Publications

Order by: publication date number of citations

• QCD factorization for hadronic quarkonium production at high $p_T$

  Kyle Lee, Jian-Wei Qiu, George Sterman, Kazuhiro Watanabe

  SciPost Phys. Proc. 8, 143 (2022) · published 14 July 2022 | Toggle abstract · pdf

  Heavy quarkonium production at high transverse momentum ($p_T$) in hadronic collisions is explored in the QCD factorization approach. We find that the leading power in the $1/p_T$ expansion is responsible for high $p_T$ regime, while the next-to-leading power contribution is necessary for the low $p_T$ region. We present the first numerical analysis of the scale evolution of coupled twist-2 and twist-4 fragmentation functions (FFs) for heavy quarkonium production and demonstrate that the QCD factorization approach is capable of describing the $p_T$ spectrum of hadronic $J/\psi$ production at the LHC.

  5 citations

• Parity and spin CFT with boundaries and defects

  Ingo Runkel, Lóránt Szegedy, Gérard M. T. Watts

  SciPost Phys. 15, 207 (2023) · published 27 November 2023 | Toggle abstract · pdf

  This paper is a follow-up to [J. High Energy Phys. 06, 025 (2020)] in which two-dimensional conformal field theories in the presence of spin structures are studied. In the present paper we define four types of CFTs, distinguished by whether they need a spin structure or not in order to be well-defined, and whether their fields have parity or not. The cases of spin dependence without parity, and of parity without the need of a spin structure, have not, to our knowledge, been investigated in detail so far. We analyse these theories by extending the description of CFT correlators via three-dimensional topological field theory developed in [Nucl. Phys. B 646, 353 (2002)] to include parity and spin. In each of the four cases, the defining data are a special Frobenius algebra $F$ in a suitable ribbon fusion category, such that the Nakayama automorphism of $F$ is the identity (oriented case) or squares to the identity (spin case). We use the TFT to define correlators in terms of $F$ and we show that these satisfy the relevant factorisation and single-valuedness conditions. We allow for world sheets with boundaries and topological line defects, and we specify the categories of boundary labels and the fusion categories of line defect labels for each of the four types. The construction can be understood in terms of topological line defects as gauging a possibly non-invertible symmetry. We analyse the case of a $\mathbb{Z}_2$-symmetry in some detail and provide examples of all four types of CFT, with Bershadsky-Polyakov models illustrating the two new types.

  5 citations

• Ground-state phase diagram of quantum link electrodynamics in $(2+1)$-d

  Tomohiro Hashizume, Jad C. Halimeh, Philipp Hauke, Debasish Banerjee

  SciPost Phys. 13, 017 (2022) · published 12 August 2022 | Toggle abstract · pdf

  The exploration of phase diagrams of strongly interacting gauge theories coupled to matter in lower dimensions promises the identification of exotic phases and possible new universality classes, and it facilitates a better understanding of salient phenomena in Nature, such as confinement or high-temperature superconductivity. The emerging new techniques of quantum synthetic matter experiments as well as efficient classical computational methods with matrix product states have been extremely successful in one spatial dimension, and are now motivating such studies in two spatial dimensions. In this work, we consider a $\mathrm{U}(1)$ quantum link lattice gauge theory where the gauge fields, represented by spin-$\frac{1}{2}$ operators are coupled to a single flavor of staggered fermions. Using matrix product states on infinite cylinders with increasing diameter, we conjecture its phase diagram in $(2+1)$-d. This model allows us to smoothly tune between the $\mathrm{U}(1)$ quantum link and the quantum dimer models by adjusting the strength of the fermion mass term, enabling us to connect to the well-studied phases of those models. Our study reveals a rich phase diagram with exotic phases and interesting phase transitions to a potential liquid-like phase. It thus furthers the collection of gauge theory models that may guide future quantum-simulation experiments.

  5 citations

• High-precision muon decay predictions for ALP searches

  Pulak Banerjee, Antonio Coutinho, Tim Engel, Andrea Gurgone, Adrian Signer, Yannick Ulrich

  SciPost Phys. 15, 021 (2023) · published 21 July 2023 | Toggle abstract · pdf

  We present an improved theoretical prediction of the positron energy spectrum for the polarised Michel decay $\mu^+\to e^+ \nu_e\bar{\nu}_\mu$. In addition to the full next-to-next-to-leading order correction of order $\alpha^2$ in the electromagnetic coupling, we include logarithmically enhanced terms at even higher orders. Logarithms due to collinear emission are included at next-to-leading accuracy up to order $\alpha^4$. At the endpoint of the Michel spectrum, soft photon emission results in large logarithms that are resummed up to next-to-next-to-leading logarithmic accuracy. We apply our results in the context of the MEG II and Mu3e experiments to estimate the impact of the theory error on the branching ratio sensitivity for the lepton-flavour-violating decay $\mu^+\to e^+ X$ of a muon into an axion-like particle $X$.

  5 citations

• Topological and quantum critical properties of the interacting Majorana chain model

  Natalia Chepiga, Nicolas Laflorencie

  SciPost Phys. 14, 152 (2023) · published 13 June 2023 | Toggle abstract · pdf

  We study Majorana chain with the shortest possible interaction term and in the presence of hopping alternation. When formulated in terms of spins the model corresponds to the transverse field Ising model with nearest-neighbor transverse and next-nearest-neighbor longitudinal repulsion. The phase diagram obtained with extensive DMRG simulations is very rich and contains six phases. Four gapped phases include paramagnetic, period-2 with broken translation symmetry, $\mathbb{Z}_2$ with broken parity symmetry and the period-2-$\mathbb{Z}_2$ phase with both symmetries broken. In addition there are two floating phases: gapless and critical Luttinger liquid with incommensurate correlations, and with an additional spontaneously broken $\mathbb{Z}_2$ symmetry in one of them. By analyzing an extended phase diagram we demonstrate that, in contrast with a common belief, the Luttinger liquid phase along the self-dual critical line terminates at a weaker interaction strength than the end point of the Ising critical line that we find to be in the tri-critical Ising universality class. We also show that none of these two points is a Lifshitz point terminating the incommensurability. In addition, we analyzed topological properties through Majorana zero modes emergent in the two topological phases, with and without incommensurability. In the weak interaction regime, a self-consistent mean-field treatment provides a remarkable accuracy for the description of the spectral pairing and the parity switches induced by the interaction.

  5 citations

• Automation of Beam and Jet functions at NNLO

  Guido Bell, Kevin Brune, Goutam Das, Marcel Wald

  SciPost Phys. Proc. 7, 021 (2022) · published 21 June 2022 | Toggle abstract · pdf

  We present a novel framework to streamline the calculation of jet and beam functions to next-to-next-to-leading order (NNLO) in perturbation theory. By exploiting the infrared behaviour of the collinear splitting functions, we factorise the singularities with suitable phase-space parametrisations and perform the observable-dependent integrations numerically. We have implemented our approach in the publicly available code {\tt pySecDec} and present first results for sample jet and beam functions.

  5 citations

• Special transition and extraordinary phase on the surface of a two-dimensional quantum Heisenberg antiferromagnet

  Chengxiang Ding, Wenjing Zhu, Wenan Guo, Long Zhang

  SciPost Phys. 15, 012 (2023) · published 18 July 2023 | Toggle abstract · pdf

  Continuous phase transitions exhibit richer critical phenomena on the surface than in the bulk, because distinct surface universality classes can be realized at the same bulk critical point by tuning the surface interactions. The exploration of surface critical behavior provides a window looking into higher-dimensional boundary conformal field theories. In this work, we study the surface critical behavior of a two-dimensional (2D) quantum critical Heisenberg model by tuning the surface coupling strength, and discover a direct special transition on the surface from the ordinary phase into an extraordinary phase. The extraordinary phase has a long-range antiferromagnetic order on the surface, in sharp contrast to the logarithmic decaying spin correlations in the 3D classical O(3) model. The special transition point has a new set of critical exponents, $y_{s}=0.86(4)$ and $\eta_{\parallel}=-0.33(1)$, which are distinct from the special transition of the classical O(3) model and indicate a new surface universality class of the 3D O(3) Wilson-Fisher theory.

  5 citations

• Emergent XY* transition driven by symmetry fractionalization and anyon condensation

  Michael Schuler, Louis-Paul Henry, Yuan-Ming Lu, Andreas M. Läuchli

  SciPost Phys. 14, 001 (2023) · published 11 January 2023 | Toggle abstract · pdf

  Anyons in a topologically ordered phase can carry fractional quantum numbers with respect to the symmetry group of the considered system, one example being the fractional charge of the quasiparticles and quasiholes in the fractional quantum Hall effect. When such symmetry-fractionalized anyons condense, the resulting phase must spontaneously break the symmetry and display a local order parameter. In this paper, we study the phase diagram and anyon condensation transitions of a $\mathbb{Z}_2$ topological order perturbed by Ising interactions in the Toric Code. The interplay between the global (``onsite'') Ising ($\mathbb{Z}_2$) symmetry and the lattice space group symmetries results in a non-trivial symmetry fractionalization class for the anyons, and is shown to lead to two characteristically different confined, symmetry-broken phases. To understand the anyon condensation transitions, we use the recently introduced critical torus energy spectrum technique to identify a line of emergent 2+1D XY* transitions ending at a fine-tuned (Ising$^2$)* critical point. We provide numerical evidence for the occurrence of two symmetry breaking patterns predicted by the specific symmetry fractionalization class of the condensed anyons in the explored phase diagram. In combination with large-scale quantum Monte Carlo simulations we measure unusually large critical exponents $\eta$ for the scaling of the correlation function at the continuous anyon condensation transitions, and we further identify lines of (weakly) first order transitions in the phase diagram. As an important additional result, we discuss the phase diagram of a resulting 2+1D Ashkin-Teller model, where we demonstrate that torus spectroscopy is capable of identifying emergent XY/O(2) critical behaviour, thereby solving some longstanding open questions in the domain of the 3D Ashkin-Teller models. To establish the generality of our results, we propose a field theoretical description capturing the transition from a $\mathbb{Z}_2$ topological order to either $\mathbb{Z}_2$ symmetry broken phase, which is in excellent agreement with the numerical results.

  5 citations

• Decays of a bino-like particle in the low-mass regime

  Florian Domingo, Herbi K. Dreiner

  SciPost Phys. 14, 134 (2023) · published 30 May 2023 | Toggle abstract · pdf

  We study the phenomenology associated with a light bino-like neutralino with mass under the tau mass in the context of the R-parity violating Minimal Supersymmetric Standard Model. This is a well-motivated example of scenarios producing potentially light and long-lived exotic particles, which might be testable in far-detector experiments, such as the FASER experiment at the Large Hadron Collider. A quantitative assessment of the discovery potential or the extraction of limits run through a detailed understanding of the interactions of the light exotic fermion with Standard Model matter, in particular, the hadronic sector. Here, we propose a systematic analysis of the decays of such a particle and proceed to a model-independent derivation of the low-energy effects, so that this formalism may be transposed to other UV-completions or even stand as an independent effective field theory. We then stress the diversity of the possible phenomenology and more specifically discuss the features associated with the R-parity violating supersymmetric framework, for example neutron-antineutron oscillations.

  5 citations

• Multiple relaxation times in perturbed XXZ chain

  M. Mierzejewski, J. Pawłowski, P. Prelovšek, J. Herbrych

  SciPost Phys. 13, 013 (2022) · published 5 August 2022 | Toggle abstract · pdf

  We study numerically the relaxation of correlation functions in weakly perturbed integrable XXZ chain. While the decay of spin-current and energy-current correlations at zero magnetization are well described by single, but quite distinct, relaxation rates governed by the square of the perturbation strength $g$, the correlations at finite magnetization reveal multiple relaxation rates. The result can be understood in terms of decays of several quantities, conserved in the reference integrable system. On the other hand, the correlations of non-commuting quantities, being conserved at particular anisotropies $\Delta$, decay non-exponentially with characteristic time scale linear in $g$.

  5 citations