In this paper, we study 𝑝-adic endoscopy on eigenvarieties for
SL
2
\mathrm{SL}_{2}
over totally real fields, taking a geometric perspective.
We show that non-automorphic members of endoscopic 𝐿-packets of regular weight contribute eigenvectors to overconvergent cohomology at critically refined endoscopic points on the eigenvariety, and we precisely quantify this contribution.
This gives a new perspective on and generalizes previous work of the second author.
Our methods are geometric, and are based on showing that the
SL
2
\mathrm{SL}_{2}
-eigenvariety is locally a quotient of an eigenvariety for
GL
2
\mathrm{GL}_{2}
, which allows us to explicitly describe the local geometry of the
SL
2
\mathrm{SL}_{2}
-eigenvariety.
In particular, we show that it often fails to be Gorenstein.