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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 raise market-wide tail activity by at most a few percent of
its base rate 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) common information
is impounded within the minute, ordinary extreme minutes became an order of
magnitude rarer after decimalization, and severe co-jump minutes are roughly
ten times more frequent in 2008 and 2020 than in calm years. The manuscript
reports the design diagnostics that bound each of these statements.

The analysis is fully reproducible: the data snapshot is pinned by checksum,
every headline 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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