Defect conformal field theory from Sachdev-Ye-Kitaev interactions

The coupling between defects and extended critical degrees of freedom gives rise to the intriguing theory known as defect conformal field theory (CFT). In this work, we introduce a novel family of boundary and interface CFTs by coupling $N$ Majorana chains with SYK$_q$ interactions at the defect. Our analysis reveals that the interaction with $q=2$ constitutes a new marginal defect. Employing a versatile saddle-point method, we compute unique entanglement characterizations, including the $g$ function and effective central charge, of the defect CFT. Furthermore, we analytically evaluate the transmission coefficient using CFT techniques. Surprisingly, the transmission coefficient deviates from the universal relation with the effective central charge across the defect at the large $N$ limit, suggesting that our defect CFT extends beyond all known examples of Gaussian defect CFT.