Universe最新文献

Constraints on Metastable Dark Energy Decaying into Dark Matter 可迁移暗能量衰变为暗物质的制约因素

IF 2.9 4区物理与天体物理

Universe Pub Date : 2024-09-18 DOI: 10.3390/universe10090371

Jônathas S. T. de Souza, Gustavo S. Vicente, Leila L. Graef

引用次数: 0

Quantum Field Theory of Black Hole Perturbations with Backreaction: I General Framework 具有反作用的黑洞扰动量子场论：I 总体框架

IF 2.9 4区物理与天体物理

Universe Pub Date : 2024-09-18 DOI: 10.3390/universe10090372

Thomas Thiemann

{"title":"Quantum Field Theory of Black Hole Perturbations with Backreaction: I General Framework","authors":"Thomas Thiemann","doi":"10.3390/universe10090372","DOIUrl":"https://doi.org/10.3390/universe10090372","url":null,"abstract":"In a seminal work, Hawking showed that natural states for free quantum matter fields on classical spacetimes that solve the spherically symmetric vacuum Einstein equations are KMS states of non-vanishing temperature. Although Hawking’s calculation does not include the backreaction of matter on geometry, it is more than plausible that the corresponding Hawking radiation leads to black hole evaporation which is, in principle, observable. Obviously, an improvement of Hawking’s calculation including backreaction is a problem of quantum gravity. Since no commonly accepted quantum field theory of general relativity is available yet, it has been difficult to reliably derive the backreaction effect. An obvious approach is to use the black hole perturbation theory of a Schwarzschild black hole of fixed mass and to quantize those perturbations. However, it is not clear how to reconcile perturbation theory with gauge invariance beyond linear perturbations. In recent work, we proposed a new approach to this problem that applies when the physical situation has an approximate symmetry, such as homogeneity (cosmology), spherical symmetry (Schwarzschild), or axial symmetry (Kerr). The idea, which is surprisingly feasible, is to first construct the non-perturbative physical (reduced) Hamiltonian of the reduced phase space of fully gauge invariant observables and only then apply perturbation theory directly in terms of observables. The task to construct observables is then disentangled from perturbation theory, thus allowing to unambiguously develop perturbation theory to arbitrary orders. In this first paper of the series we outline and showcase this approach for spherical symmetry and second order in the perturbations for Einstein–Klein–Gordon–Maxwell theory. Details and generalizations to other matter and symmetry and higher orders will appear in subsequent companion papers.","PeriodicalId":48646,"journal":{"name":"Universe","volume":"2 1","pages":""},"PeriodicalIF":2.9,"publicationDate":"2024-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142250905","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

Bayesian Knowledge Infusion for Studying Historical Sunspot Numbers 贝叶斯知识注入法研究历史太阳黑子数量

IF 2.9 4区物理与天体物理

Universe Pub Date : 2024-09-14 DOI: 10.3390/universe10090370

Wenxin Jiang, Haisheng Ji

{"title":"Bayesian Knowledge Infusion for Studying Historical Sunspot Numbers","authors":"Wenxin Jiang, Haisheng Ji","doi":"10.3390/universe10090370","DOIUrl":"https://doi.org/10.3390/universe10090370","url":null,"abstract":"A scientific method that proposes a value Y to estimate a target value ρ is often subject to some level of uncertainty. In the Bayesian framework, the level of uncertainty can be measured by the width of the 68% interval, which is the range of the middle 68% of the ranked ρ values sampled from the posterior distribution p(ρ|Y). This paper considers Bayesian knowledge infusion (BKI) to reduce the uncertainty of the posterior distribution p(ρ|Y) based on additional knowledge that an event A happens. BKI is achieved by using a conditional prior distribution p(ρ|A) in the Bayes theorem, assuming that given the true ρ, its error-contaminated value Y is independent of event A. We use two examples to illustrate how to study whether or not it is possible to reduce uncertainty from 14C reconstruction (Y) of the annual sunspot number (SSN) (ρ) by infusing additional information (A) using BKI. Information (A) that SSN is from a year that has a Far Eastern record of naked eye sunspots is found to be not so effective in reducing the uncertainty. In contrast, information that SSN is from a year at a cycle minimum is found to be very effective, producing much narrower 68% intervals. The resulting Bayesian point estimates of SSN (the posterior medians of ρ) are cross-validated and tested on a subset of telescopically observed SSNs that were unused in the process of Bayes computation.","PeriodicalId":48646,"journal":{"name":"Universe","volume":"3 1","pages":""},"PeriodicalIF":2.9,"publicationDate":"2024-09-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142250906","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

Predicting Solar Cycles with a Parametric Time Series Model 用参数时间序列模型预测太阳周期

IF 2.9 4区物理与天体物理

Universe Pub Date : 2024-09-11 DOI: 10.3390/universe10090364

Kristof Petrovay

{"title":"Predicting Solar Cycles with a Parametric Time Series Model","authors":"Kristof Petrovay","doi":"10.3390/universe10090364","DOIUrl":"https://doi.org/10.3390/universe10090364","url":null,"abstract":"The objective of this paper is to reproduce and predict the series of solar cycle amplitudes using a simple time-series model that takes into account the variable time scale of the Gleissberg oscillation and the absence of clear evidence for odd–even alternation prior to Solar Cycle 9 (SC9). It is demonstrated that the Gleissberg oscillation can be quite satisfactorily modelled as a sinusoidal variation of constant amplitude with a period increasing linearly with time. Subtracting this model from the actual cycle amplitudes, a clear even–odd alternating pattern is discerned in the time series of the residuals since SC9. For this period of time, the mean value of the residuals for odd-numbered cycles is shown to exceed the value for even-numbered cycles by more than 4σ, providing the clearest evidence yet for a persistent odd–even–odd alternation in cycle amplitudes. Random deviations from these means are less than half the standard deviation of the raw cycle amplitude time series for the same period, which allows the use of these regularities for solar cycle prediction with substantially better confidence than the simple climatological average. Predicted cycle amplitudes are found to be robust against the addition or omission of some data points from the input set, and the method correctly hindcasts SC23 and SC24. The potential physical background of the regularities is also discussed. Our predictions for the amplitudes of SC25, SC26, and SC27 are 155.8±20.7, 96.9±25.1 and 140.8±20.7, respectively. This suggests that the amplitude of SC26 will be even lower than that of SC24, making it the weakest cycle since the Dalton Minimum.","PeriodicalId":48646,"journal":{"name":"Universe","volume":"177 1","pages":""},"PeriodicalIF":2.9,"publicationDate":"2024-09-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142210886","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

Comparing Analytic and Numerical Studies of Tensor Perturbations in Loop Quantum Cosmology 环路量子宇宙学中张量扰动的分析研究与数值研究的比较

IF 2.9 4区物理与天体物理

Universe Pub Date : 2024-09-11 DOI: 10.3390/universe10090365

Guillermo A. Mena Marugán, Antonio Vicente-Becerril, Jesús Yébana Carrilero

{"title":"Comparing Analytic and Numerical Studies of Tensor Perturbations in Loop Quantum Cosmology","authors":"Guillermo A. Mena Marugán, Antonio Vicente-Becerril, Jesús Yébana Carrilero","doi":"10.3390/universe10090365","DOIUrl":"https://doi.org/10.3390/universe10090365","url":null,"abstract":"We investigate the implications of different quantization approaches in Loop Quantum Cosmology for the primordial power spectrum of tensor modes. Specifically, we consider the hybrid and dressed metric approaches to derive the effective mass that governs the evolution of the tensor modes. Our study comprehensively examines the two resulting effective masses and how to estimate them in order to obtain approximated analytic solutions to the tensor perturbation equations. Since Loop Quantum Cosmology incorporates preinflationary effects in the dynamics of the perturbations, we do not have at our disposal a standard choice of privileged vacuum, like the Bunch–Davies state in quasi-de Sitter inflation. We then select the vacuum state by a recently proposed criterion which removes unwanted oscillations in the power spectrum and guarantees an asymptotic diagonalization of the Hamiltonian in the ultraviolet. This vacuum is usually called the NO-AHD (from the initials of Non-Oscillating with Asymptotic Hamiltonian Diagonalization) vacuum. Consequently, we compute the power spectrum by using our analytic approximations and by introducing a suitable numerical procedure, adopting in both cases an NO-AHD vacuum. With this information, we compare the different spectra obtained from the hybrid and the dressed metric approaches, as well as from the analytic and numerical procedures. In particular, this proves the remarkable accuracy of our approximations.","PeriodicalId":48646,"journal":{"name":"Universe","volume":"17 1","pages":""},"PeriodicalIF":2.9,"publicationDate":"2024-09-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142210888","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

Dark Atoms of Nuclear Interacting Dark Matter 核相互作用暗物质的暗原子

IF 2.9 4区物理与天体物理

Universe Pub Date : 2024-09-11 DOI: 10.3390/universe10090368

Vitaly A. Beylin, Timur E. Bikbaev, Maxim Yu. Khlopov, Andrey G. Mayorov, Danila O. Sopin

{"title":"Dark Atoms of Nuclear Interacting Dark Matter","authors":"Vitaly A. Beylin, Timur E. Bikbaev, Maxim Yu. Khlopov, Andrey G. Mayorov, Danila O. Sopin","doi":"10.3390/universe10090368","DOIUrl":"https://doi.org/10.3390/universe10090368","url":null,"abstract":"The lack of positive evidence for Weakly Interacting Massive Particles (WIMPs) as well as the lack of discovery of supersymmetric (SUSY) particles at the LHC may appeal to a non-supersymmetric solution for the Standard Model problem of the Higgs boson mass divergence, the origin of the electroweak energy scale and the physical nature of the cosmological dark matter in the approach of composite Higgs boson. If the Higgs boson consists of charged constituents, their binding can lead to stable particles with electroweak charges. Such particles can take part in sphaleron transitions in the early Universe, which balance their excess with baryon asymmetry. Constraints on exotic charged species leave only stable particles with charge −2n possible, which can bind with n nuclei of primordial helium in neutral dark atoms. The predicted ratio of densities of dark atoms and baryonic matter determines the condition for dark atoms to dominate in the cosmological dark matter. To satisfy this condition of the dark-atom nature of the observed dark matter, the mass of new stable −2n charged particles should be within reach of the LHC for their searches. We discuss the possibilities of dark-atom binding in multi-atom systems and present state-of-the-art quantum mechanical descriptions of dark-atom interactions with nuclei. Annual modulations in such interactions with nuclei of underground detectors can explain the positive results of DAMA/NaI and DAMA/LIBRA experiments and the negative results of the underground WIMP searches.","PeriodicalId":48646,"journal":{"name":"Universe","volume":"321 1","pages":""},"PeriodicalIF":2.9,"publicationDate":"2024-09-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142227829","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

The Operational Meaning of Total Energy of Isolated Systems in General Relativity 广义相对论中孤立系统总能量的操作意义

IF 2.9 4区物理与天体物理

Universe Pub Date : 2024-09-11 DOI: 10.3390/universe10090367

Abhay Ashtekar, Simone Speziale

引用次数: 0

Initial State in Quantum Cosmology and the Proper Mass of the Universe 量子宇宙学中的初始状态与宇宙的适当质量

IF 2.9 4区物理与天体物理

Universe Pub Date : 2024-09-11 DOI: 10.3390/universe10090366

Natalia Gorobey, Alexander Lukyanenko, Alexander V. Goltsev

引用次数: 0

On the Propagation of Gravitational Waves in the Weyl Invariant Theory of Gravity 论韦尔引力不变理论中引力波的传播