Stringy multifield quintessence and the Swampland

We investigate the scalar potential in the parametric regime of string moduli space where string loops and higher derivative corrections to 10d supergravity can be ignored and where the fields are rolling down exponential slopes leading to powerlaw FLRW cosmologies, a.k.a. scaling solutions. We argue that these scaling solutions, if describing an accelerating expansion, are likely to be perturbatively unstable, for reasons identical to the perturbative instabilities in tree-level dS vacua.

Section: Jcap01(2024)055mentioning

confidence: 85%

No accelerating scaling cosmologies at string tree level?

Riet

2024

“…Strong non-geodesic motion, characterized by rapid turns in field space with Ω ≫ 1 (in Hubble units), can lead to intriguing and rich phenomenology. Examples have been provided in the context of inflation (see, e.g., [7][8][9][10][11][12][13][14][15][16][17][18][19][20]) and also for quintessence models (see, e.g., [21][22][23][24][25][26][27][28]). These can be modifications of the inflationary power spectrum [10,12], production of primordial black holes [29][30][31], possibility to inflate on a steep potential [15,23,25] (namely with large potential gradient) and also enhanced growth of large-scale structure [23].…”

Section: Introductionmentioning

confidence: 99%

Cosmic acceleration and turns in the Swampland

Freigang,

Lüst,

Nian

et al. 2023

We argue that field trajectories, which lead to cosmic acceleration and feature rapid turns near the boundary of the moduli space, are in the Swampland. We obtain this result by assuming the validity of the Swampland Distance Conjecture (SDC) in the presence of a positive scalar potential and by focusing on hyperbolic spaces, as prototype geometries of infinite distance limits of Calabi-Yau compactifications. We find that, in a quasi-de Sitter space with Hubble rate H and acceleration parameter ϵ, the turning rate Ω is upper bounded such as Ω/H < 𝒪(√(ϵ)). Therefore, field trajectories consistent with the SDC can only have a negligible deviation from geodesics. This has direct implications for the realization and consistency of multi-field scenarios in string theory. Moreover, it implies a tension between asymptotic accelerating expansion, consistent with observations, and the de Sitter conjecture.

“…Additionally, a coupling of the scalar to some sectors in the theory are expected. Based on these observations, several phenomenological models have been proposed recently [21][22][23][24][25][26].…”

Section: Introductionmentioning

confidence: 99%

Constraints on late time violations of the equivalence principle in the dark sector

Thomas

Bruck²

2023

If dark energy is dynamical due to the evolution of a scalar field, then in general it is expected that the scalar is coupled to matter. While couplings to the standard model particles are highly constrained by local experiments, bounds on couplings to dark matter (DM) are only obtained from cosmological observations and they are consequently weaker. It has recently been pointed out that the coupling itself can become non-zero only at the time of dark energy domination, due to the evolution of dark energy itself, leading to a violation of the equivalence principle (EP) in the dark sector at late times. In this paper we study a specific model and show that such late-time violations of the EP in the DM sector are not strongly constrained by the evolution of the cosmological background and by observables in the linear regime (e.g. from the cosmic microwave background radiation), although the model is not preferred over ΛCDM. A study of perturbations in non-linear regime is necessary to constrain late-time violations of the equivalence principle much more strongly.