20 research outputs found
Swampland Bounds on Dark Sectors
We use Swampland principles to theoretically disfavor regions of the
parameter space of dark matter and other darkly charged particles that may
exist. The Festina Lente bound, the analogue of the Weak-Gravity conjecture in
de Sitter, places constraints on the mass and charge of dark particles, which
here we show cover regions in parameter space that are currently allowed by
observations. As a consequence, a broad set of new ultra-light particles are in
the Swampland, independently of their cosmic abundance, showing the
complementarity of Quantum Gravity limits with laboratory and astrophysical
studies. In parallel, a Swampland bound on the UV cutoff associated to the
axion giving a St\"{u}ckelberg photon its longitudinal mode translates to a new
constraint on the kinetic mixings and masses of dark photons. This covers part
of the parameter space targeted by upcoming dark-photon direct-detection
experiments. Moreover, it puts astrophysically interesting models in the
Swampland, including freeze-in dark matter through an ultra-light dark photon,
as well as radio models invoked to explain the 21-cm EDGES anomaly.Comment: 31 pages, 5 figure
Chern-Simons bubbles: Lopsided false vacuum decay in axion electrodynamics
We study axion electrodynamics, including the Chern-Simons interaction term,
in the presence of parallel background electric and magnetic fields, as can for
example occur in certain models of axion inflation and in the study of dyonic
black holes. In this setup, we find a new back-reacted instanton solution which
corresponds to the nucleation of an axion domain wall that screens the
electromagnetic fields in a process analogous to Schwinger pair production,
despite the absence of light charged particles. The full solution includes the
effect of the Chern-Simons induced charges and currents on the axion domain
wall arising from the Witten and Sikivie (anomalous Hall) effects,
respectively. The Euclidean solution has a reduced symmetry
which describes the nucleation of a prolate bubble in its rest-frame. A unique
feature of this solution is that the region of lower energy density is outside
the bubble rather than inside. We also describe the time evolution of this
initial configuration, showing how the bubble can become further elongated
along the direction of the background electric and magnetic fields. We describe
potential applications of this process in particle physics and cosmology.Comment: 30 page
Astrophysical constraints on decaying dark gravitons
In the dark dimension scenario, which predicts an extra dimension of micron scale, dark gravitons (KK modes) are a natural dark matter candidate. In this paper, we study observable features of this model. In particular, their decay to standard matter fields can distort the CMB and impact other astrophysical signals. Using this we place bounds on the parameters of this model. In particular we find that the natural range of parameters in this scenario is consistent with these constraints and leads to the prediction that the mean mass of the dark matter today is close to a few hundred keV and the effective size of the extra dimension is around 1–30 μm