Article
Astronomy & Astrophysics
Sergei D. Odintsov, Tanmoy Paul
Summary: We propose a new entropy function that avoids singularities throughout the cosmic evolution of the universe and generalizes several known entropies. Unlike existing entropies, the new function remains nonsingular even when the Hubble parameter is zero, making it useful for describing bouncing scenarios in cosmology. The nonsingular behavior allows for symmetric bounce scenarios, and the parameters of the entropy function affect observable quantities such as the spectral tilt and the tensor-to-scalar ratio. The new entropic cosmology is also shown to be equivalent to generalized holographic cosmology. (c) 2022 Elsevier B.V. All rights reserved.
PHYSICS OF THE DARK UNIVERSE
(2023)
Article
Astronomy & Astrophysics
Ivan Agullo, Dimitrios Kranas, V. Sreenath
Summary: The model discussed explores a scenario in the early universe where a cosmic bounce precedes the inflationary epoch, providing a common origin for several anomalous features observed in the cosmic microwave background (CMB) at large angular scales. These features include power suppression, dipolar asymmetry, and odd-parity correlations, with amplitude and scale dependence consistent with observations. Additionally, the model alleviates tension in the lensing amplitude.
GENERAL RELATIVITY AND GRAVITATION
(2021)
Article
Astronomy & Astrophysics
Debottam Nandi
Summary: The main difficulties in constructing a viable early Universe bouncing model include bypassing observational and theoretical no-go theorems, constructing a stable non-singular bouncing phase, and developing a stable attractor solution to evade BKL instability. The study shows that the bouncing solution remains stable and can avoid BKL instability for a wide range of model parameters, with ekpyrosis being identified as the most stable solution in any scenario.
Article
Computer Science, Interdisciplinary Applications
Friedemann Klass, Alessandro Gabbana, Andreas Bartel
Summary: High-order lattice Boltzmann methods offer a systematic approach for incorporating thermal and compressible effects in the study of regimes with finite Knudsen numbers. However, defining boundary conditions becomes non-trivial due to the presence of multiple layers. This study introduces a thermal extension of a non-equilibrium bounce-back boundary condition and compares it with established algorithms through simulations of wall-bounded flows.
JOURNAL OF COMPUTATIONAL SCIENCE
(2021)
Article
Computer Science, Software Engineering
Diego Royo, Talha Sultan, Adolfo Munoz, Khadijeh Masumnia-Bisheh, Eric Brandt, Diego Gutierrez, Andreas Velten, Julio Marco
Summary: Non-line-of-sight imaging methods use indirect illumination to reconstruct complex scenes that are not directly visible. By leveraging the specular behavior of planar diffuse surfaces, known as virtual mirrors, we expand the capabilities of NLOS imaging beyond third-bounce illumination. This approach allows us to image objects with limited visibility angles and objects hidden behind two corners.
ACM TRANSACTIONS ON GRAPHICS
(2023)
Article
Engineering, Electrical & Electronic
Connor Henley, Joseph Hollmann, Ramesh Raskar
Summary: This paper introduces a new lidar imaging mode called bounce-flash lidar, which indirectly illuminates most surfaces in the scene. The authors utilize a laser spot projected onto a diffusely reflecting surface as a point source, and use time-of-flight measurements to determine the position of this point source. They propose simple methods for estimating scene range and reflectance using time-of-flight and intensity measurements. The paper also highlights the advantages of bounce-flash lidar, including the use of cast shadows to estimate occluded surfaces' geometry and the strategic positioning of the illumination source.
IEEE TRANSACTIONS ON COMPUTATIONAL IMAGING
(2022)
Article
Physics, Multidisciplinary
U. S. Jong, U. G. Ri
Summary: In this study, we investigated the production of matter during the bounce phase in a non-singular bounce scenario with non-minimal kinetic coupling between two scalar fields. We found that a significant amount of matter is generated during the bounce phase, which is consistent with cosmological observations and leads to the formation of a hot big bang universe after the bounce.
INDIAN JOURNAL OF PHYSICS
(2023)
Article
Physics, Particles & Fields
Joao Luis Rosa, Nailya Ganiyeva, Francisco S. N. Lobo
Summary: In this work, we analyze traversable wormhole spacetimes within the framework of energy-momentum squared gravity. We show that a wide variety of wormhole solutions satisfying all energy conditions exist without the need for fine-tuning of model parameters. The solutions are obtained through an analytical recursive algorithm, and matching conditions with an external vacuum are derived. By matching the interior wormhole spacetime with the Schwarzschild solution, we obtain localized static and spherically symmetric wormhole solutions that satisfy all energy conditions for the entire spacetime range.
EUROPEAN PHYSICAL JOURNAL C
(2023)
Article
Physics, Particles & Fields
M. Ilyas, W. U. Rahman
Summary: This paper analyzes modified f(R) gravity models in the FLRW background, studying bouncing cosmology actions under different viable models in f(R) gravity theory. The study resolves the difficulty of singularity in standard Big-Bang cosmology and reconstructs cosmological parameters to infer accelerated universe expansion. The stability of the situation is evaluated using a sound speed feature, demonstrating late-time stability.
EUROPEAN PHYSICAL JOURNAL C
(2021)
Article
Astronomy & Astrophysics
Neil D. Barrie
Summary: This study investigates the possibility of successful Gravitational Leptogenesis during an Ekpyrotic contraction phase through coupling the Ekpyrotic scalar to a gravitational Chern-Simons term or a U(1) gauge field Chern-Simons term, leading to the production of chiral gravitational waves and subsequent generation of lepton and then baryon asymmetry. The findings suggest that Gravitational Leptogenesis can occur in Ekpyrotic bounce cosmologies through both mechanisms.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
Daniela Perez, Gustavo E. Romero
Summary: This study analyzes whether a black hole can survive in a universe that undergoes cosmological bounce. The findings suggest that in a specific class of bouncing models, black holes can exist at different cosmological epochs, potentially playing a role in the subsequent cosmic expansion.
Article
Physics, Particles & Fields
Benedikt Bachmann, Nicolas Borghini, Nina Feld, Hendrik Roch
Summary: In order to understand anisotropic transverse flow in nonequilibrium systems, we compare different kinetic-theoretical models in the regime of few rescatterings. By comparing flow harmonics v(n) from various transport simulations and analytical calculations, we find that even harmonics are similar in all approaches while odd harmonics differ significantly. This indicates that the mechanisms underlying odd v(n) coefficients are different from those for even v(n) harmonics.
EUROPEAN PHYSICAL JOURNAL C
(2023)
Article
Chemistry, Multidisciplinary
Bikash Das, Subrata Ghosh, Shamashis Sengupta, Pascale Auban-Senzier, Miguel Monteverde, Tamal Kumar Dalui, Tanima Kundu, Rafikul Ali Saha, Sujan Maity, Rahul Paramanik, Anudeepa Ghosh, Mainak Palit, Jayanta K. Bhattacharjee, Rajib Mondal, Subhadeep Datta
Summary: Manipulation of long-range order in 2D van der Waals magnetic materials can be achieved through various methods such as applying electric fields, mechanical constraint, or chemical substitution. However, exposure to air can actually result in the formation of a stable nonlayered ferromagnetic phase in a parent magnetic semiconductor, opening possibilities for air-stable materials with multiple magnetic phases. This discovery challenges the common understanding of the poor environmental stability of van der Waals magnets.
Article
Astronomy & Astrophysics
Indrani Banerjee, Tanmoy Paul, Soumitra SenGupta
Summary: The scenario of a bouncing universe is a highly active field of research aiming to develop singularity-free cosmological models. In this work, three different approaches are considered to address this problem, each going beyond General Relativity while remaining within the framework of classical cosmology. The common feature of these approaches is that the bouncing mechanism naturally arises within the geometrical framework of the model, without the need for external sources. Various constraints that these viable cosmological models need to satisfy are also discussed in the context of these scenarios.
GENERAL RELATIVITY AND GRAVITATION
(2022)
Article
Astronomy & Astrophysics
Jie-Wen Chen, Mian Zhu, Sheng-Feng Yan, Qing-Qing Wang, Yi-Fu Cai
Summary: This article illustrates the enhancement of primordial black hole abundance due to the bounce phase, and presents a method to calculate the non-linear evolution of delta rho and PBH abundance. The results indicate that the bounce phase indeed has the potential to enhance PBH abundance, and can be used to constrain the parameters of the bounce phase.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2023)
Article
Astronomy & Astrophysics
Pierre Zhang, Guido D'Amico, Leonardo Senatore, Cheng Zhao, Yifu Cai
Summary: By analyzing the Full Shape of the BOSS Correlation Function and combining it with other measurements, we have determined the present day Hubble constant, matter fraction, and parameters of the primordial power spectrum. We have also placed constraints on the total neutrino mass. These results are consistent with previous studies and show no tension or inconsistency.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Astronomy & Astrophysics
Pierre Zhang, Yifu Cai
Summary: The study re-analyzed the full shape of the BOSS galaxy two-point function within Lambda-CDM, with results constraining various cosmological parameters. The effect of redshift selection on the results was discussed, emphasizing the importance of systematic assessments for ongoing and future large-volume surveys.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Astronomy & Astrophysics
Przemyslaw Malkiewicz, Patrick Peter, Sandro Dias Pinto Vitenti
Summary: We clarify the issue of clock transformations and trajectories in quantum cosmology in a vacuum Bianchi I minisuperspace. By deparametrising the Hamiltonian, we obtain a natural clock variable and different bouncing trajectories. The emphasis is placed on the symmetry across the bounce.
Article
Astronomy & Astrophysics
Claus Kiefer, Patrick Peter
Summary: This article provides a brief review of the problem of time in quantum cosmology and presents two possible solutions. Using the formalism of quantum geometrodynamics, the authors discuss the dilemma of time in quantum gravity and propose two approaches to address this issue. The main focus of this article is the application of quantum gravity to the Universe as a whole.
Article
Astronomy & Astrophysics
Xin Ren, Sheng-Feng Yan, Yaqi Zhao, Yi-Fu Cai, Emmanuel N. Saridakis
Summary: In this study, we investigate the effective field theory formulation of torsional gravity in a cosmological framework and reconstruct the f(T) form in a model-independent way. By considering observational data and performing fitting using polynomial functions, we find an analytic expression that describes the cosmological evolution in great agreement with observations.
ASTROPHYSICAL JOURNAL
(2022)
Article
Astronomy & Astrophysics
Yi-Fu Cai, Xiao-Han Ma, Misao Sasaki, Dong-Gang Wang, Zihan Zhou
Summary: This study reports a novel prediction from single-field inflation that a tiny step in the inflaton potential can alter our understanding of primordial non-Gaussianities of the curvature perturbation. By analyzing the tail of the probability distribution generated by an upward step transition between two stages of slow-roll evolution, it is found that a highly non-Gaussian tail can be generated even when the conventional nonlinearity parameters remain small. This research demonstrates for the first time the sensitive dependence of non-perturbative effects on the tail of the probability distribution and proposes potential applications to primordial black holes.
Article
Astronomy & Astrophysics
Yi-Fu Cai, Xiao-Han Ma, Misao Sasaki, Dong-Gang Wang, Zihan Zhoua
Summary: This paper investigates the relationship between deviations from Gaussian statistics in primordial perturbations and non-perturbative effects. It presents specific examples where the tail of the distribution becomes highly non-Gaussian despite remaining almost Gaussian in the perturbative regime. The study reveals the rich phenomenology of non-Gaussian tails, which has been overlooked in conventional analyses.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Multidisciplinary Sciences
Hang Liang, Man Jiao, Yue Huang, Pei Yu, Xiangyu Ye, Ya Wang, Yijin Xie, Yi-Fu Cai, Xing Rong, Jiangfeng Du
Summary: Laboratory search for exotic interactions is crucial for exploring physics beyond the standard model. We report new experimental constraints on two exotic spin-dependent interactions at the micrometer scale based on ensembles of nitrogen-vacancy (NV) centers in diamond. Our results establish new bounds for these exotic spin interactions at the micrometer scale.
NATIONAL SCIENCE REVIEW
(2023)
Article
Astronomy & Astrophysics
Dongdong Zhang, Jia-Rui Li, Jiaqi Yang, Yufei Zhang, Yi-Fu Cai, Wenjuan Fang, Chang Feng
Summary: We use the Ali Cosmic Microwave Background Polarization Telescope (AliCPT) to forecast the constraints on neutrino physics parameters using the Cosmic Microwave Background (CMB) temperature, E-mode polarization, and lensing spectra. Our numerical simulations show that AliCPT can achieve a precision of sigma(N (eff)) = 0.56 and M (nu) < 1.10 eV (95% CL.) for the first year of observation, based on TT, TE, EE, and CMB lensing power spectra. We also investigate how instrumental parameters such as noise level, FWHM, and sky coverage affect these constraints on neutrino parameters.
ASTROPHYSICAL JOURNAL
(2023)
Article
Physics, Multidisciplinary
Tinggui Wang, Guilin Liu, Zhenyi Cai, Jinjun Geng, Min Fang, Haoning He, Ji-an Jiang, Ning Jiang, Xu Kong, Bin Li, Ye Li, Wentao Luo, Zhizheng Pan, Xuefeng Wu, Ji Yang, Jiming Yu, Xianzhong Zheng, Qingfeng Zhu, Yi-Fu Cai, Yuanyuan Chen, Zhiwei Chen, Zigao Dai, Lulu Fan, Yizhong Fan, Wenjuan Fang, Zhicheng He, Lei Hu, Maokai Hu, Zhiping Jin, Zhibo Jiang, Guoliang Li, Fan Li, Xuzhi Li, Runduo Liang, Zheyu Lin, Qingzhong Liu, Wenhao Liu, Zhengyan Liu, Wei Liu, Yao Liu, Zheng Lou, Han Qu, Zhenfeng Sheng, Jianchun Shi, Yiping Shu, Zhenbo Su, Tianrui Sun, Hongchi Wang, Huiyuan Wang, Jian Wang, Junxian Wang, Daming Wei, Junjie Wei, Yongquan Xue, Jingzhi Yan, Chao Yang, Ye Yuan, Yefei Yuan, Hongxin Zhang, Miaomiao Zhang, Haibin Zhao, Wen Zhao
Summary: The Wide Field Survey Telescope (WFST) is a dedicated photometric surveying facility being built jointly by University of Science and Technology of China (USTC) and the Purple Mountain Observatory (PMO). It is equipped with a 2.5-meter diameter primary mirror and a mosaic CCD camera, and it will scan the northern sky in four optical bands to detect transient phenomena and study the variability of Galactic and extragalactic objects.
SCIENCE CHINA-PHYSICS MECHANICS & ASTRONOMY
(2023)
Article
Astronomy & Astrophysics
Lei-Hua Liu, Mian Zhu, Wentao Luo, Yi-Fu Cai, Yi Wang
Summary: We systematically investigate the microlensing effect of a charged spherically symmetric wormhole, where the light source is remote from the throat. The numerical result shows that the range of total magnification is from 105 to 10-2 depending on various metrics. Our theoretical investigation could shed new light on exploring the wormhole with the microlensing effect.
Article
Astronomy & Astrophysics
Yu-Min Hu, Yaqi Zhao, Xin Ren, Bo Wang, Emmanuel N. Saridakis, Yi-Fu Cai
Summary: This study investigates the scalar perturbations and possible strong coupling issues of f(T) gravity using the effective field theory (EFT) approach. The generalized EFT framework of modified teleparallel gravity is revisited and applied to examine both linear and second-order perturbations in f(T) theory. The results suggest that there is no new scalar mode present in f(T) gravity, indicating a strong coupling problem. However, an estimation of the strong coupling scale based on the ratio of cubic to quadratic Lagrangians shows that the strong coupling problem can be avoided for certain modes.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2023)
Article
Astronomy & Astrophysics
Yiqi Huang, Jiajun Zhang, Xin Ren, Emmanuel N. Saridakis, Fuyu Dong, Yi-Fu Cai
Summary: In this study, we perform N-body simulations to investigate the structure formation process in f(T) gravity. By comparing with ACDM cosmology, we find clear observational differences due to the modifications brought about by f(T) gravity in the evolution of the Hubble function and the effective Newton's constant. We extract several physical quantities and observe differences in the matter density distribution, matter power spectrum, counts-in-cells, halo mass function, and excess surface density around low-density positions.
Article
Physics, Particles & Fields
Yi-Fu Cai, Chao Chen, Qianhang Ding, Yi Wang
Summary: A novel class of celestial objects called stellar bubbles, dominated by primordial black holes, is proposed, which can be generated through phase transitions in the primordial Universe. The radiations emitted by these stellar bubbles have distinct features in the gamma-ray spectra and gravitational waves.
EUROPEAN PHYSICAL JOURNAL C
(2022)
Article
Astronomy & Astrophysics
Jaime de Cabo Martin, Przemyslaw Malkiewicz, Patrick Peter
Summary: In a simple one fluid model, the choice of relevant variables may lead to incompatible observational physical predictions. While the well-known ambiguity of factor ordering can be resolved through an actual choice, a new ambiguity depends on the choice of variables themselves. Bouncing scenarios may have predictability issues, while inflationary models can avoid these issues due to the monotonic behavior of their scale factor.
