Beyond Schr{o}dinger-Poisson: Nonrelativistic Effective Field Theory for Scalar Dark Matter

Massive scalar fields provide excellent dark matter candidates, whose dynamics are often explored analytically and numerically using nonrelativistic Schr{o}dinger-Poisson (SP) equations in a cosmological context. In this paper, starting from the nonlinear and fully relativistic Klein-Gordon-Einstein (KGE) equations in an expanding universe, we provide a systematic framework for deriving the SP equations, as well as relativistic corrections to them, by integrating out `fast modes and including nonlinear metric and matter contributions. We provide explicit equations for the leading-order relativistic corrections, which provide insight into deviations from the SP equations as the system approaches the relativistic regime. Upon including the leading-order corrections, our equations are applicable beyond the domain of validity of the SP system, and are simpler to use than the full KGE case in some contexts. As a concrete application, we calculate the mass-radius relationship of solitons in scalar dark matter and accurately capture the deviations of this relationship from the SP system towards the KGE one.

Gravitational effects on oscillon lifetimes

Many scalar field theories with attractive self-interactions support exceptionally long-lived, spatially localized and time-periodic field configurations called oscillons. A detailed study of their longevity is important for understanding their applications in cosmology. In this paper, we study gravitational effects on the decay rate and lifetime of dense oscillons, where self-interactions are more or at least equally important compared with gravitational interactions. As examples, we consider the $alpha$-attractor T-model of inflation and the axion monodromy model, where the potentials become flatter than quadratic at large field values beyond some characteristic field distance $F$ from the minimum. For oscillons with field amplitudes of $mathcal{O}(F)$ and for $Fll 0.1 M_mathrm{pl}$, we find that their evolution is almost identical to cases where gravity is ignored. For $Fsim 0.1 M_mathrm{pl}$, however, including gravitational interactions reduces the lifetime slightly.

Classical Decay Rates of Oscillons

Oscillons are extremely long-lived, spatially-localized field configurations in real-valued scalar field theories that slowly lose energy via radiation of scalar waves. Before their eventual demise, oscillons can pass through (one or more) exceptionally stable field configurations where their decay rate is highly suppressed. We provide an improved calculation of the non-trivial behavior of the decay rates, and lifetimes of oscillons. In particular, our calculation correctly captures the existence (or absence) of the exceptionally long-lived states for large amplitude oscillons in a broad class of potentials, including non-polynomial potentials that flatten at large field values. The key underlying reason for the improved (by many orders of magnitude in some cases) calculation is the systematic inclusion of a spacetime-dependent effective mass term in the equation describing the radiation emitted by oscillons (in addition to a source term). Our results for the exceptionally stable configurations, decay rates, and lifetime of large amplitude oscillons (in some cases $gtrsim 10^8$ oscillations) in such flattened potentials might be relevant for cosmological applications.