We attempt to clarify several aspects concemi ng the recently presented four-dimensional Ein stein-Gauss-Bonnet gravity.We argue that the limiting procedure outlined in[Phys.Rev.Lett.124,081301(2020)]generally involve...We attempt to clarify several aspects concemi ng the recently presented four-dimensional Ein stein-Gauss-Bonnet gravity.We argue that the limiting procedure outlined in[Phys.Rev.Lett.124,081301(2020)]generally involves ill-defined terms in the four dimensional field equations.Potential ways to circumvent this issue are discussed,alongside remarks regarding specific solutions of the theory.We prove that,although linear perturbations are well behaved around maximally symmetric backgrounds,the equations for second-order perturbations are illdefined even around a Minkowskia n background.Additi on ally,we perform a detailed analysis of the spherically symmetric solutions and find that the central curvature singularity can be reached within a finite proper time.展开更多
In this White Paper we present the potential of the enhanced X-ray Timing and Polarimetry(eXTP) mission for studies related to Observatory Science targets. These include flaring stars, supernova remnants, accreting wh...In this White Paper we present the potential of the enhanced X-ray Timing and Polarimetry(eXTP) mission for studies related to Observatory Science targets. These include flaring stars, supernova remnants, accreting white dwarfs, low and high mass X-ray binaries, radio quiet and radio loud active galactic nuclei, tidal disruption events, and gamma-ray bursts. eXTP will be excellently suited to study one common aspect of these objects: their often transient nature. Developed by an international Consortium led by the Institute of High Energy Physics of the Chinese Academy of Science, the eXTP mission is expected to be launched in the mid 2020s.展开更多
基金supported by PhD contracts of the program FPU 2015 with references FPU15/02864 and FPU15/05406(Spanish Ministry of Economy and Competitiveness),respectivelysupported by the Spanish Projects(FIS2017-84440-C2-1-P)(MINECO/FEDER,EU)and FIS2016-78198-P(MINECO)+5 种基金the Project No.H2020-MSCA-RISE-2017 Grant No.Fun Fi CO-777740Project No.SEJI/2017/042(Generalitat Valenciana)the Consolider Program CPANPHY-1205388the Severo Ochoa Grant No.SEV-2014-0398(Spain)financial support from the Spanish Government through the project FIS2017-86497-C2-2-P(with FEDER contribution)from the State Agency for Research of the Spanish MCIU through the"Center of Excellence Severo Ochoa"award to the Instituto de Astrofísica de Andalucía(SEV-2017-0709)。
文摘We attempt to clarify several aspects concemi ng the recently presented four-dimensional Ein stein-Gauss-Bonnet gravity.We argue that the limiting procedure outlined in[Phys.Rev.Lett.124,081301(2020)]generally involves ill-defined terms in the four dimensional field equations.Potential ways to circumvent this issue are discussed,alongside remarks regarding specific solutions of the theory.We prove that,although linear perturbations are well behaved around maximally symmetric backgrounds,the equations for second-order perturbations are illdefined even around a Minkowskia n background.Additi on ally,we perform a detailed analysis of the spherically symmetric solutions and find that the central curvature singularity can be reached within a finite proper time.
基金supported by the Royal Society,ERC Starting(Grant No.639217)he European Union Horizon 2020 Research and Innovation Programme under the Marie Sklodowska-Curie Global Fellowship(Grant No.703916)+10 种基金the National Natural Science Foundation of China(Grant Nos.11233001,11773014,11633007,11403074,11333005,11503008,and 11590781)the National Basic Research Program of China(Grant No.2015CB857100)NASA(Grant No.NNX13AD28A)an ARC Future Fellowship(Grant No.FT120100363)the National Science Foundation(Grant No.PHY-1430152)the Spanish MINECO(Grant No.AYA2016-76012-C3-1-P)the ICCUB(Unidad de Excelencia’Maria de Maeztu’)(Grant No.MDM-2014-0369)EU’s Horizon Programme through a Marie Sklodowska-Curie Fellowship(Grant No.702638)the Polish National Science Center(Grant Nos.2015/17/B/ST9/03422,2015/18/M/ST9/00541,2013/10/M/ST9/00729,and 2015/18/A/ST9/00746)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDA15020100)the NWO Veni Fellowship(Grant No.639.041.647)
文摘In this White Paper we present the potential of the enhanced X-ray Timing and Polarimetry(eXTP) mission for studies related to Observatory Science targets. These include flaring stars, supernova remnants, accreting white dwarfs, low and high mass X-ray binaries, radio quiet and radio loud active galactic nuclei, tidal disruption events, and gamma-ray bursts. eXTP will be excellently suited to study one common aspect of these objects: their often transient nature. Developed by an international Consortium led by the Institute of High Energy Physics of the Chinese Academy of Science, the eXTP mission is expected to be launched in the mid 2020s.