Recently,corrections to the standard Einstein Hilbert action were proposed to explain the current cosmicacceleration in stead of introducing dark energy.In the Palatini formulation of those modified gravity models,the...Recently,corrections to the standard Einstein Hilbert action were proposed to explain the current cosmicacceleration in stead of introducing dark energy.In the Palatini formulation of those modified gravity models,thereis an important observation due to Arkani Hamed:matter loops will give rise to a correction to the modified gravityaction proportional to the Ricci scalar of the metric.In the presence of such a term,we show that the current formsof modified gravity models in Palatini formulation,specifically,the 1/R gravity and in R gravity,will have phantoms.Then we study the possible instabilities due to the presence of phantom fields.We show that the strong instability inthe metric formulation of 1/R gravity indicated by Dolgov and Kawasaki will not appear and the decay timescales forthe phantom fields may be long enough for the theories to make sense as effective field theory.On the other hand,if wechange the sign of the modification terms to eliminate the phantoms,some other inconsistencies will arise for the variousversions of the modified gravity models.Finally,we comment on the universal property of the Palatini formulation ofthe matter loops corrected modified gravity models and its implications.展开更多
Now,there have been many different methods to calculate one-loop amplitudes.Two of them are the unitarity cut method and the generalized unitarity cut method.In this short paper,we present an explicit connection betwe...Now,there have been many different methods to calculate one-loop amplitudes.Two of them are the unitarity cut method and the generalized unitarity cut method.In this short paper,we present an explicit connection between these two methods,especially how the extractions of triangle and bubble coefficients are equivalent to each other.展开更多
New physics could be explored through loop effects using the precision measurements at the Circular Electron Positron Collider(CEPC)owing to its clean collision environment and high luminosity.In this paper,we focus o...New physics could be explored through loop effects using the precision measurements at the Circular Electron Positron Collider(CEPC)owing to its clean collision environment and high luminosity.In this paper,we focus on two dark matter models that involve additional electroweak fermionic multiplets.We calculate their one-loop corrections in five processes,i.e.,e^(+)e^(-)→μ^(+)μ^(-),Zh,W^(+)W^(-),ZZ,and,Zγ,and investigate the corresponding signatures at the CEPC with the projected sensitivity.We observe that the detectable parameter regions of these processes are complementary.The combined analysis shows that the mass of dark matter m_(χ^(0)_(1))in these two models can be probed up to-150GeV and-450GeV,respectively,at a 95%confidence level.展开更多
基金National Natural Science Foundation of China under Grant No.10675062the Second Stage Brain Korea 21 Program in Hanyang University
文摘Recently,corrections to the standard Einstein Hilbert action were proposed to explain the current cosmicacceleration in stead of introducing dark energy.In the Palatini formulation of those modified gravity models,thereis an important observation due to Arkani Hamed:matter loops will give rise to a correction to the modified gravityaction proportional to the Ricci scalar of the metric.In the presence of such a term,we show that the current formsof modified gravity models in Palatini formulation,specifically,the 1/R gravity and in R gravity,will have phantoms.Then we study the possible instabilities due to the presence of phantom fields.We show that the strong instability inthe metric formulation of 1/R gravity indicated by Dolgov and Kawasaki will not appear and the decay timescales forthe phantom fields may be long enough for the theories to make sense as effective field theory.On the other hand,if wechange the sign of the modification terms to eliminate the phantoms,some other inconsistencies will arise for the variousversions of the modified gravity models.Finally,we comment on the universal property of the Palatini formulation ofthe matter loops corrected modified gravity models and its implications.
基金supported by Chinese NSF funding under contract No.11575156。
文摘Now,there have been many different methods to calculate one-loop amplitudes.Two of them are the unitarity cut method and the generalized unitarity cut method.In this short paper,we present an explicit connection between these two methods,especially how the extractions of triangle and bubble coefficients are equivalent to each other.
基金Supported by the National Natural Science Foundation of China (12175248)Supported by the research grant"the Dark Universe:A Synergic Multi-messenger Approach"number (2017X7X85K) under the program PRIN 2017 funded by the Ministero dell’Istruzione,Universitàe della Ricerca (MIUR)
文摘New physics could be explored through loop effects using the precision measurements at the Circular Electron Positron Collider(CEPC)owing to its clean collision environment and high luminosity.In this paper,we focus on two dark matter models that involve additional electroweak fermionic multiplets.We calculate their one-loop corrections in five processes,i.e.,e^(+)e^(-)→μ^(+)μ^(-),Zh,W^(+)W^(-),ZZ,and,Zγ,and investigate the corresponding signatures at the CEPC with the projected sensitivity.We observe that the detectable parameter regions of these processes are complementary.The combined analysis shows that the mass of dark matter m_(χ^(0)_(1))in these two models can be probed up to-150GeV and-450GeV,respectively,at a 95%confidence level.
