A necessary condition for a generally covariant scalar-tensor theory to be ghostfree is that it contains no extra degrees of freedom in the unitary gauge, in which the Lagrangian corresponds to the spatially covariant gravity. Comparing with analysing the scalar-tensor theory directly, it is simpler to map the spatially covariant gravity to the generally covariant scalar-tensor theory using the gauge recovering procedures. In order to ensure the resulting scalar-tensor theory to be ghostfree absolutely, i.e., no matter if the unitary gauge is accessible, a further covariant degeneracy/constraint analysis is required. We develop a method of covariant 3+1 correspondence, which map the spatially covariant gravity to the scalar-tensor theory in 3+1 decomposed form without fixing any coordinates. Then the degeneracy conditions to remove the extra degrees of freedom can be found easily. As an illustration of this approach, we show how the Horndeski theory is recovered from the spatially covariant gravity. This approach can be used to find more general ghostfree scalar-tensor theory.
A complete correspondence between the Newman-Penrose and 1+1+2 formalisms
Institute of Mathematics, Henan Academy of Sciences（河南省科学院数学研究所）；University of Cape Town（开普敦大学）；North-West University（西北大学）；South African Astronomical Observatory（南非天文台）
Parity-violating spatially covariant gravity at total derivative order $d=5$
School of Physics, Sun Yat-sen University（中山大学物理学院）；Guangdong Provincial Key Laboratory of Quantum Metrology and Sensing, Sun Yat-sen University（中山大学广东省量子计量与传感重点实验室）
A note on gravity and fluid dynamic correspondence on a null hypersurface
Birla Institute of Technology and Science, Pilani, Dubai Campus（比拉理工学院，Pilani校区迪拜分校）；University of Warsaw（华沙大学）；Indian Institute of Technology Guwahati（古瓦哈提印度理工学院）
Bi-scalar-tensor theory: a spatially covariant gravity approach
School of Physics, Sun Yat-sen University（中山大学物理学院）；Guangdong Provincial Key Laboratory of Quantum Metrology and Sensing, Sun Yat-sen University（中山大学广东省量子计量与传感重点实验室）；Department of Physics, Rikkyo University（立教大学物理系）
