发布求助
文献互助 智能选刊 最新文献

Universe最新文献

筛选
英文 中文
Lorentzian Quantum Cosmology from Effective Spin Foams 从有效自旋泡沫看洛伦兹量子宇宙学
IF 2.9 4区 物理与天体物理
Universe Pub Date : 2024-07-13 DOI: 10.3390/universe10070296
Bianca Dittrich, José Padua-Argüelles
{"title":"Lorentzian Quantum Cosmology from Effective Spin Foams","authors":"Bianca Dittrich, José Padua-Argüelles","doi":"10.3390/universe10070296","DOIUrl":"https://doi.org/10.3390/universe10070296","url":null,"abstract":"Effective spin foams provide the most computationally efficient spin foam models yet and are therefore ideally suited for applications, e.g., to quantum cosmology. Here, we provide the first effective spin foam computations of a finite time evolution step in a Lorentzian quantum de Sitter universe. We will consider a setup that computes the no-boundary wave function and a setup describing the transition between two finite scale factors. A key property of spin foams is that they implement discrete spectra for the areas. We therefore study the effects that are induced by the discrete spectra. To perform these computations, we had to identify a technique to deal with highly oscillating and slowly converging or even diverging sums. Here, we illustrate that high-order Shanks transformation works very well and is a promising tool for the evaluation of Lorentzian (gravitational) path integrals and spin foam sums.","PeriodicalId":48646,"journal":{"name":"Universe","volume":"154 1","pages":""},"PeriodicalIF":2.9,"publicationDate":"2024-07-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141608980","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
On the Choice of Variable for Quantization of Conformal GR 关于共形 GR 量子化变量的选择
IF 2.9 4区 物理与天体物理
Universe Pub Date : 2024-07-13 DOI: 10.3390/universe10070294
A. B. Arbuzov, A. A. Nikitenko
{"title":"On the Choice of Variable for Quantization of Conformal GR","authors":"A. B. Arbuzov, A. A. Nikitenko","doi":"10.3390/universe10070294","DOIUrl":"https://doi.org/10.3390/universe10070294","url":null,"abstract":"The possibility of using spin connection components as basic quantization variables of a conformal version of general relativity is studied. The considered model contains gravitational degrees of freedom and a scalar dilaton field. The standard tetrad formalism is applied. Properties of spin connections in this model are analyzed. Secondary quantization of the chosen variables is performed. The gravitational part of the model action turns out to be quadratic with respect to the spin connections. So at the quantum level, the model looks trivial, i.e., without quantum self-interactions. Meanwhile the correspondence to general relativity is preserved at the classical level.","PeriodicalId":48646,"journal":{"name":"Universe","volume":"2010 1","pages":""},"PeriodicalIF":2.9,"publicationDate":"2024-07-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141608981","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Isospin QCD as a Laboratory for Dense QCD 作为高密度 QCD 实验室的等空间 QCD
IF 2.9 4区 物理与天体物理
Universe Pub Date : 2024-07-12 DOI: 10.3390/universe10070293
Toru Kojo, Daiki Suenaga, Ryuji Chiba
{"title":"Isospin QCD as a Laboratory for Dense QCD","authors":"Toru Kojo, Daiki Suenaga, Ryuji Chiba","doi":"10.3390/universe10070293","DOIUrl":"https://doi.org/10.3390/universe10070293","url":null,"abstract":"QCD with the isospin chemical potential μI is a useful laboratory to delineate the microphysics in dense QCD. To study the quark–hadron continuity, we use a quark–meson model that interpolates hadronic and quark matter physics at microscopic level. The equation of state is dominated by mesons at low density but taken over by quarks at high density. We extend our previous studies with two flavors to the three-flavor case to study the impact of the strangeness, which may be brought by kaons (K+,K0)=(us¯,sd¯) and the UA(1) anomaly. In the normal phase, the excitation energies of kaons are reduced by μI in the same way as hyperons in nuclear matter at the finite baryon chemical potential. Once pions condense, kaon excitation energies increase as μI does. Moreover, strange quarks become more massive through the UA(1) coupling to the condensed pions. Hence, at zero and low temperature, the strange hadrons and quarks are highly suppressed. The previous findings in two-flavor models, sound speed peak, negative trace anomaly, gaps insensitive to μI, persist in our three-flavor model and remain consistent with the lattice results to μI∼ 1 GeV. We discuss the non-perturbative power corrections and quark saturation effects as important ingredients to understand the crossover equations of state measured on the lattice.","PeriodicalId":48646,"journal":{"name":"Universe","volume":"25 1","pages":""},"PeriodicalIF":2.9,"publicationDate":"2024-07-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141608982","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Stochastic Tunneling in de Sitter Spacetime 德西特时空中的随机隧道效应
IF 2.9 4区 物理与天体物理
Universe Pub Date : 2024-07-11 DOI: 10.3390/universe10070292
Taiga Miyachi, Jiro Soda, Junsei Tokuda
{"title":"Stochastic Tunneling in de Sitter Spacetime","authors":"Taiga Miyachi, Jiro Soda, Junsei Tokuda","doi":"10.3390/universe10070292","DOIUrl":"https://doi.org/10.3390/universe10070292","url":null,"abstract":"Tunneling processes in de Sitter spacetime are studied by using the stochastic approach. We evaluate the Martin–Siggia–Rose–Janssen–de Dominicis (MSRJD) functional integral by using the saddle-point approximation to obtain the tunneling rate. The applicability conditions of this method are clarified using the Schwinger–Keldysh formalism. In the case of a shallow potential barrier, we reproduce the Hawking–Moss (HM) tunneling rate. Remarkably, in contrast to the HM picture, the configuration derived from the MSRJD functional integral satisfies physically natural boundary conditions. We also discuss the case of a steep potential barrier and find an interesting Coleman–de Luccia (CDL) bubblelike configuration. Since the starting point of our analysis is the Schwinger–Keldysh path integral, which can be formulated in a more generic setup and incorporates quantum effects, our formalism sheds light on further studies of tunneling phenomena from a real-time perspective.","PeriodicalId":48646,"journal":{"name":"Universe","volume":"2 1","pages":""},"PeriodicalIF":2.9,"publicationDate":"2024-07-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141586208","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Wormhole Restrictions from Quantum Energy Inequalities 从量子能量不等式看虫洞限制
IF 2.9 4区 物理与天体物理
Universe Pub Date : 2024-07-06 DOI: 10.3390/universe10070291
Eleni-Alexandra Kontou
{"title":"Wormhole Restrictions from Quantum Energy Inequalities","authors":"Eleni-Alexandra Kontou","doi":"10.3390/universe10070291","DOIUrl":"https://doi.org/10.3390/universe10070291","url":null,"abstract":"Wormhole solutions, bridges that connect different parts of spacetime, were proposed early in the history of General Relativity. Soon after, it was shown that all wormholes violate classical energy conditions, which are non-negativity constraints on contractions of the stress–energy tensor. Since these conditions are violated by quantum fields, it was believed that wormholes can be constructed in the context of semiclassical gravity. But negative energies in quantum field theory are not without restriction: quantum energy inequalities (QEIs) control renormalized negative energies averaged over a geodesic. Thus, QEIs provide restrictions on the construction of wormholes. This work is a review of the relevant literature, thus focusing on results where QEIs restrict traversable wormholes. Both ‘short’ and ‘long’ (without causality violations) wormhole solutions in the context of semiclassical gravity are examined. A new result is presented on constraints on the Maldacena, Milekhin, and Popov ‘long’ wormhole from the recently derived doubled smeared null energy condition.","PeriodicalId":48646,"journal":{"name":"Universe","volume":"79 1","pages":""},"PeriodicalIF":2.9,"publicationDate":"2024-07-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141566973","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Molecular Formation in Low-Metallicity Hot Cores 低金属性热核中的分子形成
IF 2.9 4区 物理与天体物理
Universe Pub Date : 2024-07-04 DOI: 10.3390/universe10070290
Yara Sobhy, Hideko Nomura, Tetsuo Yamamoto, Osama Shalabeia
{"title":"Molecular Formation in Low-Metallicity Hot Cores","authors":"Yara Sobhy, Hideko Nomura, Tetsuo Yamamoto, Osama Shalabeia","doi":"10.3390/universe10070290","DOIUrl":"https://doi.org/10.3390/universe10070290","url":null,"abstract":"The chemical complexity in low-metallicity hot cores has been confirmed by observations. We investigate the effect of varying physical parameters, such as temperature, density and the cosmic ray ionisation rate (CRIR), on the molecular abundance evolution in low-metallicity hot cores using the UMIST gas phase chemical model. CRIR had the strongest effect on molecular abundance. The resultant molecular abundances were divided into three categories with different trends in time evolution. We compared our results with the observations of hot cores in the Large Magellanic Cloud (LMC). Our model fits best with the observations at a time of around 105 years after the evaporation of ice and at the CRIR of 1.36×10−16 s−1. The resultant abundances of the oxygen-bearing complex organic molecules (COMs), such as CH3OH, HCOOCH3 and CH3OCH3, do not fit with observations in the same physical condition and may be located in a different physical environment. Our results suggest that investigating the CRIR value is crucial to predict the molecular evolution in LMC hot cores.","PeriodicalId":48646,"journal":{"name":"Universe","volume":"52 1","pages":""},"PeriodicalIF":2.9,"publicationDate":"2024-07-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141553080","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
On the Nature of the Radio Calibrator and Gamma-Ray Emitting NLS1 Galaxy 3C 286 and Its Multiwavelength Variability 论射电校准器和伽马射线发射 NLS1 星系 3C 286 的性质及其多波长变异性
IF 2.9 4区 物理与天体物理
Universe Pub Date : 2024-07-02 DOI: 10.3390/universe10070289
S. Komossa, S. Yao, D. Grupe, A. Kraus
{"title":"On the Nature of the Radio Calibrator and Gamma-Ray Emitting NLS1 Galaxy 3C 286 and Its Multiwavelength Variability","authors":"S. Komossa, S. Yao, D. Grupe, A. Kraus","doi":"10.3390/universe10070289","DOIUrl":"https://doi.org/10.3390/universe10070289","url":null,"abstract":"The quasar 3C 286, a well-known calibrator source in radio astronomy, was found to exhibit exceptional multiwavelength properties. Its rich and complex optical emission-line spectrum revealed its narrow-line Seyfert 1 (NLS1) nature. Given its strong radio emission, this makes 3C 286 one of the radio-loudest NLS1 galaxies known to date. 3C 286 is also one of very few known compact steep-spectrum (CSS) sources detected in the gamma-ray regime. Observations in the X-ray regime, rarely carried out so far, revealed evidence for variability, raising the question whether it is driven by the accretion disk or jet. 3C 286 is also well known for its damped Lyman alpha system from an intervening absorber at z = 0.692, triggering a search for the corresponding X-ray absorption along the line-of-sight. Here, we present new observations in the radio, X-ray, optical, and UV bands. The nature of the X-ray variability is addressed. Spectral evidence suggests that it is primarily driven by the accretion disk (not the jet), and the X-ray spectrum is well fit by a powerlaw plus soft excess model. The radio flux density and polarization remain constant at the Effelsberg telescope resolution, reconfirming the use of 3C 286 as radio calibrator. The amount of reddening/absorption along the line-of-sight intrinsic to 3C 286 is rigorously assessed. None is found, validating the derivation of a high Eddington ratio (L/LEdd∼ 1) and of the very high radio-loudness index of 3C 286. Based on the first deep Chandra image of 3C 286, tentative evidence for hard X-ray emission from the SW radio lobe is reported. A large variety of models for the gamma-ray emission of 3C 286 are briefly discussed.","PeriodicalId":48646,"journal":{"name":"Universe","volume":"34 1","pages":""},"PeriodicalIF":2.9,"publicationDate":"2024-07-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141501867","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Mono-Higgs and Mono-Z Production in the Minimal Vector Dark Matter Model 最小矢量暗物质模型中的单希格斯和单Z生产
IF 2.9 4区 物理与天体物理
Universe Pub Date : 2024-07-02 DOI: 10.3390/universe10070288
Gonzalo Benítez-Irarrázabal, Alfonso Zerwekh
{"title":"Mono-Higgs and Mono-Z Production in the Minimal Vector Dark Matter Model","authors":"Gonzalo Benítez-Irarrázabal, Alfonso Zerwekh","doi":"10.3390/universe10070288","DOIUrl":"https://doi.org/10.3390/universe10070288","url":null,"abstract":"The minimal vector dark matter is a viable realization of the minimal dark matter paradigm. It extends the standard model by the inclusion of a vector matter field in the adjoint representation of SU(2)L. The dark matter candidate corresponds to the neutral component of the new vector field (V0). Previous studies have shown that the model can explain the observed dark matter abundance while evading direct and indirect searches. At colliders, the attention has been put on the production of the charged companions of the dark matter candidate. In this work, we focus on the mono-Higgs and mono-Z signals at Hadron colliders. The new charged vectors (V±) are invisible unless a dedicated search is performed. Consequently, we assume that the mono-Higgs and mono-Z processes correspond to the pp→hV+,0V−,0 and pp→ZV+,0V−,0 reactions, respectively. We show that, while the pp→hV+,0V−,0 is more important, both channels may produce significant signals at the HL-LHC and colliders running at s=27 TeV and 100 TeV, probing almost the complete parameter space.","PeriodicalId":48646,"journal":{"name":"Universe","volume":"17 1","pages":""},"PeriodicalIF":2.9,"publicationDate":"2024-07-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141501868","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Energetic Particles and High-Energy Processes in Cosmological Filaments and Their Astronomical Implications 宇宙学细丝中的高能粒子和高能过程及其天文学意义
IF 2.9 4区 物理与天体物理
Universe Pub Date : 2024-07-01 DOI: 10.3390/universe10070287
Kinwah Wu, Ellis R. Owen, Qin Han, Yoshiyuki Inoue, Lilian Luo
{"title":"Energetic Particles and High-Energy Processes in Cosmological Filaments and Their Astronomical Implications","authors":"Kinwah Wu, Ellis R. Owen, Qin Han, Yoshiyuki Inoue, Lilian Luo","doi":"10.3390/universe10070287","DOIUrl":"https://doi.org/10.3390/universe10070287","url":null,"abstract":"Large-scale cosmic filaments connect galaxies, clusters, and voids. They are permeated by magnetic fields with a variety of topologies. Cosmic rays with energies up to 1020eV can be produced in astrophysical environments associated with star-formation and AGN activities. The fate of these cosmic rays in filaments, which cannot be directly observed on Earth, are rarely studied. We investigate the high-energy processes associated with energetic particles (cosmic rays) in filaments, adopting an ecological approach that includes galaxies, clusters/superclusters, and voids as key cosmological structures in the filament ecosystem. We derive the phenomenology for modelling interfaces between filaments and these structures, and investigate how the transfer and fate of energetic cosmic ray protons are affected by the magnetism of the interfaces. We consider different magnetic field configurations in filaments and assess the implications for cosmic ray confinement and survival against hadronic pion-producing and photo-pair interactions. Our analysis shows that the fate of the particles depends on the location of their origin within a filament ecosystem, and that filaments act as ‘highways’, channelling cosmic rays between galaxies, galaxy clusters, and superclusters. Filaments can also operate as cosmic ‘fly paper’, capturing cosmic ray protons with energies up to 1018eV from cosmic voids. Our analysis predicts the presence of a population of ∼1012–1016eV cosmic ray protons in filaments and voids accumulated continually over cosmic time. These protons do not suffer significant energy losses through photo-pair or pion production, nor can they be cooled efficiently. Instead, they form a cosmic ray fossil record of the power generation history of the Universe.","PeriodicalId":48646,"journal":{"name":"Universe","volume":"24 1","pages":""},"PeriodicalIF":2.9,"publicationDate":"2024-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141501919","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
X17: Status and Perspectives X17：现状与展望
IF 2.9 4区 物理与天体物理
Universe Pub Date : 2024-06-29 DOI: 10.3390/universe10070285
Carlo Gustavino
{"title":"X17: Status and Perspectives","authors":"Carlo Gustavino","doi":"10.3390/universe10070285","DOIUrl":"https://doi.org/10.3390/universe10070285","url":null,"abstract":"Recently, a group directed by A. J. Krasznahorkay observed an anomaly in the emission of electron–positron pairs in three different nuclear reactions, namely, the 3H(p,e−e+)4He, 7Li(p,e−e+)8Be, and 11B(p,e−e+)12C processes. Kinematics indicate that this anomaly might be due to the de-excitation of 4He, 8Be, and 12C nuclei with the emission of a boson with a mass of about 17 MeV, rapidly decaying into e−e+ pairs. The result of the experiments performed with the singletron accelerator of ATOMKI is reviewed, and the consequences of the so-called X17 boson in particle physics and in cosmology are discussed. Forthcoming experiments designed to shed light on the possible existence of the X17 boson are also reported.","PeriodicalId":48646,"journal":{"name":"Universe","volume":"24 1","pages":""},"PeriodicalIF":2.9,"publicationDate":"2024-06-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141501921","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
首页 上一页 下一页 尾页
0
×
引用
GB/T 7714-2015
复制
MLA
复制
APA
复制
导出至
BibTeX EndNote RefMan NoteFirst NoteExpress
×
提示
您的信息不完整，为了账户安全，请先补充。
现在去补充
×
提示
您因"违规操作"
具体请查看互助需知
我知道了
×
提示
现在去查看 取消
×
提示
确定
请完成安全验证×
相关产品
×
本文献相关产品
联系我们：info@booksci.cn Book学术提供免费学术资源搜索服务，方便国内外学者检索中英文文献。致力于提供最便捷和优质的服务体验。 Copyright © 2023 布克学术 All rights reserved.
京ICP备2023020795号-1
ghs 京公网安备 11010802042870号
Book学术文献互助
Book学术文献互助群
群 号：481959085
Book学术官方微信