Well tempering is one of the few classical field theory methods for solving the original cosmological constant problem, dynamically canceling a large (possibly Planck scale) vacuum energy and leaving the matter component intact, while providing a viable cosmology with late time cosmic acceleration and an end de Sitter state. We present the general constraints that variations of Horndeski gravity models with different combinations of terms must satisfy to admit an exact de Sitter spacetime that does not respond to an arbitrarily large cosmological constant. We explicitly derive several specific scalar-tensor models that well temper and can deliver a standard cosmic history including current cosmic acceleration. Stability criteria, attractor behavior of the de Sitter state, and the response of the models to pressureless matter are considered. The well tempered conditions can be used to focus on particular models of modified gravity that have special interest -- not only removing the original cosmological constant problem but providing relations between the free Horndeski functions and reducing them to a couple of parameters, suitable for testing gravity and cosmological data analysis.

中文翻译：

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温和的宇宙常数：Horndeski 变体

井回火是为数不多的用于解决原始宇宙常数问题的经典场论方法之一，动态消除大的（可能是普朗克尺度）真空能量并保持物质成分完好无损，同时提供了一个可行的宇宙学，具有后期宇宙加速和结束德西特州。我们提出了具有不同项组合的 Horndeski 引力模型的变化必须满足的一般约束，以允许不响应任意大的宇宙常数的精确德西特时空。我们明确地推导出了几个特定的​​标量张量模型，这些模型可以很好地调节并且可以提供标准的宇宙历史，包括当前的宇宙加速度。考虑了稳定性标准、德西特态的吸引子行为以及模型对无压物质的响应。