Inflatable Dark Matter

Heavy Thermal Dark Matter from a New Collision Mechanism

We propose a new thermal freeze-out mechanism that results in dark matter masses exceeding the unitarity bound by many orders of magnitude, without violating perturbative unitarity or modifying the standard cosmology. The process determining the relic abundance is χζ^{†}→ζζ, where χ is the dark matter candidate. For m_{ζ}<m_{χ}<3m_{ζ}, χ is cosmologically long-lived and scatters against the exponentially more abundant ζ. Therefore, such a process allows for exponentially heavier dark matter for the same interaction strength as a particle undergoing ordinary 2→2 freeze-out, or equivalently, exponentially weaker interactions for the same mass. We demonstrate this mechanism in a leptophilic dark matter model, which allows for dark matter masses up to 10^{9}  GeV.

Superheavy Thermal Dark Matter

We propose a mechanism of elementary thermal dark matter with a mass up to 10^{14}  GeV, within a standard cosmological history, whose relic abundance is determined solely by its interactions with the standard model, without violating the perturbative unitarity bound. The dark matter consists of many nearly degenerate particles which scatter with the standard model bath in a nearest-neighbor chain, and maintain chemical equilibrium with the standard model bath by in-equilibrium decays and inverse decays. The phenomenology includes super heavy elementary dark matter and heavy relics that decay at various epochs in the cosmological history, with implications for the cosmic microwave background, structure formation, and cosmic ray experiments.

First Results from ABRACADABRA-10 cm: A Search for Sub-μeV Axion Dark Matter

The axion is a promising dark matter candidate, which was originally proposed to solve the strong-CP problem in particle physics. To date, the available parameter space for axion and axionlike particle dark matter is relatively unexplored, particularly at masses m_{a}≲1  μeV. ABRACADABRA is a new experimental program to search for axion dark matter over a broad range of masses, 10^{-12}≲m_{a}≲10^{-6}  eV. ABRACADABRA-10 cm is a small-scale prototype for a future detector that could be sensitive to the QCD axion. In this Letter, we present the first results from a 1 month search for axions with ABRACADABRA-10 cm. We find no evidence for axionlike cosmic dark matter and set 95% C.L. upper limits on the axion-photon coupling between g_{aγγ}<1.4×10^{-10} and g_{aγγ}<3.3×10^{-9}  GeV^{-1} over the mass range 3.1×10^{-10}-8.3×10^{-9}  eV. These results are competitive with the most stringent astrophysical constraints in this mass range.

Dark Matter Coannihilation with a Lighter Species

We propose a new thermal freeze-out mechanism for ultraheavy dark matter. Dark matter coannihilates with a lighter unstable species that is nearby in mass, leading to an annihilation rate that is exponentially enhanced relative to standard weakly interactive massive particles. This scenario destabilizes any potential dark matter candidate. In order to remain consistent with astrophysical observations, our proposal necessitates very long-lived states, motivating striking phenomenology associated with the late decays of ultraheavy dark matter, potentially as massive as the scale of grand unified theories, M_{GUT}∼10^{16}  GeV.

Fuzzy Dark Matter from Infrared Confining Dynamics

A very light boson of mass O(10^{-22})  eV may potentially be a viable dark matter (DM) candidate, which can avoid phenomenological problems associated with cold DM. Such "fuzzy DM (FDM)" may naturally be an axion with a decay constant f_{a}∼10^{16}-10^{18}  GeV and a mass m_{a}∼μ^{2}/f_{a} with μ∼10^{2}  eV. Here, we propose a concrete model, where μ arises as a dynamical scale from infrared confining dynamics, analogous to QCD. Our model is an alternative to the usual approach of generating μ through string theoretic instanton effects. We outline the features of this scenario that result from various cosmological constraints. We find that those constraints are suggestive of a period of mild of inflation, perhaps from a strong first order phase transition, that reheats the standard model (SM) sector only. A typical prediction of our scenario, broadly speaking, is a larger effective number of neutrinos compared to the SM value N_{eff}≈3, as inferred from precision measurements of the cosmic microwave background. Some of the new degrees of freedom may be identified as "sterile neutrinos," which may be required to explain certain neutrino oscillation anomalies. Hence, aspects of our scenario could be testable in terrestrial experiments, which is a novelty of our FDM model.