Dark radiation and the Hagedorn phase

Frey, Andrew R.; Mahanta, Ratul; Maharana, Anshuman

doi:10.1103/physrevd.105.066007

Cited by 8 publications

(4 citation statements)

References 43 publications

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“…Although it is fair to describe LVS as the most developed scenario for precise studies of reheating and dark radiation production, similar questions of dark radiation production have also been studied for other scenarios of moduli-stabilisation, for example see [711,712,651,713,714,715,716].…”

Section: Dark Radiation Constraints On Moduli Decaysmentioning

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: Dark Radiation Constraints On Moduli Decaysmentioning

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%

“…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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String thermodynamics in and out of equilibrium: Boltzmann equations and random walks

Frey,

Mahanta,

Maharana

et al. 2024

J. High Energ. Phys.

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We revisit the study of string theory close to the Hagedorn temperature with the aim towards cosmological applications. We consider interactions of open and closed strings in a gas of Dp-branes, and/or one isolated Dp-brane, in an arbitrary number d of flat non-compact dimensions and general compact dimensions. Leading order string perturbation theory is used to obtain the basic interaction rates in a flat background, which are shown to be consistent with the random walk picture of highly excited strings that should apply in more general backgrounds. Using the random walk interpretation we infer the structure of more general semi-inclusive string scattering rates and then write down the corresponding Boltzmann equations describing ensembles of highly excited closed and open strings. We organise the interaction terms in Boltzmann equations so that detailed balance becomes manifest. We obtain the equilibrium solutions and show that they reduce to previously computed solutions for d = 0. We further study the behaviour of non-equilibrium fluctuations and find explicit analytic expressions for the equilibration rates (and for the number of open strings in d = 0). Potential implications for an early universe with strings at high temperatures are outlined.

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Dark radiation and the Hagedorn phase

Cited by 8 publications

References 43 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

String thermodynamics in and out of equilibrium: Boltzmann equations and random walks

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