Axion hilltops, Kahler modulus quintessence and the swampland criteria

Abstract

We study the interplay between extrema of axion potentials, Kahler moduli stabilization and the swampland criteria. We argue that moving away from the minima of non-perturbatively generated axion potentials can lead to a runaway behavior of moduli that govern the couplings in the effective field theory. The proper inclusion of these degrees of freedom resolves the conflict between periodic axion potentials and the gradient de Sitter criterion, without the need to invoke the refined de Sitter criterion. We investigate the possibility of including this runaway direction as a model of quintessence that satisfies the swampland criteria. Using a single non-perturbative effect, the axionic maximum provides a runaway direction that is unstable in the axion directions, sensitive to initial conditions and too steep to allow for a Hubble time of expansion without violating the field excursion criterion. Adding a second non-perturbative effect generates a saddle point in the potential, which solves the steepness problem and improves the initial conditions problem although some fine-tuning remains required. arXiv:1811.07378v3 [hep-th]

Further Refining the de Sitter Swampland Conjecture

“…unstable (tachyonic) de Sitter solutions: such a criterion has been formulated recently [13] (see also [12]) in the form of (1.3) detailed below. This refined de Sitter conjecture has been tested with various phenomenological models, [14][15][16][17][18][19] and has been discussed in relation to stringy constructions [20][21][22][23][24][25][26][27] or in a more general swampland context. [28][29][30][31] In the present paper, we propose an alternative refined de Sitter conjecture.…”

Thermal dark energy

“…Various no-go theorems have shown that string theory constructions of vacua with a positive cosmological constant will be, at best, at the limits of theoretical control given current calcula- * ehardy@liv.ac.uk † susha@liv.ac.uk tional techniques, as reviewed in [7]. Meanwhile string models of quintessence suffer from similar challenges (see [8] for a review and [9][10][11][12][13][14][15][16][17] for some recent works).…”

The F -term problem and other challenges of stringy quintessence

“…The most promising candidates for stringy quintessence are moduli (see e.g. [51][52][53]) and axions (see e.g. [14,44,[54][55][56][57][58]), which are both ubiquitous in string compactifications.…”