RDepending on Perl itself

Writing correct dependency specifications is an art in itself. So, here's a small guide for Gentoo developers how to specify runtime dependencies on dev-lang/perl. First, the general rule.
Check the following two things: 1) is your package linking anywhere to libperl.so, 2) is your package installing any Perl modules into Perl's vendor directory (e.g., /usr/lib64/perl5/vendor_perl/5.20.1/)? If at least one of these two questions is answered with yes, you need in your dependency string a slot operator, i.e. "dev-lang/perl:=" Obviously, your ebuild will have to be EAPI=5 for that. If neither 1) nor 2) are the case, "dev-lang/perl" is enough.
Now, with eclasses. If you use perl-module.eclass or perl-app.eclass, two variables control automatic adding of dependencies. GENTOO_DEPEND_ON_PERL sets whether the eclass automatically adds a dependency on Perl, and defaults to yes in both cases. GENTOO_DEPEND_ON_PERL_SUBSLOT controls whether the slot operator ":=" is used. It defaults to yes in perl-module.eclass and to no in perl-app.eclass. (This is actually the only difference between the eclasses.) The idea behind that is that a Perl module package always installs modules into vendor_dir, while an application can have its own separate installation path for its modules or not install any modules at all.
In many cases, if a package installs Perl modules you'll need Perl at build time as well since the module build system is written in Perl. If a package links to Perl, that is obviously needed at build time too.

So, summarizing:

eclass	1) or 2) true	1) false, 2) false
none	"dev-lang/perl:=" needed in RDEPEND and most likely also DEPEND	"dev-lang/perl" needed in RDEPEND, maybe also in DEPEND
perl-module.eclass	no need to do anything	GENTOO_DEPEND_ON_PERL_SUBSLOT=no possible before inherit
perl-app.eclass	GENTOO_DEPEND_ON_PERL_SUBSLOT=yes needed before inherit	no need to do anything

NJP accepted: Thermally induced subgap features in the cotunneling spectroscopy of a carbon nanotube

Today's good news is that our manuscript "Thermally induced subgap features in the cotunneling spectroscopy of a carbon nanotube" has been accepted for publication by New Journal of Physics.
In a way, this work is directly building on our previous publication on thermally induced quasiparticles in niobium-carbon nanotube hybrid systes. As a contribution mainly from our theory colleagues, now the modelling of transport processes is enhanced and extended to cotunneling processes within Coulomb blockade. A generalized master equation based on the reduced density matrix approach in the charge conserved regime is derived, applicable to any strength of the intradot interaction and to finite values of the superconducting gap.
We show both theoretically and experimentally that also in cotunneling spectroscopy distinct thermal "replica lines" due to the finite quasiparticle occupation of the superconductor occur at higher temperature T~1K: the now possible transport processes lead to additional conductance both at zero bias and at finite voltage corresponding to an excitation energy; experiment and theoretical result match very well.

"Thermally induced subgap features in the cotunneling spectroscopy of a carbon nanotube"
S. Ratz, A. Donarini, D. Steininger, T. Geiger, A. Kumar, A. K. Hüttel, Ch. Strunk, and M. Grifoni
New J. Phys. 16, 123040 (2014), arXiv:1408.5000 (PDF)