collider. The predicted sensitivities with 300 fb$^{-1}$ are better by two or three orders of magnitude compared to the more standard methods at the LHC without measuring intact protons after collision.