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Anharmonic Effects on the Squeezing of Axion Perturbations

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arXiv 2023年

作者： Danieli, Valentina Kobayashi, Takeshi Bartolo, Nicola Matarrese, Sabino Viel, Matteo SISSA International School for Advanced Studies Via Bonomea 265 Trieste34136 Italy INFN - Sezione di Trieste via Valerio 2 Trieste34127 Italy IFPU Institute for Fundamental Physics of the Universe Via Beirut 2 Trieste34014 Italy Kobayashi-Maskawa Institute for the Origin of Particles the Universe Nagoya University Nagoya464-8602 Japan Dipartimento di Fisica e Astronomia "G. Galilei" Università degl Studi di Padova Via Francesco Marzolo 8 Padova35131 Italy INFN - Sezione di Padova Via Francesco Marzolo 8 Padova35131 Italy INAF - Osservatorio Astronomico di Padova Vicolo dell’Osservatorio 5 Padova35122 Italy Gran Sasso Science Institute Viale F. Crispi 7 L’AquilaI-67100 Italy INAF - Osservatorio Astronomico di Trieste Via G.B. Tiepolo 11 TriesteI-34131 Italy ICSC - Italian Research Center on High Performance Computing Big Data and Quantum Computing Italy

It is assumed in standard cosmology that the Universe underwent a period of inflation in its earliest phase, providing the seeds for structure formation through vacuum fluctuations of the inflaton scalar field. These fluctuations get stretched by the quasi-exponential expansion of the Universe and become squeezed. The aim of this paper is to deepen the understanding of the squeezing process, considering the effect of self-interactions. Axion-like particles can provide a useful setup to study this effect. Specifically we focus on the consequences that a non-trivial evolution of the background axion field has on the squeezing of the perturbations. We follow the evolution of the axion’s fluctuation modes from the horizon exit during inflation to the radiation-dominated epoch. We compute Bogoliubov coefficients and squeezing parameters, which are linked to the axion particle number and isocurvature perturbation. We find that the quantum mechanical particle production and the squeezing of the perturbations are enhanced, if one accounts for anharmonic effects, i.e., the effect of higher order terms in the potential. This effect becomes particularly strong towards the hilltop of the potential. Copyright © 2023, The Authors. All rights reserved.

关键词： Quantum theory

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

Correction to “Privacy-Preserving Blockchain-Based Federated Learning for IoT Devices” [Feb 20 1817-1829]

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IEEE Internet of Things Journal 2022年第1期10卷 973-973页

作者： Yang Zhao Jun Zhao Linshan Jiang Rui Tan Dusit Niyato Zengxiang Li Lingjuan Lyu Yingbo Liu School of Computer Science and Engineering Nanyang Technological University Jurong West Singapore Institute of High Performance Computing A*STAR Fusionopolis Singapore Department of Computer Science National University of Singapore Queenstown Singapore Big Data Research Institute of Yunnan Economy and Society Yunnan University of Finance and Economics Kunming China

In [1] , on page 1824, Fig. 3 should be as follows:

关键词： Federated learning Internet of Things Bockchains Differential learning Crowdsourcing

DSRGAN: Explicitly learning disentangled representation of underlying structure and rendering for image generation without tuple supervision

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arXiv 2019年

作者： Hao, Guang-Yuan Yu, Hong-Xing Zheng, Wei-Shi School of Data and Computer Science Sun Yat-sen University Key Laboratory of Machine Intelligence and Advanced Computing Ministry of Education Collaborative Innovation Center of High Performance Computing Nudt Guangdong Key Laboratory of Big Data Analysis and Processing Guangzhou

We focus on explicitly learning disentangled representation for natural image generation, where the underlying spatial structure and the rendering on the structure can be independently controlled respectively, yet using no tuple supervision. The setting is significant since tuple supervision is costly and sometimes even unavailable. However, the task is highly unconstrained and thus ill-posed. To address this problem, we propose to introduce an auxiliary domain which shares a common underlying-structure space with the target domain, and we make a partially shared latent space assumption. The key idea is to encourage the partially shared latent variable to represent the similar underlying spatial structures in both domains, while the two domain-specific latent variables will be unavoidably arranged to present renderings of two domains respectively. This is achieved by designing two parallel generative networks with a common Progressive Rendering Architecture (PRA), which constrains both generative networks' behaviors to model shared underlying structure and to model spatially dependent relation between rendering and underlying structure. Thus, we propose DSRGAN (GANs for Disentangling Underlying Structure and Rendering) to instantiate our method. We also propose a quantitative criterion (the Normalized Disentanglability) to quantify disentanglability. Comparison to the state-of-The-Art methods shows that DSRGAN can significantly outperform them in disentanglability. Copyright © 2019, The Authors. All rights reserved.

关键词： Rendering (computer graphics)

The Three Hundred project hydrodynamical simulations: Hydrodynamical weak-lensing cluster mass biases and richnesses using different hydro models.

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arXiv 2025年

作者： Giocoli, C. Despali, G. Meneghetti, M. Rasia, E. Moscardini, L. Borgani, S. Lesci, G.F. Marulli, F. Cui, W. Yepes, G. INAF-Osservatorio di Astrofisica e Scienza dello Spazio di Bologna Via Piero Gobetti 93/3 Bologna40129 Italy INFN – Sezione di Bologna viale Berti Pichat 6/2 BolognaI-40127 Italy Dipartimento di Fisica e Astronomia "Augusto Righi" Alma Mater Studiorum Università di Bologna via Gobetti 93/2 BolognaI-40129 Italy INAF – Osservatorio Astronomico di Trieste via Tiepolo 11 TriesteI-34131 Italy IFPU Institute for Fundamental Physics of the Universe Via Beirut 2 Trieste34014 Italy Department of Physics University of Michigan Ann ArborMI48109 United States Dipartimento di Fisica Università di Trieste Sez. di Astronomia via Tiepolo 11 TriesteI-34131 Italy ICSC - Italian Research Center on High Performance Computing Big Data and Quantum Computing via Magnanelli 2 Casalecchio di Reno40033 Italy INFN Instituto Nazionale di Fisica Nucleare Via Valerio 2 TriesteI-34127 Italy Departamento de Física Teórica Facultad de Ciencias Universidad Autónoma de Madrid Módulo 15 MadridE-28049 Spain Facultad de Ciencias Universidad Autónoma de Madrid MadridE-28049 Spain Institute for Astronomy University of Edinburgh Royal Observatory EdinburghEH9 3HJ United Kingdom

Context. The mass of galaxy clusters estimated from weak-lensing observations is affected by projection effects, leading to a systematic underestimation compared to the true cluster mass. This bias varies with both mass and redshift. Additionally, the magnitude of this bias depends on the criteria used to select clusters and the spatial scale over which their mass is measured. In this work, we leverage state-of-the-art hydrodynamical simulations of galaxy clusters carried out with GadgetX and GIZMO-SIMBA as part of the Three Hundred project. We used them to quantify weak-lensing mass biases with respect also to the results from dark matter-only simulations. We also investigate how the biases of the weak-lensing mass estimates propagate into the richness-mass relation. Aims. We aim to shed light on the effect of the presence of baryons on the weak-lensing mass bias and also whether this bias depends on the galaxy formation recipe;in addition, we seek to model the richness-mass relation that can be used as guidelines for observational experiments for cluster cosmology. Methods. We produced weak-lensing simulations of random projections to model the expected excess surface mass density profile of clusters up to redshift z = 1. We then estimated the observed richness by counting the number of galaxies in a cylinder with a radius equal to the cluster radius and correcting by large-scale projected contaminants. We adopted a Bayesian analysis to infer the weak lensing cluster mass and concentration. Results. We derived the weak-lensing mass-richness relation and found consistency within 1σ uncertainties across hydrodynamical simulations. The intercept parameter of the relation is independent of redshift but varies with the minimum of the stellar mass used to define the richness value. At the same time, the slope is described by a second-order polynomial in redshift, which is relatively constant up to z = 0.55. The scatter in observed richness at a fixed weak-lensing mass,

关键词： Dark Matter

Dynamical friction and the evolution of black holes in cosmological simulations: A new implementation in OpenGadget3

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arXiv 2024年

作者： Damiano, Alice Valentini, Milena Borgani, Stefano Tornatore, Luca Murante, Giuseppe Ragagnin, Antonio Ragone-Figueroa, Cinthia Dolag, Klaus Dipartimento di Fisica dell’Università di Trieste Sez. di Astronomia via Tiepolo 11 TriesteI-34131 Italy INAF – Osservatorio Astronomico di Trieste via Tiepolo 11 TriesteI-34131 Italy IFPU Institute for Fundamental Physics of the Universe Via Beirut 2 Trieste34014 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 INAF-Osservatorio di Astrofisica e Scienza dello Spazio di Bologna Via Piero Gobetti 93/3 BolognaI-40129 Italy Dipartimento di Fisica e Astronomia "Augusto Righi" Alma Mater Studiorum Università di Bologna via Gobetti 93/2 BolognaI-40129 Italy Universidad Nacional de Córdoba Laprida 854 CórdobaX5000BGR Argentina Universitäts-Sternwarte München Scheinerstr. 1 MünchenD-81679 Germany Max-Plank-Institut für Astrophysik Karl-Schwarzschild Strasse 1 GarchingD-85740 Germany

Aims. We introduce a novel sub-resolution prescription to correct for the unresolved dynamical friction (DF) onto black holes (BHs) in cosmological simulations, to describe BH dynamics accurately, and to overcome spurious motions induced by numerical effects. Methods. We implemented a sub-resolution prescription for the unresolved DF onto BHs in the OpenGadget3 code. We carried out cosmological simulations of a volume of (16 comoving Mpc)3 and zoomed-in simulations of a galaxy group and of a galaxy cluster. We assessed the advantages of our new technique in comparison to commonly adopted methods for hampering spurious BH displacements, namely repositioning onto a local minimum of the gravitational potential and ad hoc boosting of the BH particle dynamical mass. We inspected variations in BH demography in terms of offset from the centres of the host sub-halos, the wandering population of BHs, BH–BH merger rates, and the occupation fraction of sub-halos. We also analysed the impact of the different prescriptions on individual BH interaction events in detail. Results. The newly introduced DF correction enhances the centring of BHs on host halos, the effects of which are at least comparable with those of alternative techniques. Also, the correction becomes gradually more effective as the redshift decreases. Simulations with this correction predict half as many merger events with respect to the repositioning prescription, with the advantage of being less prone to leaving substructures without any central BH. Simulations featuring our DF prescription produce a smaller (by up to ∼ 50% with respect to repositioning) population of wandering BHs and final BH masses that are in good agreement with observations. Regarding individual BH–BH interactions, our DF model captures the gradual inspiraling of orbits before the merger occurs. By contrast, the repositioning scheme, in its most classical renditions, describes extremely fast mergers, while the dynamical mass misrepresents t

关键词： Cosmology

The Study on the Botnet and its Prevention Policies in the Internet of Things

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The Study on the Botnet and its Prevention Policies in the I...

International Conference on Computer Supported Cooperative Work in Design

作者： Yimu Ji Lu Yao Shangdong Liu Haichang Yao Qing Ye Ruchuan Wang Institute of High Performance Computing and Big Data Processing Nanjing University of Posts and Telecommunications

With the rapid development of Internet of Things (IOT), IOT is more and more important. Also, it faces serious security issues. This paper analyzes Mirai's architecture. The core components are C & C server and Loader server that take charge of command and control, IOT equipments are in charge of broadcast and attack. Paper analyzes Botnet propagation model, Mirais infection attack procedure, impact factor and then proposes the corresponding anti-virus strategy.

关键词： Botnet Servers Command and control systems Password Internet of Things Cameras Protocols

Unveiling Dark Matter free-streaming at the smallest scales with high redshift Lyman-alpha forest

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arXiv 2023年

作者： Iršič, Vid Viel, Matteo Haehnelt, Martin G. Bolton, James S. Molaro, Margherita Puchwein, Ewald Boera, Elisa Becker, George D. Gaikwad, Prakash Keating, Laura C. Kulkarni, Girish Kavli Institute for Cosmology University of Cambridge Madingley Road CambridgeCB3 0HA United Kingdom Cavendish Laboratory University of Cambridge 19 J. J. Thomson Ave. CambridgeCB3 0HE United Kingdom SISSA- International School for Advanced Studies Via Bonomea 265 Trieste34136 Italy INFN - National Institute for Nuclear Physics Via Valerio 2 TriesteI-34127 Italy IFPU Institute for Fundamental Physics of the Universe via Beirut 2 Trieste34151 Italy INAF Osservatorio Astronomico di Trieste Via G. B. Tiepolo 11 TriesteI-34131 Italy ICSC - Centro Nazionale di Ricerca in High Performance Computing Big Data e Quantum Computing Via Magnanelli 2 Bologna Italy Institute of Astronomy University of Cambridge Madingley Road CambridgeCB3 0HA United Kingdom School of Physics and Astronomy University of Nottingham University Park NottinghamNG7 2RD United Kingdom Leibniz-Institut für Astrophysik Potsdam An der Sternwarte 16 Potsdam14482 Germany Department of Physics and Astronomy University of California RiversideCA92521 United States Max-Planck-Institut für Astronomie Königstuhl 17 HeidelbergD-69117 Germany Institute for Astronomy University of Edinburgh Blackford Hill EdinburghEH9 3HJ United Kingdom Tata Institute of Fundamental Research Homi Bhabha Road Mumbai400005 India

This study introduces novel constraints on the free-streaming of thermal relic warm dark matter (WDM) from Lyman-α forest flux power spectra. Our analysis utilises a high-resolution, high-redshift sample of quasar spectra observed using the HIRES and UVES spectrographs (z = 4.2 − 5.0). We employ a Bayesian inference framework and a simulation-based likelihood that encompasses various parameters including the free-streaming of dark matter, cosmological parameters, the thermal history of the intergalactic medium, and inhomogeneous reionization, to establish lower limits on the mass of a thermal relic WDM particle of 5.7 keV (at 95% C.L.). This result surpasses previous limits from the Lyman-α forest through reduction of the measured uncertainties due to a larger statistical sample and by measuring clustering to smaller scales (kmax = 0.2 km−1 s). The approximately two-fold improvement due to the expanded statistical sample suggests that the effectiveness of Lyman-α forest constraints on WDM models at high redshifts are limited by the availability of high-quality quasar spectra. Restricting the analysis to comparable scales and thermal history priors as in prior studies (kmax −1 s) lowers the bound on the WDM mass to 4.1 keV. As the precision of the measurements increases, it becomes crucial to examine the instrumental and modelling systematics. On the modelling front, we argue that the impact of the thermal history uncertainty on the WDM particle mass constraint has diminished due to improved independent observations. At the smallest scales, the primary source of modeling systematic arises from the structure in the peculiar velocity of the intergalactic medium and inhomogeneous reionization. © 2023, CC BY.

关键词： Galaxies

A DECONSTRUCTION OF METHODS TO DERIVE ONE-POINT LENSING STATISTICS

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arXiv 2024年

作者： Alfradique, Viviane Castro, Tiago Marra, Valerio Quartin, Miguel Giocoli, Carlo Monaco, Pierluigi Instituto de Física Universidade Federal do Rio de Janeiro RJ Rio de Janeiro21941-972 Brazil Centro Brasileiro de Pesquisas Físicas Rua Dr. Xavier Sigaud 150 RJ Rio de Janeiro22290-180 Brazil INAF - Osservatorio Astronomico di Trieste via Tiepolo 11 TriesteI-34131 Italy INFN - Sezione di Trieste TriesteI-34100 Italy IFPU - Institute for Fundamental Physics of the Universe via Beirut 2 Trieste34151 Italy ICSC - Centro Nazionale di Ricerca in High Performance Computing Big Data e Quantum Computing Via Magnanelli 2 Bologna Italy Departamento de Física Universidade Federal do Espírito Santo ES Vitória29075-910 Brazil PPGCosmo Universidade Federal do Espírito Santo ES Vitória29075-910 Brazil Observatório do Valongo Universidade Federal do Rio de Janeiro RJ Rio de Janeiro20080-090 Brazil INAF - Osservatorio Astronomico di Bologna via Piero Gobetti 93/3 BolognaI-40129 Italy INFN Sezione di Bologna viale Berti Pichat 6/2 BolognaI-40127 Italy Università di Trieste Dipartimento di Fisica via Tiepolo 11 Trieste34143 Italy

Gravitational lensing is a crucial tool for exploring cosmic phenomena, providing insights into galaxy clustering, dark matter, and dark energy. Given the substantial computational demands of N-body simulations, approximate methods like PINOCCHIO and turboGL have been proposed as viable alternatives for simulating lensing probability density functions (PDFs). This paper evaluates these methods and their effectiveness across both weak and strong lensing regimes, with a focus in the context where baryonic effects are negligible. Our comparative analysis reveals that these methods are effective for applications where lensing is mild, such as the majority of sources of electromagnetic and gravitational waves. However, both PINOCCHIO and turboGL break down for large values of convergence and magnification due to their loss of accuracy in capturing small-scale nonlinear matter fields, owing to oversimplified assumptions about internal halo structures and reliance on perturbation theory. PINOCCHIO yields second-to-fourth moments of the lensing PDFs, which are 6-10% smaller than those resulting from N-body simulations in regimes where baryonic effects are minimal. These findings aim to inform future studies on gravitational lensing of point sources, which are increasingly relevant with upcoming supernova and gravitational wave datasets. © 2024, CC BY.

关键词： Probability density function