Gravitational wave forest from string axiverse

Kitajima, Naoya; Soda, Jiro; Urakawa, Yuko

doi:10.1088/1475-7516/2018/10/008

Cited by 85 publications

(119 citation statements)

References 72 publications

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“…As was argued in Ref. [9], the reason for this can be understood as follows. Equating the time scale of the cosmic expansion with the one of the potential driven force, we can roughly evaluate H osc as…”

Section: Field Equationmentioning

confidence: 83%

“…The flapping resonance instability, pointed out in Ref. [9], is qualitatively different from either of the broad and narrow resonance instability. This instability occurs during an oscillation which goes across the inflection points.…”

Section: Flapping Resonancementioning

confidence: 90%

“…As we have discussed in this section, the parameterq indeed characterizes the width of the resonance band for the parametric resonance described by the Hill's equation (2.11). Therefore, usingq, we categorize the parametric resonance as In the succeeding subsections, we will show that the flapping resonance [9] is classified as the intermediate resonance.…”

Section: Self-resonance Described By Hill's Equationmentioning

confidence: 99%

“…In particular, in Ref. [9], two of the authors pointed out a new type of resonance instability, dubbed the flapping resonance instability.…”

Section: Introductionmentioning

confidence: 99%

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Efficient self-resonance instability from axions

Fukunaga

Kitajima

Urakawa

2019

J. Cosmol. Astropart. Phys.

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It was recently shown that a coherent oscillation of an axion can cause an efficient parametric resonance, leading to a prominent emission of the gravitational waves (GWs). In this paper, conducting the Floquet analysis, we investigate the parametric resonance instability, which potentially triggers the emission of the GWs from axions. Such a resonance instability takes place, when the time evolution of the background field significantly deviates from the harmonic oscillation. Therefore, the resonance instability cannot be described by the Mathieu equation, whose stability/instability chart is well known. In this paper, introducing an explicitly calculable parameterq, which can be used to classify different types of the parametric resonance described by the general Hill's equation, we investigate the stability/instability chart for the general Hill's equation. This can also apply to the case where the background oscillation is anharmonic. We show that the flapping resonance instability, which takes place forq = O(1), typically leads to the most significant growth of the inhomogeneous modes among the self-resonance instability. We also investigate whether the flapping resonance takes place for the cosine potential or not.

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Section: Field Equationmentioning

confidence: 83%

Section: Flapping Resonancementioning

confidence: 90%

Section: Self-resonance Described By Hill's Equationmentioning

confidence: 99%

“…In particular, in Ref. [9], two of the authors pointed out a new type of resonance instability, dubbed the flapping resonance instability.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Efficient self-resonance instability from axions

Fukunaga

Kitajima

Urakawa

2019

J. Cosmol. Astropart. Phys.

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“…Let us denote by φ 0 the amplitude of oscillations once they start. A good criterium for the Hubble rate at the beginning of the field oscillations is given by [41] H…”

Section: Life and Death Of An Oscillon 21 Birthmentioning

confidence: 99%

Oscillons and dark matter

Ollé

Pujolàs

Rompineve

2020

J. Cosmol. Astropart. Phys.

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Oscillons are bound states sustained by self-interactions that appear in rather generic scalar models. They can be extremely long-lived and have a built-in formation mechanism -parametric resonance instability. These features suggest that oscillons can affect the standard picture of scalar ultra-light dark matter (ULDM) models. We explore this idea along two directions. First, we investigate numerically oscillon lifetimes and their dependence on the shape of the potential. We find that scalar potentials that occur in well motivated axion-like models can lead to oscillons that live up to 10 8 cycles or more. Second, we discuss the observational constraints on the ULDM models once the presence of oscillons is taken into account. For a wide range of axion masses, oscillons decay around or after matter-radiation equality and can thus act as early seeds for structure formation. We also discuss the possibility that oscillons survive up to today.In this case they can most easily play the role of dark matter.

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Audible axions

Machado

Ratzinger

Schwaller

et al. 2019

J. High Energ. Phys.

130

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Conventional approaches to probing axions and axion-like particles (ALPs) typically rely on a coupling to photons. However, if this coupling is extremely weak, ALPs become invisible and are effectively decoupled from the Standard Model. Here we show that such invisible axions, which are viable candidates for dark matter, can produce a stochastic gravitational wave background in the early universe. This signal is generated in models where the invisible axion couples to a dark gauge boson that experiences a tachyonic instability when the axion begins to oscillate. Incidentally, the same mechanism also widens the viable parameter space for axion dark matter. Quantum fluctuations amplified by the exponentially growing gauge boson modes source chiral gravitational waves. For axion decay constants f 10 17 GeV, this signal is detectable by either pulsar timing arrays or space/ground-based gravitational wave detectors for a broad range of axion masses, thus providing a new window to probe invisible axion models.

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Gravitational wave forest from string axiverse

Cited by 85 publications

References 72 publications

Efficient self-resonance instability from axions

Efficient self-resonance instability from axions

Oscillons and dark matter

Audible axions

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