Thermal dark energy

Abstract

We present a novel source of dark energy, which is motivated by the prevalence of hidden sectors in string theory models and is consistent with all of the proposed swampland conjectures. Thermal effects hold a light hidden sector scalar at a point in field space that is not a minimum of its zero temperature potential. This leads to an effective 'cosmological constant', with an equation of state w = −1, despite the scalar's zero temperature potential having only a 4D Minkowski or AdS vacuum. For scalar masses µeV, which could be technically natural via sequestering, there are large regions of phenomenologically viable parameter space such that the induced vacuum energy matches the measured dark energy density. Additionally, in many models a standard cosmological history automatically leads to the scalar having the required initial conditions. We study the possible observational signals of such a model, including at fifth force experiments and through ∆N eff measurements. Similar dynamics that are active at earlier times could resolve the tension between different measurements of H0 and can lead to a detectable stochastic gravitational wave background.

The F -term problem and other challenges of stringy quintessence

“…It appears that one needs further SUSY breaking and the F -term problem re-emerges. An interesting alternative to quintessence has been introduced in [104]: The zero-temperature scalar potential is assumed to satisfy the de Sitter conjecture, but a thermally excited hidden sector stabilizes a scalar field at a positive-energy hilltop. The authors illustrate this idea using a simple Higgs-like potential V = −m 2 φ φ 2 /2 + λφ 4 + C. Since the hidden sector must not introduce too much dark radiation, the temperature and hence also m φ are bounded from above by today's CMB temperature, which is roughly 0.24 meV.…”

Dark Energy in String Theory

“…The Dine-Seiberg runaway argument and several no-go theorems then indicate that moduli stabilisation in a de Sitter vacuum will be at the limits of theoretical control, requiring a delicate interplay between diverse string theoretic ingredients. We have focussed, therefore, on two alternative scenarios for Dark Energy: runaway quintessence (reviewing [30] and presenting some further results) and Thermal Dark Energy [31].…”

“…We will then discuss quintessence models in string theory, focusing on the runaway potentials that are ubiquitous in string compactifications, summarising [30] and including some further results using supergravity. Finally we will review Thermal Dark Energy [31].…”

“…Given the difficulties encountered in building de Sitter vacua and quintessence in string theory, and the several upcoming observational probes into Dark Energy, it is extremely interesting to consider well-motivated alternative Dark Energy scenarios in string theory. In the remainder of this talk we will review the proposal [31].…”

“…The lack of any compelling model of de Sitter or quintessence from string theory thus far, drives the search for completely novel string theory origins for Dark Energy. In Thermal Dark Energy [31], high temperature effects in a light hidden sector hold a string theory modulus away from its zero temperature minimum. This sources a positive potential energy density that mimics a cosmological constant, until, as the temperature falls, a phase transition to the true minimum takes place.…”