Aligned natural inflation in the Large Volume Scenario

Angus, Stephen; Choi, Kwonho; Shin, Chang Sub

doi:10.1007/jhep10(2021)248

Cited by 7 publications

(5 citation statements)

References 84 publications

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“…The effective field theory is also marginally under control and it is rather hard to build explicit Calabi-Yau orientifold models which are globally consistent due to the need to rely on large ranks for the condensing gauge groups. Interesting models have however been proposed using combinations of C 0 , C 2 and C 4 axions [459,460,461,462,463,464,465]. A survey on axion inflation in type IIB string theory compactifications and the possibility of enlarging the field range via alignment was performed in [466].…”

Section: Natural Inflation From Alignmentmentioning

confidence: 99%

String Cosmology: from the Early Universe to Today

Cicoli¹,

Conlon²,

Maharana³

et al. 2023

Preprint

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We review applications of string theory to cosmology, from primordial times to the present-day accelerated expansion. Starting with a brief overview of cosmology and string compactifications, we discuss in detail moduli stabilisation, inflation in string theory, the impact of string theory on post-inflationary dynamics (reheating, moduli domination, kination), dark energy (the cosmological constant from a string landscape and models of quintessence) and various alternative scenarios (string/brane gases, the pre big-bang scenario, rolling tachyons, ekpyrotic/cyclic cosmologies, bubbles of nothing, S-brane and holographic cosmologies). The state of the art in string constructions is described in each topic and, where relevant, connections to swampland conjectures are made. The possibilities for novel particles and excitations (axions, moduli, cosmic strings, branes, solitons, oscillons and boson stars) are emphasised. Implications for the physics of the CMB, gravitational waves, dark matter and dark radiation are discussed along with potential observational signatures.

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Section: Natural Inflation From Alignmentmentioning

confidence: 99%

String Cosmology: from the Early Universe to Today

Cicoli¹,

Conlon²,

Maharana³

et al. 2023

Preprint

View full text Add to dashboard Cite

show abstract

“…Significant dark radiation abundance is a familiar problem or, more optimistically, a prediction of LVS cosmology [27][28][29][30][31][32][33][34][35][36][37][38][39][40]. It arises in the simplest, sequestered setting because the light volume modulus is the last one to decay.…”

Section: Dark Radiation I: a New Solution To An Old Problem By Higgs-...mentioning

confidence: 99%

“…1 However, having a more complete theory also has important implications for cosmology. A by now well-known example is the prediction of a significant amount of dark radiation [27][28][29][30][31][32][33][34][35][36][37][38][39][40]. In the present paper we aim for a consistent cosmological picture by facing the challenge of dark radiation in combination with that of a stringy QCD axion.…”

Section: Jhep09(2022)198 1 Introductionmentioning

confidence: 96%

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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“…Significant dark radiation abundance is a familiar problem or, more optimistically, a prediction of LVS cosmology [25][26][27][28][29][30][31][32][33][34][35][36][37]. It arises in the simplest, sequestered setting because the light volume modulus is the last one to decay.…”

Section: Dark Radiation I: An Old Problem and Its New Resolution Bymentioning

confidence: 99%

“…[23,24]. now well-known example is the prediction of a significant amount of dark radiation [25][26][27][28][29][30][31][32][33][34][35][36][37]. In the present paper we aim for a consistent cosmological picture by facing the challenge of dark radiation in combination with that of a stringy QCD axion.…”

Section: Introductionmentioning

confidence: 96%

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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Aligned natural inflation in the Large Volume Scenario

Cited by 7 publications

References 84 publications

String Cosmology: from the Early Universe to Today

String Cosmology: from the Early Universe to Today

Axions in string theory — slaying the Hydra of dark radiation

Axions in String Theory and the Hydra of Dark Radiation

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