Article
Astronomy & Astrophysics
Tingqi Cai, Jie Jiang, Yi Wang
Summary: This study presents the first lattice simulation to investigate the nature of multi-stream inflation. The simulation confirms the physical picture of multi-stream inflation and reveals new findings in parameter space and field behaviors. It shows that gradient energy plays a significant role in multi-stream inflation. The bifurcation probability in a double field potential with a shifted Gaussian barrier is controlled by the shift distance with an error function relation. The bubbles created by bifurcation tend to be more spherical as bifurcation probability decreases. Furthermore, bifurcation is more likely to introduce oscillations of field values inside the bubbles than outside.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Astronomy & Astrophysics
Jason Kristiano, Jun'ichi Yokoyama
Summary: By calculating the one-loop correction to the two-point functions of curvature perturbation in single-field inflation generated by cubic self-interaction, we find that the correction is finite and inversely proportional to the spectral tilt. Requiring the correction to be much smaller than the tree-level contribution leads to an upper bound on primordial non-Gaussianity. Observationally, the allowed region of non-Gaussian parameter space is entirely included by the region where the one-loop correction is smaller than the tree-level contribution, but there exists a significantly large region where the one-loop correction is larger than 1% or even 10% of the latter. If future observations confirm non-Gaussianity falling within such a region, it would be important to incorporate higher-order corrections to the spectrum in order to achieve precise cosmology. In some extreme cases, where the one-loop correction has a comparable magnitude to the tree-level contribution, it might indicate a breakdown of the cosmological perturbation theory in the context of single-field inflation.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Astronomy & Astrophysics
Guido D'Amico, Nemanja Kaloper
Summary: Inflation does not have to occur all at once, and can be solved by a series of short bursts of cosmic acceleration interrupted by brief periods of decelerated expansion. This allows for more flexibility in theory and can lead to interesting predictions regarding scalar and tensor spectra of perturbations at short wavelengths. Future CMB spectroscopy searches and primordial gravity probes may help test these features and reveal potential populations of rare particles or primordial black holes as dark matter.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
Fengge Zhang, Yungui Gong, Jiong Lin, Yizhou Lu, Zhu Yi
Summary: The study of non-Gaussianities of primordial curvature perturbations in G-inflation models reveals that even though f(NL) becomes large at certain scales, it remains to be small at peak scales. This suggests that the contributions of non-Gaussianity to scalar induced secondary gravitational waves and primordial black hole abundance are expected to be negligible.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
Jinn-Ouk Gong, Maria Mylova
Summary: In this study, we examine the validity of the classical approximation of the waterfall phase transition in hybrid inflation from an effective field theory perspective. By integrating out the fluctuations of the waterfall field up to one-loop order, an effective field theory is constructed. Assuming slow-roll conditions are satisfied, we find that the backreaction of the waterfall field fluctuations can significantly impact the evolution of the system, rendering the classical approximation invalid. We derive the necessary constraint to ensure the validity of the effective field theory.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Astronomy & Astrophysics
Markus B. Froeb, William C. C. Lima
Summary: We introduce a recent approach to construct gauge-invariant relational observables in gravity within the framework of cosmological perturbation theory. These observables are built using a field-dependent coordinate system, specifically geodesic lightcone coordinates. We demonstrate that these observables are gauge-independent in the fully nonlinear theory and take the expected form when the geodesic lightcone gauge for the metric is adopted. Explicit expressions for the Sasaki-Mukhanov variable at linear order and the Hubble rate, as measured by both geodesic and inflaton co-moving observers, to second order are provided. Furthermore, we show that the well-known linearized equations of motion for the Sasaki-Mukhanov variable and the scalar constraint variables are derived from the gauge-invariant Einstein's equations.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Astronomy & Astrophysics
Harry Goodhew, Sadra Jazayeri, Mang Hei Gordon Lee, Enrico Pajer
Summary: This paper discusses the initial conditions of the universe and the impact of quantum mechanics on late-time observables, deriving a set of single-cut rules, discussing the analytical structure of the wave function, and verifying the applicability of these rules in some specific examples.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
Arunoday Sarkar, Chitrak Sarkar, Buddhadeb Ghosh
Summary: By defining the k-modes of quantum fluctuations during inflation through the dynamical horizon crossing condition k = aH, and solving the equations of cosmological first-order perturbations self-consistently with chaotic alpha-attractor type potentials, we were able to study the behavior of various parameters in k-space. Comparison with Planck data in the low-k regime constrained the values of the alpha parameter through microscopic calculations. The calculated results matched the Planck-2018 data with 68% or near 95% CL for various values of alpha.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
Mohammad Ali Gorji, Hayato Motohashi, Shinji Mukohyama
Summary: We investigate a novel single field inflationary scenario that allows a transition from slow-roll inflation to ghost inflation, achieved through smoothly unifying the two phases with the introduction of a higher derivative scordatura term. The model avoids strong coupling and gradient instability and provides a self-consistent approach to accessing ghost inflation.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Astronomy & Astrophysics
Matteo Braglia, Xingang Chen, Dhiraj Kumar Hazra
Summary: This paper introduces a methodology for directly comparing numerical predictions from complicated multi-field feature models with Planck data using a complete model of classical primordial standard clocks as an example. Although no statistically significant candidates were found, this methodology can facilitate future research on primordial features and data analysis, providing a framework for further testing with upcoming cosmic microwave background polarization observations and galaxy surveys.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
Manuel Alejandro Jaramillo Rodrguez, Antonio Enea Romano, Sergio Andres Vallejo-Pena
Summary: This study analyzes the effects of a momentum dependent effective sound speed (MESS) on cosmic microwave background (CMB) data, showing a significant improvement in fit compared to models without MESS. The research suggests that primordial entropy perturbations could explain deviations observed in the curvature perturbation spectrum.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
Amjad Ashoorioon, Ghazal Geshnizjani, Hyung J. Kim
Summary: In this paper, we study the validity and non-Gaussianity of Extended Effective Field Theory of Inflation (EEFToI) with initial conditions set with dispersion relations omega(2) a k(6). By computing the bispectrum and investigating the shape of triangles, we find interesting regions of parameter space where EEFToI with these initial conditions is sensible.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Astronomy & Astrophysics
Nicola Bartolo, Giovanni Battista Carollo, Sabino Matarrese, Luigi Pilo, Rocco Rollo
Summary: “We analyze the physical content of squeezed bispectra involving long-wavelength tensor perturbations and show that these modes cannot be gauged away, except in the unphysical limit of infinite wavelength, k = 0. This result has a direct implication on the validity of the Maldacena consistency relation, which is respected by a subclass of inflationary models. Consequently, future experiments can observe squeezed mixed correlators in the squeezed limit, similar to the scalar-scalar-scalar bispectrum, and they remain a key channel to study Early Universe physics and discriminate among different models of inflation.”
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Astronomy & Astrophysics
Keisuke Inomata, Evan McDonough, Wayne Hu
Summary: Future experiments on cosmic microwave background, gravitational wave, and large scale structure will allow us to study the primordial power spectrum on small scales, potentially revealing the mechanisms and correlations behind the formation of primordial black holes.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Astronomy & Astrophysics
Yuichiro Tada, Vincent Vennin
Summary: This study presents a generic framework to compute the one-point statistics of cosmological perturbations at an arbitrary scale, considering the presence of quantum diffusion. The study derives explicit formulae for the probability density function of the curvature perturbation, the comoving density contrast, and the compaction function. The framework is applied to calculate the mass distribution of primordial black holes and confirms the heavy-tailed distribution and the impact of stochastic contamination effects.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Physics, Particles & Fields
Amara Ilyas, Mian Zhu, Yunlong Zheng, Yi-Fu Cai
Summary: This article presents an emergent universe scenario derived from DHOST cosmology. The universe transitions from an asymptotic Minkowski state in the far past to a radiation dominated period in the late stage, providing a graceful exit. Analysis shows that cosmological perturbations are stable, and the primordial scalar spectrum is discussed for achieving scale invariance.
JOURNAL OF HIGH ENERGY PHYSICS
(2021)
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
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)
Editorial Material
Physics, Multidisciplinary
Yi-Fu Cai
SCIENCE CHINA-PHYSICS MECHANICS & ASTRONOMY
(2022)
Article
Physics, Multidisciplinary
Guan-Wen Yuan, Lei Zu, Lei Feng, Yi-Fu Cai, Yi-Zhong Fan
Summary: This study investigates new particles and fields to explain the excess in W-boson mass. The interpretations of axion-like particle and dark photon have been significantly narrowed down by global electroweak fits. The possibility of attributing the W-boson mass anomaly to chameleon dark energy is ruled out by other experiments.
SCIENCE CHINA-PHYSICS MECHANICS & ASTRONOMY
(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)