  This work investigates dense packings of congruent hard infinitesimally--thin
circular arcs in the two-dimensional Euclidean space. It focuses on those
denotable as major whose subtended angle $\theta \in \left ( \pi, 2\pi \right
]$. Differently than those denotable as minor whose subtended angle $\theta \in
\left [0, \pi \right]$, it is impossible for two hard infinitesimally-thin
circular arcs with $\theta \in \left ( \pi, 2\pi \right ]$ to arbitrarily
closely approach once they are arranged in a configuration, e.g. on top of one
another, replicable ad infinitum without introducing any overlap. This makes
these hard concave particles, in spite of being infinitesimally thin, most
densely pack with a finite number density. This raises the question as to what
are these densest packings and what is the number density that they achieve.
Supported by Monte Carlo numerical simulations, this work shows that one can
analytically construct compact closed circular groups of hard major circular
arcs in which a specific, $\theta$-dependent, number of them (anti-)clockwise
intertwine. These compact closed circular groups then arrange on a triangular
lattice. These analytically constructed densest-known packings are compared to
corresponding results of Monte Carlo numerical simulations to assess whether
they can spontaneously turn up.
