Inflatable Dark Matter

Abstract: We describe a general scenario, dubbed "Inflatable Dark Matter", in which the density of dark matter particles can be reduced through a short period of late-time inflation in the early universe. The overproduction of dark matter that is predicted within many otherwise well-motivated models of new physics can be elegantly remedied within this context, without the need to tune underlying parameters or to appeal to anthropic considerations. Thermal relics that would otherwise be disfavored can easily be accommodated within this class of scenarios, including dark matter candidates that are very heavy or very light. Furthermore, the non-thermal abundance of GUT or Planck scale axions can be brought to acceptable levels, without invoking anthropic tuning of initial conditions. A period of late-time inflation could have occurred over a wide range of scales from ~ MeV to the weak scale or above, and could have been triggered by physics within a hidden sector, with small but not necessarily negligible couplings to the Standard Model.

Overview of "Inflatable Dark Matter"

The paper titled "Inflatable Dark Matter" introduces a theoretical framework where a brief period of late-time inflation can significantly alter the density of dark matter particles produced in the early universe. This concept addresses the overproduction issues found in various models of dark matter without necessitating fine-tuning or anthropic reasoning.

Main Concepts and Findings

1. Late-Time Inflation: The study proposes an inflationary phase after the production of dark matter. This paradigm generates a scenario where models predicting excess dark matter align with observed cosmic abundances. Inflation driven by vacuum energy density, extending from sub-MeV to possibly above the weak scale, might originate from hidden sector physics weakly coupled to the Standard Model.

2. Implications for Dark Matter Models: Such inflation could accommodate dark matter candidates that are outside of the commonly expected parameter space. Heavy thermal relics, which would otherwise violate unitarity bounds, and lightweight axions, previously dismissed due to excessive production predictions, can be reconsidered viable candidates under this framework.

3. Implications for High-Scale Physics: The null results from direct detection efforts and accelerators like the LHC may prompt a reevaluation of models predicting higher interaction scales with dark matter. Late-time inflation could reopen theoretical possibilities, allowing high-scale physics models to remain phenomenologically feasible.

Theoretical and Practical Implications

• Dilution Factor: The research introduces a dilution factor stemming from inflation which can effectively reconcile models where dark matter is overly abundant. This implies a paradigm shift, where weakly interacting massive particles (WIMPs) with lower annihilation cross-sections can still represent the viable dark matter candidate.

• Axion Production: The framework posits that late-time inflation near the QCD phase transition could mitigate axion overproduction without anthropic tuning. This corrigibility is appealing for theories motivated by high-scale physics.

• Viability of Asymmetric Dark Matter: The paper outlines potential impacts on asymmetric dark matter models where a primordial asymmetry exists between matter and antimatter components. It explores possibilities where late-time inflation coupled with symmetric or asymmetric reheating affect the observed dark matter quantity.

Prospects for Future Research

The findings suggest further exploration into the hidden sector dynamics that could induce such inflationary phases. Prospective experimental avenues might include probing high energy scales for associated phase transitions contributing to late-time inflation. Additionally, investigating relations between baryogenesis and inflatable dark matter could yield significant insights.

In conclusion, "Inflatable Dark Matter" advocates for a cosmological model where non-standard thermal histories provide a mechanism to explain dark matter's constraints, advocating flexibility in interpreting null results from current experimental efforts. This adaptability in dark matter research hints at a broader interplay between particle physics, cosmology, and high-scale theories in the quest to understand the universe's composition.