I'm interested in understanding how one may associate modular symbols to the L-functions and $p$-adic L-functions associated to the Rankin Selberg convolution of two modular forms/ elliptic curves and the symmetric square of a modular form/elliptic curves. Looking through the literature I see that the $\operatorname{GL}\_{n-1}\times \operatorname{GL}\_n$ case has been treated in general, for instance "Modular symbols for reductive groups and p-adic Rankin-Selberg convolutions over number fields"-Januszewski ([arXiv](https://arxiv.org/abs/0903.1625)/[publisher link](https://www.degruyter.com/view/j/crll.2011.2011.issue-653/crelle.2011.018/crelle.2011.018.xml)) and "Relative modular symbols and $p$-adic Rankin-Selberg convolutions"-Schmidt ([behind paywall](https://link.springer.com/article/10.1007/BF01232425)).


Is there a reference for the theory of modular symbols in the $\operatorname{GL}\_{2}\times \operatorname{GL}\_2$ and $\operatorname{Sym}^2$ cases?



Modular symbols associated to Rankin Selberg convolutions and the symmetric square
I do not think there is a reference for this theory, because as far as I know no such theory exists. I have spent a substantial portion of my career studying the arithmetic of the special values of the $GL\_2 \times GL\_2$ Rankin--Selberg L-function, and I am not aware of a theory of modular symbols in this setting.


