We focus on a series of f（R） gravity theories in Palatini formalism to investigate the probabilities of producing late-time acceleration for the flat Friedmann-Robertson-Walker（FRW） universe.We apply a statefinder...We focus on a series of f（R） gravity theories in Palatini formalism to investigate the probabilities of producing late-time acceleration for the flat Friedmann-Robertson-Walker（FRW） universe.We apply a statefinder diagnostic to these cosmological models for chosen series of parameters to see if they can be distinguished from one another. The diagnostic involves the statefinder pair{r,s},where r is derived from the scale factor a and its higher derivatives with respect to the cosmic time t,and s is expressed by r and the deceleration parameter q. In conclusion,we find that although two types of f（R） theories：（i） f（R） = R ＋ αR^m-βR^-n and（ii） f（R） = R ＋ α lnR-β can lead to late-time acceleration,their evolutionary trajectories in the r-s and r-q planes reveal different evolutionary properties,which certainly justify the merits of the statefinder diagnostic. Additionally,we utilize the observational Hubble parameter data（OHD） to constrain these models of f（R） gravity. As a result,except for m = n = 1/2 in case（i）,α = 0 in case（i） and case（ii） allow the ΛCDM model to exist in the 1σ confidence region. After applying the statefinder diagnostic to the best-fit models,we find that all the best-fit models are capable of going through the deceleration/acceleration transition stage with a late-time acceleration epoch,and all these models turn to the de Sitter point（{r,s}={1,0}） in the future. Also,the evolutionary differences between these models are distinct,especially in the r-s plane,which makes the statefinder diagnostic more reliable in discriminating cosmological models.展开更多
Constraining neutrino mass remains an elusive challenge in modern physics.Precision measurements are expected from several upcoming cosmological probes of large-scale structure.Achieving this goal relies on an equal l...Constraining neutrino mass remains an elusive challenge in modern physics.Precision measurements are expected from several upcoming cosmological probes of large-scale structure.Achieving this goal relies on an equal level of precision from theoretical predictions of neutrino clustering.Numerical simulations of the non-linear evolution of cold dark matter and neutrinos play a pivotal role in this process.We incorporate neutrinos into the cosmological N-body code CUBEP3M and discuss the challenges associated with pushing to the extreme scales demanded by the neutrino problem.We highlight code optimizations made to exploit modern high performance computing architectures and present a novel method of data compression that reduces the phase-space particle footprint from 24 bytes in single precision to roughly 9 bytes.We scale the neutrino problem to the Tianhe-2 supercomputer and provide details of our production run,named Tian Nu,which uses 86%of the machine(13 824 compute nodes).With a total of 2.97 trillion particles,Tian Nu is currently the world’s largest cosmological N-body simulation and improves upon previous neutrino simulations by two orders of magnitude in scale.We finish with a discussion of the unanticipated computational challenges that were encountered during the Tian Nu runtime.展开更多
Neutral hydrogen clouds are known to exist in the Universe, however their spatial distributions and physical properties are poorly understood. Such missing information can be studied by the new generation of Chinese r...Neutral hydrogen clouds are known to exist in the Universe, however their spatial distributions and physical properties are poorly understood. Such missing information can be studied by the new generation of Chinese radio telescopes through a blind search of 21-cm absorption systems. We forecast the capabilities of surveys of 21-cm absorption systems by two representative radio telescopes in China - the Five-hundred-meter Aperture Spherical radio Telescope （FAST） and Tianlai 21-cm cosmology experiment （Tianlai）. Facilitated by either the high sensitivity （FAST） or wide field of view （Tianlai） of these telescopes, more than a thousand 21-cm absorption systems can be discovered in a few years, representing orders of magnitude improvement over the cumulative discoveries in the past half a century.展开更多
基金supported by the National Natural Science Foundation of China (NSFC,Grant Nos.11573006,11528306 and 11347163)the Fundamental Research Funds for the Central Universities+1 种基金the Special Program for Applied Research on Super Computation of the NSFC-Guangdong Joint Fund (the second phase)the Science and Technology Program Foundation of the Beijing Municipal Commission of Education of China (Grant No.KM201410028003)
文摘We focus on a series of f（R） gravity theories in Palatini formalism to investigate the probabilities of producing late-time acceleration for the flat Friedmann-Robertson-Walker（FRW） universe.We apply a statefinder diagnostic to these cosmological models for chosen series of parameters to see if they can be distinguished from one another. The diagnostic involves the statefinder pair{r,s},where r is derived from the scale factor a and its higher derivatives with respect to the cosmic time t,and s is expressed by r and the deceleration parameter q. In conclusion,we find that although two types of f（R） theories：（i） f（R） = R ＋ αR^m-βR^-n and（ii） f（R） = R ＋ α lnR-β can lead to late-time acceleration,their evolutionary trajectories in the r-s and r-q planes reveal different evolutionary properties,which certainly justify the merits of the statefinder diagnostic. Additionally,we utilize the observational Hubble parameter data（OHD） to constrain these models of f（R） gravity. As a result,except for m = n = 1/2 in case（i）,α = 0 in case（i） and case（ii） allow the ΛCDM model to exist in the 1σ confidence region. After applying the statefinder diagnostic to the best-fit models,we find that all the best-fit models are capable of going through the deceleration/acceleration transition stage with a late-time acceleration epoch,and all these models turn to the de Sitter point（{r,s}={1,0}） in the future. Also,the evolutionary differences between these models are distinct,especially in the r-s plane,which makes the statefinder diagnostic more reliable in discriminating cosmological models.
基金the Special Program for Applied Research on Super Computation of the NSFC-Guangdong Joint Fund(the second phase)supported under the U.S.Department of Energy contract DE-AC02-06CH11357+12 种基金General Financial Grant No.2015M570884Special Financial Grant No.2016T90009 from the China Postdoctoral Science Foundationsupport from the European Commission under a Marie-Sklodwoska-Curie European Fellowship(EU project 656869)support from Mo ST 863 program 2012AA121701NSFC grant 11373030CAS grant QYZDJ-SSW-SLH017supported by the National Natural Science Foundation of China(Grant Nos.11573006,11528306,10473002 and 11135009)the National Basic Research Program of China(973 program)under grant No.2012CB821804the Fundamental Research Funds for the Central UniversitiesSciNet is funded by:the Canada Foundation for Innovation under the auspices of Compute Canadathe Government of Ontariothe Ontario Research Fund Research Excellencethe University of Toronto
文摘Constraining neutrino mass remains an elusive challenge in modern physics.Precision measurements are expected from several upcoming cosmological probes of large-scale structure.Achieving this goal relies on an equal level of precision from theoretical predictions of neutrino clustering.Numerical simulations of the non-linear evolution of cold dark matter and neutrinos play a pivotal role in this process.We incorporate neutrinos into the cosmological N-body code CUBEP3M and discuss the challenges associated with pushing to the extreme scales demanded by the neutrino problem.We highlight code optimizations made to exploit modern high performance computing architectures and present a novel method of data compression that reduces the phase-space particle footprint from 24 bytes in single precision to roughly 9 bytes.We scale the neutrino problem to the Tianhe-2 supercomputer and provide details of our production run,named Tian Nu,which uses 86%of the machine(13 824 compute nodes).With a total of 2.97 trillion particles,Tian Nu is currently the world’s largest cosmological N-body simulation and improves upon previous neutrino simulations by two orders of magnitude in scale.We finish with a discussion of the unanticipated computational challenges that were encountered during the Tian Nu runtime.
基金supported by the National Natural Science Foundation of China (Grant Nos. 11573006 and 11528306)General Financial (Grant No. 2015M570884) and Special Financial Grant (No. 2016T90009) from the China Postdoctoral Science Foundation+3 种基金support of the National Science and Engineering Research Council of Canadasupport from the FAST fellowship program administered by the Astronomical Mega-science center of the Chinese Academy of Sciencespartially supported by the International Partnership Program of CAS, Grant No. 114A11KYSB20160008CAS Interdisciplinary Innovation Team program
文摘Neutral hydrogen clouds are known to exist in the Universe, however their spatial distributions and physical properties are poorly understood. Such missing information can be studied by the new generation of Chinese radio telescopes through a blind search of 21-cm absorption systems. We forecast the capabilities of surveys of 21-cm absorption systems by two representative radio telescopes in China - the Five-hundred-meter Aperture Spherical radio Telescope （FAST） and Tianlai 21-cm cosmology experiment （Tianlai）. Facilitated by either the high sensitivity （FAST） or wide field of view （Tianlai） of these telescopes, more than a thousand 21-cm absorption systems can be discovered in a few years, representing orders of magnitude improvement over the cumulative discoveries in the past half a century.
