Publications

Order by: publication date number of citations

• Local Unitarity

  Zeno Capatti

  SciPost Phys. Proc. 7, 024 (2022) · published 21 June 2022 | Toggle abstract · pdf

  Within the Local Unitarity formalism, any physical cross-section is re-written in such a way that cancellations of infrared singularities between real and virtual contributions are realised locally. Consequently, phase-space and loop integrals are regulated locally without the need of any counter-terms or dimensional regularisation aside from those strictly needed to achieve ultraviolet regularisation. This Local Unitarity representation is especially suitable to direct Monte Carlo integration. As such, it offers a clear and direct path to automate the computation of fixed-order differential observables in Quantum Field Theories.

  3 citations

• Determination of the rapidity evolution kernel from Drell-Yan data at low transverse momenta

  F. Hautmann, I. Scimemi, A. Vladimirov

  SciPost Phys. Proc. 8, 123 (2022) · published 13 July 2022 | Toggle abstract · pdf

  We report recent results on the extraction of the rapidity evolution kernel for Sudakov processes from experimental measurements of Drell-Yan (DY) transverse momentum distributions. We discuss the role of high-precision Large Hadron Collider (LHC) data, and illustrate the interplay of this analysis with transverse momentum dependent and collinear parton density functions.

  3 citations

• Holographic Weyl anomaly in string theory

  Lorenz Eberhardt, Sridip Pal

  SciPost Phys. 16, 027 (2024) · published 24 January 2024 | Toggle abstract · pdf

  We compute the worldsheet sphere partition function of string theory on global AdS$_3$ with pure NS-NS flux. Because of an unfixed Möbius symmetry on the worldsheet, there is a cancellation of infinities and only a part of the answer is unambiguous. We show that it precisely reproduces the holographic Weyl anomaly and the ambiguous terms correspond to the possible counterterms of the boundary CFT.

  3 citations

• Gaussian-state Ansatz for the non-equilibrium dynamics of quantum spin lattices

  Raphaël Menu, Tommaso Roscilde

  SciPost Phys. 14, 151 (2023) · published 12 June 2023 | Toggle abstract · pdf

  The study of non-equilibrium dynamics is one of the most important challenges of modern quantum many-body physics, in relationship with fundamental questions in quantum statistical mechanics, as well as with the fields of quantum simulation and computing. In this work we propose a Gaussian Ansatz for the study of the nonequilibrium dynamics of quantum spin systems. Within our approach, the quantum spins are mapped onto Holstein-Primakoff bosons, such that a coherent spin state - chosen as the initial state of the dynamics - represents the bosonic vacuum. The state of the system is then postulated to remain a bosonic Gaussian state at all times, an assumption which is exact when the bosonic Hamiltonian is quadratic; and which is justified in the case of a nonlinear Hamiltonian if the boson density remains moderate. We test the accuracy of such an Ansatz in the paradigmatic case of the $S=1/2$ transverse-field Ising model, in one and two dimensions, initialized in a state aligned with the applied field. We show that the Gaussian Ansatz, when applied to the bosonic Hamiltonian with nonlinearities truncated to quartic order, is able to reproduce faithfully the evolution of the state, including its relaxation to the equilibrium regime, for fields larger than the critical field for the paramagnetic-ferromagnetic transition in the ground state. In particular the spatio-temporal pattern of correlations reconstructed via the Gaussian Ansatz reveals the dispersion relation of quasiparticle excitations, exhibiting the softening of the excitation gap upon approaching the critical field. Our results suggest that the Gaussian Ansatz correctly captures the essential effects of nonlinearities in quantum spin dynamics; and that it can be applied to the study of fundamental phenomena such as quantum thermalization and its breakdown.

  3 citations

• Solution of Baxter equation for the $q$-Toda and Toda$_2$ chains by NLIE

  Olivier Babelon, Karol K. Kozlowski, Vincent Pasquier

  SciPost Phys. 5, 035 (2018) · published 18 October 2018 | Toggle abstract · pdf

  We construct a basis of solutions of the scalar $\boldsymbol{ \texttt{t} }- \boldsymbol{ \texttt{Q} }$ equation describing the spectrum of the $q$-Toda and Toda$_2$ chains by using auxiliary non-linear integral equations. Our construction allows us to provide quantisation conditions for the spectra of these models in the form of thermodynamic Bethe Ansatz-like equations.

  3 citations

• A Framework for Studying a Quantum Critical Metal in the Limit $N_f\rightarrow0$

  Petter Säterskog

  SciPost Phys. 4, 015 (2018) · published 27 March 2018 | Toggle abstract · pdf

  We study a model in 1+2 dimensions composed of a spherical Fermi surface of $N_f$ flavors of fermions coupled to a massless scalar. We present a framework to non-perturbatively calculate general fermion $n$-point functions of this theory in the limit $N_f\rightarrow0$ followed by $k_F\rightarrow\infty$ where $k_F$ sets both the size and curvature of the Fermi surface. Using this framework we calculate the zero-temperature fermion density-density correlation function in real space and find an exponential decay of Friedel oscillations.

  3 citations

• Tau-decay determination of the strong coupling

  Antonio Pich

  SciPost Phys. Proc. 1, 036 (2019) · published 21 February 2019 | Toggle abstract · pdf

  We review the current status of the determination of the strong coupling from tau decay. Using the most recent release of the ALEPH data, a very comprehensive phenomenological analysis has been performed, exploring all strategies previously considered in the literature and several complementary approaches. Once their actual uncertainties are properly assessed, the results from all adopted methodologies are in excellent agreement, leading to a very robust and reliable value of the strong coupling, $\alpha_s^{(n_f=3)}(m_\tau^2) = 0.328\pm 0.013$, which implies $\alpha_s^{(n_f=5)}(M_Z^2) = 0.1197\pm 0.0015$.

  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

• Error-correcting codes for fermionic quantum simulation

  Yu-An Chen, Alexey V. Gorshkov, Yijia Xu

  SciPost Phys. 16, 033 (2024) · published 26 January 2024 | Toggle abstract · pdf

  Utilizing the framework of $\mathbb{Z}_2$ lattice gauge theories in the context of Pauli stabilizer codes, we present methodologies for simulating fermions via qubit systems on a two-dimensional square lattice. We investigate the symplectic automorphisms of the Pauli module over the Laurent polynomial ring. This enables us to systematically increase the code distances of stabilizer codes while fixing the rate between encoded logical fermions and physical qubits. We identify a family of stabilizer codes suitable for fermion simulation, achieving code distances of d=2,3,4,5,6,7, allowing correction of any $\lfloor \frac{d-1}{2} \rfloor$-qubit error. In contrast to the traditional code concatenation approach, our method can increase the code distances without decreasing the (fermionic) code rate. In particular, we explicitly show all stabilizers and logical operators for codes with code distances of d=3,4,5. We provide syndromes for all Pauli errors and invent a syndrome-matching algorithm to compute code distances numerically.

  3 citations

• A coupling prescription for post-Newtonian corrections in quantum mechanics

  Jelle Hartong, Emil Have, Niels A. Obers, Igor Pikovski

  SciPost Phys. 16, 088 (2024) · published 27 March 2024 | Toggle abstract · pdf

  The interplay between quantum theory and general relativity remains one of the main challenges of modern physics. A renewed interest in the low-energy limit is driven by the prospect of new experiments that could probe this interface. Here we develop a covariant framework for expressing post-Newtonian corrections to Schrödinger's equation on arbitrary gravitational backgrounds based on a $1/c^2$ expansion of Lorentzian geometry, where $c$ is the speed of light. Our framework provides a generic coupling prescription of quantum systems to gravity that is valid in the intermediate regime between Newtonian gravity and General Relativity, and that retains the focus on geometry. At each order in $1/c^2$ this produces a nonrelativistic geometry to which quantum systems at that order couple. By considering the gauge symmetries of both the nonrelativistic geometries and the $1/c^2$ expansion of the complex Klein-Gordon field, we devise a prescription that allows us to derive the Schrödinger equation and its post-Newtonian corrections on a gravitational background order-by-order in $1/c^2$. We also demonstrate that these results can be obtained from a $1/c^2$ expansion of the complex Klein-Gordon Lagrangian. We illustrate our methods by performing the $1/c^2$ expansion of the Kerr metric up to $\mathcal{O}(c^{-2})$, which leads to a special case of the Hartle-Thorne metric. The associated Schrödinger equation captures novel and potentially measurable effects.

  3 citations