Building boundary/interface conformal theory from SYK interactions

Coupling defects to extended critical degrees of freedom results in a class of intriguing theories known as the defect conformal field theory (CFT), which aids in our understanding of both quantum entanglement and holographic aspects of gravity. We construct such a theory by coupling the 1+1D CFT of N Majorana chains with an SYK-type interaction at a defect site. This gives rise to a family of boundary/interface CFTs between the SYK side of the chains to the rest. We compute the entanglement entropy between these two segments and found a logarithmic dependence on the system size. Notably, increasing the coupling strength leads to a continuous decrease of the coefficient to the logarithm, i.e., the central charge at the boundary. The result is buttressed by a saddle point analysis for large N values and a Gaussian fermionic state simulation for smaller N's. Our contributions highlight a novel defect conformal theory, extending the traditional concepts found in the Ising CFT.