On the matrix Cauchy-Schwarz inequality (2205.02657v3)

Abstract: The main goal of this work is to present new matrix inequalities of the Cauchy-Schwarz type. In particular, we investigate the so-called Lieb functions, whose definition came as an umbrella of Cauchy-Schwarz-like inequalities, then we consider the mixed Cauchy-Schwarz inequality. This latter inequality has been influential in obtaining several other matrix inequalities, including numerical radius and norm results. Among many other results, we show that [\left| T \right|\le \frac{1}{4}\left( \left| \left| T \right|+\left| {{T}^{*}} \right|+2\mathfrak RT \right|+\left| \left| T \right|+\left| {{T}^{*}} \right|-2\mathfrak RT \right| \right),] where $\mathfrak RT$ is the real part of $T$.