Axiverse Strings

March-Russell, John; Tillim, Hannah

doi:10.48550/arxiv.2109.14637

Cited by 3 publications

(5 citation statements)

References 51 publications

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“…• There can be additional contributions to the density from topological configurations such as axion strings and domain walls (see e.g. [71][72][73][74][75]).…”

Section: Axion Realization and Consequence For Pre-vs Post-inflationa...mentioning

confidence: 99%

“…Exceptions may arise if the SM model cycle can be realized in the geometric regime in a strongly warped region, as noted before. This could allow for cosmologically relevant axionic strings[75] and also impact the dark radiation problem[38]. However, apart from the model building challenge, one presumable faces a considerable tadpole issue related to such an appropriately large throat[61].…”

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confidence: 99%

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Axions in string theory — slaying the Hydra of dark radiation

Cicoli

Hebecker

Jaeckel

et al. 2022

J. High Energ. Phys.

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It is widely believed that string theory easily allows for a QCD axion in the cosmologically favored mass range. The required small decay constant, fa ≪ MP, can be implemented by using a large compactification volume. This points to the Large Volume Scenario which in turn makes certain cosmological predictions: first, the closed string axion behaves similarly to a field-theoretic axion in the pre-inflationary scenario, i.e. the initial value can be tuned but one is constrained by isocurvature fluctuations. In addition, the volume represents a long-lived modulus that may lead to an early matter-dominated phase. Finally, the decay of the volume modulus to its own axion tends to overproduce dark radiation. In this paper we aim to carefully analyze the cosmology by studying models that not only allow for a QCD axion but also include inflation. Quite generally, limits on isocurvature fluctuations restrict us to relatively low-scale inflation, which in the present stringy context points to Kähler moduli inflation. As a novel feature we find that the lightest (volume) modulus couples strongly to the Higgs. It hence quickly decays to the SM, thus resolving the original dark radiation problem. This decay is much faster than that of the inflaton, implying that reheating is determined by the inflaton decay. The inflaton could potentially reintroduce a dark radiation problem since it decays to lighter moduli and their axions with equal rates. However, due its mixing with the QCD-saxion, the inflaton has also a direct decay rate to the SM, enhanced by the number of SM gauge bosons. This results in an amount of dark radiation that is consistent with present limits but potentially detectable in future measurements.

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“…• There can be additional contributions to the density from topological configurations such as axion strings and domain walls (see e.g. [71][72][73][74][75]).…”

Section: Axion Realization and Consequence For Pre-vs Post-inflationa...mentioning

confidence: 99%

mentioning

confidence: 99%

Axions in string theory — slaying the Hydra of dark radiation

Cicoli

Hebecker

Jaeckel

et al. 2022

J. High Energ. Phys.

View full text Add to dashboard Cite

show abstract

“…• There can be additional contributions to the density from topological configurations such as axion strings and domain walls (see e.g. [65][66][67][68][69]).…”

Section: Axion Realization and Consequence For Pre-vs Postinflationar...mentioning

confidence: 99%

“…6 Exceptions may arise if the SM model cycle can be realized in the geometric regime in a strongly warped region, as noted before. This could allow for cosmologically relevant axionic strings [69] and also impact the dark radiation problem [35]. However, apart from the model building challenge, one presumable faces a considerable tadpole issue related to such an appropriately large throat [55].…”

Section: Dark Matter Abundancementioning

confidence: 99%

Axions in String Theory and the Hydra of Dark Radiation

Cicoli¹,

Hebecker²,

Jaeckel³

et al. 2022

Preprint

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It is widely believed that string theory easily allows for a QCD axion in the cosmologically favoured mass range. The required small decay constant, f a M P , can be implemented by using a large compactification volume. This points to the Large Volume Scenario (LVS), which in turn makes certain cosmological predictions: First, the axion behaves similarly to a field-theoretic axion in the pre-inflationary scenario, i.e. the initial value can be tuned but one is constrained by isocurvature fluctuations. In addition, the volume naively represents a long-lived modulus, that may lead to an early matter-dominated phase. Finally, the volume modulus' decay to its own axion tends to produce excessive dark radiation. In this paper we aim to carefully analyze the cosmology by studying models that not only allow for a QCD axion but also include inflation. Quite generally, limits on isocurvature fluctuations restrict us to relatively low-scale inflation, which in the present stringy context points to Kahler or blowup inflation models. Moreover, we find as a novel and at first sight encouraging feature that the lightest (volume) modulus is likely to couple strongly to the Higgs. It hence quickly decays to the Standard Model, thus seemingly resolving the dark radiation problem. This decay is much faster than that of the inflaton such that the latter comes to dominate the Universe. Since the inflaton distributes its energy equally between the QCD axion and the Standard Model, this turns out to be a curse rather than a blessing: Generically, the dark radiation abundance remains too high. We briefly discuss possibilities to circumvent this issue. In particular, the rapid decay of the volume modulus into Higgses demotes dark radiation from a generic LVS problem to an issue resolvable by inflationary model building.

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“…In the Standard Model of particle physics, almost a hundred among mass-less scalar fields, Dirac spinors and vectors are considered, and this number may be doubled if the Standard Model is embedded in a supersymmetric theory. Moreover, the number of scalar fields may skyrocket up to 10 5 if one considers axion-like particles coming from string compactification [43,44,45]. Fields action in curved space-time is conformal invariant, but a renormalization must be introduced in order to cancel the divergences from the one-loop vacuum contributions.…”

Section: Trace Anomalymentioning

confidence: 99%

Local solutions of General Relativity in the presence of the Trace Anomaly

Calzá,

Casalino,

Sebastiani

2022

Preprint

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Local solutions are a vivid and long-living topic in gravitational physics. We consider exact static pseudo-spherically symmetric solutions of semi-classical Einstein's equations in presence of the trace anomaly contribution. We investigate black hole solutions and propose new metrics describing traversable wormholes. Thanks to the trace anomaly, wormholes are realized in the vacuum and, nevertheless, violate the null energy condition.

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Axiverse Strings

Cited by 3 publications

References 51 publications

Axions in string theory — slaying the Hydra of dark radiation

Axions in string theory — slaying the Hydra of dark radiation

Axions in String Theory and the Hydra of Dark Radiation

Local solutions of General Relativity in the presence of the Trace Anomaly

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