Particles in the early universe : high energy limit of the standard model from the contraction of its gauge group The aim of this book is to develop a contraction method for Cayley Klein orthogonal and unitary groups (algebras) and apply it to the investigation of physical structures. Readers will find a comprehensive study summarized as follows: The space time models (or kinematics) are described on the motion group level. The Jordan Schwinger representations of the groups are closely connected to the properties of stationary quantum systems whose Hamiltonians are quadratic in creation and annihilation operators. The high temperature limit of the Standard Model is associated with the contraction of its gauge group. The tending to zero contraction parameter is connected to the inverse average energy (temperature) of the Universe which makes it possible to re establish the evolution of particles and their interactions in the early Universe up to Planck energy. Properties of the elementary particles change drastically in the infinite temperature limit: all particles lose mass all quarks are monochromatic electroweak interactions become long range and are mediated by neutral currents The Cayley Klein groups and algebras Space time models The Jordan Schwinger representations of Cayley Klein groups Gelfand Tsetlin representations of Cayley Klein algebras High temperature limit of the Standard model.