Constraints and horizons for de Sitter with extra dimensions

We study de Sitter configurations in ten-dimensional string models where supersymmetry is either absent or broken at the string scale. To this end, we derive expressions for the cosmological constant in general warped flux compactifications with localized sources, which yield no-go theorems that extend previous works on supersymmetric cases. We frame our results within a dimensional reduction and connect them to a number of Swampland conjectures, corroborating them further in the absence of supersymmetry. Furthermore, we construct a top-down string embedding of de Sitter brane-world cosmologies within unstable anti-de Sitter landscapes, providing a concrete realization of a recently revisited proposal.

“…Similar conclusions can be reached studying the Raychaudhuri equation in higher-dimensional settings[60], or employing a world-sheet analysis as in[61].…”

supporting

confidence: 68%

de Sitter in non-supersymmetric string theories: no-go theorems and brane-worlds

Basile

Lanza

2020

“…Since the solutions we construct are classical flux compactifications, (3.18), or the assumptions leading to it, must be violated whenever the Maldacena-Nuñez theorem [47] (and its extensions, see e.g. [48]) hold, if the single-scalar truncation is consistent. For instance, massive IIA supergravity seems to have all ingredients already in 10D; a runaway exponential potential for the dilaton and a dilaton coupling to the U(1)-field:…”

Section: Jhep05(2020)114mentioning

confidence: 99%

A dS obstruction and its phenomenological consequences

Riet

Venken

2020

In this note we observe that positive runaway potentials can generically be stabilized by abelian p-form fluxes, leading to parametrically controlled de Sitter solutions after compactification to a lower dimension. When compactifying from 4d to 2d the dS solutions are metastable, whereas all higher dimensional cases are unstable. The existence of these dS solutions require that a certain inequality involving the derivatives of the potential and p-form gauge coupling is satisfied. This inequality is not satisfied in simple stringy examples (outside of the scope of Maldacena-Nuñez), which unsurprisingly avoid this route to dS solutions. We can apply our techniques to construct dS 2 solutions in the Standard Model plus an additional runaway scalar such as quintessence. Demanding that these are avoided leads to (weak) phenomenological constraints on the time variation of the fine structure constant and QCD axion-photon coupling.

“…-The validity of the smearing approximation: see e.g. [57,58] and some possible implications for de Sitter solutions in [59]. Here for instance, the warp factor would replaced by its average (constant) value and sources contributions by the C constant.…”

Section: Jhep06(2020)100mentioning

confidence: 99%

Gravitational waves in warped compactifications

Andriot

Tsimpis

2020

We study gravitational waves propagating on a warped Minkowski space-time with D − 4 compact extra dimensions. While Kaluza-Klein scales are typically too high for any current detection, we analyse how the warp factor changes the Kaluza-Klein spectrum of gravitational waves. To that end we provide a complete and explicit expression for the warp factor, as well as the Green's function, on a d-dimensional torus. This expression differs from that of braneworld models and should find further uses in string compactifications. We then evaluate the Kaluza-Klein spectrum of gravitational waves. Our preliminary numerical results indicate not only a deviation from the standard toroidal spectrum, but also that the first masses get lowered due to the warp factor.