Publications

Order by: publication date number of citations

• Why space could be quantised on a different scale to matter

  Matthew J. Lake

  SciPost Phys. Proc. 4, 014 (2021) · published 13 August 2021 | Toggle abstract · pdf

  The scale of quantum mechanical effects in matter is set by Planck's constant, $\hbar$. This represents the quantisation scale for material objects. In this article, we present a simple argument why the quantisation scale for space, and hence for gravity, may not be equal to $\hbar$. Indeed, assuming a single quantisation scale for both matter and geometry leads to the `worst prediction in physics', namely, the huge difference between the observed and predicted vacuum energies. Conversely, assuming a different quantum of action for geometry, $\beta \ll \hbar$, allows us to recover the observed density of the Universe. Thus, by measuring its present-day expansion, we may in principle determine, empirically, the scale at which the geometric degrees of freedom should be quantised.

  6 citations

• The Virasoro minimal string

  Scott Collier, Lorenz Eberhardt, Beatrix Muehlmann, Victor A. Rodriguez

  SciPost Phys. 16, 057 (2024) · published 26 February 2024 | Toggle abstract · pdf

  We introduce a critical string theory in two dimensions and demonstrate that this theory, viewed as two-dimensional quantum gravity on the worldsheet, is equivalent to a double-scaled matrix integral. The worldsheet theory consists of Liouville CFT with central charge c$≥$ 25 coupled to timelike Liouville CFT with central charge 26-c. The double-scaled matrix integral has as its leading density of states the universal Cardy density of primaries in a two-dimensional CFT, thus motivating the name Virasoro minimal string. The duality holds for any value of the continuous parameter $c$ and reduces to the JT gravity/matrix integral duality in the large central charge limit. It thus provides a precise stringy realization of JT gravity. The main observables of the Virasoro minimal string are quantum analogues of the Weil-Petersson volumes, which are computed as absolutely convergent integrals of worldsheet CFT correlators over the moduli space of Riemann surfaces. By exploiting a relation of the Virasoro minimal string to three-dimensional gravity and intersection theory on the moduli space of Riemann surfaces, we are able to give a direct derivation of the duality. We provide many checks, such as explicit numerical - and in special cases, analytic - integration of string diagrams, the identification of the CFT boundary conditions with asymptotic boundaries of the two-dimensional spacetime, and the matching between the leading non-perturbative corrections of the worldsheet theory and the matrix integral. As a byproduct, we discover natural conformal boundary conditions for timelike Liouville CFT.

  6 citations

• Extreme boundary conditions and random tilings

  Jean-Marie Stéphan

  SciPost Phys. Lect. Notes 26 (2021) · published 12 March 2021 | Toggle abstract · pdf

  Standard statistical mechanical or condensed matter arguments tell us that bulk properties of a physical system do not depend too much on boundary conditions. Random tilings of large regions provide counterexamples to such intuition, as illustrated by the famous 'arctic circle theorem' for dimer coverings in two dimensions. In these notes, I discuss such examples in the context of critical phenomena, and their relation to 1+1d quantum particle models. All those turn out to share a common feature: they are inhomogeneous, in the sense that local densities now depend on position in the bulk. I explain how such problems may be understood using variational (or hydrodynamic) arguments, how to treat long range correlations, and how non trivial edge behavior can occur. While all this is done on the example of the dimer model, the results presented here have much greater generality. In that sense the dimer model serves as an opportunity to discuss broader methods and results. [These notes require only a basic knowledge of statistical mechanics.]

  6 citations

• The Meson Production Targets in the high energy beamline of HIPA at PSI

  Daniela Kiselev, Pierre-André Duperrex, Sven Jollet, Stefan Joray, Daniel Laube, Davide Reggiani, Raffaello Sobbia, Vadim Talanov

  SciPost Phys. Proc. 5, 003 (2021) · published 6 September 2021 | Toggle abstract · pdf

  Two target stations in the 590 MeV proton beamline of the High Intensity Proton Accelerator (HIPA) at the Paul Scherrer Institut (PSI) produce pions and muons for seven secondary beamlines, leading to several experimental stations. The two target stations are 18m apart. Target M is a graphite target with an effective thickness of 5mm, Target E is a graphite wheel with a thickness of 40 mm or 60 mm. Due to the spreading of the beam in the thick target, a high power collimator system is needed to shape the beam for further transport. The beam is then transported to either the SINQ target, a neutron spallation source, or stopped in the beam dump, where about 450 kW beam power is dissipated. In the following, the targets, collimators and beam dumps are further described.

  6 citations

• Exact solution for the Lindbladian dynamics for the open XX spin chain with boundary dissipation

  Kohei Yamanaka, Tomohiro Sasamoto

  SciPost Phys. 14, 112 (2023) · published 15 May 2023 | Toggle abstract · pdf

  We obtain exact formulas for the time-dependence of a few physical observables for the open XX spin chain with Lindbladian dynamics. Our analysis is based on the fact that the Lindblad equation for an arbitrary open quadratic system of $N$ fermions is explicitly solved in terms of diagonalization of a $4N\times4N$ matrix called structure matrix by following the scheme of the third quantization. We mainly focus on the time-dependence of magnetization and spin current. As a short-time behavior at a given site, we observe the plateau regime except near the center of the chain. Basic features of this are explained by the light-cone structure created by propagations of boundary effects from the initial time, but we can explain their more detailed properties analytically using our exact formulas. On the other hand, after the plateau regime, the magnetization and spin current exhibit a slow decay to the steady state values described by the Liouvillian gap. We analytically establish its $O(N^{-3})$ scaling and also determine its coefficient.

  6 citations

• Magnetic impurity in a one-dimensional few-fermion system

  Lukas Rammelmüller, David Huber, Matija Čufar, Joachim Brand, Hans-Werner Hammer, Artem G. Volosniev

  SciPost Phys. 14, 006 (2023) · published 24 January 2023 | Toggle abstract · pdf

  We present a numerical analysis of spin-$\tfrac{1}{2}$ fermions in a one-dimensional harmonic potential in the presence of a magnetic point-like impurity at the center of the trap. The model represents a few-body analogue of a magnetic impurity in the vicinity of an $s$-wave superconductor. Already for a few particles we find a ground-state level crossing between sectors with different fermion parities. We interpret this crossing as a few-body precursor of a quantum phase transition, which occurs when the impurity "breaks" a Cooper pair. This picture is further corroborated by analyzing density-density correlations in momentum space. Finally, we discuss how the system may be realized with existing cold-atoms platforms.

  6 citations

• Current Status of inclusive hadronic tau determinations of |V_us|

  K. Maltman, P.A. Boyle, R.J. Hudspith, T. Izubuchi, A. Juttner, C. Lehner, R. Lewis, H. Ohki, A. Portelli, M. Spraggs, J.M. Zanotti

  SciPost Phys. Proc. 1, 006 (2019) · published 18 February 2019 | Toggle abstract · pdf

  We review the status of the determination of |V_{us}| from both flavor-breaking finite-energy sum rules based on inclusive non-strange and strange hadronic tau decay data and the recent lattice-based analysis of inclusive strange hadronic tau decay data. In particular, we update the results from these analysis frameworks taking into account recent improvements to a number of strange branching fractions reported by HFLAV at CKM2018 and this meeting. We find that inclusive tau decay data yields results for |V_{us}| compatible within errors with the expectations of three-family unitarity.

  6 citations

• Non-Markovian noise that cannot be dynamically decoupled by periodic spin echo pulses

  Daniel Burgarth, Paolo Facchi, Martin Fraas, Robin Hillier

  SciPost Phys. 11, 027 (2021) · published 10 August 2021 | Toggle abstract · pdf

  Dynamical decoupling is the leading technique to remove unwanted interactions in a vast range of quantum systems through fast rotations. But what determines the time-scale of such rotations in order to achieve good decoupling? By providing an explicit counterexample of a qubit coupled to a charged particle and magnetic monopole, we show that such time-scales cannot be decided by the decay profile induced by the noise: even though the system shows a quadratic decay (a Zeno region revealing non-Markovian noise), it cannot be decoupled by periodic spin echo pulses, no matter how fast the rotations.

  6 citations

• Nested Algebraic Bethe Ansatz in integrable models: recent results

  Stanislav Pakuliak, Eric Ragoucy, Nikita Slavnov

  SciPost Phys. Lect. Notes 6 (2018) · published 29 October 2018 | Toggle abstract · pdf

  This short note summarizes the works done in collaboration between S. Belliard (CEA, Saclay), L. Frappat (LAPTh, Annecy), S. Pakuliak (JINR, Dubna), E. Ragoucy (LAPTh, Annecy), N. Slavnov (Steklov Math. Inst., Moscow) and more recently A. Hutsalyuk (Wuppertal / Moscow) and A. Liashyk (Kiev / Moscow). It presents the construction of Bethe vectors, their scalar products and the form factors of local operator for integrable models based on the (super)algebras $gl_n$, $gl_{m|p}$ or their quantum deformations. It corresponds to two talks given by E.R. and N.S. at \textsl{Correlation functions of quantum integrable systems and beyond}, in honor of Jean-Michel Maillet for his 60's (ENS Lyon, October 2017).

  6 citations

• Higher-form symmetries, anomalous magnetohydrodynamics, and holography

  Arpit Das, Ruth Gregory, Nabil Iqbal

  SciPost Phys. 14, 163 (2023) · published 20 June 2023 | Toggle abstract · pdf

  In $U(1)$ Abelian gauge theory coupled to fermions, the non-conservation of the axial current due to the chiral anomaly is given by a dynamical operator $F_{\mu\nu} \tilde{F}^{\mu\nu}$ constructed from the field-strength tensor. We attempt to describe this physics in a universal manner by casting this operator in terms of the 2-form current for the 1-form symmetry associated with magnetic flux conservation. We construct a holographic dual with this symmetry breaking pattern and study some aspects of finite temperature anomalous magnetohydrodynamics. We explicitly calculate the charge susceptibility and the axial charge relaxation rate as a function of temperature and magnetic field and compare to recent lattice results. At small magnetic fields we find agreement with elementary hydrodynamics weakly coupled to an electrodynamic sector, but we find deviations at larger fields.

  6 citations