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\signature{Simon-Pierre Boucher\\Universit\'e du Qu\'ebec en Outaouais}
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\begin{letter}{The Editors\\International Review of Financial Analysis}
\opening{Dear Editors,}

Please consider the enclosed manuscript, ``Faster, Wider, More Fragile? The
Evolution of Intraday Shock Propagation in U.S. Equity Markets, 1992--2026,''
for publication in the \emph{International Review of Financial Analysis}.

The paper measures how idiosyncratic intraday shocks travel across the U.S.
equity cross-section using 7.7 billion one-minute bars spanning thirty-four
years, including delisted securities. Its three findings are, we believe, of
direct interest to the journal's readership: (i) isolated six-sigma
one-minute shocks show no market-wide propagation relative to 1.8 million
matched within-stock placebos, in any decade; (ii) propagation is instead
concentrated in the shocked stock's lagged-correlation neighborhood, and this
network channel roughly tripled between the floor-trading and algorithmic
eras; and (iii) tail synchronization migrated to market-wide co-jump minutes,
whose severity spikes in 2008 and 2020 while ordinary extreme minutes became
an order of magnitude rarer.

The analysis is fully reproducible: the data snapshot is pinned by checksum,
every number in the manuscript is generated programmatically from
machine-readable results, and replication code accompanies the submission.
The manuscript is not under consideration elsewhere, and there are no
competing interests to declare.

\closing{Sincerely,}
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