Abstract
In this Letter, we investigate the effects of single derivative mixing in massive bosonic fields. In the regime of large mixing, we show that this leads to striking changes of the field dynamics, delaying the onset of classical oscillations and decreasing, or even eliminating, the friction due to Hubble expansion. We highlight this phenomenon with a few examples. In the first example, we show how an axionlike particle can have its number abundance parametrically enhanced. In the second example, we demonstrate that the QCD axion can have its number abundance enhanced allowing for misalignment driven axion dark matter all the way down to f_{a} of order astrophysical bounds. In the third example, we show that the delayed oscillation of the scalar field can also sustain a period of inflation. In the last example, we present a situation where an oscillating scalar field is completely frictionless and does not dilute away in time.
Highlights
Introduction.—Light scalar fields are present in many scenarios of physics beyond the standard model
The dynamics of scalar fields in the early Universe is largely determined by the form of their potential and by the Hubble expansion
In this Letter, we study how their evolution can be dramatically changed by introducing mixing with another massive field via a single derivative interaction
Summary
In this Letter, we investigate the effects of single derivative mixing in massive bosonic fields. In the regime of large mixing, we show that this leads to striking changes of the field dynamics, delaying the onset of classical oscillations and decreasing, or even eliminating, the friction due to Hubble expansion. We highlight this phenomenon with a few examples. As a case study we present a scenario where the QCD axion and a massive dark photon mix in a background magnetic field The change is only modest if M > B=f but can be substantial for B=f ≫ M
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