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On the range of validity of perturbative models for galaxy clustering and its uncertainty

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arXiv 2023年

作者： Gambardella, Giosuè Biagetti, Matteo Moretti, Chiara Sefusatti, Emiliano Institute for Fundamental Physics of the Universe Via Beirut 2 Trieste34151 Italy Campus UAB Carrer de Can Magrans s/n Barcelona08193 Spain Area Science Park Località Padriciano 99 Trieste34149 Italy Scuola Internazionale di Studi Superiori Avanzati via Bonomea 265 Trieste34136 Italy Istituto Nazionale di Astrofisica Osservatorio Astronomico di Trieste via Tiepolo 11 Trieste34143 Italy Istituto Nazionale di Fisica Nucleare Sezione di Trieste via Valerio 2 Trieste34127 Italy Centro Nazionale "High Performance Computer Big Data and Quantum Computing" Italy

We explore the reach of an analytical model at one-loop in Perturbation Theory (PT) to accurately describe measurements of the galaxy power spectrum from numerical simulations in redshift space. We consider the validity range in terms of three different diagnostics: 1) the goodness of fit;2) a figure-of-bias quantifying the error in recovering the fiducial value of a cosmological parameter;3) an internal consistency check of the theoretical model quantifying the running of the model parameters with the scale cut. We consider different sets of measurements corresponding to an increasing cumulative simulation volume in redshift space. For each volume we define a median value and the associated scatter for the largest wavenumber where the model is valid (the k-reach of the model). We find, as a rather general result, that the median value of the reach decreases with the simulation volume, as expected since the smaller statistical errors provide a more stringent test for the model. This is true for all the three definitions considered, with the one given in terms of the figure-of-bias providing the most stringent scale cut. More interestingly, we also find that the error associated with the k-reach value is quite large, with a significant probability of being as low as 0.1 ℎMpc−1 (or, more generally, up to 40% smaller than the median) for all the simulation volumes considered. We explore as well the additional information on the growth rate parameter encoded in the power spectrum hexadecapole, compared to the analysis of monopole and quadrupole, as a function of simulation volume. While our analysis is, in many ways, rather simplified, we find that the gain in the determination of the growth rate is quite small in absolute value and well within the statistical error on the corresponding figure of merit. Copyright © 2023, The Authors. All rights reserved.

关键词： Power spectrum

Many-body localization in a non-Hermitian quasiperiodic system

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Physical Review B 2020年第6期102卷 064206-064206页

作者： Liang-Jun Zhai Shuai Yin Guang-Yao Huang The School of Mathematics and Physics Jiangsu University of Technology Changzhou 213001 China School of Physics Sun Yat-Sen University Guangzhou 510275 China Institute for Quantum Information & State Key Laboratory of High Performance Computing College of Computer National University of Defense Technology Changsha 410073 China

In the present study, the interplay among interaction, topology, quasiperiodicity, and non-Hermiticity is studied. The hard-core bosons model on a one-dimensional lattice with asymmetry hoppings and quasiperiodic onsite potentials is selected. This model, which preserves time-reversal symmetry (TRS), will exhibit three types of phase transition: Real-complex transition of eigenenergies, topological phase transition, and many-body localization (MBL) phase transition. For the real-complex transition, it is found that the imaginary parts of the eigenenergies are always suppressed by the MBL. Moreover, by calculating the winding number, a topological phase transition can be revealed with the increase of potential amplitude, and we find that the behavior is quite different from the single-particle systems. Based on our numerical results, we conjecture that these three types of phase transition occur at the same point in the thermodynamic limit, and the MBL transition of quasiperiodic system and disordered system should belong to different universality classes. Finally, we demonstrate that these phase transitions can profoundly affect the dynamics of the non-Hermitian many-body system.

关键词： Phase transitions quantum phase transitions Topological phase transition Topological phases of matter

Extreme data compression for Bayesian model comparison

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arXiv 2023年

作者： Heavens, Alan F. Mootoovaloo, Arrykrishna Trotta, Roberto Sellentin, Elena Department of Physics Imperial College Blackett Laboratory Prince Consort Road LondonSW7 2AZ United Kingdom Department of Physics University of Oxford Denys Wilkinson Building Keble Road OxfordOX1 3RH United Kingdom via Bonomea 265 Trieste34136 Italy Centro Nazionale "High Performance Computer Big Data and Quantum Computing" Italy Mathematical Institute Leiden University Snellius Gebouw Niels Bohrweg 1 LeidenNL-2333 CA Netherlands Leiden Observatory Leiden University Oort Gebouw Niels Bohrweg 2 LeidenNL-2333 CA Netherlands

We develop extreme data compression for use in Bayesian model comparison via the MOPED algorithm, as well as more general score compression. We find that Bayes factors from data compressed with the MOPED algorithm are identical to those from their uncompressed datasets when the models are linear and the errors Gaussian. In other nonlinear cases, whether nested or not, we find negligible differences in the Bayes factors, and show this explicitly for the Pantheon-SH0ES supernova dataset. We also investigate the sampling properties of the Bayesian Evidence as a frequentist statistic, and find that extreme data compression reduces the sampling variance of the Evidence, but has no impact on the sampling distribution of Bayes factors. Since model comparison can be a very computationally-intensive task, MOPED extreme data compression may present significant advantages in computational time. © 2023, CC BY.

关键词： Data compression

Unconventional Landau level transitions in Weyl semimetal NbP

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Physical Review Materials 2022年第5期6卷 054204-054204页

作者： Minhao Zhao Zhongbo Yan Xiaoyi Xie Yunkun Yang Pengliang Leng Mykhaylo Ozerov Dayu Yan Youguo Shi Jinshan Yang Faxian Xiu Shaoming Dong State Key Laboratory of Surface Physics and Department of Physics Fudan University Shanghai 200433 China Shanghai Qi Zhi Institute 41st Floor AI Tower No. 701 Yunjin Road Xuhui District Shanghai 200232 China School of Physics Sun Yat-Sen University Guangzhou 510275 China National High Magnetic Field Laboratory Tallahassee Florida 32310 USA Institute of Physics and Beijing National Laboratory for Condensed Matter Physics Chinese Academy of Sciences Beijing 100190 China School of Physical Sciences University of Chinese Academy of Sciences Beijing 100190 China State Key Laboratory of High Performance Ceramics & Superfine Microstructure Shanghai Institute of Ceramics Chinese Academy of Sciences Shanghai 200050 China Institute for Nanoelectronic Devices and Quantum Computing Fudan University Shanghai 200433 China Zhangjiang Fudan International Innovation Center Fudan University Shanghai 201210 China Shanghai Research Center for Quantum Sciences Shanghai 201315 China

Weyl semimetals were experimentally discovered as a new quantum phase of matter that exhibits topologically protected states characterized by separated Weyl points. Similar to other topological materials, the research of Landau level transitions can provide abundant information on Fermi surfaces. Extensive experimental efforts on low-temperature transport and optical properties have been dedicated to investigating the nontrivial topology structure. However, there are some theoretically predicted unconventional Landau level transitions in Weyl semimetals that have not been observed experimentally. And, their contribution to the electromagnetic response of Weyl semimetal remains elusive. Here, we report the magneto-optical study of Landau quantization and selection rules in Weyl semimetal NbP under Voigt geometry. By changing the direction of the electric vector of the incoming light under Voigt and Faraday geometry, abundant Landau level transition modes which contain Δ=0, ±1, ±2 selection rules are obtained. The richness of the optical spectra, particularly the ones from the Voigt geometry, allows us to determine the location of Fermi energy and its evolution with magnetic fields. We further extract the transitions between Landau levels and Fermi energy and deduce the Landau index. Our results reveal the track of Fermi energy under varying magnetic fields based on the Landau level transitions under Voigt geometry and suggest that a combination of the magneto-optical spectra under Voigt and Faraday geometry can effectively determine the key properties of topological materials that are otherwise inaccessible.

关键词： Magneto-optical spectra Weyl fermions Weyl semimetal

Density Fluctuations in the Intracluster Medium: An Attempt to Constrain Viscosity with Cosmological Simulations

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arXiv 2024年

作者： Marin-Gilabert, Tirso Steinwandel, Ulrich P. Valentini, Milena Vallés-Pérez, David Dolag, Klaus Universitäts-Sternwarte Fakultät für Physik Ludwig-Maximilians-Universität München Scheinerstr.1 München81679 Germany Center for Computational Astrophysics Flatiron Institute 162 5th Avenue New YorkNY10010 United States Astronomy Unit Department of Physics University of Trieste via Tiepolo 11 TriesteI-34131 Italy INAF - Osservatorio Astronomico di Trieste via Tiepolo 11 TriesteI-34131 Italy INFN Instituto Nazionale di Fisica Nucleare Via Valerio 2 TriesteI-34127 Italy ICSC - Italian Research Center on High Performance Computing Big Data and Quantum Computing via Magnanelli 2 Casalecchio di Reno40033 Italy Departament d'Astronomia i Astrofísica Universitat de València C/Doctor Moliner 50 València BurjassotE-46100 Spain Max-Planck-Institut für Astrophysik Karl-Schwarzschild-Straße 1 Garching85741 Germany

The impact of viscosity in the Intracluster Medium (ICM) is still an open question in astrophysics. To address this problem, we have run a set of cosmological simulations of three galaxy clusters with a mass larger than MVir > 1015M☉ at z = 0 using the SPMHD-code OpenGadget3. We aim to quantify the influence of viscosity and constrain its value in the ICM. Our results show significant morphological differences at small scales, temperature variations, and density fluctuations induced by viscosity. We observe a suppression of instabilities at small scales, resulting in a more filamentary structure and a larger amount of small structures due to the lack of mixing with the medium. The conversion of kinetic to internal energy leads to an increase of the virial temperature of the cluster of ∼5% - 10%, while the denser regions remain cold. The amplitude of density and velocity fluctuations are found to increase with viscosity. However, comparison with observational data indicates that the simulations, regardless of the viscosity, match the observed slope of the amplitude of density fluctuations, challenging the direct constraint of viscosity solely through density fluctuations. Furthermore, the ratio of density to velocity fluctuations remains close to 1 regardless of the amount of viscosity, in agreement with the theoretical expectations. Our results show for the first time in a cosmological simulation of a galaxy cluster the effect of viscosity in the ICM, a study that is currently missing in the literature. Copyright © 2024, The Authors. All rights reserved.

关键词： Cosmology

Nonreciprocal enhancement of optomechanical second-order sidebands in a spinning resonator

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Physical Review A 2020年第3期102卷 033526-033526页

作者： Wen-An Li Guang-Yao Huang Ji-Pei Chen Yuan Chen School of Physics and Materials Science Guangzhou University Guangzhou 510006 China Research Center for Advanced Information Materials Guangzhou University Guangzhou 510006 China Institute for Quantum Information and State Key Laboratory of High Performance Computing College of Computer National University of Defense Technology Changsha 410073 China

We theoretically study optomechanically induced second-order sideband generation in a spinning resonator. Due to the splitting of resonance frequencies of the countercirculating modes via the Sagnac effect, we find that second-order sidebands can be enhanced in one direction but suppressed in the other. Furthermore, the enhancement or suppression of second-order sidebands is closely related to the rotation speed of a resonator, incident direction of input fields, and frequency of driving fields. Finally, we study the influence of power of control fields on second-order sidebands, and find that the operating bandwidth for observing an obvious nonreciprocal enhancement of second-order sidebands can be significantly widened as the power of control fields increases. Our paper offers a promising route towards achieving tunable optical nonlinearity and convenient nonreciprocal optomechanical control in integrated photonic chips.

关键词： Optomechanics Second order nonlinear optical processes

Neural posterior estimation with guaranteed exact coverage: The ringdown of GW150914

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Physical Review D 2023年第4期108卷 044029-044029页

作者： Marco Crisostomi Kallol Dey Enrico Barausse Roberto Trotta SISSA Via Bonomea 265 34136 Trieste Italy and INFN Sezione di Trieste 34127 Trieste Italy IFPU—Institute for Fundamental Physics of the Universe Via Beirut 2 34014 Trieste Italy School of Physics Indian Institute of Science Education and Research Thiruvananthapuram Maruthamala PO Vithura Thiruvananthapuram 695551 Kerala India Physics Department Imperial College London Prince Consort Road SW7 2AZ London United Kingdom Centro Nazionale “High Performance Computer Big Data and Quantum Computing” Via Magnanelli 2 40033 Casalecchio di Reno (BO) Italy

We analyze the ringdown phase of the first detected black-hole merger, GW150914, using a simulation-based inference pipeline based on masked autoregressive flows. We obtain approximate marginal posterior distributions for the ringdown parameters, namely the mass, spin, and the amplitude and phases of the dominant mode and its first overtone. Thanks to the locally amortized nature of our method, we are able to calibrate our posteriors with injected simulations, producing posterior regions with guaranteed (i.e., exact) frequentist coverage of the true values. For GW150914, our calibrated posteriors provide only mild evidence (∼2σ) for the presence of an overtone, even if the ringdown is assumed to start at the peak of the amplitude.

关键词： Classical black holes General relativity Gravitational waves

Characterize and optimize the four-wave mixing in dual-interferometer coupled silicon microrings

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Chinese Physics B 2019年第10期28卷 198-203页

作者： Chao Wu Yingwen Liu Xiaowen Gu Shichuan Xue Xinxin Yu Yuechan Kong Xiaogang Qiang Junjie Wu Zhihong Zhu Ping Xu Institute for Quantum Information and State Key Laboratory of High Performance Computing College of ComputerCollege of Advanced Interdisciplinary StudiesNational University of Defense TechnologyChangsha 410073China Science and Technology on Monolithic Integrated Circuits and Modules Laboratory Nanjing Electronic Devices InstituteNanjing 210016China National Laboratory of Solid State Microstructures and School of Physics Nanjing UniversityNanjing 210093China

By designing and fabricating a series of dual-interferometer coupled silicon microrings, the coupling condition of the pump, signal, and idler beams can be engineered independently and then we carried out both the continuous-wave and pulse pumped four-wave mixing experiments to verify the dependence of conversion efficiency on the coupling conditions of the four interacting beams, respectively. Under the continuous-wave pump, the four-wave mixing efficiency gets maximized when both the pump and signal/idler beams are closely operated at the critical coupling point, while for the pulse pump case, the efficiency can be enhanced greatly when the pump and converted idler beams are all overcoupled. These experiment results agree well with our theoretical calculations. Our design provides a platform for explicitly characterizing the four-wave mixing under different pumping conditions, and offers a method to optimize the four-wave mixing, which will facilitate the development of on-chip all-optical signal processing with a higher efficiency or reduced pump power.

关键词： silicon resonators four-wave mixing Mach-Zehnder interferometer

quantum Hall admittance in non-Hermitian systems

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arXiv 2021年

作者： Fan, Annan Huang, Guang-Yao Liang, Shi-Dong School of Physics Sun Yat-Sen University Guangzhou510275 China Institute for Quantum Information State Key Laboratory of High Performance Computing College of Computer National University of Defense Technology Changsha410073 China State Key Laboratory of Optoelectronic Material and Technology Guangdong Province Key Laboratory of Display Material and Technology Sun Yat-Sen University Guangzhou510275 China

We propose a pair of the complex Berry curvatures associated with the non-Hermitian Hamiltonian and its Hermitian adjoint to reveal new physics in non-Hermitian systems. We give the complex Berry curvature and Berry phase for the two-dimensional non-Hermitian Dirac model. The imaginary part of the complex Berry phase induces the quantum Hall susceptance such that the quantum Hall conductance is generalized to quantum Hall admittance for non-Hermitian systems, which implies that the non-Hermiticity of systems could induce an intrinsic quantum capacitance or inductance of systems depending on the non-Hermitian parameters. We analyze the complex energy band structures of the two-dimensional non-Hermitian Dirac model and demonstrate the point and line gaps and their closings as the exceptional degeneracy of the energy bands in the parameter space, which are associated with topological phases. In the continuum limit, we obtain the complex Berry phase in the parameter space. © 2021, CC BY-NC-ND.

关键词： Fruits