Hidden sectors in string theory: kinetic mixings, fifth forces and quintessence

Abstract

Light moduli fields in string compactifications can have interesting implications for particle physics and cosmology. Fifth force bounds impose stringent constraints on the interactions of such moduli with the visible sector. To be consistent with the bounds, they need to be part of hidden sectors which interact with the Standard Model with weakerthan-Planck suppressed interactions. We consider scenarios in which the visible sector degrees of freedom are localised in the compactification and light moduli arise as closed string degrees of freedom associated with hidden sectors which are geometrically separated (in the extra-dimensions) from the Standard Model. Kinetic mixings lead to interactions between the moduli and the visible sector -we compute these using Kähler potentials of string/M-theory compactifications. We argue that in general these interactions provide a lower bound on the strength of the interactions between the moduli and the visible sector. The interactions scale with inverse powers of the volume of the compactification, thus fifth force bounds can be translated to lower bounds on the volume of the extra-dimensions. We find that compactification volumes have to be large to evade the bounds. This imposes interesting constraints on quintessence model building in string theory. Our results for the strength of the interactions can also be used to quantify the fine-tuning necessary for the stability of the potential of a light modulus against quantum corrections involving visible sector loops.

Thermal dark energy

“…As seen in Figure 8, the fifth force constraints at these masses are far weaker than those on scalars with masses 10 −12 eV. Consequently, whereas in string theory it has proven difficult to obtain sufficient sequestering between quintessence and the visible sector for models to not already be excluded [15,[57][58][59][60][61][62], the required suppression of couplings seems within reach in our models.…”

The F -term problem and other challenges of stringy quintessence

“…We also note that such Kähler moduli couple to matter, though not as strongly as V. These couplings tend to violate the equivalence principle, forcing them to remain about a factor of 10 −11 below gravitational strength [70]. Fifth-force constraints on stringy quintessence models have recently been studied in detail in [47], where a lower bound on the compactification volume, which suppresses the couplings to other Kähler moduli, was found for a number of models. Our focus in this paper is different and concerns the more elementary issue of mass hierarchies in the scalar potential and the SUSY-breaking scale.…”

“…This cannot be coincidental but has to be based on some mechanism or symmetry. Although in our specific model such a perfect decoupling of one Kähler modulus from the loop corrections seems implausible, there might of course be other constructions where the required sequestering can be achieved (see [47,97] for discussions).…”

“…Finally, the fourth requirement is obtained if one notices that, after compactification, the Ricci scalar of the 4D theory obtains a prefactor V. Then, after Weyl rescaling to the 4D Einstein frame, the scalar field corresponding to V couples to matter fields (both from D3 and D7 branes) with approximately gravitational strength. However, such fifth-force effects are ruled out by the very same experiments that test gravity at the sub-millimeter scale [47,69,70] (measuring the Eddington parameter in the post-Newtonian expansion). Hence the volume modulus must be sufficiently heavy.…”

Swampland implications of GW170817-compatible Einstein-Gauss-Bonnet gravity

“…In the literature there is currently a lot of activity regarding the implications of the Swampland criteria, see Refs. [40][41][42][43][44][45][46][47][48][49][50][51][52][53][54][55][56][57][58][61][62][63][64][65][66][67][68][69][70][71]. Also in Ref.…”