Suppose $(X,Y), (X_1,Y_1),(X_2,Y_2),\dots$ is a $\mathbb{P}$-i.i.d. sequence of pairs of real-valued random variables such that the support of $\mathbb{P}_{(X,Y)}$ is contained in the square $[-1,1] \times [-1,1]$.

Assume that there exists a noisy linear relation with slope $m \in [-1,1]$ between $X$ and $Y$, i.e., $\mathbb{E}[Y \mid X] = mX$.

Our goal is to give a reliable estimate of $m$ having access to a sample of size $T\in \mathbb{N}$, say $S_T := \big((X_1,Y_1), \dots , (X_T,Y_T)\big)$. Our performances will be measured via the square loss, i.e., if we predict $\hat{m}$, we pay the loss \begin{equation*} \ell(\hat{m}) :=\mathbb{E}\big[(Y-\hat{m}X)^2\big]\;, \end{equation*} which has its minimum at $\hat{m} = m$ (since $\mathbb{E}[Y \mid X] = mX$).

A viable strategy seems to minimize a proxy of $\ell$, for example its empirical version based on the sample $S_T$ we have access to: \begin{equation*} \hat{\ell}_{S_T}(\hat{m}) := \frac{1}{T} \sum_{t=1}^T(Y_t-\hat{m}X_t)^2\;, \end{equation*} whose minimum occurs at \begin{equation*} \hat{m}_{S_T} := \frac{\sum_t^T X_tY_t}{\sum_{t=1}^T X_t^2}\;. \end{equation*}

I'm interested in high-probability exponential guarantees about the performance of the estimator $\hat{m}_{S_T}$ in the spirit of Hoeffding's inequality. Specifically:

Can we guarantee that there exists constants $c,d\ge0$ such that \begin{equation*} \forall \varepsilon >0, \forall T \in \mathbb{N}, \qquad \mathbb{P}\big[|\hat{m}_{S_T} - m| \ge \varepsilon \big] \le c \cdot \exp (- d \cdot \varepsilon ^2 \cdot T) \end{equation*}

If that's true, how do these two constants $c,d$ look like?

If that's not true, which kind of guarantees can we give?