23. The function $y=\sin \left[2\left(x-\frac{\pi}{3}\right)+\varphi\right]$ is an even function, and $0<\varphi<\pi$. Then $\varphi=$ $\qquad$ , and its interval of monotonic decrease is $\qquad$ .
23. $\frac{\pi}{6},\left[k \pi-\frac{\pi}{2}, k \pi\right](k \in \mathbf{Z})$.

Since $y=\sin \left[2\left(x-\frac{\pi}{3}\right)+\varphi\right]=\sin \left(2 x-\frac{2 \pi}{3}+\varphi\right)$ is an even function, we have
$$
-\frac{2 \pi}{3}+\varphi=k \pi+\frac{\pi}{2}(k \in \mathbf{Z}) \text {. }
$$

Also, because $0<\varphi<\pi$, we get $\varphi=\frac{\pi}{6}$.
When $\varphi=\frac{\pi}{6}$, we have $y=\sin \left(2 x-\frac{\pi}{2}\right)=-\cos 2 x$.
From the inequality $2 k \pi-\pi \leqslant 2 x \leqslant 2 k \pi$, we get
$$
k \pi-\frac{\pi}{2} \leqslant x \leqslant k \pi(k \in \mathbf{Z}) \text {. }
$$

Therefore, the interval of monotonic decrease is $\left[k \pi-\frac{\pi}{2}, k \pi\right](k \in \mathbf{Z})$.