Field theory axiverse

Abstract

Axion and axionlike particles are a prominent candidate for physics beyond the Standard Model and can play an important role in cosmology, serving as dark matter or dark energy, or both, drawing motivation in part from the string theory axiverse. Axionlike particles can also arise as composite degrees of freedom following chiral symmetry breaking in a dark confining gauge theory, analogous to the Standard Model (SM) pion. A dark sector with arbitrary Nf flavors of dark quarks leads to Nf2−1 axionlike states, effectively a (or “π-axiverse”). A portal to the visible sector can be achieved through the standard kinetic mixing between the dark photon and SM photon, generating millicharges for the dark quarks and consequently couplings, both parity even and parity odd, between the SM and the dark pions. This scenario has been studied for the Nf=2 case and more recently for a dark Standard Model with Nf=6. In this work, we study the spectrum of this field theory axiverse for an arbitrary number of flavors and apply this to the example Nf=10. We calculate the couplings to the SM photon analogous to the conventional axion-photon coupling, including the Nf and Nc dependence, and compute the present and future constraints on the Nf=10 Nc=3 π-axiverse. We elucidate the accompanying “baryverse” of superheavy dark baryons, namely, an ensemble of charged and neutral dark baryons with a mass set by the dark pion decay constant. Published by the American Physical Society 2024