include signatures that depend on neutrino mass, e.g., neutrino decay, neutrino magnetic moments, or neutrinoless double beta decay. The weak interactions of neutrinos make them unique messengers for studying astrophysical systems. The extreme scales of astrophysics allow tests of neutrino properties far beyond what is possible in the laboratory, and may reveal new interactions that shed light on the origin of neutrino mass and other important questions.

The term “secret neutrino interactions" ($\nu$SI) indicates new physics that couples neutrinos to neutrinos. A wide variety of models have already been considered, and some have implications for neutrino masses. A way to characterize these models is by their mediator mass. For massless mediators, such as in Majoron models [@Chikashige:1980ui; @Gelmini:1980re; @Georgi:1981pg; @Gelmini:1982rr; @Nussinov:1982wu], there is at least one stable new particle. For very heavy mediators, one can use an effective theory to study the phenomenology of a class of models [@Kolb:1987qy; @Bilenky:1992xn; @Bilenky:1994ma; @Bilenky:1999dn]. In between, the mediator mass is more moderate, and could induce resonances [@Chacko:2003dt; @Chacko:2004cz; @Davoudiasl:2005ks; @Goldberg:2005yw; @Baker:2006gm; @Wang:2006jy; @Gabriel:2006ns]. In some models, the neutrinos also interact with dark matter [@1992hena.conf..173W; @Fayet:2006sa; @Barenboim:2006dj; @Mangano:2006mp; @Lindner:2010rr; @Palomares:2011xx; @Aarssen:2012fx; @Shoemaker:2013tda; @Dasgupta:2013zpn; @Bringmann:2013vra; @Farzan:2014gza].

It is challenging to directly test $\nu$SI through 